Dihydrazone Ligand Research Articles

Bimetallic homoleptic divalent metal-complexes of diisatin dihydrazone ligand. Biological activity and catalytic oxidation of sulfides

According to the significant role of transition metals in their metallo-organic frameworks catalytically and biologically, two new dinuclear homoleptic complexes of Pd2+ and VO2+ ions (PdLC2 and VOLC2, respectively) with succinyl dihydrazone diisatin ligand (H2LC2) were constructed. The effect of the M2+ ion type was distinguished in the productive redox protocol of diphenyl sulfide (DiPhS) and methylphenyl sulfide (MePhS) within H2O2. Considerable productivity was assigned by the yielding percentages of diphenyl sulfoxide (DiPhSO) and methylphenyl sulfoxide (MePhSO) (the mono-oxo-selective product) catalyzed by PdLC2 or VOLC2, in which VOLC2 catalyst exhibited little more classified efficiency than that of PdLC2, referring to the progressed redox potential of V4+ ion in VOLC2 catalyst.Their biological performance was recorded based on their inhibited potential against the growing power of some cancer/normal cells of humans, bacteria, as well as, fungi. The bio-studies appointed the role and job of M2+ ion (Pd2+ or VO2+ ion) in its chelated MLC2 complex over the free ligand, H2LC2. Moreover, their interacted modes with ctDNA (i.e. calf thymus DNA) were examined via the viscometries and spectrophotometric titration. Since the two chelates (PdLC2 and VOLC2) represented an attractive performance for the inhibited action for the current microorganisms and the cancer cell lines of humans’ growth over the free H2LC2 ligand. PdLC2 and VOLC2 complexes displayed an appreciable reaction with ctDNA more than that of their free organo-ligand H2LC2. From the binding constant (Kb) and Gibb’s free energy (ΔGb≠) values, both PdLC2 and VOLC2 exhibited more binding interaction within ctDNA than that of the H2LC2 ligand, with the progressed Lewis acidity, electronegativity, and lipophilic feature (hydrophobicity).

Complexation behavior of copper and zinc divalent ions towards diisatin malonyl dihydrazone ligand with biological and catalytic assessments

According to the interesting reactivity of arylhydrazones in coordination chemistry and biological assays, malonyl dihydrazone ligand of diisatin derivative (H2Lm) was reacted with Cu2+ and Zn2+ ions forming two complexes of dinuclear homoleptic mode (CuLm and ZnLm, respectively). Demonstration of their chemical structures was confirmed through various spectroscopic ways alongside the elemental analyses (EA), conductivity measurements, and magnetic characteristics.Their bio‐performance was recorded based on their inhibited potential of the growing ability of some common bacteria, fungi, and human cancer/normal cell lines. The biological studies appointed the role and job of M2+ ion = Cu2+ or Zn2+ in its chelated MLm complex to perform the bio‐reactivity over the free ligand, H2Lm. Moreover, their interacted modes with ctDNA (i.e., calf thymus DNA) were examined via the viscometry and spectrophotometric titration. Because the two chelates (CuLm and ZnLm) represented an attractive job for the inhibited action against the current microorganisms and the human cancer/normal strains' growth over the free H2Lm ligand, CuLm and ZnLm complexes displayed a distinguished interaction with ctDNA more than that of their uncoordinated H2Lm ligand. From the values of binding constant (Kb) and Gibb's free energy ( ), CuLm assigned more bio‐action within ctDNA more than ZnLm H2Lm ligand, referring to the role of Cu2+ ion with more electronegativity to enhance the reactivity of CuLm over their free H2Lm ligand and ZnLm.The catalytic behavior of CuLm and ZnLm was given within the epoxidation of 1,2‐cyclohexene (an example of unsaturated hydrocarbons) homogeneously using hydrogen peroxide (the oxidant). Their catalytic action was optimized through various temperatures, solvents, time, and type of M2+ ion in the catalyst.

