SYNTHESIS AND STRUCTURE OF NA3B5O8S, THE 1ST OXOTHIOBORATE

Na3B5O8S was prepared from the reaction of sodium sulphide with boron oxide and sodium carbonate at 500-degrees-C in a graphitized silica tube. It is the first oxothioborate that could be synthesized and characterized by single-crystal X-ray diffraction. Na3B5O8S crystallizes in the monoclinic space group P2(1)/c with a = 11.390(2) angstrom, b = 6.249(1) angstrom, c = 10.934(2) angstrom and beta = 93.94(2)-degrees. In the structure, polymeric [B5O8S3-]n anions form two-dimensionally infinite layers containing groups of two spirocyclically connected six-membered B3O3 rings with one exocyclic sulphur atom bonded to one of them. Two of the five boron atoms are in tetrahedral BO4 coordination (B-O = 1.433-1.504 angstrom) and three have trigonal planar BO3 or BO2S coordination (B-O = 1.353-1.393 angstrom, B-S = 1.813 angstrom). The three types of sodium cations between the layers are coordinated by 7 O, 4S + 2O and 1S + 6O atoms.