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European Journal of Inorganic Chemistry - Current Research Articles

Current research articles: Inorganic Chemistry

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European Journal of Inorganic Chemistry - published by Wiley-VCH

EurJIC is the fastest growing journal in inorganic chemistry. It publishes Full Papers, Short Communications, and Microreviews from the entire spectrum of inorganic, organometallic, bioinorganic, and solid-state chemistry.

Current articles of the journal:

New Gold(I) Organometallic Compounds with Biological Activity in Cancer Cells (Eur. J. Inorg. Chem. 27/2014)

The cover picture shows the uptake of organometallic gold(I) N-heterocyclic (NHC) complexes, bearing a fluorescent coumarin moiety, in cancer cells and the resulting anticancer effects. Notably, the most effective compound of the reported series bears the 1-thio-?D-glucose tetraacetate ligand, which may enhance its cellular uptake, therefore making the compound more cytotoxic. Once inside the cells, the gold compound may target the selenoenzyme thioredoxin reductase and induce mitochondrial damage. Details are discussed in the Short Communication by E. Bodio, A. Casini et al. on p. 4532 ff. For more on the story behind the cover research, see the Cover Profile.

Posted on 22 September 2014 | 2:58 pm

Masthead: Eur. J. Inorg. Chem. 27/2014

Posted on 22 September 2014 | 2:58 pm

On the Investigation of the Droplet–Droplet Interactions of Sodium 1,4-Bis(2-ethylhexyl) Sulfosuccinate Reverse Micelles upon Changing the External Solvent Composition and Their Impact on Gold Nanoparticle Synthesis (Eur. J. Inorg. Chem. 27/2014)

The inside cover picture shows the high versatility of reverse micelles as nanoreactors. The composition of the nonpolar organic medium has a huge effect on properties such as the interfacial micropolarity, the hydrogen-bonding ability, and the sequestrated water structure of sodium 1,4-bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles (RMs). Therefore, not only gold nanoparticles (in n-heptane) but also evidence of subnanometer clusters (in benzene) was obtained by using RMs as nanoreactors. The results are very promising for many applications. Details are discussed in the article by N. M. Correa et al. on p. 2095 ff.

Posted on 22 September 2014 | 2:58 pm

New Gold(I) Organometallic Compounds with Biological Activity in Cancer Cells

Invited for the cover of this issue is the group of Angela Casini at the Department of Pharmacokinetics, Toxicology and Targeting, Groningen Research Institute of Pharmacy, The Netherlands. The cover image shows the uptake of gold N-heterocyclic (NHC) complexes, bearing a fluorescent coumarin moiety, in cancer cells and the resulting anticancer effects. One of the most interesting aspects in this project is the highly interdisciplinary approach covering inorganic chemistry, biology, pharmacology, and biophysics...Read more about the story behind the cover in the Cover Profile and about the research itself on p. 4532 ff.

Posted on 22 September 2014 | 2:58 pm

Masthead: Eur. J. Inorg. Chem. 27/2014

Posted on 22 September 2014 | 2:58 pm

(Eur. J. Inorg. Chem. 27/2014)

The back cover picture highlights Werner's legacy, which is celebrated by coordination chemistry contributions describing observations both in the first coordination sphere, the second coordination sphere and beyond. Specific orbital requirements define the geometry of complexes with Tc–Tc multiple bonds (Poineau et al.), and the binding of tetrathiafulvalene ligands to the DyIII dimer results in a single-molecule magnet (Pointillart et al.). In addition, noncovalent interactions can order a system in layers as found for the organometallic Pd–uracil compound (Moriuchi, Hirao et al.), the ordering can be critical for the resulting spin polarization mechanism in cyanido-bearing CoIII/CoII complexes (Alexandru, Marino, Julve et al.) and for the ability of vapochromic PtII complexes to support water binding in the solid state (Kobayashi and Kato). The background shows a group photo of the delegates taken at the 4th Zing Coordination Chemistry Conference held in Mexico in December 2013 (the background photo is used with permission from Zing Conferences Ltd.). Thanks to Guest Editor Debbie Crans for putting the parts of the composite cover together.

Posted on 22 September 2014 | 2:58 pm

Graphical Abstract: Eur. J. Inorg. Chem. 27/2014

Posted on 22 September 2014 | 2:57 pm

The Legacy of Alfred Werner

Posted on 22 September 2014 | 2:57 pm

Modern Coordination Chemistry 100 Years after Werner

Posted on 22 September 2014 | 2:57 pm

The First Family of Actinide Carboxy­phosphinates: Two- and Three-Dimensional Uranyl Coordination Polymers

Reaction of uranyl dications with (2-carboxyethyl)(phenyl)phosphinic acid (CPPA, H2L) under hydrothermal conditions gave two layered isomers (UO2)2(L)2, namely, CPP-U1 and CPP-U2. Both of them feature edge-sharing uranyl dimers as structure-building units, which are ligated by CPP ligands in different ways, thus leading different layered arrangements. With the addition of imidazole derivatives, two three-dimensional structures UO2(L)(dib)0.5 (CPP-U3) and UO2(L)(bbi)0.5 (CPP-U4) were generated, in which the similar uranyl-phosphinate layers are connected by two different imidazole derivatives by means of the U–N connection [dib = 1,4-di(1H-imidazol-1-yl)benzene; bbi = 1,1?-(1,4-butanediyl)bis(imidazole)]. The syntheses, structure, as well as the IR spectra, and luminescent and photocatalytic properties of these uranyl organophosphinates are reported in this paper. The first family of actinide carboxyphosphinates has been synthesized using (2-carboxyethyl)(phenyl)phosphinic acid as the ligand including two layered assemblies and two framework structures pillared by imidazole derivatives. Well-defined charge-transfer vibronic transitions of green light emission and effective degradation of RhB under visible light are illustrated.

Posted on 22 September 2014 | 2:20 pm

Organic–Inorganic Hybrid Membranes Based on Sulfonated Poly(ether ether ketone) and Tetrabutylphosphonium Bromide Ionic Liquid for PEM Fuel Cell Applications

Ionic liquids (ILs), with their inherent ionic conductivity and negligible vapor pressure, can be exploited in proton exchange membrane (PEM) fuel cells for which thermal management is a major problem and the cell operation temperature is limited by the boiling point of water. In this work, sulfonated poly(ether ether ketone) (SPEEK) membranes were modified by the incorporation of tetrabutylphosphonium bromide ([P4 4 4 4]Br) by solvent-casting. Electrochemical impedance spectroscopy (EIS) was used to study the electrical properties of the modified membranes. Simultaneous TGA and FTIR studies were used to evaluate the thermal stability and chemical structure of the modified membranes, respectively. 1H NMR spectroscopy was applied to probe the changes in the chemical environment due to the interaction between the ionic liquid and the polymer. Mechanical properties were studied by dynamic mechanical analysis. The temperature-dependent behavior of the viscosity of the [P4 4 4 4]Br ionic liquid was observed to obey the Vogel–Fulcher–Tammann (VFT) equation, and was correlated to the ion-conducting properties of the IL-doped SPEEK membranes. Polymer–ionic liquid electrolyte membranes were fabricated from tetrabutylphosphonium bromide ([P4 4 4 4]Br) and sulfonated poly(ether ether ketone) (SPEEK). Their thermal, mechanical, structural and electrical properties show promise for their use in high-temperature fuel cell applications.

Posted on 19 September 2014 | 10:20 am

The Effect of ZnII Coordination on the Addition of 2-(Aminomethyl)benzimidazole to Acrylonitrile

The effects of NZn coordination, solvent, and pH on the aza-addition reaction between 2-(aminomethyl)benzimidazole (HL) and acrylonitrile were studied. In the absence of ZnII ion, the aza-addition reactions between HL and acrylonitrile (in aqueous media) depended on pH and were not selective. The mono-addition compound {3-[(1H-benzimidazol-2-ylmethyl)amino]propanenitrile} was always obtained in a greater proportion than the di-addition products [3,3?-[(1H-benzimidazol-2-ylmethyl)imino]dipropanenitrile and 3-(2-{[(2-cyanoethyl)amino]methyl}-1H-benzimidazol-1-yl)propanenitrile]. Acrylonitrile selectively reacted at the amine group in the [ZnCl3(H2L)] and [ZnCl2(HL)] complexes in aqueous solutions. Moreover, [ZnCl(HL)2]Cl and [Zn(H2O)2(HL)2]Cl2 complexes yielded mixtures of mono- and di-addition products. In contrast, Zn complexes formed with HL did not react with acrylonitrile in solution in DMSO. The synthesis of mono- and di-addition compounds was studied by 1H and 13C NMR spectroscopy and X-ray diffraction crystallography. Quantum theory of atoms in molecules (QTAIM) computations were used to demonstrate the probable presence of a mono-addition chelate complex. The aza additions of 2-(aminomethyl)benzimidazole (HL) to acrylonitrile depend on pH and are not selective. However, the NZn coordination bonds in HL increase the selectivity of the aza addition to acrylonitrile because the ZnII protects the imidazolic nitrogen atoms. Moreover, the aza addition of ZnII complexes requires an aqueous medium.

Posted on 19 September 2014 | 10:20 am

Exploring the Effects of Axial Pseudohalide Ligands on the Photophysical and Cyclic Voltammetry Properties and Molecular Structures of MgII Tetraphenyl/porphyrin Complexes

The (meso-tetraphenylporphyrinato)magnesium(II) complexes with azido (1), cyanato-N (2), and thiocyanato-N (3) ligands were prepared by using 2.2.2-cryptand to solubilize the azide, cyanato, and thiocyanato salts in dichloromethane solvent. These species were characterized by UV/Vis and IR spectroscopy, mass spectrometry, and electrochemistry. The first reduction potential and the two first oxidation potentials of the porphyrin rings of these species are not affected by the nature of the axial ligand, and an unusual third irreversible oxidation of the porphyrin ring is observed. The anodic behavior of the magnesium azide derivative is complicated by the appearance of additional signals for ligand-centered electron transfers that originate from the release of the azido ligand of 1. The room-temperature fluorescence spectra of the magnesium complexes 1–3 indicate that the Soret and Q bands are not particularly affected by the nature of the axial ligands. The quantum yields of the S1S0 fluorescence are between 0.10 and 0.19, and the fluorescence lifetimes range between 3.7 and 6.1 ns at room temperature. Complexes 1–3 crystallize in the monoclinic crystal system in the same space group, P21/n. The molecular structure of 1 is the first example of a magnesium azide complex. The average equatorial magnesium–Npyrrole bond lengths (Mg–Np) are higher than those of the related pentacoordinate magnesium porphyrin species and decreases from 1 [2.1187(16) Å] to 2 [2.1108(15) Å] to 3 [2.0962(13) Å]; the distance between the magnesium center and the 24-atom mean plane of the porphyrin ring (Mg–PC) also decreases from 1 to 2 to 3 with values of 0.6629(7), 0.6598(7), and 0.5797(6) Å, respectively. Complex 1 shows major doming and saddle distortions, whereas 2–3 exhibit relatively high ruffling and moderate doming deformations. The molecular structure of 1 is stabilized by weak intermolecular C–H···N hydrogen bonds between one carbon atom of the phenyl ring and the terminal nitrogen atom of the azido ligand, and the lattice of 2 exhibits weak intermolecular C–H···O H bonds between one carbon atom of the phenyl ring and the terminal oxygen atom of the NCO– ligand. The crystal structure of 3 is mainly sustained by weak intermolecular C–H···Cg ? interactions between a carbon atom of 2.2.2-cryptand and the centroid of one pyrrole ring. The [Mg(TPP)X]– (TPP = tetraphenylporphyrinato; X = N3–, NOC–, NCS–) complex ions were characterized by X-ray diffraction. The effects of the nature of the axial pseudohalide ligand X on the photophysical and redox properties of these species in dichloromethane have also been studied by cyclic voltammetry, UV/Vis spectroscopy, and fluorescence spectroscopy techniques.

Posted on 18 September 2014 | 10:12 am

2-Pyridylcyanoxime–NiII Clusters with Unusual Topologies: Lone-Pair–? Interactions and Magnetic Properties

Three new complexes derived from the reaction of the 2-pyridylcyanoxime ligand (pyC{CN}NOH) with several non-carboxylate nickel salts have been structural and magnetically characterized. The compounds with the formula [Ni3(MeOH)2(CF3COO)(OH)(pyC{CN}NO)4] (1), [NaNi(tfacac)3]n (2; tfacac = 1,1,1-trifluoroacetylacetone), [Ni5(H2O)2(N3)2(pyC{CN}NO)8] (3), and [Ni3(pyC{CN}NO)5(pyC{CN}NOH)](BF4) (4) exhibit unusual topologies with a triangular {Ni3(?3-OH)(pyC{R?}NO)3}2+ core for 1, vertex-shared triangles with a {Ni5(?1,1-N3)2(pyC{CN}NO)6}2+ core for 3, and a {Ni3(pyC{CN}NO)4}2+ core for 4. Direct-current (DC) magnetic measurements performed in the 2–300 K temperature range reveal antiferromagnetic interactions induced by the ?3-OR or oximato superexchange pathways and ferromagnetic interactions promoted by the azido bridges, thereby resulting in ground states S = 0, 3, and 1 for 1, 3, and 4, respectively. Supramolecular lone-pair–?-ring interactions are reported for the first time for the pyC{CN}NO– ligand and its importance in the crystal packing is discussed. Magnetic properties and supramolecular lone-pair–?-ring interactions have been analyzed for a series of new tri- and pentanuclear nickel derivatives of the 2-pyridylcyanoximate ligand.

Posted on 18 September 2014 | 10:12 am

A Pair of Enantiopure Cubane-Type CuII4O4 Clusters: Synthesis, Structure, Chirality and Magnetism

A pair of enantiopure cubane-type CuII4O4 clusters was constructed from simple chiral ligands (R or S)-2-[(2-hydroxy-1-phenylethylimino)methyl]phenol (H2LR or S). Single-crystal X-ray diffraction studies demonstrated that complexes 1R and 1S are enantiomers. They consist of a CuII4O4 cubane core in which the four CuII centres are linked by a ?3-oxo bridge. The four CuII ions in one cluster are all in a distorted square-pyramidal geometry. Circular dichroism (CD) spectroscopy also confirmed that complexes 1R and 1S are enantiomers and that the chirality was successfully transferred and amplified from the ligand to the coordination environment of the CuII ions. Magnetic susceptibility measurements show an overall antiferromagnetic interaction which could be fitted by using MAGPACK with a two parameter model (J1 = –5.58 cm–1, J2 = 3.80 cm–1). A pair of enantiopure cubane-type CuII4O4 clusters was obtained from a chiral Schiff base ligand. The chirality and weak antiferromagnetic interactions within the CuII4L4 core were studied.

Posted on 18 September 2014 | 10:12 am

Designing Near-Infrared and Visible Light Emitters by Postsynthetic Modification of Ln+3–IRMOF-3

The postsynthetic modification of metal–organic frameworks is a promising new route for engineering optical centres and tuning the light emission properties of materials. Here, the postsynthetic modification of isoreticular metal–organic framework-3 (IRMOF-3) with ethyl oxalyl monochloride and ethyl acetoacetate followed by the chelation of trivalent lanthanide ions afforded efficient near-infrared (Nd3+) and visible (Eu3+ and Tb3+) light emitters. IRMOF-3 was used as an example owing to its highly porous crystalline structure and the presence of non-coordinating amino groups on the benzenedicarboxylate (bdc) linker, which are amenable to modification. The conversion of the amino groups was 100 and 65?% for ethyl oxalyl monochloride and ethyl acetoacetate, respectively. The materials were characterised by elemental analysis, powder X-ray diffraction, optical and scanning electron microscopy, Fourier transform infrared spectroscopy, and solution (1H) and (13C) solid-state nuclear magnetic resonance spectroscopy. The solid-state luminescence properties of Ln-modified IRMOF-3 were investigated at room temperature. The presence of the bdc aromatic ring, ?-diketonates and oxamate enhanced the Ln3+ sensitization through ligand-to-metal energy transfer. The magnetic behaviour of all compounds was further analysed. The spin–orbit coupling and zero-field splitting parameters were evaluated by fitting the experimental magnetic susceptibility to the analytical expressions for the free Ln3+ ions. The postsynthetic modification of IRMOF-3 with ethyl oxalyl monochloride and ethyl acetoacetate followed by the chelation of trivalent lanthanide ions is a suitable route for the preparation of efficient near-infrared (Nd3+) and visible (Eu3+ and Tb3+) light emitters.

Posted on 17 September 2014 | 2:10 pm

Reactivity of a Seven-Membered Zirconacyclocumulene towards CN Multiple Bonds – Formation of Metallaheterocycles by Insertion of C?N and C=N Groups

The reactions of the seven-membered zirconacyclocumulene [Cp2Zr{?4-Me3SiC4(SiMe3)–C(C2SiMe3)=CSiMe3}] (1) with nitriles (RC?N, R = Me, Ph) started with an insertion of a cyanide group into the metal–butadiyne bond followed by an alkyne–nitrile coupling and formation of 1-zircona-2-azacyclopenta-2,4-dienes. The reaction product for R = Me is stabilized by dimerization to give a compound containing a four-membered –N–Zr–N–Zr– ring and two identical five-membered 1-metalla-2-aza-cyclopentadiene rings. In case of R = Ph, a metallacycle could not be isolated, and a pyrimidine was formed. The catalytic potential of this reaction was investigated. For PhN=C(H)Ph, again after insertion and coupling, a corresponding 1-zircona-2-azacyclopenta-4-ene was established. The reaction of this compound with carbon dioxide led to ring expansion and formation of a seven-membered product, which released CO2 at higher temperature and to give back the reactant. The above-mentioned products were characterized by NMR spectroscopy and single-crystal X-ray structure analysis. Reactions of RC?N (R = Me, Ph) and PhCH=NPh with the seven-membered zirconacyclocumulene [Cp2Zr{?4-Me3SiC4(SiMe3)–C(C2SiMe3)=CSiMe3}] (1) give five-membered cycles by insertion of CN bonds. For the nitrile with R = Me, stabilization by dimerization occurs to yield 2, whereas for R = Ph with a second nitrile, pyrimidines are formed. Compound 4 reversibly inserts CO2.

