Complexes of N-heterocyclic carbenes (NHCs) with copper(II) halogenides are unstable. Upon formation, these complexes decompose to give haloamidinium salts. Contrastingly, O-substituted copper(II) NHC complexes are fairly stable. A series of new five-, six- and seven-membered ring NHC complexes of Cu(OAc)(2) have been synthesised and characterised in the solid state.