Manganese(II) complexes of substituted thio-and selenosemicarbazones of 2-acetylpyridine: E.s.r., magnetic and electronic spectral studies

Summary Manganese(II) bis(ligand) complexes of substituted thiosemicarbazones and selenosemicarbazones derived from 2-acetylpyridine of general formula [MnL₂] (where L=deprotonated ligand) have been synthesized and characterised by elemental analyses, electronic spectra in solution, i.r. spectra, magnetic measurements and e.s.r. spectra recorded in polycrystalline state and in solution at room temperature and 77K. The terdentate character of the ligands in all the complexes is inferred from i.r. spectra. The electronic spectra along with e.s.r. spectra suggest an octahedral environment around the manganese(II). The metal-ligand bonds are moderately covalent. Thus all the complexes reported here are six-coordinated and high-spin octahedral.     

Characterization of copper(II) complexes of N4,N4-disubstituted thiosemicarbazones of 2-acetylpyridine by combined evaluation of electronic and ESR parameters

Copper(II) complexes of 2-acetylpyridine 4,4-dimethyl-3-thiosemicarbazone (L′H) and 2-acetylpyridine 4-(4-methylpiperidinyl)-3-thiosemicarbazone (LH) of the general formula CuLX (where L is a deprotonated ligand and X = F⁻, Cl⁻, Br⁻, I⁻, OAc⁻ and NO⁻₃) have been synthesized and characterized by elemental analysis, magnetic susceptibility measurements between 93 and 298 K in the polycrystalline state, i.r. spectra, electronic spectra, conductivity measurements and ESR spectra recorded in the polycrystalline state, in chloroform and dimethylformamide solution at room temperature and at 77K. The molar conductivities measured in dimethylformamide for all complexes show them to be non-electrolytes. The terdentate character of the ligands in all the complexes is inferred from i.r. spectral studies. The i.r. spectra also confirm the monodentate nature of the polyatomic anions such as nitrate and acetate. The electronic spectra in Nujol mulls, chloroform or dimethylformamide solution suggest planar geometry for all of the complexes. The calculated ESR parameters show an axial d_x²−y² ground state and suggest coordination through sulphur in agreement with the i.r. results. Little change in the value of g with temperature indicates no significant change in planarity of these four coordinated species. ESR spectra in solution at room temperature and 77 K also suggest a strong covalent environment with strong in-plane sigma and pi bonds provided by the ligands.     

New iron(III) complexes with thiosemicarbazones derived from 5-methyl-3-formylpyrazole

New iron(III) complexes of 5-methyl-3-formylpyrazole thiosemicarbazone (HMPzTS) and 5-methyl-3-formylpyrazole-4-phenylthiosemicarbazone (HMPzPTS), namely [Fe(MPzTS)₂]X and [Fe(MPzPTS)₂]X respectively, where X=Cl, NO₃, SCN and ClO₄, have been synthesised and physico-chemically characterised by magnetic measurements (polycrystalline state), electronic, i.r., e.s.r. and Mössbauer spectra. All are cationic complexes containing two monoprotonic tridentate ligands with NNS donor sites and an anionic counterpart; they behave as 1:1 electrolytes in MeOH/DMF. Coordination to central iron(III) via the pyrazolyl nitrogen (²N), the azomethine nitrogen and the thiolato sulphur atom is confirmed in the complexes from i.r. data. E.s.r. data (RT & LNT) reveal the presence of a spin-paired iron(III) cation with d² _xyd² _yzd¹ _xy configuration. The ⁵⁷Fe Mössbauer spectral data (RT) are commensurate with the presence of two iron(III) spin states, the percentage of each being dependent upon the counterion of the species.     

Spectroscopic studies on copper(II) complexes derived from a substituted 2-acetylpyridine thiosemicarbazone

Summary Copper(II) complexes of general formula [Cu(L4A)X] (where L4A is the deprotonated ligand, 1 H-hexahydroazepine-1-thiocarboxylic acid-2-[1-(2-pyridinyl)ethylidene]hydrazide and X=Cl, Br, I, NCS, NO₃ and OAc) and [Cu(HL4A)(L4A)]ClO₄ have been prepared and characterized by elemental analyses, magnetic susceptibility measurements, i.r. spectra, electronic spectra, conductivity measurements and e.s.r. spectra in the polycrystalline state and in chloroform solution. For all complexes, except the perchlorate salt, coordination occurs via imine nitrogen, pyridine nitrogen and thione sulphur. For the perchlorate salt, L4A is tridentate, while HL4A is monodentate via imine nitrogen. Electronic spectra suggest planar geometry for all the complexes. The calculated e.s.r parameters suggest coordination through sulphur in agreement with the i.r. results.     

