Spectroscopic studies on pyrazolyl-gallate and -borate complexes of copper(II) and nickel(II)

Abstract

Variable-temperature ¹H n.m.r. data are presented for the square-planar Ni^II complexes, [{Me₂M(pz)₂}₂Ni](M = Ga or B, and pz = pyrazolyl, N₂C₃H₃), and stereochemical nonrigidity for the molecules in solution is invoked to account for the spectral changes observed. Activation energies obtained for the suggested interconversion processes are 46 for the gallium and 67 kJ mol^–1for the boron complex. The Cu^II complexes, [{Me₂M(pz)₂}₂Cu](M = Ga or B), and [{Me₂Ga(dmpz)₂}₂Cu](dmpz = 3,5-dimethylpyrazolyl, N₂C₅H₇), have been studied by electronic absorption spectroscopy, ESCA, and e.s.r. spectroscopy. Data have been interpreted to provide tentative one-electron orbital sequences for copper in these complexes. The colour change observed from solid to solution for square-planar [{Me₂Ga(pz)₂}₂Cu] has been interpreted in terms of a tetrahedral distortion of the square-planar CuN₄ chromophore in solution. The e.s.r. results for the pseudotetrahedral complex, [{Me₂Ga(dmpz)₂}₂Cu], indicate substantial d–p mixing in the ground state.