Single-crystal electronic and electron spin resonance spectra of four trigonal bipyramidal copper(II) complexes

Abstract

The polarised single-crystal electronic and e.s.r. spectra of four complexes of the copper(II) ion involving a trigonal bipyramidal stereochemistry have been measured. The g-factors of each of the complexes correlate with a d_z² ground state and justify a trigonal bipyramidal description of the local molecular stereochemistries. The electronic spectra have been assigned in C_2v symmetry and yield one-electron orbital sequences consistent with that predicted by a crystal field model in D_3h symmetry, namely d_z² > d_x²–y²,d_xy > d_xz,d_yz. The detailed sequence observed for each complex is interpreted in terms of the local bond lengths and bond angles present and an attempt is made to assess the role of π-bonding in the Cu(bipy)₂²⁺ cation.