Synthesis and characterisation of nickel(II), cobalt(II), manganese(II), copper(II), zinc(II), dioxouranium(VI) and dioxomolybdenum(VI) complexes of tridentate dibasic ONO donor Schiff bases derived from 2-benzothiazolecarbohydrazide and salicylaldehyde/2-hydroxy-1-naphthaldehyde

Summary The syntheses of several new coordination complexes of nickel(II), cobalt(II), manganese(II), copper(II), zinc(II), dioxouranium(VI) and dioxomolybdenum(VI) with new Schiff bases derived from 2-benzothiazolecarbohydrazide and salicylaldehyde or 2-hydroxy-1-naphthaldehyde are described. These complexes have been characterised by elemental analyses, electrical conductance, magnetic susceptibility, molecular weight, i.r. and electronic spectra. The Schiff bases behave as dibasic and tridentate ligands coordinating through the ONO donor system and form complexes of the types NiL · 3H₂O, MnL · 2H₂O, CoL · 2H₂O, CuL, ZnL · H₂O, UO₂L · MeOH and MoO₂L · MeOH (where LH₂ = Schiff base). The copper(II) complexes exhibit subnormal magnetic moments indicating the presence of an antiferromagnetic exchange interaction, whereas the nickel(II), cobalt(II) and manganese(II) complexes behave normally at room temperature. Zinc(II), dioxouranium(VI) and dioxomolybdenum(VI) complexes are diamagnetic; the zinc (II) complexes are tetrahedral, the copper(II) complexes are square planar, all the other complexes are octahedral. Thev(C=N),v(C-O),v(N-N) andv(C-S) shifts have been measured in order to locate the Schiff base coordination sites.     

New dioxouranium(VI) complexes with tridentate dibasic Schiff bases containing ONO donor sets

Summary Several new dioxouranium(VI) complexes with the tridentate dibasic Schiff bases derived from salicylaldehyde, 5-chloro-, 5-bromo-, 5-nitro-, 3,5-dichloro-, 4-methoxy-, 5-methoxy- and 3-ethoxysalicylaldehyde and 2-hydroxy-1-naphthaldehyde ando-aminobenzyl alcohol, have been synthesized from uranyl acetate dihydrate and the Schiff base in methanol. The complexes are of the type UO₂(AAA). MeOH (where AAAH₂ = a tridentate dibasic Schiff base). The complexes have been characterized by elemental analyses, i.r. and electronic spectra, conductance, magnetic susceptibility and molecular weight measurements. Thev (U=O) stretching frequency of the complexes occurs atca. 900 cm^–1 and the U-O distance is 1.74Å. The complexes are monomers, diamagnetic and octahedral.     

Synthesis and characterization of new dioxomolybdenum(VI) complexes of ONS donor Schiff bases derived from thiosemicarbazide,S-methyldithiocarbazate,S-benzyldithiocarbazate ando-hydroxy-aromatic aldehydes/ketones

Summary Syntheses of several new dioxomolybdenum(VI) complexes with composition MoO₂L · MeOH (where LH₂ = Schiff base derived from salicylaldehyde, 2-hydroxy-1-naphthaldehyde,o-hydroxyacetophenone,o-hydroxybenzophenone, pyridoxal and thiosemicarbazide,S-methyldithiocarbazate orS-benzyldithiocarbazate) are reported. The complexes have been characterized by elemental analysis, i.r., n.m.r. and electronic spectra, conductance, molecular weight and magnetic susceptibility measurements. The complexes are monomers, nonelectrolytes, diamagnetic and six-coordinated. The Schiff bases behave as dibasic tridentate ligands and coordinate through phenolic oxygen, thioenolic sulphur and azomethine nitrogen atoms. The complexes have acis-O=Mo=O structure as evidenced by the presence of two strong bands at 880–915 and 925–955 cm^–1. All of the complexes exhibit a band atca. 25000 cm^–1 due to the ligand to metal charge transfer transition.     

Molybdenum complexes of bioinorganic interest. New dioxomolybdenum(VI) complexes of schiff bases derived from salicylaldehydes and salicylhydrazide

Summary New dioxomolybdenum(VI) complexes MoO₂L · H₂O (LH₂=Schiff base) derived from Salicylhydrazide and salicylaldehyde, 5-chloro-, 5-bromo-, 5-nitro-, 3-methoxy, 3-ethoxy-, 3,5-dichlorosalicylaldehyde and 2-hydroxy-1-naphthaldehyde have been synthesized and characterized, together with the MoO₂L · THF adducts. The complexes are monomers, nonelectrolytes and diamagnetic, and contain acis O=Mo=O     

