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

摘要

The crystal structures of Pb(OH)Br, Pb(OH)Cl, Pb(OD)Br, and Pb(OD)I have been refined by single-crystal X-ray and neutron diffraction, and neutron powder Rietveld methods, respectively. The laurionite-type structures (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 = 420.40(1), and c = 1045.88(3) pm (Pb(OD)I)) have been confirmed. In contrast to the corresponding barium and strontium compounds, the hydrogen bonds formed are considerably stronger. This is caused by (i) the stronger synergetic effect of lead(II) ions compared to barium and strontium ions and (ii) by the action of the lone pair of Pb2+ as a hydrogen-bond acceptor. The existence of a O(H,D).... Pb hydrogen bond is confirmed by cohesive energy calculations with respect to the orientation of the hydroxide ions in the structure. Thus, the OH- ions are inclined toward the lead ions as compared to the electrostatic potential minimum. (C) 1996 Academic Press, Inc. [References: 23]