NEUTRON-DIFFRACTION ANALYSIS OF POSITIONAL OXYGEN AND HYDROGEN DISORDER IN BA[FE(CN)5NO].3H2O

Ba[Fe(CN)5NO] . 3H-2O, M(r) = 730.591, Pbcm, a = 7.610(1) angstrom, b = 19.389(6) angstrom, c = 8.628(1) angstrom, V = 1273.1 angstrom 3, Z = 4, D = 2.13 g cm-3, lambda = 0.87013 angstrom, mu = 0.031 cm-1, F(000) = 418.4 fm, T = 297 K, R = 0.037, wR = 0.033, S2 = 1.17(0.03), two crystals: 2615 and 1098 measured, 1102 and 968 unique intensities, 143 parameters, refinement on \F\2 including weak and negative intensities. The intensities are shown to be normally and independently distributed and their variances to be properly determined. Two water molecules occupy split positions forming enantiomorphous chains parallel c. Left- and right-handed forms of the chains are statistically distributed over the crystal.