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 NiII 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 CuII 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.