Kinetic study on the reaction of cis-dioxo-(N-(5-X-salicylidene)-2-aminobenzenethiolato) molybdenum(VI) with ethyldiphenylphosphine

The reactions of ethyldiphenylphosphine with a number of cis-dioxomolybdenum(VI) Schiff base coordination complexes are described. These molybdenum complexes incorporate tridentate Schiff base ligands obtained from the condensation of 5-X-salicylaldehyde (X = Cl, Br, H, CH₃O) with o-aminobenzenethiol. Oxomolybdenum(IV) Schiff base complexes were observed as products of the reaction of these Mo(VI) complexes with PEtPh₂. The kinetics for these reactions were followed spectrophotometrically and the applicable rate law is ? d[MoO₂L]/dt = k₁[MoO₂L][PEtPh₂]. The k₁'s were shown to vary systematically as the X-substituent on the ligand was changed. For MoO₂(5-X-SSP), the specific rate constants at 30°C span the range from 19.6 × 10^?4 M^?1 sec^?1 (X = Br) to 8.4 × 10^?4 M^?1 sec^?1 (X = CH₃O). It was also observed that a correlation exists between the cathodic reduction potentials (E_pc) and the k₁'s within the series. The rate of reaction of MoO₂(5-X-SSP) with PEtPh₂ was altered and systematically controlled through ligand design.     

Partial processes during cobalt and molybdenum codeposition from solutions containing oxyacids

Distribution of citrate complexes of Co(II) and Mo(VI) in weakly acidic solutions is analyzed. It is found that the primary cathodic process is hydrogen evolution. When cathodic polarization is increased, Co(II) reduction is possible, while more negative potentials may result in full reduction of Mo(VI) to the metallic state. Reduction of H₃O⁺ ions in the solutions of oxyacids occurs with participation of a ligand playing the role of proton donor. Hydrogen evolution also remains the main electrochemical process in the molybdate solutions. It is assumed that Mo(VI) reduction occurs with participation of atomic hydrogen, but not all molybdate is reduced to metallic state. Co(II) reduction in solutions containing Mg(II) occurs to a higher extent but the degree of Mo(VI) reduction depends on the Co(II) concentration: increase in the latter results in a decrease in the content of metallic molybdenum in coatings.     

Synthesis, structure studies and electrochemistry of molybdenum(VI) Schiff base complexes in the presence of different donor solvent molecules

The reactions between bis(acetylacetonato)dioxomolybdenum(VI) and Schiff base ligands derived from 5-chlorosalicylaldehyde or 3-ethoxy-salicylaldehye, and 3-methoxy-benzoic hydrazide (m-anisic hydrazide), 2-furoic hydrazide or 2,4-dihydroxy-benzoic hydrazide in the presence of donor solvents yielded cis-dioxomolybdenum(VI) complexes with the general formula MoO₂L(D), where L = tridentate Schiff base ligand and D = dimethylsulfoxide, hexamethylphosphoramide, dimethylformamide, imidazole or methanol. The complexes were characterized by elemental analysis, electronic spectra, IR, ¹H and ¹³C NMR spectroscopies, thermogravimetric analysis, cyclic voltammetry, and the molecular structures of five of the dioxomolybdenum complexes were elucidated by single crystal X-ray diffractometion studies. In general, the complexes adopt an octahedral environment around the Mo center with a cis-oxo configuration. The other coordination sites are occupied by the imino nitrogen, phenoxyl oxygen, hydroxyl oxygen of the tridentate Schiff base and the donor atom of the solvent molecule. The structural data revealed that the labile coordination site, which is occupied by N or O atoms from the donor solvents, has a longer Mo-O or Mo-N bond distance.     

Oxomolybdenum(VI) and (IV) complexes of pyrazole derived ONO donor ligands – synthesis,crystal structure studies and spectroelectrochemical correlation

Four cis-dioxomolybdenum complexes of general formula [MoO₂(Lⁿ)EtOH] (n = 1–4) and one oxomolybdenum(IV) complex [MoO(L⁴)EtOH], with potentially tridentate Schiff bases derived from 5-methyl pyrazole-3-carbohydrazide and salicylaldehyde/substituted salicylaldehyde/o-hydroxy acetophenone have been prepared. The Mo(IV) complex is derived from the Mo(VI) dioxo complex by oxotransfer reaction with PPh₃. The complexes are characterized by elemental analysis, electronic spectra, IR, ¹H NMR, and by cyclic voltammetry. All the Mo(VI) species are crystallographically characterized. The complexes have a distorted octahedral structure in which the ligand behaves as a binegative donor one, leaving the pyrazole –N uncoordinated towards the metal center. It is also revealed from the crystal structure that the Mo(VI) center enjoys an NO₅ donor environment.     

