Dinuclear Oxidovanadium Research Articles

Synthesis, Characterization and X-Ray Crystal Structures of Oxidovanadium(V) Complexes Derived from N'-(2-Hydroxy-5-methylbenzylidene)-4-methylbenzohydrazide with Antibacterial Activity.

A dinuclear oxidovanadium(V) complex [V2O2L2(OMe)2] (1) was synthesized from N'-(2-hydroxy-5-methylbenzylidene)-4-methylbenzohydrazide (H2L) and VO(acac)2 in MeOH. Reaction of complex 1 with 3-hydroxy-2-methyl-4-pyrone (HL') afforded a mononuclear oxidovanadium(V) complex [VOLL'] (2). The hydrazone and both complexes were characterized by IR, UV and 1H NMR spectroscopy, as well as X-ray single crystal determination. X-ray powder diffraction of the complexes was performed. The V atoms in the two complexes are in octahedral coordination. The molecules of complex 2 are linked through non-classical hydrogen bonds of type C-H∙∙∙O to form one-dimensional chains running along the a axis. The biological assay indicates that the complexes have good antimicrobial activities on the bacteria strains P. aeroginosa, S. aureus, B. subtilis and E. coli.

Crystal structure of (μ-hydrogen di-sulfato)-μ-oxido-bis-[(4,4'-di-tert-butyl-2,2'-bi-pyridine)-oxidovanadium(IV/V)] aceto-nitrile monosolvate.

The dinuclear oxidovanadium(IV/V) complex, [V2(HS2O8)O3(C18H24N2)2]·CH3CN or [V2O2(μ-O)(μ-H(SO4)2)(4,4'-tBubpy)2]·CH3CN (4,4'-tBubpy = 4,4'-di-tert-butyl-2,2'-bi-pyridine), has crystallographic C 2 symmetry and exhibits a distorted octa-hedral geometry around the vanadium center, where the two 4,4'-tBubpy ligands are nearly orthogonal to each other. The two vanadium ions are linked by an oxo anion and a unique protonated sulfate anion [H(SO4)2 3-]. In the crystal, inter-molecular C-H⋯π and π-π inter-actions between the 4,4'-tBubpy ligands are present, leading to a three-dimensional network.

Dinuclear oxidovanadium complexes with dihydrazone ligands derived from diethyl 2,6-dimethylpyridine-3,5-dicarboxylate obtained from Hantzsch reaction; crystal structure and catalytic activity

Hantzsch pyridine ester has been used as a precursor for the synthesis of dihydrazone ligands. Two dinuclear V(v) complexes obtained by these ligands show high catalytic activity in the oxidation of sulfides.

Cytotoxic oxidovanadium(IV) complexes of tridentate halogen‐substituted Schiff bases: First dinuclear V(IV) complexes with O → VIV = O → VIV = O core

The reaction of potentially N,N,O-tridentate Schiff base ligands, Cl-LH, Br-LH, BrCl-LH and H-LH, with [VIVO(acac)2] in 2:1 ratio in methanol gave the corresponding mononuclear and dinuclear oxidovanadium(IV) complexes, VO(Cl-L)2 (1), VO(Br-L)2 (2), [(BrCl-L)2(H2O)V(μ-O)VO(BrCl-L)2] (3) and [(H-L)2(H2O)V(μ -O)VO(H-L)2] (4), in good yields. The ligands and complexes were fully characterized by elemental analysis and FT-IR spectroscopy. The ligands were also characterized by 1H NMR spectroscopy. The oxidation state of V(IV)O with d1 configuration in all synthesized complexes was confirmed by EPR. Moreover, the structures of 2 and 3 were determined by X-ray diffraction (XRD) analysis which revealed them as mono- and dinuclear vanadium(IV) complexes, respectively, with the ligands coordinated as bidentate chelates. The structure of 3 represents the first example of dinuclear V(IV) complex with O → VIV = O → VIV = O core (Cambridge Structural Database (CSD)​, version 5.42, update of May 2021). The cytotoxicity of ligands and complexes was evaluated towards ovarian (A2780), breast (MCF7) and prostate (PC3) cancer cells at 48 h. While ligands showed modest IC50 values (>42 μM), all complexes turned out to be effective in the range 3.9–17.2 μM. In particular, A2780 and MCF7 cell lines were the most sensitive to the newly synthesized V(IV)O complexes.

Aroylhydrazone Schiff Base Derived Cu(II) and V(V) Complexes: Efficient Catalysts towards Neat Microwave-Assisted Oxidation of Alcohols.

