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Three unique mixed-valence polyoxofluorovanadate clusters have been synthesized through a facile preparation process. The structure of these clusters is controlled by the addition of organic ligands. Single-crystal X-ray diffraction revealed that the clusters have the formula (XyH2)4[VV10VIV4O14(μ-O)10(μ3-O)10(μ3-F)2F4] (1), (Xy = m-xylylenediamine), (pyH)4(H)2[VV10VIV2O12(μ-O)8(μ3-O)10(μ3-F)2(pic)2] (2) and (pyH)4(H)3(Na+)[VV7VIV2O9(μ-O)8(μ3-O)4(μ5-F)(pic)4]2 (3), (py = pyridine, pic− = picolinate), with 2 and 3 representing the first examples of polyoxofluorovanadate clusters coordinated to a chelating ligand. The electron paramagnetic resonance (EPR) spectroscopy of 1 revealed that the spins of the VIV centers are coupled to each other, in contrast to the isolated spins of the isostructural [VV12VIV2O16(μ-O)10(μ3-O)10(μ3-F)2(L)2]6−, where L: im = imidazole (4) py (5). The trigonal bipyramidal coordinated VV atoms of 1, 4 and 5 mimic the structure of the active site of the vanadium dependent peroxidases and 4 and 5 exhibit peroxidase like activity. 43 45 17595 17602

Mixed-valent polyoxometalate (POM) clusters are one of the most interesting host species, showing a wide range of structural features and properties. The facile preparation and functionalisation of a mixed-valent polyoxofluorovanadates is reported, where two electrons are trapped to antipodal sites of the clusters. The first members of this family of clusters with the general formula, [VV12VIV2O16(?-O)10(?3-O)10(?3-F)2(L)2]6?, where L: py=pyridine?(1) pyr=pyrazine?(2) im=imidazole?(3), are unique organic-inorganic hybrids with the addition of a N-donor ligand at either end of the polyoxofluorovanadate. The composition and connectivity of 1?3 were characterised by single-crystal X-ray diffraction and electrospray ionisation mass spectrometry. Electron paramagnetic resonance spectroscopy revealed that the two well-separated VIV ions in each cluster are fully uncoupled with J=0, giving a degenerate singlet?triplet ground state. This attenuation of the exchange interaction is probed with density functional theoretical calculations that reveal that the inclusion of the fluoride ion in the cluster produces a bond pathway biased toward destructive interference between competing ferromagnetic and antiferromagnetic interactions. These robust molecular materials are the ideal combination of desirable electronic properties, with an organic handle with which they can be integrated into spintronic circuitry for molecular devices. 24 15 3836 3845

In recent years, the crystal engineering library has been enriched with a number of previously unrecognized or unnoticed intermolecular interactions, such as agostic, tetrel, chalcogen, pnicogen bonding and chelate ring stacking – collectively referred to as “unconventional interactions”. Many open questions remain unaddressed regarding their ability to form synthon interactions, specificity, and cooperativity, for example with π–π stacking interactions. In this work, we throw light on the formation of chelate ring stacking in metal–organic assemblies of nicotinohydrazide ligands (N′-(1-(2-pyridyl)ethylidene)nicotinohydrazide (HL) and N′-(phenyl(pyridin-2-yl)methylene)nicotinohydrazide (HL1)) with mercury(II) halide (HgBr2, HgI2) salts. Their reaction produced five compounds, namely [Hg(μ-L)BrHgBr2]n (1), [Hg(μ-L1)Br]n (2), [Hg(L)I2] (3), [Hg(HL1)I2]·(CH3OH) (4), and [Hg(μ-L1)I]n (5). Crystal structure analysis reveals that chelate ring stackings are formed in four of the reported metal–organic compounds, and are common also in the literature precedents. The energies of chelate ring stackings and π–π heterocycle stackings have been computed and analyzed by means of DFT calculations, and the results were verified using Bader's theory of “atoms in molecules”. These results provide a rationale for preferential formation of both unconventional and conventional stackings and allow us to conclude that chelate ring interaction may be considered as a synthon interaction for nicotinohydrazide metal complexes. Interpretations for packing differences imposed by the substituent effect (substitution of methyl group in HL for phenyl group in HL1) were provided based on the Hirshfeld surface analysis and 2D fingerprint plots of the crystal structures reported here. 20 8 1065 1076

Reaction of the cyclic ligand (2Z,6Z)-piperidine-2,6-dione dioxime with TiCl4 and KOH yielded the hexanuclear cluster K6[TiIV6(μ3-O)2(μ2-O)3(CH3O)6(μ2–η1,η1,η2-Hpidiox-O,N,O′)4(μ2–η1,η1,η2-pidiox-O,N,O′)2]·7.5CH3OH possessing a new {Ti6O5} structural motif. The cluster core {Ti6O5} is wrapped by external tripodal imide dioxime ligands, showing good solubility and stability and thus, allowing its solution to be studied by means of electrospray ionization mass spectrometry, electrochemistry and 2D NMR, c. w. EPR and UV-vis spectroscopies. Density Functional Theory (DFT) calculations reveal that the cyclo-Ti3 metallic cores exhibit metallaromaticity which is expected to contribute to the stabilization of this system. 48 17 5551 5559

The activation of dioxygen by metal ions is critical in chemical and bio-chemical processes. A scientific challenge is the elucidation of the activation site of dioxygen in some copper metalloproteins, which is either the metal center or the substrate. In an effort to address this challenge, we prepared a series of new copper(ii) complexes (1·2H2O, 2·CH3OH, 3) with bio-inspired amidate ligands and investigated their activity towards dioxygen activation. The secondary amine group ligated to copper(ii) of the complex 1·2H2O in methyl alcohol is oxidized (2e-) by air dioxygen in a stepwise fashion to an imine group, affording complex 2. The copper(ii) complex 2 in methyl alcohol induces the 4e- oxidation by air dioxygen of the imine functionality ligated to copper(ii) to an azinate group, resulting in the isolation of a dinuclear azinate copper(ii) compound (4). Experimental and computational studies, including X-band c. w. EPR, UV-vis and ESI-MS spectroscopy and density functional theory computations, indicate a direct attack of the dioxygen on the -HC[double bond, length as m-dash]N- group ligated to copper(ii), and a possible mechanism of the oxidation of the -HC[double bond, length as m-dash]N- functionality ligated to copper(ii) to an azinate group is provided. This unprecedented activation of dioxygen by a copper substrate paves the way for further exploration of the O2 activation mechanisms in enzymes and the development of effective catalysts in O2-involved green organic synthesis.

The development of ligands with high selectivity and affinity for uranium is critical in the extraction of uranium from human body, radioactive waste, and seawater. A scientific challenge is the improvement of the selectivity of chelators for uranium over other heavy metals, including iron and vanadium. Flat ligands with hard donor atoms that satisfy the geometric and electronic requirements of the UVIO22+ exhibit high selectivity for the uranyl moiety. The bis(hydroxylamino)(triazine) ligand, 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (H2bihyat), a strong binder for hard metal ions (FeIII, TiIV, VV, and MoVI), reacted with [UVIO2(NO3)2(H2O)2]·4H2O in aqueous solution and resulted in the isolation of the complexes [UVIO2(bihyat)(H2O)], [UVIO2(bihyat)2]2–, and {[UVIO2(bihyat)(μ-OH)]}22–. These three species are in equilibrium in aqueous solution, and their abundance varies with the concentration of H2bihyat and the pH. Reaction of H2bihyat with [UVIO2(NO3)2(H2O)2]·4H2O in CH3CN gave the trinuclear complex [UVI3O6(bihyat)2(μ-bihyat)2]2–, which is the major species in organic solvents. The dynamics between the UVIO22+ and the free ligand H2bihyat in aqueous and dimethyl sulfoxide solutions the metal binding ability of the H2bihyat over pyridine-2,6-dicarboxylic acid (H2dipic) or glutarimidedioxime for UVIO22+, and the selectivity of the H2bihyat to bind UVIO22+ in comparison to VVO43– and FeIII in either UVIO22+/VVO43– or UVIO22+/FeIII solutions were examined by NMR and UV–vis spectroscopies. The results revealed that H2bihyat is a superior ligand for UVIO22+ with high selectivity compared to FeIII and VVO43–, which increases at higher pHs. Thus, this type of ligand might find applications in the extraction of uranium from the sea and its removal from the environment and the human body. 57 13 7631 7643