A comparative investigation: evaluating the epoxidation of styrene with binuclear molybdenum(VI) complexes under conventional heating and microwave-assisted conditions

Two bis-[cis-MoO2]2+ core bearing complexes, designated as [{MoVIO2}2(L1)(H2O)2] (1) and [{MoVIO2}2(L2)(H2O)2] (2), were created by reacting MoO2(acac)2 with dihydrazone ligands, namely H4L1(i) and H4L2(ii) (generated from a 2:1 ratio of hydrazide of terephthalate and salicylaldehyde or o-vanillin) in a 2:1 ratio in a methanolic solution. These complexes were extensively characterized using several spectroscopic techniques. The shape of the complex [{MoVIO2}2(L1)(H2O)2] (1) was confirmed by SC-XRD, revealing an octahedral geometry. Moreover, the crystallographic analysis of complex (1) elucidates the substitution of a single facet of the water molecule with DMF, accompanied by the inclusion of an additional DMF molecule within the crystal lattice. These synthesized compounds were evaluated as potential catalysts for the epoxidation of styrene in the existence of oxidant (H2O2). The oxidation reactions were conducted using both conventional and microwave-assisted methods, and the obtained data were compared in terms of activity and selectivity.

Zn(II)-complexes of diisatin dihydrazones as effective catalysts in the oxidation protocol of benzyl alcohol and effective reagents for biological studies

Two new dinuclear complexes of Zn2+ ion (ZnLC2 and ZnLC6, respectively) with two novel diisatin dihydrazone ligands of succinyl (H2LC2) and terephthalyl (H2LC2) derivatives were constructed. Their structure confirmation was achieved by different spectroscopic tools. The catalytic action of two ZnLCX was estimated under an aerobic atmosphere in the selective oxygenation protocol of benzyl alcohol within hydrogen peroxide. ZnLC6 represented more significant action by 88 % awarding of the monooxo-product, i.e. benzaldehyde, (with loaded catalyst amount = 0.005 mmol, at reaction temperature 70 °C for about 3 h), whereas ZnLC2 showed less reactivity with 87 % of the monooxo-product (with the same supplied amount, at 70 °C for 5 h).The biochemical action of H2LCX and ZnLCX was studied spectroscopically with some microbial-series and three human cancer cells. In addition, their biological action was studied through the interacting mode with calf thymus DNA (ctDNA) through viscometric and spectrophotometric assays. Both ZnLCX complexing reagents manifested a regarded inhibiting action versus the titled microbial (bacterial and fungal) series and with three human cancer cells growth (according to the zone values in mm of inhibition, MIC in μM, and IC50 values in µM) than that of free H2LCX ligands. ZnLC6 exhibited a distinguished interacting ability with ctDNA more than that interaction behavior of ZnLC2 based on the derived magnitudes of Kb (the binding constants), and ΔGb≠ (the Gibbs’ free energy), respectively. Such results referred to the lipophilic feature of the terphthalyl derivative compare to that of the succinyl one of the bonded ligands. Also, both ZnLC2 and ZnLC6 exhibited an observable higher reactivity over their both H2LC2 and H2LC6 ligands pointing to the function of Zn2+ ion and the structural effect of the free ligands for their progressing reactivity against the studied bacterial series, fungal series, human cancer cell lines and ctDNA.

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.

New bis[cis-{MoO2}] complexes with dihydrazone ligands: synthesis, characterization, theoretical investigation and their peroxidase mimicking activity.

