Dynamic Jahn–Teller Effects and Magnetic Anisotropies in Aqueous Solutions and Water–Ethanol Glasses of Copper(II) Solvates and Complexes with 2,2′-Dipyridine

Dynamic Jahn–Teller effects have been recognized previously in solids which contain copper(II) ions in octahedral environments. In solutions, dynamic Jahn–Teller effects have now been observed in the EPR spectrum of the tris(2,2′-dipyridine) copper(II) complex. This is shown by the small temperature coefficient of the apparent tumbling correlation time, τc, which is associated with anisotropy contributions to the EPR linewidth and by the insensitivity of τc to variations of the solvent viscosity. In partially substituted complexes, such as the tetraaquo (2,2′-dipyridine) copper(II) species which has also been studied here, the dynamic Jahn–Teller effects are inhibited due to the inhomogeneous nature of the first coordination sphere. The possible importance of dynamic Jahn–Teller effects in homogeneous solvates of copper(II) is discussed. Evidence is presented to show that addition of ethanol to aqueous solutions of copper(II) nitrate results in the formation of inhomogeneous species.