Five new Pb(II) complexes of hydrazone-based and Schiff-based ligands and three different anionic co-ligands (azide, thiocyanate and bromide) have been synthesized and characterized by structural, analytical and spectroscopic methods. This variety of ligands can coordinate to the Pb(II) metal center in a tridentate or tetradentate fashion via a different combination of any of nitrogen, oxygen and sulphur donor atoms. Moreover, the organic ligands can be in mono-deprotonated or neutral forms. By using single-crystal X-ray crystallography, we show that the synthesized complexes aggregate into larger supramolecular entities due to the formation of noncovalent tetrel bonding interactions. The Pb(II) center is hemidirectionally coordinated even in those complexes where the coordination number is six. Consequently, this is sterically ideal for establishing tetrel bonding interactions with electron-rich nitrogen, bromide or sulphur atoms. These contacts are significantly larger than the sums of the covalent radii. Hence, they can be described as non-covalent tetrel bonding interactions. They interconnect the covalently bonded units into supramolecular assemblies (dimers or tetramers). The contribution of contacts involving the Pb atom has been studied using Hirshfeld surface analysis and fingerprint plots. We have analysed the supramolecular assemblies observed in the solid state by means of DFT calculations and characterized them using Bader's theory of atoms-in-molecules. 20 34 5033 5044

The objective of the present work was the geographical discrimination of the most common honeydew honeys produced in Greece, namely pine and fir, on the basis of sugar, free amino acid and organic acid content, determined by nuclear magnetic resonance spectroscopy (1H NMR) and high-performance liquid chromatography (HPLC), along with moisture content, sugar ratios, or sugars to moisture ratio, using chemometrics. For this purpose, 39 pine and 31 fir honey samples were collected from professional beekeepers from eight different regions in Greece. Data were subjected to multivariate analysis and modeled using supervised statistical methods. The combination of 1H NMR and HPLC based on metabolites along with the aforementioned physicochemical data resulted in the geographical discrimination of pine and fir honeys. Respective prediction rates were 76.9 and 80.6%, using a model validation technique: the cross-validation method. Present results support the combined use of instrumental and conventional methods for honey geographical origin differentiation. 244 7 1249 1259

Although, the investigation of the interactions of MoVI ion with the “non-innocent” phenols/hydroquinones is essential for the understanding of the role of molybdenum in the biological systems, the MoVI complexes of phenolate/hydroquinonate and their functionalized variants remain mainly unexplored. Reaction of Na2MoVIO4 with tripod iminodiacetate phenol/hydroquinone ligands in aqueous solutions resulted in the synthesis of mononuclear phenolate/hydroquinonate and dinuclear bridged-hydroquinonate cis-MoVIO22+ complexes. The new complexes were isolated and characterized in solid state by X-ray crystallography. The 1H, 13C and 95Mo NMR spectra of the aqueous solutions of the complexes show that they retain their structure at the pD range 2–4, with the dinuclear bridged-hydroquinonate cis-MoVIO22+ to form two isomers which are in dynamic equilibrium. At pDs 4–7 the MoVI-Ophenolate bond of the cis-MoVIO22+ compounds hydrolyzes to form MoVIO3-iminodiacetate species. Variable temperature (VT) and 2D {1H} EXSY NMR spectroscopies where employed for the determination of the thermodynamic and activation parameters of the isomerization reaction between the dinuclear bridged-hydroquinonate cis-MoVIO22+ isomers. The exchange mechanism between cis-MoVIO22+ and the MoVIO3 species were also investigated by 2D {1H} EXSY NMR spectroscopy. Despite of the higher strength of the MoVI-Ophenolate bond, it is more labile than the MoVI-Ocarboxylate bond. The rate determining step of the above exchange reactions was found to be the dissociation of the phenolate/hydroquinonate oxygen atom from MoVI ion.

Although directly relevant to metal mediated biological nitrification and the coordination chemistry of peroxide, the transition metal complexes of hydroxylamines and their functionalized variants remain mainly unexplored except vanadium(V) and molybdenum(VI). Reaction of the chelating hydroxylamine ligand 3,3′-(hydroxyazanediyl)dipropanamide (Hhydia) with [MII(CH3COO)2]·xH2O (M = CoII, ZnII) in methyl alcohol solution yields the complexes [CoII(η1:η1-CH3COO)(η1-CH3COO)(Hhydia)], (1) and [ZnII(η1-CH3COO)2(Hhydia)], (4), while reaction of Hhydia with trans-[NiIICl2(H2O)4]·2H2O yields [NiII(Hhydia)2]Cl2 (3). The X-ray structure analysis of 1 and 4 revealed that the CoII and ZnII atoms are bonded to a neutral tridentate O,N,O-Hhydia ligand and a chelate and a monodentate acetate groups in a severely distorted octahedral geometry for 1 and two monodentate acetate groups for 4 in a highly distorted trigonal bipyramidal geometry (τ = 0.63). The X-ray structure analysis of 3 revealed that the nickel atom in [NiII(Hhydia)2]2+ is bonded to two neutral tridentate O,N,O-Hhydia ligands. The twist angle, θ, in [NiII(Hhydia)2]2+ is 55.1(2)°, that is, very close to an ideal octahedron. The metal/Hhydia complexes were studied by UV–Vis (cobalt and nickel compounds), NMR (zinc compounds), HR-MS spectroscopy. The 1H and 13C NMR spectra of the methyl alcohol or acetonitrile solutions of ZnII-Hhydia complexes show the existence of both the 1:1 and 1:2 metal:ligand species being in dynamic equilibrium. The exchange processes between the ZnII-Hhydia is through complete dissociation-association of the ligand from the complexes as it is evident from the 2D {1H} EXSY NMR spectroscopy. UV–Vis spectroscopy of the CoII-Hhydia in methyl alcohol also shows the existence of both the 1:1 and 1:2 metal:ligand species in contrast to 1:2 complex [NiII(Hhydia)2]2+ which is the only species found in solution. The NMR and UV–Vis observations are additionally supported by the HR-MS studies. 151 417 425

Reaction of hydroxylamine hydrochloride with prop-2-enamide in dichloromethane in the presence of triethylamine resulted in the isolation of the N,N′-disubstituted hydroxylamine-(diamido) ligand, 3,3′-(hydroxyazanediyl)dipropanamide (Hhydia). The ligand Hhydia was characterized by multinuclear NMR, high-resolution electrospray ionization mass spectrometry (ESI-MS), and X-ray structure analysis. Interaction of Hhydia with trans-[CrIIICl2(H2O)4]Cl·2H2O in ethanol yields the ionization isomers [CrIII(Hhydia)2]Cl3·2H2O(1·2H2O) and cis/trans-[CrIIICl2(Hhydia)2]Cl·2H2O (2·2H2O). The X-ray structure analysis of 1 revealed that the chromium atom in [CrIII(Hhydia)2]3+ is bonded to two neutral tridentate O,N,O-Hhydia ligands. The twist angle, Î, in [CrIII(Hhydia)2]3+ is 54.5(6)0, that is, very close to an ideal octahedron. The intramolecular hydrogen bonds developed between the N-OH group of the first ligand and the amidic oxygen atom of the second ligand and vice versa contribute to the overall stability of the cation [CrIII(Hhydia)2]3+. The reaction rate constant of the formation of Cr(III) complexes 1·2H2O and 2·2H2O was found to be 8.7(±0.8) × 10-5 M-1 s-1 at 25 °C in methyl alcohol and follows a first-order law kinetics based on the biologically relevant ligand Hhydia. The reaction rate constant is considerably faster in comparison with the corresponding water exchange rate constant for the hydrated chromium(III). The modification of the kinetics is of fundamental importance for the chromium(III) chemistry in biological systems. Ultraviolet-visible and electron paramagnetic resonance studies, both in solution and in the solid state, ESI-MS, and conductivity measurements support the fact that, irrespective of the solvent used in the interaction of Hhydia with trans-[CrIIICl2(H2O)4]Cl·2H2O, the ionization isomers[CrIII(Hhydia)2]Cl3·2H2O (1·2H2O) and cis/trans-[CrIIICl2(Hhydia)2]Cl·2H2O (2·2H2O) are produced.The reaction medium affects only the relevant percentage of the isomers in the solid state. The thermodynamic stability of the ionization isomers 1·2H2O and cis/trans-2·2H2O, their molecular structures as well as the vibrational spectra and the energetics of the CrIII- Hhydia/hydia- were studied by means of density functional theory calculations and found to be in excellent agreement with our experimental observations. © 2014 American Chemical Society. 53 21 11404 11414