Synthesis, crystal, and molecular structure of the solvated complex [MoO2(L)] · DMF (L2− = 2-[N-(2-hydroxynaphthylidene)amino]propane-1,2,3-triol anion)

A new dioxomolybdenum(VI) complex, [MoO₂(L)] · DMF, where L^2? = 2-[N-(2-hydroxynaphthylidene)amino]propane-1,2,3-triol, has been synthesized. Its structure has been determined by X-ray diffraction analysis. The Mo atom is octahedrally coordinated by two oxo ligands that are in cis-positions with respect to each other, two oxygen atoms, the nitrogen atom of the tridentate bis(chelate) ligand L, and the DMF oxygen atom.     

A Series of New Molybdenum(VI) Complexes with the ONS Donor Thiosemicarbazone Ligands

New dioxomolybdenum(VI) complexes were obtained by the reaction of [MoO₂(acac)₂] with 4‐phenylthiosemicarbazone ligands derived from salicylaldehyde, 2‐hydroxy‐1‐naphthaldehyde, 2‐hydroxy‐3‐methoxybenzaldehyde or from 4‐(diethylamino)salicylaldehyde. In all complexes the ligands are coordinated to molybdenum as tridentate ONS‐donors through phenolic‐oxygen, imine‐nitrogen and thiol‐sulphur. Octahedral coordination of each Mo atom is completed either by one neutral donor molecule (D) or by the oxygen atom of the Mo=O unit from the neighbouring molecule. All compounds were characterized by means of chemical analysis, IR spectroscopy, TG and in some cases by DSC measurements, some of them by X‐ray crystallography, and by one and two‐dimensional NMR method.     

Ligational behavior of thiosemicarbazone,semicarbazone and thiocarbohydrazone ligands towards VO(IV), Ce(III), Th(IV) and UO2(VI) ions: Synthesis,structural characterization and biological studies

Mono- and binuclear VO(IV), Ce(III), Th(IV) and UO₂(VI) complexes of thiosemicarbazone, semicarbazone and thiocarbohydrazone ligands derived from 4,6-diacetylresorcinol were synthesized. The structures of these complexes were elucidated by elemental analyses, IR, UV–vis, ESR, ¹H NMR and mass spectra as well as conductivity and magnetic susceptibility measurements and thermal analyses. The thiosemicarbazone (H₄L¹) and the semicarbazone (H₄L²) ligands behave as dibasic pentadentate ligands in case of VO(IV) and UO₂(VI) complexes, tribasic pentadentate in case of Ce(III) complexes and monobasic pentadentate in case of Th(IV) complexes. However, the thiocarbohydrazone ligand (H₃L³) acts as a monobasic tridentate ligand in all complexes except the VO(IV) complex in which it acts as a dibasic tridentate ligand. The antibacterial and antifungal activities were also tested against Rhizobium bacteria and Fusarium-Oxysporium fungus. The metal complexes of H₄L¹ ligand showed a higher antibacterial effect than the free ligand while the other ligands (H₄L² and H₃L³) showed a higher effect than their metal complexes. The antifungal effect of all metal complexes is lower than the free ligands.     

Synthesis,characterization and pronounced epoxidation activity of cis-dioxo-molybdenum(VI) tridentate Schiff base complexes using tert-butyl hydroperoxide

The synthesis and catalytic performance of novel cis-dioxo-Mo(VI) complexes containing simple ONO tridentate Schiff base ligands in the epoxidation of various olefins using tert-butyl hydroperoxide in desired times with excellent chemo- and stereoselectivity have been described. The study of turnover numbers and the UV–Vis spectra of the Mo complexes in the present epoxidation system indicate well the high efficiency and stability of the catalysts during the reaction. The electron-deficient and bulky groups on the salicylidene ring of the ligand promote the effectiveness of the catalyst.     

Synthesis,characterization and X-ray crystal structures of the bis–ligand zinc(II) and cadmium(II) complexes of the methylpyruvate Schiff base of <Emphasis Type="Italic">S</Emphasis>-methyldithiocarbazate

New bis-chelated Zn^II and Cd^II complexes of empirical formula, [M(mpsme)₂] (mpsme=the anionic form of the tridentate ONS donor ligand formed from methylpyruvate and S-methyldithiocarbazate) have been prepared and characterized by conductance, i.r., electronic and n.m.r. spectroscopic techniques. Spectral evidence supports a six-coordinate distorted octahedral structure for these complexes. X-ray crystallographic structural analysis also confirms that, in both the [Zn(mpsme)₂] and [Cd(mpsme)₂] complexes, the methylpyruvate Schiff base of S-methyldithiocarbazate is coordinated to the metal ions as a uninegatively charged tridentate ONS chelating agent via the carbonyl oxygen atom, the azomethine nitrogen atom and the thiolate sulfur atom. Both complexes are assigned a distorted octahedral geometry in which the ligands are arranged meridionally around the metal ions. The distortion from regular octahedral geometry is attributable to the restricted bite angles of the ligand.     

