Static and Dynamic Distortions in Five‐Coordinate Complexes of cobalt(II) and rhodium(I)

Abstract
Five‐coordinate complexes have been prepared, of the general formulae [CoX(L'L3)]+ and [RhX(L'L3)], where X = halogen and L'L3 = a quadridentate tripod‐like ligand containing various Group V donor atom sets. The electronic spectra and magnetism of the cobalt(II) series can be interpreted on the basis of a low‐spin d7‐ion in a trigonal bipyramidal environment distorted by a static Jahn‐Teller effect. Electronic spectral data for the trigonal bipyramidal rhodium(I) series show that the low‐energy 1A → 1E ligand field transition is split at room temperature, but that the splitting collapses on reducing the temperature. This behaviour has been attributed to the operation of a dynamic Jahn‐Teller effect.