A new hexa-nuclear Cu(II) complex [Cu3(μ2-1κNO2,2κNO2-L)(μ-Cl)2(Cl)(MeOH)(DMF)2]2 (1), where H4L = N′1,N′2-bis(2-hydroxybenzylidene)oxalohydrazide, was synthesized and fully characterized by IR spectroscopy, ESI-MS, elemental analysis, and single crystal X-ray diffraction. Complex 1 and the dinuclear oxidovanadium(V) one [{VO(OEt)(EtOH)}2(1κNO2,2κNO2-L)]·2H2O (2) were used as catalyst precursors for the neat oxidation of primary (cinnamyl alcohol) and secondary (1-phenyl ethanol, benzhydrol) benzyl alcohols and of the secondary aliphatic alcohol cyclohexanol, under microwave irradiation using tert-butyl hydroperoxide (TBHP) as oxidant. Oxidations proceed via radical mechanisms. The copper(II) compound 1 exhibited higher catalytic activity than the vanadium(V) complex 2 for all the tested alcohol substrates. The highest conversion was found for 1-phenylethanol, yielding 95.3% of acetophenone in the presence of 1 and in solvent and promoter-free conditions. This new Cu(II) complex was found to exhibit higher activity under milder reaction conditions than the reported aroylhydrazone Cu(II) analogues.

Two dinuclear oxidovanadium(V) complexes of N2O2 donor amine-bis(phenolate) ligands with bromo-peroxidase activities: Kinetic, catalytic and computational studies

Two dinuclear oxidovanadium(V) complexes [LiVVO(µ2-O)VVO(Li)] (i = 1, H2L1, complex 1 and i = 2 for H2L2, complex 2) of two ONNO donor amine-bis(phenolate) ligands have been synthesized and characterized by X-ray diffraction studies which exhibited distorted octahedral geometry around each V center. In MeCN the complexes exist as dimers as indicated by HRMS studies, however, in the presence of 2 or more equivalents of H+ the dimers turned into monomers, ([LiVV = O]+ which exists in equilibrium with ([LiVV = OH]2+ and evidenced from the shift in λmax from 685 nm to 765 nm for complex 1 and 600 to 765 nm for complex 2. The complexes 1 and 2 efficiently catalyze the oxidative bromination of salicylaldehyde in the presence of H2O2 to produce 5-bromo-salicylaldehyde as the major product with TONs 405 and 450, respectively in the mixed solvent system (H2O:MeOH:THF = 4:3:2, v/v). The kinetic analysis of the bromide ion oxidation reaction indicates a mechanism which is first order in peroxidovanadium complex and bromide ion and limiting first-order on [H+]. The evaluated kBr and kH values are (8.82 ± 0.35) and (65.0 ± 2.23) M−1 s−1 for complex 1 and (6.74 ± 0.19) and (61.87 ± 2.27) M−1 s−1 for complex 2, respectively. The Ka of protonated species ([LiVV = OH]2+ are: Ka = (4.3 ± 0.40) × 10−3 (pKa = 2.37) and (4.7 ± 0.50) × 10−3 (pKa = 2.33) for complex 1 and 2 respectively. On the basis of the chemistry displayed by these model compounds, a mechanism of bromide oxidation and a tentative catalytic cycle have been framed which might be relevant to vanadium haloperoxidase enzymes and supported by DFT calculations.

Anionic Dinuclear Oxidovanadium(IV) Complexes with Azo Functionalized Tridentate Ligands and μ-Ethoxido Bridge Leading to an Unsymmetric Twisted Arrangement: Synthesis, X-ray Structure, Magnetic Properties, and Cytotoxicity.

The synthesis of ethoxido-bridged dinuclear oxidovanadium(IV) complexes of the general formula (HNEt3)[(VOL1-3)2(μ-OEt)] (1-3) with the azo dyes 2-(2'-carboxy-5'-X-phenylazo)-4-methylphenol (H2L1, X = H; H2L2, X = NO2) and 2-(2'-carboxy-5'-Br-phenylazo)-2-naphthol (H2L3) as ligands is reported. The ligands differ in the substituents at the phenyl ring to probe their influence on the redox behavior, biological activity, and magnetochemistry of the complexes, for which the results are presented and discussed. All synthesized ligands and vanadium(IV) complexes have been characterized by various physicochemical techniques, namely, elemental analysis, electrospray ionization mass spectrometry, spectroscopic methods (UV/vis and IR), and cyclic voltammetry. X-ray crystallography of 1 and 3 revealed the presence of a twisted arrangement of the edged-shared bridging core unit. In agreement with the distorted nature of the twisted core, antiferromagnetic exchange interactions were observed between the vanadium(IV) centers of the dinuclear complexes with a superexchange mechanism operative. These results have been verified by DFT calculations. The complexes were also screened for their in vitro cytotoxicity against HeLa and HT-29 cancer cell lines. The results indicated that all the synthesized vanadium(IV) complexes (1-3) were cytotoxic in nature and were specific to a particular cell type. Complex 1 was found to be the most potent against HeLa cells (IC50 value 1.92 μM).