Synthesis,characterization, X-ray structure and DFT calculation of two Mo(VI) and Ni(II) Schiff-base complexes

In this study, the syntheses of two new Mo(VI) and Ni(II) complexes with H₂L tridentate (ONO) Schiff-base ligand have been described and fully characterized by means of elemental analysis, FT–IR, electronic, ¹H-NMR spectroscopy and single-crystal X-ray diffraction. In both complexes, the Schiff-base completely deprotonates and coordinates to the metal ion as a dianionic tridentate ligand via the donor oxygens and nitrogen atoms. The coordination numbers of Mo(VI) and Ni(II) are six and four, respectively. The DFT-B3LYP/6–31 + G (d,p) and PBEPBE/6–31 + G (d,p) calculations are carried out for the determination of the optimized structures. Frequency calculations and NBO analysis are also performed for characterization. According to the theoretical analysis of the complexes, ligand-to-metal donation is greater than back donation. NBO data revealed that the main contribution of the frontier orbitals belongs to L⁻².     

Crystal Structure and Catalytic Property of an Oxidomolybdenum(VI) Complex Derived from <Emphasis Type="Italic">N′</Emphasis>-(2-Hydroxy-3,5-Di-<Emphasis Type="Italic">Tert</Emphasis>-Butylbenzylidene)-4-Methylbenzohydrazide

With a tridentate Schiff base ligand N′-(2-hydroxy-3,5-di-tert-butylbenzylidene)-4-methylbenzohydrazide (H₂L) and MoO₂(acac)₂, an oxidomolybdenum(VI) complex is prepared and characterized by elemental analysis, IR spectroscopy and X-ray structure determination. The complex crystallizes in the monoclinic space group C2/c with unit cell dimensions a = 20.187(2) Å, b = 7.9094(8) Å, c = 33.233(3) Å, β = 97.394(2)°, V = 5262.1(9) ų, Z = 8, R₁ = 0.0491, and wR₂ = 0.1322. The single crystal X-ray diffraction analysis reveals that the Mo atom is coordinated by NOO donor atoms of the Schiff base ligand, the methanol O atom, and two oxo groups in an octahedral coordination. Catalytic oxidation of the complex on some olefins is performed.     

Metal complexes of pyrimidine derived ligands – Syntheses,characterization and X-ray crystal structures of Ni(II), Co(III) and Fe(III) complexes of Schiff base ligands derived from S-methyl/S-benzyl dithiocarbazate and 2-S-methylmercapto-6-methylpyrimidine-4-carbaldehyde

Two new pyrimidine based NNS tridentate Schiff base ligands S-methyl-3-((2-S-methyl-6-methyl-4-pyrimidyl)methyl)dithiocarbazate [HL₁] and S-benzyl-3-((2-S-methyl-6-methyl-4-pyrimidyl)methyl)dithiocarbazate [HL₂] have been synthesised by the 1:1 condensation of 2-S-methylmercapto-6-methylpyrimidine-4-carbaldehyde and S-methyl/S-benzyl dithiocarbazate. A Ni(II) complex of HL₁ and Co(III) and Fe(III) complexes of HL₂ have been prepared and characterized by elemental analyses, molar conductivities, magnetic susceptibilities and spectroscopic studies. All the bis-chelate complexes have a distorted octahedral arrangement with an N₄S₂ chromophore around the central metal ion. Each ligand molecule binds the metal ion using the pyrimidyl and azomethine nitrogen and thiolato sulfur atoms (except in the nickel complex, one ligand molecule uses the thione sulfur in lieu of thiolato sulfur atom). In the Ni(II) complex, one of the ligand molecules behaves as a neutral tridentate and the other molecule functions as a uninegative tridentate, whereas in the Co(III) and Fe(III) complexes, the ligand molecules behave as monoanionic tridentate. All the complexes were analyzed by single crystal X-ray diffraction and significant differences concerning the distortion from an octahedral geometry of the coordination environment were observed.     