A new two-electron photosensitizer, H2BBQ2+[ZnCl4]2−/[(ZnCl)2(μ-BBH)] (BBQ stands for 2,5-bis[bis(pyridin-2-ylmethyl)amino]-1,4-quinone and BBH stands for 2,5-bis[bis(pyridin-2-ylmethyl)amino]-1,4-hydroquinone), has been synthesized and the oxidation state of the ligand was determined by X-ray crystallography and NMR spectroscopy. Under light illumination the H2BBQ2+[ZnCl4]2− + ZnCl2 is reduced quantitatively to [(ZnCl)2(μ-BBH)] (pH ∼ 5) oxidizing H2O to H2O2 as is evident by trap experiments. Electrochemistry gave a reversible two-electron ligand-centered redox wave for [(ZnCl)2(μ-BBH)]. UV-Vis, luminescence and EPR spectroscopies reveal the slow formation of a stable quinone diradical, intermediate of the reaction. DFT calculations are in agreement with the proposed mechanism. Based on this property an aqueous {[(ZnCl)2(μ-BBH)] H2O2} solar rechargeable galvanic cell has been constructed. © The Royal Society of Chemistry. 46 11 3688 3699

New Eu3+, Sm3+ and Gd3+ complexes of triazine ligands 2,4,6-tri(2-pyridyl)-1,3,5-triazine, 3,5,6-tri(2-pyridyl)-1,2, 4-triazine and 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine were synthesized. The structure of five of them was established by single crystal X-ray crystallography. Various aspects of the triazine ligands such as steric interactions, deviation from the planarity and coordination mode define the structure of the complexes. The 1H NMR spectra of the solutions of Eu3+ and Sm3+ molecules showed broad paramagnetic shifted peaks assigned to the protons of the ligated triazines. The powder EPR spectra of the Gd3+ complexes exhibited a broad peak centered at g = 2. All Eu3+ and Sm3+ complexes display characteristic lanthanide emission upon UV excitation. The enhancement of the luminescence is attributed to the effective energy transfer from the triazine ligand to the lanthanide ion. 1,2,4-Triazines show to be better sensitizers for Eu3+ and Sm 3+ than the 1,3,5-triazine ligand. Co-coordination of the triazines with β-diketonate ligands further enhances the luminescence of the lanthanides. This enhancement was attributed to the synergistic effect of the two ligands and/or the decrease of the vibrational quenching processes. 52 856 865 Cited By :12

Reaction of the oxidovanadium(IV)-LN-N species (LN-N is bipy = 2,2′-bipyridine or bipy-like molecules) with either BF4- or HF and/or KF results in the formation of compounds of the general formula cis-[VIV(=O)(F)(LN-N)2]+. Structural and spectroscopic (electron paramagnetic resonance) characterization shows that these compounds are in the tetravalent oxidation state containing a terminal fluorido ligand. Density functional theory calculations reveal that the VIV-F bond is mainly electrostatic, which is reinforced by reactivity studies that demonstrate the nucleophilicity of the fluoride ligand in a halogen exchange reaction and in fluorination of various organic substrates. © 2016 American Chemical Society. 55 4 1364 1366 Cited By :2

Four europium complexes with enhanced luminescent properties have been synthesized. Thin transparent films of the complexes were prepared on glass panes and then were examined as efficient luminescent solar concentrators for full spectrum utilization in crystalline silicon photovoltaic cells. The complexes could behave as efficient solar concentrators since they absorb UV light, where the spectral response of the crystalline silicon solar cells is low and they emit at 615 nm where the spectral response is maximum. The glass panes covered with europium complexes act as planar waveguides of the emitted light that is collected by the solar cells, which are attached to the edges of the solar concentrators. The europium complexes as solar concentrators were examined in terms of the optimum concentrations and the number of coatings, which were determined in order to evaluate the maximum performance of the solar cells. The case of multiple glass panes with europium complexes was also examined while a 28% maximum increase in the photocurrent was finally established. © 2011 Elsevier B.V. 131 8 1776 1781

Reaction of NH4VO3 with (phenolate/hydroquinonate) iminodiacetate tripod ligands in aqueous solution in the pH range 7–8 results in the isolation of three new dioxido vanadium(V) complexes, one dinuclear (NH4)4{(VVO)2[μ-bicah(6-)-N,O,O,O]}·8H2O, (H6bicah, 2,5-bis[N,N'-bis(carboxymethyl)aminomethyl]-hydroquinone), and two mononuclear (NH4)2{(VVO)2[Hcah(3-)-N,O,O,O]·2H2O, (H4cah, 2-[N,N'-bis(carboxymethyl)aminomethyl]-hydroquinone) and (NH4)2{(VVO)[Hcacp(3-)-N,O,O,O]}·4H2O, (H4cacp, 2-[N,N'-bis(carboxymethyl)aminomethyl]-4-carboxyphenol). The 51V, 1H, and 13C NMR spectra in D2O show the coordination environment of vanadium in the above complexes to be octahedral, with four out of six positions to be occupied by the two carboxylate oxygen, one hydroquinonate oxygen, and one amine nitrogen atoms of the tripod ligand. The two acetate arms are in cis position to each other. Variable-temperature 1H and 13C NMR measurements show that the complexes are kinetically labile. An intramolecular exchange that proceeds through the opening of the phenolate/hydroquinonate chelate ring has been revealed by 2D{1H} NMR EXSY (exchange spectroscopy).

New donor-acceptor (ETOEDT-PDT-TTF)2I3 salt showing the layered structure was synthesized and spectrally characterized. It was shown that unsymmetrical (1,4-thioxane-2,3-diyldithio)-propylenedithiotetrathiafulvalene (ETOEDT-PDT-TTF) donor molecule with its extended shape and flexible form is a good system for salts preparation with numerous short contacts and strong intermolecular interactions. Both, Raman and infrared spectra of the donor and its iodine salt were analyzed and discussed. Important role of C{double bond, long}C vibrations was stressed. © 2008 Elsevier B.V. All rights reserved. 887 1-3 67 74

Corrosiveness is one of the main drawbacks of using the iodide/triiodide redox couple in dye-sensitized solar cells (DSSCs). Alternative redox couples including transition metal complexes have been investigated where surprisingly high efficiencies for the conversion of solar to electrical energy have been achieved. In this paper, we examined the development of a DSSC using an electrolyte based on square pyramidal oxidovanadium(IV/V) complexes. The oxidovanadium(IV) complex (Ph4P)2[VIVO(hybeb)] was combined with its oxidized analogue (Ph4P)[VVO(hybeb)] {where hybeb4- is the tetradentate diamidodiphenolate ligand [1-(2-hydroxybenzamido)-2-(2-pyridinecarboxamido)benzenato}and applied as a redox couple in the electrolyte of DSSCs. The complexes exhibit large electron exchange and transfer rates, which are evident from electron paramagnetic resonance spectroscopy and electrochemistry, rendering the oxidovanadium(IV/V) compounds suitable for redox mediators in DSSCs. The very large self-exchange rate constant offered an insight into the mechanism of the exchange reaction most likely mediated through an outer-sphere exchange mechanism. The [VIVO(hybeb)]2-/[VVO(hybeb)]- redox potential and the energy of highest occupied molecular orbital (HOMO) of the sensitizing dye N719 and the HOMO of [VIVO(hybeb)]2- were calculated by means of density functional theory electronic structure calculation methods. The complexes were applied as a new redox mediator in DSSCs, while the cell performance was studied in terms of the concentration of the reduced and oxidized form of the complexes. These studies were performed with the commercial Ru-based sensitizer N719 absorbed on a TiO2 semiconducting film in the DSSC. Maximum energy conversion efficiencies of 2% at simulated solar light (AM 1.5 1000 W m-2) with an open circuit voltage of 660 mV, a short-circuit current of 5.2 mA cm-2, and a fill factor of 0.58 were recorded without the presence of any additives in the electrolyte. © 2015 American Chemical Society. 54 8 3979 3988 Cited By :10

