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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:

Influence of Metal Cations and Coordination Modes on Luminescent Group 1 and 2 Metal Sulfonate Complexes Constructed from 4,4?-Dihydroxybiphenyl-3,3?-disulfonic Acid

The reactions of 4,4?-dihydroxybiphenyl-3,3?-disulfonic acid (H4L) with group 1 and 2 metal salts in aqueous solution lead to six metal sulfonate complexes, [K2(H2L)]n (1), {[Cs2(H2L)(H2O)]n·nH2O} (2), 2[Mg(H2O)6]2+·2(H2L)2–·2H2O (3), {[Ca(H2L)(H2O)2]n·4nH2O} (4), {[Sr(H2L)(H2O)4]n·3nH2O} (5), and {[Ba(H2L)(H2O)]n·nH2O} (6), which have been characterized by elemental analysis, IR spectroscopy, thermogravimetry (TG), photoluminescence (PL) spectroscopy, powder XRD, and single-crystal XRD. Complexes 1, 2, and 6 exhibit 3D pillared-layered networks formed by M–O–S layers bridged by the biphenyl rings of H2L2– dianions. The [Mg(H2O)6]2+ cations and sulfonate groups in 3 are held together by second-sphere interactions to generate layer motifs. Complex 4 presents a layer structure formed by Ca–O chains bridged by the biphenyl rings of H2L2– dianions. Complex 5 has a 3D interdigitating architecture (2D + 2D??3D), in which the 44 hydrogen-bonding layer is constructed from linear chains. Meanwhile, the recrystallization of H4L from aqueous solution affords the supramolecular complex 2(H3O+)·(H2L)2–·3H2O (S1), which exhibits a 3D pillared-layered network. The solid-state luminescence properties demonstrate that 1–6 exhibit violet emission at room temperature and can sensitize EuIII and TbIII ions to exhibit their characteristic emissions. The self-assembly of 4,4?-dihydroxybiphenyl-3,3?-disulfonic acid with group 1 and 2 metal salts results in diverse second-coordination-sphere networks, hybrid layers, interdigitating 2D + 2D??3D architectures, and 3D pillared-layered networks tuned by the metal cations and the coordination mode of the ligand.

Posted on 26 March 2015 | 1:10 pm

Ferrocenyl–Bipyridinium Cations and Their Platinum Complexes Related to Viologens – Preparation, Redox Properties, and Crystal Structures

N-R1-N?-R2-4,4?-Bipyridinium and N-R1-4,4?-bipyridinium salts containing ferrocenyl substituents were prepared as donor–acceptor compounds (R1 = ferrocenyl, ferrocenylphenyl; R2 = ferrocenyl, ferrocenylphenyl, phenyl, methyl). Platinum(II)-bridged diferrocene compounds were prepared by using the N-R1-4,4?-bipyridinium ligands. These compounds display multistage redox properties. The redox potentials of the ferrocenyl and bipyridinium moieties in these compounds are independently affected by molecular modifications, which indicates that conjugation between the donor and acceptor moieties is less effective. Single-crystal X-ray diffraction analyses revealed large twist angles between the two moieties in the solid state. The compounds exhibit broad charge-transfer absorption bands in the range 450–800 nm. No electronic communication was observed between the terminal ferrocenes in the diferrocene complexes. 4,4?-Bipyridinium cations bearing ferrocenyl or ferrocenylphenyl substituents at the N-positions were prepared as donor–acceptor compounds. Platinum(II)-bridged diferrocene compounds were also prepared by using bipyridinium cations. These cations display multistage redox properties, and the compounds exhibit broad charge-transfer absorption bands in the range 450–800 nm.

Posted on 26 March 2015 | 1:10 pm

Effects of Big Planar Anions on the Spin Transition of a Mononuclear Manganese(III) Complex with a Hexadentate Schiff-Base Ligand

Two new ion-pair complexes [Mn(3-MeO-sal-N-1,5,8,12)][Ni(dmit)2] (1) and [Mn(3-MeO-sal-N-1,5,8,12)][Pt(mnt)2]·2CH3CN (2), based on the known six-coordinate mononuclear Schiff-base manganese(III) spin-crossover complex [Mn(3-MeO-sal-N-1,5,8,12)]NO3, have been synthesized and structurally characterized. Their crystal structures indicate that increasing the size of the anion from NO3– to [Pt(mnt)2]– and [Ni(dmit)2]– leads to the dimerization of the cations and formation of alternating cation–anion stacks with loss of the most effective cation–anion interactions; only weak short contacts exist between the cations and anions. Magnetic measurements and variable-temperature single-crystal X-ray crystallography analysis provided firm evidence for spin-crossover (SCO) effects in 1. The magnetic susceptibility of compound 2 is typical of a simple paramagnet, and the manganese(III) complex cations remain in the high-spin state in the temperature range 2–300 K. Spin-crossover in d4 ions is a most rare event. Changing the size of the anion from NO3– to [Pt(mnt)2]– and [Ni(dmit)2]– leads to significant changes in the overall crystal packing of Mn ion-pair complexes and furthermore in the spin state of the MnIII center.

Posted on 26 March 2015 | 1:10 pm

Potent Reactivity in Solubilised Oxo-Titanium Polymers

[TiO(salen)]n polymers are solubilised in aldehyde solution giving highly reactive entities. Unprecedented carbon-based chemistry is demonstrated by the formation of new ligands about the titanium centre. Identified by X-ray crystallography are a polymer deconstructed [Ti(salen)] oxo dimer, a [Ti(salen)] catecholato complex and an unusual [Ti(salen)] diolato complex. Formation of the new ligands appears to be related to the salicylidene ligand aromatic ring ortho substituent and the aldehyde used. [TiO(salen)]n polymers solubilised in aldehyde solution show potent activity when ortho substituents are present on the salicylidene ligand aromatic rings. Unprecedented carbon-based chemistry is demonstrated by the formation of new ligands about the titanium centre.

Posted on 25 March 2015 | 11:40 am

Monoclinic Copper(I) Selenide Nanocrystals and Copper(I) Selenide/Palladium Heterostructures: Synthesis, Characterization, and Surface-Enhanced Raman Scattering Performance

We have developed a simple and facile approach to the fabrication of monoclinic Cu2Se nanocrystals and Cu2Se/Pd heterostructures. [(C2H5)4N]2[CuCl4] was chosen as the copper source and SeO2/terpineol was used as the Se–II precursor for the generation of hexagonal CuSe and cubic Cu2–xSe through the “hot-injection” and “one-pot” methods, respectively. Both CuSe and Cu2–xSe could be further transformed into monoclinic Cu2Se through heat treatment with trioctylphosphine (TOP) at 220 °C. Cu2Se/Pd as well as CuSe/Pd and Cu2–xSe/Pd were readily obtained by simply mixing copper selenides and Pd(NO3)2 in a 2-propanol solution. The Pd nanoparticles were distributed on the surface of the copper selenides. The effect of certain reaction parameters on the formation of copper selenides was studied. The amount of terpineol used played an important role in the phase-selective synthesis of CuSe and Cu2–xSe. The surface-enhanced Raman scattering (SERS) performance of the heterostructures was investigated with 4-mercaptopyridine (4-Mpy) as a probe molecule. Owing to the strong synergistic effects between Cu2Se and Pd, Cu2Se/Pd showed greater SERS performance than pure Pd or Cu2Se. Moreover, compared to those of CuSe/Pd and Cu2–xSe/Pd, Cu2Se/Pd exhibited the highest SERS sensitivity to 4-Mpy with a detection limit as low as 1.0?×?10–9 M, which revealed its phase- and composition-dependent characteristics. This Cu2Se/Pd heterostructure exhibits potential applications in the chemical and biological sensing fields. Monoclinic Cu2Se nanocrystals and Cu2Se/Pd heterostructures have been synthesized by simple and facile methods. Owing to strong synergistic effects and phase-dependent characteristics, the surface-enhanced Raman scattering performance of the Cu2Se/Pd heterostructure is superior to those of Cu2Se, Pd, CuSe/Pd, and Cu2–xSe/Pd.

Posted on 25 March 2015 | 11:40 am

Phenylpyrazole-Based Hypervalent Phosphorus Compounds: From Positional Isomerism to Stacking Interactions

The lithium salt of 3,5-dimethyl-1-phenyl-1H-pyrazole (PyrC6H4Li) reacts with (Et2N)2PCl to give the precursor [PyrC6H4P(NEt2)2] (2), which, after reaction with PCl3, affords PyrC6H4PCl2 (3) in 79?% yield. The phosphorus atom in 3 has four-coordinate disphenoidal geometry with an axial arrangement of Cl atoms. The length of the hypervalent N–P bond in this compound [1.775(1) Å] is comparable to that of common single bonds. The structure of 3 is better described by canonical formulae containing charges on the N, P, and Cl atoms. The 1H NMR spectrum of 3 in CDCl3 shows five pairs of nonequivalent Me groups, which correspond to the positional isomers that exist in the equilibrium mixture. Compound 3 easily exchanges chlorine with methyl iodide to form the diiodo derivative 4 (PyrC6H4PI2) with nonequivalent P–I bonds. The reduction of 3 with aluminium foil or [GeCl2(diox)] gave cationic diphosphines [(PyrC6H4P)2(?-Cl)][AlCl4] (8) and [(PyrC6H4P)2(?-Cl)][GeCl3] (9), respectively, with a chloride bridge between the phosphorus atoms. Compounds 4, 8 and 9 show a disphenoidal arrangement around the hypervalent phosphorus atoms. The dichloro and diiodo derivatives 3 and 4 are destroyed on heating in pyridine to give diphosphines [(PyrC6H4PCl)2] (10) and [(PyrC6H4P)2(?-I)]+[I] (12), respectively, containing hypervalent (trivalent four-coordinate) phosphorus. The crystal structure of 10 shows multiple C···C, C···Cl, H···H, and C···H short contacts between the adjacent molecules. Compound 3 exchanges chlorine for oxygen atoms on heating in dimethylformamide to give the dioxide PyrC6H4PO2 (13) with an N–PV distance [1.808(1) Å] even longer than that in 3. The dichlorophosphino derivative of 3,5-dimethyl-1-phenyl-1H-pyrazole exists in solution as an equilibrium mixture of positional isomers. Its reduction leads to cationic diphosphines with a chloride bridge between the phosphorus atoms. The hypervalent N···P (1.774–1.885 Å) and Hal···P interactions influence the behavior in solution and the arrangement of molecules in the crystal form.

Posted on 24 March 2015 | 1:10 pm

External-Template-Assisted Formation of Octacyanometalate-Based MV–MnII (M = W, Mo) Bimetallic Coordination Polymers with Magnetic Properties

Three manganese–molybdenum/tungsten bimetallic coordination polymers, two 2D {{[?4-M(CN)8]2[Mn(dmf)3]2[Mn(dmf)4]}·2DMF}n (M = W 1, Mo 2) and a 1D {{[?4-Mo(CN)8][Mn(dmf)4]2}·(ClO4)}n (3), were constructed from the reaction of the (Bu3NH)3[M(CN)8] (M = W, Mo) and Mn(ClO4)2·6H2O molecular building blocks in DMF solvent in the presence (for 1 and 2) or absence (for 3) of the organic ligand bis(benzimidazol-2?-yl)pyridine. Single-crystal X-ray diffraction structure analysis indicated that compounds 1 and 2 both crystallize in the monoclinic crystal system with the P21/c space group and possess the same 2D network. The 2D layer structures of 1 and 2 have a (3,4)-connected 2-nodal topology with the point symbol {42·63·8}{42·6}. Compound 3 crystallizes in the tetragonal crystal system with the P42/m space group. All three compounds are further assembled into 3D supramolecular structures through intermolecular C–H···N or C–H···O hydrogen bonds. The magnetic susceptibility of compounds 1 and 3 was investigated in the temperature range of 2–300 K; these compounds exhibit typical ferrimagnetic properties. 2D coordination polymers {{[?4-M(CN)8]2[Mn(dmf)3]2[Mn(dmf)4]}·2DMF}n (M = W, Mo) and a 1D chain compound {{[?4-Mo(CN)8][Mn(dmf)4]2}·(ClO4)}n are constructed by external-template-assisted formation in the presence and absence of bis(benzimidazol-2?-yl)pyridine. All three compounds can be assembled into 3D supramolecular structures, and two of the compounds exhibit typical ferrimagnetic properties.

Posted on 24 March 2015 | 1:10 pm

Facile Preparation of Ammonium Molybdophosphate/Al-MCM-41 Composite Material from Natural Clay and Its Use in Cesium Ion Adsorption

Ordered hexagonal mesoporous aluminosilicate matrix (Al-MCM-41) with incorporated ammonium molybdophosphate (AMP) was successfully synthesized by a one-pot synthesis method with natural clay from low-grade potash ores of Qinghai salt lake as the silica and aluminum source. We introduced a modified “liquid-phase transport” step, which allowed the use of impure natural clay as a starting material to directly produce pure product without sedimentation pretreatment. The resultant product was characterized by X-ray fluorescence (XRF) spectroscopy, FTIR spectroscopy, XRD, TEM, 27Al and 31P magic-angle spinning (MAS) NMR spectroscopy, and N2 adsorption/desorption, which indicated that the AMP was immobilized in the mesoporous structure of Al-MCM-41. The adsorption capacity of the final product for the removal of cesium ions in solution was also investigated. The results suggested that salt lake clay is a promising low-cost precursor for the production of mesoporous aluminosilicate supports through one-pot syntheses, and the final composite material is effective for the adsorption of cesium ions from solutions containing other alkali metal ions. A composite ammonium molybdophosphate/Al-MCM-41 material is synthesized by a one-pot method with natural clay as the silica and aluminum source. A modified “liquid-phase transport” step allows the use of impure natural clay as the starting material to produce pure product without sedimentation pretreatment. The composite material is effective for the adsorption of cesium ions from brine.

Posted on 23 March 2015 | 11:10 am

Thymol Bromination – A Comparison between Enzymatic and Chemical Catalysis

The catalytic activity of the vanadium-dependent bromoperoxidase isolated from the brown alga Ascophyllum nodosum is compared with the activity of a cheap, commercially available V-catalyst precursor in the bromination of thymol. Organic solvents have been avoided to make the system appealing from a sustainable chemistry point of view. It is noteworthy that, notwithstanding the low solubility of the substrate, the thymol bromination reactions were performed in water, with a safe brominating source, under mild conditions, and with relatively inexpensive reagents. In this regard, the greenness of the systems was evaluated by the estimation of the E-factor value; the result is that the chemical reaction has a lower environmental impact than the enzymatic process, with an E-factor in the range of eco-friendly processes. Catalysis of thymol bromination by vanadium derivatives is directly compared to catalysis by a V-dependent bromoperoxidase. All reactions were performed under mild and sustainable conditions with relatively inexpensive reagents. Appealing results were obtained in terms of selectivity and sustainability.

