Hyperfine Coupling Constants and Covalency in Sandwich Complexes

Abstract

An analysis of the isotropic proton hyperfine coupling constants of V(C5H5)2, Ni(C5H5)2, and Cr(C6H6)2+ is given. The unpaired electrons in the e1g* molecular orbitals in Ni(C5H5)2 are found to be rather strongly delocalized into the carbon 2pz–π framework of the ligands. In agreement with bonding theories this indicates that the interaction between the metal 3dxz and 3dyz orbitals and the ligand e1g–π molecular orbitals is very important for the chemical bonding in sandwich complexes. In Cr(C6H6)2+ and V(C5H5)2 the proton coupling constants are determined mainly by σ delocalization of the unpaired electron in the a1g(3dz2) orbital into the hydrogen 1s orbitals. In V(C5H5)2, also, delocalization into the ligand π framework is present and this is thought to be due to the e2g orbitals. It is concluded that the interaction of the metal 3dxy and 3dx2−y2 orbitals with the ligand e2g–π molecular orbitals is appreciable.