Single crystal EPR spectra of a natural mineral, apophyllite, containing VO(II) ion as an impurity have been investigated. The EPR spectra of the mineral, as obtained, was complex in nature, but was simplified by annealing the crystals at 490 K. The EPR parameters of the VO(II) species in the annealed crystal,g_∥ = 1.924 (2);g_⊥ = 1.983 (2);A_∥ = 18.35 (5); andA_⊥ = 7.24 (5)mT, are very close to a typical VO(II) impurity. Theoretically calculated line positions, using second-order hyperfine terms in the spin Hamiltonian with an axially symmetricg andA tensor values, agreed very well with the experimental ones. The EPR analysis of the annealed crystal has further revealed that the most preferred location of the VO(II) impurity is a substitutional Ca(II) site. The calculated bonding parameters and admixture coefficients indicate a fair amount of covalent bonding in the complex.

Preparation of the ligands HL¹ = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-ethylphenol; HL² = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-methoxyphenol and HL³ = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-nitrophenol are described together with their Cu(II) complexes with different bridging units. The exogenous bridges incorporated into the complexes are: hydroxo [Cu₂L(OH)(H₂O)₂](ClO₄)₂.H₂O (L¹=1a, L² =1b, L³ =1c), acetato [Cu₂L(OAc)₂]ClO₄.H₂O (L¹ =2a, L² =2b, L³ =2c) and nitrito [Cu₂L¹(NO₂)₂(H₂O)₂]ClO₄.H₂O (L¹=3a, L² =3b, L³ =3c). Complexes1a,1b,1c and2a,2b,2c contain bridging exogenous groups, while3a,3b,3c possess only open μ-phenolate structures. Both the ligands and complexes were characterized by spectral studies. Cyclic voltammetric investigation of these complexes revealed that the reaction process involves two successive quasireversible one-electron steps at different potentials. The first reduction potential is sensitive to electronic effects of the substituents at the aromatic ring of the ligand system, shifting to positive potentials when the substituents are replaced by more electrophilic groups. EPR studies indicate very weak interaction between the two copper atoms. Various covalency parameters have been calculated.

Single crystal EPR studies of VO(II)-doped cadmium potassium phosphate hexahydrate (CPPH) have been carried out at room temperature. The angular variation spectra in the three orthogonal planes indicate that the paramagnetic impurity has entered the lattice only substitutionally in place of Cd(II). Spin Hamiltonian parameters have been obtained from single crystal data. Powder spectra show a set of eight parallel and perpendicular features indicating the presence of only one site. The admixture coefficients have been calculated from the data, which agree well with the literature values.

New symmetrical compartmental binucleating ligands 2,6-bis[N-(2-dimethylaminoethyl)-N-methyl)aminomethyl]-3,4-dimethylphenol [HL¹] and 2,6-bis[N-(2-diethylaminoethyl)-N-ethyl)aminomethyl]-3,4-dimethylphenol [HL²], and their copper(II) complexes [Cu₂L^1–2(X)]ClO₄, (X = NO₂^-, OAc^- and OH^-) have been prepared. Spectral, catalytic, magnetic, EPR and electrochemical studies have been carried out. A catecholase activity study indicates that only HL¹ complexes have efficient catalytic activity due to a less sterically hindered methyl group and enhanced planarity (larger-2J values) with respect to the oxidation of 3,5-di-t-butylcatechol to the corresponding quinone. Variable temperature magnetic susceptibility studies of the complexes show antiferromagnetic interaction between the copper atoms. X-band EPR signals could not be observed for polycrystalline samples both at room temperatures and liquid nitrogen, consistent with two antiferrromagnetically coupled copper centres in the solid state. EPR spectral studies in methanol solvent show well-defined four hyperfine signals at room temperature due to decomposition of the dimer into monomers. This however is not seen in frozen methanol glass, may be owing to restructuring of the monomers into dimers due to an increase in viscosity of the solvent. Electrochemical studies revealed chemically irreversible behaviour due to chemical or/and stereochemical changes subsequent to electron transfer.

A bimetallic nickel(II) complex with the ligand Hsalamp (2-[(4-methyl-pyridin-2-ylimino)-methyl]-phenol), having the molecular formula, Ni₂C₂₆H₂₂ N₄O₁₀Cl₂, is synthesized and characterized by elemental, UV-Vis, IR and EPR studies. The IR spectrum confirms the presence of coordinated perchlorate ion and the UV-Vis. spectrum substantiates that the geometry around the metal ion is distorted square pyramidal. In the solvent methanol, the complex undergoes dissociation indicating the nature of the complex to be 1:2 electrolyte. The single crystal EPR studies indicate that the zero-field splitting is not large and the spectra can be observed even at room temperature, not so common for a nickel(II) ion. The spin Hamiltonian parameters calculated from single crystal rotations are:g - 2.377, 2.219, 2.071 and D - 9.7, 4.2 and -13.9 mT. Optical and electron paramagnetic spectral data have been used to obtain the parametersDq,B andC.