The State of Cu~(2+) Ions in Concentrated Aqueous Ammonia Solutions of Copper Nitrate

摘要

Stabilization of Cu~(2+) ions in concentrated aqueous ammonia solutions of copper nitrate in a wide range of ammonium ion concentrations has been studied by EPR and electronic absorption spectroscopy. Three types of Cu~(2+) associates with different types of orbital ordering have been identified. The ammonium ion concentration in a solution has a decisive effect on the type of orbital ordering of Cu~(2+) ions in associates. In all cases, Cu~(2+) ordering in associates is caused by the existence of bridging OH groups in the axial and equatorial positions of [Cu(NH_3)_n(H_2O)_(6-n)]~(2+) complexes (n < 6). At a high concentration of ammonium ions, weakly bound associates of tetramminecopper with the d_(x~2-y~2) ground state are formed. In solutions with low ammonium concentrations, bulky associates with the d_(y~2) and d_(x~2-z~2) ground states and associates of Cu~(2+) ions with the d_(x~2-y~2) ground state with hydroxyl groups in the equatorial plane and axial water molecules are formed.