The crystal structure of tin sulphate, SnSO4, and comparison with isostructural SrSO4, PbSO4, and BaSO4

The crystal structure of tin (II) sulphate, SnSO 4 , was obtained by Rietveld refinement using synchrotron high-resolution powder X-ray diffraction (HRPXRD) data. The structure was refined in space group Pbnm . The unit-cell parameters for SnSO 4 are a = 7.12322(1), b = 8.81041(1), c = 5.32809(1) Å, and V = 334.383(1) Å 3 . The average 〈Sn–O〉 [12] distance is 2.9391(4) Å. However, the Sn 2+ cation has a pyramidal [3]-coordination to O atoms and the average 〈Sn–O〉 [3] = 2.271(1) Å. If Sn is considered as [12]-coordinated, SnSO 4 has a structure similar to barite, BaSO 4 , and its structural parameters are intermediate between those of BaSO 4 and PbSO 4 . The tetrahedral SO 4 group has an average 〈S–O〉 [4] = 1.472(1) Å in SnSO 4 . Comparing SnSO 4 with the isostructural SrSO 4 , PbSO 4 , and BaSO 4 , several well-defined trends are observed. The radii, rM, of the M 2+ (=Sr, Pb, Sn, and Ba) cations and average 〈S–O〉 distances vary linearly with V because of the effective size of the M 2+ cation. Based on the trend for the isostructural sulphates, the average 〈Sn–O〉 [12] distance is slightly longer than expected because of the lone pair of electrons on the Sn 2+ cation.