Angira Koch

Synthesis and characterization of a binuclear copper(II) complex [Cu(H2slox)]2 from polyfunctional disalicylaldehyde oxaloyldihydrazone and its heterobinuclear copper(II) and molybdenum(VI) complexes

The binuclear copper complex [Cu(H2slox)]2 (1) and heterobinuclear copper and molybdenum complexes [Cu(slox)MoO2(A)2] (slox = tetranegative disalicylaldehyde oxaloyldihydrazone) (A = H2O (2), py (3), 2-pic (4), 3-pic (5), 4-pic (6)) and [Cu(slox)MoO2(NN)] (NN = bpy (7) and phen (8)) have been synthesized from disalicylaldehyde oxaloyldihydrazone in methanol and characterized by various physico-chemical and spectroscopic techniques. The stoichiometry of the complexes has been established based on elemental analyses and thermoanalytical studies. The µ eff values for the complexes rule out metal–metal interaction between the metal centers in the structural unit of the complexes. The dihydrazone has keto-enol forms; in 1, it is a dibasic tetradentate bridging ligand in enol form and in heterobinuclear complexes as a tetrabasic hexadentate bridging ligand. Electronic spectra of the complexes show that copper(II) is square-planar in binuclear and heterobinuclear complexes; molybdenum is a distorted octahedral stereochemistry in heterobinuclear complexes. EPR spectra suggest that in all complexes, the unpaired electron is in the d x 2− y 2 orbital of copper and that the copper in heterobinuclear complexes is tetrahedrally distorted.

Solvent free selective oxidation of alcohols catalyzed by a trinuclear complex with a dicopper(II)–monozinc(II) centre using hydrogen peroxide as an oxidant

The oxidation of alcohols to carbonyl compounds was investigated by an efficient catalytic system comprising of a new heterotrinuclear complex containing a dicopper(II)–monozinc(II) centre, [ZnCu2(slsch)(NO3)2(H2O)8]·2H2O with hydrogen peroxide under solvent free conditions. Primary and secondary alcohols were oxidized to the corresponding aldehydes and ketones in good to excellent yield. The newly developed catalyst system can be reused in four consecutive runs without any significant loss of activity.

Heterobimetallic dioxomolybdenum(VI) complexes derived from bis(2-hydroxy-1-naphthaldehyde)malonoyldihydrazone: Synthesis and characterization

The heterobimetallic complexes [MMoO2(L)(H2O)2] (where M = Zn2+ (1), Cu2+ (2), and Co2+ (4)) and [{MMoO3(H2L)(H2O)2}2] (where M = Ni2+ (3) and Mn2+ (5)) are synthesized from bis(2-hydroxy-1-naphthaldehyde)malonoyldihydrazone (H4L) using the monometallic precursor complex [MoO2(H2L)]·H2O in ethanol. The composition of the complexes is established based on the data obtained from the elemental analysis and molecular weight determinations. The structure of the complexes is discussed in the light of data obtained from molar conductance, magnetic moment, electronic, EPR and IR spectroscopic studies.

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=1/2). At lower temperature, the ground state for the complexes is dx(2)-y(2) with considerable contribution from dz(2) 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 characterization of a copper–zinc heterobinuclear complex of 2,2′-bipyridine

The synthesis of the heterobinuclear copper–zinc complex [CuZn(bz)3(bpy)2]BF4 from benzoic acid and bipyridine is described. Single crystal X-ray diffraction of the heterobinuclear complex reveals the geometry of the benzoate-bridged Cu(II)–Zn(II) center. The copper and zinc ions are five coordinates, having distorted square pyramidal geometry. The Cu–Zn distance is 3.384 Å. The complex is normal paramagnetic having μeff value equal to 1.75 BM, ruling out the possibility of Cu–Cu interaction in the structural unit of the complex. The ESR spectrum of the complex in CH3CN at RT exhibits an isotropic four-line spectrum centered at g = 2.082 and hyperfines coupling constants Aav = 63 × 10−4 cm−1, characteristic of mononuclear square-pyramidal copper(II) complexes. At LNT, the complex shows anisotropic spectra with g║ = 2.260 and g = 2.070 and A║ = 170 × 10−4 cm−1, respectively, characteristic of distorted square-pyramidal geometry. The complex is an efficient catalyst for oxidation of alcohols to aldehydes and ketones.