Preparation,crystal structure,spectroscopic studies,DFT calculations,antibacterial activities and molecular docking of a tridentate Schiff base ligand and its cis‐MoO2 complex

We synthesized a tridentate Schiff base ligand, 6‐(((2‐hydroxyphenyl)amino)methylene)‐2‐methoxycyclohexa‐2,4‐dienone [H₂L], as well as its Mo(VI) complex [MoO₂(L)(DMSO)], and then characterized them completely using elemental analysis, FT‐IR, UV–Vis and ¹HNMR spectroscopy techniques. X‐ray single crystal diffraction method was used for the determination of the structure of the synthesized ligand and complex. All other spectroscopic techniques performed, confirmed that [MoO₂(L)(DMSO)]had an octahedral geometry around the Mo(VI) central ion coordinated by the donor atoms of the deprotonated ligand, two oxido groups and one oxygen atom of DMSO molecule. Hybrid functional B3LYP with DGDZVP as basis set was applied for DFT calculations of the compounds in their ground state. The MEP, Mulliken, HOMO‐LUMO energy gap and thermodynamic properties of the compounds were also theoretically predicted. In‐vitro antimicrobial studies on the synthesized compounds indicated the great antibacterial activities of the Mo(VI) complex against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Bacillus cereus bacteria.     

Synthesis and structure of mononuclear molecular complexes of molybdenum(VI) and tungsten(VI) oxy- and dioxyhalides

Specific features of the synthesis and structure of mononuclear molecular halide oxide complexes of Group VI d ⁰ metals molybdenum(VI) and tungsten(VI) are surveyed. Various methods of synthesis of adducts based on MOX₄ and MO₂X₂ (M = Mo, W; X = F, Cl, Br) are described, such as direct interaction, ligand exchange, and the method of nascent reagents. The principles of formation of a particular geometric isomer are discussed: according to the self-consistency rule, the coordination of a neutral donor ligand L trans to a multiply bonded oxo ligand is preferable to that of acido ligands X⁻ (anions). Rare exceptions are mentioned.     

Synthesis and ROMP activity of aminophenol-substituted tungsten(VI) and molybdenum(VI) complexes

Tungsten(VI) and molybdenum(VI) complexes [MO(L¹)Cl₂] and [M(X)(L²)Cl₃] (X = O, NPh) with tridentate aminobis(phenolate) ligand L¹ = methylamino-N,N-bis(2-methylene-4,6-dimethylphenolate) and bidentate aminophenolate ligand L² = 2,4-di-tert-butyl-6-((dimethylamino)methyl)phenolate) were prepared and characterised. These complexes are principally stable in open atmosphere under ambient conditions. When activated with Et₂AlCl, they exhibited high activity in ring-opening metathesis polymerisation (ROMP) of 2-norbornene (NBE) and its derivatives. Especially complexes [M(NPh)(L²)Cl₃], which are easily available from corresponding metal oxides MO₃ by a simple three-step synthesis, were found very efficient ROMP catalysts for NBE (M = Mo, W) and 2-norbornen-5-yl acetate (M = Mo).     

Inner complex compounds of dioxomolybdenum(VI) with o-oxyazomethines, derivatives of substituted salicylaldehydes and tris(hydroxymethyl)aminomethane. crystal structures of two complexes [MoO(L)] · CH3OH; L = Z-substituted salicylalimines, Z = 3-NO2 and 3-OCH3

Ten new dioxomolybdenum(VI) compounds with o-oxyazomethines, derivatives of substituted salicylaldehydes (I–X) and tris(hydroxymethyl)aminomethane, are synthesized. The structures of two of them, [MoO₂(L)] · CH₃OH; L = Z-substituted salicylalimines, Z = 3-NO₂ (IV) and 3-OCH₃ (V), are determined by X-ray diffraction analysis. Compounds IV and V have similar structures and geometric parameters. The Mo atoms are coordinated through the octahedral mode by two oxo ligands in the cis positions to each other, two O atoms, one N atom of the tridentate bis(chelating) ligand L, and the O atom of the MeOH molecule.     

New sulfanyl- and selanyl-substituted Schiff bases derived from 2-chalcogenoalkylamines and aromatic aldehydes. Synthesis and complex formation reactions

A number of β-phenyl(or benzyl)selanyl- and β-phenylsulfanyl-substituted imines possessing an additional donor nitrogen, oxygen, or sulfur atom were synthesized by reaction of 2-phenylsulfanylethanamine, 2-phenylsulfanylcyclohexanamine, 2-phenylselanylcyclohexanamine, and 2-benzylselanylaniline with salicylaldehyde, 2-pyridinecarbaldehyde, or 2-tert-butylsulfanylbenzaldehyde. The resulting Schiff bases were tested as ligands in the complex formation with nickel(II) and copper(II), and mononuclear (L-H)MCl or LMCl₂ coordination compounds were isolated (L = sulfur- or selenium-containing imine). The redox properties of the selenium-containing ligands and complexes were studied by cyclic voltammetry. The complexes were found to undergo reduction of the metal ion in two one-electron steps. The reduction is reversible for copper complexes and irreversible for nickel complexes.     