Posted on 17 September 2014 | 2:10 pm

Synthesis of Co/Ni Unitary- or Binary-Doped CeO2 Mesoporous Nanospheres and Their Catalytic Performance for CO Oxidation

In this paper, ceria, ceria doped with transition metal ions (Co2+, Ni2+), and Co/Ni binary-doped ceria mesoporous notched hollow nanospheres were prepared from a one-step solvothermal synthesis. By introducing metal ions, the composition can be freely manipulated. The morphologies and crystalline structures of the products were characterized in detail by XRD, TEM, SEM, and HRTEM. The surface compositions of the as-prepared ceria samples were detected by Raman spectroscopy, energy-dispersive X-ray spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS). The surface areas and pore-size distributions of the as-obtained doped ceria mesoporous nanospheres were investigated by N2 adsorption–desorption measurements. Temperature-programmed reduction measurements under H2 (H2-TPR) showed the better reduction behavior of the doped ceria samples. Preliminary CO catalytic oxidation experiments indicated that the doped ceria samples showed strikingly higher catalytic activity, owing to the intrinsic surface defects of the samples. In addition, the as-obtained ceria nanospheres can be used as excellent supports for gold nanoparticles to remove CO by catalytic oxidation; therefore, they demonstrate a promising potential in environmental remediation. This one-step synthesis is a versatile approach and it could be extended to other binary or ternary metal oxide systems. Ceria, pure ceria doped with transition metal ions (Co2+, Ni2+), and Co/Ni binary-doped ceria mesoporous notched hollow nanospheres were prepared from a one-step solvothermal synthesis. The incorporation of metal ions into the ceria fluorite lattice results in higher catalytic activity. In addition, the mesoporous nanospheres can be used as an excellent support for noble metals.

Posted on 17 September 2014 | 2:10 pm

Synthesis, Characterization of Some Ferrocenoyl Cysteine and Histidine Conjugates, and Their Interactions with Some Metal Ions

The synthesis and characterization of a series of 1,n?-disubstituted ferrocenoyl cysteine and histidine conjugates is reported. Their interaction with a range of metal ions was studied. The results show that metal coordination in His-containing peptides involved the imidazole group. Metal coordination affects the structural properties of the ferrocene (Fc) conjugates, as judged by CD spectroscopy, and also the redox properties of the Fc group. A series of disubstituted ferrocenoyl cysteine and histidine derivatives as well as iron–sulfur cluster analogs were synthesized. According to circular dichroism (CD) spectra, all ferrocenoyl compounds have P-helical conformation. Conversely, after the addition of ZnII, the configuration for ferrocene (Fc) amino acid conjugates 6a and 6b changed from P-helical to M-helical in the 480 nm region.

Posted on 17 September 2014 | 2:10 pm

Ruthenium(II) Photosensitizers with Electron-Rich Diarylamino-Functionalized 2,2?-Bipyridines and Their Application in Dye-Sensitized Solar Cells

New ruthenium(II) photosensitizers [Ru(dcbpy)(L)(NCS)2] (dcbpy = 4,4?-dicarboxylic acid-2,2?-bipyridine; L = 4,4?-bis{di[4-(N,N?-dimethylamino)phenyl]amino}-2,2?-bipyridine (1), 4,4?-bis[di(4-methoxyphenyl)amino]-2,2?-bipyridine (2), and 4,4?-bis[di(4-tolyl)amino]-2,2?-bipyridine (3)) were prepared and characterized and their application in dye-sensitized solar cells is presented. The optical absorption of these photosensitizers gives a peak at around 540 nm, which is very similar to that of the standard N719. The maximum incident photon-to-current conversion efficiency (IPCE) of 80.6?% was obtained for 3, which corresponded to a power conversion efficiency (?) of 5.68?% under standard air mass (AM) 1.5 sunlight (versus N719 at 6.76?%). Molecular cosensitization of 3 with an organic dye, QS-DPP-I, yielded higher ? values up to 6?% relative to the cells based on individual photosensitizers, and the corresponding IPCE can reach 93.6?% at 549 nm. A preliminary stability test of the devices was also conducted. New ruthenium(II)-based photosensitizers with electron-rich diarylamino-2,2?-bipyridine ligands have been developed. They can be used to afford decent and reasonably stable device performance in dye-sensitized solar cells (up to 5.95?% in cosensitized cells versus 6.76?% for N719), thereby revealing the great potential of these dyes.

Posted on 17 September 2014 | 2:10 pm

Investigating the Formation Mechanism of Arene Ruthenium Metallacycles by NMR Spectroscopy

The stereochemical properties of twelve dinuclear arene ruthenium complexes have been studied in solution. The dinuclear complexes of the general formula [(p-cymene)2Ru2(OO?OO)(Ln)2](CF3SO3)2 (OO?OO = oxalato, 2,5-dioxido-1,4-benzoquinonato, 5,8-dioxido-1,4-naphthoquinonato; Ln = 4-phenylpyridine, 4-styrylpyridine, 4-methylpyridine, 4-tert-butylpyridine) have been isolated as mixtures of the cis and trans isomers. All of the complexes showed lability of the pyridyl-based ligands (Ln) in solution and rapid exchange between the cis and trans isomers. The equilibrium between the cis and trans isomers was confirmed by 1H NMR spectroscopy, and the intermediate species were identified and, thus, provided valuable insights into the formation mechanism of arene ruthenium metalla-assemblies. The stereochemical properties of twelve dinuclear arene ruthenium complexes have been studied in solution by NMR spectroscopy. All complexes showed lability of the pyridyl-based ligands in solution and rapid exchange between the cis and trans isomers. The intermediate species have been identified and, thus, provided insights into the formation mechanism of arene ruthenium metalla-assemblies.

Posted on 12 September 2014 | 10:10 am

Prospective Electroluminescent Hybrid Materials

Tris(8-hydroxyquinoline)boron (Bq3) was synthesized by means of a high-temperature substitution reaction. Mixtures of different Bq3 polymorphs were obtained and their spectral and structural properties were investigated. A comparison of organic light-emitting diode (OLED) structures with Bq3 and Alq3 as emitting materials showed the prospective application of Bq3 as a blue-light emitter. Thin-film hybrid materials (HM) were made by vacuum thermal deposition. HM films were produced by layer-by-layer thermal vacuum sputtering of B2O3/Alq3/B2O3/MoO3/Al on a glass substrate with an indium tin oxide (ITO) conducting layer. The HM films were locally heated by a diode laser (785 nm). The pumping of 150 W?cm–2 energy for one second resulted in an irreversible change in the HM film. Chromaticity coordinates for the as-prepared and laser-induced HM films showed a significant difference in their photoluminescent properties. Three polymorphs of tris(8-hydroxyquinoline)boron (Bq3) were obtained by high-temperature substitution reaction. Their spectral and structural properties were investigated and showed Bq3 to be a potential blue emitter. Hybrid material (HM) films B2O3/Alq3/B2O3 on a glass substrate were made by vacuum sputtering. Laser heating of the HM film resulted in an irreversible change in its photoluminescence.

Posted on 12 September 2014 | 10:10 am

Spatially Confined Functionalization of Transparent NiO Thin Films with a Luminescent (1,10-Phenanthroline)tris(2-thenoyltrifluoroacetonato)europium Monolayer

Transparent MOCVD-grown NiO films have been functionalized with the luminescent (1,10-phenanthroline)tris(2-thenoyltrifluoroacetonato)europium(III) complex [Eu(TTA)3phen] by combining sputter activation with a solution synthetic route. To introduce the Eu complex only on selected regions, some areas of the NiO surface were activated by Ar+ ion sputtering and then functionalized with 3-phosphonopropionic acid (CPPA) followed by the anchoring of Eu(TTA)3phen through a ligand-exchange reaction between ?-diketonato ligands and the carboxylic groups of CPPA. The functionalized material was characterized by X-ray photoelectron, UV/Vis and luminescence spectroscopy. XPS measurements indicated that CPPA prefunctionalization and, in turn, the Eu(TTA)3phen anchoring occurs only on the sputter-activated region, while no anchoring takes place on the unactivated surface. The optical properties of the Eu(TTA)3phen–NiO system were evaluated by UV/Vis and luminescence spectroscopy. Anchoring of the Eu(TTA)3phen complex on MOCVD-grown NiO films is reported. The NiO surface was activated by means of a sputtering process and functionalized with a phosphonic linker, followed by the coordination of the Eu complex through a ligand-exchange reaction. The luminescent hybrid system has been proven to retain the optical properties of the Eu complex.

Posted on 12 September 2014 | 10:10 am

Solvochemical Synthesis and Crystal Structure of the Fluoride-Derivatized Early Lanthanoid(III) ortho-Oxidomolybdates(VI) LnF[MoO4] (Ln = Ce–Nd)

The development of a new solvochemical synthesis route resulted in single crystals of lanthanoid(III) fluoride oxidomolybdates(VI) with the formula LnF[MoO4] for the early lanthanoids (Ln = Ce–Nd); to date, these compounds could not be obtained by solid-state reactions. The preparation strategy comprises the dropwise combination of an alkaline aqueous solution containing molybdenum trioxide, sodium hydroxide and sodium fluoride with an acidic aqueous solution of the lanthanoid(III) nitrate. After the purification of the obtained gel, the noncrystalline product has to be dried at 120 °C and converted into a crystalline phase by a final thermal treatment for 24 h at 850 °C in evacuated silica ampoules. The crystal structure of the lanthanoid(III) fluoride oxidomolybdates(VI) with formula LnF[MoO4] (Ln = Ce–Nd) is not isotypic to those for the smaller rare-earth metals. The title compounds crystallize monoclinically in the space group P21/n (a = 703–694, b = 660–653, c = 939–933 pm and ? ? 106°) with four formula units per unit cell. The structure contains crystallographically unique Ln3+ cations, which are surrounded by two F– and six O2– anions to form distorted bicapped trigonal prisms (CN = 8). These polyhedra are fused together by two common edges (e) consisting of two oxide anions to form ?1{[LnFOe4/2Ot2/1]6–} strands, which are finally condensed through shared fluoride vertices (v) to build up a three-dimensional ?3{[LnFv2/2Oe4/2Ot2/1]6–} network that still contains terminal (t) oxygen atoms. The Mo6+ cations reside in the tetrahedral voids of the aforementioned arrangement. This is the fundamental difference compared to the structures of the representatives with the smaller lanthanoids, in which the Mo6+ cations interconnect anionic ?2{[LnFe2/2Oe4/2Ot2/1]6–} layers to achieve their tetrahedral oxygen coordination spheres. Vibrational spectroscopic measurements such as bulk solid-state and single-crystal Raman spectroscopy as well as diffuse reflectance spectroscopy (DRS) were performed for the crystalline lanthanoid(III) fluoride oxidomolybdates(VI) and the noncrystalline samples of the dried raw products. A new solvochemical synthesis leads to noncrystalline lanthanoid(III) fluoride oxidomolybdates(VI). After thermal treatment of the crude products, single crystals of the LnF[MoO4] series (Ln = Ce–Nd) are obtained. The crystal structures are determined, and spectroscopic measurements are performed for the crystalline samples and the noncrystalline crude product.

Posted on 12 September 2014 | 10:10 am

Furan-Modified Spherosilicates as Building Blocks for Self-Healing Materials

Octafunctional spherosilicates were used to prepare self-healing hybrid materials. The hydrosilation of the octakis(hydridodimethylsiloxy)-substituted spherosilicate with furfuryl allyl ether generates an inorganic nano-building-block that is used to formulate various self-healing hybrid materials based on a reversible Diels–Alder reaction. Curing with a molecular bismaleimide results in a hard, glassy but reversibly cross-linkable hybrid material. The reversibility of the curing mechanism allows the preparation of films with a heated press, which also opens the possibility to process the materials by injection molding. Substitution of the molecular cross-linker with an oligomeric poly(dimethylsiloxane) bismaleimide results in an elastomeric material. The kinetics of the Diels–Alder reaction upon cooling after a retro-Diels–Alder reaction are mainly controlled by the mobility of the cross-linker within the system. Octameric furfuryl-functionalized spherosilicates were used to prepare self-healing hybrid materials based on a reversible Diels–Alder reaction. Two different bismaleimides were used as dienophilic cross-linkers for the self-healing materials. The healing abilities are dictated by the nature of the cross-linker.

Posted on 9 September 2014 | 10:20 am

Coordination Polymers Based on Alkylboronate Ligands: Synthesis, Characterization, and Computational Modelling

Boronate ligands [R–B(OH)3–] have recently started to attract attention for the elaboration of coordination polymer networks. Here, three new crystalline structures involving butyl- and octylboronate ligands are described: Sr[Bu–B(OH)3]2, Ca[Oct–B(OH)3]2 and Sr[Oct–B(OH)3]2 (Bu = C4H9, Oct = C8H17). All were obtained as microcrystalline powders, and their structures were solved by synchrotron powder X-ray diffraction. IR and multinuclear (13C, 11B, 43Ca, 87Sr and 1H) solid-state NMR characterizations were performed on the materials. Computational models of the new Sr[Bu–B(OH)3]2 phase and the previously reported Sr[Ph–B(OH)3]2·H2O structure were then developed. The IR O–H stretching modes and NMR parameters were calculated for these models and are discussed in view of the experimental spectra. This work confirms the importance of computational studies on boronate phases to determine the nature of the H-bond network within the materials and to better understand their spectroscopic signatures. The synthesis and characterization of three new crystalline alkylboronate structures are described, together with their DFT modelling and calculations of solid-state NMR parameters and IR O–H stretching frequencies.

Posted on 9 September 2014 | 10:20 am

Complex Formation between [(?6-p-cymene)Ru(H2O)3]2+ and Hydroxycarboxylates or their Sulfur Analogues – The Role of Thiolate Groups in Metal Ion Binding

The interactions between [(?6-p-cymene)Ru(H2O)3]2+ and L-malic acid (H2mal), L-tartaric acid (H2tart), and their sulfur-containing analogues dl-thiomalic acid (H3thiomal) and meso-2,3-dimercaptosuccinic acid (H4dmsa) were studied by pH potentiometry, NMR spectroscopy, and ESI-MS. The hydroxycarboxylates are potent metal ion binders and prevent hydrolysis at pH 7.4 in aqueous solution. Although H2mal forms mononuclear complexes with different degrees of protonation by the involvement of the alcohol/alkoxide group in addition to the carboxylate groups, the presence of binding isomers is detected for the H2tart system. The replacement of the alcohol group by a thiolate group results in the formation of dinuclear [Ru2A2] complexes as the single species over a wide pH range. Complexes with identical binding modes with H3thiomal or polymeric species with H4dmsa are identified, and the X-ray structure of [{(?6-p-cym)Ru}2(Hthiomal)2] is reported. The stereochemistry of the chiral-at-metal complexes was explored by NMR spectroscopy and is also discussed. Although the hydroxycarboxylates L-malic acid and L-tartaric acid form mostly mononuclear complexes with [(?6-p-cymene)Ru(H2O)3]2+ and can prevent hydrolysis of the metal ion, their sulfur analogues thiolactate and thiomalate prefer to bind through bridging thiolate groups to yield highly stable dinuclear [Ru2A2]-type complexes.

Posted on 8 September 2014 | 1:10 pm

Water-Soluble Heteronuclear [NaCuII6] Metallomacrocyclic Sandwich Complexes: Synthesis, Structure, Properties and In Vitro Biological Studies

The water-soluble heteronuclear metallomacrocyclic sandwich clusters [NaCu6(hpnbpda)3(OH)3(OH2)3](NO3)·4H2O (1), [NaCu6(hpnbpda)3(OH)3(OH2)3](ClO4) (2), and [NaCu6(hpnbpda)3(OH)3(OH2)3](PF6) (3) [H3hpnbpda = N,N?-bis(2-pyridylmethyl)-2-hydroxy-1,3-propanediamine-N,N?-diacetic acid] have been synthesized in methanol at room temperature and fully characterized using several analytical techniques including single-crystal X-ray diffraction. The molecular architecture of complex 1 is built from the template assembly of three dinuclear [Cu2(hpnbpda)]+ fragments through their weak oxophillic interactions with a central sodium(I) cation. A close analysis of the single-crystal X-ray structure reveals that the metallic core of cluster 1 consists of six highly distorted octahedral CuII ions arranged at the corners of a trigonal prism that encapsulates the sodium(I) ion. Complex 1 displays a rare ?3:?2:?1:?1 bridging mode of six carboxylate groups of three hpnbpda3– ligands with each bridging between two copper(II) atoms and the sodium(I) center. Variable-temperature magnetic-susceptibility measurements (2–300 K) on a powdered microcrystalline sample reveal that the paramagnetic copper centers in complex 1 are antiferromagnetically coupled to one another. Systematic biological investigation such as cytotoxicity assessment, DNA content analysis in terms of cell-cycle distribution by means of the fluorescence-activated cell sorting (FACS) method, DNA binding, DNA cleavage, and the underlying mechanism of possible apoptotic cell-death events in human cervical cancer cells (HeLa) were carried out in detail using complex 1. The in vitro assays using complex 1 in HeLa cells provided new findings that indicate its possible future therapeutic application. Theoretical calculations were carried out to find the Fukui functions at the metal sites in complex 1 to predict the possible metal centers involved in the DNA binding. Water-soluble heteronuclear metallomacrocyclic sandwich clusters [NaCu6(hpnbpda)3(OH)3(OH2)3](X) [H3hpnbpda = N,N?-bis(2-pyridylmethyl)-2-hydroxy-1,3-propanediamine-N,N?-diacetic acid; X = NO3 (1), ClO4 (2), and PF6 (3)] have been synthesized. The cytotoxicity, DNA content analysis, DNA binding and cleavage, and mechanism of possible apoptotic cell-death events in HeLa cells were performed using complex 1.