Three binuclear dioxidomolybdenum complexes designated as [{MoVIO2}2(L1)(H2O)2] 1, [{MoVIO2}2(L2)(H2O)2] 2, and [{MoVIO2}2(L3)(H2O)2] 3 with dihydrazone ligands, H4L1I, H4L2II, and H4L3III, have been prepared by the process with ligands and MoO2(acac)2 in a ratio of 1 : 2. Many analytical techniques have been used to describe these complexes, including elemental (CHN) analysis, spectroscopy (FT-IR, UV-vis, 1H, and 13CNMR), and TGA analysis. SC-XRD analysis has been employed to study the structures of these complexes 1a, 2a, and 3a revealing the octahedral geometry and the binding of one molybdenum atom to each side of azomethine nitrogen, enolate oxygen, and a phenolic oxygen atom. The second molybdenum is bound to donor atoms similarly to the first. Powder X-ray investigations of the complexes are also performed to ensure the purity of the bulk material, and it was discovered that the single crystal reflects the bulk material. DFT was used to calculate the theoretical properties of ligands at the B3LYP/6-31G(d,p) level of the model. In contrast, the LANL2DZ level of the model was used to compute the theoretical properties of the synthesised complexes. Frequency, 1H NMR, and 13C NMR calculations were also attempted, and the calculated results were found to correspond well with the experimental data. Furthermore, the peroxidase-mimicking activity of these complexes was investigated, followed by the oxidation of pyrogallol and dopamine. The Kcat values observed in the pyrogallol oxidation were 0.44 h-1, 0.52 h-1, and 0.54 h-1 for catalysts 1, 2, and 3, respectively. However, high Kcat values of 5.2 h-1, 4.8 h-1, and 3.7 h-1 were achieved in dopamine oxidation employing catalysts 1, 2, and 3, respectively.

New organotin(IV) complexes with a bis-acyl-hydrazone ligand: Synthesis, crystal structure and immobilization on magnetic mesoporous silica nanoparticles as a strategy in cancer therapy

The new binuclear organotin(IV) complexes, (Me2Sn)2L (1) and (Ph2Sn)2L (2), have been synthesized from reaction of R2SnCl2 (R = Me or Ph) with bis(2-hydroxy-1-naphthaldehyde) Succinic dihydrazone (H4L). The synthesized compounds have been characterized by elemental analysis and IR, 1H NMR, and 119Sn NMR spectroscopy. The structures of 1 have been also determined by X-ray crystallography. Both complexes are binuclear with bis-hydrazone coordinated via enolic and phenolic oxygens and imine nitrogen in two tridentate ONO domains. Dihydrazone ligand and its diphenyltin(IV) complex were also chemically immobalized on functionalized magnetic mesoporous silica nanoparticles. The new organic-inorganic hybrid nanocomposites were characterized by FT‐IR, PXRD, BET, TGA, VSM, FE‐SEM, HRTEM and EDX techniques. Then, the in vitro cytotoxicity of the synthesized compounds against A549 cancer cell lines was evaluated. Diphenyltin(IV)-loaded magnetic mesoporous silica nanoparticles, Fe3O4@mSiO2-SnPh2, displayed the highest cytotoxic activity compared to other nanoparticles and also was able to reduce the cell viability in a more efficient manner in comparison with the free (Ph2Sn)2L. The inverted microscopy morphology and acridine orange staining indicate that A549 cells progress to cell death after being treated with Fe3O4@mSiO2-SnPh2 nanoparticles.

Self-assembly of fish-bone and grid-like CoII-based single-molecule magnets using dihydrazone ligands with NNN and NNO pockets.

Three CoII complexes, [Co2(H2L1)2](ClO4)4·4CH3OH (1), [Co2(H4L2)2](ClO4)4 (2) and [Co4(H4L2)4](ClO4)8 (3), were constructed by the self-assembly of the symmetrical dihydrazone ligands H2L1 and H4L2 with CoII ions under different synthetic conditions. The fish-bone-like complex 1 was obtained using the ligand H2L1 in methanol via the solvothermal method, while the self-assembly of H4L2 with CoII ions is solvent-dependent, producing the fish-bone-like complex 2 and [2 × 2] grid-like complex 3. Magnetic susceptibility measurements and theoretical calculations reveal that the large negative D values for the three complexes stem from their easy-axis magnetic anisotropy. Ac magnetic susceptibility measurements disclosed field-induced slow magnetic relaxation behaviors and the presence of Raman and/or direct processes of the three complexes at various applied dc fields.

