Determination of the orbital ground state symmetry of paramagnetic complexes by nuclear magnetic resonance

Abstract

Analysis of the non-Curie temperature dependence of the ligand contact shifts in mixed ligand complexes of Cr(III) with 4,7-dimethyl- ortho-phenanthroline and 4,4′-dimethyl-α,α′-bipyridine has shown that one of the mixed ligand chelates, ML 2L′, possesses an A orbital ground state, while MLL 2′ possesses the B orbital ground state in C 2 symmetry. Depending on the assumed spin delocalization mechanism, a given ground state may be associated with a given mixed ligand chelate. Simple orbital energy considerations indicate that the different orbital ground states are to be expected for the pair of mixed ligand complexes. Some applications of this technique for obtaining information on metal-ligand bonding are discussed.