Syntheses,characterization, and crystal structures of oxovanadium(V) complexes with similar tridentate hydrazones

Reactions of bis(acetylacetonato)oxovanadium(IV) with N′-[2-hydroxy-4-diethylaminobenzylidene)]-2-methylbenzohydrazide (H₂HMB) and N′-[5-bromo-2-hydroxy-3-methoxybenzylidene)]-2-methylbenzohydrazide (H₂BMB), respectively, produce two oxovanadium(V) species with the formulas [VO(OMe)(HMB)]₂ (I) and [VO(OMe)(HOMe)(BMB)] (II). The complexes have been characterized by elemental analysis, IR spectra, and single-crystal X-ray diffraction. The crystal of I is triclinic: space group P \(\bar 1\), a = 8.843(1), b = 9.937(1), c = 12.327(2) Å, α = 96.500(2)°, β = 110.070(2)°, γ = 104.220(2)°, V = 962.8(2) ų, Z = 1. The crystal of II is monoclinic: space group P2₁/c, a = 9.908(2), b = 19.968(3), c = 11.065(3), β = 109.362(3)°, V = 2065.3(8) ų, Z = 4. Compound I is the methoxide-bridged dimeric oxovanadium(V) complex, and II is the mononuclear oxovanadium(V) complex. Each V atom in the complexes is in an octahedral coordination.     

Syntheses and crystal structures of neutral oxorhenium(V) complexes of N2O2-donor tripodal ligands

The neutral distorted octahedral complexes [ReOCl(L)] {H₂L = N,N-bis(2-hydroxybenzyl)-2-(2-aminoethyl)dimethylamine (H₂had); N,N-bis(2-hydroxybenzyl)-aminomethylpyridine (H₂hap); N,N-bis(2-hydroxybenzyl)-2-(2-aminoethyl)pyridine (H₂hae)} were prepared by the reaction of trans-[ReOCl₃(PPh₃)₂] with a twofold molar excess of H₂L in ethanol. X-ray structure determinations of [ReOCl(had)] (1) and [ReOCl(hap)] (2) were performed, and the structures compared. In both complexes the choride is coordinated trans to the tripodal tertiary amino nitrogen, with a phenolate oxygen trans to the oxo oxygen.     

Synthesis,crystal structures,and biological activity of oxovanadium(V) complexes with similar tridentate hydrazone ligands

Two new oxovanadium(V) complexes, [VOL¹(OEt)(EtOH)] (1) and [VOL²(OMe)(MeOH)] (2), were prepared by reaction of [VO(acac)₂] (where acac?=?acetylacetonate) with N′-(3-bromo-2-hydroxybenzylidene)-4-methylbenzohydrazide (H₂L¹) in ethanol and N′-(3-bromo-2-hydroxybenzylidene)-4-methoxybenzohydrazide (H₂L²) in methanol, respectively. Crystal and molecular structures of the complexes were determined by elemental analysis, infrared spectra, and single-crystal X-ray diffraction. The V ions have octahedral coordination. Thermal stability and the inhibition of urease of the complexes were studied.     

Synthesis,X-ray crystal structure and DFT studies of cobalt(II) and vanadium(V) complexes with N,N,O-tridentate aroyl-hydrazone based ligand

A new aroyl-hydrazone, 2-pyridine carboxaldehyde-derived hydrazone ligand and its cobalt(II) (1) and vanadium(V) (2) complexes were prepared. The structures of these compounds were investigated using elemental analysis, spectral (IR, UV), and X-ray diffraction measurements. The electrochemical properties of the complexes were studied by cyclic voltammetry. The hydrazone ligand acted as tridentate and coordinated to vanadium and cobalt via N-imine, N-pyridine, and O-benzohydrazide atoms. The Co(II) complex crystallizes in the monoclinic system, space group P2₁/c, and has a binuclear structure. Chloride ions behave as the linking bridge and a tridentate hydrazine ligand HL and water as the terminal capping ligands. The central Co(II) ion has distorted octahedral geometry. The vanadium(V) complex crystallizes in the monoclinic crystal system, space group P2₁/n, and can be described as having highly distorted trigonal-bipyramidal coordination. The geometries and electronic properties of the complexes were also obtained using DFT and TD-DFT calculations.     

