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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:

1D Heterometallic Oxalate Compounds as Precursors for Mixed Ca–Cr Oxides – Synthesis, Structures, and Magnetic Studies

The heterodimetallic compounds {[CaCr2(L)2(C2O4)4]·xH2O}n [L = 2,2?-bipyridine (bpy), x = 0.83 (1); L = 1,10-phenanthroline (phen), x = 0.33 (2)] were synthesized and characterized by IR spectroscopy, X-ray diffraction and magnetic measurements. The crystal structure of 2 is reported: the chelation of a [Cr(phen)(C2O4)2]– units towards Ca cations results in 1D double zigzag chains. The ability of 1 and 2 to act as single-source precursors for the formation of Ca–Cr oxides is explored by thermal analysis, powder X-ray diffraction and IR spectroscopy. The thermal processing of 1 and 2 at 1100 °C in air led to the appearance of the ?-CaCr2O4 phase as the major crystalline oxide. By heating the samples up to 1100 °C in nitrogen, only the ?-CaCr2O4 phase formed, whereas heating at 1400 °C caused the crystallization of two polymorphs, ?- and ?-CaCr2O4. The magnetic behaviour of ?-CaCr2O4 pointed to the freezing of magnetic moments in coexistence with a weak ferromagnetic order. The heat treatment of {[CaCr2(L)2(C2O4)4]·xH2O}n [L = 2,2?-bipyridine, x = 0.83 (1) and 1,10-phenanthroline, x = 0.33 (2)] at 1100 °C in a nitrogen flow resulted in the isolation of the ?-CaCr2O4 phase, whereas heating at 1400 °C caused the crystallization of two polymorphs, ?-CaCr2O4 and ?-CaCr2O4. The spectroscopic, structural and magnetic properties of the single-source precursors and the ? phase are investigated.

Posted on 15 October 2014 | 4:11 pm

Lithium Complexes of Asymmetric Hydrogen Tetraimido Sulfate

Two novel monolithiated complexes, [(thf)2Li(NtBu)2(NHtBu)S(Ndipp)] (3) and [(thf)2Li(NtBu)2(NHtBu)S(Ndmp)] (4), are presented from the reaction of the neutral tri(tert-butyl)sulfur triimide S(NtBu)3 (1), nBuLi, and diisopropylaniline and dimethylaniline, respectively. These asymmetrically substituted hydrogen tetraimido sulfate complexes of lithium provide the opportunity to switch the metal in a transmetalation reaction and to introduce another substituent at the protonated imide function. Asymmetrically substituted hydrogen tetraimido sulfate ligands provide two opportunities to generate metal complexes. Firstly, the lithium metal can be exchanged in a transmetalation reaction, and secondly, the proton can be replaced by an additional substituent or another metal. This gives access to heterobimetallic complexes.

Posted on 15 October 2014 | 4:11 pm

Mono-Oxido-Bridged Heterobimetallic and Heterotrimetallic Compounds Containing Titanium(IV) and Chromium(III)

A series of oxido-bridged heterobi- and heterotrimetallic complexes, [(tmtaa)Ti=OCr(Por)Cl] and [(tmtaa)Ti=OCr(Por)O=Ti(tmtaa)]+ (tmtaa = 7,16-dihydro-6,8,15,17-tetramethyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecine; Por = 5,10,15,20-tetraarylporphyrin), have been synthesized. To the best of our knowledge, these complexes are the first structurally characterized examples to contain a Ti=OCr or Ti=OCrO=Ti structural motif. Crystal structures of representative heterobimetallic compounds, including the Ti=OCr binuclear complex 2 and two separate trimers, [Ti=OCrO=Ti]SbF6 (10) and [Ti=OCrO=Ti]Cl (12), are reported. The bi- and trimetallic molecules have similar structural parameters, including Ti–O, Cr–O, and Ti–O–Cr bond lengths and angles with a linear Ti=OCr geometry. Magnetic studies showed that a high-spin CrIII (S = 3/2) center is present in both the bi- and trinuclear molecules. The redox potentials for CrIV/III (?E = 320 mV) and Por/Por·– (?E = 260 mV) can be tuned by modifying the porphyrin ligand. By determining the thermodynamics and kinetics of the formation of these complexes by titration experiments and electrochemistry, it was found that the bi- and trimetallic species undergo isomerization in solution, allowing easy substitution of the apical chlorido ligand. A series of heterobi- and heterotrimetallic molecules containing an unsupported oxido bridge have been synthesized. The molecular structures are controlled by the stoichiometry of the reagents, and the heterotrimetallic structural motif Ti=OCrO=Ti is hitherto unknown. Electrochemistry and magnetic studies were performed to identify the intermediates and their thermodynamic properties.

