A Neutron Powder Diffraction Study of Fully Deuterated Laumontite

The crystal structure of fully deuterated laumontite, Ca4Al8Si16O48.18D2O, has been refined from neutron powder diffraction data using the Rietveld method, lambda = 1.468(1) angstrom T = 295 K, C2/m, Z = 1, M(r) = 1935.94, a = 14.863(2), b = 13.169(2), c = 7.537(1) angstrom, beta = 110.18(1)degrees, V = 1384.7(6) angstrom3, 6.04-degrees less-than-or-equal-to 2theta less-than-or-equal-to 125.00-degrees in 1488 steps, R(p) = 3.57 %, R(wp) = 4.57 %, GOF = 1.61, R(F) = 0.63 % (1374 Bragg reflections) and 96 refined parameters. The sample was-submerged in D2O during data collection. A D2O SpeCtrum was measured separately and, after smoothing, subtracted from the laumontite spectrum. Of the four water sites present, two are coordinated to Ca while the other two act as bridges between the Ca-coordinated waters through-hydrogen bonding. All water sites are disordered to some degree and essentially fully occupied. Elementary restrictions on bond distances and angles to the apparently large number of possible water arrangements impose a high degree of local water ordering. Local cation and/or water vacancies will disrupt the ordering scheme and result in an average symmetry in agreement with the overall symmetry.