Hafnium(IV) complexes with Schiff bases

Summary Hafnium(IV) complexes have been prepared by the reactions of hafnium(IV) isopropoxide isopropanol with Schiff bases [bis(salicylaldehyde)hydrazine] (Sal-AH₂), (bis(o-hydroxyacetophenone)hydrazine] (Acp-AH₂), [bis(resacetophenone)hydrazine] (Res-AH₂), [bis(salicylaldehyde)ethylenediimine) (SaleneH₂), [bis(o-hydroxyacetophenone)ethylenediimine] (AcpeneH₂) and [bis(salicylaldehyde)o-phenylenediimine] (SalpheneH₂) (derived from salicylaldehyde,o-hydroxyacetophenone, resacetophenone and diamines) in appropriate molar ratios using benzene as solvent. The complexes [Hf(OPr-i)₂(SB)] and [Hf(SB)₂] (where SB^2– represents the dianion of the Schiff base) are reported. The complexes of Sal-A, Acp-A and Res-A are 5-and 6-coordinate while those of salene, acpene and salphene are 6-and 8-coordinate. The Schiff bases draw on Sal-A, Acp-A and Res-A are tridentate and salene, acpene and salphene are tetradentate. The mode of bonding through nitrogen and oxygen and the stereochemistry of the complexes are discussed in relation to the elemental analyses and spectra (electronic, infrared and nuclear magnetic resonance).     

Catalytic and antimicrobial activities of new ruthenium(II) unsymmetrical Schiff base complexes

Hexa-coordinated ruthenium(II) complexes of the type [Ru(CO)(PPh₃)(Z)(L)] [Z = PPh₃, pyridine (py) or piperidine (pip); L = anion of the Schiff base] have been prepared by reacting [RuHCl(CO)(PPh₃)₂(Z)] with tridentate Schiff bases derived by condensing anthranilic acid with acetylacetone, salicylaldehyde, o-vanillin and o-hydroxyacetophenone. The complexes were characterised by analytical and spectral (i.r., electronic, ¹H- and ³¹P-n.m.r.) data, and were found to be effective catalysts for oxidising primary alcohols to aldehydes in the presence of N-methylmorpholine-N-oxide (NMO) as co-oxidant. The Schiff bases and their ruthenium(II) complexes show growth inhibitory activity against pathogenic fungi Aspergillus flavus, Fusarium oxysporium and Rhizoctonia solani.     

Ruthenium(II) complexes containing bidentate Schiff bases and their antifungal activity

The reactions of ruthenium(II) complexes, [RuHCl(CO)(PPh₃)₂(B)] [B = PPh₃, pyridine (py) or piperidine (pip)], with bidentate Schiff base ligands derived by condensing salicylaldehyde with aniline, o-, m- or p-toluidine have been carried out. The products were characterised by analytical, i.r., electronic, ¹H-n.m.r. and ³¹P-n.m.r. spectral studies and are formulated as [RuCl(CO)(L)(PPh₃)(B)] (L = Schiff base anion; B = PPh₃, py or pip). An octahedral structure has been tentatively proposed for the new complexes. The Schiff bases and the new complexes were tested in vitro to evaluate their activity against the fungus Aspergillus flavus.     

Zirconium(IV) Thorium(IV) and Dioxouranium(VI) Complexes of Salicylidene o-Aminobenzothiol

Salicylidene-o-aminobenzothiol and its 5-chloro and 5-bromo derivatives, dibasic tridentate Schiff bases, dervied from the condensation of o-aminothiol and Salicylaldehyde, 5-chloro salicylaldehyde and 5-bromo salicylaldehyde, were used for coordination with Zr(IV), Th(IV) and UO₂(VI) metal inos. The I:I (metal-ligand) stoichiometry of these complexes is shown by elemental analysis and conductometric titrations. Molecular structure of these complexes are proved by Infra-red spectroscopy and thermogravimetric analysis. Magnetic susceptibility measurements of Zr(IV), Th(IV) and UO₂(VI) complexes show their diamagnetic and octahedral geometry. Results show that all the complexes have solvent molecules in coordination with metal ion.     

Ruthenium(II) carbonyl complexes with tridentate Schiff bases and their antibacterial activity

The products obtained by reacting ruthenium (II) complexes [RuHCl(CO)(PPh₃)₂(B)] [B = PPh₃, pyridine (py) or piperidine (pip)] with tridentate Schiff base ligands derived by condensing salicylaldehyde or o-vanillin with o-aminophenol and o-aminothiophenol, have been characterised by analytical, i.r., electronic, ¹H-n.m.r. and ³¹P-n.m.r. spectral studies and formulated as [Ru(L)(CO)(PPh₃)(B)] (L = bifunctional tridentate Schiff base anion, B = PPh₃, py or pip). An octahedral structure has been tentatively proposed for the new complexes. Some have been tested for the in vitro growth inhibitory activity against bacteria Escherichia coli, Bacillus sp. and Pseudomonas sp.     

