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

Abstract

The crystal structure of tin (II) sulphate, SnSO4, 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 SnSO4 are a = 7.12322(1), b = 8.81041(1), c = 5.32809(1) Å, and V = 334.383(1) Å3. The average 〈Sn–O〉 [12] distance is 2.9391(4) Å. However, the Sn2+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, SnSO4 has a structure similar to barite, BaSO4, and its structural parameters are intermediate between those of BaSO4 and PbSO4. The tetrahedral SO4 group has an average 〈S–O〉 [4] = 1.472(1) Å in SnSO4. Comparing SnSO4 with the isostructural SrSO4, PbSO4, and BaSO4, several well-defined trends are observed. The radii, rM, of the M2+(=Sr, Pb, Sn, and Ba) cations and average 〈S–O〉 distances vary linearly with V because of the effective size of the M2+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 Sn2+cation.