The State of Copper Ions in Aqueous and Aqueous Ammonia Solutions of Copper Acetate

Stabilization of Cu2+ ions in aqueous and aqueous ammonia solutions of copper acetate was studied for a wide range of ammonia concentrations. The structure of copper acetate hydrate complexes was shown to markedly change upon dissolution in water. In aqueous solutions, copper is stabilized as strongly bound Cu2+ associates (dimers) in a distorted octahedral environment composed of water molecules and acetate groups oxygen atoms in equatorial positions with strong exchange interaction via acetate groups. In solutions of copper acetate in aqueous ammonia, the concentration of ammonia has a crucial effect on the ordering of Cu2+ ions in associates. At high ammonia concentration, disordered copper tetra-ammoniate associates with the d(x2-y2) ground state are formed, whereas at low ammonia concentration, bulky Cu2+ ion associate structures are generated, with the d(x2-y2) ground state, hydroxyl groups in the equatorial plane, and water molecules in the axial positions.