Synthesis and structural characterization of a new rubidium borosulfate, Rb5BS4O16

A new rubidium borosulfate, Rb5BS4O16, has been synthesized using (NH4)2SO4 as a source of sulfate ions for the first time. The compound crystallizes in the space group P43212 (No. 96) of the tetragonal system with a = 10.148(4) Å, c = 16.689(14) Å, V = 1718.8(17) Å3, and Z = 4. Zero-dimensional anion groups, [B(SO4)4]5−, a central BO4 tetrahedron sharing all its four vertices with neighboring sulfate tetrahedra, exist in the title compound, and then the rubidium atoms are situated in the voids of the resulting structure. The IR spectrum confirms the presence of BO4 and SO4 units. The UV–vis-NIR diffuse reflectance spectrum exhibits a band gap of about 3.99 eV. The TG-DSC analysis suggests that Rb5BS4O16 is an incongruent melting compound.