X-Ray Structure and Conformational Analyses of Cobalt(III) Complexes Containing 1,3-Propanediamine and 1,4-Butanediamine.

Crystal structures of octahedral cobalt(III) complexes containing diamines, NH2 (CH2)n NH2 with n = 3 or 4 (abbreviations are tn and tmd, respectively), were determined by X-ray analysis. In crystals of [Co(tn)(tmd)2] Cl3, (1), the tn chelate ring takes skew-boat form, and the conformation of the complex is lel lel2. In crystals of [Co(tn)2(tmd)]Br3·2.7H2O, (2), both two independent complex cations take syn-chair2 lel configuration. Molecular mechanics calculation indicated that the six-membered tn chelate ring may take skew-boat form in a crowded system to reduce the steric repulsions between the chelate rings, although the tn chelate ring originally prefers the chair form.