Exploring Main Group Metal Borosulfates: Similarities and Differences of Two New Borosulfates M[B2O(SO4)3] (M = Sr, Pb)

Abstract

The first strontium borosulfate Sr[B2O(SO4)3] and a novel lead borosulfate Pb[B2O(SO4)3] were obtained by solvothermal reaction of the respective anhydrous metal chlorides MCl2 (M = Sr, Pb) with H[B(HSO4)4] at 300 °C. The crystal structure of Sr[B2O(SO4)3] [Pnma, Z = 4, a = 1657.38(27) pm, b = 1203.68(19) pm, c = 439.484(8) pm] is isotypic with Ba[B2O(SO4)3] and consists of chains, built up by three membered rings of two borate tetrahedra and a sulfate tetrahedron. These rings are further connected via corner-sharing sulfate tetrahedra and hence can be classified as loop branched zweier double chains. Pb[B2O(SO4)3] crystallizes in a new structure type [P21/m, Z = 2, a = 440.00(2) pm, b = 1210.19(5) pm, c = 860.43(4) pm, β = 103.587(2) °] closely related to Sr[B2O(SO4)3]. Both structures share the common supergroup Pnmm and basically differ by the orientation of adjacent anionic chains. The coordination surrounding of Pb2+ indicates a lone pair activity and DFT calculations confirmed a weak polarizability. Moreover, the compounds were characterized by electrostatic calculations, vibrational spectroscopy and thermal analysis and broaden the structural and chemical diversity of borosulfates.