Posted on 20 March 2015 | 12:10 pm

Flux Crystal Growth of the Ternary Polygermanide LaPtGe2, a p-Type Metal

Large plate crystals of LaPtGe2 have been grown by using an inert indium metal flux. This compound crystallizes in the CeNiSi2-type structure (orthorhombic space group Cmcm) with lattice parameters a = 4.3770(9) Å, b = 17.186(3) Å, and c = 4.3942(9) Å. The structure of LaPtGe2 is a three-dimensional framework with alternating PbO-type layers of PtGe and infinite Ge chains, separated by La atoms. Electrical resistivity and Hall effect measurements characterize LaPtGe2 as a metal with holes that act as the charge carriers. Strong temperature dependence of the Hall coefficient and a violation of Kohler's rule (from magnetoresistance data) both indicate possible multiband effects. The electronic structure calculations suggest the metallic nature of LaPtGe2 and show that the strongest bonding exists between Pt and Ge within the PbO-type layers. Plate crystals of LaPtGe2 have been grown from a molten indium flux. This compound crystallizes in the CeNiSi2-type structure. Electrical resistivity, Hall effect, and thermopower measurements have shown that LaPtGe2 exhibits p-type metallic behavior, which is consistent with electronic band structure calculations.

Posted on 20 March 2015 | 12:10 pm

Room-Temperature Hydrogenation of Citral Catalyzed by Palladium–Silver Nanocrystals Supported on SnO2

We have developed two strategies to optimize Pd catalysts. On one hand, Ag was introduced into Pd and then they were applied to the selective hydrogenation of citral under mild conditions. The addition of metallic Ag could tune the selectivity of Pd and made it suitable for the selective hydrogenation of the conjugated double bond. The selectivity of citronellal increased from 0 (for Pd/C and Pd0.7Ag0.3/C) to 96?% (for Pd0.4Ag0.6/C) as the Ag content increased. On the other hand, the addition of SnO2 made the Pd catalysts more inclined to activate the C=O bond and gave better performance for the hydrogenation of the conjugated double bond compared with the corresponding Pd–Ag catalysts. The selectivity of citronellal increased from 0 (for Pd0.7Ag0.3/C) to 76?% (for Pd0.7Ag0.3–SnO2/C was used) after the addition of SnO2. On the basis of these results, we developed a catalyst (Pd0.6Ag0.4–SnO2/C) with the best catalytic performance for the selective hydrogenation of citral (the conversion of citral reached 99?%, and the selectivity was up to 96?%). We have developed two strategies to optimize Pd catalysts for the selective hydrogenation of citral and exploited a catalyst (Pd0.6Ag0.4–SnO2/C) with the best catalytic performance (the conversion of citral reached 99?%, and the selectivity was up to 96?%).

Posted on 20 March 2015 | 12:10 pm

Synthesis, Crystal Structures, Molecular Docking, and Urease Inhibitory Activities of Transition-Metal Complexes with a 1,2,4-Triazolecarboxylic Acid Derived Ligand

Four novel complexes, [Cu(L)2(NH3)2(H2O)2] (1), {[Cu(L)2(H2O)2]·2H2O}n (2), {[Zn(L)2(H2O)2]·2H2O}n (3), and {[Fe(L)2(H2O)2]·2H2O}n (4) (HL = 2-{[4-amino-3-(pyridin-4-yl)-4,5-dihydro-1H-1,2,4-triazol-5-yl]thio}acetic acid) were synthesized and characterized by single-crystal X-ray diffraction analysis. Complex 1 exhibited a mononuclear structure. Complexes 2, 3, and 4 featured 2D networks. The crystal structures were stabilized by intermolecular hydrogen bonds to generate 3D supramolecular frameworks. The inhibitory activity was tested in vitro against jack bean urease. Among the four complexes, the two CuII complexes 1 and 2 exhibited better inhibitory activity than the positive reference acetohydroxamic acid, with IC50 values of 4.052 and 6.868 ?M, respectively, whereas the ZnII and FeII complexes showed no activity. To explore the mechanism of inhibition of the enzyme, kinetics studies were carried out; the results indicated that both the activated complexes 1 and 2 operated through a mixed-competitive inhibitory mechanism. Molecular docking was used to insert the most active complex 1 into the crystal structure of jack bean urease at the active site to determine the probable mode of binding. Four novel crystals of copper, zinc, and iron complexes based on 1,2,4-triazole carboxylic acid derivatives were determined by single-crystal X-ray diffraction. The inhibitory activity and kinetic studies were tested in vitro against jack bean urease. The computational predications, biological evaluation, and mechanism study will help in the discovery of new urease inhibitors.

Posted on 20 March 2015 | 12:10 pm

Synthesis and Characterization of 4-, 5-, and 6-Coordinate Tris(1-ethyl-4-isopropylimidazolyl-?N)phosphine Cobalt(II) Complexes

The synthesis and characterization of [Co(T1Et4iPrIP)X2] {T1Et4iPrIP = tris(1-ethyl-4-isopropylimidazolyl)phosphine; X = OTf– (1), Cl– (2), Br– (3)} and [Co(T1Et4iPrIP)(CH3CN)3](OTf)2 (4) were investigated. In compounds 1 and 4, T1Et4iPrIP binds in a tridentate fashion, whereas 2 and 3 feature bidentate ligation. Compound 1 additionally coordinates two triflate ligands to complete a distorted square pyramidal geometry. Compound 4 also binds three acetonitrile ligands to afford a distorted octahedral geometry. Compounds 2 and 3 exhibit a distorted tetrahedral geometry for which the ligands comprise two imidazole nitrogen atoms and two halides. Bidentate coordination by using a tris(imidazolyl)phosphine ligand is unprecedented. Compounds 2 and 3 can be derived from 1 by the addition of either Cl– or Br– salts, respectively, whereas 4 can be generated by dissolving 1 in acetonitrile. DFT studies indicate that the HOMO–LUMO gaps of all compounds are comparable; however, steric factors stabilize the formation of 2 and 3 over 1 in the presence of halide ligands. [Co(T1Et4iPrIP)X2] {T1Et4iPrIP = tris(1-ethyl-4-isopropylimidazolyl)phosphine; X = OTf– (1), Cl– (2), Br– (3)}, and [Co(T1Et4iPrIP)(CH3CN)3](OTf)2 (4) are reported. Dissolution of 1 in MeCN affords 4. Reaction of 1 with Cl– or Br– yields 2 or 3, respectively. DFT studies indicate that 1 has the largest HOMO–LUMO gap, which suggests that the formation of 2 or 3 from 1 is primarily sterically driven.

Posted on 20 March 2015 | 12:10 pm

Ionic Ferrocene-Based Burning-Rate Catalysts with Polycyano Anions: Synthesis, Structural Characterization, Migration, and Catalytic Effects during Combustion (Eur. J. Inorg. Chem. 9/2015)

The cover picture shows how to develop low-migratory ferrocene-based burning-rate catalysts (BRC) for the next generation of rocket propellants. When the pieces of the “puzzle” fit perfectly, the combustion catalysts have optimal qualities, and the fuels last longer. The polycyano-based ionic ferrocene compounds described in this study exhibit high catalytic activity in the thermal degradation of ammonium perchlorate. Details are discussed in the article by G. Zhang et al. on p. 1496 ff. For more on the story behind the cover research, see the Cover Profile.

Posted on 19 March 2015 | 12:53 pm

Graphical Abstract: Eur. J. Inorg. Chem. 9/2015

Posted on 19 March 2015 | 12:53 pm

Ionic Ferrocene-Based Burning-Rate Catalysts with Polycyano Anions: Synthesis, Structural Characterization, Migration, and Catalytic Effects during Combustion

Invited for the cover of this issue is the group of Guofang Zhang from Shaanxi Normal University, China. The cover image shows how to develop low-migratory ferrocene-based burning-rate catalysts (BRCs) for the next generation of rocket propellants. Our research is highly interdisciplinary. It involves organometallic chemistry, energetic materials, high-temperature chemistry, heterogeneous catalysis, thermodynamics...Read more about the story behind the cover in the Cover Profile and about the research itself on p. 1496 ff.

Posted on 19 March 2015 | 12:53 pm

Masthead: Eur. J. Inorg. Chem. 9/2015

Posted on 19 March 2015 | 12:53 pm

Pentanuclear and Octanuclear Manganese Helices

Two helical manganese complexes, [Mn5(L)3(?3-O)(NO3)(OMe)2(MeOH)](NO3)·4MeOH·H2O (1) and [Mn8(L)6(?3-Cl)2]Cl2·3C2H4Cl2·60H2O·2DMF (2, DMF = N,N-dimethylformamide), were obtained by the reaction of the multidentate polypyridine ligand 2,6-bis[5-(2-pyridinyl)-1H-pyrazole-3-yl]-pyridine (H2L) with manganese nitrate and chloride, respectively. The compounds were characterized by elemental analyses and single-crystal X-ray structural analyses. The pentanuclear complex 1 is composed of three ligands and five manganese ions with ?3-oxido bridges, whereas the octanuclear complex 2 is constructed from six ligands and eight manganese ions with two ?3-chlorido bridges. Both compounds have helix-type structures. The manganese ions in 1 are present in a mixture of +2 and +3 valence states, whereas 2 is homovalent and contains only +2 ions. The magnetic properties of both compounds were investigated in the temperature range 1.8–300 K, and antiferromagnetic interactions between the manganese ions are dominant in both complexes. Pentanuclear and octanuclear manganese helices are obtained by the reactions of a multidentate polypyridine ligand with manganese nitrate and chloride. The Mn ions in the pentanuclear complex are in a mixture of +2 and +3 valence states, whereas those of the octanuclear complex are homodivalent. Both compounds show antiferromagnetic interactions.

Posted on 19 March 2015 | 12:14 pm

Chiral Ruthenium Catalyst Immobilized within Magnetically Retrievable Mesoporous Silica Microcapsules for Aqueous Asymmetric Transfer Hydrogenations

The preparation of magnetically separable silica microcapsules that incorporate in their inner shell a chiral catalyst and their application in asymmetric transfer hydrogenation reactions are described. The preparation method is based on the emulsification of an oil phase containing chloroform, a modified Noyori Ru-TsDPEN catalyst, tetraethoxysilane (TEOS), and hydrophobic magnetic nanoparticles in water in the presence of an appropriate surfactant, followed by an interfacial polycondensation process under basic conditions to generate a silica shell around the oil droplets. The resulting catalytic microreactors can be considered a “quasi-homogeneous” system because the immobilized chiral catalyst reacts in a homogeneous zone, the microcapsule core filled with an organic solvent. The catalytic activity was tested in the asymmetric transfer hydrogenation of ketones in an aqueous medium. The catalytic reactions took place only in the presence of surfactants. In addition, the judicious selection of the surfactant plays a crucial role in enhancing the reaction progress through the emulsion-solid transfer (EST) approach. The catalytic activity of the Ru-TsDPEN catalyst immobilized within the silica microcapsules was superior to the same catalyst supported on silica microspheres or linked to the backbone of a silica sol–gel matrix, which indicates the importance of the homogeneous zones for the reactions. We report the design of a “quasi-homogeneous” catalytic system, based on a modified Noyori Ru-TsDPEN catalyst confined within mesoporous silica-based microreactors, for the efficient asymmetric transfer hydrogenation of ketones in water. The new system demonstrates excellent reactivity and enantioselectivity characteristic of homogeneous catalysts, but can be easily recovered.

Posted on 19 March 2015 | 12:13 pm

The Effects of Alkaline-Earth Counterions on the Architectures, Band-Gap Energies, and Proton Transfer of Triazole-Based Coordination Polymers

Three coordination polymers based on alkaline-earth metals (Ca, Sr, and Ba) have been synthesized with 3-amino-1,2,4-triazole-5-carboxylic acid (3-AmTrZAc). Structural analysis reveals that the Ca-based structure [Ca(3-AmTrZAc)(5-AmTrZAc)(H2O)] (1) is two-dimensional, and the Sr- and Ba-based structures [Sr(3-AmTrZAc)2(H2O)] (2) and [Ba(3-AmTrZAc)2(H2O)] (3) are three-dimensional. In the Ca-based structure 1, the 3-AmTrZAc reactant converts to 5-AmTrZAc. The relative stability of the two isomers is controlled by a dipole–ion interaction between the triazole ring and the carboxylate group. We have measured the band-gap energies, and the Ca-based structure has the largest band-gap energy. Density functional theoretical investigations showed that internal electric fields generated by the alkaline-earth counterions increase the band gap in the 5-AmTrZAc anion and lower it in the 3-AmTrZAc anion. The effects of alkaline-earth ions on the architectures, band-gap energies, and proton transfer of triazole-based coordination polymers are investigated.

Posted on 19 March 2015 | 12:13 pm

Accessible Syntheses of Late Transition Metal (Pre)Catalysts Bearing N-Heterocyclic Carbene Ligands

This microreview details and discusses some selected examples of the accessible syntheses of useful complexes bearing N-heterocyclic carbenes (NHCs). The term “accessible”, as used here, is defined as a synthetic route that does not require the isolation of the free NHC. These routes typically rely on either the generation of low equilibrium concentrations of the free NHC, which is then trapped by a metal centre, the deprotonation of the azolium salt by a suitable ligand or the activation of the C–H bond. These approaches can help to overcome a key weakness of NHCs in that they must be handled under stringently inert conditions. Studies of complexes based on metal centres from groups 8–11 are presented and discussed. Selected examples of the synthesis of useful (pre)catalysts bearing N-heterocyclic carbenes (NHCs) are discussed. All of these examples avoid the generation and isolation of free carbenes and the use of strong, sensitive bases; therefore, they are presented as useful preparative methods that can allow these catalysts to be utilised more widely.

Posted on 18 March 2015 | 2:10 pm

Low Dielectric Behavior of a Robust, Guest-Free Magnesium(II)–Organic Framework: A Potential Application of an Alkaline-Earth Metal Compound

A robust and low dielectric 3D metal–organic framework [Mg(phen)(bdc)]n (1; phen = 1,10-phenanthroline, bdc2– = 1,4-benzenedicarboxylate) was hydrothermally synthesized from magnesium acetate, H2bdc, and phen ligands. Compound 1 has a non-interpenetrated network with an uncommon cds-type topology. Chemical and dielectric investigations of this material indicate that it retains a high chemical stability and has a low dielectric constant of 3.33?±?0.1 (at 100 kHz), which is the lowest value for Mg-based MOFs reported to date. In addition, temperature-dependent dielectric studies revealed that its low dielectric constant is retained over a wider temperature range. Mg-based MOFs have the advantage of being a new class of dielectric materials because of their many intrinsic properties. A 3D, robust, and low dielectric (low-?) Mg-based MOF with a non-interpenetrated cds-type topology was prepared. Dielectric measurements revealed the ? value to be 3.33?±?0.1 (at 100 kHz). It is evident that the incorporation of alkaline-earth metal ions in highly porous frameworks could result in materials with low-? properties.

Posted on 18 March 2015 | 2:10 pm

Retention of the Cluster Core Structure during Ligand Exchange Reactions of Carboxylato-Substituted Metal Oxo Clusters

The exchange of the carboxylato ligands of Zr4O2(methacrylato)12 in reactions with carboxylic acids proceeds with retention of the composition and structure of the cluster core. This was concluded from exchange/re-exchange experiments and from comparison of the IR bands of the cluster core of the original and ligand-exchanged clusters. The IR bands were assigned on the basis of DFT calculations. Scrambling reactions between two Zr4O2(OOCR)12 clusters with different carboxylato ligands are a new way to prepare mixed-ligand oxo clusters. Ligand exchange in Zr4O2(OOCR)12 clusters proceeds with retention of the cluster core. A new scrambling reaction is introduced for the preparation of mixed-ligand clusters.

