Additive electric field gradients and the correlation of Mossbauer quadrupole splitting with stereochemistry

Abstract

The assumption that the electric field gradient at the nucleus of a Mossbauer atom is an additive function of the ligands leads to correlations between Mossbauer quadrupole splitting and the coordination geometry. These correlations are associated with a situation known as intermediate symmetry, in which the electric field gradient has higher symmetry than that required by the point symmetry of the complex. The theory of additive electric field gradients is developed by use of cartesian tensors, irreducible tensors, and Shubnikov antisymmetry operators. Underlying symmetry features responsible for the intermediate symmetry are elucidated, and particular models for rationalizing the correlations are seen as manifestations of these symmetries. On making the convenient (but not indispensable) assumption that the metal-ligand bonds have cylindrical symmetry, the so-called ‘point-charge model’ is obtained.