The Role of the Bi3+ Lone Pair Effect in Bi(H3O)(SO4)2, Bi(HSO4)3, and Bi2(SO4)3.

Abstract

Three new members in the Bi2O3-SO3-H2O system are identified by single crystal X-ray diffraction and Rietveld refinement after a fundamental examination of this phase space. Bi(H3O)(SO4)2 crystallizes in space group P21/c (no. 14, a = 1203.5(4), b = 682.9(2), c = 821.2(2) pm, β = 102.99(1)°, 861 independent reflections, 88 refined parameters, wR2 = 0.14) homeotypic with Nd(H3O)(SO4)2 featuring edge-sharing BiO9 polyhedra. Bi(HSO4)3 crystallizes in a new structure type in space group P1 (no. 2, a = 492.04(7), b = 910.8(1), c = 1040.8(2) pm, α = 85.443(5)°, β = 86.897(5)°, γ = 74.542(4)°, 3227 independent reflections, 154 refined parameters, wR2 = 0.05) comprising dimers of edge-sharing BiO8 polyhedra. For Bi2(SO4)3, a new modification crystallizing in space group P21/n (no. 14, a = 1308.03(7), b = 473.25(3), c = 1452.61(8) pm, β = 100.886(2)°, 3189 independent reflections, 155 refined parameters, wR2 = 0.03) isotypic to Sb2(SO4)3 with noncondensed BiO7 polyhedra is presented. The role of the Bi3+ lone pair effect as elucidated by density functional theory (DFT) calculations is discussed for all three compounds with respect to their structural and optical properties. Additionally, the Bi3+ lone pair activity is compared to the recently reported borosulfates Bi(H3O)[B(SO4)2]4 and Bi2[B2(SO4)6]. Geometrical calculations based on structural data are correlated with electron localization function (ELF) calculations to establish the origin of the direction and strength of the lone pair stereoactivity of Bi3+ in oxidic compounds. Finally, the thermal properties of the three compounds are reported.