Electropolymerization of [2 × 2] grid-type cobalt(II) complex with thiophene substituted dihydrazone ligand

The grid-type complex [Co4(L1-2H)4] containing dihydrazone ligand decorated with thiophene rings has been prepared. The complex undergoes oxidative electropolymerization onto ITO electrode to form purple thin film. The morphology of polymer film on ITO electrode was analyzed by SEM and AFM imagining. It was found that polymer obtained by electropolymerization method is homogenous and uniform. The obtained thin film exhibits color transition from purple via violet to blue due to the stepwise reduction of poly-[CoII4(L1-2H)4] into poly-[CoII2CoI2(L1-2H)4]2− and poly-[CoI4(L1-2H)4]4−. Its electrochromic properties such as long-term stability coloration efficiency and switching times have been investigated.

Synthesis, characterization, reactivity, and catalytic studies of heterobimetallic vanadium(V) complexes containing hydrazone ligands

Six heterobimetallic alkali metal dioxidovanadium(V) coordination polymer complexes {[M6{VO(μ-O)}2(μ-OH)4(μ4-slox/nph)].n DMF}∞ where M = Na, K, and Cs; n = 1 for (1), 0 for (2)-(6) of two dihydrazone ligands, disalicylaldehydeoxaloyldihydrazone (H4slox) and bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone (H4nph) are reported. All the complexes have been characterized by various physicochemical techniques such as elemental analyses, molar conductance, IR, NMR, UV–vis, and cyclic voltammetry. The IR, 1HNMR, and 13CNMR spectral data suggest that the dihydrazones are coordinated through phenolate/naphtholate oxygen, enolate oxygen, and azine nitrogen atoms to the metal centres. The structure of complex {[Na6{VO(μ-O)}2(μ-OH)4(μ4-slox)].DMF}∞ (1) is also determined by single-crystal X-ray data, which revealed that the H4slox coordinated via all possible dative sites to metal centres as tetrabasic octadentate ligand. The vanadium metal centres adopted distorted square-pyramidal coordination geometries, and the sodium atoms are also in five coordination atmospheres. The electronic spectra of the complexes showed LMCT bands in addition to intra-ligand π → π* and n → π* transitions. As evident from the cyclic voltammetry, the complexes showed two metal-centred electron transfer reactions {[(VVVV(slox)2−/VVVIV(slox)3−] and [(VVVIV(slox)3−/VVVIV(slox)4−]}, in addition to the ligand centred electron transfer reactions. Further, bovine serum albumin (BSA interaction studies of the complexes {[Na6{VO(μ-O)}2(μ-OH)4(μ4-slox)].DMF}∞ (1) and [Na6{VO(μ-O)}2(μ-OH)4(μ4-nph)]∞ (4) revealed strong binding affinity. Moreover, the catalytic studies of the complexes (1) and (4) were found to be effective for the oxidation of alcohols into their corresponding aldehydes and ketones and bromination of some organic substrates in the presence of H2O2 as an oxidizing agent.

Synthesis, crystal structure and reactivity of homobimetallic vanadium(V) complexes derived from oxaloyldihydrazone ligands

Treatment of V2O5 with dihydrazone ligands (H4L) (disalicylaldehydeoxaloyldihydrazone (H4L1 = H4slox), bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone (H4L2 = H4nph) and bis(5-bromosalicylaldehyde)oxaloyldihydrazone (H4L3 = H4sloxBr)) in methanol leads to the formation of homobimetallic vanadium(V) complexes of the composition [(CH3)2NH2]2[(VO2)2(L)]·nH2O, where n = 2 (1, 2) and n = 4 (3). The reaction of complexes 1–3 with H2O2 results in the formation of bis(monooxidoperoxidovanadate(V)) complexes[{VO(O2)}2(L)]2− and the reaction with HCl leads to the formation of oxidohydroxido species of the composition [(VO(OH)(L)]2−. The complexes show great potential for the oxidation of alcohols and the oxidative bromination of some organic substrates.

