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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:

Zirconocene Complexes as Catalysts for the Cycloaddition of CO2 to Propylene Oxide

Six zirconocene derivatives were systematically designed; one of the cyclopentadienyl (Cp) ligands of zirconocene dichloride [Cp2ZrCl2] was silylated and this group was then incrementally increased in size; furthermore, one derivative with a 4,4?-disilylbiphenyl bridge between the two zirconocene fragments was prepared. One zirconium complex was characterized by single-crystal X-ray analysis. All zirconium complexes were effective catalysts for the cycloaddition of CO2 to propylene oxide. Two complexes containing a biphenyl group attached to a SiMe2 group showed higher activity than the other complexes. In addition, the dinuclear complex containing the biphenylenebis(dimethylsilyl) bridge showed the highest activity among all the zirconium complexes reported. Furthermore, these complexes are the first examples of zirconocene catalytic systems for the cycloaddition reaction of CO2 to propylene oxide. Six zirconocene derivatives for which the size of the cyclopentadienyl (Cp) ligands is incrementally increased are systematically designed and prepared. These zirconocene complexes demonstrate catalytic activity in the cycloaddition of CO2 to propylene oxide in the presence of a cocatalyst.

Posted on 1 October 2014 | 7:30 pm

Protection of the Gold(I) Catalyst by AsPh3 in Reactions of Enynes

Neutral gold complexes with hydrogen-bond-supported heterocyclic carbene (HBHC) and nitrogen acyclic carbene (NAC) ligands have been synthesized by the reactions of isocyanogold derivatives [AuCl(CNR)] with amines. Cationic [Au(carbene)(AsPh3)][SbF6] complexes have also been prepared. The catalytic activity of both types of complex (for the former, AgSbF6 is used to extract the halide ligand) in the skeletal rearrangement and methoxycyclization of enynes has been studied. The cationic complexes with AsPh3 are active but slower; advantageously, they do not decompose during the catalysis. In contrast, the catalysts formed in situ from the neutral halide complexes are very fast but undergo decomposition. An interesting trade-off was found by adding substoichiometric amounts of AsPh3 (e.g., 10 mol-%) relative to the gold catalyst {[Au(carbene)Cl] + AgSbF6}, which prevents or dramatically reduces the decomposition. This protecting ligand promises to prevent or minimize the undesired decomposition of gold catalysts. The decomposition of cationic gold catalysts [AuL]Y, generated in situ from [AuClL] and AgY, can be prevented with AsPh3, either as a substoichiometric additive or in the form of the isolable [AuL(AsPh3)]Y. The reaction rates become slower, but fairly fast conversions are still achieved in most cases. The catalyst loading can also be considerably reduced.

Posted on 1 October 2014 | 7:30 pm

Interplay of Photoabsorption, Electronic Structure, and Recombination Rate of Charge Carriers on Visible Light Driven Photocatalytic Activity of Cu- and N-Doped Ba3V2O8

Palmierite Ba3V2O8 and related Cu- and N-doped congeners were prepared by sol-gel, ion-exchange, and solid-state reactions, respectively, with the aim of tailoring their optical, electronic, and photocatalytic properties. The catalysts were characterized by XRD analyis, UV/Vis diffuse reflectance spectroscopy, SEM with energy-dispersive X-ray spectroscopy, photoluminence spectroscopy, BET measurements, thermogravimetric analysis, X-ray photoelectron spectroscopy, and TEM analysis. The electronic structures of Cu- and N-doped optimal compositions were calculated theoretically on the basis of density functional theory. A series of photocatalytic degradation experiments of methylene blue under visible light irradiation disclosed the optimal dopant concentrations of Cu and N into Ba3V2O8, and the photocatalytic ability of the optimal compositions was also tested by the degradation of aniline. The differences in the degradation performance of Cu- and N-doped samples are discussed on the basis of inextricably linked parameters such as photoabsorption, electronic structure, and mobility of the photoinduced charge carriers. Doping of copper and nitrogen into Ba3V2O8 modifies its electronic and optical properties to enhance visible light photodegradation of organic contaminants. Spectroscopic studies suggest that a lower rate of recombination of charge carriers is responsible for their superior photoactivity.

Posted on 1 October 2014 | 7:23 pm

Non-Nuclear Attractor in a Molecular Compound under External Pressure

The dimeric magnesium(I) compound [{(DipNacnac)Mg}2] [1, DipNacnac = (DipNCMe)2CH, Dip = 2,6-diisopropylphenyl] has previously been shown to exhibit a non-nuclear attractor (NNA) between the two Mg atoms in the molecular ground state by both experimental and theoretical electron-density studies. To study the stability and characteristics of this topological entity, we have determined the molecular structure of 1 in the pressure range from 0.4 to 1.9 GPa by high-pressure single-crystal X-ray diffraction. The central Mg–Mg bond contracts significantly in this range to 97?% of the value at ambient pressure and a temperature of 100 K. High-level single-point theoretical calculations with the resulting atomic coordinates show that the NNA is persistently present in the topology at all pressures and that the difference between the value of the electron density at the NNA and the Mg–NNA bond critical point (bcp) is close to a maximum at the Mg–Mg separation that is found experimentally. The existence of a non-nuclear maximum in the electron density of a Mg–Mg-containing molecular compound at elevated pressures has been verified from theoretical calculations. The calculations include experimental Mg–Mg distances obtained from high-pressure single-crystal X-ray diffraction data.

Posted on 1 October 2014 | 7:23 pm

Nanostructuring of Bridged Organosilane Precursors with Pendant Alkyl Chains

The copper-catalyzed alkyne azide cycloaddition (CuAAC) reaction was combined with sol-gel reactions for the production of bridged silsesquioxanes (BSs) in which hexyl and icosanyl chains are pendant and anchored on a single position to a triazole ring. The influence of the alkyl chain length on the structure of the BSs, represented by the notation Cn/siloxane (where n = 6 and 20), was examined. The C20/siloxane hybrid is a hydrophobic material that exhibits a hierarchically structured lamellar bilayer organization, a texture composed of microplates of nanometer thickness, and a reversible time-independent order/disorder phase transition (onset at 60 °C). The driving forces for self-assembly are van der Waals interactions between the icosanyl chains and ?-? interactions between the triazole rings. In the essentially amorphous C6/siloxane hybrid, the latter contribution promotes the genesis of a pre-lamellar phase similar to that found in C20/siloxane. A new bridged silsesquioxane with hierarchically structured lamellar bilayer structure and a texture composed of microplates of nanometer thickness was obtained by sol-gel and self-assembly by using a bridged organosilane carrying a pendant icosanyl chain produced by click chemistry. The hybrid exhibits a time-independent reversible order/disorder phase transition in a heating-cooling cycle.