Synthesis, Crystal Structure, and Antibacterial Activity of a Dinuclear Oxidovanadium(V) Complexes Derived from 2-[(2-Methylaminoethylimini)methyl]- 4-Trifluoromethoxyphenol

A new dinuclear oxidovanadium(V) complex, [V2O2(μ-O)2L2], where L is the monoanionic form of 2-[(2-methylaminoethylimini)methyl]-4-trifluoromethoxyphenol (HL), was prepared and characterized by IR, UV-Vis and 1H NMR spectra, as well as single crystal X-ray diffraction (CIF file CCDC no. 1567062). The complex crystallizes as the monoclinic space group P21/c with unit cell dimensions a = 12.974(3), b = 6.572(2), c = 17.205(3) A, β = 107.300(3)°, V = 1400.7(5) A3, Z = 2, R1 = 0.0879, wR2 = 0.1208, GOOf = 1.068. X-ray analysis indicates that the complex is a centrosymmetric dinuclear oxidovanadium(V) species with the V atoms in octahedral coordination. The Schiff base and the complex were evaluated for their antibacterial (Bacillus subtilis, Staphylococcus aureus, Escherichia coli, and Pseudomonas fluorescence) activities. The complex has the most activity against B. subtilis with the MIC value of 1.2 μg mL–1.

Mono- and dinuclear oxidovanadium(v) complexes of an amine-bis(phenolate) ligand with bromo-peroxidase activities: synthesis, characterization, catalytic, kinetic and computational studies

The mono- and dinuclear oxidovanadium(v) complexes [VVO(L1)(Cl)] (1) and [L1VVO(μ2-O)VO(L1)] (2) of ONNO donor amine-bis(phenolate) ligand (H2L1) were readily synthesized by the reaction between H2L1 and VCl3.(THF)3 or VO(acac)2 in MeOH or MeCN, respectively, and then characterized through mass spectroscopy, 1H-NMR and FTIR techniques. Both the complexes possess distorted octahedral geometry around each V centre. Upon the addition of 1 equivalent or more acid to a MeCN solution of complex 1, it immediately turned into the protonated form, which might be in equilibrium as: [L1ClVV[double bond, length as m-dash]OH]+ ↔ [L1ClVV-OH]+ (in the case of [L1ClVV[double bond, length as m-dash]OH]+ oxo-O is just protonated, whereas in [L1ClVV-OH]+ it is a hydroxo species), with the shift in λmax from 610 nm to 765 nm. Similar was the case for complex 2. The complexes 1 and 2 could efficiently catalyze the oxidative bromination of salicylaldehyde in the presence of H2O2 to produce 5-bromo salicylaldehyde as the major product with TONs of 405 and 450, respectively, in the mixed solvent system (H2O : MeOH : THF = 4 : 3 : 2, v/v). The kinetic analysis of the bromide oxidation reaction indicated a first-order mechanism in the protonated peroxidovanadium complex and a bromide ion and limiting first-order mechanism on [H+]. The evaluated kBr and kH values were 5.78 ± 0.20 and 11.01 ± 0.50 M-1 s-1 for complex 1 and 6.21 ± 0.13 and 20.14 ± 0.72 M-1 s-1 for complex 2, respectively. The kinetic and thermodynamic acidities of the protonated oxido species of complexes 1 and 2 were pKa = 2.55 (2.35) and 2.16 (2.19), respectively, which were far more acidic than those reported by Pecoraro et al. for peroxido-protonation instead of oxido protonation. On the basis of the chemistry observed for these model compounds, a mechanism of halide oxidation and a detailed catalytic cycle are proposed for the vanadium haloperoxidase enzyme and these were substantiated by detailed DFT calculations.