Posted on 15 October 2014 | 4:11 pm

Structurally Characterized Antipyrine-Based Dual Fluorescent Probe: Enhanced AlIII Selectivity of a Dinuclear ZnII Complex for Intracellular Sensing by a Displacement Approach

The antipyrine-based fluorescence probe daph, structurally characterized by single-crystal X-ray diffraction, can recognize both Zn2+ (at 520 nm, yellow) and Al3+ (at 490 nm, green). However, Al3+ selectivity is enhanced significantly when the dinuclear ZnII-daph complex is used as a sensor, which senses Al3+ by a displacement approach. The binding constants of daph for Zn2+ and Al3+ are (4.9?±?0.2)?×?104 and (3?±?0.1)?×?105 M–1, respectively. The higher water solubility of the ZnII-daph complex allows the detection of Al3+ in a greener way (0.1 M HEPES buffer, ethanol/water = 1:9, v/v, pH 7.4). Moreover, the detection limit of the ZnII-daph complex for Al3+ is higher (2.5?×?10–9 M) than that of free daph (4.6?×?10–8 M). Alkali and alkaline-earth metal ions, Cd2+, Hg2+, and Pb2+, and 3d metal ions do not interfere. Both daph and the ZnII-daph complex are capable of intracellular Al3+ detection. The antipyrine-based fluorescent probe daph recognizes both Zn2+ and Al3+ at two different wavelengths. However, Al3+ selectivity is enhanced significantly when the corresponding ZnII-daph complex is used as a sensor. Moreover, the detection limit of the ZnII-daph complex for Al3+ is higher than that of free daph. Both daph and ZnII-daph are capable of intracellular Al3+ detection.

Posted on 15 October 2014 | 4:11 pm

Generation of Group VI Piano-Stool and Triple-Decker Complexes from [(IMes)2PtH(Cl-boratabenzene)] Species

Species [(IMes)2Pt(H)(1-Cl-2-SiMe3–BC5H4)] (1) was used as the source of the Cl-boratabenzene anion for coordination to group VI transition metals, resulting in the formation of piano-stool complexes [(?6-1-Cl-2-SiMe3–BC5H4)M(CO)3]– [M = Cr (2), Mo (4), W (5)] and a homodimetallic triple-decker complex [(CO)3Cr(?6-1-Cl-2-SiMe3–BC5H4)Cr(CO)3]– (3). All species were spectroscopically characterized and the first X-ray structure of a Cl-boratabenzene species is reported. Group VI piano-stool and triple-decker complexes of a Cl-boratabenzene ligand were prepared. All species were spectroscopically characterized and the first X-ray structure of the Cl-boratabenzene triple-decker complex is reported.

Posted on 15 October 2014 | 4:11 pm

A Tetradentate ?-Diiminato Ligand Containing Phenolate Substituents: Flexivalent Coordination to MnIII, CoIII, NiII, and CuII

A functionalized ?-dialdimine was prepared, bearing a 3,3-dimethylindoleninyl group at the meso-position and two N-phenolic groups. The structure contains three labile protons, which can be lost or migrate through tautomerism to provide an N2O2 coordination core. A number of divalent and trivalent metal ions (CuII, NiII, CoII/III, and MnIII) were accommodated inside the core, forming a series of intensely colored products consisting of a tricyclic MN2O2 chelate. In the resulting divalent metal complexes, the dialdimine ligand is deprotonated only at the two phenolic oxygen atoms and is thus dianionic, whereas in the trivalent metal complexes, the dialdiminato ligand is triply deprotonated. The copper and nickel complexes adopt square-planar geometries, whereas in the trivalent cobalt and manganese complexes, two neutral ancillary ligands complete an octahedral geometry around the metal center. In each case, the denticity of the diimino–diiminato ligand is four. The electrochemical oxidation of the copper and nickel complexes was studied by cyclic voltammetry. meso-Substituted dialdimine/dialdiminate acts as a di- or trianionic N2O2 ligand and exhibits redox-non-innocent character.

Posted on 14 October 2014 | 3:10 pm

On the Preparation and Structure of Caesium Aluminium Tetrahydride

A new tetragonal phase of CsAlH4 was observed after the precipitation of CsAlH4 from a diglyme solution with an inert solvent. This new phase and the previously described orthorhombic phase were characterized by a combination of X-ray powder diffraction analysis and 27Al and 133Cs solid-state NMR spectroscopy. The transformation of the tetragonal CsAlH4 phase into the orthorhombic CsAlH4 phase can be induced by thermal treatment, whereas the opposite process can be stimulated by mechanical treatment. The phase transformation processes are almost completely reversible and can be performed several times without any observable decomposition of CsAlH4. The structure of the tetragonal CsAlH4 phase (space group I41/a) was solved from X-ray powder diffraction data, and the lattice parameters were determined to be a = 5.6732(4) and c = 14.2795(11) Å. The transformation of a newly observed tetragonal polymorph of CsAlH4 into the previously described orthorhombic CsAlH4 phase can be induced by thermal treatment. The reverse transformation can be induced by mechanical treatment. Both phases were characterized by X-ray diffraction and 27Al and 133Cs MAS NMR spectroscopy.