Posted on 1 October 2014 | 7:23 pm

Endogenous and Exogenous Ligand-Dependent Formation of a Superoxide-Bridged Dicobalt(III) Complex and Mononuclear CoIII Complexes with Amide-Based Macrocyclic Ligands

We report superoxide-bridged dicobalt(III) complex 1 supported by 13-membered amide-based macrocyclic ligand H2LH. Complex 1 displays a sharp radical-type EPR spectrum (g = 2.031) and a short O–O distance (1.303 Å). Complex 1 can be synthesized by the reaction of in situ generated [Co2+(LH)] species with O2 or KO2 as well as by the reaction of (Et4N)[Co3+(LH)(Cl)2] (2) with KO2. In contrast, analogous macrocyclic ligands carrying Cl and CH3 substituents on the aromatic ring produced the mononuclear Co3+ complexes [Co(LCl)(Cl)(dmf)] (3) and [Co(LMe)(Cl)(dmf)] (4) under identical reaction conditions. Furthermore, the reaction of H2LH with Co(OAc)2 yielded the mononuclear Co3+ complex [Co(LH)(?2-OAc)] (5) with a unique bidentate acetate group and a highly distorted six-coordinate geometry around the metal. Steric factors induced by the endogenous and exogenous ligands are believed to control the formation of the distinct cobalt complexes. The amide-based macrocyclic ligands show interesting cobalt chemistry by forming superoxide-bridged dicobalt(III) complex 1 and distinct mononuclear CoIII complexes 2–5. The steric factors originating from the endogenous and exogenous ligands are believed to control the formation of distinct complexes.

Posted on 1 October 2014 | 7:23 pm

Combined Stabilizing Effects of Trifluoromethyl Groups and Semifluorinated Side Chains on the Thermotropic Liquid-Crystal Behavior of ?-Enamino Ketone Ligands and Their Bischelate PdII Complexes

Several linear ?-enamino ketone ligands and their corresponding bischelate PdII complexes bearing various combinations of methyl and trifluoromethyl groups at the chelating center as well as peripheral hydrocarbon and perfluorinated side chains were prepared. The effect of these structural modifications on the thermotropic liquid-crystalline behavior of both the ligands and the corresponding metal complexes was studied. The relationships between the molecular structures and the corresponding thermal properties are discussed. As expected, the persistence of liquid-crystalline behavior was highly sensitive to both applied structural manipulations. On the one hand, increased steric congestion around the chelating moiety clearly appears detrimental to the retention of mesomorphism. On the other hand, perfluorinated chains at the molecular extremity can occasionally restore it. Therefore, the regulation of the balance between both structural parameters permits a precise control of the mesomorphic properties of the compounds. The first liquid-crystalline ?-enamino ketonato PdII complexes with semifluorinated tails are described. In contrast to their n-alkoxy parent compounds, they exhibit a smectic A (SmA) phase. This is a clear indication of a fluorophobic effect in the metal-containing liquid crystals. Different substitution patterns at the chelate unit show the limitation of microphase segregation in these materials.

Posted on 1 October 2014 | 7:23 pm

Chromophores, Fluorophores and Robust Ancillary Ligands for Molecular Catalysts: 1,3-Bis(2-pyridylimino)isoindolines (Eur. J. Inorg. Chem. 28/2014)

The cover picture shows the representation of a 1,3-bis(2-pyridylimino)isoindoline (BPI) compound along with its C2-symmetric derivatives. These ligands were first reported in the early 1950s and have found widespread applications in organic, inorganic and materials chemistry. In particular, recent advancements in the use of BPI ligands are in the development of chiral BPI derivatives for applications in enantioselective catalysis such as cyclopropanation. Such chiral BPI ligands have been developed, inter alia, in Heidelberg, a picture of which is shown in the background. Further details on the applications of BPI ligands are presented in the Microreview by L. H. Gade et al. on p. 4715 ff. For more on the story behind the cover research, see the Cover Profile.

Posted on 1 October 2014 | 5:23 pm

Masthead: Eur. J. Inorg. Chem. 28/2014

Posted on 1 October 2014 | 5:23 pm

Graphical Abstract: Eur. J. Inorg. Chem. 28/2014

Posted on 1 October 2014 | 5:23 pm

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

Invited for the cover of this issue is the group of Professor L. H. Gade at the University of Heidelberg, Germany. The cover image shows the representation of a 1,3-bis(2-pyridylimino)isoindoline (BPI) compound along with its C2-symmetric derivatives. These ligands were first reported in the early 1950s and have found widespread application in organic, inorganic and materials chemistry. Significant advancements in the synthesis of chiral BPI derivatives have recently established them as ligands for use in enantioselective catalytic transformations...Read more about the story behind the cover in the Cover Profile and about the research itself on p. 4715 ff.

Posted on 1 October 2014 | 5:23 pm

Synthesis of Cyclopentadiene Ligands with Fluorinated Substituents by Reaction of Cobaltocene with Fluoroalkenes

The hitherto difficult introduction of fluorinated and perfluorinated substituents onto cyclopentadienes is possible by the simple reaction of cobaltocene with fluorinated olefins(CF2=CFX; X = I, Br, Cl, CF3). Two structurally different products, that is, a mononuclear complex and a dinuclear complex, are formed. Reaction of cobaltocene with iodotrifluoroethene yields ?5-cyclopentadienyl-?4-trifluorovinylcyclopentadienecobalt and cobaltocenium iodide. Reaction of cobaltocenium salts with hexafluoropropene and trifluorovinyllithium represents an alternative high-yielding synthesis of the corresponding compounds. The molecular structures of three compounds were elucidated by using single-crystal X-ray diffraction. The introduction of fluorinated and perfluorinated substituents onto cyclopentadienes is performed by reaction of cobaltocene with fluorinated olefins. Two structurally different products, a mononuclear complex and a dinuclear complex, are formed. Reaction of cobaltocene with iodotrifluoroethene yields ?5-cyclopentadienyl-?4-trifluorovinylcyclopentadienecobalt and cobaltocenium iodide.

Posted on 30 September 2014 | 9:40 pm

Electron-Transfer Studies of trans-Platinum Bis(acetylide) Complexes

The complexes trans-[Pt(C?CFc)2(PFcmnBu3–m)2] (Fc = ferrocenyl; m = 0, 9a; m = 1, 9b; m = 2, 9c) were prepared by the reactions of PFcmnBu3–m (m = 0, 3a; m = 1, 3b; m = 2, 3c) with cis-[PtCl2(SEt2)2] (6) to form [PtCl2(PFcmnBu3–m)2] (m = 0, 7a; m = 1, 7b; m = 2, 7c), which on treatment with [CuC?CFc] (8) produced 9a–9c. The reactions of PFcmnBu3–m (m = 1–3; m = 3, 3d) with S8 or Se gave (S=)PFcmnBu3–m (m = 1, 4b; m = 2, 4c; m = 3, 4d) and (Se=)PFcmnBu3–m (m = 1, 5b; m = 2, 5c; m = 3, 5d). Compounds 5d, 7b, 7c, 9b, and 9c were structurally characterized by single-crystal X-ray diffraction studies; a trans arrangement of the phosphine units at the Pt center is typical. The redox behavior of 3, 4, 7, and 9 was investigated by cyclic and square-wave voltammetry. The Fc units of 9a–9c could be oxidized separately indicating electronic interactions between the Fc/Fc+ groups of the FcC?C units [?E°? = 105 (9a), 115 (9b), 120 mV (9c)]. Cationic [9b]+ and [9c]+ exhibit weak intervalence charge-transfer (IVCT) absorptions at $\tilde {\nu}$ = 6700 cm–1. The synthesis of trans-[Pt(C?CFc)2(PFcmnBu3–m)2] (m = 0, 1, 2; Fc = ferrocenyl) is presented. Spectroelectrochemical investigations indicate electronic communication between the iron centers of the FcC?C units; therefore, these compounds are classified as weakly coupled class II systems, according to Robin and Day.