Synthesis, reactivity, and X-ray crystal structure of some mixed-ligand oxovanadium(V) complexes: first report of binuclear oxovanadium(V) complexes containing 4,4'-bipyridine type bridge

Reaction of the tridentate ONO Schiff-base ligand 2-hydroxybenzoylhydrazone of 2-hydroxybenzoylhydrazine (H2L) with VO(acac)2 in ethanol medium produces the oxoethoxovanadium(V) complex [VO(OEt)L] (A), which reacts with pyridine to form [VO(OEt)L.(py)] (1). Complex 1 is structurally characterized. It has a distorted octahedral O4N2 coordination environment around the V(V) acceptor center. Both complexes A and 1 in ethanol medium react with neutral monodentate Lewis bases 2-picoline, 3-picoline, 4- picoline, 4-amino pyridine, imidazole, and 4-methyl imidazole, all of which are stronger bases than pyridine, to produce dioxovanadium(V) complexes of general formula BH[VO2L]. Most of these dioxo complexes are structurally characterized, and the complex anion [VO2L]- is found to possess a distorted square pyramidal structure. When a solution/suspension of a BH[VO2L] complex in an alcohol (ROH) is treated with HCl in the same alcohol, it is converted into the corresponding monooxoalkoxo complex [VO(OR)L], where R comes from the alcohol used as the reaction medium. Both complexes A and 1 produce the 4,4'-bipyridine-bridged binuclear complex [VO(OEt)L]2(mu-4,4'-bipy) (2), which, to the best of our knowledge, represents the first report of a structurally characterized 4,4'-bipyridine-bridged oxovanadium(V) binuclear complex. Two similar binuclear oxovanadium(V) complexes 3 and 4 are also synthesized and characterized. All these binuclear complexes (2-4), on treatment with base B, produce the corresponding mononuclear dioxovanadium(V) complexes (5-10).     

Catalytic asymmetric coupling of 2-naphthols by chiral tridentate oxovanadium (IV) complexes

A series of chiral oxovanadium(IV) complexes derived from tridentate N-3,5-substituted and N-3,4-benzo- and N-5,6-benzo-salicylidene-alpha-amino acids can serve as efficient catalysts for the enantioselective oxidative couplings of various 3-, 6-, and 7-substituted 2-naphthols under O(2). The best scenario involves the use of a vanadyl complex arising from 2-hydroxy-1-naphthaldehyde and valine (or phenylalanine) in CCl(4), leading to BINOLs in good yields (75-100%) and with enantioselectivities of up to 68%.     

Dimeric 5-coordinate oxovanadium(IV) complexes of tridentate benzoyl hydrazones

The oxovanadium(IV) complexes of the hydrazones derived from benzoylhydrazine and salicylaldehyde (BSH), o-hydroxyacetophenone (BAH), o-hydroxypropiophenone (BPH), o-hydroxybutyrophenone (BBH) and 2-hydroxy-1-naphthaldehyde (BNH) have been described. These complexes have been characterised by elemental analyses and by molecular weight, conductance, magnetic, IR and electronic spectral measurements. The IR spectra suggest the presence of phenoxide bridging and thus the complexes are formulated as dimers, each unit having 5-coordinate distorted square-pyramidal geometry. The low μ_eff values (1.02 – 1.26 B.M.) have been attributed to antiferromagnetic exchange coupling and the principal path for spin coupling is direct σ-metal-metal interaction. The electronic spectra have been interpreted in terms of energy level scheme delineated for distorted square-pyramidal geometry. Various ligand field parameters Dq, Ds, Dt along with NSH parameters DQ, DS and DT have been evaluated and the degree of distortion (DT/DQ) lies in the range 0.169 – 0.233.     