Posted on 14 October 2014 | 3:10 pm

High Adsorption Capacity for Cationic Dye Removal and Antibacterial Properties of Sonochemically Synthesized Ag2WO4 Nanorods

?-Ag2WO4 nanorods with an average diameter of 15 to 25 nm and a surface area of ca. 115.0?±?0.2 m2/g have been synthesized by a facile sonochemical technique. These nanorods have been used for the adsorption of various cationic dyes (rhodamine B, methylene blue, and malachite green) from aqueous solution. The adsorption process is fast, and ca. 100?% adsorption of a 20 ppm mixture of all three dyes occurs within 10 min. The adsorption process was studied by varying different regulating parameters such as the solution pH and the initial dye and Ag2WO4 concentrations, and the results were analyzed with various isotherm and kinetic models. The mechanistic pathway for the selective adsorption of cationic dyes has been explained through zeta potential studies. Moreover, the thermal regeneration of the sorbent was possible by furnace heating at 250 °C, and the nanorods were efficient for multicyclic use. X-ray photoelectron spectroscopy (XPS) has been performed on the thermally regenerated samples to ascertain their surface purity. The Ag2WO4 nanorods have a bactericidal effect and are active against both Gram-negative and -positive bacterial strains of Escherichia coli and Bacillus subtilis, respectively. However, the efficiency is more pronounced for Gram-positive bacteria. Thus, these sonochemically synthesized Ag2WO4 nanorods have great potential for the treatment of dye industry effluents as a promising adsorbent for cationic dyes from aqueous solution and are also useful as an antibacterial agent. Sonochemically synthesized ?-Ag2WO4 nanorods exhibit superior sorption affinity for cationic dyes such as rhodamine B and methylene blue and also display good antibacterial activity.

Posted on 14 October 2014 | 3:10 pm

Seleno-Nucleobases and Their Water-Soluble Ruthenium–Arene Half-Sandwich Complexes: Chemistry and Biological Activity

Half-sandwich organometallic ruthenium complexes of seleno-nucleobases, 3 and 4, were synthesized and characterized. The structures of both complexes were determined by X-ray crystallography and are the first crystal structures of ruthenium complexes with seleno-nucleobases. Interestingly, 3 self-assembles aided by adventitious water in DMF to give a tetranuclear square 3a·6H2O. Complex 4 is active against Jurkat and Molt-4 cell lines but inactive against the K562 cell line, whereas 3 is completely inactive against all three cell lines. The free ligand 6-selenopurine (1) and 6-selenoguanine (2) are highly active against these cell lines. Compound 2, like its thio analogue, is unstable under UVA light, whereas 4 is stable under similar conditions, which suggests that the ruthenium complex could reduce problems associated with the instability of the free ligand, 2, under irradiation. Water-soluble bioorganometallic ruthenium complexes with seleno-nucleobases have been studied. The complex with 6-selenoguanine is shown to be more stable, although less cytotoxic, relative to the free ligand.

Posted on 14 October 2014 | 2:40 pm

Ionic Liquid Based Approaches to Carbon Materials Synthesis

Ionic liquids (ILs) have attracted continuous interest because of their remarkable physicochemical properties, including high thermal and chemical stability, nonflammability, negligible vapor pressure, designable cation/anion pairs, electrical and ionic conductivity, low melting points, and affinity towards many compounds. These properties make ionic liquids valuable in the creation of new materials and new processes throughout almost the entire field of materials chemistry. An emerging field is the use of ionic liquids in carbon-based nanomaterials. Initially, ionic liquids were used as self-templating carbon sources for the generation of unusual carbon materials in which homogeneous heteroatom doping (e.g., N, B, S) can be accomplished fairly easily. Later, ionic liquids were recognized as suitable for use in the conversion of biomass into porous carbon materials, acting as both reaction media and porosity-directing regulator. Such applications open the door towards the synthesis and accurate tuning of carbon nanostructures, for example, pore structure, morphology, heteroatom doping, and surface functionality. In addition, the hybridization of ionic liquids and nanocarbons enables the development of composites by combining the properties of the ionic liquid (e.g., ionic conductivity or catalytic activity) and those of a host (e.g., chemical or mechanical stability). Currently, although the research of this topic is rapidly expanding, the rational design and synthesis of carbon-based materials, particularly their applications in energy storage and transformation, is still in its infancy. In this review, we focus on several aspects of ionic liquid derived carbons with the aim of shedding light on this new topic: 1) Ionic liquids as an advanced medium for carbon synthesis, 2) ionogels derived from nanocarbon, 3) ionic liquids as fluid precursors for functional carbons, and 4) ionic liquid derived carbons for heterogeneous catalysis. Ionic liquids are currently established solvents, precursors for carbon materials, and components of carbon-based ionogels. The unique properties of ionic liquids are beneficial for the formation of unusual carbon materials or composites with homogeneous heteroatom doping (e.g., N, B, S) and controllable porosity.

Posted on 14 October 2014 | 2:40 pm

Lithium-Containing Pnictides with Supertetrahedral Cluster Chains

Invited for the cover of this issue is the group of Svilen Bobev at the University of Delaware, USA. The cover image shows the crystal structure of Ba4Li2Cd3Pn6 (Pn = P, As, Sb), which is based on infinite chains of supertetrahedral T2 clusters. This work was aimed at the discovery and synthesis of “first-of-a-kind” quaternary pnictide-based compounds with complex, low-dimensional structures...Read more about the story behind the cover in the Cover Profile and about the research itself on p. 5113 ff.

Posted on 13 October 2014 | 12:10 pm

Unprecedented Borylene Insertion into a C–N Bond

Invited for the cover of this issue is the group of Rajendra S. Ghadwal at Georg-August-Universität Göttingen, Germany. The cover image shows insertion of a borylene into a C–N bond with an N-heterocyclic olefin (NHO) ligand. Insertion of a borylene into a C?N bond is reported for the first time...Read more about the story behind the cover in the Cover Profile and about the research itself on p. 4921 ff.

