Azido(imidazole)bis(acetylacetonato)cobalt(III) Complexes — Facile trans ⇋ cis Interconversion in Solution

Abstract

A number of mixed-ligand complexes of cobalt(III) containing coordinated azide ion, acetyl- acetonatc anion and the neutral base imidazole and, having the general formula [Co(acac)2(N3)(Im)] (Im = imidazole or its derivatives) have been synthesised by the reaction of K[trans-Co(acac)2(N3)2] with the biologically active ligand imidazole or its derivatives. IR and electronic spectra alongwith 1H and 13C NMR spectra have been employed to characterise the complexes and determine their geometry. In contrast to the stable trans-[Co(acac)2(NO2)(Im)] complexes, these azido complexes arc shown to undergo facile trans ⇋ cis interconversion in CHCl3 solution. The NMR spectra (1H and 13C) can be interpreted by assuming the presence of an equilibrium mixture of the cis- and trans-isomers in solution.