Hexaco-ordination of a diamino-substituted tetra-azameacrocycle to cobalt(III) and nickel(II): compressed Co–N bonds?

Abstract

The substituted cyclam macrocycle 6,13-diamino-6,13-dimethyl-1,4,8,11-tetra-azacyclotetradecane (L₂) can co-ordiante to metal ions as a hexadentate ligand; whereas M–N distances for the Ni^II complex are ‘normal,’ those for the Co^III complex are unusually short, and this is reflected in a very negative Co^III/II redox couple and a significant shift of the electronic spectrum mmaxima to higher energy.