Laurionite-type M(OH)X (MBa, Pb; XCl, Br, I) and Sr(OH)I. An IR and Raman spectroscopic study

Abstract

Abstract IR, Raman and single-crystal Raman spectra of laurionite-type Sr(OH)I, Ba(OH)Cl, Ba(OH)Br, Ba(OH)I, Pb(OH)Cl, Pb(OH)Br and Pb(OH)I, and of deuterated specimens and Ba(OH)Cl1−xBrx, solid solutions recorded at 90–520 K are presented and assigned to OH (OD) stretching, librational and translational modes. The main results obtained are (i) unusually large structural H/D isotope effects of Ba(OH)Cl due to Landau-type isostructural reorientation of OH− ions and (ii) the very different nature and strengths of the hydrogen bonds formed. Thus, the strengths of the partly linear (Ba(OH)Cl), partly multifurcated hydrogen bonds range as Pb(OH)I (vOH: 3497 cm−1) > Pb(OH)Br > Pb(OH)Cl > Sr(OH)I (3591 cm−1), as shown by the red-shift of the OH stretches and the blue-shift of the OH librations. In the cases of Ba(OH)Br (3605 cm−1) and Ba(OH)I (3590 cm−1), hydrogen bonding is negligible. The stronger hydrogen bonds formed in the lead compounds are caused by the greater synergetic effect of Pb2+ ions compared to those of Sr2+ and Ba2+.