Posted on 10 October 2014 | 1:48 pm

Masthead: Eur. J. Inorg. Chem. 29/2014

Posted on 10 October 2014 | 1:48 pm

Unprecedented Borylene Insertion into a C–N Bond (Eur. J. Inorg. Chem. 29/2014)

The cover picture shows insertion of a borylene into a C–N bond with an N-heterocyclic olefin (NHO) ligand. Selective borylene insertion into a C–N bond to yield boryl-functionalized NHOs [{N(Dipp)N(DippBH)CHCH}CCH2]2 and [{N(Dipp)N(DippBPh)CHCH}CCH2][{N(Dipp)N(2-iPr-6-CHMeCH2BC6H3)CHCH}CCH2] (Dipp = 2,6-iPr2C6H3) is reported for the first time. (IPrCH2)BHCl2 affords completely unexpected diborane compound (IPr)BH2BH2(IPr). Lewis acid induced ring opening of THF to form the borenium ion [(IPrCH2)B{O(CH2)4I}2]I is demonstrated. Details are discussed in the Short Communication by R. S. Ghadwal et al. on p. 4921 ff. For more on the story behind the cover research, see the Cover Profile.

Posted on 10 October 2014 | 1:48 pm

Graphical Abstract: Eur. J. Inorg. Chem. 29/2014

Posted on 10 October 2014 | 1:48 pm

An Insight into the Complexation of Pyrazine-Functionalized Calix[4]arenes with Am3+ and Eu3+ – Solvent Extraction and Luminescence Studies in Room-Temperature Ionic Liquids

The complexation behaviour of six pyrazine-functionalized calix[4]arenes, containing substituents such as carbamoyl dioctyl (L-1, L-2), diisopropyl phosphonate (L-3, L-4) and diphenyl phosphoryl (L-5, L-6), with Am3+ and Eu3+ ions was investigated by solvent extraction as well as by luminescence spectroscopy (only for Eu3+) in room-temperature ionic liquids (RTILs), [Cnmim][NTf2] (1-alkyl-3-methylimidazolium, n = 4, 6, and 8). The spectacular enhancement in the extraction values of the trivalent metal ions in RTILs, as compared to those reported in a molecular diluent from 3 M HNO3, was rather unusual and was further investigated by luminescence studies. Luminescence studies involving Eu3+ and performed with L-4 and L-6 confirmed the 1:1 stoichiometry of the extracted species (Eu3+?L) with log?? values of 4.42?±?0.51 and 5.18?±?0.38 for L-4 and L-6, respectively. Judd–Ofelt parameters, which give information about the nature of bonding as well as the coordinating environment, were computed from the emission spectra of the Eu3+?L-4 and Eu3+?L-6 complexes. Complexation of Am3+ and Eu3+ with six pyrazine-functionalized calix[4]arene ligands was investigated in room-temperature ionic liquids (RTIL) by carrying out solvent extraction as well as luminescence (only for Eu3+) studies. Solvent extraction with RTIL resulted in a large enhancement in D values, and the nature of the complexes was investigated by luminescence spectroscopy.

Posted on 10 October 2014 | 1:11 pm

Palladium(II) and Platinum(II) Complexes Containing Six-Membered N-Heterocyclic Ligands: Synthesis, Characterization, Interaction with DNA, DFT Calculation, and Cytotoxicity

Four novel complexes based on the ligand piperazine (Pip) in a chair conformation have been synthesized, namely [Pd(5,5?-dcbpy)Pip]·4H2O (1), [Pt(5,5?-dcbpy)Pip]·3H2O (2), [Pd(4,4?-dcbpy)Pip]·4H2O (3), and [Pt(4,4?-dcbpy)Pip]·2H2O (4; 4,4?-dcbpy = 2,2?-bipyridyl-4,4?-dicarboxylate, 5,5?-dcbpy = 2,2?-bipyridyl-5,5?-dicarboxylate). The four complexes were characterized by elemental analysis, FTIR spectroscopy, 1H and 13C NMR spectroscopy, and single-crystal X-ray diffraction analysis. In addition, gel electrophoresis was performed on the four complexes and further insight into these complexes was gained by quantum chemistry calculations. The interaction of these complexes with fish sperm DNA (FS-DNA) was studied by UV/Vis and fluorescence spectroscopy, which revealed that they have the ability to bind to FS-DNA. The IC50 values of the four complexes range from 8.3 to 32.5 ?M. Finally, we studied the cytotoxic activities of complexes 1–4 against two different cancer cell lines. A series of bioactive experiments have revealed four Pd and Pt complexes exhibit good biological activity towards DNA. The in vitro cytotoxicity of these complexes was investigated against two different cancer cell lines, showing good cytotoxic activity.