The effects of halogen substituents on the catalytic oxidation of benzyl-alcohols in the presence of dinuclear oxidovanadium(IV) complex

A new dinuclear complex of oxidovanadium(IV), namely [(VO)2(HL)(μ-O)] (1), has been synthesized by the reaction of VO(acac)2 with the heptadentate N4O3-donor Schiff base ligand, 2-(5-Bromo-2-hydroxyphenyl)-1,3-bis(2-(5-bromo-2-hydroxybenzylideneamino)ethyl)imidazolidine (H3L). The complex has been characterized by elemental analysis, spectroscopic methods and single-crystal X-ray diffraction. The latter technique revealed that the vanadium ions have distorted octahedral geometry and are connected together by oxido and phenolic oxygen atoms. The bridging oxido ligand shares the equatorial positions of the two metal centers while the oxygen atom of the bridging phenol group connects the axial positions. The catalytic activity of this complex has been tested for the oxidation of some benzyl alcohol derivatives by using H2O2 as a green oxidant. In order to maximize the yields, the effects of various influential parameters in catalytic reactions such as the oxidant-to-substrate molar ratio, the temperature and the solvent, were studied. Moreover, the electronic and steric effects of halogen substituents on the phenyl group of the substrate were also explored by analyzing the oxidation of benzyl alcohol derivatives with F, Cl and Br atoms in the relative para-position (electronic effect), and of another set of substrates with a Cl substituent in relative ortho-, meta, and para-positions (steric effect). The results of these catalytic studies show that complex 1 catalyzes the oxidation of benzyl alcohol derivatives to the corresponding benzaldehydes with little amounts of the benzoic acid being detectable in the reaction mixture. Both the reaction conditions and the substituents on the phenyl group of the benzyl alcohols affect the selectivity and the activity of this catalytic system.

Structural characterization and biological properties of a new dinuclear oxidovanadium(IV) N-(phosphonomethyl)iminodiacetate complex with the 4-amino-2-methylquinolinium cation

The crystal and molecular structures of a new dinuclear oxidovanadium(IV) complex with the N-(phosphonomethyl)iminodiacetate (pmida) ligand and the 4-amino-2-methylquinolinium ([amqH]+) cation of the molecular formula [amqH]4[V2O2(pmida)2]6H2O have been determined. The phosphonate groups in the two pmida4− ligands form two bridges between adjacent V4+ atoms, resulting in the formation of a [V2O2(pmida)2]4− dimer with a V2O4P2 eight-membered ring. This is the first example of a quinoline derivative complex containing the [V2O2(pmida)2]4− ion. The susceptibility curve for the complex exhibits a maximum at approximately 10K, indicating the presence of antiferromagnetic interactions transmitted in the crystal lattice. Furthermore, the biological properties of the complex in the concentration range 1–100μM were investigated in relation to its cytoprotective activity against oxidative damage generated exogenously using hydrogen peroxide in the hippocampal neuronal HT22 cell line (MTT tests). The obtained results were subsequently referred to the [amqH][VO(nta)(H2O)]H2O analogue as well as trolox and ascorbic acid, used as known antioxidants. It has been established that the title compound effectively protects HT22 from oxidative damage and is a potentially good candidate for further evaluation of the mechanism of its action.

Synthesis, structural characterization, DFT studies and catalytic properties of dinuclear oxidovanadium(V) complexes derived from adipohydrazone ligands

Two new dinuclear oxidovanadium(V) complexes, [V2O2(L1)(OCH3)2(CH3OH)2]·2(CH3OH) (1) and [V2O2(L2)(OCH3)2(CH3OH)2]·2(CH3OH) (2), were synthesized from the reaction of VO(acac)2 and hexa-dentate N2O4-donor hydrazone ligands (H4L1 and H4L2) in methanol solvent. The ligands and complexes were characterized by elemental analysis and spectroscopic methods. Single crystal X-ray analysis of the brown crystals of complexes 1 and 2 indicated that these complexes are dinuclear oxidovanadium(V) complexes which the metal ions have distorted octahedral geometry. There are several strong and directed hydrogen bonding interactions in the crystal packing of 1 and 2 which stabilize their crystalline format. The catalytic activity of these complexes was tested in the oxidation of thioanisole using H2O2. These studies indicated both complexes have high catalytic activity in the oxidation of thioanisole. The complexes were further studied by DFT and TDDFT theoretical calculations.

