Preparation of new tetraaza macrocyclic nickel(II) and copper(II) complexes bearing N-propionic methyl ester groups

A 14-membered tetraaza macrocycle, 2,13-bis(2-carbomethoxyethyl)-5,16-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.1.1807.12]docosane (L2) bearing two N-CH2CH2COOMe groups, and its nickel(II) and copper(II) complexes have been prepared and characterized. The nickel(II) and copper(II) complexes of 2-(2-carbomethoxyethyl)-5,16-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.1.1807.12]docosane (L3) containing one N-CH2CH2COOMe group have also been prepared. The crystal structure of [NiL2](ClO4)2 shows that the complex has a slightly distorted trans-octahedral coordination geometry with two relatively short axial Ni–O (N-CH2CH2COOMe group) bonds (2.136(3) Å). In various solvents, however, a considerable proportion of [NiL2]2+ exists as a square-planar form, in which the functional pendant arms are not involved in coordination. The proportion of the square-planar isomer varies with solvents in the order of nitromethane ⩽ acetonitrile < H2O < DMF ⩽ DMSO. In the case of [CuL2](ClO4)2, only one N-CH2CH2COOMe group is involved in coordination. The N-CH2CH2COOMe group of [NiL3](ClO4)2 is not directly involved in coordination even in the solid state, though the functional group of [CuL3](ClO4)2 is coordinated to the metal ion.