Cis di-oxomolybdenum(VI) complexes with a tridentate ONO donor ligand; synthesis,X-ray crystal structure,spectroscopic properties and oxotransfer chemistry

The molybdenum complexes of Schiff base ligands viz. [MoO₂LH₂O] where L¹ = tris(hydroxymethyl)(salicylide-neamino)methane, L² = tris(hydroxymethyl)(2,3-dihydroxybenzylideneamino)methane and L³ = tris(hydroxymethyl)(2,3,4-trihydroxybenzylideneamino)methane have been synthesized and characterized by spectroscopic and electrochemical techniques. The X-ray crystal structure of the complex [MoO₂L¹H₂O] reveals a distorted octahedral geometry with one ligand and a water molecule coordinated to the MoO₂ center. No previous complex of this type contains a coordinated water molecule. The complex undergoes an oxotransfer in the presence of Bu₃P to form a -oxobridged molybdenum(V,V) dimer. This rules out Mo—S coordination as a prerequisite for oxotransfer in such molybdenum(VI) complexes.     

Synthesis,crystal structures,and biological property of dinuclear oxovanadium(V) complexes derived from tridentate Schiff bases

A pair of structurally similar dinuclear oxovanadium(V) complexes, [VO₂L¹]₂ (I) and [VO₂L²]₂ (II), where L¹ and L² are the mono-anionic form of 2-[(2-isopropylaminoethylimino)methyl]-4-methylphenol (HL¹) and 4-fluoro-2-[(2-isopropylaminoethylimino)methyl]phenol (HL²), respectively, have been synthesized and characterized by elemental analysis, FT-IR spectra, and single crystal X-ray determination. The crystal of I is monoclinic: space group P2₁/c, a = 12.528(1), b = 12.266(1), c = 9.432(1) Å, β = 104.814(3)°, V = 1401.2(3) ų, Z = 2. The crystal of I is monoclinic: space group P2₁/n, a = 12.3128(5), b = 6.5124(3), c = 17.1272(7) Å, β = 105.863(1)°, V = 1321.1(1) ų, Z = 2. The V…V distances are 3.210(1) Å in I and 3.219(1) Å in II. The V atoms in the complexes are in octahedral coordination. Biological assay indicates that complex II, bearing fluoro-substitute groups, has stronger antimicrobial activity against most bacteria than complex I which bearing methyl-substitute groups.     

Synthesis and structural characterisation of neutral pentacoordinate silicon(IV) complexes with a tridentate dianionic N,N,S chelate ligand

A series of novel neutral pentacoordinate silicon(IV) complexes with SiClSN(2)C, SiBrSN(2)C, SiSN(3)C, SiSON(2)C, SiS(2)N(2)C, SiSeSN(2)C and SiTeSN(2)C skeletons (compounds 1-12) was synthesised, starting from PhSiCl(3), PhSiBr(3), PhSi(NCO)(3), MeSiCl(3) or C(6)F(5)SiCl(3). Compounds 1-12 contain (i) a tridentate dianionic N,N,S chelate ligand (derived from 2-{[(pyridin-2-yl)methyl]amino}benzenethiol), (ii) a phenyl, methyl or pentafluorophenyl group and (iii) a monodentate monoanionic ligand (Cl, Br, NCO, NCS, N(3), OS(O)(2)CF(3), OPh, SPh, SePh, TePh). The pentacoordinate silicon(iv) complexes 1-12 were characterised by elemental analyses, NMR spectroscopic studies in the solid state and in solution and crystal structure analyses. These experimental investigations were complemented by computational studies.     