Posted on 18 March 2015 | 2:10 pm

Molecular Rectangles with Rod-Shaped Disulfonic Acids

Polysulfonic acids and their compounds have been scarcely investigated, despite the huge knowledge that we have of the respective polycarboxylic acids and polycarboxylates. This is because of the limited availability of polysulfonic acids, for which reliable synthetic protocols are often lacking. Here, we present the first compound of the recently reported disulfonic acid 1,4-bis(4-sulfophenyl)butadiyne (H2DPBDS) prepared in our groups and a new compound of the commercially available 4,4?-biphenyldisulfonic acid (H2BPDS). The zinc sulfonates [Zn2(BPDS)2(NMP)6]·2NMP [I, NMP = N-methylpyrrolidone; triclinic, P$\bar {1}$, Z = 2, a = 972.8(2), b = 981.5(2), c = 1915.2(2) pm, ? = 87.73(3)°, ? = 77.68(3)°, ? = 89.36(3)°, V = 1785.0(6) Å3] and [Zn2(DPBDS)2(DMA)6]·2DMA [II, DMA = dimethylacetamide; triclinic, P$\bar {1}$, Z = 2, a = 973.79(2), b = 1347.53(2), c = 1411.08(2) pm, ? = 110.531(1)°, ? = 92.445(1)°, ? = 101.931(1)° V = 1683.11(5) Å3] display rigid molecular rectangles constructed from two zinc atoms and two sulfonate ligands. The rectangles are assembled through weak interactions to form soft host lattices that incorporate the solvent DMA or NMP molecules, partly through Zn2+ coordination. Thermal analysis shows that the solvent molecules can be completely removed without decomposition of the coordination polymers. Rod-shaped disulfonic acids are suitable for the construction of zinc-based molecular rectangles. These rectangles form flexible lattices that incorporate solvent molecules. The removal of the solvent molecules leads to disulfonates of astonishingly high thermal stability, in strong contrast to the behavior of comparable polycarboxylates.

Posted on 18 March 2015 | 2:10 pm

Modulating Sonogashira Cross-Coupling Reactivity in Four-Coordinate Nickel Complexes by Using Geometric Control

Herein, we present the synthesis of nickel complexes with tripodal phosphine ligands, CH3Si(CH2PPh2)3 and CH3C(CH2PPh2)3, and their application as catalysts in Sonogashira cross-coupling reactions in water. Although both types of nickel complexes are based on similar tripodal ligands, the Si-derived compounds adopt stable tetrahedral coordination geometries, whereas the C-derived counterparts adopt a square-planar coordination environment. This structural and electronic difference has an important effect on the catalytic properties of the complexes. Our study demonstrates that C-derived complexes are catalytically inactive, whereas the complexes [CH3Si(CH2PPh2)3NiX2] (X = Cl–, Br–) are competent catalysts for cross-coupling reactions of aryl halides with phenylacetylenes. This investigation reveals the importance of structural tuning on catalysis and strongly supports the theory that tetrahedral (PR3)2NiCl2 complexes are the active species in Sonogashira cross-coupling reactions. Two tripodal phosphines CH3E(CH2PPh2)3 (E = C, Si) are applied as ligands in Ni-catalyzed cross-coupling reactions; various coordination modes at the Ni center can be achieved. For the first time, experimental evidence is provided to prove that tetrahedral instead of planar (PR3)2NiCl2 moieties are required to perform effective Sonogashira coupling reactions.

Posted on 17 March 2015 | 12:30 pm

Oxide-Bridged Heterobimetallic Aluminum/Zirconium Catalysts for Ethylene Polymerization

A bimetallic aluminum/zirconium complex Cp*2Zr(Me)OAl(DIPH) [DIPH-H2 = 3,3?-bis(2-methylallyl)-(1,1?-biphenyl)-2,2?-diol; Cp* = C5Me5] was prepared in good yield by the reaction of (DIPH)AlMe with Cp*2Zr(Me)OH. In contrast to Roesky's catalyst, Cp2Zr(Me)O(Me)Al(DIPP-nacnac) {DIPP-nacnac = CH[(CMe)(2,6-iPr2C6H3N)]2}, it contains no Al–Me functionality and has increased Lewis acidity at Al. Crystal structures and the NMR spectra of the aluminum complex (DIPH)AlMe and the bimetallic Al/Zr species reveal in both cases dimeric complexes. The crystal structure of [Cp*2Zr(Me)OAl(DIPH)]2 shows a planar Al2O2 core and a terminal Cp*2Zr(Me)O group. Ethylene polymerization in toluene was studied for the bimetallic complex with a variety of scavengers. Under comparable polymerization conditions, the methylalumoxane-activated species show high activities that are similar to those obtained with Cp*2ZrCl2 and Roesky's bimetallic complex Cp2Zr(Me)OAl(Me)(DIPP-nacnac), with a relatively narrow polydispersity index (2.47). The targeted synthesis of a new bimetallic aluminum/zirconium species with remaining Lewis acidity on aluminum gives a dimeric Al–O–Zr complex. In the presence of methylalumoxane, this ?-oxo complex is able to activate ethylene to produce polyethylene with high activity.

Posted on 17 March 2015 | 12:30 pm

Thermally Stable Four-Coordinate Silicon(IV) Complexes with an Si=N Double Bond and an SiN3El Skeleton (El = O, S, Se, Te)

The donor-stabilized silylene 1 reacts with N2O and PhElElPh (El = S, Se, Te) to form the respective silicon(IV) complexes 2–5 with an Si=N double bond. Compounds 2–5 were structurally characterized by crystal structure analyses and NMR spectroscopic studies in the solid state and in solution. The donor-stabilized silylene 1 reacts with N2O and PhElElPh (El = S, Se, Te) to form the respective silicon(IV) complexes 2–5 with an Si=N double bond. Compounds 2–5 were structurally characterized by crystal structure analyses and NMR spectroscopic studies in the solid state and in solution

Posted on 17 March 2015 | 12:20 pm

Carbene Complexes Based on Dilithium Methandiides

In the last 15 years, methandiide ligands have given access to a new class of carbene complexes with unique electronic properties. The metal–carbon interactions in these complexes cover a range of bonding situations, from highly polar interactions to metal–carbon double bonds. This flexibility has allowed the isolation of complexes with metals covering the whole periodic table, including metals that had long been reluctant to form multiple bonds with carbon atoms. Thus, recent years have seen the revelation of many unusual carbene species with interesting reactivities. In this microreview, we focus on the latest developments in the chemistry of methandiides and their use as ligands in carbene complexes. We give an overview of the geminal dianionic compounds, their properties, and molecular and electronic structures, with special focus on those compounds that are applied in transition metal chemistry. The second part of the article deals with the preparation and electronic structures of methandiide-derived carbene complexes, and we highlight important examples that display the unique properties and efficiency of the ligands. The last section gives an overview of the reactivity and the non-innocent behavior of these methandiide ligands. Methandiide ligands give access to carbene complexes with unique electronic properties. The metal–carbon interactions in these complexes cover a range of bonding situations and allow the isolation of complexes with metals from the whole periodic table. We focus on the latest developments in methandiide chemistry and give an overview of the preparation and electronic structures of these complexes.

Posted on 17 March 2015 | 12:20 pm

Germanium(II) and Tin(II) Halide Complexes Containing the Triimido Sulfur(VI) Phosphanyl Ligand

The monomeric compounds [GeCl{(NtBu)3SCH2PPh2}] (1) and [SnBr{(NtBu)3SCH2PPh2}] (2) have been synthesized from equimolar reactions of [(tmeda)Li{(NtBu)3SCH2PPh2}] and GeCl2·dioxane or SnBr2, respectively, to introduce the N,N?-chelating triimidosulfonate anion Ph2PCH2S(NtBu)3–. The complexes were fully characterized by single-crystal X-ray structural analysis, NMR spectroscopy, and mass spectrometry. The P-functionalized triimido sulfur ligand [(NtBu)3SCH2PPh2]– can be used without ligand scrambling to stabilize synthetically useful group 14 metal(II) halides. It chelates the metal through two S-bound imido nitrogen atoms only. The additional coordination site is provided by the phosphorus atom; although with germanium the P side-arm is pendant, it forms a long-range interaction with tin.

Posted on 17 March 2015 | 12:20 pm

Niobium–Containing Lindqvist Isopolyanions [NbxW6–xO19](2+x)– Used as Precursors for Hydrodesulfurization Catalysts with Isomerization Properties

Lindqvist isopolyanions [NbxW6–xO19](2+x)– (x = 0–4 and 6) were prepared and their spectroscopic and thermal properties were determined by Raman and IR spectroscopy as well as TGA/DSC. The structure of the [NbW5O19]3– anion obtained as single crystal was determined. Ni-promoted alumina-supported hydrodesulfurization (HDS) catalysts were prepared from the best soluble NbW polyoxometalates. In the calcined catalysts, better dispersion of the metallic species is observed when using NbW isopolyanions instead of the conventional ammonium metatungstate. The presence of niobium was expected to introduce acidity leading to isomerization property in classical NiW HDS catalysts. In HDS reaction conditions (under hydrogen pressure and sulfided environment) the cyclohexane isomerization into methylcyclopentane activity of niobium-based catalysts was found up to 5 times superior to that of conventional NiW catalyst, showing the beneficial effect of niobium for this reaction. [NbxW6–xO19](2+x)– Lindqvist type isopolyanions were synthesized and characterized to prepared NbWNi-based alumina-supported hydrodesulfurization catalysts. Nb-containing catalysts showed improved CC6 isomerization properties under HDS conditions (H2 pressure and H2S presence) compared to those of a reference NiW catalyst related to the acid properties induced by niobium.

Posted on 13 March 2015 | 11:10 am

On the Reactivity of RSnCl and RSiMe3 {R = 4-tBu-2,6-[P(O)(OiPr)2]2C6H2} towards BF3·OEt2: Competing Lewis Acidities

The reactions of boron trifluoride with the organostannylene RSnCl {R = 4-tBu-2,6-[P(O)(OiPr)2]2C6H2} and the organosilane RSiMe3 provided the corresponding 1:1 and 1:2 complexes, respectively, through the formation of P=OB interactions. In the former reaction, even with excess BF3·OEt2, no SnB complexation involving the lone electron pair at the tin(II) center was observed. The experimental results are supported by DFT calculations. The reactions of boron trifluoride with the organostannylene RSnCl {R = 4-tBu-2,6-[P(O)(OiPr)2]2C6H2} and the organosilane RSiMe3 provided the corresponding 1:1 and 1:2 complexes, respectively, through the formation of P=OB interactions. The experimental results are supported by DFT calculations.

Posted on 11 March 2015 | 10:20 am

Synthesis of Two Coordination Polymer Photocatalysts and Significant Enhancement of Their Catalytic Photodegradation Activity by Doping with Co2+ Ions

The coordination polymers (CPs) [Zn2(tipm)(1,3-BDC)2] (1) and [Co2(tipm)(1,3-BDC)2]·0.5CH3CN (2·0.5CH3CN) were synthesized by the reactions of Zn(NO3)2 or Co(NO3)2 with tetrakis[4-(1-imidazolyl)phenyl]methane (tipm) and benzene-1,3-dicarboxylic acid (1,3-H2BDC) under solvothermal conditions. Compounds 1 and 2 are isostructural and possess complicated three-dimensional frameworks with the Schläfli symbol (4·72)(62·73·12)(4·62·73). Cobalt ions were incorporated into the Zn-based CP framework 1 during solvothermal crystallization to yield [Zn(2–2x)Co2x(tipm)(1,3-BDC)2]·bH2O (x = 2.4?%, b = 0 for 1a, x = 23?%, b = 1 for 2a·H2O). Doped CPs 1a and 2a·H2O exhibited greater catalytic photodegradation of the dye rhodamine B (RhB) than the undoped complexes 1 and 2 and many literature examples. Two coordination polymers are prepared, and their catalytic activity for the photodegradation of rhodamine B (RhB) is enhanced by doping with Co2+ ions.

Posted on 9 March 2015 | 12:10 pm

Synthesis, Characterization, and Stereoselective Oxidations of the Dinuclear Copper(II) Complex Derived from a Chiral Diamino-m-xylenetetra(benzimidazole) Ligand

Recent advances in dinuclear copper complexes as mimics of the catalytic centers of tyrosinase and catechol oxidase allowed the reproduction of the structural and mechanistic aspects of the enzymes. However, a challenging objective is the development of chiral complexes for bioinspired enantioselective oxidation reactions. Here, we report the synthesis and characterization of a dinuclear copper(II) complex with a new chiral diamino-m-xylenetetra(benzimidazole) ligand (L55Bu4), which has chiral centers at the four 2-methylbutyl substituents of the benzimidazole rings. The spectral characteristics, ligand binding properties, and reactivity of [CuII2L55Bu4]4+ in the catalytic oxidations of several biogenic catechols (L-/D-dopa, L-/D-DopaOMe, and L-/D-norepinephrine) and thioanisole are reported. The best discriminating properties are displayed towards the DopaOMe derivatives, for which the oxidation rate of the L enantiomer is approximately one order of magnitude larger than that of the opposite D isomer. A dinuclear copper(II) complex derived from a chiral hexadentate nitrogen ligand is reported as a new catalyst for asymmetric oxidations. For biogenic catechols as model substrates, the best enantioselectivity is obtained in the oxidation of the methyl esters of L-/D-Dopa, for which 70?%?ee is obtained in favor of the L enantiomer.

Posted on 9 March 2015 | 12:10 pm

Evidence for Photochemical Linkage Isomerism of the Phenylazo Ligand in M(CO)2(N2Ph)(PPh3)2 Cations (M = Fe and Ru)

Frozen-matrix photolysis studies of M(CO)2(N2Ph)(PPh3)2 cations (M = Fe and Ru) have revealed end-on/side-on photochemical linkage isomerism of the phenylazo ligand. The previously reported solvent-dependent vibrational bands of the Ru(CO)2(N2Ph)(PPh3)2 cation have now been identified as an equilibrium between the two linkage isomers. DFT calculations have been performed on the end-on and side-on isomers of the iron and ruthenium complexes. Frozen-matrix photolysis studies of M(CO)2(N2Ph)(PPh3)2 cations (M = Fe and Ru) have revealed end-on/side-on photochemical linkage isomerism of the phenylazo ligand. The previously reported solvent-dependent vibrational bands of the Ru(CO)2(N2Ph)(PPh3)2 cation have now been identified as an equilibrium between the two linkage isomers.

Posted on 9 March 2015 | 12:10 pm

Synthesis, Structure, and Optical Properties of SiO2:Eu3+ Nanowires

SiO2:Eu3+ nanowires were prepared by a solvothermal method followed by subsequent calcination and acid washing processes. The structure, morphology, and properties of the products were characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and photoluminescence (PL) spectroscopy. The results indicated that the obtained SiO2:Eu3+ nanowires exhibited red emission under ultraviolet light excitation and may have potential applications in optical and biological areas. In addition, a possible formation process for the SiO2:Eu3+ nanowires is proposed in detail. SiO2:Eu3+ nanowires are prepared by a solvothermal method followed by subsequent calcination and acid washing processes. A possible formation mechanism is proposed in detail. In the solvothermal process, ethylenediamine (EDA) bridges between Zn ions and SiO2:Eu3+ nanowires by coordination and hydrogen bonding.

