Ligand-field traces in three- and five-co-ordinated transition-metal(III) complexes

Abstract

Ligand-field analyses of published ‘d–d’ transition energies, paramagetic susceptibilities, zero-field splittings, and g values in two series of transition-metal(III) complexes have been performed within the cellular ligand-field (c.l.f.) approach. One series comprises the three-co-ordinated tris[bis(trimethylsilyl)amido] complexes of Ti^III, V^III, Cr^III, and Fe^III. The other involves trigonal-bipyramidal complexes [MX₃(NMe₃)₂](X = Cl or Br for M = Ti^III or V^III; X = Cl for Cr^III). The silylamido groups are demonstrated to act as σ donors and strong π donors throughout the series. The sum of all c.l.f. parameters in each complex, called the ligand-field trace, Σ, is likely to be constant throughout that series, with a value of ca. 31 500 cm^–1. The trace is probably also constant throughout the five-co-ordinate set of compounds, taking a value between 50 000 and 61 000 cm^–1. Detailed variations of all ligand-field parameters throughout each series are shown to accord well with general principles of chemical bonding.