Synthesis,spectral, electrochemical and magnetic properties of new symmetrical and unsymmetrical dinuclear copper(II) complexes derived from binucleating ligands with phenol and benzimidazole donors

New symmetrical 2,6-bis{N-[2-(2-benzimidazolyl)-phenyl]iminomethyl}-4-methylphenol (L¹) and unsymmetrical 2-N-[2-(2-benzimidazoyl)phenyl]iminomethyl-6-[(4-methylpiperazin-1-yl)-methyl]-4-methylphenol (L²) binucleating ligands have been synthesized. Complexation of these ligands with Cu(II) perchlorate and appropriate sodium salt offered the binuclear copper(II) complexes, [Cu₂L(X)](ClO₄)₂, (X=Cl, OH and OAc 1–6). Their spectral, electrochemical and magnetic properties have been studied. Two distinct reduction peaks were observed at negative potentials. The electrochemical data shows that the complexes of L² undergo reduction at less negative potential (E¹_pc=−0.15 to −0.25 V, E²_pc=−0.45 to −0.65 V) when compared to the complexes of L¹ (E¹_pc=−0.45 to −0.58 V, E²_pc=−1.07 to −1.103 V). A variable temperature magnetic study on the complexes of the ligand L¹ showed strong antiferromagnetic coupling between the copper atoms (−2J=285–295 cm⁻¹), in contrast, the complexes of the ligand L² showed weak antiferromagnetic interaction (−2J=60–85 cm⁻¹). Electron spin resonance (ESR) spectra (RT) of the complexes of ligand L¹ showed no signal and the complexes of ligand L² showed a broad feature.     

The electrochemical behavior of Os(II) complexes with α,α′-bipyridine and o-phenanthroline in non-aqueous solvents

The electrode reactions of Os(II) complexes with α,α′-bipyridine and o-phenanthroline have been studied in non aqueous solvents. Tris bipyridine and tris phenanthroline complexes of Os(II) give one-step oxidation waves and three-step reduction waves, while bis bipyridine complexes of Os(II) containing py₂, en, CN₂, Cl₂ and Br₂ as mixed ligands give one-step oxidation waves and two-step reduction waves. Most of these waves correspond to reversible single electron transfers. It is noticed that the half-wave potentials or the peak potentials of bis bipyridine complexes are shifted to more negative direction than those of the tris complex in both oxidation and reduction processes. This is attributable to less electron with drawing nature of substituted ligands than bipyridine. These potential data, the shifts of E_1/2 or E_p from those of tris complexes, and δE*, the potential difference between two consecutive single electron waves, are discussed in terms of molecular orbital scheme.     

A ‘preformed chelate approach’ model for coupling amine-modified rhenium and technetium ‘3+1’ mixed ligand complexes to carboxylate residues: Crystal structure of ReO[CH3SCH2CH2N(CH2CH2S)2][p-SC6H4NH2] and ReO[CH3SCH2CH2N(CH2CH2S)2][p-SC6H4NHCOC6H5]

Selected ‘3+1’ mixed ligand oxorhenium and oxotechnetium complexes containing the SNS/S donor atom set have been modified by introduction of a bifunctional amine anchor on the p-position of the thiophenolato monodentate ligand. A representative series of complexes containing several tridentate ligands was prepared both at macromolar (Re complexes) and nanomolar (^99mTc complexes) amounts. Coupling of these complexes to activated carboxylate groups was performed according to the ‘preformed chelate approach’ using benzoyl chloride as a model molecule. Coupling yields were high both at nanomolar and millimolar metal concentration, as revealed by high-performance liquid chromatographic analysis of ^99mTc and Re species adopting parallel radiometric and photometric detection modes. All Re compounds have been characterized by classical analytical methods. In addition, the structures of representative parent ReO[CH₃SCH₂CH₂N(CH₂CH₂S)₂][p-SC₆H₄NH₂] and daughter ReO[CH₃SCH₂CH₂N(CH₂CH₂S)₂][p-SC₆H₄NHCOC₆H₅] complexes were solved by X-ray crystallography. Both compounds adopt a distorted trigonal bipyramidal geometry around rhenium, wherein the oxo group and the sulfur atoms of the SNS ligand occupy the equatorial plane and the nitrogen atom and the sulfur of the monothiol are located at the apical positions trans to each other.