International Conference on METALS IN SOLUTION
J. Phys. IV France 01 (1991) C5-345-C5-349
THE EFFECT OF ANION SUBSTITUTION IN NICKEL HEXAMMINE SALTSH. BLANK and G.J. KEARLEY
Institut Laue-Langevin, 156X, F-38042 Grenoble cedex, France
Several metal hexammine salts show rotational tunnelling of the NH3 groups in their low-temperature phases /1,2/. This NH3 tunnelling on one hexammine cation is strongly influenced by NH3 groups of the neighbouring cations. It is important to elucidate whether the anions play a direct rôle in determining the rotational barrier or whether changes in the barrier result simply from changes in the lattice parameter. To this end we have started a study of Ni(NH3)6l2 in which we replaced varying amounts of the iodide ions with bromides as substitutional impurities. We synthesised mixtures of Ni(NH3)6(l,Br)2 with 1, 5, 10, 20 and 50 atom% Br. A normal distribution of next neighbours fits the low-resolution neutron scattering data well. The presence of the bromide ions as substitutional impurities creates regions of "negative pressure" in the nickel hexammine iodide lattice.
© EDP Sciences 1991