Posted on 30 September 2014 | 9:40 pm

Low-Temperature Synthesis of Highly Crystallized Hexagonal Boron Nitride Sheets with Li3N as Additive Agent

Highly crystallized hexagonal boron nitride (h-BN) sheets were obtained by a versatile method modifying the original synthesis by using an additive agent and, as a consequence, decreasing the temperature for the ceramization step (1200–1400 °C). This synthesis is based on the polymer-derived ceramics (PDCs) route using liquid-state polyborazylene (PBN) mixed with lithium nitride (Li3N) micropowders as additive agent. We have demonstrated that incorporation of Li3N as a crystallization promoter allows the onset of crystallization of h-BN at lower temperatures. Consequently, a high crystallization rate can be obtained from 1000 °C for bulk boron nitride, whereas the temperature has to be 1600–1800 °C under classical conditions. A series of samples incorporating Li3N (5 wt.-%) and annealed at various temperatures from 600 to 1400 °C was prepared and structurally characterized by Raman spectroscopy, XRD analyis, and TEM. Well-crystallized sheets with thicknesses of nanometers can be easily obtained by applying this method. A versatile method based on polymer-derived ceramics was used to prepare highly crystallized hexagonal BN sheets. Li3N was used as a crystallization promoter to reach highly crystallized states at a lower temperature than is required for processes without an additive agent.

Posted on 30 September 2014 | 9:40 pm

Encapsulation of Bimetallic Nanoparticles into a Metal–Organic Framework: Preparation and Microstructure Characterization of Pd/Au@ZIF-8

The zinc-imidazolate-based framework ZIF-8 was loaded with preformed surfactant-stabilized bimetallic Pd/Au nanoparticles and its corresponding monometallic counterparts Au and Pd by a controlled encapsulation process during the ZIF-8 crystal growth. The nanoparticle-loaded materials were characterized by powder X-ray diffraction (PXRD), FTIR spectroscopy, N2-sorption measurements, as well as by transmission electron microscopy (TEM). The ZIF-8 matrix material remained intact and the NP@ZIF-8 materials revealed the permanent porosity of Brunauer–Emmett–Teller (BET) surface areas above 1100 m2?g–1. The nanoparticles are exclusively found inside the volume of the nanocrystals and exhibit unchanged composition and size distribution as revealed by TEM investigations. Additionally, scanning transmission electron microscopy (STEM) coupled with energy-dispersive X-ray spectroscopy (EDX) confirmed the solid solution-type alloying of Pd and Au in the embedded Pd/Au nanoparticles. The materials were briefly evaluated in aqueous-phase aerobic alcohol oxidation to investigate the synergetic effects of alloyed Pd/Au nanoparticles and the microporous, hydrophobic matrix ZIF-8. The imidazolate-based framework ZIF-8 was loaded with catalytically active mono- and bimetallic nanoparticles (Au, Pd, Pd/Au) by a seed-and-growth concept. Characterization of the synthesized materials was carried out by powder X-ray diffraction, N2 sorption, and advanced transmission electron microscopy. The catalytic activity towards aerobic alcohol oxidations was studied.

Posted on 30 September 2014 | 9:40 pm

Solution Speciation of the Dinuclear ZrIV-Substituted Keggin Polyoxometalate [{?-PW11O39Zr(?-OH)(H2O)}2]8– and Its Reactivity towards DNA-Model Phosphodiester Hydrolysis

The solution speciation of the ZrIV-substituted Keggin polyoxometalate (Et2NH2)8[{?-PW11O39Zr(?-OH)(H2O)}2]·7H2O (ZrK 2:2) was fully determined under different pD, temperature, and concentration conditions. Subsequently, phosphodiester bond hydrolysis of the DNA model substrate bis(4-nitrophenyl) phosphate (BNPP) promoted by ZrK 2:2 was studied in detail. In the presence of ZrK 2:2, phosphoester bond hydrolysis in BNPP proceeded with a rate constant of kobs = (4.75?±?0.25)?×?10–6 s–1 at pD 6.4 and 60 °C, which represented a 320-fold rate enhancement relative to the spontaneous hydrolysis of BNPP. The pD dependence of kobs exhibits a bell-shaped profile, with the fastest rate observed at pD 6.4. An activation energy (Ea) of 60.16 kJ?mol–1, enthalpy of activation (?H#) of 57.44 kJ?mol–1, entropy of activation (?S#) of –173.16 J?mol–1?K–1, and Gibbs activation energy (?G#) of 111.12 kJ?mol–1 at 37 °C were calculated. The influence of the concentration of ZrK 2:2 on the reaction rate constant was studied in the concentration range 0.5 to 6.0 mM. The results showed that ZrK 2:2 is able to hydrolyze an excess amount of BNPP, thus demonstrating that ZrK 2:2 acts as a catalyst for phospho(di)ester bond hydrolysis. In addition, the influence of ionic strength and the inhibitor diphenyl phosphate on BNPP hydrolysis were examined. A detailed 31P NMR spectroscopic aqueous solution study on the ZrIV-substituted Keggin-type polyoxometalate (Et2NH2)8[{?-PW11O39Zr(?-OH)(H2O)}2]·7H2O (ZrK 2:2) describes the influence of pD, temperature, reaction time, ionic strength, and ZrK 2:2 or substrate concentration, which allowed for a full characterization of the speciation equilibria.

Posted on 29 September 2014 | 11:40 am

Constitutional Hybrid Materials – Toward Selection of Functions

This microreview reveals a new strategy to transcribe supramolecular architectures in self-organized constitutional hybrids. In particular, the use of communicating reversible-covalent and supramolecular hydrophobic interfaces between organic/supramolecular and inorganic/siloxane networks represents a useful approach for improving their compatibility. Interpenetrated hybrid components lead, after the sol–gel process, to materials in which the features of supramolecular and inorganic networks are expressed through cross-over and linear processing schemes. Such a “dynamic marriage” between the processes of supramolecular self-assembly and inorganic sol–gel polymerization, which communicate synergistically, leads to higher self-organized hybrid materials on increased micrometric scale. Considering the simplicity of this strategy, possible applications in membranes and sensors are effective, reaching close to novel expressions of complex matter. This review will focus on the implementation of constitutional dynamic chemistry (CDC) toward constitutional hybrid materials, emphasizing recent developments in biomimetic ion channels, membranes, and constitutional hybrid materials.

