Selenoboratoborates [B_(12)(BSe_3)_6l~(8-): A New Class of Chalcogen-Substituted Icosahedral Boron Clusters

摘要

Binary and ternary boron-sulfur and boron-selenium compounds are accessible through high-temperature solid-state syntheses starting from the elements or binary components. This novel class of compounds, which has been established over the past two decades, shows some remarkable structural principles and interesting physical properties. For instance, there are compounds with trigonal-planar coordinated boron atoms such as isolated BS_3~(3-) ions, dinuclear strained B2S2 four-membered ring systems B_2S_4~(2-) trinuclear B_3S_6~(3-) ions, dinuclear B_2S_5~(2-) ions with trithiadiborolane rings, octanuclear porphin-analogous B_8S_(16) molecules, and planar two-dimensional polymers formed by interconnected B_2S_2 and B_3S_3 rings. Thioborates with tetrahedral coordination of the boron atoms show a structural diversity that ranges from chains of corner-sharing tetrahedra over layers of corner- and edge-sharing tetra-hedra to three-dimensional macrotetrahedra. Lithium and silver thioborates such as Ag_6B_(10)S_(18), Li_5B_7S_(13), and Li_9B_(19)S_(33) are particularly interesting for use as fast ionic conductors. The only known example of a compound with an isolated BSe_3~(3-) ion is Tl_3BSe_3. In all other reported selenobo-rates a tetrahedrally coordinated boron atom is present. They form polymeric chain structures with spirocyclically fused B_2Se_3 and B_2Se_4 rings.