Cab2s4o16: A Borosulfate Exhibiting A New Structure Type With Phyllosilicate Analogue Topology

The reaction of Ca(CO3) with H3BO3 in oleum (20% SO3) yielded colorless single-crystals of CaB2S4O16 (monoclinic, P2(1)/c, a=5.5188(2), b=15.1288(6), c=13.2660(6) angstrom, beta=92.88(1)degrees, V=1106.22(8) angstrom(3)). X-ray single-crystal structure analysis revealed a phyllosilicate-analogue anionic sub-structure, forming 2D infinite anionic layers, which exhibit an un-precedented arrangement of condensed twelve-membered (zwolfer) and four-membered (vierer) rings of corner-shared (SO4) and (BO4) tetrahedra. Charge compensation is achieved by Ca2+ cations, residing exclusively above the centers of the twelve-membered rings. DFT investigations on the solid-state structure corroborate the experimental findings and allow for a detailed valuation of charge distribution within the anionic network and an assignment of vibrational frequencies.