The high-spin ground state of quadridentate salicylaldehyde Schiff-base complexes of cobalt(II) in N-heterocyclic solvents

Abstract

Formation of species with a high-spin ground state (S=) has been observed by e.s.r., n.m.r., and magnetic susceptibility measurements for quadridentate salicylaldehyde Schiff-base complexes of cobalt(II) in solution containing N-heterocyclic bases. It was found that a bidentate base, 1,10-phenanthroline, also gave similar high-spin species. The high-spin species were shown to be the base adducts having a six-co-ordinate structure. Magnetic susceptibility measurements revealed that 22% of NN′- ethylenebis(salicylideneiminato)cobalt(II) exists as the high-spin base di-adduct in pyridine at 295 K. The thermodynamic parameter ΔH^⊖ for the formation of this high-spin species was found to be –4.25 × 10³J mol^–1. The amount of the high-spin species increased as the temperature decreased. The analysis of the isotropic shifts in ¹H n.m.r. Revealed that the unpaired electron spins in the high-spin species mainly delocalize through σ orbitals.