Posted on 9 March 2015 | 12:10 pm

Structural Influencing Factors on ZnII/CdII Coordination Polymers Based on Tri-pyridyl-bis-amide: Assembly, Structures, Fluorescent Sensing and Selective Photocatalysis

Fourteen new ZnII/CdII coordination polymers tuned by semi-rigid “V”-like tri-pyridyl-bis-amide ligands with different spacers and different dicarboxylates co-ligands, namely, {[Zn(L1)(mip)]·H2O}n (1), {[Zn2(L1)2(hip)2]·H2O}n (2), {[Zn(L1)(oba)]·H2O}n (3), {[Zn(L1)(chda)]·H2O}n (4), {[Cd2(L1)(mip)2(H2O)]·2H2O}n (5), {[Cd(L1)(hip)]·4H2O}n (6), {[Cd(L1)(oba)]·H2O}n (7), {[Cd3(L1)(chda)3]·4H2O}n (8), [Zn(L2)(mip)]n (1a), {[Zn(L2)(hip)(H2O)]·3H2O}n (2a), [Zn(L2)(oba)]n (3a), {[Cd(L2)(hip)]·3H2O}n (6a), {[Cd(L2)(oba)]·H2O}n (7a), [Cd(L2)(chda)]n (8a), [L1 = N,N?-di(pyridin-3-yl)pyridine-2,6-dicarboxamide, L2 = N,N?-di(pyridin-3-yl)pyridine-3,5-dicarboxamide, H2mip = 5-methylisophthalic acid, H2hip = 5-hydroxyisophthalic acid, H2oba = 4,4?-oxybis(benzoic acid), H2chda = trans-1,4-cyclohexanedicarboxylic acid] have been hydrothermally synthesized and structurally characterized. Complexes 1–4 based on the same L1 ligand and ZnII ion show various structures. Complex 1 features a two-dimensional (2D) network, which consists of a linear [Zn-mip]n chain and [Zn-L1]n left-, right-handed helixes. Complex 2 is a twofold interpenetrating 2D2D network. In complex 3, Zn2(L1)2 loops were connected by oba anions creating a 1D channel-like structure. Complex 4 is a 2D layer containing [Zn-chda]n right-handed helixs and Zn2(L1)2 loops. Complexes 5–8 with CdII ion exhibit different structures. Complex 5 features a 1D belt structure based on Cd4(COO)4 subunits. However, complex 6 exhibits a 2D network constructed from [Cd-hip]n ladder-like chains and Cd2(L1)2 loops. Complex 7 shows a 1D double chain structure containing [Cd-oba]n zigzag chain and [Cd-L1]n meso-right-handed helix. Complex 8 exhibits a 2D network based on 2D [Cd-chda] layer and 1D [Cd-L1]n meso-helical chain. For complexes 1a–8a based on L2 ligand, complex 1a is a 2D layer containing [Zn-mip]n linear chain and [Zn-L2]n meso-helical chain. The structure of complex 2a is very similar to that of 3. Complex 3a exhibits a 2D grid network containing 1D [Zn-oba]n and [Zn-L2]n chains. Complex 6a shows a 2D layer based on [Cd2(hip)2]n double chain and [Cd-L2]n chain. The structure of complex 7a is very similar to that of 7. Complex 8a is a 3,5-connected 3D framework with the Schläfli symbol of (42.65.83)(42.6), which is constructed from [Cd-L2]n channel-like chains and chda linkers. The structural diversity of the title complexes indicates that the tri-pyridyl-bis-amide ligands with different spacers, the dicarboxylates and central metals play important roles in tuning the dimensionalities and structures of the target complexes. The title complexes exhibit excellent photocatalytic activity and selectivity for organic dyes degradation under UV light. In addition, fluorescent sensing behaviors of 3, 6, 7 and 7a toward different organic solvents have been investigated in detail. Fourteen new ZnII/CdII coordination polymers based on tri-pyridyl-bis-amide were hydrothermally synthesized and characterized, which show photocatalytic activity and selectivity for the degradation of organic dyes. The fluorescent selectivity of these compounds makes them promising candidates as fluorescent sensor materials.

Posted on 6 March 2015 | 10:10 am

Analysis and Prediction of Stacking Sequences in Intercalated Lamellar Vanadium Phosphates

An approach is presented that enables the analysis and prediction of stacking sequences in intercalated lamellar vanadium phosphates. A comparison of previously reported vanadium phosphates reveals two modes of intercalation: (i) 3d transition metal ions intercalated between VOPO4 layers and (ii) alkali/alkaline earth metal ions between VOPO4·H2O layers. Both intercalations were investigated using DFT calculations in order to understand the relative shifts of the vanadium phosphate layers. These calculations in addition to an analysis of the stacking sequences in previously reported materials enable the prediction of the crystal structures of Mx(VOPO4)·yH2O (M = Cs+, Cd2+ and Sn2+). Experimental realization and structural determination of Cd(VOPO4)2·4H2O by single-crystal X-ray diffraction confirmed the predicted stacking sequences. Stacking sequences of intercalated lamellar vanadium phosphates have been analyzed by DFT calculations. The relative shifts of layers have been predicted and confirmed by single-crystal X-ray diffraction for Cd(VOPO4)2·4H2O.

Posted on 6 March 2015 | 10:10 am

Heteroleptic Phenanthroline Complexes of Trinuclear Molybdenum Clusters with Luminescent Properties

Neutral Mo3(?3-S)(?-S2)3X3(diimine) (X = Cl–, Br–) heteroleptic cluster complexes containing the 1,10-phenanthroline ligands 1H-imidazo[4,5-f][1,10]phenanthroline-2-[3,4-bis(dodecyloxy)phenyl] (IPDOP), 4,7-diphenyl-1,10-phenanthroline (BPhen), and 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen) were prepared in high yields by straightforward ligand-substitution reactions starting from the [Mo3(?3-S)(?-S2)3X6]2– cluster anion. The complexes Mo3S7X4(BPhen) [X = Br– (for 3) and Cl– (for 4)] and Mo3S7X4(tmpphen) [X = Br– (for 5) and Cl– (for 6)] crystallized as tetra-n-butylammonium salts of anionic aggregates (3–6·X)–, in which neutral Mo3S7X3(diiimine)3 cluster molecules participate in non-valence interactions between the axial sulfur atoms, Sax, and a halide anion. The complexes Mo3S7Br4(IPDOP) (1) and Mo3S7Cl4(IPDOP) (2) are luminescent when excited at 330 nm and have maximum emission intensities around 450 nm in DMF and around 435 nm in dichloromethane. The maximum fluorescence quantum yield and the maximum emission lifetime were achieved for complex 2 in DMF(?F = 0.15 and ? = 7.5 ns, respectively). The most important property of complexes 1 and 2 is the shift of their emission spectra in the presence of proton-abstractor anions, such as F–, OH–, and AcO–. When these anions are added to solutions of complexes 1 or 2 in DMF or dichloromethane, the maximum emission wavelength shifts by approximately 90 nm to higher wavelengths. Coordination of diimine ligands to a Mo3S7 cluster afforded complexes of the formula Mo3S7X4(diimine) (X = Cl– or Br–). The clusters with the novel imidazophenanthroline ligand IPDOP are luminescent and have moderate quantum yields. Furthermore, interaction of the NH group of IPDOP with several anions (F–, AcO–, and OH–) resulted in a remarkable shift of the emission spectrum to longer wavelengths.

Posted on 6 March 2015 | 10:10 am

PEPPSI-Effect on Suzuki–Miyaura Reactions Using 4,5-Dicyano-1,3-dimesitylimidazol-2-ylidene-Palladium Complexes: A Comparison between trans-Ligands

The PEPPSI (Pyridine Enhanced Precatalyst Preparation, Stabilization and Initiation) complexes 12–15 with the structure [PdCl2{(CN)2IMes}(3-R-py)] (12: R = H; 13: R = Cl; 14: R = Br; 15: R = CN) bearing the maleonitrile-based N-heterocyclic carbene (NHC) (CN)2IMes ({(CN)2IMes}: 4,5-dicyano-1,3-dimesitylimidazol-2-ylidene) were prepared. Solid state structures of 14 and 15 were obtained. Complexes 14 and 15 adopt a slightly distorted square-planar coordination geometry in the solid state with the substituted pyridine ligand trans to the NHC. Catalytic activities of precatalysts 12–15 were studied and subsequently compared to complexes [PdCl2{(CN)2IMes}(PPh3)] (4) and [PdCl(dmba){(CN)2IMes}] (5) recently reported by our group in the Suzuki–Miyaura reaction of various aryl halides and phenylboronic acid. Reactions using previously reported [PdCl2(IMes)(py)] (IMes: 1,3-dimesitylimidazol-2-ylidene) (1) were also carried out and their results contrasted to those involving 12–15, 4 and 5. Differences in initiation rates and the catalytically active species related to the seven complexes in regards to the “throw away ligand” were investigated. Poisoning experiments with mercury show that palladium nanoparticles are responsible for the catalytic activity. Four PEPPSI (Pyridine Enhanced Precatalyst Preparation, Stabilization and Initiation) complexes 12–15, bearing different 3-substituted pyridines, were prepared and used as precatalysts in Suzuki–Miyaura reactions with 20 aryl bromides and three aryl chlorides. The catalytic activities of 12–15 were compared to those of complexes 4 and 5, recently presented by our group.

Posted on 6 March 2015 | 10:10 am

Exfoliation of Bulk Inorganic Layered Materials into Nanosheets by the Rapid Quenching Method and Their Electrochemical Performance

We report herein the results of our investigations on the synthesis of transition-metal dichalcogenide (TMDC) semiconductor layered materials of MoS2, WS2, MoSe2, and WSe2 by the rapid quenching method. The bulk powders were added to deionized water in a polypropylene tube and subsequently flushed with argon gas. Thirty rapid freezing (30 s in a liquid nitrogen bath) and heating (20 min in an oil bath at 60 °C) cycles were then carried out. The reaction product was obtained in a yield in excess of 60 wt.-%, which indicates that the method can be utilized on an industrial scale for the production of 2D nanosheets. The as-synthesized products were then characterized by TEM, which revealed nanosheet-like morphologies. Raman spectroscopy confirmed the high quality of the nanosheet samples. The exfoliated samples also showed good electrochemical performance. Of the TMDC samples investigated, the WSe2 nanosheets were found to give the best performance due to their uniform morphology, large surface area, and fewest number of defects. We have synthesized layered materials of MoS2, WS2, MoSe2, and WSe2 by the rapid quenching method and investigated their electrochemical performance.

Posted on 6 March 2015 | 10:10 am

Solvent-Dependent Iodoargentate Hybrids: Syntheses, Structural Diversity, Thermochromism, and Photocatalysis

Charge-balanced by protonated pyridine, four iodoargentate hybrids, [(Hpy)(Ag2I3)]n (1, 2D), {[(Hpy)2·dmf][Ag6I8]}n (2, 2D), {[(Hpy)2·H2O][Ag3I5]}n (3, 1D) and [(Hpy)(Ag5I6)]n (4, reported 3D) (Hpy+ = protonated pyridine, dmf = N,N-dimethylformamide), were synthesized in the system comprising pyridine/AgI/HI/solvent (solvent: acetone for 1, DMF for 2, acetone/H2O for 3, and acetonitrile for 4). Structural analysis revealed the significant influence of the solvent on the assembly and crystallization of the iodoargentate hybrids. Noteworthy, compounds 2–4 reveal a good structural match between the structure-directing agents and the inorganic frameworks. The band gaps of 1–4 (2.93, 3.05, 2.99, and 2.71 eV for 1, 2, 3, and 4, respectively) also exhibit an intense correlation between the structural features of the hybrids and their photocatalytic properties in the degradation of rhodamine B under UV-light irradiation. Moreover, compound 4 shows interesting thermochromism owing to its temperature-dependent intermolecular charge transfer. Four iodoargentate hybrids are fabricated through reaction of the same reactants in different solvent systems. The solvent impacts the aggregation modes of the cationic species, which consequently directs the formation of anionic frameworks. These hybrids display excellent photocatalytic properties for the degradation of rhodamine B, and 4 displays low-temperature reversible thermochromism.

Posted on 6 March 2015 | 10:10 am

Chiral Radical-Cation Salts of BEDT-TTF Containing a Single Enantiomer of Tris(oxalato)aluminate(III) and -chromate(III)

Radical-cation salts of BEDT-TTF with chiral anions provide the opportunity to combine chirality with conductivity in the same molecular material. We report here two salts, (BEDT-TTF)3NaAl(C2O4)3·nitromethane and (BEDT-TTF)3(NH4)0.83Cr1.17(C2O4)3·nitromethane. The former crystallises in space group P21 and the latter in P212121. The use of nitromethane alone as the electrolyte for electrocrystallisation produces no crystals, but the addition of chiral (R)-(–)-carvone yields crystals of these two new chiral radical-cation salts of BEDT-TTF through chiral induction from racemic tris(oxalato)aluminate(III) and tris(oxalato)chromate starting materials. The honeycomb anion layers in these salts contain a single enantiomer of tris(oxalato)metallate and creates hexagonal cavities that are smaller than those found in the superconducting ?? salts in this tris(oxalate)metallate family, which gives preference for smaller solvents to be included, such as nitromethane. The chromium salt has a non-stoichiometric composition of the anion layer, which provides an electron doping effect to the donor layer. The use of a chiral electrolyte has produced two new chiral radical-cation salts of BEDT-TTF from racemic ammonium tris(oxalato)aluminate(III) and -chromate. One of the salts has a non-stoichiometric composition of 0.11 electrons per molecule doped to the band-insulating donor layer.

Posted on 6 March 2015 | 10:10 am

A Chemoselective and Modular Post-Synthetic Multi-Functionalization of NHC–Platinum Complexes

We report oxime ligation in combination with metal ligand exchange as a novel orthogonal and practical approach to the multifunctionalization of NHC–platinum complexes. This strategy, which enables strong diversity enhancement of metallodrug candidates, could also be applied to selective bioconjugation. We report oxime ligation in combination with metal ligand exchange as a novel orthogonal and practical approach to the multi-functionalization of NHC–platinum complexes.

Posted on 6 March 2015 | 10:10 am

Facile Synthesis of ZnO–Reduced Graphene Oxide Nanocomposites for NO2 Gas Sensing Applications

Graphene and its exotic forms have been widely recognized as exceptional materials for gas-sensing applications because of their extraordinary electrical conductivity and large surface area to volume ratios. Herein, chemically reduced graphene oxide (rGO) and zinc oxide–reduced graphene oxide (ZrGO) nanocomposite powders have been successfully synthesized through a simple hydrolysis method followed by annealing in ambient N2 gas. The reduction of graphene oxide by hydrazine hydrate and the decoration of the graphene surface by ZnO nanoparticles have occurred during the synthesis process. The prepared samples were characterized by various microscopic techniques to explore the surface morphology and uniformity. Spectroscopic techniques were used to investigate the quality of the as-synthesized powder samples as well as the extent of graphitization of the samples. Coil sensors with two Pt terminals and a heating element have been designed to extensively monitor the effect of temperature on the electrical and gas-sensing properties of the rGO and ZrGO nanocomposite samples. The ZrGO nanocomposites possess better electrical and NO2 gas sensing properties than the pristine rGO. The ZrGO nanocomposite sensor exhibits a high response (ca. 32?%) for 50 ppm NO2 at relatively low temperature (50 °C). Our results suggest that the ZrGO nanocomposite material could be used to fabricate a new generation of low-power portable NO2 sensors. A facile route for the synthesis of zinc oxide–reduced graphene oxide nanocomposites has been achieved for NO2 gas sensing applications.