The reaction of 2,5-bis[N,N′-bis(2-pyridyl-aminomethyl)aminomethyl]-p-hydroquinone (H2bpymah) with VO2+ salts in acetonitrile or water at a low pH (2.2-3.5) results in the isolation of [{VIV(O)(Cl)}2(μ-bpymah)], the p-semiquinonate complex [{VIV(O)(Cl)}2(μ-bpymas)](OH), the cyclic mixed-valent hexanuclear compound [{VV(O)(μ-O)VIV(O)}(μ-bpymah)]3, and [(VVO2)2(μ-bpymah)]. [{VIV(O)(Cl)}2(μ-bpymas)](OH) is an intermediate of the radical-mediated oxidation of [{VIV(O)(Cl)}2(μ-bpymah)] from O2. At lower pH values (2.2), a reversible intramolecular electron transfer from the metal to the ligand of [{VIV(O)(Cl)}2(μ-bpymas)](OH) is induced with the concurrent substitution of chlorine atoms by the oxygen-bridging atoms, resulting in the formation of [{VV(O)(μ-O)VIV(O)}(μ-bpymah)]3. The metal complexes were fully characterized by X-ray crystallography, infrared (IR) spectroscopy, and magnetic measurements in the solid state, as well as by conductivity measurements, UV-vis spectroscopy, and electrochemical measurements in solution. The oxidation states of the metal ions and ligands were determined by the crystallographic data. The [{VIV(O)(Cl)}2(μ-bpymah)]-[{VIV(O)(Cl)}2(μ-bpymas)](OH) redox process is electrochemically reversible. The VIV ion in the semiquinonate compound exhibits a surprisingly low oxophilicity, resulting in the stabilization of OH- counterions at acidic pH values. An investigation of the mechanism of this reaction reveals that these complexes induce the reduction of O2 to H2O2, mimicking the activity of enzymes incorporating two redox-active centers (metal-organic) in the active site. © 2015 American Chemical Society. 54 15 7218 7229 Cited By :7

A simple donor atom additivity relationship has been used to calculate the donor atom electrochemical contribution (DEC) of the Oac (acetylacetonate-enolic oxygen), OPh (phenolic oxygen), SPh (mercaptophenol sulfur), Nam (deprotonate amide nitrogen), Nim (imine nitrogen) and Npy (pyridine nitrogen) to the redox processes of the square pyramidal vanadyl complexes. The study focuses on the amidate vanadyl complexes because of (a) their biological interest and (b) the existence of data from plethora complexes studied in great details. The electrochemical contributions for the vanadyl oxidation and reduction processes increase following the same order, OPh ~ Oac(enolic) Ph ~ Nam im py. These values predict the electrochemical potentials of square pyramidal vanadyl complexes with high accuracy. Octahedral complexes with the same equatorial environment show significant shift of the oxidation potentials to lower values. The DEC influence to the square pyramidal vanadyls' electrochemical potentials has been evaluated. © 2015 Elsevier Inc. All rights reserved. 147 39 43 Cited By :5

An organic light emitting diode (OLED) emitting reddish-orange light has been constructed using a Sm 3+ complex, composed of 4,4,4-trifluoro-1-phenyl-1,3-butanedione and 1,10-phenanthroline, as emitting layer and poly(vinylcarbazole) (PVK) and 2-(4-biphenylyl)-5-(4- tert -butylphenyl)-1,3,4-oxadiazole (PBD) as hole and electron transporters, respectively. Photoluminescence (PL) spectra suggest that energy pumping is made through both Sm 3+ -complexed ligands and poly(vinylcarbazole) providing an efficient electroluminescent system.

A new VIII complex (1) of 2,5-bis[N,N-bis(carboxymethyl) aminomethyl]hydroquinone (bicah6-) was synthesized by reaction of H6bicah with two equivalents of VCl3 and six equivalents of base in aqueous solution. Crystallographic characterization shows the neutral complex to have a dinuclear hydroquinonate bridged structure. The octahedral environment of vanadium is occupied by the four (N, O, O, O) donor atoms in each binding site of the ligand and two H2O oxygen atoms. Addition of 2,2-bipyridine (bipy) in the reaction mixture resulted in the synthesis of a new dinuclear VIII-μ-bicah6- complex (2) containing a bipy chelated to each vanadium center. The structure of 1 was compared with the respective dinuclear structures of the bicah6- complexes with V IVO2+ (3) and VVO2+ (4). Strong hydrogen bonds between the free, the ligated to vanadium water molecules and the carboxylate and hydroquinonate oxygen atoms result in supramolecular 3D structures by self-assembly of the dinuclear units. These structures are controlled by synthesis conditions and vanadium ion coordination environment. The cyclic voltammogram of 1 showed a reversible VIV+e -⇋VIII process at 0.48 V versus NHE. The EPR spectra of 3 gave a broad peak indicating magnetic interactions between the uncoupled electrons of the two vanadium centers through the hydroquinone bridge. In acidic pHs bellow 2.0, EPR data reveal protonation of the hydroquinonate oxygen and hydrolysis of the complex. The relation of these results with the reduction of VIV and stabilization of VIII ions is discussed. © 2014 Elsevier B.V. All rights reserved. 420 103 111 Cited By :3

Vanadium compounds mimic insulin actions in different cell types. The present study concerns the insulin-like effects of three vanadium(V) derivatives and one vanadium(IV) complex on osteoblast-like (UMR106 and MC3T3E1) cells in culture. The vanadium oxalate and vanadium citrate complexes hydrolyzed completely under the culture conditions, whereas more than 40% of the vanadium tartrate and nitrilotriacetate complexes remained. Vanadate, as well as vanadium oxalate, citrate, and tartrate complexes enhanced cell proliferation (as measured by the crystal violet assay), glucose consumption, and protein content in UMR106 and MC3T3E1 osteoblast- like cells. The vanadium nitrilotriacetate complex (the only peroxo complex tested) stimulated cell proliferation in UMR106 but not in MC3T3E1 cells. This derivative strongly transformed the morphology of the MC3T3E1 cells. All vanadium(V) compounds inhibited cell differentiation (alkaline phosphatase activity) in UMR106 cells. Our data are consistent with the interpretation that vanadium oxalate and citrate complexes hydrolyze to vanadate. Vanadium nitrilotriacetate would appear to be toxic for normal MC3T3E1 osteoblasts. In contrast, the vanadium tartrate complex induced a proliferative effect however, it did not alter cell differentiation. 338 1 7 14 Cited By :61

Reaction of an aqueous solution of NaVO3 or a methanol solution of [VO(acac)2] with 2,5-bis((bis(2-hydroxyethyl)amino)methyl) hydroquinone, H6bdeah, results in the formation of two major vanadium species characterized by X-ray crystallography: the [(V5+O) 2(bdeah)] and the [(V4.5+O)2(bdeas)S 2] (S = DMSO or MeOH). The vanadium ions in the two species have a trigonal pyramidal and an octahedral coordination sphere respectively. Variable temperature UV-Vis and 51V NMR spectroscopy as well as EPR and electrochemistry showed a temperature induced electron transfer. The diamagnetic [(V5+O)2(bdeah)] is the main species at high temperature. At low temperature one electron is transferred from the bdeah6- to the two vanadium centers resulting in the [(V4.5+O) 2(bdeas)S2] species [H5bdeas = 2,5-bis((bis(2-hydroxyethyl)amino)methyl)-1,4-semiquinone]. The thermodynamic parameters of this intramolecular electron transfer were calculated by UV-Vis (ΔH = -36 ± 2 kJ mol-1 and ΔS = -129 ± 5 J mol-1 K-1) and 51V NMR spectroscopy (ΔH = -37 ± 2 kJ mol-1 and ΔS = -109 ± 5 J mol -1 K-1). The electron transfer is a result of the large change of entropy which is associated with the ligation of the solvent molecules and the geometry change. EPR spectroscopy shows that most of the electron density in [(V4.5+O)2(bdeas)S2] is mainly located on the two vanadium ions.