Metal-cinnamic acids interactions. Part III. Synthesis and study of copper(II) complexes of 3, 4- and 3, 5-dimenthoxycinnamic acid

Summary Copper(II) complexes derived from substituted cinnamic acids 3, 4-dimethoxycinnamic acid (3, 4-DMCH) and 3, 5-dimethoxycinnamic acid (3, 5-DMCH), of the formula [Cu(3, 4-DMC)₂]·H₂O (1), [Cu(3, 5-DMC)₂]·H₂O (2) were prepared. The magnetic properties of the complexes suggest dimeric structures typical of copper(II) acetate monohydrate-like complexes. X-band e.s.r. spectra of polycrystalline samples at low temperature are typical of triplet state systems S=1. Their ability to catalyze the aerial oxidation of 3, 5-di-t-butylcatechol was measured spectrophotometrically at 30°C. The complexes are models for oxidases.     

Crystal Structure of 2-[2-hydroxy-3-methoxyphenyl]-3-[2-hydroxy-3-methoxybenzylamino]-1,2-dihydroquinazolin-4(3H)-one and the Synthesis, Spectral and Thermal Investigation of its Transition Metal Complexes

A new 1,2-dihydroquinazolin-4(3H)-one ligand, 2-[2-hydroxy-3-methoxyphenyl]-3-[2-hydroxy-3-methoxybenzylamino]-1,2-dihydroquinazolin-4(3H)-one (Hmpbaq), formed by the condensation of 2-aminobenzoylhydrazide with 2-hydroxy-3-methoxybenzaldehyde and its copper(II), nickel(II), cobalt(II), manganese(II), zinc(II) and cadmium(II) complexes, have been synthesized. Their structures have been elucidated on the basis of elemental analyses, conductance measurements, magnetic moments, spectral (i.r., ¹H-n.m.r., u.v.–vis., e.p.r. and FAB-mass) and thermal studies. The formation of 1,2-dihydroquinazolin-4(3H)-one rather than hydrazone in the reaction of 2-aminobenzoylhydrazide with 2-hydroxy-3-methoxybenzaldehyde is confirmed by the ¹H-n.m.r. spectra and single crystal X-ray diffraction studies. The tridentate behavior of the ligand was proposed on the basis of spectral studies. X-band e.p.r. spectra of the copper(II) and manganese(II) complexes in the polycrystalline state at room temperature and liquid nitrogen temperature were recorded and their salient features are reported. Thermal stabilities of the manganese(II) and zinc(II) complexes have been studied.     

Unusual redox and chemical properties of N4-substituted pyridoxal thiosemicarbazone copper(II) complexes: their preparation,properties and reactivities

Summary New copper(II) complexes with pyridoxal N⁴-methylthiosemicarbazone (H₂Methsa), N⁴-ethylthiosemicarbazone (H₂Etthsa) and N⁴-phenylthiosemicarbazone (H₂Phthsa) have been prepared and characterized by analytical, magnetic, spectral, e.s.r. and electrochemical methods. All the compounds exhibit normal magnetic moments at room temperature. The variable temperature magnetic moments, however, show the presence of very weak intramolecular antiferromagnetic interaction (–2J = ca. 30cm^-1) between the copper(II) centres in the complexes. The e.s.r. spectra at 77 K in DMSO indicate the presence of a mixture of monomers and dimers consistent with the dissociation of the complexes. Electrochemical studies in non-aqueous solvents show that the complexes undergo a quasi-reversible one electron facile reduction at markedly low negative potentials versus saturated calomel electrode (s.c.e.).     

Spectral characterization of iron(III) complexes of 2-benzoylpyridine N(4)-substituted thiosemicarbazones

Three iron(III) complexes (1-3) of 2-benzoylpyridine N(4)-phenyl thiosemicarbazone (HL1) and one iron(III) complex (4) of 2-benzoylpyridine N(4)-cyclohexyl thiosemicarbazone (HL2) were synthesized and characterized by means of different physicochemical techniques viz., molar conductivity measurements, magnetic susceptibility studies and electronic, infrared and EPR spectral studies. The analytical data and the molar conductance measurements of the complexes reveal that two molecules of the ligand and the anion are coordinated to the metal atom in all the four complexes. The magnetic moments of the complexes suggest that they are of low spin. From the infrared spectra of the ligands and the complexes it is confirmed that the ligands coordinate to iron(III) as an anion coordinating via the azomethine nitrogen, pyridyl nitrogen, and the thiolate sulphur. The EPR spectra of the complexes in the polycrystalline state at 298 and 110 K and in DMF solution at 110 K were recorded and all the spectra show three g values indicating that these complexes have rhombic distortion. All the iron(III) complexes in DMF solution at 110 K have similar anisotropic spectra with almost the same gav values, indicating that the bonding in all the complexes is similar and is unaffected by the coordination of the anion.     

