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, 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.