Twelve Pr3+, Sm3+, Eu3+, Gd3+, Tb3+ and Dy3+ complexes of N-(pyridin-2-ylmethylene) picolinohydrazonate (phzp-) were synthesized by the Ln3+ assisted hydrolysis of 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine. Crystallographic characterization of Pr3+, Sm3+ and Eu3+ hydrazonate complexes with nitrate or trifluoroacetyleacetonate co-ligands shows them to have binuclear structures with a planar Ln2O2 core and the ligand to be in its mono-anionic form. Exception is the Pr 3+ complex with nitrate co-ligand, which is a mononuclear species containing the neutral hydrazone. Paramagnetic 1D 1H and 2D gCOSY and gNOESY-gEXSY 1H NMR spectroscopies revealed the presence of different isomers exhibiting a sterically controlled fluxional behavior. In addition, phzp- significantly enhances the luminescence of Eu 3+ and Tb3+. Magnetic measurements show antiferromagnetic coupling between the Ln3+ ions in the dinuclear complexes. The structural characterization of the complexes in both solid state and solution show the versatility of phzp- ligand to adopt various ligating motifs. © 2013 Elsevier Ltd. All rights reserved. 64 308 320 Cited By :3

The stability of 11 vanadium compounds is tested under physiological conditions and in administration fluids. Several compounds including those currently used as insulin-mimetic agents in animal and human studies are stable upon dissolution in distilled water but lack such stability in distilled water at pH7. Complex lability may result in decomposition at neutral pH and thus may compromise the effectiveness of these compounds as therapeutic agents Even well characterized vanadium compounds are surprisingly labile. Sufficiently stable complexes such as the VEDTA complex will only slowly reduce, however, none of the vanadium compounds currently used as insulin-mimetic agents show the high stability of the VEDTA complex. Both the bis(maltolato)oxovanadium(IV) and peroxovanadium complexes extend the insulin-mimetic action of vanadate in reducing cellular environments probably by increased lifetimes under physiological conditions and/or by decomposing to other insulin mimetic compounds. For example, treatment with two equivalents of glutathione or other thiols the (dipicolinato)peroxovanadate(V) forms 9dipicolinato)oxovanadate(V) and vanadate, which are both insulin-mimetic vanadium(V) compounds and can continue to act. The reactivity of vanadate under physiological conditions effects a multitude of biological responses. Other vanadium complexes may mimic insulin but not induce similar responses if the vanadate formation is blocked or reduced. We conclude that three properties, stability, lability and redox chemistry are critical to prolong the half-life of the insulin-mimetic form of vanadium compounds under physiological conditions and should all be considered in development of vanadium-based oral insulin-mimetic agents. © 1995 Kluwer Academic Publishers. 153 1-2 17 24 Cited By :81

Reaction of the N,N-disubstituted bis(hydroxylamino) ligand 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (H2bihyat) with cis-[MoVIO2(acac)2] in tetrahydrofuran resulted in isolation of the mononuclear compound cis-[MoVIO 2(bihyat)] (1). The treatment of Na2MoVIO 4·2H2O with the ligand H2bihyat in aqueous solution gave the dinuclear compounds cis-[MoVI 2O4(bihyat)2(H2O)2] (2) and trans-[MoVI2O4(bihyat)2(H 2O)2] (3) at pH values of 3.5 and 5.5, respectively. The structures for the three molybdenum(VI) compounds were determined by X-ray crystallography. Compound 1 has a square-pyramidal arrangement around molybdenum, while in the two dinuclear compounds, each molybdenum atom is in a distorted pentagonal-bipyramidal environment of two bridging and one terminal oxido groups, a tridentate (O,N,O) bihyat2- ligand that forms two five-membered chelate rings, and a water molecule trans to the terminal oxido group. The dinuclear compounds constitute rare examples containing the {Mo 2VIO2(μ2-O2)} 4+ moiety. The potentiometry revealed that the Mo VIbihyat2- species exhibit high hydrolytic stability in aqueous solution at a narrow range of pH values, 3-5. A subtle change in the coordination environment of the five-coordinate compound 1 with ligation of a weakly bound water molecule trans to the oxido ligand (1w) renders the equatorial oxido group in 1w more nucleophilic than that in 1, and this oxido group attacks a molybdenum atom and thus the dinuclear compounds 2 and 3 are formed. This process might be considered as the first step of the oxido group nucleophilic attack on organic substrates, resulting in oxidation of the substrate, in the active site of molybdenum enzymes such as xanthine oxidase. Theoretical calculations in the gas phase were performed to examine the influence of water on the dimerization process (1 → 2/3). In addition, the molecular structures, cis/trans geometrical isomerism for the dinuclear molybdenum(VI) species, vibrational spectra, and energetics of the metal-ligand interaction for the three molybdenum(VI) compounds 1-3 have been studied by means of density functional theory calculations. © 2012 American Chemical Society. 51 24 13138 13147 Cited By :3

Bisphosphonates are biologically relevant therapeutics for bone disorders and cancer. Reaction ofγ-chlorobutyric acid, phosphorus acid, and phosphorus trichloride without the use of solvent gave the tetrahydrofuranyl-2,2-bisphosphonate sodium salt (Na2H2L). TheNa2H2Lwas isolated, characterized in solution byH,C, andPNMR spectroscopy and in solid state by single X-Ray crystallography. The crystal structure showed that theNa2H2Lforms in the crystal infinite two-dimensional sheets stacked one parallel to the other. A comparison of the chelating properties ofH2L2−with similar hydroxyl bisphosphonate ligands shows that the strength of the Na–O(furanyl/hydroxyl) bond is directly related to the total charge of the ligand anion.

Although dogma states that vanadate is readily reduced by glutathione, cysteine, and other thiols, there are several examples documenting that vanadium(V)-sulfur complexes can form and be observed. This conundrum has impacted life scientists for more than two decades. Investigation of this problem requires an understanding of both the complexes that form from vanadium(IV) and (V) and a representative thiol in aqueous solution. The reactions of vanadate and hydrated vanadyl cation with 2-mercaptoethanol have been investigated using multinuclear NMR, electron paramagnetic resonance (EPR), and UV-vis spectroscopy. Vanadate forms a stable complex of 2:2 stoichiometry with 2-mercaptoethanol at neutral and alkaline pH. In contrast, vanadate can oxidize 2-mercaptoethanol this process is favored at low pH and high solute concentrations. The complex that forms between aqueous vanadium(IV) and 2-mercaptoethanol has a 1:2 stoichiometry and can be observed at high pH and high 2-mercaptoethanol concentration. The solution structures have been deduced based on coordination induced chemical shifts and speciation diagrams prepared. This work demonstrates that both vanadium(IV) and (V)-thiol complexes form and that redox chemistry also takes place. Whether reduction of vanadate takes place is governed by a combination of parameters: pH, solute- and vanadate-concentrations and the presence of other complexing ligands. On the basis of these results it is now possible to understand the distribution of vanadium in oxidation states (IV) and (V) in the presence of glutathione, cysteine, and other thiols and begin to evaluate the forms of the vanadium compounds that exert a particular biological effect including the insulin-enhancing agents, antiamoebic agents, and interactions with vanadium binding proteins. © 2010 American Chemical Society. 49 9 4245 4256 Cited By :59

Copper ions in the active sites of several proteins/enzymes interact with phenols and quinones, and this interaction is associated to the reactivity of the enzymes. In this study the speciation of theCu2+with iminodiacetic phenolate/hydroquinonate ligands has been examined by pH-potentiometry. The results reveal that the iminodiacetic phenol ligand forms mononuclear complexes withCu2+at acidic and alkaline pHs, and a binuclearOphenolate-bridged complex at pH range from 7 to 8.5. The binucleating hydroquinone ligand forms only 2 : 1 metal to ligand complexes in solution. The pK values of the protonation of the phenolate oxygen of the two ligands are reduced about 2 units after complexation with the metal ion and are close to the pK values for the copper-interacting tyrosine phenol oxygen in copper enzymes.

