The energy levels of some 5-coordinate adducts of cobalt(II) Schiff's base complexes

Abstract

The state energies of a series of low-spin 5-coordinate adducts of N,N′-ethylenebis(salicylaldiminato)-cobalt(II), Co(salen), and the high-spin complex Aquo-N,N′-ethylenebis(3-methoxysalicylideneimina-to)cobalt(II), Co(3MeOsalen)·H 20, have been calculated using ligand bonding parameters derived from analogous copper(II) complexes by means of the angular overlap simple molecular orbital model The results are in reasonable agreement with the electronic and EPR spectra, and magnetic properties of the complexes and suggest that the ground state of 4-coordinate Co(salen) is 2A 2(d yz), with this changing to 2A 1(d z 2 ) in the low-spin adducts of this complex, and to 4B 1 (d yz, d z 2 , d x 2 − y 2 ) in Co(3-MeOsalen)· H 20, the unpaired electrons occupying the orbitals in parentheses. The calculations suggest that the lowest spin quartet and doublet states are quite close in energy in the 5-coordinate complexes. The relative importance of the structural changes accompanying axial ligand coordination on the state energies was investigated and it was found that the axial ligand perturbation has little direct effect on the energy difference between the low-lying spin doublet and quartet states. The relative lowering in energy of the quartet states on adduct formation was found instead to be correlated with the increase in the in-place bond lengths and, to a lesser extent, the raising of the cobalt(II) ion out of the plane of the Schiff's base ligand.