Synthesis, characterization and magnetic properties of a dinuclear oxidovanadium(IV) complex: Magneto-structural DFT studies on the effects of out-of-plane –OCH3 angle

A new dinuclear oxidovanadium(IV) complex with a symmetric heptadentate N4O3-donor ligand, [V2(O)2L(μ-OCH3)] CH3OH (1), was synthesized and characterized by elemental analysis, spectroscopic methods (FT-IR, UV–Vis and EPR) and single crystal X-ray analysis, where H3L is the Schiff base ligand obtained by the condensation of triethylenetetramine and 5-bromosalicylaldehyde. Single crystal X-ray analysis indicated that the vanadium(IV) ions have distorted octahedral geometry and are connected together by phenoxy and methoxy bridging groups. The EPR and magnetic susceptibility measurements show weak V⋯V antiferromagnetic interactions. The analysis of the magnetic susceptibility data with the Bleaney–Bowers equation gave a value for the magnetic coupling constant of J=−1.60cm−1 (H=−JS1S2). A Broken-Symmetry DFT study also agreed with an intramolecular character of the magnetic coupling giving a comparable value for J and showed an important dependence of the magnetic interaction with the out-of-plane shift of the methyl group of the methoxy bridging group.

Versatile Reactivity and Theoretical Evaluation of Mono- and Dinuclear Oxidovanadium(V) Compounds of Aroylazines: Electrogeneration of Mixed-Valence Divanadium(IV,V) Complexes.

The substituted hydrazones H2L(1-4) (L(1-4) = dibasic tridentate ONO(2-) donor ligands) obtained by the condensation of 2-hydroxy-1-naphthaldehyde and 2-aminobenzoylhydrazine (H2hnal-abhz) (H2L(1)) , 2-hydroxy-1-naphthaldehyde and 2-hydroxybenzoylhydrazine (H2hnal-hbhz) (H2L(2)), 2-hydroxy-1-acetonaphthone and benzoylhydrazine (H2han-bhz) (H2L(3)), or 2-hydroxy-1-acetonaphthone and 2-aminobenzoylhydrazine (H2han-abhz) (H2L(4)) are prepared and characterized. Reaction of ammonium vanadate with the appropriate H2L(1-4) results in the formation of oxidoethoxidovanadium(V) [V(V)O(OEt)(L(1-4))] (1-4) complexes. All compounds are characterized in the solid state and in solution by spectroscopic techniques (IR, UV-vis, (1)H, (13)C, and (51)V NMR, and electrospray ionization mass spectrometry). Single-crystal X-ray diffraction analysis of 1, 3, and 4 confirms the coordination of the corresponding ligands in the dianionic (ONO(2-)) enolate tautomeric form. In solution, the structurally characterized [V(V)O(OEt)(L)] compounds transform into the monooxido-bridged divanadium(V,V) [(V(V)OL)2-μ-O] complexes, with the processes being studied by IR and (1)H, (13)C, and (51)V NMR. The density functional theory (DFT) calculated Gibbs free energy of reaction 2[V(V)O(OEt)(L(4))] + H2O ⇆ [(V(V)OL(4))2-μ-O] + 2EtOH is only 2-3 kcal mol(-1), indicating that the dinuclear complexes may form in a significant amount. The electrochemical behavior of the complexes is investigated by cyclic voltammetry, with the V(V)-V(IV) E1/2(red) values being in the range 0.27-0.44 V (vs SCE). Upon controlled potential electrolysis, the corresponding (L)(O)V(IV)-O-V(V)(O)(L) mixed-valence species are obtained upon partial reduction of the [(V(V)OL)2-μ-O] complexes formed in solution, and some spectroscopic characteristics of these dinuclear mixed-valence complexes are investigated using DFT calculations and by electron paramagnetic resonance (EPR), with the formation of V(IV)-O-V(V) species being confirmed by the observation of a 15-line pattern in the EPR spectra at room temperature.

Oxidative coupling of 2-naphthol catalyzed by a new methoxido bridged dinuclear oxidovanadium(V) complex

