Trigonal Prismatic Versus Octahedral Coordination: The Crystal and Molecular Structures of Dy{S2P(C6H11)2} 3 and Lu{S2P(C6H11)2} 3

Abstract

Simple arguments concerning ligand-ligand repulsion are often used to predict coordination polyhedra. This approach has been quantified over the past few years by Kepert et al. for a number of different ligand types and coordination numbers (1). For the specific case of M(bidentate)3 the structures are found to be intermediate between octahedral and trigonal prismatic if the ligands are not of the dithiolene type (2). The ideal coordination polyhedron may be described by the twist angle, θ, between opposite triangular faces where θ =0° for a trigonal prism and θ = 60° for an octahedron. Calculations of ligand-ligand repulsions predict small values of θ for ligands with a small “bite”, b, and more octahedral geometry for ligands with larger values of b. This approach was extended by Avdeef et al. (3) who presented a large number of examples to illuminate the discussion which spanned a number of ligand, central ion and charge types. We thus thought it worthwhile to examine a series of compounds which are iso-electronic (excluding f electrons), have the same ligand, the same total charge and only differ in the radius of the central ion.