The Jahn-Teller effect in solutions of flexible molecules: A neutron diffraction study on the structure of a cu²⁺ solution in ethylene glycol

The method of isotopic substitution in time-of-flight neutron diffraction is used to measure the coordination environment of Cu²⁺ in a 2-180(2) molal solution of Cu(CF₃SO₃)2 in fully deuterated ethylene glycol (EG). The results show that EG acts as a bidentate ligand to form [Cu(EG)₃]²⁺ tris-chelate complexes. There is strong evidence for Jahn-Teller distortion of the complex which is best represented by a model wherein the octahedron is tetragonally elongated to give a (4 + 2) configuration with 4 oxygen atoms at 1·98 Å and 2 oxygen atoms at 2·26 Å. The cation correlations display intermediate range ordering, having a correlation length of approximately 32 Å, which can be interpreted in terms of an arrangement of the Cu^{2 +} complexes which maximizes their mean separation. A new analysis is made for the results obtained from previous neutron diffraction experiments on a 2·00 molal solution of Cu(ClO₄)₂ in D₂O and a 1·00 molal solution of Cu(NO₃)₂ in D₂O. The [Cu(D₂O)₆]^{2 +} complex in both solutions comprises a (4 + 2) structural configuration for which the degree of distortion is larger than indicated by the majority of X-ray diffraction and extended X-ray absorption fine structure measurements.