Posted on 8 September 2014 | 1:10 pm

Effect of the Metal Ion on the anti T. cruzi Activity and Mechanism of Action of 5-Nitrofuryl-Containing Thiosemicarbazone Metal Complexes

Chagas disease, caused by the protozoan parasite Trypanosoma cruzi, is a major health problem worldwide. In this work, we report the development of palladium and platinum metal complexes with 5-nitrofuryl-containing thiosemicarbazones (L) as bioactive ligands against T. cruzi and PTA (1,3,5-triaza-7-phosphaadamantane) as co-ligand. Eight new complexes of the formula [MCl(L)(PTA)] with M = Pd or Pt were synthesized and fully characterized. Most complexes showed similar activities against T. cruzi to those of the corresponding free thiosemicarbazone ligands. No significant differences between palladium and platinum complexes were observed. Metal compounds with the phenylthiosemicarbazone derivative were the most active ones (IC50 = 9.84?±?0.32 and 4.94?±?0.24 ?M for Pd2+ and Pt2+, respectively). The prepared complexes were not toxic on mammalian cells, showing selective indexes of more than 10–20. The ability of the complexes to be reduced in the parasite, which leads to toxic free radical species, was confirmed by the detection of OH· and nitroanion free radical species by ESR spectroscopy experiments. Gel electrophoresis and fluorescence experiments were consistent with an intercalating-like mode of DNA interaction for the complexes, but DNA interaction does not seem to be the main mechanism of anti T. cruzi action for these compounds. The results obtained show that complexation of the bioactive ligands with the selected metals is a valid strategy to obtain improved metal-based antiparasitic compounds. Eight complexes of formula [MCl(L)(PTA)] (M = Pd or Pt, L = 5-nitrofuryl-containing thiosemicarbazone ligands, PTA = 1,3,5-triaza-7-phosphaadamantane) were obtained. Most were active in vitro against T. cruzi. The mechanism involves bioreduction and formation of free radical species. All interact with DNA in an intercalative-like manner, but this does not lead to their antichagasic activity.

Posted on 8 September 2014 | 1:10 pm

Synthesis and Properties of a Bis[(nitronyl nitroxide)-2-ide radical anion]–Palladium Complex

The chemical reduction of a bis[(nitrosonium nitroxide)-2-ide]palladium dication, NN+-Pd-NN+, selectively produced reduced complexes: a stable radical cationic species, NN-Pd-NN+, composed of a nitronyl nitroxide (NN) and a nitrosonium nitroxide (NN+), and a stable diradical species, NN-Pd-NN. NN-Pd-NN+ showed spin-localization in one of the nitronyl nitroxide groups, i.e., slow exchange between NN and NN+, whereas NN-Pd-NN exhibited a moderately large negative exchange interaction of J/kB = –36 K with a singlet ground state. The chemical reduction of a bis[(nitrosonium nitroxide)-2-ide]–palladium dication selectively gave two different reduced species: a stable radical cationic species featuring a nitronyl nitroxide and a nitrosonium nitroxide, and a stable diradical species composed of two nitronyl nitroxide species. The radical cation species showed spin-localization in one of nitronyl nitroxide framework, whereas the diradical species exhibited spin-delocalization with a exchange interaction of J/kB = –36 K in a singlet ground state.

Posted on 8 September 2014 | 1:10 pm

Activation of a 1-Chlorophosphirane Complex by Aluminum Trichloride: Generation and Trapping of [Fc-P-W(CO)5] (Fc = Ferrocenyl)

Aluminum trichloride catalyzes the ring opening of a 1-chlorophosphirane W(CO)5 complex and its reaction with thiophene and ferrocene to give the corresponding 1-(2-thienyl)- and 1-ferrocenylphosphirane derivatives. The W(CO)5 complex of the 1-ferrocenylphosphirane is an efficient precursor of the phosphinidene complex [FcP-W(CO)5], which is trapped by tolan, trans-stilbene, and water. AlCl3 promotes the reaction of a 1-chlorophosphirane tungsten complex with thiophene and ferrocene. The 1-ferrocenylphosphirane complex is a source of [FcP-W(CO)5]; Fc = ferrocenyl.

Posted on 8 September 2014 | 1:10 pm

Structure and Vibrational Analyses of LiP15

LiP15 was synthesized by reaction of the elements in the presence of CuCl2 as a mineralizer additive in sealed silica ampoules at 823 K. The product was characterized by powder and single-crystal X-ray diffraction experiments, quantum chemical calculations and IR and Raman spectroscopy. It crystallizes in the triclinic crystal system in space group P$\bar {1}$ with the lattice parameters a = 6.974(1) Å, b = 9.008(1) Å, c = 11.294(2) Å, ? = 104.51(1)°, ? = 93.78(1)°, ? = 106.330(10)° and V = 652.1 Å3. The structure of the phosphorus-rich polyphosphide consists of tubular polyphosphide strands that are coordinated by lithium atoms to form double strands with an antiparallel arrangement. Quantum chemical investigations and structure optimizations were applied to localize the Li positions within the polyphosphide framework, and a full factor group analysis was done to understand the complex IR and Raman spectra of the title compound. LiP15 does not crystallize isotypically to compounds with the higher homologues of lithium but forms its own structure type, in contrast to previous reports. On the basis of our results, a LiP15 polymorph isotypic to KP15 might exist energetically separated by a few kJ/mol. We also predict that a second KP15 polymorph with the reported LiP15 structure would be energetically as favourable as the known one. LiP15, the most phosphorus-rich polyphosphide in the Li–P phase diagram, has been characterized by single-crystal X-ray diffraction, quantum chemical investigations and vibrational spectroscopy. It features a pronounced needlelike morphology and is extremely sensitive to mechanical stress. It crystallizes in its own structure type, which has been confirmed by XRD and quantum calculations.

Posted on 8 September 2014 | 12:40 pm

CH3N=SF2=NCH3: Structural, Conformational, and Configurational Properties in the Gaseous and in the Condensed Phases

CH3–N=SF2=N–CH3 (1) was obtained in 88?% yield from the reaction of a bis(silylated) amine RN(Si–Me3)2 with a sulfur tetrafluoride imide R?N=SF4 (R = R? = CH3). Single crystals suitable for X-ray crystallography were obtained by low-temperature crystallization; the data were collected at 120 K. Compound 1 crystallizes in the monoclinic space group P21/c with a = 5.8356(7) Å, b = 12.1665(14) Å, c = 8.1488(8) Å, ? = 110.381(7)°, Z = 4, in the anti–anti form (whereby anti or syn describe the orientation of the N–CH3 bonds with respect to opposite S=N bonds). The structural, conformational, and configurational properties of CH3–N=SF2=N–CH3 were studied by vibrational spectroscopy [IR (gas) and Raman (liquid)] and quantum chemical calculations [B3LYP and MP2 with 6-311+G(2df,p) and cc-pVTZ basis sets]. Vibrational spectroscopy in the gas and liquid phases shows evidence of a configurational equilibrium of the anti–anti form and a slightly less favored anti–syn form of CH3–N=SF2=N–CH3. The structural and configurational properties of CH3–N=SF2=N–CH3 were studied by vibrational spectroscopy, quantum chemical calculations, and X-ray crystallography. Only vibrational spectroscopy shows evidence of a conformational equilibrium of the anti–anti form and a slightly less favored anti–syn configuration. The crystalline solid at 120 K is consistent with an anti–anti form.

Posted on 8 September 2014 | 12:40 pm

Synthesis of Bulk Kesterite – A Prospective Photovoltaic Material

A rapid development of photovoltaics has been observed recently. Permanent interest in new cheap and efficient photovoltaic devices stimulates a constant search for new semiconductor materials and structures. The success of materials based on CIGS (CuIn1–xGaxSe2) is limited by the prohibitive prices of the elements In and Ga. A family of quaternary semiconducting materials of the Cu2ZnSnS4 type, crystallizing mainly in the kesterite structure, offers a promise of new cheap photovoltaic materials. Kesterite is manufactured from nontoxic and naturally abundant materials. The energy gap of Cu2ZnSnS4 is about 1.5 eV, and the absorption coefficient of this direct-band-gap material is ? > 104 cm–1 for photon energies higher than the energy gap. In this paper, we report a method of obtaining free-standing single crystals of kesterite (Cu2ZnSnS4). An advanced synthesis and characterization of bulk single crystals of kesterite are reported. Mixtures of powders of CuS, ZnS, and SnS2 were annealed in vacuo in quartz ampoules at 500–1100 °C to obtain free-standing single crystals of kesterite. SEM, TEM, XRD, Raman, and EXAFS measurements confirm the excellent structural properties of Cu2ZnSnS4 bulk single crystals.

Posted on 8 September 2014 | 12:40 pm

Monomeric Germanium(II) Amides Bearing ?-Diketiminato Ligands: Synthesis, Structural Characterization, and Thermal Properties

Germanium(II) compounds featuring ?-diketiminate-type ligands are attractive for applications as nanoparticle precursors, imaging agents, and components of electronic devices. In this work, we report the synthesis of ?-diketiminatogermanium(II) amides L?Ge(NHPh) [1, L? = {HC(CMeN–2,4,6-Me3C6H2)2}–], L?Ge(4-NHPy) (2), L?Ge(2-NHPy) (3), and LGe(2-NHPy) (4), L = {HC(CMeN–2,6-iPr2C6H3)2}–], which were obtained by the reaction of a low-valent organogermanium halide (L?GeCl or LGeCl) with a lithium salt of the respective aromatic amine (LiNHPh) or aminopyridine [Li(4-NHPy) and Li(2-NHPy)]. Compounds 1–4 were characterized with several techniques such as melting point, FTIR, 1H and 13C NMR spectroscopy, elemental analysis, X-ray diffraction, and thermogravimetric analysis (TGA). Compounds 1–3 and 4 crystallized in the orthorhombic (space group Pnma) and monoclinic (space group P21/c) crystal systems, respectively. In all cases, the geometry around the central germanium atom was highly tetrahedrally distorted. According to TGA data, 1–4 do not sublime intact but rather exhibit thermal decomposition. Steric and electronic fine-tuning of ?-diketiminate ligands led to the formation of monomeric germanium(II) amides by means of metathesis pathway. X-ray structural data show the germanium atom in a distorted-tetrahedral geometry. Thermogravimetric measurements of the Ge-based compounds suggest thermal decomposition.

Posted on 5 September 2014 | 1:30 pm

Reactivity of Bis(organoamino)phosphanes with Aluminum(III) Compounds: Straightforward Access to Diiminophosphinates by Means of Hydrogen-Atom Migration – An Experimental and Theoretical Study

The reactivity of bis(organoamino)phosphanes PhP(NHR)(NHR?) (1a–1c, in which R, R? = tBu for 1a; tBu, Dip for 1b; and Ph for 1c; Dip = C6H3–2,6-iPr2) and tBuP(NHDip)2 (1d) with Me3Al was investigated. The reaction of 1a or 1b gave in the first step compounds [PhP(NHR)(NR?)]AlMe2 (in which R, R? = tBu for 2a; tBu, Dip for 2b) as a result of methane elimination that upon heating underwent nitrogen-to-phosphorus hydrogen-atom migration under the formation of diiminophosphinates [Ph(H)P(NR)(NR?)]AlMe2 (in which R, R? = tBu for 3a; tBu, Dip for 3b). In contrast, phosphane 1c showed a reversed reaction sequence that yielded an intermediate [Ph(H)P(NHPh)(=NPh)]AlMe3 (2c) first as a consequence of hydrogen-atom migration followed by the methane elimination and formation of diiminophosphinate [Ph(H)P(NPh)2]AlMe2 (3c). The partial deprotonation of 1a,b,d using one molar equivalent of nBuLi followed by the treatment with AlCl3 smoothly produced compounds [Ph(H)P(NR)(NR?)]AlCl2 (in which R, R? = tBu for 4a; tBu, Dip for 4b) and [tBu(H)P(NDip)2]AlCl2 (4d), in which the hydrogen atom was again shifted from the nitrogen to the phosphorus atom. All studied compounds were characterized with the help of elemental analysis; 1H, 13C{1H}, 31P, and 31P{1H} NMR spectra; and in the case of 3c, 4a, 4b, and 4d by using single-crystal X-ray diffraction analysis. The phenomenon of the hydrogen-atom migration was subjected also to a theoretical survey with particular emphasis on the influence of the phosphane used. The hydrogen-atom migration in the structure of bis(organoamino)phosphanes smoothly leads to a monoanionic diiminophosphinate backbone.

Posted on 5 September 2014 | 1:30 pm

Synthesis and Structure of [Et3NH]­[Fe(HL)2] [H3L = L-2-(3,5-Di-tert-butyl-2-hydroxybenzylamino)succinic Acid] and Its Catalytic Activity towards Efficient Photodegradation of Dyes in the Presence of H2O2

A new biogenic potentially tetradentate ligand, L-2-(3,5-di-tert-butyl-2-hydroxybenzylamino)succinic acid, has been synthesized. Upon reaction with FeCl3 in the presence of triethylamine, it afforded the complex [Et3NH][Fe(HL)2] (1). The complex was structurally characterized and was used for homogeneous photocatalytic degradation of methylene blue (MB), malachite green (MG), crystal violet (CV) and rhodamine B (RhB) under visible-light irradiation in aqueous solution in the presence of H2O2. A new biomimetic amino acid ligand, L-2-(3,5-di-tert-butyl-2-hydroxybenzylamino)succinic acid (LH3), and its iron(III) complex, [Et3NH][Fe(LH)2], have been synthesized. The complex was structurally characterized. The complex was found to be an efficient catalyst for the environmentally friendly visible-light-mediated degradation and decolouriation of a number of dyes such as methylene blue.

Posted on 5 September 2014 | 1:30 pm

Structural and Reactivity Consequences of Reducing Steric Bulk of N,N?-Diarylformamidinates Coordinated to Lanthanoid Ions

Redox transmetallation/protolysis reactions between rare-earth metals, Hg(C6F5)2, and N,N?-bis(4-methylphenyl)formamidine (p-TolFormH) in THF initially produce a THF solvated species [Ln(p-TolForm)3(thf)2] (Ln = La, Ce, Nd, Sm). Upon addition of non-coordinating solvents, coordinated THF is rapidly liberated, producing unsolvated, dimeric complexes of the general formula [Ln(p-TolForm)3]2 [Ln = La (La1), Ce (Ce2), Nd (Nd3a), Sm (Sm4a)], containing rare ?-1?(N,N?):2?(N,N?) formamidinate ligands bridging between the two metal centres. Such binding is unprecedented in rare-earth N,N?-diarylformamidinate chemistry, and is generally uncommon in formamidinate or amidinate coordination chemistry. This tendency for THF liberation is metal size dependent since the smaller lutetium analogue [Lu(p-TolForm)3(thf)] (Lu5) remains solvated with a seven coordinate monomeric structure. The dimeric species Sm4a is cleaved by treatment with Ph3PO, N,N?-bis(2,6-difluorophenyl)formamidine (DFFormH), or [K(p-TolForm)(18-Crown-6)] producing [Sm(p-TolForm)3(Ph3PO)2] (Sm4b), [Sm(DFForm)2(p-TolForm)(thf)2] (Sm4c), and the charge separated [K(18-Crown-6)][Sm(p-TolForm)4] (Sm4e) respectively, the last being the first complex with a discrete [Ln(ArForm)4]– ion. A variety of rare-earth dimeric complexes of general formula [Ln(p-TolForm)3]2 [Ln = La, Ce, Nd, or Sm; p-TolForm = N,N?-bis(4-methylphenyl)formamidinate], were obtained showing unusual ?-1?(N,N?):2?(N,N?) formamidinate bridging. Dimer formation was metal size dependent.