Reaction of the non-innocent dinucleating ligand 2,5-bis[N,N-bis(carboxymethyl) aminomethyl]hydroquinone (H 6bicah) with VO (2+) and VO 4 (3-) salts in water in the pH range 2 to 4.5 provides a series of novel tetranuclear V (IV) and/or V (V) macrocycles with the main core consisting of the anions [V (V) 4O 4(mu-O) 2(mu-bicah) 2] (4-) isolated at pH = 2.5 and [V (IV) 2V (V) 2O 4(mu-O) 2(mu-bicas)(mu-bicah)] (5-) and [V (IV) 4O 4(mu-O) 2(mu-bicas) 2] (6-) isolated at pH = 4.5 (bicas (*5-) = 2,5-bis[N,N-bis(carboxymethyl) aminomethyl]- p-semiquinonate), whereas at pH = 2 the dinuclear [(V (IV)O) 2(OH 2) 2(mu-bicah)] (2-) was obtained. All vanadium compounds have been characterized, and the charge of the ligand has been assigned in solid state by X-ray crystallography and infrared spectroscopy. The structures of the tetranuclear anions consist of four vanadium atoms arranged at the corners of a rectangle with the two bridging bicas (*5-) and/or bicah (6-) ligands on the long and the two V (IV/V)-O-V (IV/V) bridges on the short sides of the rectangle. UV-vis, (51)V and (1)H NMR spectroscopy and electrochemistry showed that these complexes interconvert to each other by varying the pH. This pH induced redox transformation of the tetranuclear anions has been attributed to the shift of the reduction potential of the bicas (*5-) to higher values by decreasing the pH. The electron is transferred intramolecularly from the metal ion to the electron accepting semiquinones resulting in reduction of bicas (*5-) to bicah (6-) and concurrent oxidation of the V (IV) to V (V). The resulting complexes are further oxidized by atmospheric oxygen. This system as a model for the H (+) coupled redox reactions in metalloenzymes and its relevance is discussed briefly.

The reaction of Cu2+ acetate monohydrate with 2-[N,N′-bis(carboxymethyl)aminomethyl]-4-carboxyphenol (H 4cacp), 2-[N,N-bis(carboxymethyl)aminomethyl]hydroquinone (H 4cah) and the dinucleating 2,5-bis[N,N-bis(carboxymethyl)aminomethyl] hydroquinone (H6bicah) in water results in the formation of several Cu2+ species, which are in dynamic equilibrium in aqueous solution and their stability is pH dependent. A systematic crystallographic study of these species was pursued, resulting in the characterization of most of the species. Additional techniques were employed to characterize the molecules in the solid state (infrared spectroscopy) and in solution (UV-vis spectroscopy and electrochemistry). These measurements show that the Cu2+ ions are ligated mainly to the iminodiacetate at pH 6, the phenol oxygen was deprotonated and dinuclear-bridged species, from the phenolate oxygen complexes exhibiting a Cu2+2O2 core, were isolated. The coordination environment around the copper ions varies between trigonal bipyramidal, tetragonal pyramidal and distorted octahedral geometries. The two unpaired electrons of the Cu2+ ions are found to be antiferromagnetically coupled. A survey of the magnetic and structural properties of the dinuclear phenoxide bridged Cu2+ complexes shows that the strength of the antiferromagnetic coupling is linearly dependent on the Cu-Ophenolate bond lengths, at bond distances below 1.98 . The effect of the Cu-O-Cu angles on the magnetic properties of the complexes is also discussed. © The Royal Society of Chemistry 2008. 44 6188 6204 Cited By :25

Partial oxidation of an aqueous solution of CoIICl 2·6H2O with (NH4)6[Mo 7VIO24]·4H2O in the presence of (NH4)2SO3·H2O and LiCl, at pH ≈ 5.3, leads to isolation of the octanuclear cluster (NH 4)11(Li⊂[Co4IICo 4III(SO3)16(NH3) 8]·10H2O), 1. The structure of the anion of 1 consists of a central [Co4II], almost ideal square planar unit, and a pair of symmetry-related CoIII dimers above and below the Co4II plane grafting onto the tetramer by 16 bridging sulfite groups. The [Co8(SO3)16(NH 3)8]12- cluster encapsulates a lithium cation which lies at the center of the Co4II square. © 2008 American Chemical Society. 47 11 4451 4453 Cited By :19

The title compound was synthesized and its crystal structure was determined by X-ray diffraction analysis. The compound is monoclinic, space group P21/a with Z = 4. The unit-cell dimensions are a = 12.287(2)Å, b = 3.8287(5)Å, c = 16.0936(19)Å, b = 97.409° and V = 750.77(19)Å3. The R value is 0.0313 for 1223 observed reflections. Intermolecular hydrogen bonds of the type N-H···O and N-H···N were observed in the structure. 2008 © The Japan Society for Analytical Chemistry. 24 5 x103 x104 Cited By :6

Reaction of the ligand 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5- triazine (H2bihyat) with NaVVO3 in aqueous solution followed by addition of either Ph4PCl or C(NH 2)3Cl, respectively, gave the mononuclear vanadium(V) compounds Ph4P[VVO2(bihyat)]·1.5H 2O (1) and C(NH2)3[VVO 2(bihyat)] (2). Treatment of VIVOSO4· 5H2O with the ligand H2bihyat in methyl alcohol under specific conditions gave the oxo-bridged dimer [VV2O 2(μ2-O)(bihyat)2] (3). The structures for 1 and 3 were determined by X-ray crystallography and indicate that these compounds have distorted square-pyramidal arrangement around vanadium. The ligand bihyat2- is bonded to vanadium atom in a tridentate fashion at the pyridine-like nitrogen atom and the two deprotonated hydroxylamino oxygen atoms. The high electron density of the triazine ring nitrogen atoms, which results from the resonative contribution of electrons of exocyclic nitrogen atoms (Scheme 4), leads to very strong V-N bonds. The cis-[VVO 2(bihyat)]- species exhibits high hydrolytic stability in aqueous solution over a wide pH range, 3.3-11.0, as it was evidenced by 1H and 51V NMR spectroscopy and potentiometry. The high affinity of the H2bihyat ligand for the VVO 2+ unit, its tridentate character, as well as its small size, paves the way for potential applications in medicine, analysis, and catalysis for the C(NH2)3[VVO 2(bihyat)] compound. The molecular structures, vibrational and electronic spectra, and the energetics of the metal-ligand interaction for compounds 1 and 3 have been studied by means of density functional calculations. © 2008 American Chemical Society. 47 24 11698 11710 Cited By :17

Reaction of Na(2)Mo(VI)O(4) x 2H(2)O with (NH(4))(2)SO(3) in the mixed-solvent system H(2)O/CH(3)CN (pH = 5) resulted in the formation of the tetranuclear cluster (NH(4))(4)[Mo(4)(VI)SO(16)] x H(2)O (1), while the same reaction in acidic aqueous solution (pH = 5) yielded (NH(4))(4)[Mo(5)(VI)S(2)O(21)] x 3H(2)O (2). Compound {(H(2)bipy)(2)[Mo(5)(VI)S(2)O(21)] x H(2)O}(x) (3) was obtained from the reaction of aqueous acidic solution of Na(2)Mo(VI)O(4) x 2H(2)O with (NH(4))(2)SO(3) (pH = 2.5) and 4,4'-bipyridine (4,4'-bipy). The mixed metal/sulfite species (NH(4))(7)[Co(III)(Mo(2)(V)O(4))(NH(3))(SO(3))(6)] x 4H(2)O (4) was synthesized by reacting Na(2)Mo(VI)O(4) x 2H(2)O with CoCl(2) x 6H(2)O and (NH(4))(2)SO(3) with precise control of pH (5.3) through a redox reaction. The X-ray crystal structures of compounds 1, 2, and 4 were determined. The structure of compound 1 consists of a ring of four alternately face- and edge-sharing Mo(VI)O(6) octahedra capped by the trigonal pyramidal sulfite anion, while at the base of the Mo(4) ring is an oxo group which is asymmetrically shared by all four molybdenum atoms. Compound 3 is based on the Strandberg-type heteropolyion [Mo(5)(VI)S(2)O(21)](4-), and these coordinatively saturated clusters are joined by diprotonated 4,4'-H(2)bipy(2+) through strong hydrogen bonds. Compound 3 crystallizes in the chiral space group C2. The structure of compound 4 consists of a novel trinuclear [Co(III)Mo(2)(V)SO(3)(2-)] cluster. The chiral compound 3 exhibits nonlinear optical (NLO) and photoluminescence properties. The assignment of the sulfite bands in the IR spectrum of 4 has been carried out by density functional calculations. The cobalt in 4 is a d(6) octahedral low-spin metal atom as it was evidenced by magnetic susceptibility measurements, cw EPR, BVS, and DFT calculations. The IR and solid-state UV-vis spectra as well as the thermogravimetric analyses of compounds 1-4 are also reported.