Posted on 29 September 2014 | 11:30 am

Conformational Changes and Phase Behaviour in the Protic Ionic Liquid 1-Ethylimidazolium Bis(trifluoromethylsulfonyl)imide in the Bulk and Nano-Confined State

We report a Raman spectroscopic study of conformational changes to the TFSI anion in the protic ionic liquid 1-ethylimidazolium bis(trifluoromethylsulfonyl)imide, [C2HIm][TFSI], in its bulk and nano-confined state. We show that the TFSI anion is found as a mixture of cis and trans conformations at room temperature and in the liquid state, whereas this equilibrium shifts towards an increased cis population upon confinement in silica. In addition, the strong Raman signature at ca. 743 cm–1 assigned to TFSI is found at systematically higher frequencies in the confined state. These findings suggest a higher packing efficiency, or density, for the ionic liquid at the silica surface. Moreover, the enthalpy of conformational change is only marginally affected upon confinement (4.32?±?1.30 vs. 5.27?±?1.09 kJ?mol–1), and the entropy is found to be a few J?mol–1?K–1 higher in the confined state. Raman spectra recorded upon heating from very low temperatures show that the phase behaviour of the ionic liquid is also affected by confinement, with crystallization upon cooling being frustrated in favour of an amorphous glassy phase. To summarize, our results indicate that the interaction established in the ionogels between the silica surface and the protic ionic liquid [C2HIm][TFSI] favours local structural disorder, in conceptual agreement with the slightly higher experimentally estimated entropy. Conformational changes of the TFSI anion in the protic ionic liquid C2HImTFSI have been monitored by temperature-dependent Raman spectroscopy for the bulk and nano-confined states. Phase behaviours have also been spectroscopically investigated at a range of temperatures. In the nano-confined state the cis form predominates and the enthalpic term was higher.

Posted on 29 September 2014 | 11:30 am

Nanomolar Detection of AgI Ions in Aqueous Medium by Using Naphthalimide-Based Imine-Linked Fluorescent Organic Nanoparticles – Application in Environmental Samples

The synthesis of fluorescent organic nanoparticles (FONPs) with an imine-linked 1,8-naphthalimide-based dipodal chemosensor for AgI is described. The FONPs were prepared by using a re-precipitation method, and they were successfully applied for the nanomolar detection of AgI ions in aqueous media. More specifically, the chemosensor was utilized for the selective and ratiometric sensing of AgI in a concentration range 15–65 nM with a 15.5 nM detection limit. The work was extended to monitor the AgI concentration in samples of environmental importance. A naphthalimide-based dipodal chemosensor for the ratiometric detection of AgI ions in aqueous media has been synthesized, which has a detection limit in the nanomolar range. The chemosensor was successfully utilized for the detection of AgI in environmental samples.

Posted on 29 September 2014 | 11:30 am

Synthesis, Characterization, and Interconversion of ?-Diketiminato Nickel NxHy Complexes

The ?-diketiminato nickel(II) hydrazido(–1) complex [LtBuNi(?2-N2H3)], (IV) was investigated with respect to its deprotonation/protonation behavior. Deprotonation with KOtBu led to [LtBuNi(?,?2:?2-N2H2)K(solv)] (1), and this process was proven to be reversible. Spectroscopic and DFT studies revealed an electronic structure intermediate between nickel(II) hydrazido(–2) and nickel(0) diazene. On the other hand, protonation of IV with [LutH]OTf reversibly generated the hydrazine complex [LtBuNi(?2-N2H4)]OTf (2). Warming a solution of IV led to N–N bond cleavage yielding the nickel(I) ammine complex [LtBuNi(NH3)], (3). Hence, LtBuNi moieties were shown to effectively activate NxHy species for diverse conversions. In the coordination sphere of ?-diketiminato nickel(II) moieties hydrazine can be reversibly deprotonated, once to yield a hydrazido(–1) complex (which decomposes to an ammine complex at elevated temperatures) and twice to give a Ni(N2H2) complex with an electronic structure intermediate between nickel(II) hydrazido(–2) and nickel(0) diazene.

Posted on 26 September 2014 | 11:23 am

Cyclizations of Aryl Enynes Containing Propargyl Alcohol and Diallylamine Groups to Yield Indolecarbaldehydes Induced by Ruthenium Complexes

The reactions of RuCl(PPh3)2Cp ([Ru]Cl, Cp = cyclopentadienyl) with aryl enynes 1a–1c containing propargyl alcohol and diallylamine groups on the aryl ring give the carbene complexes 2a–2c, each of which contains an indole group. With an additional methylene group, the aryl enyne 1d reacts with [Ru]Cl to afford the dihydroisoquinoline complex 3d. For 1a–1d, the C–N bond-forming process occurs when the triple bond is ?-coordinated to the metal center. The reaction of [Ru]Cl with the aryl enyne 1e containing an isoxazole group affords the carbene complex 2e by a C–C bond formation between the isoxazole group and C-? of the triple bond, accompanied by the opening of the isoxazole ring. The reactions of 2a–2c and 2e with O2/NEt3 are assisted by visible light to afford the corresponding aldehydes 4a–4c and 5e. From DFT calculations, visible light results in the partial population of the lowest unoccupied molecular orbital (LUMO), which has Ru=C antibonding character; therefore, the bond is weakened, and the oxygenation/demetallation reactions are slightly promoted. The cyclization of aryl enynes 1a–1c containing propargyl alcohol and ortho-substituted amine groups on the aryl ring with a ruthenium complex first generates the carbene complexes 2a–2c; the oxygenation/demetallation of 2a–2c is promoted by visible light and causes the cleavage of the Ru=C bond to afford aldehyde products 4a–4c, respectively.

Posted on 26 September 2014 | 11:20 am

Selective C–H Bond Activation of 1,2-Dicarba-closo-dodecaborane by the Donor-Stabilized Silylene Bis[N,N?-diisopropyl­benzamidinato(–)]silicon(II)

Reaction of donor-stabilized silylene 1 (which is three-coordinate in the solid state and four-coordinate in solution) with 1,2-dicarba-closo-dodecaborane affords neutral six-coordinate silicon(IV) complex 2 with a carboranyl ligand through selective Ccluster–H bond activation. Compound 2 undergoes selective Si–C bond cleavage with acetonitrile to form neutral six-coordinate silicon(IV) complex 3 with a cyanomethyl ligand and 1,2-dicarba-closo-dodecaborane. Compounds 2 and 3 were characterized by crystal structure analyses and multinuclear NMR spectroscopy in the solid state and in solution. In addition, compound 2 was studied by DFT calculations. Reaction of donor-stabilized silylene 1 with 1,2-dicarba-closo-dodecaborane leads to the formation of neutral six-coordinate silicon(IV) complex 2 (selective C–H bond activation). Compound 2 reacts with acetonitrile to form neutral six-coordinate silicon(IV) complex 3 and 1,2-dicarba-closo-dodecaborane.