Posted on 4 September 2014 | 2:12 pm

Reactions of Bis(dibenzobarrelenyl) Dichalcogenides with a Palladium(0) Complex: Unexpected Formations of Mono­nuclear Chalcogenide(dichalcogenolato)­palladium(II) Complexes and Dichalco­genahexacyclo Compounds

Thermal reactions of bis(dibenzobarrelenyl) dichalcogenides [(DbbS)2 and (DbbSe)2] with [Pd(PPh3)4] in toluene afforded novel mononuclear chalcogenide(dichalcogenolato)PdII complexes [Pd(EDbb-12-EDbb)(EDbb)(PPh3)] (E = S, Se) together with dichalcogenahexacyclo compounds. The reaction in the presence of PPh3 in toluene at 110 °C led to a cyclometalation to furnish the corresponding four-membered 1,2-chalcogenapalladacycles [Pd(EDbb)(PPh3)2] (E = S, Se) with dichalcogenahexacyclo compounds. The structures of these PdII complexes and cyclization products were fully characterized on the basis of their NMR spectroscopic data and X-ray analyses. In the crystalline state of [Pd(SDbb-12-SDbb)(SDbb)(PPh3)], two thiolato sulfur atoms occupy cis positions with respect to the PPh3, and the sulfide sulfur atom from the chelating sulfido(thiolato) ligand is situated at the trans position. Mononuclear chalcogenide(dichalcogenolato)PdII complexes were obtained by the reactions of bis(dibenzobarrelenyl) dichalcogenides with [Pd(PPh3)4] in toluene heated at reflux. The formations of these PdII complexes can be reasonably explained by the reaction of the 1,2-chalcogenapalladacycles with dichalcogenides through ?-bond metathesis.

Posted on 4 September 2014 | 2:12 pm

Theoretical Design of cis-Bis(imido)uranium Iodides – Electronic Structures and Spectroscopic Properties

To understand the structural and electronic properties of uranium complexes, the cis-bis(imido)uranium iodides cis-[U(NPh)2(THF)3I2] (3Ph) and cis-[U(NPh)2(THF)2I2] (2Ph) have been designed, and their structures and properties have been calculated by density functional theory (DFT) and time-dependent DFT. Four isomers (3Ph1, 3Ph2, 2Ph1, 2Ph2) were addressed in the study; these isomers have the structural feature that one iodide atom is trans to one imido group in the axial direction, and the other iodine atom is cis to the other imido group in the equatorial plane. The total system energies, geometry parameters, and vibrational spectra were similar among the respective isomers. Analyses of the electronic structures in tetrahydrofuran solution revealed that these isomeric complexes show mixed ?(U=N) and ?(Ph) character for the highest occupied molecular orbital (HOMO) and HOMO–1; the lone pairs of electrons of the iodine atom are dominant in the energetically lower occupied orbitals. U(f)-type orbitals contribute to the low-lying unoccupied orbitals, as has been generally accepted for analogous hexavalent trans-dioxouranium complexes. Three main absorption peaks were observed for 3Ph1/3Ph2 and 2Ph1/2Ph2 from time-dependent long-range-corrected functional calculations. The first one originates from the ?(U=N) bonds and the phenyl groups, and the third is related to character of the iodine atoms [?(U–I) and ?(I)]; combined ?(I) and ?(U=N) character is attributed to the middle peak. We also calculated the experimentally known trans-U(NPh)2(THF)3I2 (trans-3Ph). The comparison of trans-3Ph, 3Ph1, and 3Ph2 indicates that the cis/trans isomerism has a relatively large effect on their structural and electronic properties. The electronic and spectroscopic properties of cis-bis(imido)uranium iodides have been explored by DFT. A mixed ?(U=N) and ?(Ph) character was calculated for their highest occupied molecular orbitals. Each U=N bond forms one orbital, which contributes to the bent N=U=N molecular skeleton. The delocalized character of the N=U=N unit in the corresponding trans isomer allows its linear structure.

Posted on 4 September 2014 | 2:12 pm

Barium Titanate Torus-Like Particles: Low-Temperature Synthesis and Formation Mechanism

This work aims to clarify the mechanism of formation of torus-like barium titanate (BaTiO3) particles with a view to evaluating the properties of these hollow perovskite oxide crystals. Crystalline BaTiO3 powders have been synthesized by hydrothermal treatment of titanium-based nanotubes and barium chloride in alkaline media at 90, 110 and 200 °C for various reaction times. The possibility of obtaining hollow barium titanate particles at intermediate stages of crystallization by a low-temperature template-free process is demonstrated. The formation of a hollow in the centre of the particles is attributed to the Kirkendall effect associated with the different diffusion rates of Ba2+ and Ti4+ hydrothermal species through the (010) crystallographic plane of the BaTiO3 lattice and with the formation of vacancies. This work reports the mechanism of formation of the hollow torus-like barium titanate particles by a template-free hydrothermal method with a view to evaluating the properties of these hollow perovskite oxide crystals nanomaterials.

Posted on 4 September 2014 | 1:23 pm

Modelling the Luminescence of Phosphonate Lanthanide–Organic Frameworks

The suitability of the computer package LUMPAC to calculate the photoluminescence properties of metal–organic frameworks was assessed by considering three systems based on the ditopic 1,4-phenylenebis(methylene)diphosphonic acid (H4pmd) ligand and Ln3+ ions, namely, [Eu(Hpmd)(H2O)] (1), [La2(H2pmd)(pmd)(H2O)2] (2) and [La2(H2pmd)3(H2O)12] (3, previously reported) and their isotypical materials doped with Eu3+ cations, [(La0.95Eu0.05)2(H2pmd)(pmd)(H2O)2] (4) and [(La0.95Eu0.05)2(H2pmd)3(H2O)12] (5). These materials were prepared, and their structures and luminescence properties were characterized. A straightforward approximation based on the simple crystallographic structural subunits of these materials was used and resulted in an excellent agreement between the calculated and experimental properties. The intramolecular energy transfer and back-transfer rates were predicted, and the T1??5D1 channel was shown to be the dominant pathway (9.03?×?104 s–1 for 1, 1.06?×?104 s–1 for 4 and 2.18?×?105 s–1 for 5). The applicability of the LUMPAC software for calculations of the photoluminescence properties of metal–organic frameworks is assessed by considering three systems with a ditopic 1,4-phenylenebis(methylene)diphosphonic acid ligand and Eu3+ ions. A simple method based on the crystallographic structural subunits affords excellent agreement between the calculated and experimental photoluminescence.

Posted on 4 September 2014 | 1:23 pm

TiO2/Eu3+ Thin Films with High Photoluminescence Emission Prepared by Electrophoretic Deposition from Nanoparticulate Sols

The light emission properties of anatase TiO2/Eu3+ thin films prepared by electrophoretic deposition and of the corresponding precursor nanoparticulate sols and xerogels with different Eu3+ contents are reported. Transparent anatase TiO2 thin films were successfully obtained by electrophoretic deposition after dilution of the original sols with ethanol in order to inhibit the water hydrolysis and facilitate the drying process. The topography of the films shows a high homogeneous distribution in terms of grain size and roughness of the surface of the thin films. The film thickness varied from 50 nm to 800 nm and it was found to be strongly dependent on the Eu3+ content of the sols, probably because of uncompensated electrical charges provided by Eu3+ ions located at the surface of the nanoparticles. A spontaneous densification of the films occurs at a thickness above 400 nm and, concomitantly, a significant increase of the Eu3+ emission efficiency is detected. Transparent and nanoparticulate anatase TiO2/Eu3+ thin films were obtained by electrophoretic deposition. A densification of the films occurs at a thickness above 400 nm and, concomitantly, a significant increase of the Eu3+ emission efficiency is detected. Similar values of PL efficiency to those of the xerogels (bulk material) could be achieved.

Posted on 4 September 2014 | 1:20 pm

Nickel and Copper Complexes of Pyrrolecarboxamide Ligands – Stabilization of M3+ Species and Isolation of Ni3+ Complexes

We report NiII and CuII complexes of a few pyrrolecarboxamide ligands containing –H, –Cl, and –CH3 substituents on the phenylene ring. Solid-state X-ray diffraction and solution-based spectral studies substantiated a square-planar geometry around the metal ions in all six of the MII complexes. Electrochemical studies showed that the electronic substituents considerably influence the M3+/2+ redox potentials. All of the complexes exhibit considerably low M3+/2+ redox potentials owing to their tetraanionic coordination environments. Chemical and/or electrochemical oxidation has resulted in the isolation of Ni3+ complexes and the generation of Cu3+ species. The spectroscopic studies revealed square-planar geometries around the metal ions in the resultant Ni3+ and Cu3+ complexes. NiII and CuII complexes of pyrrolecarboxamide ligands containing –H, –CH3, and –Cl substituents are presented. Chemical and electrochemical oxidation results in the isolation of Ni3+ complexes and the generation of Cu3+ species. Spectroscopic studies reveal square-planar geometries around the Ni3+ and Cu3+ ions.

Posted on 4 September 2014 | 1:20 pm

Efficient Hybrid-Type CO2 Adsorbents of Reassembled Layered Double Hydroxide 2D Nanosheets with Polyoxometalate 0D Nanoclusters

Porous nanohybrids of cationic Mg-Al-LDH 2D nanosheets and anionic polyoxometalate (POM, V10O286– and W7O246–) 0D nanoclusters are synthesized by an exfoliation–reassembling process. The electrostatically derived reassembling between two kinds of nanostructures yields a layer-by-layer-ordered intercalation structure with porous structures composed of mesopores and micropores. The hybridization with POM leads to the remarkable enhancement of CO2 adsorption capacity (adsorptivity) of Mg-Al-LDH by about 10-fold. Of prime importance is that the CO2 adsorptivity of the nanohybrid is strongly dependent on the type of guest POM species, strongly suggesting that the CO2 adsorptivity of the LDH-based nanohybrid materials can be optimized by ones selection of guest species. The present study clearly demonstrates that the exfoliation–reassembling method is quite effective at enabling synthesis of new LDH nanosheet-based hybrid materials with improved CO2 adsorption capabilities. Porous nanohybrids of Mg-Al-layered double hydroxide (LDH) 2D nanosheets and polyoxometalate 0D nanoclusters are synthesized by an exfoliation–reassembling process. The resulting nanohybrid materials show promising CO2 adsorption capabilities exceeding those of pristine Mg-Al-LDH, underscoring the usefulness of the present hybridization method in optimizing gas adsorption by LDH materials.

Posted on 4 September 2014 | 1:20 pm

Synthesis and Characterization of the Nitrophenol Energetic Ionic Salts of 5,6,7,8-Tetrahydrotetrazolo[1,5-b][1,2,4]triazine

Nitrophenol energetic ionic salts based on the 5,6,7,8-tetrahydrotetrazolo[1,5-b][1,2,4]triazine (TZTN, 1) cation and nitrophenol anions have been synthesized in high yields by neutralization reactions. All the salts were characterized by X-ray single-crystal diffraction technology, IR spectroscopy, elemental analysis, and DSC measurements. The heats of formation of 2–4 were calculated by using isodesmic reactions. The calculated detonation pressures of these salts range from 29.7 to 32.6 GPa and their detonation velocities fall between 8337 and 8613 m?s–1; these properties make them competitive energetic materials. In addition, the sensitivities towards impact, friction, and flame were tested, and the results indicated that salts 2 and 3 have acceptable sensitivities, whereas salt 4 shows relatively high sensitivity towards impact and flame. Three nitrogen-rich energetic salts of 5,6,7,8-tetrahydrotetrazolo[1,5-b][1,2,4]triazine (TZTN) have been prepared and characterized by single-crystal X-ray diffraction analysis. The salts exhibit excellent detonation performance and combine good thermal stabilities with acceptable sensitivities.

Posted on 1 September 2014 | 2:10 pm

Main-Chain Oligomers from NiII- and CuII-Centered Unsymmetrical N2O2 Schiff-Base Complexes: Synthesis and Spectral, Structural, and Second-Order Nonlinear Optical Properties

Oligomeric main-chain Schiff-base compounds 4 and 5 have been synthesized by the trans-esterification of their respective doubly functionalized monomeric precursors [M{(?5-C5H5)Fe(?5-C5H4)C(=O)CH=C(4-C6H4OH)NCH2CH2N=CH-(2-O,4-CO2H–C6H3)}] [M = Ni (2), Cu (3)] in dmf. The new compounds were characterized by elemental analysis, FTIR and multidimensional NMR spectroscopy, mass spectrometry, and cyclic voltammetry. Compounds 2, 3, and 6, the corresponding amide of 2, were characterized by X-ray structural investigation. Gel permeation chromatography established that oligomers 4 and 5 are formed of approximately six monomeric units, and differential scanning calorimetry and thermal gravimetric analysis indicated that they are thermally stable with decomposition temperatures exceeding 230 °C. Harmonic light scattering measurements showed that compounds 2–5 exhibit rather high second-order nonlinear responses, between 224?×?10–30 and 399?×?10–30 esu, with hyperpolarizability ?1.91 values that increase significantly on passing from the monomeric to the oligomeric species. The esterification of binuclear phenol and carboxylic acid functionalized ferrocenyl-containing metal-centered Schiff-base complexes (M = Ni, Cu) in the presence of N,N?-dicyclohexylcarbodiimide and dmap afforded their corresponding main-chain oligomers. They are formed of approximately six monomeric units, are redox active, and exhibit good thermal stability and high second-order NLO responses.

Posted on 29 August 2014 | 12:20 pm

Triangular [Ag3]3+ Complexes Supported by Picolyl-Substituted N-Heterocyclic Carbene Ligands

A series of 12 picolyl-containing NHC ligand precursors and their AgI salts are reported. The complexes [Ag3{Sim(CH2pyCl)2}3]X3 [2(PF6)3], [Ag3{Sim(CH2pyBr)2}3]X3 [3(PF6)3], [Ag3{Sim(CH2isoquin)2}3]X3 [4(PF6)3], [Ag3{5,6-Cl2-benzim(CH2py)2}3]X3 [6(BF4)3], [Ag3{5,6-Me2-benzim(CH2py)2}3]X3 [7(PF6)3], [Ag3(benzim{CH2py-3,4-(OMe)2}2)3]X3 [8(PF6)3], [Ag3{benzim(CH2py-3,5-Me2-4-OMe)2}3]X3 [9(PF6)3], [Ag3(5,6-Me2-benzim{CH2py-3,4-(OMe)2}2)3]X3 [10(PF6)3], [Ag3{5,6-Me2-benzim(CH2py-3,5-Me2-4-OMe)2}3]X3 [11(PF6)3], and [Ag3{5-OMe-benzim(CH2py)2}3]X3 [12(PF6)3] (X = PF6– or BF4–) each contain a central [Ag3]3+ core spanned by three NHC ligands. The optically pure [Ag3{(R,R)-cyclohexylim(CH2py)2}3](PF6)3 [(R,R)-5(PF6)3] adopts a different coordination mode. All complexes were characterized by NMR spectroscopy and HRMS. In addition, complexes 3(PF6), (R,R)-5(PF6), 6(BF4), 7(PF6), and 8(PF6) were characterized by single-crystal X-ray diffraction and found to exhibit Ag–Ag distances of approximately 2.7 Å. A series of 12 picolyl-substituted benzimidazolylidene- and imidazolinylidene-based N-heterocyclic carbene ligands have been prepared. Eleven underwent complexation with AgI to form trimetallic complexes with short AgI–AgI metal–metal separations. In solution, all but one of these complexes are dynamic and dissociate and exchange ligands.

Posted on 29 August 2014 | 12:20 pm

Mechanistic Insights into the PdII-Catalyzed Chemoselective N-Demethylation vs. Cyclometalation Reactivity Pathways in 1-Aryl-N,N-dimethylethanamines

Two structurally isomeric substituted N,N-dimethylethanamines have been prepared. Treatment of the 2,4-di-tert-butylphenyl isomer with PdII ions generated the ortho-metalated complexes. On the other hand, treatment of the 2,5-di-tert-butylphenyl-substituted amine resulted in the unexpected chemoselective cleavage of one of the three N–C bonds, thus generating the corresponding secondary amine. The N-demethylation process could be catalyzed at room temperature by palladium(II) catalysts such as PdCl2 or Pd(OAc)2. Furthermore, treatment with a stoichiometric amount of PdII ions gave a metal complex in which both secondary amines were bound to Pd in an N-monodentate fashion. When triethylamine was introduced, one of the N-ethyl groups in NEt3 was cleaved, and an unexpected heteroamine complex was produced. The products generated were isolated and characterized by X-ray crystallography. Mechanistic insights into the cyclometalation and C–N cleavage observed are discussed. Two structurally isomeric substituted N,N-dimethylethanamines have been prepared. Treatment of one isomer with PdII ions generated the ortho-metalated complex, whilst the other isomer resulted in the unexpected chemoselective C–N bond cleavage to afford the corresponding secondary amine.

Posted on 29 August 2014 | 12:20 pm

Synthesis, Structures and Coordination Chemistry of Singly Bridged Phosphane-Boranes with Coordinately Unsaturated Platinum Group Metals

A range of singly bridged phosphane-boranes (PBs) have been investigated as potential ligands for basic transition metals. The PBs Ph2PC(Ph)=C(R)BR2 (R = Bu 1, Ph 2, Et 3), based on a rigid cis-ethylene bridges, have been prepared, improving upon limited literature precedent. All three compounds have been comprehensively characterised for the first time, including by X-ray diffraction studies. Significant intramolecular PB association is apparent in each case, which serves to preclude their engagement as ligands. In contrast, the more flexible PBs R2P(CH2)2BBN (R = Fu 5, Ph 6) readily coordinate to the platinum group metals Pt, Pd and Rh. These complexes have been fully characterised, including an X-ray diffraction study of [Rh(CO){Fu2P(CH2)2BBN}2Cl] (13). The synthesis and characterisation of a range of singly bridged phosphane-boranes is described. Their coordination complexes with co-ordinately unsaturated platinum group metals demonstrate a propensity for adopting structures with pendant borane moieties occupying distal positions.

