Structure of a carboxylate-bridged tetra-azamacrocyclic complex of cobalt(III)

Abstract

A new macrocyclic ligand having a carefully selected pendant group has been synthesized and its cobalt(III) complex has been prepared and characterized by X-ray crystallography. 1,4,7,10-Tetra-azacyclododecane-N-m-toluic acid was prepared via the corresponding nitrile, from m-cyanobenzyl-bromide and the tetra-azamacrocycle, followed by formation of the cobalt(III) complex and then hydrolysis of the cyano group in the complex. The structure reveals a novel dinuclear structure in which the dangling carboxyl groups like the two metal ions. This is consistent with the molecular design since the pendant group was selected to prevent chelation of the carboxyl group to the same metal ion as the parent macrocycle. Crystal data: [{Co(C₁₆H₂₅N₄O₂)H₂O}₂][ClO₄]₄·6H₂O: orthorhombic, space group Pbcn, a= 25.346(7), b= 15.722(2), c= 25.720(4)Å, Z = 8 (dimers), and R= 0.064 for 2 806 unique observed [I/σ(I) 3.0] reflections. The crystal contains two independent but essentially identical dimers with two-fold symmetry, containing octahedral cobalt(III), cis-co-ordinated to four nitrogen atoms of the macrocycle, to a carboxylate oxygen, and to a water molecule.