Posted on 10 October 2014 | 12:40 pm

Assemblies of Alkaline-Earth-Metal Ions with o-Tetramethyl-Substituted Cucurbituril in the Presence of the Cadmium Tetrachloride Anion

o-Tetramethyl-substituted cucurbituril (o-TMeQ[6]), a polydentate ligand, has been synthesized and isolated in a controlled manner by using a dimer of dimethyl-substituted glycoluril and a dimer of unsubstituted glycoluril. Coordination assemblies have been investigated by reactions between alkaline earth cations and o-TMeQ[6] in the presence of [CdCl4]2–, a structure inducer, in HCl aqueous solution. X-ray diffraction analysis revealed that o-TMeQ[6] coordinates with Ca2+ or Sr2+ and forms centrosymmetric tetranuclear assemblies in the presence of [CdCl4]2–. [CdCl4]2– typically produces the “honeycomb effect” by forming honeycomb-like frameworks, which assist metal ions in coordinating to o-TMeQ[6]. The driving forces of this effect are the “outer-surface interactions” of cucurbit[n]urils. Coordination assemblies have been investigated by reactions between alkaline earth cations and o-tetramethyl-substituted cucurbituril (o-TMeQ[6]) in the presence of [CdCl4]2–, a structure inducer, in HCl aqueous solution. [CdCl4]2– forms honeycomb-like frameworks, which assist metal ions in coordinating to o-TMeQ[6].

Posted on 9 October 2014 | 7:13 pm

Copper(II) Clusters of Two Pairs of 2,3-Dihydroxybutanedioyl Dihydrazones: Synthesis, Structure, and Magnetic Properties

Condensation reactions of (2R,3R)- and (2S,3S)-2,3-dihydroxybutanedihydrazide with salicylaldehyde and 3-methoxysalicylaldehyde gave two enantiomeric pairs, (2R,3R)/(2S,3S)-2,3-dihydroxybutanedioylbis(salicylaldehydehydrazone) [(2R,3R)-BSH and (2S,3S)-BSH] and (2R,3R)/(2S,3S)-2,3-dihydroxybutanedioyl bis(3-methoxysalicylaldehydehydrazone) [(2R,3R)-MBSH and (2S,3S)-MBSH]. Their reactions with CuII salts provided two chiral hexanuclear clusters [Cu6L2(C5H5N)10]2[C5H6N]3(ClO4)7·(CH3OH)·(C5H5N) [L = (2R,3R)-BSH; (2S,3S)-BSH] and four chiral tridecanuclear clusters [Cu13L3(OH)2(CH3COO)6(C5H5N)6(DMF)3]·6DMF·3H2O [L = (2R,3R)-BSH; (2S,3S)-BSH] and [Cu13X3(OH)2(CH3COO)6(C5H5N)2(DMF)8]·6H2O [X = (2R,3R)-MBSH, (2S,3S)-MBSH]. Their structures were determined by single-crystal X-ray diffraction analysis. All six compounds are enantiomers of each other. The two hexanuclear clusters exhibit two orthogonal linear trinuclear units. The two pairs of tridecanuclear clusters display esthetic structures with different symmetries; they feature rare heptanuclear vertex-sharing dicubane cores and their six unshared CuII vertexes are linked to another six CuII ions. These represent the first examples of chiral clusters bearing dicubane cores. Magnetic studies revealed the presence of overall antiferromagnetic interactions in these compounds. Six chiral clusters of two pairs of 2,3-dihydroxybutanedioyl dihydrazones, four of which represent the first examples of chiral clusters bearing dicubane cores, are presented. All six compounds are enantiomers of each other. Magnetic studies reveal the presence of overall antiferromagnetic interactions in these compounds.

Posted on 8 October 2014 | 12:23 pm

High-Temperature Synthesis of Ordered Hexagonal Mesoporous Silica Materials (SBA-15) with Adjustable Large Mesopores for Selective Adsorption of Biomolecules

AL-SBA-15 materials with additional large-mesopore networks have been successfully synthesized at high-temperature (200 °C) in the presence of inorganic salts. Compared with conventional SBA-15 which has monomesopores, the samples synthesized by using cations and assisted by high-temperature show a bimodal pore size distribution. Interestingly, the large mesopores in the samples can be tuned by a simple adjustment in the preparation time and temperature. In addition, this route also results in the formation of a high degree of silica condensation which is favorable for improvement of sample hydrothermal stability. More importantly, the adsorption and separation of biomolecules over AL-SBA-15 materials and conventional SBA-15100 or SBA-15200 samples shows that AL-SBA-15 samples exhibit superior selective adsorption and separation capabilities compared with conventional samples and this is potentially important for their applications in adsorption and separation of bulky biomolecules. This paper describes a new method for preparing ordered hexagonal mesoporous SBA-15, with large adjustable mesopores, in the presence of inorganic salts and explores their application in selective adsorption of biomolecules.