Posted on 29 August 2014 | 12:20 pm

Unusual Solvent Dependence of a Molecule-Based FeII Macrocyclic Spin-Crossover Complex

This work illustrates in detail the reversible hydration–dehydration process of a molecule-based material, which involves a drastic change of the switchable magnetic properties of the sample. Concretely, the complex [FeL222N3O2(CN)2]·H2O exhibits a spin crossover (SCO) accompanied by a change of the coordination number. The dehydration and rehydration of this SCO complex was carried out and monitored by different methods, which include X-ray diffraction analysis. The corresponding samples display a thermal spin transition as well as a thermal quenching of the metastable high-spin state at low temperature. In particular it was observed that the rehydrated material exhibits a particularly high temperature of relaxation, T(TIESST), of the metastable high-spin state. On the other hand, it was shown that this compound exhibits a uncommon correlation between T(TIESST) and the thermal SCO, as compared with other spin-crossover compounds that do not exhibit a change in coordination number. The solvent dependence of spin-crossover behavior and metastability of the FeII complex [FeL222N3O2(CN)2]·H2O were investigated. Compared with the pristine and the dehydrated complex, the rehydrated complex shows enhanced metastability and an increased spin-transition temperature. This solvent dependence indicates new possibilities to improve metastability toward further applications.

Posted on 29 August 2014 | 12:20 pm

Evolution of the Coordination-Sphere Symmetry in Copper(II), Nickel(II), and Zinc(II) Complexes with N,N?-Double-Armed Diaza-Crown Ethers: Experimental and Theoretical Approaches

N,N?-Bis(triazolyl)diaza[18]crown-6 and corresponding diaza[15]crown-5 ethers were synthesized by means of click chemistry. The interaction of these ligands with NiII, CuII, and ZnII cations were studied by UV/Vis and 1H and 13C NMR spectroscopy. The solid-state structure of NiII and ZnII complexes formed by the diaza[18]crown-6 ligand were determined by means of X-ray crystallography. The NiII complex is centrosymmetric; the geometry around the metal ion is slightly distorted octahedral whereby the equatorial sites were occupied by four N atoms, and the axial positions by two O atoms that come from the crown moiety. For the ZnII–diaza[18]crown-6 complex, an irregular octahedral coordination was observed whereby the metal ion is asymmetrically placed in the macrocyclic cavity. The equatorial plane is occupied by two N and two O atoms of the crown moiety, and two N atoms of the triazolyl motifs on the pendant arms occupy the axial positions. The diamagnetic character of the ZnII ion allows its structural study in solution by NMR spectroscopy. A dynamic behavior was observed at room temperature, which corresponds to the displacement of the ZnII ion between the bond end and the nonbond end of the macrocycle. This movement results in an S4-symmetrical structure in solution. Quantum chemical calculations at the DFT level have allowed us to interpret the experimental results observed in the solid state for the symmetry of the complexes in terms of covalent and noncovalent interactions, which favor the centrosymmetric and irregular octahedral coordination modes, respectively. Only the structure of the CuII complex with N,N?-bis(triazolyl)diaza[15]crown-5 ligand has been investigated in the solid state, for which a pentagonal bipyramidal coordination sphere was observed. This coordination geometry was confirmed in solution in MeCN by UV/Vis spectroscopy, and also for the ZnII complex by NMR spectroscopy. In the case of the NiII complex, a structural modification was suggested in solution in MeCN based on the UV/Vis spectrum. The rearrangement of heptadentate coordination to hexadentate is proposed. Symmetric versus asymmetric octahedral coordination geometry changes were observed for Cu2+, Ni2+, and Zn2+ complexes of a N,N?-triazolyl-biarmed diaza[18]crown-6 macrocycle. Quantum chemical calculations at the DFT level confirmed these observations and allowed us to interpret them in terms of covalent or noncovalent metal–ligand interactions.

Posted on 29 August 2014 | 12:10 pm

New Lithium-Containing Pnictides with 1-D Infinite Chains of Supertetrahedral Clusters: Synthesis, Crystal and Electronic Structure of Ba4Li2Cd3Pn6 (Pn = P, As and Sb)

The novel complex pnictides Ba4Li2Cd3Pn6 (Pn = P, As and Sb) have been synthesized by direct combination of the respective elements at high temperature, and structurally characterized by single-crystal X-ray diffraction. The three isostructural compounds crystallize with their own structure type in the centrosymmetric orthorhombic space group Cmcm (Pearson code oC60). The crystal structure is based on one-dimensional infinite chains of supertetrahedral clusters, [Cd4Pn10], running parallel the a-axis. These chains are connected through Pn2-type dumbbells. Tight-binding electronic structure calculations show that the electronic stability of these compounds requires strong covalent Pn–Pn and Cd–Pn bonds. The interactions within the polyanionic sub-structure are complimented by weaker Ba–Pn and Li–Pn bonds, which also show a substantial degree of covalency, and the strength of all interactions correlates very well with the corresponding interatomic distances. The precise satisfaction of the valence rules and the Zintl–Klemm concept is not essential though as structural vacancies on Cd and Li sites bring about an interplay between ionicity and covalency among the electronegative components. Electronic structure calculations show that Ba4Li2Cd3P6 is expected to be a semiconductor with a band gap of ca. 0.5 eV, while the gap decreases and vanishes altogether for the As- and Sb-analogs, respectively. Solid solutions between arsenides and antimonides appear possible, which could be an effective way to fine-tune transport properties. Since the latter two compounds can be considered as moderately-to-heavily doped intrinsic semiconductors, these materials might be suitable candidates for thermoelectric applications. Three new Zintl phases have been synthesized for the first time, and their crystal structures have been established by single-crystal X-ray diffraction. They crystallize with their own-structure type in the orthorhombic space group Cmcm (Pearson code oC60) and their crystal structure is based on one-dimensional infinite chains of supertetrahedral clusters, [Cd4Pn10].

Posted on 29 August 2014 | 12:10 pm

Two-Dimensional {Co3+–Co2+} and {Fe3+–Co2+} Networks and Their Heterogeneous Catalytic Activities

We report the synthesis and characterization of two-dimensional homodimetallic {Co3+–Co2+} and heterodimetallic {Fe3+–Co2+} coordination networks with Co3+- and Fe3+-based metalloligands. The crystal structures reveal 2D networks in which the metalloligands are connected through secondary Co2+ ions. The kinetic lability of the secondary Co2+ ions, their Lewis acidity, and the presence of dissociable coordinated water molecules have been utilized in Knoevenagel condensation and cyanation reactions of assorted aldehydes. These reusable networks catalyze these reactions heterogeneously and efficiently. Reusable two-dimensional {Co3+–Co2+} and {Fe3+–Co2+} networks heterogeneously catalyze Knoevenagel condensation and cyanation reactions of assorted aldehydes owing to the kinetic lability and Lewis acidity of the secondary Co2+ ions.

Posted on 29 August 2014 | 12:10 pm

An Ionic Dysprosium Complex Made of a Hexanuclear Dy6 Cationic Cluster and a Mononuclear Dy Anionic Unit

A genuine 2-hydroxy-N?-{[3-(hydroxyimino)butan-2-ylidene]}benzohydrazide ligand, characterized by 1H, 13C, and 15N NMR spectroscopy and chemical analysis, has been used to synthesize a novel ionic dysprosium species. The structural determination confirms the existence of a hexanuclear Dy cationic entity along with a mononuclear Dy anionic unit. The topological analysis of the hexanuclear cluster indicates that it corresponds to a 2,4M6–1 graph, observed for the first time for Dy complexes. The electrostatic model for the determination of the magnetic anisotropy in Dy complexes implemented in the Magellan program confirms that it is difficult to control the orientation of the different anisotropy axes of the six Dy ions in order to obtain large anisotropy in polynuclear Dy entities, which is in agreement with the ac susceptibility measurements that show frequency-dependent signals and absence of maxima for the out-of-phase susceptibility signals above 2 K, even under a dc bias field of 0.1 T or 0.2 T. A novel hydrazide ligand allows the preparation of an ionic species made of a cationic hexanuclear Dy6 cluster and an anionic mononuclear Dy unit, which corresponds to the 2,4M6–1 + 1(0) motif observed for the first time with Ln ions.

Posted on 27 August 2014 | 12:10 pm

Efficient Ruthenium Sensitizer with a Terpyridine Ligand Having a Hexylthiophene Unit for Dye-Sensitized Solar Cells: Effects of the Substituent Position on the Solar Cell Performance

A novel ruthenium sensitizer with a terpyridine ligand having a hexylthiophene unit at the 4-position (TUS-38) has been synthesized to investigate the effects of the substituent position on the photo- and electrochemical properties and on solar cell performance. The dye-sensitized solar cell (DSC) with TUS-38 showed a 10.6?% conversion efficiency under AM 1.5 (100 mW/cm2) irradiation, which is much higher than that of the DSC with a previously reported ruthenium sensitizer with a terpyridine ligand having two hexylthiophene units at the 5- and 5?-positions. A novel ruthenium sensitizer with a terpyridine ligand having a hexylthiophene unit at the 4-position (TUS-38) has been synthesized, and the dye-sensitized solar cell with TUS-38 showed a 10.6?% conversion efficiency under AM 1.5 (100 mW/cm2) irradiation.

Posted on 27 August 2014 | 12:10 pm

Chromophores, Fluorophores and Robust Ancillary Ligands for Molecular Catalysts: 1,3-Bis(2-pyridylimino)isoindolines

Since the first report in the early 1950s, 1,3-bis(2-pyridylimino)isoindolines (BPIs) have found widespread applications in organic, inorganic and materials chemistry. This microreview focuses on recent progress towards chiral BPI derivatives as ligands for enantioselective catalysis as well as developments in the use of BPI complexes in materials science, focusing on luminescent and birefringent materials. This microreview focuses on the development of 1,3-bis(2-pyridylimino)isoindolines (BPI) from their synthesis over half a century ago through to their current diverse applications in organic, inorganic and materials chemistry.

Posted on 27 August 2014 | 12:10 pm

Unprecedented Borylene Insertion into a C–N Bond

Carbenes are well established reactive intermediates and play an important role in organic synthesis, whereas the scope of borylenes is rather limited. Selective borylene insertion into a C–N bond to yield boryl-functionalized N-heterocyclic olefins (NHOs), [{N(Dipp)N(DippBH)CHCH}CCH2]2 (6) and [{N(Dipp)N(DippBPh)CHCH}CCH2][{N(Dipp)N(2-iPr-6-CHMeCH2BC6H3)CHCH}CCH2] (8) (Dipp = 2,6-iPr2C6H3) is reported for the first time. KC8 reduction of (IPrCH2)BRX2 adducts (IPrCH2 = {N(Dipp)CH}2CCH2; R = X = I (2); R = Ph, X = Cl (4)) affords compounds 6 and 8. Surprisingly, treatment of (IPrCH2)BHCl2 (3) with KC8 yields completely unexpected diborane compound (IPr)BH2BH2(IPr) (7). Compound 2 is unstable in THF and induces ring opening reaction to form the borenium ion [(IPrCH2)B{O(CH2)4I}2]I (5). Formation of a boryl-functionalized NHO 6 as a dimer suggests the involvement of a borylene insertion into a C–N bond. The parent borylene (R = H) follows a completely different route in which hydrogen abstraction and intermolecular B–B coupling events seem operative to afford a diborane (7) stabilized by an NHC.

Posted on 26 August 2014 | 10:20 am

Chiral MnIII–salalen and –salan Complexes Derived from (S)-Pyrrolidin-2-yl­methanamine and Their Catalytic Activity in the Asymmetric Strecker Reaction

The salalen and salan ligands have been synthesized by the reactions of (S)-pyrrolidin-2-ylmethanamine and salicylaldehyde derivatives. These ligands were treated with Mn(CH3COO)2·4H2O followed by air oxidation to give (S,R)-MnIII–salalen and –salan complexes in yields of 84–88?%. The absolute configuration of (S,R)-MnIII–salalen was determined by single-crystal X-ray diffraction and CD analysis of the ligands and complexes showed similiar Cotton effects. The MnIII–salalen and –salan complexes were screened for their catalytic activity in the asymmetric Strecker reaction. (S,R)-2,4-Di-tert-butyl-6-({[1-(3,5-di-tert-butyl-2-hydroxybenzyl)pyrrolidin-2-yl]methylimino}methyl)phenolatomanganese(III) chloride (5 mol-%) was found to be a suitable catalyst for the asymmetric Strecker reaction of N-(4-methoxybenzylidene)diphenylmethanamine with ethyl cyanoformate, which gave 89?% yield and 55?% ee of 2-(benzhydrylamino)-2-(4-methoxyphenyl)acetonitrile at –15 °C after 24 h. Chiral MnIII–salalen and –salan complexes have been synthesized and used as a catalyst for the asymmetric Strecker reaction. These complexes were characterized by elemental analysis, FTIR and UV/Vis spectroscopy, exact mass determination and single-crystal XRD. The catalyst 9a catalysed the Strecker reactions of a range of substrates with moderate enantioselectivity of the corresponding products.

Posted on 26 August 2014 | 10:20 am

The Nature of the Active Site in Ziegler–Natta Olefin Polymerization Catalysis Systems – A Computational Investigation

Full quantum chemical calculations with density functional theory (DFT) show that a principal role of donors in Ziegler–Natta (ZN) olefin polymerization catalysts is to coordinate to the metal center at the active sites on the MgCl2 surface. Thereby, the behavior of the catalyst is modulated to favor insertion over termination and, thus, polymerization occurs. This is shown to be true for a range of different donors. The calculations indicate that active sites that feature anionic chloride ligands at the titanium center (the conventional model for the active site) would lead to lower-molecular-weight polymers. If an –OC2H5 group were present instead of a chloride ligand, the active site would much more effectively produce long chain polymers. Therefore, the current work provides important new insights into the nature of the ZN polymerization process. The nature of the active site in Ziegler–Natta heterogeneous catalysis systems has been explored with density functional theory (DFT). New insights include the understanding that donor coordination to the metal center can lead to an increase in the molecular weight of the polymer. The role of AlEt3 as a possible donor has also been investigated.

Posted on 26 August 2014 | 10:20 am

Electrochemical Implication of a Hydrogen-Bonded Imidazole on a Redox-Active-Bound Phenolate Group

We report the synthesis of a pentadentate N4O ligand with an imidazole group in the ortho position of the phenol group. The syntheses and crystallographic structures are reported for zinc(II) complexes by using the previously reported tert-butyl-substituted ligand and the imidazole-substituted ligand in two different protonation states. We describe the influence of the ortho substituent (tert-butyl, imidazole, and imidazolium) on the electrochemical behavior of the zinc(II) complexes. The substitution of the tert-butyl group in the ortho position by an imidazole group shifts the oxidation potential of the phenolate by more than 300 mV. The o-tert-butyl-substituted ligand allows the formation of a stable radical phenoxylzinc(II) complex upon electrochemical oxidation, but it is unstable in the case of the imidazole-substituted complex. The imidazole-substituted ligand can be reversibly protonated without altering the electrochemical properties of the phenolate group. We report the synthesis and crystallographic structures of zinc complexes with a pentadentate N4O ligand with an imidazole group placed in the ortho position of the phenol group. Furthermore, we describe the influence of the outer-sphere imidazole fragment on the electrochemical behavior of the redox-active-bound phenolate ligand.

Posted on 25 August 2014 | 12:10 pm

Mono- and Hetero-Dinuclear Complexes of Janus-Head NHC Ligands Possessing Backbone Phosphinoyl Groups: the Case of Soft and Hard Metal Centers

The synthesis and structures of RhI and IrI complexes bearing 4-phosphinoyl- and 4,5-bis(phosphinoyl)imidazol-2-ylidene ligands (NHCP) is reported. Deprotonation of the corresponding imidazolium hydrogen sulfate salts by KOtBu in the presence of [M(cod)Cl]2 afforded complexes of the formula [M(cod)Cl(NHCP)] [5a/5b: NHCP = 4-Ph2P(O)-IiPrMe, 5a: M = Rh, 5b: M = Ir and 7a/7b: NHCP = 4,5-{Ph2P(O)}2-InBuMe]. The RhI complexes 5a and 7a were then converted into [Rh(CO)2Cl(NHCP)] 8a and 9a via reaction with carbon monoxide; the average CO stretching frequencies [8a: $\tilde {\nu}$(CO)av = 2036 cm–1 and 9a: $\tilde {\nu}$(CO)av = 2038.4 cm–1] led to the conclusion that mono- and bis-functionalized NHCPs act as relatively weaker donors than backbone unsubstituted NHC. A first examination of Janus-head ligand properties of complex 7a revealed that reaction with TiCl4 afforded hetero-dinuclear 10a,a? as a mixture of isomeric monodentate phosphinoyl titanium(IV) adducts. All products were characterized by elemental analyses, spectroscopic and spectrometric methods and, in addition, complexes 7a and 7b by single-crystal X-ray structure analysis. A family of hybrid ligands composed of hard phosphine oxides and soft N-heterocyclic carbene donor sites have been employed to synthesize [M(cod)Cl(NHCP)] complexes I, which were further converted into the corresponding dicarbonyl complexes in order to study their donor properties. The advantage of backbone phosphinoyl groups was exploited to generate hetero-dinuclear TiIV, RhI complexes 10a,a?.