Syntheses, characterization, and biological activity of novel mono- and binuclear transition metal complexes with a hydrazone Schiff base derived from a coumarin derivative and oxalyldihydrazine

A hydrazone Schiff base ligand was synthesized by the condensation of 3-formyl-4-hydroxycoumarin and oxalyldihydrazide in the molar ratio 2:1. The Schiff base ligand acts as a mono-, bi-, tri- or even tetradentate ligand with metal cations in the molar ratios 1:1 or 2:1 (M:L) to yield either mono- or binuclear complexes as keto or enol isomers, where M = Co(II), Ni(II), Cu(II), VO(IV), and Fe(III). The ligand and its metal complexes were characterized by elemental analyses, IR, 1H NMR, mass, and UV–Vis spectroscopy. Furthermore, the magnetic moments were calculated from the measured electric conductivities of the complexes. According to the received data, the dihydrazone ligand contains one or two units of ONO domains and can bind to the metal ions via the azomethine nitrogen, the carbonyl oxygen atoms, and/or the phenolic oxygen atoms. Electronic spectra and the magnetic moments of all complexes show that the complexes’ geometries are either octahedral, tetrahedral, square planar, or square pyramidal. Cyclic voltammograms of the mononuclear Co(II) and Ni(II) complexes show quasi-reversible peaks. Tests against two pathogenic bacteria as Gram-positive and Gram-negative bacteria for both, the Schiff base ligand and its metal complexes were carried out. In addition, also one kind of fungi was tested. The synthesized complexes demonstrate mild antibacterial and antifungal activities against these organisms.Graphical abstract

Bis-diorganotin(IV) complexes with binucleating hydrazones derived from a methylene-bis-aromatic aldehyde as linker: Synthesis, spectral and structural characterization, antibacterial activity and DNA cleavage studies

Two bis-hydrazone, H4La and H4Lb, have been synthesized from reaction of 5,5′-methylene-bis-salicylaldehyde with benzhydrazide and furan-2-carbohydrazide, respectively. New organotin(IV) complexes, (R2Sn)2L [L = La: R = Me (1), Ph (2); L = Lb: R = Me (3), Ph (4)] have been synthesized by reaction of dihydrazone ligands with R2SnCl2 (R = Me or Ph). The synthesized compounds have been investigated by elemental analysis and IR, 1H NMR, and 119Sn NMR spectroscopy. The structures of 1 and 2 have been also confirmed by X-ray crystallography. The results show that the dihydrazone acts as a tetrabasic ligand in the enolic form and is coordinated to two SnR2 moieties via ONO donor domains by the imine nitrogen and phenolic and enolic oxygen atoms. All complexes are binuclear and the coordination number of both tin is five. The in vitro antibacterial activity of ligands and complexes has been evaluated against Gram-positive (Bacillus subtilis and Staphylococcus aureus) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria and compared with standard drugs. The synthesized compounds also have been investigated for the chromosomal and plasmid DNA cleavage activity. The complexes significantly inhibited bacterial growth, while none of compounds showed DNA cleavage activity.

