The Role of the Bi 3+ Lone Pair Effect in Bi(H 3 O)(SO 4 ) 2 , Bi(HSO 4 ) 3 , and Bi 2 (SO 4 ) 3 .

Three new members in the Bi 2 O 3 -SO 3 -H 2 O system are identified by single crystal X-ray diffraction and Rietveld refinement after a fundamental examination of this phase space. Bi(H 3 O)(SO 4 ) 2 crystallizes in space group P 2 1 / 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, wR 2 = 0.14) homeotypic with Nd(H 3 O)(SO 4 ) 2 featuring edge-sharing BiO 9 polyhedra. Bi(HSO 4 ) 3 crystallizes in a new structure type in space group P 1 (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, wR 2 = 0.05) comprising dimers of edge-sharing BiO 8 polyhedra. For Bi 2 (SO 4 ) 3 , a new modification crystallizing in space group P 2 1 / 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, wR 2 = 0.03) isotypic to Sb 2 (SO 4 ) 3 with noncondensed BiO 7 polyhedra is presented. The role of the Bi 3+ 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 Bi 3+ lone pair activity is compared to the recently reported borosulfates Bi(H 3 O)[B(SO 4 ) 2 ] 4 and Bi 2 [B 2 (SO 4 ) 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 Bi 3+ in oxidic compounds. Finally, the thermal properties of the three compounds are reported.