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

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(l) = 5.9, 7.9 and 7.8%; a = 7.7294(1), b = 4.24697(7) and c = 10.7374 (1) Angstrom [Sr(OH)I]; a = 7.7303 (8) , b = 4.2465 (4) and c = 10.7399 (10) Angstrom [Sr(OD)I]; a = 8.0291(9 ), b = 4.4961(5) and c = 11.0196(16) Angstrom [Ba(OH)I]; a = 8.0203(13 ), b = 4.4912(7) and c = 11.0193(14) Angstrom [Ba(OD)I]} proposed from IR and Raman spectra. In contrast to the respective lead compound, on ly very weak hydrogen bonds are formed. The strength of the hydrogen b onds of OH- ions in condensed material is discussed with respect to in termolecular H ... Y distances, furcation of the bonds and M-O bond le ngths (synergetic effect). The longest H ... Y distances (Y = Cl, Br, I), for which hydrogen bonds due to OH- have been established, are 2.8 0, 2.90 and 3.25 Angstrom, respectively.