Synthesis,spectral and electrochemical studies of alkoxo-bonded mixed-ligand oxovanadium(IV) and oxovanadium(V) complexes incorporating tridentate ONO donor azophenolalcoholate/aldiminealcoholates

Mixed-ligand vanadyl(IV) and vanadyl(V) complexes with tridentate ONO donor azophenolalcoholate/aldiminealcoholates [viz., 2-hydroxy-2-hydroxymethyl-5-methylazobenzene (H₂L¹), N-(2-hydroxymethylphenyl)-salicylaldimine (H₂L²) and N-(2-hydroxymethylphenyl)1-hydroxy-2-naphthaldimine (H₂L³)] and bidentate NN [viz., 2,2-bipyridine (bipy) and 1,10-phenanthroline (phen)] or NO [viz., 8-hydroxyquinoline (Hhq)] donor ligands have been prepared and characterized by elemental analyses and by i.r., e.p.r. and u.v.–vis. spectroscopies. The data show that the vanadyl(IV) complexes exist in two isomeric solid forms viz., monomers and polymers, whereas vanadyl(V) complexes exist only in the monomeric form. The polymeric structure results from intermolecular V=OV=O interactions. The complexes with NN donor ligands are one electron paramagnetic and display two ligand-field transitions in the visible region, whereas the complexes with ON donor ligands are diamagnetic and exhibit only LMCT bands. The vanadyl(IV) complexes display an irreversible oxidation peak near +0.30 V for complexes with (L¹)^2– and near +0.55 V for complexes with (L²)^2– and (L³)^2– ligands, while the vanadyl(V) complexes display a quasi-reversible one electron reduction couple near –0.23 V versus s.c.e. The trends in the (V=O), values for the visible region transitions and the redox potential values for the vanadyl(IV) complexes have been scrutinized.     

Rhenium(I), (III) and (V) complexes of tridentate ONX (X = O,N, S)-donor Schiff bases

The reactions of the potentially tridentate Schiff bases 2-[(2-hydroxyphenyl)iminomethyl]phenol (H₂ono) and 2-(2-aminobenzylideneimino)phenol (H₃onn) with trans-[ReOBr₃(PPh₃)₂] were studied, and the complexes [Re^IIIBr(PPh₃)₂(ono)] (1) and [Re^VBr(PPh₃)₂(onn)]Br (2) were isolated. In 1ono acts as a dianionic tridentate ligand, and in 2onn is coordinated as a tridentate trianionic imido-imino-phenolate. The complex [Re^I(CO)₃(ons)(Hno)] was isolated from the reaction of [Re(CO)₅Br] with 2-[(2-methylthio)benzylideneimino]phenol (Hons; Hno = 2-aminophenol), with ons coordinated as a bidentate chelate with a free SCH₃ group. These complexes were characterized by X-ray crystallography, NMR and IR spectroscopy.     

Electrochemical transformations of antimony(V) complexes containing tridentate O,N,O-donor ligands

Electrochemical transformations of antimony(V) complexes containing a tridentate redoxactive ligand, N,N-bis-(2-hydroxy-di-3,5-tert-butylphenyl)amine: R ₃Sb(Cat-NH-Cat) (R = (1) Ph; (2) Et), (3) Et₂Sb(Cat-N-Cat)) are studied. Electrochemical oxidation of complexes 1, 2 occurs irreversibly leading to formation of unstable radical cations. The next stage is the chemical process resulting in formation of neutral paramagnetic compounds. The Et₂Sb(V)(Cat-N-Cat) complex is characterized by two reversible anodic redox processes corresponding to a change of in the ligand redox level. Stable paramagnetic derivatives are formed as a result of electrochemical oxidation of compounds 1, 3; this allows considering these compounds as potential radical scavengers. Interaction of complex 1 with electrogenerated superoxide radical anion led to formation of paramagnetic reaction products.     

