T. R. Rao

Synthesis and Spectral Studies on 3d Metal Complexes of Mesogenic Schiff Base Ligands. Part 1. Complexes of N‐(4‐Butylphenyl) Salicylaldimine

A novel mesogenic Schiff base, N‐(4‐butylphenyl) salicylaldimine (Hbpsal), was prepared and its ligational behavior towards some 3d metal ions studied. All the metal complexes synthesized were of the general formula, [M(bpsal)2(H2O)2] where M=Mn(II), Co(II), Ni(II), Cu(II) and Zn(II). The complexes were structurally characterized by elemental analyses, molar conductance, IR, NMR, and electronic spectral data. The metallo mesogenic phases of the Cu(II) complex were studied by optical microscope. The spectral data show that Hbpsal acts as a bidentate ligand towards the metal ions. Mesogenic studies indicate that the ligand shows a focalconic structure with smectic‐A phase while the Cu(II) complex displays smectic‐A as well as smectic‐E phases. The authors thank the Head of the Department of Chemistry, Faculty of Science, Banaras Hindu University, for providing laboratory facilities, the Director of the Central Drug Research Institute, Lucknow, for elemental analyses, and Dr. N.V.S. Rao, Head of the Chemistry Department, Assam University, Silcher, India, for providing the optical microscope facility in identifying the mesogenic phases. One of the authors (TRR) thanks the Council of Scientific and Industrial Research, New Delhi, for financial assistance in the form of a research project (No.01(1834)/03/EMR‐II).

Coordination Behaviour of Pyridoxalisonicotinoyl Hydrazone Towards Some 3d-Metal Ions

Abstract The complexes of divalent manganese, cobalt, nickel, copper, zinc and the ligand pyridoxalisonicotinoyl hydrazone (PIH) are discussed in order to illustrate the behaviour of the ligand towards the metal ions in acidic and neutral media. The complexes [M(PIH-2H)(H2O)3] (M = Mn, Co and Zn), [Cu(PIH-2H)(H2O)2]2, [Cu(PIH)Cl(H2O)]2 2+ and [Ni(PIH)Cl2(H2O)] have distorted octahedral structures. The isostructural crystalline complexes, [M(PIH)C12]2 (M = Mn, Co and Zn) are isolated from hot solutions. The electronic spectral data of cobalt in conjunction with infrared, NMR and magnetic measurements enables the assignment of the formula [M(PIH)2][MCI4] to these complexes. The anion is tetra-hedral while the cation has an octahedral chromophore. Characterization data indicates that [Ni(PIH-2H)H2O] has a four-coordinated square-planar chromophore. The IR, 1H and 13C NMR spectral data indicate that PIH behaves as a neutral tridentate ligand in the chloro complexes and as a dinegative, tridentate species in t...

Synthesis, Characterization, Thermal and Electrical Properties of Yttrium(III) and Lanthanide(III) Complexes of Salicylaldehyde Benzoyl Hydrazone

Abstract Complexes of Y(III), La(III), Pr(III), Nd(III), Sm(III), Gd(III), Tb(III) and Dy(III) with salicylaldehyde benzoyl hydrazone, (C6H5CONHN˭CHC6H4OH), abbreviated as H2L, have been synthesized and characterized. The analytical data are suggestive of 2:3 metal: ligand stoichiometry in the complexes except in the case of Y(III), which is a 1:1 complex. A dehydration study at two temperatures, 110° C and 150° C, indicates water molecules both in the lattice and co-ordination sphere of the metal ions. Magnetic moments, IR spectra, electronic spectra and 1H NMR spectra have been recorded to establish the bonding sites of the ligand. The complexes are coloured, soluble in methanol, dimethyl sulfoxide, dimethyl formamide and insoluble in benzene, chloroform and acetonitrile. Solid state conductance at various frequencies shows the semiconducting nature of the complexes. Solution state conductance indicates their non-electrolyte nature. Optical band gap measurements on a representative complex, Dy2(L)3.12H2O show that the complex is a direct band gap material. X-ray analyses show that the structures of most of the complexes are orthorhombic.

Protonation constant of salicylidene (N-benzoyl)glycyl hydrazone and its coordination behaviour towards some bivalent metal ions

Protonation constant of an unsymmetrical Schiff base, salicylidene(N-benzoyl)glycyl hydrazone (SalBzGH), and formation constants of its complexes have been determined potentiometrically at different temperatures in aqueous dioxane medium. Complexes of SalBzGH with VO(IV), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) have been prepared. Elemental analyses, pH-metric, molar conductance, magnetic susceptibility, electronic, IR, ESR, XRD (powder) and NMR studies have been carried out to study the coordination behaviour of SalBzGH toward these metal ions. pH-metric and 1H NMR studies show the presence of two dissociable protons in the ligand. IR and NMR spectra suggest the tridentate nature of the ligand, coordinating as a uninegative species in the Mn(II) complex and as a dinegative species in all the other complexes. Presence of two different conformers of the ligand at room temperature and stabilization of a single conformer upon complex formation have been established from1H NMR spectra of the metal-free ligand, Zn(II) and Hg(II) complexes recorded at 296 K. Electronic and ESR spectra indicate highly distorted tetragonal geometry for VO(IV) and Cu(II) complexes. XRD powder patterns of the Zn(II) complexes are indexed for an orthorhombic crystal system.