Posted on 25 August 2014 | 12:10 pm

Synthesis of Metforminium(2+) Decavanadates – Crystal Structures and Solid-State Characterization

Three new compounds were formed between decavanadate and diprotonated metformin (H2Metf) at different pH values and in the presence or absence of ammonium cations, namely, [H2Metf]3[V10O28]·8H2O (1), [H2Metf]2[NH4]2[V10O28]·10H2O (2), and [H2Metf]2[NH4]2[V10O28]·4H2O (3). We present their spectroscopic, thermal, and single-crystal X-ray diffraction characterization. The solid-state structure of 1 shows that the three H2Metf2+ dications that counterbalance the charge of the decavanadate anion are in the close vicinity of the latter, as a result of the strong Coulombic forces that arise from the ionic charges. The replacement of one metforminium(2+) cation by two ammonium cations results in two hydrates 2 and 3, which differ only in their water content. Although 2 and 3 crystallize in the same centrosymmetric space group as 1, a remarkable difference for 2 and 3 is that the [V10O28]6– anion is placed on an inversion center, which is not the case for 1. The synthesis, solid-state characterization, and X-ray analyses of three new metforminium(2+) decavanadates are presented. The compositions and stabilities of the three hydrates are strongly modified by the stoichiometry of the reaction and the presence or absence of ammonium cations.

Posted on 25 August 2014 | 12:10 pm

A Nickel-Containing Model System of Acireductone Dioxygenases that Utilizes a C(1)-H Acireductone Substrate

A mononuclear NiII complex bearing the monoanion of 1-acetoxy-3-phenylpropane-2,3-dione (4) as a ligand has been prepared {[(6-Ph2TPA)Ni{PhC(O)C(O)CHOC(O)CH3)]ClO4, 5; 6-Ph2TPA = N,N-bis[(6-phenyl-2-pyridyl)methyl]-N-(2-pyridylmethyl)amine}. This complex was characterized by 1H NMR, UV/Vis and IR spectroscopy, mass spectrometry, and elemental analysis. Exposure of solutions of 5 to O2 did not result in any reaction over the course of hours. Deprotection of 5 by the addition of NaOCH3 in methanol generated a NiII species (6) that contains a coordinated dianionic C(1)-H acireductone. Exposure of 6 to O2 led to regioselective oxidative cleavage reactivity akin to that found for the NiII-containing acireductone dioxygenase enzyme. The strategy outlined herein is the first synthetic approach that enables examination of the oxidative reactivity of a synthetic NiII species containing a dianionic C(1)-H acireductone ligand. A NiII complex of a protected C(1)-H acireductone ligand can be deprotected by using NaOCH3 in the presence of O2 to give oxidative aliphatic C–C bond-cleavage products akin to those produced by the NiII-containing acireductone dioxygenase enzyme.

Posted on 25 August 2014 | 12:10 pm

Properties of an Indium Tin Oxide Electrode Modified by a Laser Nanostructured Thin Au Film for Biosensing

Structural, optical, and electrochemical characteristics of the indium tin oxide (ITO) electrode modified by Au nanoparticle (NPs) produced by pulsed UV laser irradiation of thin films are investigated in this work. Properties of the NP arrays depend on the film thickness and parameters of the laser interaction. Semi-regular structures characterized by broad size distributions of mean values ca. 62–92 nm are observed in the SEM images. In absorbance spectra the plasmon resonance peaks located around 544 nm reveal an IR shift and an increase of damping of the plasmonic enhancement with increasing NP size. Despite the broad size distribution and negative effect of damping that results in plasmon decay times of below 3.2 fs, the ITO electrode modified by Au NP arrays shows marked improvement of the electrochemical activity towards the Fe2+/Fe3+ redox couple and also glucose. Results obtained for non-enzymatic glucose detection indicate the potential for cost-effective solutions in the area of biosensing. Thin Au films on ITO that were stepwise patterned by means of nanosecond UV laser pulses transformed into semi-regular nanoparticle arrays. The modified electrode showed enhanced activity towards ferricyanide redox systems as well as glucose, and can be considered for the production of a non-enzymatic biosensor.

Posted on 21 August 2014 | 12:13 pm

Tetranuclear Nickel and Cobalt Complexes with an Incomplete Double-Cubane Structure – Homo- and Heterometallic Complexes and Their 1D Coordination Polymers

The reactions of M(OAc)2·4H2O (M = Ni, Co) with three unsymmetrical amine-diol ligands RN(CH2CH2OH)(CH2CH2CH2OH) (H2Ln: n = 1, R = benzyl; n = 2, R = 4-methylbenzyl; n = 3, R = 2-naphthalenylmethyl) in the presence of NEt3 or pyridine in MeOH or BnOH gave the tetranuclear complexes [M4(HLn)2(OAc)6(MeOH)2] {M = Ni, n = 1 (1a), 2 (1b), 3 (1c); M = Co, n = 1 (4a), 2 (4b), 3 (4c)} and [M4(HLn)2(OAc)6(BnOH)2] {M = Ni, n = 1 (2a), 2 (2b), 3 (2c); M = Co, n = 1 (5a), 2 (5b), 3 (5c)}. When p-xylene-?,??-diol was used instead of monoalcohols, the tetranuclear {M4O6} units were linked by p-xylene-?,??-diol to form the 1D coordination polymers [M4(HLn)2(OAc)6(p-HOCH2C6H4CH2OH)]m {M = Ni, n = 1 (3a), 2 (3b); M = Co, n = 1 (6a), 2 (6b)}. The structures of 1–6 were determined by X-ray crystallography and consist of centrosymmetrical tetranuclear {M4O6} face-shared defective double-cubane cores supported by two monodeprotonated (HLn)– ligands. The mixed-metal tetranuclear complexes [Ni2.2Co1.8(HL1)2(OAc)6(MeOH)2] (7) and [Mn1.7Ni2.3(HL1)2(OAc)5(OMe)2] (8) were also synthesized by using equimolar amounts of Ni2+ and M2+ (M = Co, Mn) ions. X-ray crystallographic and fluorescent analyses revealed that 7 is isomorphous with 1a and 4a and contains nonstoichiometric amounts of disordered Ni2+ and Co2+ ions in an average ratio of 2.2:1.8 with different occupancies for the two crystallographically independent metal centers. In contrast, 8 consists of a C2-symmetrical face-shared defective double-cubane {MII3MnIIIO6} core with a Ni/Mn ratio of 2.3:1.7; the amounts of Ni2+ and Mn2+ ions vary depending on the metal sites, and one of the C2 axial positions is exclusively occupied by Mn3+ ions. Detailed magnetostructural analyses on the nickel (1a, 2a, 3a) and cobalt (4a) complexes with appropriate spin-Hamiltonian models showed that both ferro- and antiferromagnetic spin exchange interactions were involved within the tetranuclear units, and their extent depends on the combination of the metal ions and the ligand systems in a delicate fashion. Unsymmetrical amine-diol ligands are suitable for the assembly of homo- and heterometallic tetranuclear {M4O6} complexes. 1D coordination polymers are formed by linking the tetranuclear nickel and cobalt complexes with a diol linker ??((<=Author: the size of the graphic for the table of contents had to be reduced for technical reasons))??.

Posted on 21 August 2014 | 12:13 pm

Mid- and Far-Infrared Marker Bands of the Metal Coordination Sites of the Histidine Side Chains in the Protein Cu,Zn-Superoxide Dismutase

Vibrational spectroscopy gives important information on the properties of ligand and metal–ligand bonds in metalloenzymes. Infrared spectroscopy is appealing for the study of metal active sites that are not amenable to Raman spectroscopy. We present a combined experimental and theoretical approach to analyze the mid- and far-IR spectra of Cu,Zn-superoxide dismutase (Cu,Zn-SOD) as a probe of the histidine ligands. This metalloenzyme provides a unique model to identify specific IR signatures of metal–histidine coordination and to study their alterations as a function of the metal (copper/zinc), the copper valence state (+I/+II), the histidine coordination mode (N? and N?) and the histidine protonation state. DFT calculations combined with normal mode descriptions from potential energy distribution calculations were performed on two slightly different cluster models. Differences in the constraints at the side chain of one histidine Cu ligand sensibly modify the geometric parameters and vibrational properties. Electrochemically induced FTIR difference spectroscopy provided mid- and far-IR fingerprint spectra of the Cu protein in aqueous media that are sensitive to the redox state of the Cu centre at the active site. Comparisons of the DFT predictions with the experimental IR modes of the histidine ligands at the Cu,Zn-SOD active site showed that useful mid-IR markers of histidine N? and N? coordination were predicted with good accuracy. The DFT analysis further demonstrated a link between the ?(C4–C5) mode frequency of His46 and the specific properties of the His46–Cu bond in Cu,Zn-SOD. A combined theoretical and experimental approach on samples in H2O and 2H2O or 15N-labelled samples identified the contributions from the histidine side chain modes in the 669–629 cm–1 region. The metal–histidine vibrations of the Cu,Zn-superoxide dismutase enzyme are analyzed by mid- and far-infrared difference spectroscopy. The histidine metal–ligand markers are analyzed and assigned from a combination of experimental and computational data. The contributions of the histidine modes are identified through additional data collected and calculated for labelled samples.

Posted on 21 August 2014 | 12:12 pm

Protonated Digermane, Distannane, and Diplumbane: Can They Be Made in the Laboratory?

The geometries, proton affinities, and relative energies of protonated digermane (Ge2H7+), distannane (Sn2H7+), and diplumbane (Pb2H7+) have been investigated by density functional theory using the correlation-consistent cc-pVnZ-PP basis sets (n = D, T, Q). The results of the caluclations are consistent with the very limited experimental and theoretical results that are available. The lowest-lying structure of Ge2H7+ is predicted to have C2 symmetry with a bent 3-center-2-electron Ge–H–Ge bridge, analogous to Si2H7+. For Sn2H7+ and Pb2H7+, the lowest-lying structures are predicted to be different, with a D3d structure for Sn2H7+ and a C1 structure for Pb2H7+. The predicted proton affinities decrease in the order Pb2H6 (9.84 eV)?>?Sn2H6 (8.48 eV)?>?Ge2H6 (8.11 eV)?>?Si2H6 (7.72 eV)?>?C2H6 (6.18 eV). Similarly to C2H7+ and Si2H7+, the Ge2H7+, Sn2H7+, and Pb2H7+ cations are predicted to be energetically favorable to varying degrees, and they appear to have different low-lying structures.

Posted on 20 August 2014 | 11:10 am

Vapochromic Platinum(II) Complexes: Crystal Engineering toward Intelligent Sensing Devices

Vapochromic materials that show reversible color change driven by vapor adsorption/desorption have drawn significant attention because of their potential applications in chemical sensors and chemical-switching modules. Among the vapochromic coordination complexes reported so far, a series of square-planar PtII complexes has been studied and represents one of the most promising systems for practical chemical sensors. For such systems, the color of the complexes strongly depends not only on the ligand-field splitting, but also on the intermolecular distance between the PtII ions. This microreview presents recent results of vapochromic complexes centered on one-dimensionally stacked PtII systems from the viewpoint of the origin of their vapochromic behavior. The design of vapochromic materials has been facilitated because several useful chromophores, including metallophilic interaction between PtII ions, have been developed. However, it is still challenging to realize a specifically sensitive and selective response to targeted vapors. This review focuses on strategies to achieve assembled PtII complexes with selective vapochromic responses. Square-planar platinum(II) complexes that exhibit intense changes in luminescence and color based on metallophilic interactions are promising vapochromic materials. In an effort to generate highly sensitive and selective vapor responses, various PtII complexes have been developed by utilizing different intra- and intermolecular interactions.

Posted on 20 August 2014 | 11:10 am

Synthesis, Characterisation and Antiproliferative Studies of Allyl(dicarbonyl)(cyclopentadienyl)molybdenum Complexes and Cyclodextrin Inclusion Compounds

The complexes [(?5-C5H4–CO–R)Mo(CO)2(?3-C3H5)] [R = OH (1), Phe–OMe (2)] have been examined as guests for the cyclodextrin (CD) hosts ?-CD and heptakis(2,3,6-tri-O-methyl)-?-CD (TRIMEB), and the resultant inclusion compounds have been characterised in the solid state by elemental and thermogravimetric analyses, powder X-ray diffraction, 13C{1H} cross-polarisation (CP) magic angle spinning (MAS) NMR spectroscopy and FTIR spectroscopy. Single-crystal X-ray analysis of 1 shows that the unit cell contains centrosymmetric supramolecular dimers comprising two dicarbonyl complexes linked through hydrogen-bonding interactions involving the carboxylic acid groups. In screening tests for antiproliferative effects, the CD adducts containing 1 displayed enhanced antitumour activity against mouse melanoma (when compared with nonincluded 1), while showing minimal activity towards human adenocarcinoma and nontumour rat myoblast cell lines. TRIMEB encapsulation resulted in a predominant toxic effect on tumour cells versus the non-neoplastic myoblast cells. The crystal structure of [(?5-C5H4–COOH)Mo(CO)2(?3-C3H5)] (1) is presented. Both 1 and its phenylalanine derivative were included into ?-cyclodextrin (CD) and per-O-methylated ?-CD (TRIMEB). Overall, the inclusion contributed to a higher and more specific action on tumour cells, thereby lowering deleterious effects on a healthy myoblast line.

Posted on 19 August 2014 | 11:20 am

Tetranuclear Copper(II) Complexes with Macrocyclic and Open-Chain Disiloxane Ligands as Catalyst Precursors for Hydrocarboxylation and Oxidation of Alkanes and 1-Phenylethanol

Two new tetranuclear copper(II) complexes [Cu4(?4-O)(L1)Cl4] (1) and [Cu4(?4-O)(L2)2Cl4] (2), where H2L1 is a macrocyclic ligand resulting from [2+2] condensation of 2,6-diformyl-4-methylphenol (DFF) and 1,3-bis(aminopropyl)tetramethyldisiloxane, and HL2 is a 1:2 condensation product of DFF with trimethylsilyl p-aminobenzoate, have been prepared. The structures of the products were established by X-ray diffraction. The complexes have been characterised by FTIR, UV/Vis spectroscopy, ESI mass-spectrometry and magnetic susceptibility measurements. The latter revealed that the tetranuclear complexes can be described as two ferromagnetically coupled dinuclear units, in which the two copper(II) ions interact antiferromagnetically. The compounds act as homogeneous catalyst precursors for a number of single-pot reactions, including (i) hydrocarboxylation, with CO, H2O and K2S2O8, of a variety of linear and cyclic(n = 5–8) alkanes into the corresponding Cn+1 carboxylic acids, (ii) peroxidative oxidation of cyclohexane, and (iii) solvent-free microwave-assisted oxidation of 1-phenylethanol. Two new tetranuclear copper(II) complexes act as homogeneous catalyst precursors for the single-pot hydrocarboxylation of a variety of linear and cyclic Cn (n = 5–8) alkanes into the corresponding Cn+1 carboxylic acids, peroxidative oxidation of cyclohexane, and solvent-free microwave-assisted oxidation of 1-phenylethanol.

Posted on 18 August 2014 | 11:10 am

Redox and Photochemistry of Bis(terpyridine)ruthenium(II) Amino Acids and Their Amide Conjugates – from Understanding to Applications

The push-pull-substituted bis(terpyridine)ruthenium(II) amino acid [Ru(4?-tpy-COOH)(4?-tpy-NH2)]2+ ([5]2+; tpy = 2,2?;6?,2?-terpyridine) with carboxylic acid and amino substituents features exceptional chemical and photophysical properties. Its interaction with photons, electrons, and/or protons results in room-temperature phosphorescence, reversible oxidative and reductive redox chemistry, reversible acid/base chemistry, proton-coupled electron transfer, photoinduced reductive and oxidative electron transfer, excited-state proton transfer and energy transfer reactions. These properties can be fine-tuned by variations of the bis(terpyridine) amino acid motif, namely extension of the ? system and expansion of the chelate ring. Furthermore, the chemically orthogonal functional groups enable the incorporation of this metallo amino acid into peptide architectures in a highly selective manner, even by solid-phase peptide synthesis protocols. Amide-linked conjugates with other metal complexes [(terpyridine)ruthenium(II), ferrocene, (bipyridine)rhenium(I), (bipyridine)platinum(II)], organic chromophores, or ZnO nanoparticles underscore the versatile synthetic, redox, and photochemistry of this building block. First real-world applications of [5]2+ and its derivatives include light-emitting electrochemical cells (LECs) and dye-sensitized solar cells (DSSCs). Ruthenium(II) amino acid [Ru(4?-tpy-COOH)(4?-tpy-NH2)]2+ interacts with photons, electrons, and/or protons, to lead to phosphorescence, oxidative and reductive chemistry, acid/base chemistry, proton-coupled electron transfer, photoinduced reductive and oxidative electron transfer, excited-state proton transfer, and energy transfer. Applications include light-emitting electrochemical and dye-sensitized solar cells.