Posted on 24 September 2014 | 12:10 pm

Prussian Blue Films Produced by Pentacyanidoferrate(II) and Their Application as Active Electrochemical Layers

Iron complexes such as ferri/ferrocyanides are usually employed as electrochemical mediators in portable devices for the quick diagnosis of diseases. Stable complexes designed for the electrochemical active layer may render devices with better performance and lifetimes than conventional devices. In this work we have synthesized and characterized spectroscopically, electrochemically, and by DFT the complex Na4[Fe(CN)5(isn)] (isn = isonicotinate). This complex was used as a single-source precursor of Prussian Blue (PB) in solution at pH 2.0 and 3.0, as confirmed by UV/Vis spectroscopy. Potentiostatic deposition of PB onto glassy carbon electrodes provided stable films at pH 3.0 and 5.0, with electrocatalytic activity for ascorbic acid oxidation with a linear response in the range 20–200 ?M and an limit of detection of 12 ?M. The anodic peak potential of the modified electrodes varied with solution pH with a minimum value of 0.350 V versus NHE at pH 5.0. Prussian Blue is widely used in electrochemical sensors due to its ability to catalyze H2O2 reduction. Glucose meters are common point-of-care devices that employ ferricyanide as a redox mediator. The sensitivity, selectivity, and specificity of these devices can be improved by using Prussian Blue produced by pentacyanidoferrate(II) as an electroactive species rather than a redox mediator.

Posted on 24 September 2014 | 12:10 pm

Syntheses and Properties of Multiferrocenylated Corannulenes

The syntheses and properties of corannulenes bearing different numbers and types of ferrocenyl groups are described. Six different monoferrocenylated corannulenes were synthesized, and the crystal structure of 1-corannulenyl-1?-(ferrocenyl)benzene was elucidated by single-crystal X-ray analysis. Further, diferrocenylated corannulenes bearing methyl or trifluoromethyl groups are reported. Buckybowls with four and five ferrocenyl substituents were synthesized from tetrabromocorannulene and the symmetrical pentachlorocorannulene. The molecular structure and nutshell-like crystal packing of a tetraferrocenylated corannulene was determined by single-crystal X-ray analysis. Additionally, all compounds presented herein were subjected to electrochemical and optical measurements in solution. The synthesis and properties of corannulenes bearing up to five ferrocenyl groups are described. All compounds were investigated electrochemically to elucidate the interactions in the multiferrocenylated corannulenes. Additionally, several molecular structures were confirmed by single-crystal X-ray analyses and are discussed with respect to those of previously studied corannulenes.

Posted on 24 September 2014 | 12:10 pm

Two 3D Coordination Frameworks Based on Benzobisimidazole Linkers Generated under Similar Conditions: Synthesis, Structures and Thermal Properties

Herein, we present two benzobisimidazole-based 3D open coordination framework structures. Single-crystal X-ray analyses reveal that the title compounds [Zn(H2-BBIM)(SO4)]·DMSO (1) (H2-BBIM = benzobisimidazole; DMSO = dimethyl sulfoxide) and [Co(H2-BBIM)(SO4)(DMSO)0.5] (2) possess two different framework structures, although both of them have been synthesized under similar conditions. Compounds 1 and 2 exhibit cubic diamondoid and tetragonal CrB4 topological nets, respectively, in which the four-connected tetrahedral {MN2O2} (MII = Zn, Co) coordination units are located at the vertices and the edges are occupied by H2-BBIM ligands and sulfate anions. Only tetracoordination is observed in 1, whereas both tetra- and pentacoordination is present in 2. The phase purity of the compounds was ascertained by X-ray powder diffraction (XRPD) analysis, infrared spectroscopy, and elemental analysis. Variable-temperature XRPD analysis indicated that 1 and 2 are stable up to 90 and 140 °C, respectively. The syntheses, crystal structures, and thermal and spectroscopic properties of two benzobisimidazole-based CoII and ZnII coordination polymers are presented.

Posted on 24 September 2014 | 12:10 pm

Chemodosimetric Detection of the Acetate Anion by Using the Template Reaction Method via a Fluorescence “Turn-Off” Signal

The compartmental ligand 2,6-bis[2-(N-ethyl)thiopheneiminomethyl]-4-chlorophenol (HL) undergoes Cu(ClO4)2 induced partial hydrolysis to yield a monoamine ligand 4-chloro-2-formyl-6-[2-(thiophen-2-yl)ethyliminomethyl]phenol (HL?). On further reaction with Cu(ClO4)2, HL? produces a dinuclear complex, [Cu2(L?)2(ClO4)2] (2), which has been characterized in solution by UV/Vis, ATR, NMR, and ESI-MS spectral techniques and in the solid state by X-ray single-crystal structure analysis. The in situ generated 2 is highly fluorescent. On reaction with sodium acetate it transforms to a fluorescence inactive tetranuclear species, [Cu4(L)2(OAc)4(O)] (3), and thereby acts as an excellent chemodosimeter for selective detection of the acetate anion via fluorescence “turn-off” signalling. The direct reaction of HL and copper(II) acetate dihydrate yielded another fluorescence inactive tetranuclear species, [Cu4(L)2(OAc)4(O)] (1), which is a diastereoisomer of 3 as is evident from X-ray single-crystal structural analyses. A highly efficient copper-based metallo–ligand chemodosimeter has been developed for selective sensing of the acetate anion in the presence and/or absence of other anions via a fluorescence “turn-off” signal arising from the transformation from the dinuclear to the tetranuclear species.

Posted on 24 September 2014 | 12:10 pm

Metallic Few-Layer Flowerlike VS2 Nanosheets as Field Emitters

We report first-principles DFT calculations of the single-layer VS2 work function, the experimental synthesis of flower-like few-layer-thick VS2 nanosheets by a simple one-step hydrothermal method, and the investigation of their field emission properties. The turn-on field required to draw emission current densities of 1 and 10 ?A/cm2 were 4 and 5.01 V/?m, respectively. The observed turn-on field values are attributed to the high field enhancement factor (ca. 2500), which is due to presence of sharp protrusions in the VS2 nanosheets. Furthermore, the field-emission current stability of the VS2 emitter shows stable behavior over a period of 12 h. Further, DFT calculations show that the work function (f) of the single-layer VS2 emitter is 6.01 eV. We report first-principles DFT calculations of the single-layer VS2 work function, the experimental synthesis of flower-like few-layer-thick VS2 nanosheets by a simple hydrothermal method, and its field emission properties.

