Studies of pendant-arm macrocyclic ligands. Part 4. Two penta-aza macrocycles based on 1-(2′-dimethylaminoethyl)-1,5,9,13-tetra-azacyclohexadecane and its complexes with bivalent metal ions

Two new pendant-arm sixteen-membered ring penta-aza macrocycles, 1-(2′-dimethylaminoethyl)-1,5,9,13-tetra-azacyclohexadecane (L1) and 1-(2′-dimethylaminoethyl)-5,9,13-trimethyl-1,5,9,13-tetra-azacyclohexadecane (L2) have been prepared, and the complexes of L1 with Ni2+, Cu2+, Co2+, Zn2+, Cd2+, and Hg2+ investigated. The ions Ni2+, Cu2+, and Co2+ form high-spin five-co-ordinate complexes. Carbon-13 n.m.r. spectroscopy shows [Zn(L1)][NO3]2 to be a 1 : 1 mixture of two species, one symmetric and the other asymmetric, and [Cd(L1)][NO3]2 is analogous but with evidence of a small amount of a third species. Attempts to prepare [Hg(L1)]2+ have led to its immediate reduction to metallic mercury.