Synthesis,spectral and EPR studies of oxovanadium(IV) complexes incorporating tridentate ONO donor hydrazone ligands: Structural study of one oxovanadium(V) complex

Five oxovanadium(IV) complexes of 2-hydroxy-4-methoxybenzaldehyde nicotinic acid hydrazone (H₂L¹), 2-hydroxy-4-methoxyacetophenone nicotinic acid hydrazone (H₂L²) and a binuclear oxovanadium(V) complex of H₂L² have been synthesized. These complexes were characterized by different physicochemical techniques like electronic, infrared and EPR spectral studies. The complexes [VOL¹]₂ · H₂O (1) and [VOL²]₂ · H₂O (4) are binuclear and [VOL¹bipy] (2), [VOL¹phen] · 1.5H₂O (3) and [VOL²phen] · 2H₂O (6) are heterocyclic base adducts and are EPR active. In frozen DMF at 77 K, all the oxovanadium(IV) complexes show axial anisotropy with two sets of eight line patterns. The complex [VOL² · OCH₃]₂ (5) is an unusual product and has distorted octahedral geometry, as obtained by X-ray diffraction studies.     

Coordination properties of bidentate (N,O) and tridentate (N,O,O) heterocyclic alcohols with dimethyltin(IV)

The complex-formation equilibria of dimethyltin(IV) (DMT) with 4-hydroxymethyl imidazole (HMI) and 2,6-dihydroxymethyl pyridine (PDC) have been investigated. Stoichiometry and stability constants for the complexes formed were determined at different temperatures and 0.1?mol?L^?1 NaNO₃ ionic strength. The concentration distribution of the complexes in solution was evaluated as a function of pH. The effect of dioxane as a solvent on both protonation constants and formation constants of DMT complexes with HMI and PDC are discussed. The thermodynamic parameters ΔH° and ΔS° calculated from the temperature dependence of the equilibrium constants were investigated.     

Binary and ternary complexes of oxovanadium(IV) and homobinuclear double-bridged oxovanadium(IV) complexes

Summary Binary and ternary complexes of oxovanadium(IV) with salicylaldehyde and/or 2-hydroxy-1-naphthaldehyde were prepared and additional homobinuclear doublybridged oxovanadium(IV) complexes were obtained from the reaction products ofmeta-orpara-phenylenediamine withortho-hydroxy aromatic aldehydes (bridging Schiff base). The complexes were characterised by elemental analysis, and by spectral and magnetic studies.     

Synthesis and characterization of a cationic oxorhenium(V) complex containing the pentadentate N3O2-donor ligand bis ( N -methylsalicylideneiminopropyl)amine

The complex salt [ReO(bsa)]PF₆ (H₂bsa?=?bis(N-methylsalicylideneiminopropyl)amine) was prepared from the reaction of cis-[ReO₂I(PPh₃)₂] with H₂bsa in toluene. The dianionic pentadentate ligand bsa is coordinated to the ReO³⁺ moiety via one secondary amino and two imino nitrogens, and two anionic phenolate oxygens. The complex was characterized by spectroscopy and analytical data, and the structure has been determined by single-crystal X-ray diffraction analysis.     

Synthesis,characterization, crystal structure,and reactivity of heterobimetallic dioxovanadium(V) complexes containing multidentate hydrazone ligands

Two new heterobimetallic complexes of the composition [(VO₂)₂(μ₃-slsch){Na₂(μ-H₂O)₂(H₂O)₂}]_n (1) and [(VO₂)₂(μ₃-npsch){Na₂(μ-H₂O)₂(H₂O)₂}(DMF)]_n (2) were obtained by reaction of the ligand and vanadium pentoxide in a 1:1 molar ratio in methanol in the presence of Na₂CO₃ (2 equivalents). The complexes obtained were characterized using various spectroscopic studies. The structures of both the complexes were established by single crystal X-ray crystallographic study. We have also explored the catalytic behavior of the complexes in oxidative bromination of phenol red, which is the bio-inspired reaction catalyzed by an enzyme haloperoxidase.