THE JAHN-TELLER EFFECT IN SOLUTIONS OF FLEXIBLE MOLECULES - A NEUTRON-DIFFRACTION STUDY ON THE STRUCTURE OF A CU2-GLYCOL( SOLUTION IN ETHYLENE)

The method of isotopic substitution in time-of-flight neutron diffract ion is used to measure the coordination environment of Cu2+ in a 2.180 (2) molal solution of Cu(CF3SO3)(2) in fully deuterated ethylene glyco l (EG). The results show that EG acts as a bidentate ligand to form [C u(EG)(3)](2+) tris-chelate complexes. There is strong evidence for Jah n-Teller distortion of the complex which is best represented by a mode l wherein the octahedron is tetragonally elongated to give a (4 + 2) c onfiguration with 4 oxygen atoms at 1.98 Angstrom and 2 oxygen atoms a t 2.26 Angstrom. The cation correlations display intermediate range or dering, having a correlation length of approximately 32 Angstrom, whic h 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 C u(NO3)(2) in D2O. The [Cu(D2O)(6)](2+) complex in both solutions compr ises a (4 + 2) structural configuration for which the degree of distor tion is larger than indicated by the majority of X-ray diffraction and extended X-ray absorption fine structure measurements.