Surface-active metalorganic complexes can be used to construct organic thin films with excellent electronic and catalytic properties. We have recently introduced a new versatile surface-active ligand, which can efficiently coordinate a wide range of transition metals. In the present work we report an investigation of Langmuir monolayers of VV, MoVI and TiIV complexes of this ligand, using surface pressure-area isotherms, Brewster-angle microscopy, and Grazing incidence X-ray diffraction. The monolayers of these complexes are stable enough over broad temperature ranges to allow efficient transfer to solid substrates. © 2007 Elsevier Inc. All rights reserved. 317 2 544 555 Cited By :4

The known crystal structures of co-ordination compounds containing p-dioxolene ligands in the form of hydroquinone, semiquinone or quinone have been examined. A simple method is proposed to correlate the oxidation state of these ligands with the structural distortion based on crystallographic data. The results fit well with the literature oxidation-state assignments for ligands ligated either to one or to two bridged through the ligand metal ions including the vanadium(IV/V) (hydro/semi)quinonate complexes. © 2007 American Chemical Society. 974 352 363 Cited By :5

Three new strongly chelating heterocyclic ligands containing pyridine, imidazole and triazine rings have been used to make ternary complexes of Europium(III) ions together with trifluoroacetylacetonate. The complex containing 5,6-diphenyl-3-(2-pyridyl)-1,2,3-triazine produced efficient electroluminescence in an Organic Light Emitting Diode in the presence of Poly(9-vinylcarbazole) and 8-Hydroxyquinoline aluminum salt, used as hole and electron transporters, respectively. The external quantum efficiency of this device was 0.16%. © 2005 Elsevier B.V. All rights reserved. 496 2 489 493 Cited By :14

Reaction of vanadate with carbasilatranes [methoxy{N,N′,N″-2, 2′,3-[bis(1-methylethanolato)(propyl)]amino}silane (1), methoxy{N,N′,N″-2,2′,3-[bis(1-ethanolethanolato)(propyl)] amino}silane (2), and {N,N′,N″-2,2′,2-[bis(ethanolato)- (glycolpropyl ether)]amino}silane (3)] in aqueous solution results in the formation of vanadosilicates and five-coordinated chelate vanadium(V) complexes as evidenced by 51V, 1H, and 13C NMR spectroscopy. Chiral carbasilatrane S,S-1 was characterized in the solid state by X-ray diffraction, revealing a trigonal bipyramidal geometry around the metal ion, with one unidentate methoxy group and one atrane nitrogen atom at the axial positions and one carbon and two atrane oxygen atoms at the equatorial plane of the bipyramid. Crystal data (Mo Kα 100(2) K) are as follows: orthorhombic space group P212121 a = 8.8751(6), b = 9.7031(7), c = 14.2263(12) Å Z = 4. The complexation of vanadium either with 1 or 2 is stereoselective yielding ∼94% of the complex containing ligand in the S,R-configuration. The lower ability of the S,S- and R,R-diastereoisomers of 1 and 2 to ligate vanadate was attributed to stereochemical factors, dictating a square pyramidal geometry for the chelated complexes. A dynamic process between the vanadium chelate complexes and the respective carbasilatranes was evaluated by 2D {1H} EXSY NMR spectroscopy. These spectra show that the vanadate complexes with the open carbasilatranes exchange more slowly with the free ligand compared to the respective alcohol aminate complexes. © 2005 American Chemical Society. 44 21 7511 7522 Cited By :5

Vitamin E succinate selenium-conjugated molecules were synthesized and their apoptogenic properties were evaluated. 4-Methyl-2-phenylselenyl succinate (4) was prepared by the reaction of sodium benzeneselenolate with 2-bromosuccinic anhydrite in methanol solution. The methyl ester was converted to the acid (5) by hydrolysis with aqueous hydrochloric acid. Reaction of the 2-phenylselenyl succinic anhydrite (6) with α-tocopherol (1a), γ-tocopherol (1c), and γ-tocotrienol (2c) in acidic conditions gave the respective esters. The free radical scavenging properties of α-tocopheryl-2-phenylselenyl succinate (7), γ-tocopheryl-2- phenylselenyl succinate (8), and γ-tocotrienyl-2-phenylselenyl succinate (9) were evaluated in comparison with those of α-tocopheryl succinate (10), γ-tocopheryl succinate (11), and γ-tocotrienyl succinate (12), respectively, and the free tocopherols and γ-tocotrienol. Compounds 7-9 induced a statistically significant decrease in prostate cancer cell viability compared to 10-12, respectively, or 5, exhibiting features of apoptotic cell death and associated with caspase-3 activation. These data show that structural modifications of vitamin E components by 5 enhance their apoptogenic properties in cancer cells. © 2005 Elsevier Ltd. All rights reserved. 14 8 2684 2696 Cited By :23

Reaction of VIVOCl2 in strongly acidic aqueous solution with either (NH4)2SO3 or Na2SO3 and Bu4NBr at ~70°C in the pH range 2.5-4.5 gives the clusters (NH4)2{[V4 IV(μ 4-O)2(μ 3-OH)2](VIVO)2(μ 3-SO3)4O4(H2O)2} and (n-Bu4N)2{[V4 IV(μ 4-O)2(μ 3-OH)2](VIVO)2(μ 3-SO3)4O4(H2O)2}, respectively. Reaction of NH4VVO3 with (NH4)2SO3 resulted in the isolation of the first compound. When the latter reaction is carried out in the presence of MgO, compound (NH4)[VIVO(SO3)1.5H2O]∞.2.5H2O was isolated instead. Compound (n-Bu4N)2{[V4 IV(μ 4-O)2(μ 3-OH)2](VIVO)2(μ 3-SO3)4O4(H2O)2} and (NH4)[VIVO(SO3)1.5H2O]∞.2.5H2O were characterized by X-ray structure analysis. The crystal structure of species (n-Bu4N)2{[V4 IV(μ 4-O)2(μ 3-OH)2](VIVO)2(μ 3-SO3)4O4(H2O)2} revealed a unprecedented hexanuclear cluster consisting of a cubane core [M4(μ 4-O)2(μ 3-OH)2] connected to two other metal atoms through the core oxo-groups and four μ 3-SO3 bridges. Compound (NH4)[VIVO(SO3)1.5H2O]∞.2.5H2O represents a rare example of an open-framework species prepared under mild conditions. Cyclic voltammetric examination of compound (n-Bu4N)2{[V4 IV(μ 4-O)2(μ 3-OH)2](VIVO)2(μ 3-SO3)4O4(H2O)2} revealed a redox process which was assigned to the oxidation of one core of vanadium(IV) to vanadium(V).

293(2) K) are as follows: (1) monoclinic space group C2/c, a = 14.561(7) Å, b = 14.871(9) Å, c = 7.250(4) Å, β = 95.40(4)°, Z = 4 (2) monoclinic space group P21/c, a = 19.080(2) Å, b = 9.834(1) Å, c = 15.156(2) Å, β = 104.62(1)°, Z = 4. 1H NMR measurements indicate that complex 2 retains its structure in CD3CN solution Reaction of [UO2(NO3)2] with the hydroxy ketones 3-hydroxy-2-methyl-4-pyrone (Hma) and 3-hydroxy-1,2-dimethyl-4(1H)- pyridone (Hdpp)(Hdpp) in aqueous acidic solutions (pH ∼ 3) yields the compounds [UO2(ma)2(H2O)]·H2O (1·H2O) and [UO2(dpp)(Hdpp)2(H 2O)]ClO4 (2), respectively. X-ray diffraction shows that the geometry around the metal ion in both complexes is pentagonal bipyramid. Uranium ion in the crystal structure of 1 were found to be ligated with two chelate ma- groups and one unidentate H2O molecule (C coordination mode) at the equatorial plane, while in 2 with two single-bonded Hdpp there were one chelate dpp- and one H2O molecule (P coordination mode). Crystal data (Mo Kα however, in DMSO-d6 both complexes adopt the C structure. Line-shape analysis for the 1H NMR peaks of 2 at various temperatures shows a fast intramolecular exchange process between the chelate dpp- and one of the single bonded Hdpp ligands and one slower exchange between all three ligands. The activation parameters and the decrease of the exchange rate by replacing unidentate ligand with DMSO indicate the dissociation of the unidentate ligand as the rate-determining step for the former exchange. Density functional calculations (DFT) support this mechanism and give a quantitative interpretation of the electronic structure of the two ligands and the geometries adopted by the complexes. 43 26 8336 8345 Cited By :9

