Borosulfates Hosting Se4 2+ Ions-Crystal Structures, Chemical Bonding, Optical Spectroscopy, and Magnetism.

Despite consistent growth in the number of compounds known to host homo- and hetero polycations of group 16 elements, only two, Se4[HS2O7]2 and Se4[S4O13], provided an exclusively oxidic coordination environment, the former being the first structural characterization of the Se4 2+ cation in 1968. With the first selenium borosulfates Se4[B(S2O7)2]2(SO3), Se4[B(S2O7)2]2, Se4[B2(SO4)2(S2O7)2]-I, Se4[B2(SO4)2(S2O7)2]-II, and Se4[B2(SO4)4] we extended this list by five compounds. Aside from Se4[HS2O7]2, Se4[S4O13] was synthesized but never structurally characterized. In this contribution we also evaluate the crystal structure of the tetrasulfate Se4[S4O13]. All compounds are synthesized under solvothermal conditions. Powder reflectance spectra of the selenium borosulfates are in accordance with the yellow body color of the compounds. Magnetic measurements confirm the diamagnetic character of the Se4 2+ ions, in agreement with the calculations. Temperature-programmed powder X-ray diffraction reveals that the borosulfates of the study form sequentially with increasing decomposition temperature, enabling their selective synthesis. Furthermore, we performed infrared spectroscopy, Rietveld refinements and thermal analyses.