Posted on 24 September 2014 | 11:40 am

Acid Treatment of Layered Double Hydroxides Containing Carbonate

Carbonate-containing Mg–Al layered double hydroxides (LDHs) with two different crystallinities were treated with acidic solutions that contain Cl–. Upon treatment with an acetate buffer/NaCl aqueous solution, low-crystallinity LDH consumed more protons for dissolution of the metal hydroxide layers than did high-crystallinity LDH, and it showed a lower extent of exchange of interlayer anions for Cl– than high-crystallinity LDH. Varying washing procedures also resulted in differences in the characteristics of the washed products, such as the presence of Al(OH)3 and the extent of exchange for Cl–. When chloride-containing LDHs were dispersed in water, Mg hydroxide species in the LDHs were found to be dissolved to some extent even in water, and Cl– ions in the LDHs were replaced with OH– ions that were formed by the dissolution. Changes in Mg–Al–CO3 layered double hydroxides (LDHs) upon treatment with acidic solutions that contain Cl anions were investigated. The extent of anion exchange of interlayer anions for Cl–, the Mg/Al atomic ratio, and the weight recovery after treatment were monitored. The composition of the acidic solutions, LDH crystallinity, and the washing procedures all affected the product properties.

Posted on 24 September 2014 | 11:40 am

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

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

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

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

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

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

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

o-Oxazolinyl- and o-Thiazolinylphenol as Antennae in Luminescent EuIII and TbIII Complexes

Europium(III) and terbium(III) complexes have been prepared using the ligands 2-(4,5-dihydro-1,3-oxazol-2-yl)phenol (HL1) and 2-(4,5-dihydro-1,3-thiazol-2-yl)phenol (HL2) in yields ranging between 74 and 100?%. Metal-to-ligand ratios of 1:3 and 1:4 can be achieved, giving rise to compounds with the formulae [Ln2(L)6] and NR4[Ln(L)4], Ln = Eu, Tb. Recrystallisation of the complexes from DMSO resulted in the formation of octanuclear complexes [Na2(Ln(L1)3)2(CO3)(DMSO)2]2 held tightly together by carbonate ions that have been formed from CO2 from the atmosphere. Five structures have been determined, showing a bidentate binding mode of the ligand through the phenolate oxygen and the nitrogen atom of the five-membered ring. Most terbium compounds show bright luminescence upon excitation with near-UV radiation, with quantum yields of 16?% to 79?%. Strong emission is observed for NBu4[Eu(L1)4] and NEt4[Eu(L2)4] with quantum yields of 43?% and 20?%, respectively. Complexes of europium(III) and terbium(III) using the ligands 2-(4,5-dihydro-1,3-oxazol-2-yl)phenol and 2-(4,5-dihydro-1,3-thiazol-2-yl)phenol have been prepared with M/L ratios of 1:3 and 1:4; five of these compounds show bright luminescence upon excitation by near-UV radiation. Crystallisation from DMSO resulted in the formation of CO3-containing octanuclear complexes.

Posted on 14 August 2014 | 12:10 pm

Towards Deep-Blue Phosphorescence: Molecular Design, Synthesis and Theoretical Study of Iridium Complexes with Cyclometalating 2-Phenyl-2H-[1,2,3]triazole Ligands

We report on the synthesis and characterization of two bis-cyclometalated iridium(III) complexes with 2-phenyl-2H-[1,2,3]triazole as a new type of cyclometalating ligand. The photophysical and electrochemical properties of the two complexes were investigated experimentally as well as theoretically by using density functional theory. The properties of the two new complexes were compared with classical blue-emitting iridium complex FIrpic. The two complexes both exhibited deep-blue emission at 77 K, indicating that the introduction of cyclometalating 2-phenyl-2H-[1,2,3]triazole ligands can, in general, cause a spectral blueshift. Two blue-emitting iridium complexes with cyclometalating 2-phenyl-2H-[1,2,3]triazole ligands were synthesized and characterized. The two complexes both show strong deep-blue emission at 77 K, but no emission at room temperature. Calculations suggest that this lack of emmission might be caused by distorted excited state structures of the complexes.

Posted on 14 August 2014 | 12:10 pm

Synthesis and Characterization of Cationic Synphos-Rhodium Complexes

Different types of cationic Rh complexes bearing the Synphos ligand were characterized by NMR and X-ray analysis for the first time. This set of compounds includes diolefin rhodium precursors [Rh(Synphos)(cod)]BF4 and [Rh(Synphos)(nbd)]BF4, solvate complexes [Rh(Synphos)(MeOH)2]BF4, [Rh(Synphos)(acetone)2]BF4 as well as the toluene complex [Rh(Synphos)(toluene)]BF4, trinuclear complexes [Rh3(Synphos)3(?3-OH)2]BF4 and [Rh3(Synphos)3(?3-Cl)2]BF4 and arene-bridged dimer [Rh2(Synphos)2](BF4)2. Several types of cationic Rh complexes generated under reaction conditions starting from the precursor [Rh(Synphos)(diolefin)]BF4 were identified by NMR spectroscopy. Furthermore, six of these species were characterized by X-ray analysis for the first time; this includes the active species [Rh(Synphos)(acetone)2]BF4 as well as deactivating arene complex [Rh(Synphos)(methyl-?6-benzene)]BF4.

Posted on 14 August 2014 | 12:10 pm

A Differential Scanning Calorimetry and Theoretical Study on the Isomerization of trans-[Co(cyclam)(ONO)2]X (X = PF6–, ClO4–)

The solid-state interconversion of trans-[Co(cyclam)(ONO)2]X (X = PF6–, ClO4–; cyclam = 1,4,8,11-tetraazacyclotetradecane, [14]aneN4; dinitrito isomer) and trans-[Co(cyclam)(NO2)2]X (dinitro isomer) was investigated by differential scanning calorimetry (DSC). The conversion of the dinitrito isomer to the dinitro isomer was accompanied by the appearance of exothermic peaks. However, no isomerization DSC peak was observed for the dinitro isomers. The observed DSC peak for the dinitrito isomer was resolved into two peaks that correspond to two isomerization stages. The low-temperature peak was ascribed to the conversion of the metastable dinitrito isomer to an unstable nitro–nitrito one, whereas the high-temperature peak was attributed to the subsequent conversion of the nitro–nitrito isomer to the dinitro isomer. The kinetic parameters of the isomerization were determined by the Kissinger method. The electronic structures and thermodynamic stabilities of the linkage isomers, as well as the nature of the transition states, were investigated by DFT. The thermal linkage isomerization of the title compounds in the solid state was studied by differential scanning calorimetry (DSC). The observed exothermic DSC peak of the dinitrito isomer was resolved into two peaks that correspond to two isomerization stages. A comparative experimental and DFT study was performed on the thermodynamics and kinetics of the dinitrito to dinitro isomerization.

