Synthesis and co-ordination chemistry of 1,7-bis(carboxymethyl)-4,10-bis(1-methylimidazol-2-ylmethyl)-1,4,7,10-tetraazacyclododecane

Abstract

The potentially octadentate ligand 1,7-bis(carboxymethyl)-4,10-bis(1-methylimidazol-2-ylmethyl)-1,4,7,10-tetraazacyclododecane (H₂L), which contains two oxygen and two nitrogen donors on the groups attached to the macrocycle, has been isolated and characterized as the pentahydro-bromide or -perchlorate, H₂L·5HY (Y = Br or ClO₄). Its co-ordination chemistry towards nickel(II) and zinc(II) ions has been investigated and the structures of the complexes which have been obtained, [NiL]·6.5H₂O 1, [Ni(H_1.5L)][ClO₄]_1.5·2H₂O 2 and [Zn₃L₂][ClO₄]₂·5H₂O 3, have been determined by single-crystal X-ray analyses. The metal ion in 1 and 2 is in an approximately octahedral environment formed by the four nitrogen donors of the macrocycle and two donors from the dangling groups, either carboxyl oxygens 1 or methylimidazole nitrogens 2. In the trimetallic zinc complex two metal ions, in peripheral positions, are seven-co-ordinated, whereas the third is tetrahedrally four-co-ordinated.