Posted on 15 August 2014 | 11:30 am

Defining the Structural Parameters of Tri­azole Ligands in the Templated Synthesis of Silver Nanoparticles

This manuscript describes a one-pot method for the synthesis of size- and shape-selected silver nanoparticles (AgNPs) using Tollens' reagent [Ag(NH3)2OH] as the silver source. Sugar triazole ligands facilitate the formation of monodisperse AgNPs in which the size and shape can be controlled according to the reaction conditions. Increasing the size of the ligand reduces size tunability but enhances colloidal stability in high-salt buffers. A key conclusion from this study is that the AgI-binding affinity of these triazole ligands determines their capacity to tune the size of the resultant AgNPs formed. Weaker AgI-binding ligands can be used to form monodisperse, angular AgNPs over a wider range of sizes [(12?±?3) to (33?±?7) nm], whereas triazole ligands that exhibit a higher AgI-binding affinity produce monodisperse, spherical AgNPs of a single size [(18?±?5) nm]. Control of both the size and shape of silver nanoparticles (AgNPs) can be achieved using triazole sugar ligands and the Tollens' reagent [Ag(NH3)2OH] as the silver source. Higher affinity for AgI results in smaller AgNPs, whereas ligands with lower affinity for AgI form larger AgNPs in which the size can be tuned according to the reaction conditions.

Posted on 15 August 2014 | 11:23 am

Mixed-Metal Oxo Clusters Structurally Derived from Ti6O4(OR)8(OOCR?)8

The mixed-metal oxo clusters FeTi5O4(OiPr)4(OMc)10 (OMc = methacrylate), Zn2Ti4O4(OiPr)2(OMc)10, Cd4Ti2O2(OAc)2(OMc)10(HOiPr)2, [Ca2Ti4O4(OAc)2(OMc)10]n, and [Sr2Ti4O4(OMc)12(HOMc)2]n were obtained from the reaction of titanium alkoxides with the corresponding metal acetates and methacrylic acid. Their structures are derived from Ti clusters with the composition Ti6O4(OR)8(OOCR?)8. The Ca and Sr derivatives consist of chains of condensed clusters. Fe/Ti, Zn/Ti, Cd/Ti, Ca/Ti, and Sr/Ti mixed-metal oxo clusters were obtained from the reaction of titanium alkoxides with the corresponding metal acetates and methacrylic acid. Their structures can be traced back to that of Ti6O4(OR)8(OOCR?)8 clusters and the structural variations to the different ionic radii and coordination numbers.

Posted on 15 August 2014 | 11:23 am

Contributions to the Chemistry of N-Methylnitramine: Crystal Structure, Synthesis of Nitrogen-Rich Salts, and Reactions towards 2-Nitro-2-azapropyl Derivatives

This work compares the hitherto unknown crystal structure of N-methylnitramine with its gas-phase diffraction structure. A series of alkaline, alkaline earth and some transition-metal salts were investigated. Furthermore, a series of new nitrogen-rich salts was synthesized and characterized for the first time. The Mannich reaction of N-methylnitramine with formaldehyde yields 2-nitro-2-azapropanol, which was treated with 2-nitro-2-azapropyl isocyanate to furnish new bis-N,O-(2-nitro-2-azapropyl)carbamate. The analogue bis-N,N?-(2-nitro-2-azapropyl)urea derivative is formed when 2-nitro-2-azapropyl isocyanate is treated with water. Owing to the energetic nature of all compounds, their energetic properties were determined. The sensitivities towards impact, friction and electrostatic discharge were determined using the BAM drophammer and friction tester as well as a small-scale electrical discharge device. Standard enthalpies of formation were calculated at the CBS-4M level of theory. With these values and the experimental densities, several detonation parameters such as detonation pressure and velocity of the compounds were computed using the EXPLO5 (V6.01) computer code and compared to currently used explosives. The hitherto unknown crystal structure of N-methylnitramine has been determined. Its Mannich product with formaldehyde was treated with 2-nitro-2-azapropyl isocyanate or water to provide products that were characterized as energetic materials and compared to currently used explosives.

Posted on 15 August 2014 | 11:20 am

Spin-State Energetics of FeII Complexes – The Continuing Voyage Through the Density Functional Minefield

Computing absolute spin-state energies continues to challenge quantum chemistry. Correlated wavefunction methods offer high accuracy but are expensive, whereas density functional theory (DFT) is faster, but its accuracy is variable. No “universal” functional has emerged, but predicting trends in spin-state energies is easier. Here, a simple DFT protocol is applied to the subtle variations in magnetic moments for FeII–R,R?Pytacn complexes (Inorg. Chem. 2013, 52, 9229). Both BP86 and OPBE give satisfactory correlation coefficients (R2 = 0.87 and 0.75, respectively), whereas the range-separated functional CAM-B3LYP performs worse (R2 = 0.37). However, even for BP86 and OPBE, the p-CO2Et substituent is predicted to be too electron-donating. The relatively poor performance of CAM-B3LYP may be due to the more exacting test of DFT provided by mixed-ligand systems, where the competition between donors is an additional factor. Calculating the absolute spin-state energies of metal complexes is a challenge for quantum chemistry. Computing trends is easier, but caution is required. Not all functionals perform equally, and even for the good ones, there are generally outliers. Despite significant progress, the “universal functional” remains elusive.

Posted on 15 August 2014 | 11:20 am

Microwave-Assisted C–C and C–S Couplings Catalysed by Organometallic Pd-SCS or Coordination Ni-SNS Pincer Complexes

A family of SCS and SNS pincer compounds of the type [PdCl{C6H3-2,6-(CH2SR)2}] {R = tBu (3a), sBu (3b), iBu (3c)} and [NiCl2{C5H3N-2,6-(CH2SR)2}] {R = tBu (4a), sBu (4b)} have been prepared. Among these, complexes 3b, 3c, 4a–4c are reported for the first time. Dimeric compounds such as [NiCl{C5H3N-2,6-(CH2SiBu)2}?-Cl]2 (4c) were found in the solid state for the nickel complexes with lower steric hindrance exhibiting octahedral metal centers, whereas other nickel structures such as [NiCl2{C5H3N-2,6-(CH2StBu)2}(iPrOH)] (4d) could also expand their coordination number by coordinating to solvents. The single crystal X-ray diffraction results for 4a, 4c and 4d are presented. The catalytic activity of the six compounds was studied in C–C and C–S cross-coupling reactions under conventional heating and under microwave irradiation conditions. The palladium catalysts enabled good to excellent conversions in Suzuki–Miyaura couplings of p-substituted halobenzenes with phenylboronic acid. Comparable yields resulted from application of the nickel complexes in the thioetherification of iodobenzene with different disulfides. The fast increase in reaction temperature associated with microwave irradiation, in combination with the robust pincer catalysts, allowed for quantitative conversions in only minutes. A series of SCS-PdII and SNS-NiII pincer compounds of the type [PdCl{C6H3-2,6-(CH2SR)2}] and [NiCl2{C5H3N-2,6-(CH2SR)2}] {R = tBu, sBu, iBu} were synthesized and used as efficient catalysts in C–C Suzuki–Miyaura and C–S thiolation cross-coupling reactions.

Posted on 5 August 2014 | 2:23 pm

BOX Ligands in Biomimetic Copper-Mediated Dioxygen Activation: A Hemocyanin Model

The ?-?2:?2-peroxodicopper(II) core found in the oxy forms of the active sites of type III dicopper proteins have been a key target for bioinorganic model studies. Here, it is shown that simple bis(oxazoline)s (BOXs), which are classified among the so-called “privileged ligands”, provide a suitable scaffold for supporting such biomimetic copper/dioxygen chemistry. Three derivatives R,HBOX-Me2 (R = H, Me, tBu) with different backbone substituents have been used. Their bis(oxazoline)-copper(I) complexes bind dioxygen to yield biomimetic ?-?2:?2-peroxodicopper(II) species. O2 can be reversibly released upon an increase in temperature. Their formation kinetics have been studied under cryo-stopped-flow conditions for the tBu derivative, giving activation parameters ?H‡on = (2.27?±?0.18) kcal?mol–1, ?S‡on = (–46.3?±?0.8) cal?K–1 mol–1 for the binding event and ?H‡off = (11.7?±?1.9) kcal?mol–1, ?S‡off = (–16.1?±?8.2) cal?K–1 mol–1 for the release of O2, as well as thermodynamic parameters ?H° = (–10.0?±?1.7) kcal?mol–1 and ?S° = (–32.7?±?7.4) cal?K–1 mol–1 for this equilibrium. The ?-?2:?2-peroxodicopper(II) complexes have been isolated as surprisingly stable solids and investigated in depth by a variety of methods, both in solution and in the solid state. Resonance Raman spectroscopy revealed a characteristic isotope-sensitive stretch $\tilde {\nu}$O–O = 731–742 cm–1 (?[18O2] ? –39 cm–1) and an intense feature around 280 cm–1 diagnostic for the fundamental symmetric Cu2O2 core vibration. A slight butterfly-shape of the Cu2O2 core has been derived from EXAFS data and DFT calculations. SQUID magnetic data evidenced strong antiferromagnetic coupled CuII2 (–2J ? 1000 cm–1). Thermal degradation in solution yields bis(hydroxo)-bridged [(tBu,HBOX-Me2)(L)Cu(OH)]2(PF6)2 (L = H2O, MeCN or THF); whereas in the case of H,HBOX-Me2, ligand oxygenation has been detected. Preliminary reactivity studies with the substrate 2,4-di-tert-butylphenol indicate the formation of the C–C coupling product 3,3?,5,5?-tetra-tert-butyl-2,2?-biphenol, whereas ortho-hydroxylation was not observed. The copper(I) complex [(tBu,HBOX-Me2)Cu(MeCN)]PF6 as well as two dicopper(II) complexes [(L)(tBu,HBOX-Me2)Cu(OH)]2(PF6)2 have been characterised by single-crystal X-ray diffraction. Considering the vast number of known BOX derivatives, a rich and versatile Cu/O2 chemistry based on this platform is anticipated. A series of bis(oxazoline)-copper(I) complexes reversibly bind dioxygen to yield biomimetic ?-?2:?2-peroxo-dicopper(II) species, which represent new functional hemocyanin models. Their kinetics of formation have been studied under cryo conditions, and the complexes have been isolated as surprisingly stable solids. All were investigated by a variety of methods, both in solution and in the solid state.

Posted on 1 August 2014 | 12:40 pm

Trigonal Bipyramidal or Square Pyramidal Coordination Geometry? Investigating the Most Potent Geometry for Vanadium Phosphatase Inhibitors

The five-coordinate geometry is an important factor in phosphoryl group transfer, particularly for phosphate ester hydrolysis. In the following review we analyze the five-coordinate geometries for a range of VO4X coordination spheres with regard to their structure from the point of view of square pyramidal or trigonal bipyramidal geometries. The actual differences for the coordination environment of the reported small molecule structures are compared to the coordination environment of vanadate complexed to a protein tyrosine phosphatase (PTP) with four coordinating O atoms and one S atom. These considerations demonstrate that actual differences between the coordination environments are very small and presumably less critical than generally anticipated. This analysis suggests that it is a combination of structural and electronic properties leading to the perfect combination of reactivity and stability for the potent protein phosphatase inhibitor complex, thus confirming the fact that some other geometries have been reported. In this microreview, we analyze the five-coordinate geometries (an important factor in phosphoryl group transfer) for a range of VO4X coordination spheres with regard to their structure, considered as square pyramidal or trigonal bipyramidal geometries. We demonstrate that actual differences between the coordination environments are very small and presumably less critical than generally anticipated.

Posted on 1 August 2014 | 12:20 pm

Photoinduced Topological Transformation in Mesoscopic Inorganic Nanoparticles: Application as a UV Sensor

Achieving topological transformation in an inorganic chemical system is an ongoing challenge. We show that such a topological transformation can be achieved in a simple metal-oxide based inorganic system of soft-oxometalates (SOMs). Starting from a dispersion of heptamolybdate-based SOM nanotubes, molybdenum blue SOM nanospheres were synthesised by application of UV-irradiation. This transformation is accompanied by a colour change of the system from colourless to blue. The starting material and product were characterised based on an array of techniques including scanning electron microscopy, dynamic light scattering, horizontal attenuated total reflectance infrared spectroscopy, and UV/Vis spectroscopy. The possibility of using this system as a UV detector is also discussed. Irradiation of ammonium heptamolybdate tetrahydrate soft-oxometalate (SOM) nanorods with UV light leads to their topological transformation into molybdenum blue SOM nanospheres. This transformation is accompanied by a colour change from colourless to blue, which can be exploited for UV sensing. Thus, when a particular threshold amount of UV irradiation is absorbed, the nanorods change colour.

Posted on 22 July 2014 | 12:10 pm

Polynuclear Copper(II) Complexes as Catalysts for the Peroxidative Oxidation of Cyclohexane in a Room-Temperature Ionic Liquid

The reaction of copper(II) nitrate hydrate with sodium 2-[2-(2,4-dioxopentan-3-ylidene)hydrazinyl]terephthalate (Na2HL1) in the absence or presence of imidazole (im) leads to the new complexes [(H2O)Cu0.5{(?-L1-1?O:2?3N,O?,O?)Cu(H2O)2}]2 (1) and [Cu(im)(?-HL1-1?O:2?3N,O,O?)]2 (2), respectively, whereas the 1D coordination polymer [Cu2(H2O)2(?-H2L2-1?3N,O,O?:2?O?)(?-L2-1?3N,O,O?:2?2N?,O?)]n (3) is obtained from Cu(NO3)2·2.5H2O and sodium 2-[2-(4,4-dimethyl-2,6-dioxocyclohexylidene)hydrazinyl]terephthalate (Na2HL2). All of the compounds were characterized by ESI-MS, IR spectroscopy, elemental analysis and X-ray diffraction analysis. Di- or tri-deprotonated ligands display different coordination modes and lead to distinct nuclearities of the CuII complexes depending on the conditions used for the syntheses. Complexes 1–3 were successfully tested as dual-role catalysts for cyclohexane oxidation under acid-free conditions in the ionic liquid [1-butyl-3-methylimidazolium tetrafluoroborate, (bmim)(BF4)] as well as in acetonitrile. The application of the ionic liquid (IL) increased the product yield and turnover number and decreased the reaction time, in comparison with those for the use of the conventional acetonitrile solvent. Easy recycling of the catalyst, with preservation of almost the initial activity and selectivity, was also achieved by using the IL medium. Multinuclear CuII complexes with a catalytic metal centre and an acid functionality catalyze the peroxidative oxidation of cyclohexane in acid-free water/air/CH3CN or ionic liquid media.

Posted on 21 July 2014 | 1:10 pm

Synthesis, Properties, and Applications of Light-Insensitive Silver(I) Cyanoximates

The reaction between AgNO3 and ML [M = K+, Na+; L = anion of the deprotonated cyanoxime – 39 of these anions are known, but only twelve form light-stable silver(I) complexes] at room temperature in aqueous solutions leads to sparingly soluble, colored AgL in high yield. All twelve of the known Ag complexes were characterized by using a variety of spectroscopic methods and single-crystal X-ray analysis, which revealed the formation of coordination polymers of various complexities. The silver(I) compounds demonstrate a very significant (for multiple years!) stability towards visible light. There are three areas of potential practical applications of these unusual complexes: (1) detectors of UV radiation that do not require electric feed, (2) non-electrical indicators for gases of industrial importance, (3) antimicrobial additives to light-curable acrylate polymeric glues, fillers, and adhesives used during the introduction of indwelling medical devices. The chemical, structural, technological, and biological aspects of the application of coordination polymers based on AgI cyanoximates are reviewed. Twelve coordination polymers of silver(I) cyanoximates of composition AgL were found to be very stable towards visible light. Three areas of potential practical relevance of these unusual complexes have emerged. The chemical, structural, technological, and biological aspects of the applications of these compounds are reviewed.

Posted on 18 July 2014 | 3:10 pm

Polynuclear Heterometallic Complexes from Metal Powders: The “Direct Synthesis” Approach

The synthesis of polynuclear coordination compounds, particularly heterometallic coordination compounds, remains a challenge for modern chemistry. Spontaneous self-assembly (SSA) is a primary approach that proceeds by broad screening, typically with simple, flexible ligands and available metal salts. The “direct synthesis” is a class of SSA, but prescribes the use of zero-valent metal(s) as a starting material, typically oxidized by air oxygen, which results in a deficiency of anions in the reaction mixture and forces deprotonation of the protic ligand(s) with the formation of unexpected products. The “direct synthesis” approach has been successfully applied to the preparation of heterometallic complexes, which has allowed the isolation of numerous complexes, many with uncommon structures. In this review we summarize our experience in the field of the “direct synthesis” of polynuclear heterometallic complexes, covering preparative and structural aspects as well as applications of the compounds obtained. In this review we summarize our experience in the field of the “direct synthesis” of polynuclear heterometallic complexes, covering preparative and structural aspects as well as applications of the compounds obtained.

Posted on 18 July 2014 | 9:40 am

Stimuli-Responsive Dynamic Gold Complexes

The role of noncovalent interactions is reviewed in the context of the stimuli-responsive behaviour of gold(I) and gold–heterometal complexes. These noncovalent interactions are often highly sensitive to physical (thermal, optical, electrical, mechanical, etc.) or chemical (solvents, guests, etc.) stimuli, which trigger alterations in molecular and crystal structures that lead to dynamic changes in the macroscopic properties of gold compounds. In this microreview, we have summarized some representative examples of gold(I) complexes that exhibit intriguing stimuli-responsive properties such as thermochromic, mechanochromic, vapochromic and solvatochromic luminescence, as well as vapochromism and gas sorption. Stimuli-responsive functional materials with specific properties have potential uses in various applications including chemical sensors, memory, data storage, security inks and separation technologies. A general overview on stimuli-responsive gold(I) and gold–heterometal derivatives is presented with a special focus on the impact of noncovalent interactions on molecular structures, packing patterns and solid-state properties. Representative examples with thermo-, mechano- and vapochromic luminescence, vapochromism and gas sorption properties have been selected.