Synthesis and characterization of nickel(II), cobalt(II), copper(II), manganese(II), zinc(II), zirconium(IV), dioxouranium(VI) and dioxomolybdenum(VI) complexes of a new Schiff base derived from salicylaldehyde and 5-methylpyrazole-3-carbohydrazide

Summary Synthesis of a new Schiff base derived from salicylaldehyde and 5-methylpyrazole-3-carbohydrazide, and its coordination compounds with nickel(II), cobalt(II), copper(II), manganese(II), zinc(II), zirconium(IV), dioxouranium(VI) and dioxomolybdenum(VI) are described. The ligand and the complexes have been characterized on the basis of analytical, conductance, molecular weight, i.r., electronic and n.m.r. spectra and magnetic susceptibility measurements. The stoichiometries of the complexes are represented as NiL · 3H₂O, CoL · 2H₂O, CuL, MnL · 2H₂O, ZnL · H₂O, Zr(OH)₂(LH)₂, Zr(OH)₂L · 2MeOH, UO₂L · MeOH and MoO₂L · MeOH (where LH₂ = Schiff base). The copper(II) complex shows a subnormal magnetic moment due to antiferromagnetic exchange interaction while the nickel(II), cobalt(II) and manganese (II) complexes show normal magnetic moments at room temperature. The i.r. and n.m.r. spectral studies show that the Schiff base behaves as a dibasic and tridentate ligand coordinating through the deprotonated phenolic.oxygen, enolic oxygen and azomethine nitrogen.     

Ruthenium(II) carbonyl complexes containing tridentate Schiff bases

New ruthenium(II) complexes, [Ru(CO)(B)(LL)(PPh₃)] (where, LL = tridentate Schiff bases; B = PPh₃, pyridine, piperidine or morpholine) have been prepared by reacting [RuHCl(CO)(PPh₃)₃] or [RuHCl(CO)(PPh₃)₂(B)] with Schiff bases containing donor groups (O, N, X) viz., salicylaldehyde thiosemicarbazone (X = S), salicylaldehyde semicarbazone (X = O), o-hydroxyacetophenone thiosemicarbazone (X = S) and o-hydroxyacetophenone semicarbazone (X = O). The new complexes were characterised by elemental analysis, spectral (i.r., ¹H- and ³¹P-n.m.r.), data.     

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.     

Structures of o-hydroxy Schiff-base copper(II) complexes derived from p-benzylamines

Nine copper(II) complexes of o-hydroxy Schiff bases derived from benzylamine, p-methoxybenzylamine, p-nitrobenzylamine, salicylaldehyde, 2-hydroxy-1-naphthalenecarboxaldehyde, and 3-hydroxy-2-naphthalenecarboxaldehyde were synthesized and characterized by chemical analysis, mass spectrometry, UV-Vis, infrared and electron paramagnetic resonance (EPR) spectroscopy, and seven X-ray crystal structures. The X-ray diffraction studies of these compounds showed that the geometry around the copper is square planar in six of the seven complexes. EPR studies of all the complexes in DMF solution at 77 K suggest that their geometries in solution are square planar as well.     

Synthesis and physico-chemical and biological studies on ruthenium (III) complexes with Schiff bases derived from aminocarboxylic acids

Summary Ruthenium(III) complexes of types [Ru(L)₃], [Ru(L)Cl(H₂O)₂], [Ru(L)Cl₂]_n, [Ru(L)Cl(H₂O)]_n(LH =Schiff bases derived from anthranilic acid and benzaldehyde, acetophenone, vanillin, cinnamaldehyde orm-hydroxyacetophenone; LH₂=Schiff bases derived from anthranilic acid and salicylaldehyde oro-hydroxyacetophenone; LH=Schiff bases derived fromp-aminobenzoic acid and benzaldehyde, acetophenone, vanillin, cinnamaldehyde orm-hydroxyacetophenone; LH₂=Schiff bases derived fromp-aminobenzoic acid and salicylaldehyde oro-hydroxyacetophenone) have been synthesized and characterized on the basis of elemental analyses, conductance, magnetic moment and spectral (electronic, i.r. and¹H n.m.r.) data. The wavelengths of the principal electronic absorption peaks have been accounted for quantitatively in terms of crystal field theory and various parameters have been evaluated. On the basis of the electronic spectra, an octahedral geometry has been established for all these complexes except [Ru(L)Cl₂]_n. The complexes [Ru(L)Cl₂]_n are pentacoordinate and a trigonal-bipyramidal environment, D_3h, is suggested for the ruthenium(III) ion. The thermal behaviour of these complexes has also been studied by t.g., d.t.g and d.s.c techniques. Heats of reaction for the decomposition steps were calculated from the d.s.c. curves. The antifungal and antiviral activities of the complexes with Schiff bases derived from anthranilic acid were also investigated.     

