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 Angstrom and 2 oxygen atoms at 2.26 Angstrom. The cation correlations display intermediate range ordering, having a correlation length of approximately 32 Angstrom, which can be interpreted in terms of an arrangement of the Cu2+ 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.