Reaction of the non-oxo VIV species [VIVCl2(LOO)2] [LOO = acetylacetonate (acac-) or benzoylacetonate (bzac-)] with a chelate nitrogen-donor ligand LNN in acetonitrile leads to the reduction of VIV to VIII and the formation of the mononuclear VIII compounds of the general formula [VIIICl2(LOO)(LNN)] (LOO and LNN are acac- and bipy for 1 acac- and 5,5′-me2bipy for 2 acac- and 4,4′-tb2bipy for 3 acac- and phen for 4 bzac- and bipy for 5 bzac- and phen for 6). The reduction of the VIV complexes was monitored by GC-MS and 1H NMR spectroscopy. Both one- and two-dimensional (2D COSY and 2D EXSY) 1H NMR techniques were used to assign the observed 1H NMR resonances of 1-6 in CD2Cl2 or CDCl3 solution. It appeared that in solution these VIII complexes form two isomers which are in equilibrium: cis-[VIIICl2(LOO)(LNN)] ⇌ trans-[VIIICl2(LOO)(LNN)]. 2D EXSY cross-peaks were clearly observed between bipy- and acac-hydrogen atoms of the two geometrical isomers of 1-3 as well as between bipy and acac- protons of the cis isomer, indicating a dynamic process that corresponds to cis-trans isomerization and a cis-cis racemization. The thermodynamic and kinetic parameters of the equilibrium between these two isomers were calculated for compounds 1 and 2 by using variable temperature (VT) NMR data. Both cis-trans isomerization and cis-cis racemization processes probably proceed with an intramolecular twist mechanism involving a trigonal prismatic transition state. Density functional calculations (DFT) also indicated such a rearrangement mechanism. 42 15 4640 4649 Cited By :7

Reaction of the p-hydroquinone derivative H2Na4bicah·4H2O with either VIVOSO4·3H2O and NaVVO3 in equivalent quantities or with NaVVO3 yields the tetranuclear VIVO2+ macrocycle-semiquinonate compound Na6{(VIVO)4-(μ2-O) 2[μ2-bicas·(-5)-N,O,O,O]2}·Na 2SO4·20H2O (1·Na2SO4·20H2O) and the dinuclear cis-VVO2+-hydroquinone species Na4{(VVO2)2[μ2- bicah(-6)-N,O,O,O]}·11H2O (2·11H2O) respectively. Compounds 1·Na2SO4·20H2O and 2·11H2O were characterized by X-ray structure analysis and ab initio calculations. 23 2786 2787 Cited By :21

Three new uranium(VI) compounds have been prepared with glycine (Hgly), N-(2-mercaptopropionyl)glycine (Hmpg) and 2,2′-dithiobis(N-propionylglycine) (tpg). The crystal structure of [UO2(Hgly)2Cl2] has been solved, revealing the uranium atom to be seven-co-ordinated. The two zwitterionic glycines are coordinated to uranium atom by the carboxylate groups, one in a monodentate and the other in a bidentate mode. Solid state studies and low temperature 1H, 13C, 2D COSY and HMQC solution NMR spectra of the [UO2(mpg)(CH3COO)], show that mpg coordinates uranium atom by the carboxylate group. 90 9-11 549 554 Cited By :19

The first polyoxomolybdenum carbonate has been synthesized and its single crystal structure as well as its IR, UV-vis and 13C NMR spectra have been determined. 23 3419 3420 Cited By :29

Reaction of the multifunctional phenolic ligands 2,5-bis[ N , N -bis(carboxymethyl)aminomethyl]hydroquinone (H 6 cahq), 2,2′-bis[ N , N -bis(carboxymethyl)aminomethyl]-4,4′-isopropylidenediphenol (H 6 capd), 2,2′,2″-tris[ N , N -bis(carboxymethyl)aminomethyl]-1,1,1-tris(4-hydroxyphenyl)ethane (H 9 catp) and the monofunctional 2-[ N,N -bis(carboxymethyl)aminomethyl]-4-carboxyphenol (H 3 cacp), with VOSO 4 and NaVO 3 affords the oxo-bridged mixed-valence vanadium(IV/V) Na 6 [(VO) 4 (μ-O) 2 (μ-cahq) 2 ]·Na 2 SO 4 ·20H 2 O ( 1 ), H n Na 3− n [(VO) 2 (μ-O)(μ-cacp) 2 ] ( 2 ), H n Na 3− n [(VO) 4 (μ-O) 2 (μ-capd) 2 ] ( 3 ), H n Na 9− n [(VO) 6 (μ-O) 3 (μ 3 -catp) 2 ] ( 4 ). In addition to the synthesis, we report the infrared, magnetic, optical and electrochemical properties of these complexes. The hydrolytic stability at different pH values was also investigated using visible spectroscopy.

The full speciation has been determined in the aqueous vanadate-uridine (UrH2) and vanadate-uridine-imidazole (ImH) systems. The studies performed allow direct comparison with the corresponding adenosine systems, and the role of the pyrimidine and purine bases on various complex properties could be evaluated. The studies also provide insight into possible biological mechanism of action. Formation constants have been determined in 0.600 M Na(Cl) medium at 25 °C in the pH range 2-11, using a combination of potentiometry and 51V NMR spectroscopy. In the H+-H2VO4---UrH2 system, two dimeric complexes form: V2Ur2 2- with log β= 7.66 ± 0.02 and V2Ur2 3- with log β= 1.09 ± 0.04. The errors given are 3ω. Both species give rise to NMR resonances at -523 ppm. A minor 51V NMR resonance at -507 ppm is probably originating from a VUr2- species. No evidence was found for a 1:1 species at -523 ppm or a 1:1 species with 51V NMR shift superimposed on the vanadate monomer. In the H+-H2VO4 - UrH2-ImH system, two monomeric, mixed ligand species are formed: VUrIm- with log β= 3.12 ± 0.04 and VUrIm2- with log β= -6.26 ± 0.20. The pKa values for the V2Ur2 2- and VUrIm- species, 8.75 and 9.38, are both close to that of uridine (9.02) and are consistent with the interpretation that the deprotonation site is located on the base pan of the nucleoside. For both the V2Ur2 2- and VUrImn- species, isomers have been identified. Equilibrium conditions are illustrated in distribution diagrams. A quantitative comparison with the analogous vanadate-adenosine and vanadate-adenosine-imidazole systems is presented. Furthermore, the solution structure of V2Ur2 2- was examined using 17O NMR spectroscopy. The complex gives rise to a broad resonance at approximately -1010 ppm, which at higher temperature sharpened into two signals of equal intensities at -1007 and -1032 ppm. This spectrum is consistent only with a solution structure containing pentacoordinate vanadium in an arrangement in which one hydroxyl group of the uridine forms an ester with one vanadium atom, and the other hydroxyl group bridges the two vanadium atoms. In addition, 13C NMR studies revealed that the dinuclear vanadate-uridine species exchange while no evidence for intermolecular exchange between the complexes and free uridine was observed. The similarity between the vanadate-uridine and vanadate-adenosine complexes suggests that the role of the base in these complexes is very limited with respect to structural features and thermodynamic and kinetic properties. 37 24 6153 6160 Cited By :23

a = 12.668(5) Å, b = 8.084(3) Å, c = 17.222(6) Å, α = 108.148(12)° A series of vanadium(III) and oxovanadium(IV/V) compounds with the ligands, N-(2-nitrophenyl)pyridine-2-carboxamide (Hpycan), N-(phenyl)pyridine-2-carboxamide (Hpheca), and N-(2-pyridyl)acetamide (Hpyra), containing the amide functionality, was prepared and characterized both in solution and in solid state. All vanadium compounds contain a vanadium - amide oxygen bond. Crystal data for [VOCl2(OC2H5)(Hpheca)] (4) are monoclinic P21la Z = 4. In addition to the synthesis and crystallographic studies, the optical, infrared, and magnetic properties of these compounds are reported. Electron paramagnetic resonance [of oxovanadium(IV) species] and 1H, 13C{'H}, and 51V nuclear magnetic resonance [of oxovanadium(V) compounds] properties are reported as well. 37 26 6785 6794 Cited By :18