New Schiff base complexes of tetrachlorouranium

Summary Tetrachlorouranium complexes containing a Schiff base ligand, p-XC₆H₄NH=CHC₆H₄OH(L), derived from p-XC₆H₄NH₂ and salicylaldehyde, have been prepared. Atris complex was obtained when X=NO₂ andbis complexes for the other p-substituted Schiff bases when X=Cl, Br, OH and Me.     

Complexes of cobalt(II), nickel(II), copper(II), zinc(II) and manganese(II) with tridentate Schiff base ligand

Summary A series of metal complexes with new tridentate Schiff base derived from salicylaldehyde and furfuraldehyde with o-phenyldiamine have been prepared and characterised by physical and chemical methods. Electronic spectra, room temperature magnetic moment values, e.p.r. and X-ray photoelectron spectroscopy studies suggest an octahedral geometry for all the complexes, where low molar conductance values are in accord with their non-electrolytic nature. The thermal stability of the complexes is discussed and the ligand-to-metal bonding modes discussed.     

Complexes of titanium(IV), vanadium(IV) and tin(IV) with schiff bases derived from 2-(2-aminophenyl)benzimidazole

Summary New titanium(IV), vanadium(IV) and tin(IV) complexes with Schiff bases derived from 2-(2-aminophenyl)benzimidazole with benzaldehyde (L₁) and salicylaldehyde (L₂) have been prepared and have the general formulae MX₄ · 2L (M = Ti, V or Sn; L = L₁ or L₂; X = Cl or Br).All the complexes have been characterized by elemental analyses, magnetic measurements, e.p.r., electronic and i.r. spectral studies. The results show that the Schiff bases act as monodentate ligands. Tentative structures for the complexes are suggested.     

Ligand effects on metal-oxygen stretching frequencies in dioxomolybdenum(VI) complexes

Summary Several new seven-coordinated dioxomolybdenum(VI) heterochelates, [MoO₂(AA)(BBB)], where AA = bidentate ligand = ethylenediamine, 2-aminoethylpyridine,o-pheny-lenediamine,o-phenanthroline or 2,2-dipyridyl; BBB = tridentate ligand (the Schiff base derived from benzoylhydrazide and salicylaldehyde), have been synthesized and characterized by elemental analysis, molar conductance, molecular weight, i.r. spectra and magnetic susceptibility measurements. The principle of coordination number expansion of a six coordinate homochelate, [MoO₂(H₂O)(BBB)] was used to prepare the complexes, which are nonelectrolytes, monomers and diamagnetic. The i.r. spectral data reveal that they possess acis-MoO₂ structure. The _sym(OMoO) and _asym(OMoO) shifts and the difference between _sym(OMoO) and _asym(OMoO) have been related to an increase in electron density at the molybdenum atom therein.     

Syntheses and characterization of doubly-bidentate bis(carboxyamide) complexes of oxomolybdenum(IV)

Summary Complexes of oxomolybdenum(IV) with doubly-bidentate bis(carboxyamide) ligands, derived by condensing benzidine (Bd) or p-phenylenediamine (PPD) with phthalic anhydride (PAH) and succinic anhydride (SAH), have been synthesized by phosphine oxo abstraction from dioxomolybdenum(VI) complexes via ligand displacement. The structures of the complexes were determined by elemental analyses, i.r. and electronic spectral data, cyclic voltammetry and thermal analysis.     

Synthesis,characterization and catalytic studies of ruthenium(II) Schiff base complexes

Complexes of the type [Ru(CO)(EPh₃)(B)(L)] (E = P or As; B = PPh₃, AsPh₃, py or pip; L = dianion of the Schiff bases derived from the condensation of salicyloyl hydrazide with acetone, ethyl methyl ketone and salicylaldehyde have been synthesised by the reaction of equimolar amounts of [RuHCl(CO)(EPh₃)₂(B)] and Schiff bases in benzene. The resulting complexes have been characterized by analytical and spectral (i.r., electronic, n.m.r.) data. The arrangements of Ph₃P groups around the Ru metal was determined from ³¹P-n.m.r. spectra. An octahedral structure has been assigned to all the new complexes. All the complexes exhibit catalytic activity for the oxidation of benzyl alcohol and cyclohexanol in the presence of N-methylmorpholine-N-oxide as co-oxidant.