Posted on 6 March 2015 | 10:10 am

Probing Chiral Recognition of Enzyme Active Sites with Octahedral Iridium(III) Propeller Complexes

Chiral bis-cyclometalated octahedral organoiridium(III) complexes were designed to target different classes of enzymes, namely carbonic anhydrases, histone deacetylases, and serine proteases. The stereoselective non-racemic synthesis of selected complexes was used to study the chiral discrimination of enzyme active sites for enantiomers of propeller-type octahedral metal complexes. Cases for negligible, modest, and significant chiral discrimination in the interaction of iridium propeller complexes with enzyme active sites were identified. Enzyme inhibiting chiral bis-cyclometalated organoiridium(III) complexes were designed to investigate the influence of the metal-centered configuration.

Posted on 5 March 2015 | 9:13 am

Unusual Luminescence Properties of Heterometallic REE Terephthalates

The influence of auxiliary rare-earth element (REE) ions (M3+, M = Y, Gd, Tb) on the luminescence properties of the (EuxM1–x)2(BDC)3(H2O)4 (BDC2– = 1,4-benzenedicarboxylate) series was studied. The overall quantum yields (QYs) of the EuxM1–x series (M = Y, Gd; x > 0.05) appeared to be independent of both the ratio and the type of auxiliary metal ion. It is shown that M = Tb3+ does not cause luminescence enhancement. The quantum yield (QY) of bimetallic terephthalates EuxM1–x(BDC)3/2(H2O)2 (M = Y, Gd; x > 0.05) remains constant (ca. 27?%) upon dilution of Eu3+ with nonluminescent Y3+ or Gd3+. This behavior, unusual for coordination compounds, is ascribed to the ability of the BDC2– environment to accumulate and transfer energy to Eu3+ ions, which sequentially emit several photons after a single excitation.

Posted on 5 March 2015 | 8:43 am

Hydrogen Bond, ?–?, and CH–? Interactions Governing the Supramolecular Assembly of Some Hydrazone Ligands and Their MnII Complexes – Structural and Theoretical Interpretation

The hydrazone Schiff base ligands (E)-N?-(2-hydroxybenzylidene)acetohydrazide (HL1) and (E)-N?-(2,3-dihydroxybenzylidene)acetohydrazide (H2L2) with a functional group variation in the aromatic moiety have been synthesized. The ligands have been used to synthesize the following MnII complexes: the mononuclear complex [Mn(HL1)2][ClO4]2·2H2O (1), the cocrystallized discrete dinuclear complex {[Mn(HL1)2]·[Mn(L1)2]}[ClO4]2 (2), and the phenoxido-bridged dinuclear complex [Mn(?-HL2)(H2O)]2[ClO4]2 (3). The ligands and the complexes were characterized by FTIR and UV/Vis spectroscopic techniques, and their crystal structures were determined by single-crystal X-ray diffraction analysis. 1H and 13C NMR spectroscopy shows evidence of keto–enol tautomerism of the ligands in solution. All of the compounds develop hydrogen-bonded assemblies of different dimensionalities and architectures. CH–? and ?–? interactions also contribute significantly to the overall binding energies of the supramolecular assemblies. The supramolecular interaction energies have been computed at the BP86-D3/def2-TZVPD level of theory. Slight steric and electronic modifications to the ligand backbone provoke differences to the nuclearities and supramolecular architectures of three MnII complexes synthesized from two different hydrazone Schiff base ligands. For all of the compounds, the binding energies through supramolecular forces have been quantitatively estimated by DFT calculations.

Posted on 5 March 2015 | 8:43 am

CuPN2: Synthesis, Crystal Structure, and Electronic Properties

CuPN2 was successfully synthesized from Cu3N and P3N5 at 5 GPa and 1000 °C by employing the Walker-type multianvil technique. Its crystal structure was elucidated from powder X-ray diffraction data. CuPN2 is isostructural to LiPN2 and NaPN2 [tetragonal I$\bar {4}$2d, no. 122, a = 4.5029(2) Å, c = 7.6157(2) Å, V = 154.42(1) Å3, Rp = 1.303, wRp = 1.741] with a structure that can be derived from both chalcopyrite and zincblende type. The electronic structure of CuPN2 was investigated by means of DFT calculations. CuPN2 is an indirect semiconductor with a bandgap of 1.67 eV. CuPN2, the first known ternary Cu phosphorus nitride, has been synthesized under high-pressure high-temperature conditions. It is isostructural to LiPN2 and an indirect bandgap semiconductor as shown by DFT calculations.

Posted on 2 March 2015 | 12:10 pm

Theoretical Insight Into the Role of Triarylboron Substituents in Tetradentate Dianionic Bis(N-heterocyclic carbene) Platinum(II) Chelates – Improving the Performance of Blue Light Emission

The electronic structures and photophysical properties of eleven PtII complexes divided into three series by their degree of ? conjugation were studied through density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. To investigate the effect of triarylboron substituents and the changes caused by the extension of the ? conjugation, the nonradiative and radiative decay efficiencies, the geometric relaxations, d orbital splitting, and spin–orbit couplings at the optimized S0 and T1 geometries were computed. The results show that complexes with triarylboron substituents may have higher phosphorescence efficiencies than those with cyano groups. Furthermore, complexes with larger ? conjugation (anthracene groups) may weaken the effects caused by the introduction of triarylboron substituents and are less likely to possess enhanced phosphorescence efficiency. Predictions of the absorption spectra and emission colors indicated that complexes with triarylboron substituents would emit blue colors, whereas the emission colors of the complexes with larger ? conjugation would be located in the near-infrared region. This work highlights that the introduction of the triarylboron substituents and appropriate ? conjugation (naphthalene groups) can result in highly efficient phosphorescence in complexes containing donor N-heterocyclic carbene (NHC) ligands. The introduction of triarylboron substituents and appropriate ?-conjugation to the N-heterocyclic (NHC) ligands of PtII complexes may improve their phosphorescence efficiencies and render them good candidates for highly efficient blue emission.

Posted on 2 March 2015 | 12:10 pm

Synthesis, Magnetic Properties, and X-ray Spectroscopy of Divalent Cobalt(II) and Nickel(II) Cubanes [MII4(HL2)4(OAc)4]

Under anaerobic conditions, the reactions of cobalt(II) and nickel(II) acetate tetrahydrate with 2,6-pyridinedimethanol (H2L2, 3) in anhydrous acetonitrile afforded two tetranuclear metal(II) complexes [MII4(HL2)4(OAc)4] (4; MII = Co2+, Ni2+) with a [M4(?3-O)4]4+ cubane core. X-ray structural analyses revealed that both MII cubanes 4a·2CH3OH and 4b·2CH3OH are isostructural and crystallize in the tetragonal space group I41/acd with eight molecules in the unit cell. In the solid state, the orientation of the cubane cores of 4 and the formation of a 3D framework were controlled by ?–? interactions as well as intra- and intermolecular O–H···O hydrogen bonds. Variable-temperature magnetic susceptibility measurements revealed that the cubanes 4 show a ferrimagnetic coupling scheme that leads to a diamagnetic ground state for both complexes. Core-level X-ray photoelectron spectroscopy confirmed that the Co and Ni ions in 4a and 4b are in a divalent state. X-ray magnetic circular dichroism was performed to extract the spin and orbital contributions to the Co and Ni magnetic moments. We compared the experimental results of the local electronic structures around the Co2+ ions in 4a and the Ni2+ ions in 4b with charge-transfer multiplet simulations. Starting from 2,6-pyridinedimethanol (H2L2, 3) and metal(II) acetate tetrahydrates, divalent CoII and NiII cubanes [MII4(HL2)4(OAc)4] (4) have been synthesized through self-organization. In addition to standard methods (e.g., IR, MS, X-ray analysis), complexes 4 were also characterized by magnetometry and X-ray spectroscopic techniques, including XPS, XAS, and XMCD.

Posted on 2 March 2015 | 12:10 pm

Luminescence Matching with the Sensitivity Curve of the Human Eye: Optical Ceramics Mg8–xMx(BN2)2N4 with M = Al (x = 2) and M = Si (x = 1)

Compounds Mg8–xMx(BN2)2N4 were prepared by solid-state reaction of MgCl2, Li3(BN2), and AlN for M = Al, and of Mg3N2, BN, and Si3N4 for M = Si. Their crystal structures were refined from powder X-ray diffraction data with the space group R$\bar {3}$m for M = Al, Si, and P21/c for M = Si. The structures of Mg8–xMx(BN2)2N4 are characterized by layered arrangements of wurtzite-related block layers alternating with a layer of di-nitridoborate ions along the c-axis direction. Cations in each structure are surrounded tetrahedrally by nitride and di-nitridoborate ions. Europium(II)-doped powders of Mg8–xMx(BN2)2N4 show exceptional broad band emissions in the visible region of the spectrum, on excitation with UV radiation at ?ex = 320 nm. Compounds Mg8–xMx(BN2)2N4 were prepared by solid-state reaction of MgCl2, Li3(BN2), and AlN for M = Al, and of Mg3N2, BN, and Si3N4 for M = Si. Their crystal structures were refined from powder X-ray diffraction data with the space group R$\bar {3}$m for M = Al, Si, and P21/c for M = Si. Eu(II)-doped Mg8–xMx(BN2)2N4 show broad band emissions in the visible region of the spectrum (?ex = 320 nm).

Posted on 27 February 2015 | 11:50 am

Mononuclear Iron(II) Dicarbonyls Derived from NNS Ligands – Structural Models Related to a “Pre-Acyl” Active Site of Mono-Iron (Hmd) Hydrogenase

We report the syntheses and characterization of dicarbonyliron complexes derived from tridentate, ortho-substituted Schiff base pyridine/thioether ligands (RNNS). Metalation reactions of RNNS (R = CH3, OCH3) at low temperature (–78 °C) with [Fe(CO)4(Br)2] afforded the desired complexes [(RNNS)Fe(CO)2Br]Br (2-COBr, 3-COBr). Reactions under similar conditions with more sterically demanding ligands [R = quinoline (Q), ClPh] afforded complex salts of the form [(RNNS)Fe(CO)2Br][Fe(CO)3(Br)3] (4-COFe and 5-COFe, respectively). Alternatively, the metalation of the RNNS ligands (for all R ? H) with [Fe(CO)4(Br)2] in Et2O at room temperature reliably affords the complex species of type [(RNNS)Fe(CO)2Br][Fe(CO)3(Br)3] (2-COFe, 3-COFe, 5-COFe). The metalation reactions of RNNS at only moderately low temperatures (–20 to 0 °C) result in the loss of CO to form the corresponding trigonal-bipyramidal iron(II) dibromide species of type [(RNNS)FeBr2] (2-Br, 4-Br, 5-Br; ?eff ? 5.3 ?B, S = 2). The IR spectrum of each dicarbonyl cation exhibits two ?(CO) stretches at $\tilde {\nu}$ ? 2070 and 2030 cm–1. Low-temperature 1H NMR spectroscopy measurements of 2-CO to 5-CO in CD3CN (–35 to 5 °C) revealed sharp resonances in the diamagnetic region. Under dark conditions, each dicarbonyl species is relatively stable (<10?% loss of CO, 1–2 h). However, photolysis revealed varying extents of photostability (stability rank: R = OMe?>?Me???Q?>?ClPh). An examination of the structural parameters reveals that higher photostabilities correlate with shorter Fe–C(O) bond lengths, which are induced by variation of the ortho substituent of the pyridine ring. DFT calculations along the putative photolysis pathway revealed that the bulky ligand substituent (in 5-CO) destabilizes the monocarbonyl intermediate, and this is a likely explanation for its more rapid rate of CO photodissociation. Relevance to a possible “apo-active site” of mono-iron hydrogenase (pre-acyl formation) is discussed. A series of iron(II) dicarbonyls are prepared from neutral Schiff base (NNS) ligands. These “phosphine-free” complexes are extremely temperature- and light-sensitive and somewhat like the active site of mono-[Fe] hydrogenase. The Fe(CO)2-bound methylpyridine unit in [(MeNNS)Fe(CO)2Br]+ may represent a “snapshot” of an intermediate during the biogenesis of the Fe–C(=O)acyl-containing active site.

Posted on 27 February 2015 | 11:50 am

CdS/g-C3N4 Hybrids with Improved Photostability and Visible Light Photocatalytic Activity

Novel composite photocatalysts consisting of CdS and graphitic carbon nitride (CdS/g-C3N4) with different ratios of CdS were prepared. The CdS/g-C3N4 composite photocatalysts were characterized in detail and their photocatalytic activity was evaluated by using rhodamine B and colorless metronidazole as probes. Compared with pure g-C3N4, the CdS/g-C3N4 composite exhibits significantly enhanced photocatalytic activity under visible-light irradiation. More importantly, g-C3N4 substantially reinforces the photostability of CdS nanowires even in a nonsacrificial system. The synergistic effect between CdS and g-C3N4 is found to be primarily responsible for enhancement of the separation of photogenerated electrons and holes, which helps improve the photocatalytic performance. A probable photodegradation process of metronidazole was proposed based on an analysis of the degradation products. This study provides new insight into the preparation of highly efficient and stable sulfide-based composite photocatalysts and facilitates their application in a number of environmentally sensitive areas. Nanocomposite photocatalysts CdS/g-C3N4 with different ratios of CdS and graphitic carbon nitride are described as high-performance photocatalysts for environmental remediation. The very stable and recyclable photocatalysts exhibit greatly enhanced photocatalytic activity under visible-light irradiation. Synergistic effects between CdS and g-C3N4 led to efficient separation of charge carriers.

Posted on 27 February 2015 | 11:50 am

Reactions of [Cp2Ti(?2-Me3SiC2SiMe3)] with 1,4-Bis(diphenylphosphanyl)but-2-yne: Coupling and Isomerization versus Phosphorylation

The reactions of [Cp2Ti(?2-Me3SiC2SiMe3)] (1; Cp = ?5-cyclopentadienyl) with 1,4-bis(diphenylphosphanyl)but-2-yne (2) have been investigated and found to yield a mixture of products. From these, through the coupling of 2, the tetrasubstituted titanacyclopentadiene [Cp2Ti(CCH2PPh2)4] (3) was isolated. In addition, small amounts of very unusual complexes were obtained and characterized. In one case, the substrate 2 isomerized to the allene Ph2PC(H)=C=C(H)CH2PPh2, which formed the complex [Cp2Ti{?3-Ph2PC(H)=C=C(H)CH2PPh2}] (4) through the coordination of a double bond and one of the phosphorus atoms. Another complex, [Cp2Ti{-C(CH2PPh2)=C(CH2PPh2)P(Ph2)H-}] (5), was identified to be the result of a formal hydrophosphorylation of the substrate 2 by HPPh2, and features a Ti–H–P bridge. It is not clear how HPPh2 was formed. One possible explanation is the dehydrophosphorylation of the substrate with the formation of HPPh2 and the butatriene H2C=C=C=C(H)PPh2 [tautomer of the but-2-en-3-yne HC?C-CH=C(H)PPh2]. The molecular structures of complexes 4 and 5 were determined by X-ray analysis. Cuttings and Couplings: The reactions of 1,4-bis(diphenylphosphanyl)but-2-yne with [Cp2Ti(?2-Me3SiC2SiMe3)] have been investigated. An initial alkyne coupling reaction led to a metallacyclopentadiene. Thermal treatment then led to an allene complex by a 1,3-H shift in the coordinated alkyne. In addition, a highly unusual complex with a Ti–H–P bridge was obtained by phosphorylation of the alkyne.