A new dinuclear oxidovanadium(V) complex, [(VO)2(μ-L-κ4O,N,N,O)(μ-OCH3)2(OMe)2]·CH3OH (1), is synthesized by the reaction of V2O5 with 1,1′-((1E,1′E)-hydrazine-1,2-diylidenebis(methanylylidene))bis(naphthalen-2-ol) (H2L) in methanol. H2L is synthesized by two different methods: (i) from the reaction of hydrazine hydrate with 2-hydroxy-1-naphthaldehyde and (ii) from the reaction of hydrazine hydrate with 2-naphthol in the presence of formaldehyde (Mannich condensation). The ligand and its vanadium complex are characterized by elemental analysis, spectroscopic methods (FT-IR, NMR and UV–Vis) and their structures are determined by single crystal X-ray analysis. X-ray studies show that 1 is a neutral dinuclear complex of oxidovanadium(V) in which two vanadium(V) ions are connected by two methoxido bridging groups. The Schiff base ligand is coordinated to both vanadium centers by two NO-donor sets. Complex 1 is employed as initiator for oxidative coupling of 2-naphthol to produce BINOL. The effect of temperature, reaction atmosphere and solvent in catalytic reaction is studied. According to the obtained results, a mechanism is proposed for catalytic oxidative coupling reaction in the presence of complex 1.

Dinuclear oxidovanadium(V) complexes incorporating N, N, O, O coordinating ligands: Synthesis, structure, spectral, DFT and TDDFT study

Dinuclear (VVVV) oxidovanadates of general formula [V2O3(L)2] have been synthesized in excellent yields by reacting bis(acetylacetonato)oxidovanadium(IV) with H2L in a 1:1 ratio in acetonitrile in air. Here L2− is the deprotonated form of 2-[((2-hydroxypropan-2-yl)(pyridin-2-ylmethyl)amino)methyl]phenol (H2L1), 2-[((1-hydroxy-2-methylpropyl)(pyridin-2-ylmethyl)amino)methyl]phenol (H2L2) and 2-[((1-hydroxy-3-methylbutyl)(pyridin-2-ylmethyl)amino)methyl]phenol (H2L3). X-ray crystallographic study for the complex 1 reveals that the relative disposition of the two VO groups in [V2O3(L1)2] is almost cis, the O6V1—V2O7 torsion angle being 42.9(2)°. Low VV/VIV reduction potentials (−0.50V versus SCE) are indicative of the considerable VO3+ stabilization due to alkoxide coordination. The gas-phase geometry optimization and the electronic structures of [V2O3(L1)2], 1; [V2O3(L2)2], 2 and [V2O3(L3)2], 3 have been investigated with the framework of density functional theory. The absorption spectra of the complexes and the CD spectra for 2 and 3 are calculated by time dependent density functional theory (TDDFT) using conductor like polarizable continuum model (CPCM). DFT calculation shows a good agreement to the experimental ground state IR and NMR value.

Dinuclear Oxidovanadium(IV) and Dioxidovanadium(V) Complexes of 5,5′‐Methylenebis(dibasic tridentate) Ligands: Synthesis, Spectral Characterisation, Reactivity, and Catalytic and Antiamoebic Activities

AbstractThe synthesis of dinuclear oxidovanadium(IV) and dioxidovanadium(V) complexes of two hydrazones [CH2(H2sal‐nah)2 (I) and CH2(H2sal‐inh)2 (II)] derived from 5,5′‐methylenebis(salicylaldehyde) [CH2(Hsal)2] and nicotinic acid hydrazide (nah) or isonicotinic acid hydrazide (inh) is described. The compounds were characterised in the solid state and in solution, namely by spectroscopic techniques (IR, UV/Vis, EPR, 1H, 13C and 51V NMR). It has been demonstrated that the dioxidovanadium(V) complexes K2[CH2{VVO2(sal‐nah)}2]·2H2O (3), Cs2[CH2{VVO2(sal‐nah)}2]·2H2O (4) and Cs2[CH2{VVO2(sal‐inh)}2]·2H2O (5) of I and II are active in the oxidative bromination of salicylaldehyde by H2O2, therefore acting as functional models of vanadium‐dependenthaloperoxidases, and it has also been shown that the corresponding oxidovanadium(IV) complexes [CH2{VIVO(sal‐nah)(H2O)}2] (1) and [CH2{VIVO(sal‐inh)(H2O)}2] (2) are catalyst precursors for the catalytic oxidation, by peroxide, of methyl phenyl sulfide and diphenyl sulfide, yielding the corresponding sulfoxide and sulfone. Plausible intermediates involved in these catalytic processes are established by UV/Vis, EPR and 51V NMR studies. The dioxidovanadium(V) complexes along with ligands I and II were also screened against HM1:1MSS strains of Entamoeba histolytica. The results showed that the IC50 values of compounds 3 and 5 are lower than the IC50 value of metronidazole. The toxicity studies against human cervical (HeLa) cell lines showed that compounds 3 and 5 are not much toxic but are more toxic than metronidazole. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)