Bent bonds probed by ligand-field analysis

Abstract

Bonding electron density need not be distributed symmetrically about the line-of-centres of bound atoms. This review describes how recent ligand-field analysis has been able to detect such circumstances and other forms of misdirected valency. Eight groups of analyses, comprising detailed studies of 25 individual complexes, involve quantitative reproductions of paramagnetic susceptibilities, electron spin resonance g² tensors, and ‘d-d’ transition energies, absorbances and rotatory strengths. These careful studies provide a showcase for the reach and power of contemporary ligand-field models as well as a level of detailed insight into transition-metal bonding that is not readily available by other means. The examples given here are prefaced with brief reviews of the parametric structures of the ligand-field method. These refer to the cellular ligand-field models for both energies and intensities of electronic transitions. An indication of how calculations of magnetic properties, transition energies, spectral intensities and circular dichroism—all within a d” basis—are implemented in practice is included.