Posted on 27 February 2015 | 11:50 am

Imidazolium 1,3-Benzazaphospholide Ion Pairs with Strong C–H···N Hydrogen Bonds – Synthesis, Structures, and Reactivity

The treatment of 2-phenyl-1H-1,3-benzazaphosphole (H[2-ph-bp], 1) with free 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes, 2) and 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene (SIMes, 3) afforded two imidazolium 1,3-benzazaphospholides, [1,3-bis(2,4,6-trimethylphenyl)imidazolium 2-phenyl-1,3-benzazaphospholide [(IMesH)+(2-ph-bp)–, 4] and 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazolium 2-phenyl-1,3-benzazaphospholide [(SIMesH)+(2-ph-bp)–, 5], which further reacted with carbodiimide to give 2-(N,N?-diisopropylcarbamimidoyl)-1,3-bis(2,4,6-trimethylphenyl)imidazolium 2-phenyl-1,3-benzazaphospholide (6) and 2-(N,N?-diisopropylcarbamimidoyl)-1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazolium 2-phenyl-1,3-benzazaphospholide (7), respectively. These compounds were characterized by multinuclear (1H, 13C{1H}, and 31P{1H}) NMR and IR spectroscopy, and X-ray diffraction analysis. The structures feature ion pair conformation in the solid state with strong charge-assisted C–H···N or N–H···N interaction. The treatment of 1H-1,3-benzazaphosphole with N-heterocyclic carbenes produces ionic species exhibiting strong charge-assisted hydrogen bonds, which further react with carbodiimide to give carbamimidoylimidazolium 1,3-benzazaphospholides. The crystal structures of the complexes indicate ion pair conformation in the solid state.

Posted on 27 February 2015 | 11:50 am

A Model Study on Molecular Properties and Mechanistic Investigations of P=C=E14 Molecules

The bonding properties and the potential energy surfaces for the chemical reactions of heteroallenic compounds with a –P=C=E14< pattern are studied by using density functional theory (M06-2X/Def2-SVPD). Five Mes*P=C=E14(tBu)Tip species, for which E14 = C, Si, Ge, Sn, and Pb, were used as model reactants in this work. The theoretical evidence shows that Mes*P=C=E14(tBu)Tip molecules have both P=C and C=E14 double bonds. Four types of chemical reaction – water addition, acetylene [3+2] cycloaddition, ketone [2+2] cycloaddition, and selenium [1+2] cycloaddition – have been used to study the reactive activity of these group 14 heteroallenic molecules. This theoretical work predicts that the heavier the group 14 element (E14) in the heteroallenic –P=C=E14< compounds, the smaller is its singlet–triplet energy splitting, the lower is its activation barrier, and the more rapid are its chemical reactions with various chemical species. As a result, this theoretical investigation shows that the relative reactivity of –P=C=E14< increases in the order: –P=C=C<, –P=C=Si<, –P=C=Ge<, –P=C=Sn<, and –P=C=Pb<. M06-2X computational results reveal that Mes*P=C=E14(tBu)Tip compounds contain both P=C and C=E14 double bonds in nature. Moreover, this theoretical work suggests that the smaller the atomic number of the group 14 element, E14, in the heteroallenic –P=C=E14< molecule, the more kinetically and thermodynamically stable is its heteroallenic –P=C=E14< species towards various chemical reactions.

Posted on 27 February 2015 | 11:40 am

Amine-bis(phenolato)cobalt(II) Catalysts for the Formation of Organic Carbonates from Carbon Dioxide and Epoxides

New monometallic amine-bis(phenolato)cobalt(II) [(ONNO)RCoII] (R = CMe2Ph; Cl; Br) complexes have been synthesized and fully characterized including X-ray crystallographic analysis. These CoII complexes show good activity for the formation of cyclic propylene carbonate in combination with tetrabutylammonium bromide (TBAB) as a co-catalyst. The reaction parameters such as carbon dioxide pressure, co-catalyst loadings and temperature were varied to determine the ideal reaction conditions. These catalysts were also employed in copolymerization reactions of cyclohexene oxide/CO2 and propylene oxide/CO2. [(ONNO)ClCoII]*(MeOH) was found to effectively copolymerize cyclohexene oxide (CHO) and CO2. This is the first reported amine-bis(phenolato) cobalt(II) complex to be active in the copolymerization of CO2 and CHO. In-depth stability studies were conducted (Evan's method) to validate CoII as the active species required for copolymerization. End-group analysis via NMR, ESI-MS and MALDI-TOF revealed the presence of 4-(dimethylamino)pyridine (DMAP) and methoxy terminated chains. New amine-bis(phenolato)cobalt(II) complexes were synthesized and employed in the coupling and copolymerization of carbon dioxide and epoxides. In combination with DMAP, complex 3 enabled poly(cyclohexene) carbonate generation. End-group analysis found DMAP and methoxy terminated polymer chains due to chain-transfer and the active species for CHO/CO2 copolymerization was found to be CoII.

Posted on 27 February 2015 | 11:30 am

[Ag{S2CNR(C2H4OH)}] as Single-Source Precursor for Ag2S – Synthesis, Decomposition Mechanism, and Deposition Studies

Silver(I) dithiocarbamates [Ag{S2CNR(C2H4OH)}] (3a, R = Me; 3b, R = Bu) were accessible by the reaction of AgNO3 with K{S2CNR(C2H4OH)} (2a, R = Me; 2b, R = Bu). Alternatively, 3b could be prepared by the condensation of CS2 and Ag2O with NHBu(C2H4OH) (1b). The thermal behavior of 3 was studied by thermogravimetric (TG) analysis. A two-step decomposition process leads to the formation of ?-Ag2S, as evidenced by X-ray powder diffraction studies. A decomposition mechanism of 3a to form Ag2S through the release of 3-methyloxazolidine-2-thione is discussed based on TG–MS, GC–MS, and NMR experiments. Because of the better solubility of 3b, this complex was tested for Ag2S spin-coating deposition studies on different substrates (SiO2/Si, TiN/SiO2/Si, glass) with subsequent annealing at 450 °C under a N2 atmosphere. Film thickness, composition, and morphology of the as-deposited films were determined by XRD, SEM, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy, which showed the formation of 200 nm thick, conformal, adherent, monoclinic ?-Ag2S layers. The synthesis, thermal behavior, and decomposition mechanism of [Ag{S2CNR(C2H4OH)}] (R = Me, Bu) is discussed. Its application as a single-source spin-coating precursor for thin-film ?-Ag2S fabrication is reported.

Posted on 27 February 2015 | 11:30 am

On the Thermal Stability and Structures of Layered Double Hydroxides Mg1–xAlx(OH)2(NO3)x·mH2O (0.18???x???0.38)

Nitrate-based layered double hydroxides, Mg1–xAlx(OH)2(NO3)x·mH2O, have been investigated to settle issues relating to stability towards humidity, dehydration and staging, nitrate group orientation, Al migration and crystal structure. Raman and IR spectroscopy together with modelling methods proved that flat-lying water and nitrate become tilted towards [001] at higher nitrate concentrations, accompanied by expansion along the c-axis. The distribution of the molecular tilts is greatest for x = 0.25, which explains the extraordinary broad diffraction peaks. The unit cell volume was modified for all samples when subjected to moist air, most strongly for x = 0.25. On heating, in situ synchrotron diffraction data showed continuous changes along the c-axis during dehydration of samples with x = 0.20 and 0.33. For x = 0.25, an intermediate phase appeared. Dehydroxylation was initiated at the OH groups bonded to the cations MgAl2, Mg2Al and Mg3 (in said order), whereas complete nitrate loss occurred at higher temperatures for higher Al contents. Some aluminium simultaneously moved to tetrahedral sites, which, according to 1H–27Al CP NMR spectroscopy, lack protons in their near neighbourhood. In contrast, octahedral aluminium remains surrounded by protons during decomposition. For the metastable oxide product, neutron diffraction indicated that 2/3 of aluminium reside in tetrahedral interstices. This oxide is defective, probably mimicking wüstite rather than a regular rock salt structure. Structural aspects of nitrate-based layered double hydroxides Mg1–xAlx(OH)2(NO3)x·mH2O have been investigated by various experimental and theoretical methods. The main focus was on the orientation of the NO3– groups in the interlayer gallery, the reversible hydration/dehydration process and the transport of Al from octahedral to tetrahedral sites during the formation of a metastable rock salt oxide.

Posted on 27 February 2015 | 11:30 am

Synthesis and Catalytic Activity of Molybdenum–Nitride Complexes Bearing Pincer Ligands

Molybdenum–nitride complexes bearing pincer ligands have been designed, prepared, and characterized spectroscopically. The synthetic method described in this paper provides a convenient and useful approach to the preparation of cationic molybdenum(V)–nitride complexes that may act as catalysts for the formation of ammonia from molecular dinitrogen under ambient reaction conditions.. Molybdenum–nitride complexes bearing pincer ligands have been designed, prepared, and characterized spectroscopically. The catalytic activities of these molybdenum–nitride complexes have been investigated in the formation of ammonia from molecular dinitrogen under ambient conditions.

Posted on 27 February 2015 | 11:30 am

Lanthanoid Induced C–F Activation of All Fluorine Atoms of One CF3 Group

The lanthanum formamidinate complex [La(CF3Form)3] {CF3FormH = N,N?-bis(2-trifluoromethylphenyl)formamidine}, which has six La–F interactions in the solid-state structure, readily undergoes C–F activation of all fluorine atoms of one CF3 group to give LaF3, and two isomeric polytrifluoromethylphenyl-substituted polyamidines, one containing a 1,2,3,4-tetrahydroquinazoline heterocyclic core. The lanthanum formamidinate complex [La(CF3Form)3] {CF3FormH = N,N?-bis(2-trifluoromethylphenyl)formamidine} readily undergoes C–F activation of all fluorine atoms of one CF3 group to give LaF3, and two isomeric polytrifluoromethylphenyl-substituted polyamidines, one containing a 1,2,3,4-tetrahydroquinazoline heterocyclic core.

Posted on 25 February 2015 | 9:50 am

Syntheses, Structures, and Photophysical Properties of Eu and Lu Diketonates with a Neutral Polydentate Imidazolylmethanamine Ligand

The Schiff base NNO ligand 1-(furan-2-yl)-N-[(2-methyl-1H-imidazol-4-yl)methylene]methanamine was synthesized and structurally characterized by XRD crystallography, mass spectrometry, and NMR spectroscopy. Quantum-chemical calculations revealed conformational flexibility of the ligand backbone to give two different conformations with nearly equal ground-state energies. The orientation of two nitrogen atoms and the oxygen atom in one conformation is a good fit for the NNO tridentate coordination mode, whereas the other would allow the NN coordination mode only. Two lanthanide complexes [Ln(tta)3(NNO)] (Ln = EuIII and LuIII; tta = thenoyltrifluoroacetone) were prepared and studied spectroscopically. The structures of the complexes were optimized by the DFT approach. The NNO ligand in the Eu complex displays tridentate NNO coordination, whereas the ligand is only NN-coordinated in the Lu complex. The Eu complex shows bright red metal-centered phosphorescence under excitation into the ligand (?–?*) absorption bands with a quantum yield of ca. 80?% and a lifetime of 580 ?s. A mechanism for energy transfer between the ligands and metal centers was suggested and confirmed by DFT and time-dependent DFT (TDDFT) studies. An organic light-emitting diode (OLED) device based on the Eu complex incorporated into a poly(9-vinylcarbazole) (PVK) matrix was prepared. A study of the characteristics of the device revealed electrochromism of the system owing to variations in the efficacy of metal-centered and matrix emission at different strengths of applied electric field. Neutral EuIII and LuIII diketonate complexes with a Schiff base NNO ligand are studied spectroscopically. The Eu complex shows red metal-centered phosphorescence with a quantum yield of ca. 80?%. An organic light-emitting device (OLED) with the Eu complex in a poly(9-vinylcarbazole) (PVK) matrix reveals electrochromism owing to variations in the efficacy of the metal-centered and matrix emission.

Posted on 25 February 2015 | 9:50 am

A Cationic Polyelectrolyte-Controlled Liquid Mineral Precursor Process in the BaCO3 System

Biomimetic BaCO3 materials with various morphologies have been synthesized in a cationic polyelectrolyte-controlled mineral solution. Investigations showed that the mineral solution initially underwent a phase separation to produce a condensed liquidlike amorphous intermediate. This mineral solution was a typical reaction-diffusion field, in which concentric ring patterns were frequently observed. Subsequently, overgrowth fibers were seen growing on large microspheres and their growth could be interpreted in terms of a mesocrystal self-assembly process. This work opens up the possibility of using positively charged polyelectrolytes to design a very wide range of inorganic materials. A polymer-induced liquid mineral precursor (PILP) provides a general pathway towards biomimetic materials with complex morphology. In this article, we expand the conception of cationic polyelectrolyte-induced liquid precursors to other inorganic systems, such as barium carbonate. Mesocrystal fibers and a self-organized concentric ring pattern were synthesized in the mineral solution.

Posted on 23 February 2015 | 11:20 am

One-Step Green Synthesis of Multifunctional Fe3O4/Cu Nanocomposites toward Efficient Reduction of Organic Dyes

Noble-metal-derived functional materials have played indispensable roles in the reduction of dye under aqueous conditions; however, their cost and separation are great limitations on their wider practical applications. Therefore, an alternative preparation of comparable materials with low cost and good ease of separation is required. Herein magnetic microspheres (i.e., Fe3O4/Cu) were synthesized through a green single-step solvothermal method for the first time with ethylene glycol serving as reductant and reaction media. The prepared materials were characterized by means of powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectrometry, a vibrating sample magnetometer, and so forth. Additionally, by employing the reduction of 4-nitrophenol to 4-aminophenol as a model reaction, the effects of preparation time and the initial dosage of Cu(NO3)2 on the rate constant of the catalytic reduction reaction were systematically investigated. Moreover, the obtained hybrid nanocatalysts were also applied to reduce and degrade common organic dyes (rhodamine B and methylene blue) in the presence of NaBH4. Quite significantly, it was shown that it could catalytically degrade different organic dyes with excellent catalytic performance and high stability in recycled reactions up to five times. More interestingly, the material can be easily separated from the catalytic system for further use. An Fe3O4/Cu nanocatalyst that exhibits excellent catalytic performance in the degradation of 4-nitrophenol (4-NP) (the reaction was accomplished within 4 min), rhodamine B (within 3 min), and methylene blue (within 1 min) as well as superior stability (can be reused at least five times) was successfully synthesized through a green one-step solvothermal method with ethylene glycol as reductant and reaction media.

