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.(1.18)0(7.12)]docosane (L-2) 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.(1.18)0(7.12)]docosane (L-3) 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) angstrom). 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 < HO < 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. (C) 2006 Elsevier B.V. All rights reserved.