Posted on 14 August 2014 | 12:10 pm

Reactions of 1,3,2-Diselenaphospholanes with Lewis Acids: Borane and (Pentamethylcyclopentadienyl)rhodium and -iridium Dichloride

2-R-1,3,2-Diselenaphospholanes (R = iPr, Ph) with an annelated 1,2-dicarba-closo-dodecaborane(12) unit were treated with Lewis acids such as borane reagents (BH3 in THF, and BH3–SMe2) as well as Cp*-rhodium and -iridium dichloride (Cp* = pentamethylcyclopentadienyl). In all cases, the adduct formation in the beginning was followed by ring expansion through insertion of the borane or Cp*MCl2 into one of the P–Se bonds accompanied by transfer of a hydrido or chlorido ligand to phosphorus. Finally, the P–R unit was displaced from the ring to give the exchange products, in which the boron or the metal had become part of the five-membered rings. The reactions were monitored by NMR spectroscopy (1H, 11B, 13C, 31P, and 77Se). The proposed reaction sequences were found to be in agreement with calculated [B3LYP/6-311+G(d,p), LANL2DZ (Rh, Ir) level of theory] relative energies of optimized gas-phase structures of the various products. The novel molecular structure of the preferred insertion product with M = Ir, R = iPr was determined by X-ray analysis. Borane reagents as well as Cp*MCl2 (Cp* = pentamethylcyclopentadienyl; M = Rh, Ir) react with 1,3,2-diselenaphospholanes by the formation of adducts, followed by ring insertion, and finally by exchange.

Posted on 12 August 2014 | 12:10 pm

Uranyl Ion Complexes with trans-3-(3-Pyridyl)acrylic Acid Including a Uranyl–Copper(II) Heterometallic Framework

As a heterofunctional pro-ligand with both hard and soft coordination sites, trans-3-(3-pyridyl)acrylic acid (LH) is of potential interest for the design of heterometallic complexes of f- and d-block cations, as previously shown in the case of lanthanides. The reaction of LH with uranyl nitrate in water/acetonitrile at 180 °C yields the complex [(UO2)3(L)(HL)(O)(OH)3]·2.5H2O·CH3CN (2), which is different from the previously reported complex [UO2(L)(OH)] (1). Complex 2 crystallizes as a ribbon-like 1D coordination polymer with a skeleton bridged by oxido and hydroxido ligands, in which the uranyl cation is bound to the bridging bidentate carboxylato groups, and the pyridyl groups (one of them protonated) are directed sideways. In the presence of copper nitrate, the reaction affords the heterometallic complex [(UO2)2Cu(L)3(O)(H2O)](NO3) (3), in which the harder uranium atom is bound to two ?3-oxido anions and to chelating and bridging carboxylato groups to generate a tetranuclear secondary building unit, whereas the softer copper cations are bound to three pyridyl groups and only one carboxylato donor. The copper atoms are further involved in cation–cation interactions with uranyl oxido groups, and the Cu–O(oxido) bond lengths of 2.162(13) and 2.248(16) Å are among the shortest measured to date. 3 crystallizes as a 3D assembly, which displays narrow channels, and it illustrates the ability of copper cations, in combination with a ditopic ligand, to assemble discrete uranyl-containing units into a framework structure. The emission spectra of complexes 1 and 2 in the solid state display the usual vibronic progression of the uranyl ion in the range 450–650 nm, and the width of the bands indicates that they may be the superposition of slightly different series, due to the inequivalent uranyl centres in the lattices. The heterofunctional pro-ligand trans-3-(3-pyridyl)acrylic acid was used to build a uranyl–copper(II) heterometallic complex, in which the preferential bonding of the two cations reflects hard and soft affinities and which crystallizes as a 3D framework. The crystal structure of a new 1D homometallic uranyl complex with the same ligand is also described.

Posted on 11 August 2014 | 1:10 pm

Rationalizing and Disrupting Fluxional Processes in Agostically Stabilized 14-Electron Alkyliridium Hydride Complexes

We have investigated the fundamental patterns of reactivity for the cationic IrIII complexes [(6-Mes)(6-Mes?)Ir(H)]+ and [(7-Mes)(7-Mes?)Ir(H)]+ [6-Mes, 7-Mes = ring-expanded N-heterocyclic carbene (NHC) ligands, ? indicates that NHC is tethered through an iridium-bound CH2 group], each of which undergoes degenerate fluxional exchange between an iridium-bound agostic C–H bond and the discrete alkyl/hydride ligands resulting from C–H activation. A comparison between the activation parameters ?H‡ and ?S‡ determined by variable-temperature NMR (VT-NMR) spectroscopy line-shape analysis and those obtained from DFT calculations on model systems offers a basis to discriminate between different possible exchange mechanisms, and an oxidative addition pathway gives the lowest barrier and also the best agreement between experiment and theory. The addition of neutral Lewis base donors to [(6-Mes)(6-Mes?)Ir(H)]+ resulted in the displacement of the weak agostic C–H···Ir interaction and the generation of static (alkyl)iridium(III) hydride complexes such as [(6-Mes)(6-Mes?)Ir(H)(CNtBu)2]+. The analogous carbonyl complex is more labile, with the enhanced ?-acceptor properties of the ancillary ligands leading to C–H reductive elimination and to the formation of the IrI complex [(6-Mes)2Ir(CO)2]+, which incorporates unactivated NHC donors and has the ability to reversibly take up H2. By NMR spectroscopy and DFT methods, the mechanism of fluxional exchange in cationic bis(NHC) IrIII systems with an agostic C–H bond and cis-alkyl/hydride ligands is shown to feature an oxidative pathway. Related nonfluxional systems can be “trapped” by the addition of two-electron donors (L), and their stability to C–H reductive elimination can be tuned through the ?-acceptor properties of L.

Posted on 11 August 2014 | 1:10 pm

Triphenylamine-Substituted Metalloporphyrins for Solution-Processed Bulk Heterojunction Solar Cells: The Effect of the Central Metal Ion on Device Performance

A series of metal(II)-substituted 5,10,15,20-tetrakis[4-(diphenylamino)phenyl]porphyrins (P) were designed and synthesized. Incorporation of the flexible and strong electron-donating triphenylamine substituent endowed the porphyrins with enhanced solubility and intermolecular interactions. The distinct properties arising from different central metal ions were investigated by studying the absorption spectra, electrochemistry behavior, charge transport properties, thermal stability, and morphology characterization of the porphyrins. The PdII 5,10,15,20-tetra(4-diphenylaminophenyl)porphyrins (PPd) were found to have more matching energy levels with methyl [6,6]-phenyl-C-61-butyrate (PC61BM), higher hole mobility and longer triplet exciton lifetime. Bulk heterojunction solar cells based on porphyrins and PC61BM have been fabricated, with PPd-based solar cells exhibiting greatly enhanced photovoltaic performance originating from a combination of elements. These results will help guide the future molecular design of porphyrins for application in organic small molecule bulk heterojunction solar cells. Porphyrins with enhanced solubility and intermolecular interactions have been developed by incorporating the flexible and strong electron-donating triphenylamine substituent. Furthermore, different metal(II) ions have been introduced to the porphyrin and applied in organic photovoltaics to study the effects of the central metal ions on device performance.