Posted on 20 February 2015 | 11:10 am

Differential Reactivity of [TpRu(?2P,N-iPr2PXPy)Cl] (X = NH, S) Bearing Hemilabile Coligands Towards NaBArF4, Lithium Acetylide, and Acetylenes

In contrast with [TpRu(?2P,N-iPr2PNHPy)Cl] (1a, Tp = trispyrazolylborate), [TpRu(?2P,N-iPr2PSPy)Cl] (1b) reacts with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBArF4) in fluorobenzene under nitrogen to afford the dinuclear complex [{TpRu(?2P,N-iPr2PSPy)}2(?-Cl)][BArF4] (1b?). Through diverse synthetic strategies, a series of neutral acetylides [TpRu(C?CR)(?2P,N-iPr2PXHPy)] [X = NH; R = Ph (2a), SiMe3 (2b); X = S; R = Ph (2c), p-C6H4Br (2d), COOMe (2e)], cationic vinylidene complexes [TpRu(=C=CHR)(?2P,N-iPr2PNHPy)]+ [X = NH; R = Ph (3a), SiMe3 (3b); X = S; R = Ph (3c), p-C6H4Br (3d)] and [TpRu(=C=CH2)(?2P,N-iPr2PNHPy)]+ (3e), and a cationic ?2-alkyne complex [TpRu(?2-HC?CCOOMe)(?2P,N-iPr2PSPy)][BArF4] have been efficiently synthesized from 1a and 1b. The methoxy(methyl)carbene complexes [TpRu{=C(OMe)CH3}(?2P,N-iPr2PXPy)][BPh4] [X = NH (5a), S (5b)] were isolated from the reactions of 1a and 1b with acetylene gas in the presence of NaBArF4 in methanol. The deprotonation of the cationic vinylidenes derived from 1b with KtBuO affords the corresponding neutral acetylide complexes, which undergo facile protonation with CF3SO3H to reproduce the cationic vinylidenes quantitatively. The behaviors of ruthenium complexes bearing 2-pyridyl(diisopropylphosphanyl)amine (iPr2PNHPy) or 2-pyridyl(diisopropylphosphanyl)thioether (iPr2PSPy) ligands are compared. The main emphasis is on the differential reactivity of [TpRuCl(iPr2PXPy)] (X = NH, S; Tp = trispyrazolylborate) towards NaBArF4 {BArF4 = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate}, lithium acetylide, and acetylenes.

Posted on 19 February 2015 | 11:53 am

Three Alkali Metal Lead Orthophosphates – Syntheses, Crystal Structures and Properties of APbPO4 (A = K, Rb, Cs)

Three alkali metal lead orthophosphates, APbPO4 (A = K, Rb, Cs), have been synthesized by conventional solid-state reaction. The single-crystal X-ray structural analyses revealed that they crystallize in the same space group, Pnma (No. 62), but they are not all isostructural. APbPO4 (A = K, Rb) are isostructural, and the three-dimensional (3D) structure of RbPbPO4 (representative) consists of [Pb1|Rb1O4]? chains connected with isolated PO4 tetrahedra, the Pb2|Rb2 atoms filling the pore space. The 3D structure of CsPbPO4 consists of another kind of chains, [PbO4]?, connected with isolated PO4 tetrahedra, and the Cs atoms reside in the channel. Thermal, IR spectroscopy, and UV/Vis/NIR diffuse reflectance spectroscopy analyses have also been performed. In addition, first-principle theoretical studies were carried out to aid in the understanding of the electronic structures and the projected density of states of CsPbPO4. Three alkali metal lead orthophosphates, APbPO4 (A = K, Rb, Cs), have been synthesized by conventional solid-state reaction. They crystallize in the same space group, Pnma, but they are not all isostructural.

Posted on 18 February 2015 | 11:50 am

Dinuclear DOTA-Based GdIII Chelates – Revisiting a Straightforward Strategy for Relaxivity Improvement

The need for magnetic resonance imaging (MRI) contrast agents with improved relaxivity maintains the development of new GdIII chelates as an intensive and demanding field of research. In this work, we introduce the new dimeric chelators bis{1,4,7,10-tetraazacyclododecane-1-[(6-amino)hexanoic]-4,7,10-triacetic acid}adipate [L2, bis(DOTA-AHA)adipate] and bis{1,4,7,10-tetraazacyclododecane-1-[(6-amino)hexanoic]-4,7,10-triacetic acid}1,3-phenyldiacetate [L3, bis(DOTA-AHA)1,3-phenyldiacetate], which are based on the bifunctional ligand 1,4,7,10-tetraazacyclododecane-1-[(6-amino)hexanoic]-4,7,10-triacetic acid (L1, DOTA-AHA). Their GdIII chelates were studied by variable-temperature 1H nuclear magnetic relaxation dispersion (NMRD) and 17O NMR spectroscopy to measure their relaxivities and the parameters that govern them. The rates of exchange of inner-sphere water from the monomer GdL1 and from the two dinuclear chelates Gd2L2 and Gd2L3 are very similar (298kex ? 6.5?×?106 s–1) and slightly faster than that for [Gd(DOTA)H2O]– (298kex = 4.1?×?106 s–1). All three compounds form weakly bound aggregates with equilibrium constants 298K of 2.9, 15.6, and 14.6 for GdL1, Gd2L2, and Gd2L3, respectively. Even though the aggregates contain only 10 to 15?% of the total amount of GdIII ions, a marked increase in relaxivity between 30 and 100 MHz is observed. Furthermore, the distance between the two GdIII centers in the dinuclear compounds has been determined by double electron–electron resonance (DEER) spectroscopy experiments and by molecular modeling studies, which afforded comparable distances. The linkers between the chelating moieties allow GdIII–GdIII distances of ca. 3.0 nm for the completely stretched linker conformation and less than 1.9 nm for the conformation with the metal centers at a closer distance. These metal-to-metal distances by themselves cannot explain the considerably long tumbling times of the chelates in solution. Only a model consistent with some level of aggregation for the dinuclear chelates in aqueous solution could satisfactorily explain our results. Two DOTA-based dimeric chelators are developed, and their dinuclear GdIII chelates are studied by variable-temperature 1H nuclear magnetic relaxation dispersion (NMRD) and 17O NMR spectroscopy. The distance between the GdIII centers is determined by double electron–electron resonance and by molecular modeling. Only a model with some level of aggregation could satisfactorily explain our results.

Posted on 18 February 2015 | 11:50 am

Further Insight into Uranium and Thorium Metaphosphate Chemistry and the Effect of Nd3+ Incorporation into Uranium(IV) Metaphosphate

A tetragonal modification of uranium polymetaphosphate U(PO3)4, a mixed U4+/Nd3+ polymetaphosphate “(U0.62Nd0.38)(PO3)4”, and two new tetraphosphates, Th(P4O12) and U(P4O12), were synthesized. The structures of the obtained materials were characterized by X-ray diffraction and Raman spectroscopy. The presence of Nd in (U0.62Nd0.38)(PO3)4 was proven by energy-dispersive X-ray spectroscopy (EDX), and the measured degree of substitution for U agrees well with the X-ray crystallography results; however, the mechanism of the necessary charge compensation could not be identified. The cation arrangements in the crystal structures of thorium and uranium polymetaphosphates have been studied in terms of Voronoi–Dirichlet polyhedra. Different conformations of the tetraphosphate polyanions were observed in the crystal structures of Th(P4O12) and U(P4O12). The Raman spectrum of a single crystal of Th(P4O12) was recorded, and the bands were assigned. Two new polymorphic modifications of uranium metaphosphate are obtained, and their crystal structures are elucidated as well as those of previously reported thorium and uranium tetraphosphates. The uranium atoms are partially substituted by neodymium atoms in the structure of one of the uranium metaphosphates, and the substitution significantly affects the structure.

Posted on 18 February 2015 | 11:50 am

Controlled Synthesis of Phase-Pure Zeolitic Imidazolate Framework Co-ZIF-9

The synthesis of phase-pure Co-ZIF-9, an important cobalt-based zeolitic imidazolate framework, could be achieved by modification of the reported synthesis procedure through pH adjustment of the starting synthesis mixture. The phase-pure Co-ZIF-9 material obtained has been characterized by a combination of UV/Vis, FTIR, and Raman spectroscopy as well as by thermogravimetric analysis (TGA) and XRD and possesses a lower overall crystallinity. This can be explained by the addition of the base for the pH adjustment method. On the basis of these findings, a synthesis pathway for the formation of the secondary phase, cobalt formate, is proposed along with its relationship to the flexibility of the coordination environment of cobalt ions. The crystal structures of both phases have been determined by single-crystal X-ray crystallography, and the resolved structures also reflect the coordination flexibility of the framework cobalt ions. Phase-pure zeolitic imidazolate framework Co-ZIF-9 can be prepared by modification of the commonly used synthesis procedure through pH adjustment, which suppresses the formation of the secondary framework, cobalt formate.

Posted on 18 February 2015 | 11:50 am

Osmium–Nitrosyl Oxalato-Bridged Lanthanide-Centered Pentanuclear Complexes – Synthesis, Crystal Structures and Magnetic Properties

A series of pentanuclear heterometallic coordination compounds of the general formula (Bu4N)5[Ln{Os(NO)(?-ox)Cl3}4(H2O)n] [Ln = Y (for 2) and Dy (for 3?) when n = 0; Ln = Dy (for 3), Tb (for 4), and Gd (for 5) when n = 1] were synthesized by the reaction of the precursor (Bu4N)2[Os(NO)(ox)Cl3] (1) with the respective lanthanide(III) (Gd, Tb, Dy) or yttrium(III) chloride. For the five new complexes, the coordination numbers eight or nine are found for the central metal ion. The compounds were fully characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction analysis, magnetic susceptibility measurements, and ESI mass spectrometry. In addition, compound 1 was studied by UV/Vis spectroscopy and cyclic voltammetry. The X-ray diffraction analyses revealed that the anionic complexes consist of a lanthanide or yttrium core bridged through oxalato ligands to four octahedral osmium–nitrosyl moieties. This picture, in which the central ion is eight-coordinate, holds for lanthanide ions with an ionic radius smaller than that of the dysprosium(III) ion. For larger ionic radii, the central metal ion is nine-coordinate, as the coordination sphere is completed by one molecule of water. Only in the case of dysprosium(III), it was possible to obtain complexes with both coordination numbers 8 and 9. This implies that dysprosium(III) is the tilt limit between the two coordination numbers in this series. The bond length Ln–O decreases from Dy to Gd. The nine-coordinate complexes are energetically more favored for lanthanide ions with a radius larger than that of the dysprosium(III) ion, and the eight-coordinate complexes are favored for smaller ions. Magnetic studies of the series of compounds showed that the osmium precursor 1 as well as the yttrium compound 2 are diamagnetic, whereas the magnetism of the gadolinium, terbium, and dysprosium complexes is due to isolated lanthanide ions. Coordination tilt: Depending on the size of the Ln(III) ion, osmium–nitrosyl oxalato-bridged lanthanide-centered pentanuclear complexes exhibit two different coordination numbers, 8 or 9, for the central lanthanide ion, and both numbers are observed for dysprosium.

Posted on 16 February 2015 | 7:10 pm

Electronic Structures of “Low-Valent” Neutral Complexes [NiL2]0 (S = 0; L = bpy, phen, tpy) – An Experimental and DFT Computational Study

The electronic structures of the neutral complexes [Ni(bpy)2]0, [Ni(tpy)2]0, and [Ni(phen)2]0 (bpy = 2,2?-bipyridine; tpy = 2,2?:6?,2?-terpyridine; phen = 1,10-phenanthroline) have been investigated by a combination of UV/Vis spectroscopy, magnetochemistry, and X-ray crystallography {the structures of [Ni(bpy)2]0, [Ni(tpy)Cl]0, [Cu(bpy)2](PF6)2 (reinvestigation), and [(bpy)2Cu(?2-NO3)Cu(bpy)2](PF6)3 are reported herein}. To further clarify the electronic structures of the title compounds and elucidate those of the electron transfer series produced by their reduction and oxidation, broken-symmetry (BS) density functional theory (DFT) calculations were performed for [Ni(bpy)2]m (m = 2+, 1+, 0, 1–, 2–), [Ni(bpy)3]m (m = 3+, 2+, 1+, 0, 1–, 2–), [Ni(tpy)2]m (m = 3+, 2+, 1+, 0), and, for calibration purposes, [Zn(phen)(NH3)xCl(2–x)]0 (x = 2, 1, 0). Through the aforementioned studies, it was shown that none of the so called “low-valent” Ni complexes contain zero-valent Ni. Instead, they each contain at least one (bpy·)1–, (tpy·)1–, or (phen·)1– ?-radical monoanionic ligand. More specifically, they are all four-coordinate and possess the following electronic structures: [NiI(bpy·)(bpy0)] (delocalized), [NiI(tpy·)(tpy0)] (delocalized), and [NiII(Mephen·)2] (Mephen = 2,9-dimethyl-1,10-phenanthroline). In addition, all members of the series [Ni(bpy)2]m with m?? 1+ contain a NiI ion (d9, SNi = 1/2), and the redox processes that link them are ligand-centered. A similar finding was made for six-coordinate [Ni(bpy)3]m and [Ni(tpy)2]m, but in this case complexes with m?? 2+ contain Ni ions posessing an invariant +II oxidation state (d8, SNi = 1). The electronic structures of the two series of complexes [Ni(bpy)3]n (bpy = 2,2?-bipyridine; n = 2–, 1–, ..., 3+) and [Ni(bpy)2]m (m = 1–, ..., 3+) have been studied experimentally and computationally (DFT). All octahedral species contain a NiII ion, and the reductions are strictly ligand-centered, whereas the [Ni(bpy)2]m series contains tetrahedral NiII and NiI ions.

Posted on 16 February 2015 | 7:10 pm

Synthesis and Structural Study of Tetravalent (Zr4+, Hf4+, Ce4+, Th4+, U4+) Metal Complexes with Cyclic Hydroxamic Acids

Six- and seven-membered cyclic hydroxamic acids, such as 1-hydroxypiperidine-2-one (1H, 1,2-PIPOH) and 1-hydroxyazepan-2-one (2H), have recently been identified in some mixed siderophores as one of their three chelating subunits. Compared to their ubiquitous noncyclic counterparts, cyclic hydroxamates are preorganized for metal binding. Surprisingly, the coordination chemistry of these bidentate, monoanionic ligands remains virtually unknown, even in the case of iron(III). We report herein the first structural study of the complexes of 1– and of 6–, an unsaturated seven-membered ring analog of 2–, with tetravalent cations of transition metals (zirconium and hafnium), lanthanide (cerium), and actinides (thorium and uranium). Structural characterization by means of X-ray crystallography of the corresponding ML4 complexes evidenced distorted square antiprismatic coordination geometries with the exception of U4+, which favors a dodecahedral arrangement. 1-Hydroxypiperidine-2-one (1H, 1,2-PIPOH) is a cyclic hydroxamic acid that occurs in several siderophores as one of the three FeIII binding units. It can form neutral homoleptic complexes with tetravalent transition-metal (Zr and Hf), lanthanide (Ce), and actinide (Th and U) cations with a diversity of coordination stereochemistries ranging from the square antiprism to the dodecahedron.

Posted on 16 February 2015 | 7:10 pm

Asymmetric Base-Free Michael Addition at Room Temperature with Nickel-Based Bifunctional Amido-Functionalized N-Heterocyclic Carbene Catalysts

A series of nickel-based chiral bifunctional catalysts (1d–3d) with N-heterocyclic carbene (NHC) ligands derived from (1R)-(–)-menthol, (1S)-(–)pinene, and (1R)-(+)-camphor have been successfully designed for asymmetric Michael addition reactions under base-free conditions. The NHC complexes, namely, [1-R-3-{N-(phenylacetamido)}imidazol-2-ylidene]2Ni [R = (1S)-menthyl (1d), (1S)-pinane (2d), and (1R)-isobornyl (3d)], bearing chiral ancillaries on the amido-functionalized side arms of the NHC ligands, performed the bifunctional catalysis of the asymmetric base-free Michael addition reaction of the ?-methyl cyano ester substrates ethyl 2-cyanopropanoate (4), isopropyl 2-cyanopropanoate (5), and tert-butyl 2-cyanopropanoate (6) with the activated olefinic substrates methyl vinyl ketone (7) and acrylonitrile (8) in 63–98?% yields with enantiomeric excess (ee) values of 2–75?% at room temperature in 8 h. More interestingly, only the longest of the three catalysts, the menthol derivative 1d, showed significant chiral induction of up to 75?%?ee; this has been attributed to the reduction of the steric influence owing to the relatively distant dispositions of the chiral ancillaries from the catalytically active metal center that arise as a consequence of the cis geometries of 1d–3d. A series of nickel-based chiral bifunctional catalysts with N-heterocyclic carbene ligands derived from readily available and inexpensive (1R)-(–)-menthol, (1S)-(–)pinene, and (1R)-(+)-camphor synthons successfully catalyze asymmetric base-free Michael addition reactions under ambient conditions.