Posted on 8 October 2014 | 12:20 pm

Gas-Phase Fragmentation Reactions of Keggin-Type {PW11O39M} (M = Rh, Ir, and Ru) Polyoxometalates as Fingerprints of the Ligands Attached at the Noble Metal Site

The gas-phase fragmentation reactions of Keggin-type [PW11O39MCl]5– (M = Rh, Ir) polyoxometalates (POMs) featuring chloride terminal ligands have been investigated. Different adducts of the general formulas [PW11O39MCl + 2cat]3– and [PW11O39MCl + 3cat]2– [cat = alkylammonium cations (Me4N+, Bu4N+), alkali cations (Na+, K+) or protons] were subjected to collision-induced dissociation (CID) conditions. The (cat)Cl (cat = H+, Na+ or K+) fragments were released as a common fragmentation pathway and were taken as a fingerprint of the ligands attached at the noble metal site. Other {PW11O39ML} POMs (M = Rh, Ir) with L = thiocyanate, nitrite, methyl, phenylacetate or phenyl were identified on the basis of CID experiments. Coordination studies of thiocyanate anions and CO to {PW11O39Ru} POMs to yield the new compounds [PW11O39RuSCN]5– and [PW11O39RuCO]4– are also reported. CID experiments were also used to validate that thiocyanate and CO ligation at the Ru metal site had occurred. The gas-phase fragmentation reactions of Keggin-type {PW11O39ML} (M = Rh, Ir) polyoxometalates (POMs) under collision-induced dissociation (CID) conditions are diagnostic of the ligand attached at the noble metal site. This is illustrated for several ligands such as chloride, thiocyanate, nitrite or metalated ligands and also extended to new Keggin-type {PW11O39RuL} POMs (L = thiocyanate and CO).

Posted on 8 October 2014 | 12:20 pm

Effects of Ultrasonic Agitation on the Structural and Magnetic Properties of CoFe2O4 Nanocrystals

Cobalt ferrite nanocrystals (CoFe2O4) were synthesized by means of ultrasonic agitation and afterward subjected to different annealing temperatures. The structural and morphological properties of the nanocrystals were investigated by means of X-ray diffraction and scanning electron microscopy. The results showed that the samples were composed of CoFe2O4 monophase nanocrystals. The particle size increased with increasing annealing temperatures. Infrared spectroscopy and magnetization showed that the samples exhibited the usual features of CoFe2O4 nanocrystals. Superparamagnetism was not observed at room temperature. However, the results indicated that the samples could be considered single-domain particles with blocking temperatures greater than 300 K. Both infrared and magnetic results indicated possible diffusion of cobalt ions from tetrahedral to octahedral sites as a function of the annealing temperature. In this work, we have demonstrated that ultrasonic agitation favors the formation of CoFe2O4 nanocrystals with uniform size and high magnetization. We confirmed these results by means of X-ray diffraction, scanning electron microscopy, IR spectroscopy, and magnetization measurements.

Posted on 8 October 2014 | 12:20 pm

Microwave-Assisted Synthesis, Characterisation and Dielectric Properties of Nanocrystalline Zirconia

Nanocrystalline zirconia particles with a diameter of about 4 nm were obtained by microwave-assisted decomposition of basic zirconium acetate in ethoxyethanol. The reaction yields optically transparent and stable dispersions, which can ideally be employed for the manufacture of dielectric thin films by spin-coating followed by a subsequent annealing step. The influence of the processing conditions on the electronic performance of an electrical capacitor device built from this nanomaterial was studied. Electron paramagnetic resonance spectroscopic studies exclude the presence of point defects within the zirconia bulk; however, they reveal the presence of surface-related paramagnetic species. Transparent, stable dispersions of zirconia nanoparticles can be obtained using basic zirconium acetate as precursor. These are suitable for the manufacture of dielectric thin films. Their electrical performance is strongly influenced by the processing and environmental conditions. Electron paramagnetic resonance spectroscopy is a valuable tool to understand these effects.

Posted on 8 October 2014 | 12:20 pm

?-Tetrasubstituted meso-Tetra(4?-n-butyl­phenyl)porphyrins and Their Metal Complexes: Synthesis and Structural Properties

A new family of -tetrasubstituted porphyrins, 2,3,12,13-tetra[phenylethynyl (PE)/4-methoxyphenyl (4?-CH3OPh)/4-carboxy methylesterphenyl (4?-CH3CO2Ph)]-5,10,15,20-tetrakis(4?-n-butylphenyl)porphyrin, H2T(4?-BuPh)P(R)4 and their metal (CoII, CuII and ZnII) complexes were synthesized using H2T(4?-BuPh)PBr4 as the precursor. These porphyrins show red-shifted absorption bands and follow the nature of the ?-pyrrole substituent, R: PE > Br > 4?-CO2CH3Ph ? 4?-OCH3Ph. Crystal structures of MT(4?-BuPh)P(PE)4 (M = 2H, CoII, CuII and ZnII) derivatives were determined by single-crystal XRD and they are isomorphous. The normal coordinate structure decomposition analysis of these structures reveal a slight wave-type of distortion of the macrocycle. Electrochemical redox properties of these derivatives show an anodic shift in potentials relative to their metallotetraphenylporphyrins (MTPPs), and this has been ascribed mainly to the electronic effect of the substituents. The synthesis of a series of ?-tetra(phenylethynyl/4?-methoxyphenyl/4?-carboxymethylesterphenyl)-meso-tetra(4?-n-butylphenyl)porphyrins and their metal complexes is reported. Single-crystal XRD analysis show interesting structural and intermolecular interactions in the solid state, and electrochemical redox properties show an anodic shift in redox potentials relative to their corresponding MTPPs (metallotetraphenylporphyrins).

