NEUTRON AND X-RAY STRUCTURE DETERMINATION OF LAURIONITE-TYPE PB(O(H,D))X, WITH X=CL,BR, AND I, HYDROGEN-BONDS TO LEAD(II) IONS AS A HYDROGEN-BOND ACCEPTOR

The crystal structures of Pb(OH)Br, Pb(OH)Cl, Pb(OD)Br, and Pb(OD)I ha ve been refined by single-crystal X-ray and neutron diffraction, and n eutron powder Rietveld methods, respectively. The laurionite-type stru ctures (Pnma, Z = 4; wR(2) = 4.85%, a = 711.2(1), b = 401.92(5), and c = 971.4(1) pm (Pb(OH)Cl); R(w) = 9%, a = 738.5(1), b = 408.53(6), and c = 1001.2(1) pm (Pb(OH)Br); R(I) = 3.6%, a = 738.38(2), b = 408.433( 9) and c = 1001.38(3) pm (Pb(OD)Br); R(I) = 6.2%, a = 780.61(2), b = 4 20.40(1), and c = 1045.88(3) pm (Pb(OD)I)) have been confirmed. In con trast to the corresponding barium and strontium compounds, the hydroge n bonds formed are considerably stronger. This is caused by (i) the st ronger synergetic effect of lead(II) ions compared to barium and stron tium ions and (ii) by the action of the lone pair of Pb2+ as a hydroge n-bond acceptor. The existence of a O(H,D).... Pb hydrogen bond is con firmed by cohesive energy calculations with respect to the orientation of the hydroxide ions in the structure. Thus, the OH- ions are inclin ed toward the lead ions as compared to the electrostatic potential min imum. (C) 1996 Academic Press, Inc.