Posted on 16 February 2015 | 7:10 pm

Coordinative Flexibility of a Thiophenolate Oxazoline Ligand in Nickel(II), Palladium(II), and Platinum(II) Complexes

The synthesis, full characterization, and molecular structures of seven new coordination compounds that feature the 2-(4?,4?-dimethyloxazolin-2?-yl)thiophenolate ligand (S-Phoz) with group 10 metals Ni, Pd, and Pt in the +II oxidation state are presented. The ML2 complexes [Pt(S-Phoz)2] (1a), [Pd(S-Phoz)2] (1b), and [Ni(S-Phoz)2] (2) were prepared starting from MCl2. Compound 1a was obtained isomerically pure in a trans arrangement, whereas its Pd analogue 1b exhibits a dynamic, solvent-dependent cis/trans equilibrium, and 2 adopts a tetrahedral arrangement. The reaction of LiS-Phoz with [cis-MCl2(PPh3)2] precursors resulted in full replacement of the PPh3 for M = Ni and in partial substitution for M = Pt, Pd to yield [Ni(S-Phoz)2] (2), [Pt(?2-S-Phoz)(?1-S-Phoz)(PPh3)] (3a), and [Pd(?2-S-Phoz)(?1-S-Phoz)(PPh3)] (3b). The Pd compound 3b exhibits an interesting solvent-dependent equilibrium with 1b and PPh3 as demonstrated by 1H and 31P NMR spectroscopy. Compounds [{PdCl(S-Phoz)}2] (4) and [PdCl(S-Phoz)(PPh3)] (5) were synthesized from [PdCl2(NCMe)2]. Molecular structures of compounds trans-1a, trans-1b, 2, 3a, 3b, 4, and 5 were determined by single-crystal X-ray diffraction studies. With the exception of the Ni complex 2, all compounds exhibit distorted square-planar geometries. A series of nickel, palladium, and platinum complexes that contain a thiophenolate oxazoline ligand were prepared. The ligand coordinates preferably in a bidentate manner but shows high coordinative flexibility depending on the metal center.

Posted on 16 February 2015 | 4:50 pm

Structural Relationship between the Mg-Containing Nitridosilicates Ca2Mg[Li4Si2N6] and Li2Ca2[Mg2Si2N6]

Ca2Mg[Li4Si2N6] and Li2Ca2[Mg2Si2N6] were synthesized in sealed tantalum ampules with Li as a fluxing agent. Both compounds crystallize in the monoclinic space group C2/m (no. 12). The crystal structures were solved and refined on the basis of single-crystal X-ray diffraction data [Z = 2; Ca2Mg[Li4Si2N6]: a = 5.9059(12), b = 9.817(2), c = 5.6109(11) Å, ? = 94.90(3)°, R1 = 0.015, wR2 = 0.049; Li2Ca2[Mg2Si2N6]: a = 5.5472(11), b = 9.844(2), c = 5.9978(12) Å, ? = 97.13(3)°, R1 = 0.024, wR2 = 0.053]. Ca2Mg[Li4Si2N6] is isomorphic to Ca3[Li4Si2N6] and its crystal structure is homeotypic to that of Li2Ca2[Mg2Si2N6]. Both structures are built up of edge-sharing [Si2N6]10– tetrahedra (bow-tie units). In the nitridolithosilicate Ca2Mg[Li4Si2N6] the bow-tie units are connected via pairs of LiN4 tetrahedra, whereas in the nitridomagnesosilicate Li2Ca2[Mg2Si2N6] the nitridosilicate substructure is connected by chains of MgN4 tetrahedra. Ca2Mg[Li4Si2N6] is only the second example of fourfold planar rectangular coordinated Mg2+ in a nitridosilicate. Li2Ca2[Mg2Si2N6] is the first nitridosilicate with Li+ in threefold coordination. The crystal structures were confirmed by lattice-energy calculations (MAPLE), EDX measurements, and powder X-ray diffraction. Novel Mg-containing nitridosilicates, namely Ca2Mg[Li4Si2N6] and Li2Ca2[Mg2Si2N6], are presented. The nitridolithosilicate Ca2Mg[Li4Si2N6] is the second example of Mg in a fourfold planar rectangular coordination with N in nitridosilicates. Li2Ca2[Mg2Si2N6] is another representative of the novel subgroup of nitridomagnesosilicates with Mg2+ in tetrahedral coordination.

Posted on 16 February 2015 | 4:50 pm

Suzuki Coupling Reactions Catalyzed with Palladacycles and Palladium(II) Complexes of 2-Thiophenemethylamine-Based Schiff Bases: Examples of Divergent Pathways for the Same Ligand

Activation of Suzuki coupling with a complex of palladium varies with the mode of coordination of its ligand. The moisture-/air-insensitive palladacycles and palladium complexes designed using the same ligand (Schiff base, coordinating as an N,C– and N,O– ligand, respectively) have been found to follow different pathways. Palladacycles are more efficient, as their 0.001 mol-% loading gives good conversion (yield > 90?%) in several cases. Higher loading than this is required for Pd complexes to obtain a similar yield. Activation with palladacycles involves the role of nanosized Pd-containing species generated in situ during catalysis, in which, as with PdII complexes, no such particle is formed and Pd0 probably remains protected by the sulfur of the thienyl group. The Schiff bases used here were designed by the reaction of 2-thiophenemethylamine with 2-hydroxybenzophenone/2-hydroxy-4-methoxybenzophenone/2-hydroxyacetophenone (L1/L2/L3). Upon treatment with [PdCl2(CH3CN)2] and [Na2PdCl4] they gave palladacycles [PdL1/L2(CH3CN)Cl] (1/3) and palladium(II) complexes [Pd(L1/L2/L3)2] (2/4/5), respectively. Compounds L1–L3 and their complexes 1–5 were authenticated with 1H and 13C{1H} NMR spectroscopy, and HRMS. Single crystal structures of 1, 2, 4, and 5 reveal nearly square-planar geometry around Pd in each case. The PPh3/Hg poisoning and two-phase tests indicate that the catalysis is homogeneous for both the palladacycle and palladium complexes, probably through leaching of Pd0 from NPs in the case of the former. Catalysis of Suzuki coupling reactions with palladacycles (??0.001 mol-%) and palladium complexes (??0.01 mol-%) proceeds with and without nanoparticles.

Posted on 16 February 2015 | 4:50 pm

Formation of Cadmium Sulfide and Zinc Sulfide Mixture in the Interlayer Space of Montmorillonite

Cadmium sulfide and zinc sulfide (CdS and ZnS) were incorporated in sodium and cetyltrimethylammonium montmorillonites by the precipitation of sulfides from soluble metal sources in the presence of montmorillonites. The resulting hybrids were characterized by XRD, themogravimetric/differential thermal analysis (TG-DTA), TEM, Raman spectroscopy, and UV/Vis and photoluminescence spectroscopy. The absorption onsets owing to CdS and ZnS in cetyltrimethylammonium-montmorillonite appeared in a shorter wavelength region (311–520 nm) relative to that (309–484 nm) of the two semiconductors in sodium montmorillonite, thus reflecting the difference in the particle sizes of CdS and ZnS in the hybrids. The appearance of the broad emission bands combined with the bands centered at 469, 451, 440, and 431 nm owing to CdS and ZnS were attributed to the existence of both CdS and ZnS in the products. The difference in the emission intensity of the hybrids is discussed in terms of the role of the cetyltrimethylammonium cation. The unique optical properties of the two products were thought to occur through the interactions of sulfides with their environment (montmorillonite and cetyltrimethylammonium cation). A mixture of CdS and ZnS was prepared in unmodified and organically modified montmorillonite. The products showed emission bands owing to both CdS and ZnS. The blueshift of absorption onsets and the increase in PL intensity were caused by the confinement effect. CdS and ZnS formed separately in different interlayer spaces (segregation).

Posted on 13 February 2015 | 10:10 am

Microwave-Assisted Synthesis of Few-Layered TaTe2 and Its Application as Supercapacitor

We report a simple and rapid microwave-assisted synthesis of tantalum telluride (TaTe2) nanosheets. The ratio of tantalum pentachloride (TaCl5) and elemental tellurium (Te) powder were adjusted in the presence of NaBH4 in such a way as to obtain the TaTe2 nanosheet. The samples were characterized by various techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), UV/Vis spectroscopy, photoluminescence (PL) spectroscopy, and XRD. Our SEM, TEM, and AFM results show the formation of sheet-like morphology, while the XRD data confirms the high crystalline quality and stable phase of the TaTe2 formed. The supercapacitor cells were fabricated by using TaTe2 nanosheets as anode material, platinum metal wire as a counterelectrode, and Ag/AgCl as reference electrode. The calculated coulombic efficiency is more than 95?%, while the cycle-to-cycle decrease in capacity is less than 5?%. The maximum discharge or charging capacity is below 2.4 W?h/kg, which is an ideal characteristic for achieving supercapacitor behavior. The first experimental investigations on the use of microwave to synthesize atomically thin few-layer TaTe2 nanosheets are described. This material also shows good performance as a supercapacitor.

Posted on 12 February 2015 | 7:10 pm

Synthesis of CpM(CO)3–DAB and –PAMAM Dendrimer Conjugates and Preliminary Evaluation of Their Biological Activity

Dendrimers of different generations and core structures [diaminobutane poly(propylenimine) (DAB) G1, G2, G3; poly(amidoamine) (PAMAM) G1] were chosen as carriers for bioactive organometallic half-sandwich complexes of the type CpM(CO)3 (Cp = cyclopentadienyl, M = Mn or Re) to study the influence of these parameters on their biological activity against cancer cells. Structure–activity relationships were determined by variation of the metal center as well as the type, molecular weight, and number of terminal functional groups of the dendrimer conjugates. All conjugates were characterized by IR and NMR spectroscopy as well as HPLC. Their biological activity was determined on MCF-7 human breast cancer cells by the resazurin assay. Interestingly, the most-active compounds were the first-generation dendrimer conjugates. The Mn and Re series showed nearly the same activities. Thus, the cytotoxicity of the dendrimer conjugates does not seem to directly correlate with the type or number of terminal functional groups. Rather, it points to a mechanism of action that is different from that previously observed for peptide conjugates with similar CpM(CO)3 functional groups. Dendrimers of different generation and core structure are used as carriers for bioactive organometallic half-sandwich complexes of the type CpM(CO)3 (Cp = cyclopentadienyl, M = Mn or Re). Interestingly, the most-active compounds are the first-generation dendrimer conjugates, and the influence of the metal center is much less pronounced.

Posted on 12 February 2015 | 7:10 pm

Intercalates of Strontium Phenylphosphonate with Alcohols – Structure Analysis by Experimental and Molecular Modeling Methods

Alcohol intercalated strontium phenylphosphonates were prepared by the addition of alcohols to an aqueous solution of strontium phenylphosphonate (SrPhP). These intercalates are unstable and de-intercalate spontaneously at ambient conditions. For the complete elucidation of their structure, a combination of a single-crystal X-ray diffraction and molecular modeling was used. The structure of the host layers in methanol (SrPhP·MeOH) and ethanol (SrPhP·EtOH) intercalates is composed of strontium atoms, which are eight-coordinate by oxygen atoms of the phosphonato groups and of water molecules. The structures of SrPhP·MeOH and SrPhP·EtOH differ in the orientation of the phenyl rings. The alcohol molecules reside in the cavities formed by the phenyl rings and are coordinated to the Sr atoms of the host layer through their oxygen atoms. On the basis of the structure of SrPhP·EtOH, the structures of propanol and butanol intercalates and of strontium phenylphosphonate dihydrate (SrPhP·2H2O) were modeled. The proposed model of SrPhP·2H2O, which features three kinds of water molecules, elucidates the temperature- and humidity-dependent behavior of the compound. Structures of alcohol intercalated strontium phenylphosphonates were suggested on the basis of a combination of single-crystal X-ray diffraction data and molecular modeling.

Posted on 11 February 2015 | 3:50 pm

Fundamental Aspects of Rare Earth Oxides Affecting Direct NO Decomposition Catalysis

The basic aspects of rare earth oxides (REOs) that affect their capacity for direct NO decomposition catalysis were investigated. A correlation between crystal structure and catalytic activity was found, which is related to the NO adsorption ability of the REOs. The crystal structure was the most important factor affecting direct NO decomposition over REOs, since the adsorption of NO was significantly dependent on the coordination environments of the rare earth cations within each crystal lattice. Among the REOs, cubic C-type oxides showed higher NO decomposition activities than those of the others. Within a series of C-type cubic REOs, the activity was typically dominated by the density of the surface basic sites, and the effects of particle morphology and lattice parameters were small. Among four fundamental factors (crystal structure, lattice parameters, particle morphology, and the density of basic sites), crystal structure is the aspect that most significantly affects direct NO decomposition activities of rare earth oxides (REOs), and the density of basic sites ranks second in importance to crystal structure.

Posted on 3 February 2015 | 10:40 am

Ionic Ferrocene-Based Burning-Rate Catalysts with Polycyano Anions: Synthesis, Structural Characterization, Migration, and Catalytic Effects during Combustion

Alkylferrocene-based burning-rate (BR) catalysts, have a high tendency to migrate during curing and storage due to their neutral and nonpolar nature. To overcome these drawbacks, fifteen novel ionic compounds, 1-(ferrocenylmethyl)imidazolium paired with polycyano anions, were synthesized and characterized. The structures of eleven of the compounds were confirmed by single-crystal X-ray diffraction. Compound 1 crystallizes in the tetragonal space group I4(1)/a; 2, 12 and 15 crystallize in the monoclinic space group P21/c, and 3 in the monoclinic space group P21/n; 4, 6–8, 13 and 14 crystallize in the triclinic space group P$\bar {1}$. Cyclic voltammetry investigations suggested that most of the compounds exhibit quasireversible redox systems. Compounds 1–10 have high thermal stability (> 190 °C). Migration studies revealed that these compounds are low-migratory materials. The thermal degradation of ammonium perchlorate (AP), hexogen (RDX), and octogen (HMX) catalyzed by these compounds was evaluated by differential scanning calorimetry (DSC) and by thermogravimetric (TG) techniques. The results show that the decomposition peak temperature of AP shifts downwards dramatically and that the released heat of AP increases significantly with the new compounds as additives (5 wt.-%). Moreover, the ionic compounds exhibit significant effects on the thermal decomposition of RDX. The catalytic activities of the new compounds are higher than those of their nitrate and picrate analogues, which supports the conclusion that high nitrogen content in a ferrocene-based BR catalyst is favorable for its combustion catalytic activity. Fifteen polycyano-based ionic ferrocene compounds were prepared and structurally characterized. The compounds exhibit low migration tendency and highly catalytic effects on thermal decomposition of ammonium perchlorate (AP), hexogen (RDX), and octogen (HMX).

Posted on 30 January 2015 | 8:43 am

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