Structure of the double salt [CoII(Cl)L3]Cl–[CoIII(CO3)L3]Cl [L3=(2R,5R,8R,11R)-1,7-dibenzyl-2,5,8,11-tetraethyl-1,4,7,10-tetraazacyclododecane] and related species

Abstract

The hydrochloride of the chiral cyclen ligand L³[(2R,5R,8R,11R)-1,7-dibenzyl-2,5,8,11-tetraethyl-1,4,7,10-tetraazacyclododecane] reacted with Na₃[Co^III(CO₃)₃] in acidic and alcoholic aqueous solution to give two crystalline complexes, [Co^II(Cl)L³]Cl–[Co^III(CO₃)L³]Cl and [Co^II(Cl)L³]Cl, the crystal structures of which have been determined. The former contains an equimolar mixture of two markedly different crystallographically independent molecules in the unit cell, which have been crystallised independently as two salts variously hydrated. These differ from one another in the oxidation state of the metal, the co-ordination number, and the configurations of asymmetric nitrogens. The molecule [Co^II(Cl)L³]Cl is distorted square pyramidal with the Cl^– ion at the apex and RRRR configurations of the four asymmetric N atoms; the carbonato cobalt(III) complex is six-co-ordinated and the N atoms have RSRS configurations. The corresponding mixed-valence compound with bromide did not separate, although the analogue of the monomeric carbonate was isolated. The structure determinations of the carbonate and [Co^II(Cl)L³]Cl show that the molecular geometries are essentially the same as those found in the double salt. The formation and stabilisation of the cobalt(II) species is probably due to the steric requirements of the macrocycle.