CaB2 S4 O16 : A Borosulfate Exhibiting a New Structure Type with Phyllosilicate Analogue Topology.

The reaction of Ca(CO3 ) with H3 BO3 in oleum (20 % SO3 ) yielded colorless single-crystals of CaB2 S4 O16 (monoclinic, P21 /c, a=5.5188(2), b=15.1288(6), c=13.2660(6) Å, β=92.88(1)°, V=1106.22(8) Å3 ). X-ray single-crystal structure analysis revealed a phyllosilicate-analogue anionic sub-structure, forming 2D infinite anionic layers, which exhibit an unprecedented arrangement of condensed twelve-membered (zwölfer) 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.