Posted on 10 July 2014 | 12:40 pm

Electron-Transfer Rate Enhancements in Nanosized Waterpools

An enhancement in the electron-transfer rates of metal complexes confined to a nanoscale environment within a sodium bis(2-ethylhexyl)sulfosuccinate/water/isooctane reverse micelle (RM) are reported. The rate constants increase up to two orders of magnitude relative to those in bulk water. These rate enhancements are attributed to changes in solvation (owing to location within the RM) and ion pairing. The kinetics of electron-transfer reactions between metal complexes and ascorbic acid (vitamin C) are reported in both aqueous media and in nanosized water droplets formed in microemulsions. Rate-constant enhancements of up to two orders of magnitude are reported.

Posted on 9 July 2014 | 11:30 am

Self-Assembly of Subnanometer-Scaled Polyhedral Oligomeric Silsesquioxane (POSS) Macroions in Dilute Solution

Both positively and negatively charged polyhedral oligomeric silsesquioxane (POSS) electrolytes were observed to self-assemble into blackberry-type supramolecular structures in water/acetone mixed solvents, driven by the counterion-mediated attraction. Laser light-scattering studies reveal that the sizes of the blackberry structures increase with increasing acetone content, which suggests a charge-regulated process. Studies on two oppositely charged POSS macroions with identical charges and similar sizes show the discrepancy between positively and negatively charged POSS macroions, which is related to counterions, ionic domains of macroions, and the water-bridged hydrogen bonding between monomers. These POSS ions further decrease the lower size limit of macroions that can self-assemble in polar solvents reported to date. The new phenomena were observed in the self-assembly process of POSS macroions relative to other macroion systems. Two oppositely charged polyhedral oligomeric silsesquioxane (POSS) macroions with identical charge and similar sizes can self-assemble into blackberry-type supramolecular structures in dilute solution. This transition from simple macroions to assemblies can be regulated by the solvent polarity.

Posted on 24 June 2014 | 5:11 pm

A NiII–Bis(diphosphine)–Hydride Complex Containing Proton Relays – Structural Characterization and Electrocatalytic Studies

The synthesis of the 1,5-diphenyl-3,7-diisopropyl-1,5-diaza-3,7-diphosphacyclooctane ligand, PiPr2NPh2, is reported. Two equivalents of the ligand react with [Ni(CH3CN)6](BF4)2 to form the bis(diphosphine)–NiII complex [Ni(PiPr2NPh2)2](BF4)2, which acts as a proton reduction electrocatalyst. In addition to [Ni(PiPr2NPh2)2]2+, we report the synthesis and structural characterization of the Ni0 complex Ni(PiPr2NPh2)2 and the NiII–hydride complex [HNi(PiPr2NPh2)2]BF4. The [HNi(PiPr2NPh2)2]BF4 complex represents the first NiII–hydride in the [Ni(PR2NR?2)2]2+ family of compounds to be structurally characterized. In addition to the experimental data, the mechanism of electrocatalysis facilitated by [Ni(PiPr2NPh2)2]2+ is analyzed by using linear free energy relationships recently established for the [Ni(PR2NR?2)2]2+ family. A new member of the [Ni(PR2NR?2)2]2+ family of electrocatalysts is reported. Complex [Ni(PiPr2NPh2)2]2+ is an electrocatalyst for proton reduction to form H2. Additionally, we have isolated and structurally characterized the NiII–hydride [HNi(PiPr2NPh2)2]+.

Posted on 24 June 2014 | 12:20 pm

A Decade of Dinuclear Technetium Complexes with Multiple Metal–Metal Bonds

Transition metal complexes with multiple metal–metal bonds exhibit interesting catalytic and biological properties. One element whose metal–metal bond chemistry has been poorly studied is technetium. Currently, only 25 technetium complexes with multiple metal–metal bonds have been structurally characterized. The nature of metal–metal interactions in these complexes, as well as the influence of ligands on the bonding in the Tc2n+ unit (n = 6, 5, 4) are not well understood. In order to better understand the influence of ligands on the Tc–Tc bonding, a study of the solid-state and electronic structure of dinuclear complexes with the Tc2n+ unit (n = 6, 5, 4) has been performed. Dinuclear technetium complexes (nBu4N)2Tc2X8, Tc2(O2CCH3)4X2, Tc2(O2CCH3)2Cl4, cesium salts of Tc2X83–, and Tc2X4(PMe3)4 (X = Cl, Br) were synthesized; their molecular and electronic structures, as well as their electronic absorption spectra, were studied by a number of physical and computational techniques. The structure and bonding in these systems have been investigated by using multiconfigurational quantum calculations. For all these complexes, the calculated geometries are in very good agreement with those determined experimentally. Bond order analysis demonstrates that all these complexes exhibit a total bond order of approximately 3. Analysis of individual effective bond order (EBO) components shows that these complexes have similar ? components, while the strength of their ? components follows the order Tc2X4(PMe3)4 > Tc2X83– > Tc2(O2CCH3)2Cl4 > Tc2X82–. Calculations indicate that the ? components are the weakest bond in Tc2X8n– (n = 2, 3) and Tc2(O2CCH3)2Cl4. Further analysis of Tc2X83– and Tc2X4(PMe3)4 (X = Cl, Br) indicates that the electronic structure of the Tc25+ and Tc24+ units is insensitive to the nature of the coordinating ligands. The electronic absorption spectra of Tc2X8n– (n = 2, 3), Tc2(O2CCH3)2Cl4, and Tc2X4(PMe3)4 (X = Cl, Br) were studied in solution, and assignment of the transitions was performed by multiconfigurational quantum chemical calculations. For the Tc2X8n– (n = 2, 3; X = Cl, Br) anions and Tc2(O2CCH3)2Cl4, the lowest-energy band is attributed to the ??* transition. For Tc2X4(PMe3)4, the assignment of the transitions follow the following order in energy: ?*?* < ?*?* < ??* < ??*. This review covers the metal–metal bond chemistry of dinuclear technetium complexes published in the period 2005–2014. The preparation, solid-state and electronic structures, and spectroscopic properties of (nBu4N)2Tc2X8, Tc2(O2CCH3)4X2, Tc2(O2CCH3)2Cl4, cesium salts of Tc2X83–, and Tc2X4(PMe3)4 (X = Cl, Br) are presented.

Posted on 24 June 2014 | 12:20 pm

Cycloruthenation of N-(Naphthyl)salicylaldimine and Related Ligands: Utilization of the Ru–C Bond in Catalytic Transfer Hydrogenation

Upon reaction with [Ru(PPh3)2(CO)2Cl2], N-(naphthyl)-4-R-salicylaldimines (R = OCH3, H, Cl; H2L1–H2L3) and 2-hydroxy-N-(naphthyl)naphthaldimine (H2L4) readily undergo cycloruthenation by C–H bond activation at the peri position to afford complexes of the type [Ru(PPh3)2(L)(CO)] (L = L1–L4). The crystal structures of the [Ru(PPh3)2(L)(CO)] (L = L1, L2, L4) complexes were determined and the structure of [Ru(PPh3)2(L3)(CO)] optimized by DFT calculations. The thermodynamics for the reaction of [Ru(PPh3)2(CO)2Cl2] with H2L2 to give [Ru(PPh3)2(L2)(CO)] were determined. All the complexes show intense absorptions in the visible and UV regions, which have been analyzed by TDDFT calculations. Cyclic voltammetry of the four cycloruthenated complexes showed two oxidations within the range 0.50–1.35 V versus SCE and a reduction at around –1.75 V versus SCE. The [Ru(PPh3)2(L)(CO)] (L = L1–L4) complexes were found to efficiently catalyze the transfer hydrogenation of carbonyl compounds. N-(Naphthyl)-4-R-salicylaldimines (R = OCH3, H, Cl; H2L1–H2L3) and 2-hydroxy-N-(naphthyl)naphthaldimine (H2L4) react with [Ru(PPh3)2(CO)2Cl2], undergoing C–H bond activation at the peri position, to afford complexes of the type [Ru(PPh3)2(L)(CO)] (L = L1–L4), which can efficiently catalyze the transfer hydrogenation of carbonyl compounds.

Posted on 17 June 2014 | 8:20 pm

Supramolecular Assemblies of Polyoxometalate-Tethered Diblock Copolymers with Tunable Sizes in N-Methyl-2-pyrrolidone/Toluene Mixed Solvents

Three diblock copolymers, each consisting of a relatively polar polyoxometalate-containing block and a nonpolar polythiophene block, were studied for their solution self-assembly behavior. Hollow spherical vesicular structures have been observed; their formation is driven by solvophobic–solvophilic interactions. The size of the vesicles can be controlled by varying the polarity of the solvent. Regular vesicles seem to form when the solvent combination is relatively polar, while reverse vesicles form when the solvent is relatively nonpolar. Rod–coil diblock copolymers, consisting of poly(3-hexylthiophene-2,5-diyl) as the rod block and a POM tethered to a polystyrene derivative as the coil block, self-assemble into vesicles in polar solvents. The vesicle size can be controlled by changing the solvent polarity. A transition to reverse vesicles with controllable size is achieved when the solvent is relatively nonpolar.

Posted on 27 May 2014 | 11:10 am

Slow Magnetic Relaxation in a Redox-Active Tetrathiafulvalene-Based Ferromagnetic Dysprosium Complex

The association of the two 4,5-bis(thiomethyl)-4?-carboxytetrathiafulvalene (HL1) and 4,5-bis(thiomethyl)-4?-(2-pyridyl-N-oxide)carbamoyltetrathiafulvalene (L2) with the metalloprecursor [Dy(tta)3]·2H2O (tta = 2-thenoyltrifluoroacetonate) leads to the formation of the dinuclear complex of formula [Dy(tta)2(L1)(L2)]2·2CH2Cl2. Static magnetic measurements highlight significant ferromagnetic interactions between the DyIII ions, and dynamic magnetic measurements demonstrate single-molecule-magnet behaviour with an energy barrier of 20 cm–1 and a relaxation time of 8.6(9)?×?10–6 s. The thermal dependence of the magnetic susceptibility was evaluated by using a crystal field approach (Stevens operators), which confirmed the Ising character of the system. Finally, electrochemistry shows a complex multiredox system with the successive oxidations of the two tetrathiafulvalene (TTF) ligands. The dinuclear coordination complex [Dy(tta)2(L1)(L2)]2·2(CH2Cl2) [tta = 2-thenoyltrifluoroacetonate, L1 and L2 = tetrathiafulvalene (TTF) ligands] shows significant ferromagnetic interactions between both DyIII ions. Owing to the two different TTF ligands, the molecule is a multiredox system. It also displays single-molecule magnetic behaviour with the Ising ground state MJ = ±15/2.

Posted on 14 May 2014 | 10:30 am

New Gold(I) Organometallic Compounds with Biological Activity in Cancer Cells

N-Heterocyclic carbene gold(I) complexes bearing a fluorescent coumarin ligand were synthesized and characterized by various techniques. The compounds were examined for their antiproliferative effects in normal and tumor cells in vitro; they demonstrated moderate activity and a certain degree of selectivity. The compounds were also shown to efficiently inhibit the selenoenzyme thioredoxin reductase (TrxR), whereas they were poorly effective towards the glutathione reductase (GR) and glutathione peroxidase enzymes. Notably, {3-[(7-methoxy-2-oxo-2H-chromen-4-yl)methyl]-1-methylimidazol-2-ylidene}(tetra-O-acetyl-1-thio-?-D-glucopyranosido)gold(I) (3) showed a pronounced inhibition of TrxR also in cell extracts, and it appeared to activate GR. Mechanistic information on the system derived from biotin-conjugated iodoacetamide assays showed selective metal binding to selenocysteine residues. Preliminary confocal fluorescence microscopy experiments proved that 3 enters tumor cells, where it reaches the nuclear compartment. Organometallic N-heterocyclic carbene gold(I) complexes bearing a fluorescent coumarin ligand are synthesized, and their antiproliferative effects in normal and tumor cells in vitro are studied. Their biological properties may be due to inhibition of thioredoxin reductases. Fluorescence confocal microscopy allows the uptake of the compounds in cancer cells to be observed.

Posted on 13 May 2014 | 1:10 pm

Cyanido-Bearing Cobalt(II/III) Metalloligands – Synthesis, Crystal Structure, and Magnetic Properties

New examples of cyanido-bearing cobalt(III/II) complexes have been obtained by treatment of CoCl2·6H2O with bidentate nitrogen donors and potassium cyanide in a methanol/water mixture. Depending on the chelating ligand, the cobalt(III) complexes PPh4[Co(en)(CN)4] (1, en = ethylenediamine), PPh4[Co(ampy)(CN)4]·1.5H2O [2, ampy = 2-(aminomethyl)pyridine], and PPh4[Co(phen)(CN)4]·CH3OH·0.25H2O (3, phen = 1,10-phenanthroline) and the cobalt(II) complex PPh4[Co(dmphen)(CN)3]·3H2O (4, dmphen = 2,9-dimethyl-1,10-phenanthroline) were obtained. The complexes were characterized by single-crystal X-ray diffraction and variable-temperature magnetic measurements. They are all mononuclear species with six-coordinate cobalt(III) (1–3) and five-coordinate cobalt(II) centers (4), and two nitrogen atoms from each bidentate ligand (1–4) and four (1–3) or three cyanide carbon atoms (4) build somewhat distorted octahedral (1–3) or square-pyramidal (4) surroundings. Complexes 1–3 are diamagnetic cobalt(III) compounds, whereas 4 is a low-spin cobalt(II) complex that exhibits Curie behavior in the temperature range 10–300 K. The g values of the X-band electron paramagnetic resonance (EPR) spectrum of 4 both in the solid state and in dichloromethane solution at 4.0 K (g? = 2.28?>?g? = 2.0) reveal that its unpaired electron is defined by a d?z?2-type orbital. Complexes 1–4 can be viewed as new metalloligands for metal assemblies. Three diamagnetic CoIII complexes PPh4[Co(L)(CN)4] [L = ethylenediamine (en), 1; 2-(aminomethyl)pyridine (ampy), 2; 1,10-phenanthroline (phen), 3] and one CoII complex PPh4[Co(dmphen)(CN)3] (4, dmphen = 2,9-dimethyl-1,10-phenanthroline) were obtained and characterized by single-crystal XRD and FTIR spectroscopy. Complex 4 forms weakly antiferromagnetically coupled CoII···CoII supramolecular dimers.

Posted on 9 May 2014 | 11:23 am

Exploring the Building-Block Potential of Readily Accessible Chiral [Zn(salen)] Complexes

The synthesis and full characterization of a series of chiral [Zn(salen)] [salen = N,N?-bis(salicylidene)ethylenediamine dianion] complexes comprising a 1,2-diphenylethane backbone is reported. The preparation method reported here simplifies the previously communicated methodology for these types of Zn complexes that utilized air-sensitive ZnEt2 (or similar) as the metalating reagent. X-ray molecular structures are also reported for representative examples of this family of [Zn(salen)] complexes. A wide range of functionality is shown to be accessible by means of the present route, thereby amplifying the potential use of these (Lewis acidic) Zn complexes as molecular building blocks. Examples in this work include the formation of supramolecular assemblies having built-in bifunctionality using versatile Zn–N and Zn–O coordination motifs as guiding tools. A convenient method for the synthesis of a series of chiral [Zn(salen)] [salen = N,N?-bis(salicylidene)ethylenediamine dianion] complexes based on a 1,2-diphenylethanediamine backbone has been developed. These complexes have been used to assemble multinuclear supramolecular assemblies of which the solid-state and solution properties were determined. These chiral [Zn(salen)] complexes hold promise as molecular building blocks with modular characteristics.

Posted on 8 May 2014 | 12:40 pm

Self-Assembly Properties of NCN Pincer Palladium(II) Complexes Bearing a Uracil Moiety

NCN pincer palladium(II) complexes bearing a 6-ethynyl-1-octyluracil moiety were designed by the combination of an NCN pincer palladium(II) complexes as an organometallic compound and a uracil derivative as a nucleobase to afford bioorganometallic compounds. The reaction of the NCN pincer ligand with Pd(dba)2 (dba = dibenzylideneacetone) led to the formation of the NCN pincer palladium(II) complex Pd-Br. The crystal structure of the cationic complex Pd-MeCN, which was prepared by the treatment of Pd-Br with AgOTf (OTf = trifluoromethanesulfonate) in acetonitrile, revealed that a dimeric structure formed through intermolecular hydrogen bonds between the uracil moieties of two independent molecules. The self-assembly properties of the NCN pincer palladium(II) complexes were found to depend on the ancillary ligands. Each hydrogen-bonded dimer was connected through an intermolecular hydrogen-bonding bridge between the coordinated water molecule and the triflate anion in the cationic complex Pd-H2O. Intermolecular hydrogen bonding between the uracil moiety and the triflate anion bound to the palladium center was observed in the NCN pincer palladium(II) complex Pd-OTf, although a dimeric structure between the uracil moieties was formed in the NCN pincer palladium(II) complex Pd-O2CCF3, which was obtained by the abstraction of the bromide ion from Pd-Br with AgO2CCF3. Bioorganometallic compounds were designed by the combination of NCN pincer complexes with a uracil moiety to form intermolecular hydrogen-bonded assemblies, wherein the hydrogen-bonding patterns were found to depend on the ancillary ligands.

Posted on 20 March 2014 | 12:32 pm

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