Magnetic circular dichroism studies. Part XXIX. Magnetic circular dichroism spectra of magnesium and zinc octaethylporphyrins and their five- and six-co-ordinated complexes

Abstract

The m.c.d. spectra of zinc and magnesium octaethylprophyrin and their five- and six-co-ordinate complexes with diethyl ether, ethanol, and pyridine are reported at 285 and 77 K. The excited state magnetic moments calculated for the electronic origin of the Q band varied from 2·9 to 5·9 Bohr magnetons depending on the complexation state and central metal. The main effect of the axial ligand is to cause zero-field splitting of the excited state. The magnitude of the splitting varies with the type of axial ligand and is largest for the monopyridine complex of zinc octaethylporphyrin where the separation of the two absorption components is 100 cm^–1. The effect is interpreted as the result of the reduction in symmetry from D_4h to C_2v introduced by the axial ligand.