The single-crystal electronic and electron spin resonance spectra of calcium copper(II) acetate hexahydrate

Abstract

The polarised single-crystal electronic spectra of CaCu(AcO)₄,6H₂O are assigned in S₄ and D_2d symmetries, with a d_xy ground state and yield the one-electron orbital sequence: d_xy > d_z² > d_xz, d_yz > d_x²–y². The e.s.r. spectra yield the orbital reduction factors r_⊥= 0·78 and r_∥= 0·926 . That r_∥ > r_⊥ indicates substantial out-of-plane bonding of the long-bonded acetate oxygen atoms. These results suggest that the molecular structure of CaCu-(AcO)₄,6H₂O should be described as a distorted dodecahedron (rather than as a distorted tetrahedron or octahedron) involving an eight co-ordinate copper(II) ion environment. Bond-length and electronic energy-level data, in support of this suggestion, are discussed and compared with related systems.