Distance Limits of OH… Y Hydrogen Bonds (Y= Cl, Br, I) in Solid Hydroxides. Structure Refinement of Laurionite-Type Ba(OD)I, Sr(OD)I and Sr(OH)I by Neutron and Synchrotron X-ray Powder Diffraction

摘要

Synchrotron X-ray and neutron powder diffraction experiments on Sr(OH)I, Sr(OD)I and Ba(OD)I have been performed at ambient temperature. The structure data obtained by Rietveld refinement confirm the laurionite-type structure {Pnma, Z = 4; R[ = 5.9, 7.9 and 7.8%; a = 7.7294(1), b = 4.24697(7) and c = 10.7374 (1) A [Sr(OH)I]; a = 7.7303 (8), b = 4.2465 (4) and c = 10.7399 (10) A [Sr(OD)I]; a - 8.0291(9), b = 4.4961(5) and c = 11.0196 (16) A [Ba(OH)I]; a = 8.0203(13), b = 4.4912(7) and c = 11.0193 (14) A [Ba(OD)I]} proposed from IR and Raman spectra. In contrast to the respective lead compound, only very weak hydrogen bonds are formed. The strength of the hydrogen bonds of OH" ions in condensed material is discussed with respect to intermolecular H--7 distances, furcation of the bonds and M-O bond lengths (synergetic effect). The longest H- o -Y distances (Y = Cl, Br, I), for which hydrogen bonds due to OH~ have been established, are 2.80, 2.90 and 3.25 A, respectively.