Anomalous spin Hamiltonian parameters of pseudotetrahedral copper(II) complexes. ESR spectra of copper(II)-doped dichlorobis(triphenylphosphine oxide)zinc(II)

The X-band (9 GHz) ESR spectra of the copper(I1)-doped pseudotetrahedral complex dichlorobis(tripheny1phosphine oxide)zinc(II) have been recorded on single crystal at 4.2 K. They are interpreted by using the spin Hamiltonian parameters g, = 2.46, gr = 2.08, g3 = 2.08, AI = 40 X lo4 cm-I, A2 = 25 X lo4 cm-I, AB = 20 X lo4 cm-I. The superhyperfine interaction of the unpaired electron with two equivalent chlorine atoms is also observed. The Q-band (35 GHz) ESR spectra have been recorded at 77 K, yielding g, = 2.43, g2 = 2.09, and g3 = 2.08. The difference in the g, values of the pure and the copper-doped zinc complex is related to structural differences between the copper and zinc lattices. A model including the spin-orbit coupling interaction of the unpaired electron with the ligands is proposed which rationalizes the spin Hamiltonian parameters of CuCI4 and CuX2C12 pseudotetrahedral chromophores. The anomalously low All values seen in the ESR spectra of some sulfur-containing copper proteins are related to the covalency of the copper(I1)-sulfur bonds.