Preparation and characterization of the isomers of (Diethylenetriamine)[di(3-aminopropyl)amine]cobalt(III) ion and the crystal structure of the mer isomer

Abstract

The reaction [Co(dpt)Cl₃]+ dien in propan-2-ol [dpt=di(3-aminopropyl)amine, dien = diethylene-triamine] gives mer-[Co(dpt)₂]³⁺ and the three geometric isomers of [Co(dien)₂]³⁺, almost quantitatively. The reaction [Co(dien)Cl₃] + dpt in propan-2-ol, catalysed by water, yields the three isomers of [Co(dien)(dpt)]³⁺ as the main products, in the approximate ratio u-fac : mer : s-fac 4 : 2 : 1. Preparation of mixed amine complexes by substitution therefore requires that the amine (dien) forming the more stable complexes be incorporated in the reactant complex. The geometric structures of the isolated [Co(dien)(dpt)] (ClO₄)₃ isomers are assigned by ¹³C n.m.r. spectra. They each hydrolyse in water or base, the mer isomer rapidly, and no isomerization has been detected. X-ray crystallographic analysis of mer-[Co(dien)(dpt)]₂ (S₂O₆)₃,H₂O,EtOH (from the isolated perchlorate by metathesis) confirms the assigned mer geometry. The two independent complex molecules in the asymmetric unit have different conformational geometries. The crystals are monoclinic, space group P2₁/c, with a 15.548(4), b 9.178(3), c 31.664(8) Å,β 89,04(2)º. The structure was refined by blocked-matrix least-squares techniques to an R-factor (on 2752 F) of 0.058.