Posted on 8 October 2014 | 12:20 pm

A Mononuclear Manganese Complex of a Tetradentate Nitrogen Ligand – Synthesis, Characterizations, and Application in the Asymmetric Epoxidation of Olefins

A new chiral manganese complex (C1) bearing a tetradentate nitrogen ligand containing chiral bipyrrolidine and benzimidazole moieties was prepared. The structure of C1 was confirmed by ESI-MS and crystallography. This manganese complex is an active catalyst for the asymmetric epoxidation of various olefins with excellent conversion (up to 99?%) and high enantiomeric excess (up to 96?%?ee) with hydrogen peroxide as the oxidant in the presence of 2-ethylhexanoic acid or acetic acid. Compared with previous structurally similar manganese complexes with different diamine backbones (C2, cyclohexanediamine; C3, diamine from L-proline), C1 showed improved asymmetric induction, especially for simple olefins such as styrene derivatives and substituted chromene. The possible reasons for the improvement of the ee values are discussed in the text on the basis of the crystal structures of the manganese complexes. A chiral manganese complex bearing a tetradentate nitrogen ligand with chiral bipyrrolidine and benzimidazole moieties is an active catalyst for the asymmetric epoxidation of various olefins with excellent conversions (up to 99?%) and up to 96?%?ee with hydrogen peroxide as the oxidant in the presence of 2-ethylhexanoic acid or acetic acid.

Posted on 8 October 2014 | 12:20 pm

Polyrotaxaned versus Interdigitated Super-Arrays of Loop-and-Chain Strands: Role of the Anion in Formation of Silver(0) Particles

Self-assembly of AgX (X– = BF4–, ClO4–, and NO3–) with C3-symmetric 1,3,5-tris(isonicotinoyloxyethyl)cyanurate (L) yields 1D loop-and-chain strands. However, the formation of a super-array of strands depends on the nature of the polyatomic anions: BF4– and ClO4– anions induce 1D polyrotaxaned loop-and-chain strands, whereas NO3– anion leads to the formation of 2D-like interdigitated loop-and-chain strands in the crystalline state. Calcination of [Ag3(L)2]3X (X– = BF4– and NO3–) crystals at 500 °C produces silver(0) particles, whereas the same treatment of [Ag3(L)2]3ClO4 crystals affords a mixture of silver(0) and silver(I) chloride. The rates of formation of Ag0 nanoparticles by reduction of crystalline products using ascorbic acid are in the order X– = ClO4– > BF4– > NO3–, and their crystalline morphologies are dependent on the nature of the polyatomic anions. The direct role of polyatomic anions in the formation of molecular super-arrays of 1D loop-and-chain strands and of silver(0) particles through both calcination and reduction are investigated.

Posted on 6 October 2014 | 6:20 pm

Complexation of NpV Ions with 1,10-Phenanthroline-2,9-dicarboxylic Acid: Spectrophotometric and Microcalorimetric Studies

The complexation of NpV ions with a tetradentate ligand with oxygen and nitrogen donors, 1,10-phenanthroline-2,9-dicarboxylic acid (denoted as H2L), was studied in aqueous solutions by spectrophotometric and calorimetric methods. NpV ions form a very strong 1:1 complex, NpO2L–, with the stability constant log?? = 11.73?±?0.02 in 0.1 M NaClO4 at 25 °C. It is a much stronger complex than those of NpV ions with related ligands such as picolinic acid or dipicolinic acid, as the higher denticity of 1,10-phenanthroline-2,9-dicarboxylic acid results in a larger entropic effect on the complexation. It is expected that the amide derivatives of 1,10-phenanthroline-2,9-dicarboxylic acid would be excellent extractants in the separation of NpV ions, which are problematic in actinide separation processes owing to their very low extractability by many extractants. The large conjugated phenanthroline moiety in 1,10-phenanthroline-2,9-dicarboxylic acid provides a planar configuration in which the four donor atoms are “preorganized” into optimal positions to coordinate to the equatorial plane of NpO2+ ions to form a very strong tetradentate complex.

Posted on 6 October 2014 | 6:10 pm

Preparation of Alginate/Graphene Oxide Hybrid Films and Their Integration in Triboelectric Generators

Sodium alginate/graphene oxide (Al/GO) nanocomposite films were prepared by solvent casting. The structure, morphology, and electrical properties of Al/GO films were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and thermal analysis. The utilization of such an Al/GO film for a device that uses friction as the charging process to convert mechanical energy into electric power is reported. The triboelectric generator (TEG) was fabricated by stacking a drop-cast Al/GO film bewteen indium–tin oxide (ITO)-coated poly(ethylene terephthalate) (PET) and a PET sheet. Furthermore, the utilization of such a TEG as a pressure sensor is also illustrated. Sodium alginate/graphene oxide nanocomposite films were prepared by a solvent-casting method. We report the proof of concept that such a hybrid system can be used as the active component of a triboelectric generator. The involvement of a biodegradable polymer might introduce new applications in biodegradable/biocompatible electronics.

