Complexation of lop-sided 16- and 17-membered tetraaza macrocycles containing fused dibenzo substituents with zinc(II) and cadmium(II)

Abstract

A series of previously reported dibenzo-substituted tetraaza macrocycles has been extended by increasing the length of the bridge between one pair of nitrogen atoms. The new ‘lop-sided’ 16- and 17-membered macrocycles as well as a range of their zinc(II) and cadmium(II) complexes have been prepared and characterized. Crystal structures of both new macrocycles and of their respective cadmium(II) complexes have been determined. The 16-membered macrocycle yields a pseudo-square-pyramidal cadmium(II) complex whereas the 17-membered one forms a distorted-octahedral complex. Comparison of these structures with those for the cadmium(II) complexes of corresponding 15-membered ring ligands shows that, as the ring size increases, the ligand is generally better able to accommodate the cadmium(II) in the centre of the cavity, thus aiding the formation of a six- rather than five-co-ordinate geometry in the complex of the 17-membered ring.