Benzyl Dihydrazone versus Thiosemicarbazone Schiff Base: Effects on the Supramolecular Arrangement of Cobalt Thiocyanate Complexes and the Generation of CoN6 and CoN4S2 Coordination Spheres

In this study, we examine the coordination chemistry of benzyl dihydrazone and thiosemicarbazone Schiff bases featuring different chelation modes, steric bulk, and reactivities towards cobalt(II) thiocyanate. The tetradentate benzyl dihydrazone ligands coordinate to the Co(SCN)2 fragment to form CoN6 coordination spheres (1–3), whereas the thiosemicarbazone ligands provide CoIII complexes featuring CoN4S2 coordination spheres (4 and 5) and charge‐balancing anions {SCN– and [Co(SCN)4]2– for 4 and 5, respectively}. Hirshfeld surface (HS) analysis revealed a substituent effect that results in an increasing number of H···H contacts in the order –H < –CH3 < –Ph (1–3, respectively). The H bonding in 4 and 5 as well as the associated energies were computed by the DFT approach, and these interactions appear to be crucial for the formation of the supramolecular systems. The DFT study also suggested that the H‐bonded dimers in 5 are examples of the recently described “antielectrostatic” H bonds.

Bimetallic cis-dioxomolybdenum(VI) complex containing hydrazone ligand: Syntheses, crystal structure and catalytic studies

Bimetallic molybdenum(VI) complex [(MoO2)2(slsch)(H2O)2] containing dihydrazone ligand was synthesized by reaction of ligand with MoO2(acac)2 in 1:2M ratio in methanol. The bimetallic complex obtained was characterized by various spectroscopic studies. The structure of complex was assigned using Single Crystal X-ray Crystallography and DFT method. We have also explored the catalytic behavior of complex for oxidation of primary benzylic, aliphatic, allylic, and propargylic alcohols.

Anion-directed assembly of lanthanide coordination polymers with SMMs properties based on a dihydrazone ligand

Abstract Four new Ln(III)-based coordination polymers (CPs), [Eu(HL)Cl2(DMF)2]·(H2L) (1), [Dy(HL)Cl2(DMF)2]·(H2L) (2), [Er(HL)Cl2(DMF)(CH3OH)]·(DMF) (3) and [Yb(HL)Cl2(DMF)(H2O)]·(DMF) (4) (H2L=2,6-bis[(3-methoxysalicylidene)hydrazinocarbonyl]pyridine) have been synthesized through the reaction of Ln(III) chloride and H2L by using the vapour diffusion method. Interestingly, Cl− as a template agent plays a vital role in the formation of the target complexes. Single-crystal X-ray diffraction studies indicate that 1 and 2 are isostructural and crystallize in triclinic space group P1̅, while complexes 3 and 4 are isostructural and crystallize in monoclinic space group C2/c. Variable temperature magnetization measurement (χ M T–T) demonstrates possible antiferromagnetic interactions in complex 2. Alternating-current (ac) susceptibility measurement furthermore indicated frequency dependence for both the in-phase (χ′) and out-of-phase (χ″) components in 2, suggesting that there is a slow relaxation behavior of the magnetization, which is typical of single-molecule magnets (SMMs). This is the first time that Ln(III) CPs based on such a dihydrazone ligand has been reported so far.

Synthesis, physicochemical studies and biological evaluation of unimetallic and heterobimetallic complexes of hexadentate dihydrazone ligands

A new coordination unimetallic and heterobimetallic complexes of hexadentate N2O4 donor dihydrazone ligands were prepared by the condensation of 4-formyl antipyrine with adipic dihydrazide and succinic dihydrazide. The ligands (1) and (11) and their complexes thoroughly characterized using various analytical, physical and spectroscopic techniques, which indicate a distorted octahedral geometry around the metal ions. The ESR spectra of solid copper(II) complexes (2–4) and (12–14) showed axial symmetry with g||>g⊥>ge, indicating distorted octahedral structure and the presence of the unpaired electron in a d(x2−y2) orbital with significant covalent bond character. The antimicrobial activity results of the metal compounds (2–5), (7), (10), (12–15) and (17) show that, all these complexes exhibit inhibitory moderate to mild effects towards Bacillus subtilis, Escherichia coli and Aspergillus niger.