Posted on 11 August 2014 | 12:40 pm

Mechanochemical Synthesis of SiO44–-Substituted Hydroxyapatite, Part II – Reaction Mechanism, Structure, and Substitution Limit

For the first time, silicate-substituted hydroxyapatites have been prepared from mixtures containing different amounts of silicon (0.2–2 mol per mol of apatite unit cell) by dry mechanochemical synthesis at room temperature in a planetary ball mill. The XRD, FTIR, TEM, and NMR spectroscopic data show that the product of the mechanochemical synthesis is a single-phase nanocrystalline apatite containing different amounts of carbonate and silicate ions and adsorbed water. In the annealed samples, three silicon concentration subranges can be distinguished, each of which is characterized by specific evolution of the lattice parameters. The formation mechanism of the silicate-substituted hydroxyapatite obtainable by this method is discussed. The studies indicate that the silicon substitution limit in the silicate-substituted lattice achievable by the dry mechanochemical synthesis followed by heat treatment is 1.2 mol per mol of apatite unit cell. Silicate-substituted hydroxyapatite powders containing different amounts of silicon have been synthesized by the mechanochemical method. Several apatite crystal structures that differ by the position of the hydroxy groups have been identified.

Posted on 11 August 2014 | 12:40 pm

Synthesis of Urchin-Like FeF2 Nanoarchitectures and Their Conversion into Three-Dimensional Urchin-Like Mesoporous ?-Fe2O3 Nanoarchitectures for Methane Activation

Novel urchin-like FeF2 nanoarchitectures have been fabricated by an unconventional nonhomogeneous ionic liquid/diphenyl ether solvothermal method. Subsequent solid-state thermal annealing was utilized to convert the FeF2 nanoarchitectures into 3D urchin-like mesoporous ?-Fe2O3 nanoarchitectures. The reaction system and temperature played important roles in the morphology of FeF2 and the growth of the 3D urchin-like ?-Fe2O3. A study of methane activation over the 3D urchin-like mesoporous ?-Fe2O3 nanoarchitectures revealed that methane was activated and converted into carbon dioxide at a low temperature (230 °C). Compounds containing C–C bonds were produced at 600 °C. This 3D urchin-like mesoporous ?-Fe2O3 shows excellent potential as a catalyst for methane conversion in the chemical industry. Novel urchin-like FeF2 nanoarchitectures have been fabricated by an unconventional nonhomogeneous ionic liquid/diphenyl ether solvothermal method and converted into 3D urchin-like mesoporous ?-Fe2O3 nanoarchitectures by solid-state thermal annealing. The ?-Fe2O3 nanoarchitectures exhibit good catalytic properties in methane activation reactions.

Posted on 11 August 2014 | 12:40 pm

Mechanochemical Synthesis of SiO44–-Substituted Hydroxyapatite, Part I – Kinetics of Interaction between the Components

The kinetics of the room-temperature dry mechanochemical synthesis of hydroxyapatite modified by SiO44– ions has been studied for the first time. The changes in the composition of the reaction mixture as a function of the time of mechanical activation in a planetary ball mill as well as the composition of the final product have been investigated by X-ray phase analysis and IR spectroscopy. Certain stages of the interaction of the reactants have been analyzed with the help of high-resolution electron microscopy. The mechanochemical synthesis conducted in air is accompanied by the incorporation of carbonate ions into the apatite lattice, which results in the formation of B-type carbonated hydroxyapatite. The apatite structure starts to form after 5 min of mechanochemical activation of the reaction mixture, and the final single-phase nanocrystalline powder of silicate-substituted carbonated hydroxyapatite is formed after 30 min of activation. The kinetics of the dry mechanochemical synthesis of hydroxyapatite modified by SiO44– ions is studied. From the first seconds of mechanical activation, the initial Ca(H2PO4)2·H2O partially reacts with CaO to form CaHPO4 (interior of the nanoparticles); the nanoparticle shell is Ca(H2PO4)2·H2O, and the material located near the nanoparticles is a mechanical mixture of the initial components.

Posted on 6 August 2014 | 2:40 pm

[Ge(H)(2-C6H4PPh2)3] as Ligand Precursor at Ruthenium: Formation and Reactivity of [Ru(Cl){Ge(2-C6H4PPh2)3}]

The germane [Ge(H)(2-C6H4PPh2)3] (2) was synthesized by reaction of Li[Ge(2-C6H4PPh2)3] (1) with water. The presence of nBuBr led to the formation of [Ge(nBu)(2-C6H4PPh2)3] (3). The complex [Ru(Cl){Ge(2-C6H4PPh2)3}] (4) was obtained by reaction of 2 with [Ru(Cl)2(PPh3)3] and NEt3. The ruthenium-bound Ge(2-C6H4PPh2)3 moiety in 4 can be converted into a Ge(Cl)(2-C6H4PPh2)2 fragment on treatment of 4 with a solution of HCl in diethyl ether to yield [Ru(Cl){Ge(Cl)(2-C6H4PPh2)2}(PPh3)] (5). The reaction of complex 4 with potassium hydride in an atmosphere of dihydrogen led to [Ru{Ge(2-C6H4PPh2)3}(H)(H2)] (6). Complex 6 reacted with hydrazine to give [Ru{Ge(2-C6H4PPh2)3}(H)(N2H4)] (7). With an excess of hydrazine, complex 6 catalyzed the disproportionation of hydrazine to produce ammonia and the ruthenium complex [Ru{Ge(2-C6H4PPh2)3}(H)(NH3)] (8). The ruthenium complex [Ru(Cl){Ge(2-C6H4PPh2)3}] can be converted into the dihydrogen complex [Ru{Ge(2-C6H4PPh2)3}(H)(H2)] on treatment with KH in a dihydrogen atmosphere. A reaction of [Ru{Ge(2-C6H4PPh2)3}(H)(H2)] with hydrazine led to its catalytic disproportionation to give ammonia and the ammonia complex [Ru{Ge(2-C6H4PPh2)3}(H)(NH3)].

Posted on 6 August 2014 | 2:40 pm

Syntheses and Solid-State Structures of Et2SbTeEt and Et2BiTeEt

Diethylstibanyl- and diethylbismuthanyl telluranes Et2MTeEt (M = Sb 1, Bi 2) as well as tBu3Sb (3) were structurally characterized by single-crystal X-ray diffraction. Single crystals of 1–3 were grown by using an IR-laser-assisted technique. Compounds 1 and 2 form short intermolecular E···Te interactions in the solid state, which were further investigated with dispersion-corrected density functional theory. Single crystals of Et2M–TeEt (M = Sb 1, Bi 2) as well as tBu3Sb (3) were grown by using an IR-laser-assisted technique. Compounds 1 and 2 form short intermolecular E···Te interactions in the solid state, which were further investigated with dispersion-corrected density functional theory.

Posted on 5 August 2014 | 2:20 pm

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