[(BH2)6S4]2-, [(BH2)6SE4]2- - NEW CHALCOGENOBORON HYDRIDE ANIONS WITH ADAMANTANE STRUCTURE

The reaction of THF.BH3/NaBH4 (2:1) with H2S produces Na[H3B-mu-2-S(B2H5)] (5) with hydrogen evolution. 5 reacts with an excess of H2S to give Na2[(BH2)6S4] (3a), which is also formed in the reaction of THF.BH3 with NaSH or anhydrous Na2S. These reactions proceed via 5 and the intermediates 7 or 8 by loss of BH4- and cyclization. The analogous compound Na2[(BH2)6Se4] (4a) is obtained by the reaction of elemental selenium with NaBH4 (1:1) in triglyme. The primary product is Na2[H3B-Se-Se-BH3] (9). Treatment of 9 at 100-110-degrees-C yields 4a and polymers. 3a and 4a react with CsBr to form the crystalline compounds Cs2[(BH2)6S4].CsBr (3b) and Cs2-[(BH2)6Se4].CsBr (4b), characterized by X-ray structure determinations. The anions of 3b and 4b consist of an adamantane skeleton. The Br- ion is octahedrally coordinated by Cs+ ions. The Cs6Br octahedra share faces to form columns along the hexagonal c axis. The crystal structures of the isotypic compounds 3b and 4b are closely related to the structure of CsNiCl3.