Structural disorder in the geometric isomers of L-tris{(–)propylenediamine}cobalt(III) salts

Abstract

Single-crystal and X-ray powder data are used to show that salts of the complex ions cis- and trans-L-tris[(–)-propylenediamine]cobalt(III) fall into two classes with regard to disorder of the complex ions. In the first class typified by the dithionate and tris(malonato)-chromate(III) salts, the geometric isomers are indistinguishable since the cations are disordered giving rise to an average D₃ symmetry. In the second class typified by the bromide salt, the cis-isomer has an ordered (C₃ symmetry) structure. In this case the lattice does not have space to accommodate the disordered cation or the trans-isomer. The trans-isomer does not crystallise but forms an amorphous glass.

A survey of nine salts revealed none in which the trans-isomer had an ordered arrangement and it was, therefore, impossible directly to prove its existence by X-ray structure analysis.