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

Abstract

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; RI = 5.9, 7.9 and 7.8%; a = 7.7294 (1), b = 4.24697 (7) and c = 10.7374 (1) Å [Sr(OH)I]; a = 7.7303 (8), b = 4.2465 (4) and c = 10.7399 (10) Å [Sr(OD)I]; a = 8.0291 (9), b = 4.4961 (5) and c = 11.0196 (16) Å [Ba(OH)I]; a = 8.0203 (13), b = 4.4912 (7) and c = 11.0193 (14) Å [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...Y distances, furcation of the bonds and M—O bond lengths (synergetic effect). The longest H...Y distances (Y′ = Cl, Br, I), for which hydrogen bonds due to OH− have been established, are 2.80, 2.90 and 3.25 Å, respectively.