The State of Cu²⁺ Ions in Concentrated Aqueous Ammonia
Solutions of Copper Nitrate

V. F. Anufrienko, R. A. Shutilov, G. A. Zenkovets, V. Yu. Gavrilov, N. T. Vasenin,
A. A. Shubin, T. V. Larina, A. V. Zhuzhgov, Z. R. Ismagilov, and V. N. Parmon

Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 5, Novosibirsk, 630090 Russia

e-mail: zenk@catalysis.ru

Received September 15, 2011

Abstract—Stabilization of Cu²⁺ 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 Cu²⁺ associates with different types of orbital ordering have been identified. The ammonium ion con-
centration in a solution has a decisive effect on the type of orbital ordering of Cu²⁺ ions in associates. In all
cases, Cu²⁺ ordering in associates is caused by the existence of bridging OH groups in the axial and equatorial
positions of [Cu(NH₃)_n(H₂O)_{6 – n}]²⁺ complexes (n < 6). At a high concentration of ammonium ions, weakly
bound associates of tetramminecopper with the ground state are formed. In solutions with low ammo-
nium concentrations, bulky associates with the and ground states and associates of Cu²⁺ ions with
the ground state with hydroxyl groups in the equatorial plane and axial water molecules are formed.

DOI: 10.1134/S0036023612090033

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