Synthesis and Spectral Investigation of Some Transition Metal Complexes Containing Pentadentate Macroacyclic <Emphasis Type="Italic">NNNNN</Emphasis>-donor Schiff Base Ligands

A new Schiff base, 2,6-diacetylpyridine bis(2-hydrazinobenzothiazole) (DPHB), has been designed, and synthesized by the condensation of 2,6-diacetylpyridine with 2-hydrazinobenzothiazole, and structurally characterized. Copper(II), cobalt(II), nickel(II), manganese(II), zinc(II), cadmium(II) and oxovanadium(IV) complexes of DPHB have been synthesized for the first time. Their structures have been elucidated on the basis of elemental analyses, conductance measurements, magnetic properties, spectral (i.r., ¹H-n.m.r., u.v.–vis., e.p.r. and FAB-mass) and thermal studies. The complexes exhibit an octahedral geometry around the metal centre. The conductance data of all the complexes suggest them to be 1:1 electrolytes. The X-band e.p.r. spectra of the copper(II) and oxovanadium(IV) complexes in the polycrystalline state at room (300 K) and liquid nitrogen temperature (77 K) were recorded and their salient features are reported. Thermal stabilities of the manganese(II) and zinc(II) complexes have been studied.     

Complexes of 1-isonicotinoyl-4-benzoyl-3-thiosemicarbazide with manganese(II), iron(III), chromium(III), cobalt(II), nickel(II), copper(II) and zinc(II)

1-Isonicotinoyl-4-benzoyl-3-thiosemicarbazide (IBtsc) and its Cr^III, Mn^II, Fe^III, Co^II, Ni^II, Cu^II and Zn^II complexes have been prepared and characterized by elemental analyses, magnetic susceptibility measurements, u.v.–vis., i.r., n.m.r. and FAB mass spectral data. The room temperature e.s.r. spectra of the Cr^III, Fe^III and Cu^II complexes yield values, characteristic of octahedral, tetrahedral and square-planar complexes, respectively. The Mössbauer spectra of [Fe(IBtsc-H)Cl₂] at room temperature and at 78 K suggest the presence of high-spin Fe^III. The Ni^II, Cr^III and Cu^II complexes show semiconducting behaviour in the solid state, but the Zn^II complex is an insulator at room temperature. IBtsc and its soluble complexes have been screened against several bacteria, fungi and tumour cell lines.     

Synthesis and characterization of two acetato-bridged dinuclear copper(II) complexes with 4-bromo-2-((4 or 6-methylpyridin-2-ylimino)methyl)phenol as ligand

The synthesis and characterization of two new acetato-bridged dinuclear copper(II) complexes are described. Both compounds have the general formula [Cu(L)(µ-O₂C–CH₃)]₂, in which L = 4-bromo-2-((4-methylpyridin-2-ylimino)methyl)phenol or 4-bromo-2-((6-methylpyridin-2-ylimino)methyl)phenol. The title compounds consist of dinuclear units with bridging acetato groups and a ligand linked to each copper via the phenol oxygen and nitrogen. Both compounds were synthesized in a one-step reaction and characterized by elemental analysis, Fourier transform infrared (FTIR), electron spin resonance (ESR), and electronic spectra and by room temperature magnetic moments. The compounds exhibit antiferromagnetic interactions at room temperature. UV-Vis spectra show four absorptions attributed to d–d transitions of copper, ligand → metal charge transfer and π → π* or n → π* transitions of ligand. The FTIR spectra indicate a Cu₂O₄C₂ ring vibration. Both complexes show room temperature magnetic moments of about 1.6 B.M. per copper. The X-band ESR studies indicate a weak half-field band, characteristic of the Cu(II)–Cu(II) dimer, observed at 1552 and 1558 G for the complexes, strongly suggesting that the hyperfine structure arises from a spin triplet species. The spectra of frozen samples in DMSO or DMF at liquid nitrogen temperature show a typical Δm = 1 transition.     