SYNTHESIS AND STRUCTURAL STUDIES OF SOME LANTHANIDE COMPLEXES OF SALICYLALDEHYDE ANTHRANOYL HYDRAZONE

Abstract Lanthanide complexes of the types Ln(sah)(OAc)·xH2O and Ln′(Hsah)2(X)·xH2O [Ln=Y, La, Nd, Gd, Tb and Dy; Ln′=Pr and Sm, X=NO3 and Cl; H2sah=salicylaldehyde anthranoyl hydrazone were synthesized and characterized by various physico-chemical techniques. The complexes are coloured and highly soluble in methanol, DMSO and DMF. Dehydration studies indicate the presence of both lattice-held and coordinated water molecules. IR, electronic and 1H NMR spectra have been recorded to establish the bonding sites of the ligand. Solution-state conductance measurements indicate the non-electrolytic nature of all of the complexes while solid-state electrical conductivity studies show Nd(sah)(OAc)·4H2O to be a semiconductor. Optical band gap measurements show the Pr, Sm and Dy complexes are direct band gap materials. X-ray diffraction patterns of selected complexes indicate orthorhombic structures.

Synthesis and Spectral Studies of Some Lanthanide Complexes of Nicotinic Acid Hydrazide

Abstract Trivalent lanthanide complexes of nicotinic acid hydrazide (NicHz) of the type Ln(NicHz)3Cl3.n EtOH [Ln = La, Pr, Nd, Sm for n = 2; Ln = Eu, Gd, Tb, Dy and Y for n = l] have been synthesised. The hypersensitive band profile of the electronic spectrum indicates an eight-coordination around neodymium and the molar absorptivity has been found to increase with increasing pH and to decrease with increasing temperature (30–80°C). FT-far IR spectra indicate a transconfiguration of the two chloro groups within the coordination sphere. A square antiprismatic structure has been proposed for the complexes.

Complexes of some 4f metal ions of the mesogenic Schiff-base, N,N′-di-(4-decyloxysalicylidene)-1′,3′-diaminobenzene: synthesis and spectral studies

A mesogenic Schiff-base, N,N′-di-(4-decyloxysalicylidene)-1′,3′-diaminobenzene, H2ddsdbz (abbreviated as H2L), that exhibits a nematic mesophase was synthesized and its structure was studied by elemental analysis, mass spectrometry, NMR, and IR spectral techniques. The Schiff-base, H2L, upon condensation with hydrated lanthanide(III) nitrates yields LnIII complexes, [Ln2(LH2)3(NO3)4](NO3)2, where Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Ho. Analyses of the IR and NMR spectral data imply bidentate Schiff-base through two phenolate oxygen atoms in its zwitterionic form to LnIII, rendering the overall geometry of the complexes as a seven-coordinate polyhedron – possibly distorted mono-capped octahedron. Polarizing optical microscope and differential scanning calorimetry studies reveal that despite H2L being mesogenic, none of the LnIII complexes synthesized under this study exhibits mesomorphism.

Synthesis and characterization of the complexes of some transition metals with 2-acetyl pyridine (N-benzoyl) glycyl hydrazone

Complexes of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) with 2-acetyl pyridine (N-benzoyl) glycyl hydrazone(2-ApBzGH) have been synthesized and characterized by elemental analyses, molar conductances, magnetic susceptibility, IR, electronic, ESR,1H,13C and113Cd NMR spectral and X-ray diffraction studies. IR and NMR data suggest the tridentate nature of the ligand coordinating as a neutral species in the addition complexes and as a uninegative species in the deprotonated complexes. The presence of more than one isomer of the ligand has been established by1H NMR spectra of the ligand and complexes recorded over the 298–396 K range. The X-ray powder diffraction patterns of [Cd(2-ApBzGH)Cl]Cl and [Cu(2-ApBzGH)Cl(H2O)2]Cl are indexed for orthorhombic and tetragonal crystal systems respectively.

Synthesis and Structural Studies on 3d Metal Complexes of Furfuralisonicotinoylhydrazone

Abstract Manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and oxovanadium(II) complexes of furfuralisonicotinoylhydrazone (Hfinh) were prepared in an effort to elucidate the behaviour of the ligand towards the metal ions in weakly acidic and neutral media. IR, 1H and 13C NMR spectral studies suggest that Hfinh interacts with the metal ions through the carbonyl oxygen and azomethine nitrogen. Octahedral geometry was proposed for the Cu(II) adduct complex and the Ni(II) deprotonated complex and five-coordinate geometry for the OV(II) complexes and the deprotonated complexes of Cu(II), Co(II). The ESR spectral features of the oxovanadium(II) complexes indicate a dXZ,YZground state.

Synthesis and Spectral Studies of Some Rare Earth Metal Complexes of Pyrazinecarboxylic Hydrazide

Abstract Trivalent lanthanide metal complexes of pyrazinecarboxylic hydrazide (pyzh) of the type [Ln(pyzh)3Cl2]Cl.EtOH where Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Y have been synthesized and their structures studied by elemental analyses, electrical conductance, magnetic susceptibility, electronic, infrared, 1H and 13C NMR spectral techniques. The bonding parameters , b½, %δ and n were calculated from the electronic spectral (hypersensitive) bands of Pr(III), Nd(III), Sm(III), Eu(III) and Dy(III) complexes. The spectral data suggest an eight-coordination around the metal ion and a neutral bidentate nature of pyzh in the complexes.