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

Abstract

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.