Synthesis and physico-chemical studies on cobalt(II), nickel(II) and copper(II) complexes of benzidine diacetyloxime

The synthesis of benzidine diacetyloxime (H₂L) and its cobalt(II), nickel(II) and copper(II) complexes is described. The complexes were characterized by elemental analyses, molar conductivities, magnetic moments, i.r., u.v.–vis. spectra, t.g.a. and e.s.r. measurements. I.r. spectra show that H₂L behaves as a neutral or dinegative ligand depending on the nature of the metal salts. The molar conductances of the complexes in DMF are commensurate with their non-ionic character. The e.s.r. spectrum of the solid copper(II) complex (7) at room temperature shows broad signal, indicating spin-exchange interactions between copper(II) ions. However, in TMHF solution at 77 K, it shows an axial type ground state with mixed ionic-covalent bond character.     

Iron(III) complexes of 2-acetylpyridine-4-phenyl-3-thiosemicarbazones: Magnetic,E.s.r. and spectral studies

Summary Iron(III) complexes of 2-acetylpyridine-4-phenyl-3-thiosemicarbazone (LH) with the general formulae FeLX₂ (X = Cl, Br, NO₃ or SCN) and FeLSO₄ have been prepared and characterised by elemental analysis and by magnetic measurements in the polycrystalline state in the 77–298 K range and by electronic, i.r. and e.s.r. spectra. The FeLX₂ species (X = Cl, NCS or NO₃) are square pyramidal of intermediate spin-state (S=3/2) with an⁴ A ₂ ground state. The magnetic behaviour of FeLSO₄ is commensurate with high order effects coupled with antiferromagnetic exchange interactions. FeLBr₂ is a spin-free dimer involving bromine bridging between two FeLBr₂ square pyramids. However, the low-spin species [FeL(DMF)₃]²⁺ exists in dimethylformamide solution.     

Synthesis and characterization of rhodium(III), iridium(III), ruthenium(III) and osmium(III) complexes containing sterically hindered heterocyclic ligands

Summary Some thiazolidine-2-thione and thiomorpholin-3-one complexes of rhodium(lll), iridium(III), ruthenium(III) and osmium(III) have been prepared and characterized by chemical analysis, conductivity measurements, room temperature magnetic moment studies, electronic, i.r. and far i.r. spectra and n.m.r. measurements. From the magnetic properties it was concluded that the above ligands form low-spin complexes with all the metal ions. The position and multiplicity of the metal-halogen stretching modes in the far-i.r. region have been extensively investigated and discussed; the results are particularly useful in distinguishing between themer- andfac-isomers in the octahedral compounds of the ML₃ X₃ type. The wavelengths of the principal electronic absorption peaks have been accounted for quantitatively in terms of the crystal field theory and the various parameters have been calculated. On the basis of the electronic spectra a trigonal bipyramidal geometry,D _3h, has been established for the Ru(tm)₂Cl₃ complex; the Ir(rm)₂Cl₃ · H₂O complex has also been prepared. It is penta-coordinated and a trigonal bipyramidal environment is suggested for the iridium(III) ion.     

Synthesis, spectroscopy and cyclic voltammetry of new iron(III) complexes with 5-methyl-3-formyl pyrazole 3-hexamethyleneiminyl thiosemicarbazone (HMPz3Hex): X-ray crystallographic identification of [Fe(MPz3Hex)2]ClO4 · 2H2O with an indication for unusual rotation about the azomethine double bond on complexation with iron(III)

New iron(III) complexes of 5-methyl-3-formylpyrazole 3-hexamethyleneiminylthiosemicarbazone (HMPz3Hex), [Fe(MPz3Hex)₂]X · nH₂O (where X = Cl, NO₃or ClO₄ and n = 1–2) have been synthesized and physico-chemically characterized by magnetic data (polycrystalline state), electronic, i.r. and e.p.r. spectral studies. The reported complexes are all cationic electrolytes (1:1) containing two moles of monodeprotonated title ligand and an anionic counterpart. I.r. spectra (4000–200 cm^?1) indicate coordination to the central iron(III) ion via the pyrazolyl (tertiary) ring nitrogen, azomethine nitrogen and thiolato sulphur atoms of the primary ligand molecule. E.p.r. data (r.t. and l.n.t.) show the presence of a low-spin iron(III) cation with d _xz ² d _xz ² d _xz ¹ configuration. Cyclic voltammograms of iron(III) complexes indicate a reversible Fe⁺³/Fe⁺² couple. X-ray data of [Fe(MPz3Hex)₂]ClO₄ · 2H₂O (P₁, triclinic) authenticate a FeN₄S₂ distorted octahedral coordination with the two azomethine nitrogens trans to each other; the pyrazolyl nitrogens and thiolato sulphurs are in cis-positions, indicating an unusual rotation about the azomethine (C=N) double bond of the free HMPz3Hex during complexation with iron(III).     