Posted on 6 October 2014 | 11:10 am

Ion-Size-Dependent Formation of Mixed Titanium/Lanthanide Oxo Clusters

The mixed-metal oxo clusters LnTi4O3(OiPr)2(OMc)11 (Ln = La, Ce; OMc = methacrylate), Ln2Ti6O6(OMc)18(HOiPr) (Ln = La, Ce, Nd, Sm) and Ln2Ti4O4(OMc)14(HOMc)2 (Ln = Sm, Eu, Gd, Ho) have been synthesized from titanium isopropoxide, the corresponding lanthanide acetate and methacrylic acid. The type of cluster obtained strongly depends on the size of the lanthanide ion. Ln/Ti mixed-metal oxo clusters with an Ln/Ti ratio of 2:4, 2:6 and 1:4 have been obtained from the reactions of titanium isopropoxide with lanthanide acetates and methacrylic acid. The type of cluster obtained strongly depends on the size of the lanthanide ion.

Posted on 6 October 2014 | 11:10 am

Supramolecular Coordination Complexes of the N-Thiophosphorylated 2,5-Dithiobiurea [NHC(S)NHP(S)(OiPr)2]2 with ZnII and CdII Ions – Cation-Induced Dinuclear Mesocate Structure versus Tetranuclear Nanoscaled Aggregate

The reaction of the deprotonated N-thiophosphorylated bisthiourea N,N?-bis(diisopropoxythiophosphorylamidothiocarbonyl)hydrazine {[NHC(S)NHP(S)(OiPr)2]2, H2L} with ZnCl2 leads to the complex [Zn2{[NHC(S)NP(S)(OiPr)2]2}2] ([Zn2L2]), in which two metal cations are each 1,5-S,S?-coordinated through the sulfur atoms of the thiocarbonyl and thiophosphoryl groups of the pendant deprotonated thioacylamidothiophosphate functions. The same reaction with CdCl2 leads to the tetranuclear nanoscaled aggregate [(Cd2{[NC(S)NHP(S)(OiPr)2]2}2)2] ([(Cd2L2)2]). This complex contains ligands that are doubly deprotonated through their hydrazine NH groups and exhibit unprecedented ?4 and ?5 coordination modes. DFT calculations have shown that both complexes are stabilized not only by typical coordination bonds (Zn–S, Cd–S) but also by numerous intramolecular “noncovalent” interactions: polar C–H···S and N–H···S, nonpolar C–H···H–C, and ?-hole bonding (S···S). The reaction of the deprotonated N-thiophosphorylated bisthiourea [NHC(S)NHP(S)(OiPr)2]2 with ZnCl2 leads to the complex [Zn2{[NHC(S)NP(S)(OiPr)2]2}2], and the same reaction with CdCl2 leads to the formation of the tetranuclear nanoscaled aggregate [(Cd2{[NC(S)NHP(S)(OiPr)2]2}2)2].

Posted on 6 October 2014 | 11:10 am

Deamination of NSn-Coordinated Organotin(II) Hydroxide: Formation of a New C–O Covalent Bond

The synthesis of the pentacarbonylchromium complex [{2,6-(Me2NCH2)2C6H3}(Cl)SnCr(CO)5] is reported. Starting with this compound, organotin(II)pentacarbonylchromium methoxide [{2,6-(Me2NCH2)2C6H3}(OMe)SnCr(CO)5] was prepared and used for the synthesis of dimeric NSn intramolecularly coordinated organotin(II)pentacarbonylchromium hydroxide [{2,6-(Me2NCH2)2C6H3}Sn(?-OH)Cr(CO)5]2 by easy hydrolytic protocol. In addition, acid–base-type reaction of this latter compound with HOTf provided unprecedented cyclization product [6-(Me2NCH2)-2,3-(C6H3CH2OSn)Cr(CO)5]2. The cyclization process is accompanied by the formation of a new C–O covalent bond along with the elimination of Me2NH. An acid–base-type reaction of NSn intramolecularly coordinated organotin(II)pentacarbonylchromium hydroxide [{2,6-(Me2NCH2)2C6H3}Sn(?-OH)Cr(CO)5]2 with trifluoromethanesulfonic acid (HOTf) provided unprecedented cyclization product [{6-(Me2NCH2)-2,3-(C6H3CH2OSn)}Cr(CO)5]2. The cyclization process is accompanied by the formation of a new C–O covalent bond along with the elimination of Me2NH.

Posted on 2 October 2014 | 12:43 pm

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

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

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

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

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

Posted on 29 August 2014 | 12:20 pm

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

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

Posted on 29 August 2014 | 12:20 pm

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

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

Posted on 29 August 2014 | 12:20 pm

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

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

Posted on 29 August 2014 | 12:20 pm

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

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

Posted on 29 August 2014 | 12:20 pm

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

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

Posted on 29 August 2014 | 12:10 pm

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

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

Posted on 29 August 2014 | 12:10 pm

Unprecedented Borylene Insertion into a C–N Bond

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

Posted on 26 August 2014 | 10:20 am

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

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

Posted on 26 August 2014 | 10:20 am

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

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

Posted on 26 August 2014 | 10:20 am

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

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

Posted on 25 August 2014 | 12:10 pm

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

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

Posted on 21 August 2014 | 12:13 pm

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

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

Posted on 20 August 2014 | 11:10 am

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

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

Posted on 19 August 2014 | 11:20 am

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

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

Posted on 18 August 2014 | 11:10 am

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

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

Posted on 15 August 2014 | 11:23 am

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