Synthesis and characterization of perchlorato bridged Cu2IIZnII heterotrinuclear complexes derived from succinoyldihydrazones

In the present paper three new heterotrimetallic Cu(II)–Zn(II)–Cu(II) complexes have been synthesized and characterized by analytical and spectroscopic studies. The molar conductance values for the complexes fall in the region 1.2–1.7Ω−1cm2mol−1 in DMSO solution indicating that all of the complexes are non-electrolyte. The dihydrazone ligand is present in enol form in all of the complexes. Both the copper centres have distorted square pyramidal stereochemistry in all of the complexes while the zinc centre in all hetero metal complexes has octahedral stereochemistry. The EPR parameters of the complexes indicate that the copper centre has dx2-y2 orbital as the ground state. The electron transfer reactions of the complexes have been investigated by cyclic voltammetry.

Synthesis, characterization and reactivity of trinuclear Cu(II) complexes derived from disalicylaldehyde malonoyldihydrazone

Three new homotrinuclear copper(II) complexes [Cu3(slmh)(μ-Cl)2(CH3OH)3]⋅0.5CH3OH (1), [Cu3(slmh)(NO3)2(CH3OH)5]⋅1.5CH3OH (2) and [Cu3(slmh)(μ-ClO4)2(CH3OH)3]⋅2CH3OH (3) from disalicylaldehyde malonoyldihydrazone have been synthesized and characterized. The composition of the complexes has been established on the basis of data obtained from analytical and thermoanalytical data. The structure of the complexes has been discussed in the light of molar conductance, electronic, FT-IR and far-IR spectral data, magnetic moment and EPR spectral studies. The molar conductance values for the complexes in DMSO solution indicate that all of them are non-electrolyte. The magnetic moment values for the complexes suggest considerable metal–metal intramolecular interaction between metal ions in the structural unit of the complexes. The EPR spectral features reveal that at RT, the ground state for the complexes is a mixture of the quartet state (S=3/2) and doublet state (S=½). At lower temperature, the ground state for the complexes is dx2−y2 with considerable contribution from dz2 orbital. Dihydrazone ligand is present in enol form in all of the complexes. The complexes have distorted square pyramidal stereochemistry. The electron transfer reactions of the complexes have been investigated by cyclic voltammetry. Hydrogen peroxide mediated oxidation of benzyl alcohol catalyzed by complex 1 has been studied.

Synthesis and spectroscopic characterization of monometallic molybdenum (VI) complexes derived from bis(2-hydroxy-1-naphthaldehyde)succinoyldihydrazone

Molybdenum complexes [(μ2-O)2(MoO2)2(H4nsh)2]·2A·2C2H5OH (where A=O (1), py (2), 2-pic (3), 4-pic (4) and 5-pic (5)) have been synthesized in absolute ethanol from bis(2-hydroxy-1-naphthaldehyde)succinoyldihydrazone. The composition of the complexes has been deduced on the basis of the data obtained from elemental analyses and thermo-analytical data. All complexes are non-electrolyte in DMSO solution as evident from low value of molar conductance in the range 2.2–3.3Ω−1cm2mol−1. The complexes are diamagnetic and have molybdenum in +6 oxidation state. The dihydrazone coordinates to the molybdenum centre as a neutral bidentate ligand through two azomethine nitrogen atoms only. This is revealed by the downfield shift of δ(CHN) signals by 0.16–0.44ppm as compared to that in the free dihydrazone. The carbon atoms closer to azomethine nitrogen atoms downfield shift confirming the coordination of azomethine nitrogen atoms. The ν(CN) stretching vibrations also shift to lower frequency in the IR spectra of the complexes. Apart from the intra ligand bands, the complexes show a new absorption band in the region 421–423nm attributed to charge-transfer transition from dihydrazone ligand to molybdenum centre. The dihydrazone is present in anti-cis conformation in all of the complexes. The complexes develop a new kind of intramolecular hydrogen bonding between naphtholic OH groups of coordinated dihydrazone.