Hydroxamic acid dinuclear complexes of molybdenum(V) and molybdenum(III)

Summary Molybdenum(V) and molybdenum(III) complexes [Mo₂O₃L₄] and [Mo₂L₆] derived from hydroxamic acids (HL) were prepared and identified by Raman, i.r., e.s.r., electronic spectra and analytical data. The low magnetic moments of the dinuclear complexes are due to in part to intramolecular interactions. Electronic spectra and vibrational studies indicate the presence of a Mo₂O₃ core in the molybdenum(V) complexes. The relative intensities of the, main and satellite peaks in e.s.r. spectra indicate the dinulcear nature of molybdenum(III) hydroxamates.     

Characterization of complexes involved in the spectrophotometric determination of cobalt with 4-(2-pyridylazo)resorcinol

Complex species involved in the spectrophotometric determination of cobalt with 4-(2-pyridylazo)resorcinol (PAR = H₂R) were studied in solution and in the solid state. An anionic [Co(III)R₂]^- species was extracted from aqueous solution in chloroform by tetraphenylarsonium or tetraphenylphosphonium chloride. Stable tetraphenylarsonium and tetraphenylphosphonium salts of di-4-(2-pyridylazo)resorcinolo cobaltate(III) with the formula [(C₆H₅)₄X][Co(III)R₂] where X=As.P; and R=C₁₁H₇N₃O₂^2-, were isolated from the chloroform phase. The complexes were characterized by elemental analyses, visible, i.r., p.m.r., e.s.r. spectra, x-ray powder photographs, magnetic susceptibility and conductivity measurements. The spectral evidence and magnetic properties indicate a tridentate coordination of two 4-(2-pyridylazo) resorcinol dibasic anions, bonded to cobalt(III) in a symmetric arrangement with both azo groups coordinated to the cobalt atom through a single nitrogen lone pair.     

STUDIES OF THE STRUCTURE OF VANADIUM(III) COMPLEXES WITH NITROGEN CONTAINING LIGANDS IN ALCOHOLIC SOLUTIONS. I. COMPLEXES OF V(III) WITH AZOLES

Abstract

Anhydrous vanadium trichloride reacts with azoles in low concentrated ethyl alcohol solution of V(III) to produce 1:1 electrolytic complexes of the type [V (azole)₄Cl₂]⁺. Studies of the visible spectra of all the above complexes demonstrate that the vanadium(III) is octahedrally co-ordinated. The room temperature magnetic moments of the complexes (～ 2.8 B.M.) are consistant with the presence of two unpaired electrons per vanadium atom. At higher concn. of V(III) the polynuclear violet-red complexes probably are formed.     

Synthesis and structural characterization of a fully conjugated macrocyclic tetraaza(14)-membered Schiff base and its bivalent metal complexes

A novel 14-membered macrocyclic Schiff base derived from 3-cinnamalideneacetoacetanilide and o-phenylenediamine acts as a tetradentate and strongly conjugated ligand to form a cationic solid complex with CuCl₂/NiCl₂/CoCl₂/ZnCl₂. The ligand and the complexes were characterized by the usual spectral and analytical techniques. The main i.r. band of the macrocyclic Schiff base was compared to that of its metal complexes. The C=N bands are shifted to the lower wave number. The cyclic voltammogram of the copper complex shows that the macrocyclic ligand is able to stabilize the copper(III) oxidation state. The e.s.r. spectra of the copper complex in DMSO solution at room temperature and liquid N₂ temperature were recorded and their salient features thoroughly discussed. The antimicrobial screening tests were also recorded and gave good results in the presence of metal ions in the ligand system.     

Complexes of N-nicotinoyl-N′-2-furanthiocarbohydrazide with oxovanadium(IV), manganese(II), iron(II & III), cobalt(II), nickel(II), copper(II) and zinc(II)

A new potential tetradentate ligand, N-nicotinoyl-N-2-furanthiocarbohydrazide (H₂Nfth), and its complexes with VO^IV, Mn^II, Fe^II,III, Co^II, Ni^II, Cu^II and Zn^II have been prepared and characterized by elemental analyses, magnetic susceptibility measurements, u.v.–vis, i.r., n.m.r., ES⁺ and FAB mass spectral data. The room temperature e.s.r spectra of the VO^IV and Fe^III complexes yield g values, characteristic of octahedral complexes. The Mössbauer spectra of [Fe(HNfth)₂] and [Fe₂(Nfth)₃] at room temperature and at 78 K suggest the presence of high-spin iron(II) and iron(III), respectively. The complexes are electrically insulating at room temperature, however, their conductivities increase as the temperature increases from 333–383 K, with a band gap of 0.46–0.77 eV, indicating their semiconducting behaviour. H₂Nfth and its soluble complexes have been screened against several bacteria and fungi.