Syntheses, crystal structures, and electronic structure of the boron halides B9X9 (X = Cl, Br, I)

The crystal structures of B9Cl9 and B9Br9 have been determined with X-ray single crystal structure analysis (subcell: R (3) over bar m (166); Z = 6; a = 1259.6(5) pm, c = 1700.1(5) pm (B9Cl9); a = 1317.5(3) pm, c = 1777.6(3) pm (B9Br9)). Both compounds are isotypic and consist of a tricapped trigonal B-9 prism (C-3v) with different bond lengths for the triangles (180.0 pm; 176.5 pm), edges (205.7 pm; 201.0 pm), and caps (174.0 pm; 173.5 pm), For better understanding of the bonding in these clusters the electronic structures of the nonaboranes(9), the dianion B9Br92-, B8Cl82-, H2B9Br9 (three types), and B10H14 have been calculated and compared with respect to their bond distances and configurations together with the experimental results, The calculation of the Electron Localization Function (ELF) of these molecules and anions shows that the 2e-3c bonds play a dominant role in these polyhedral cages, The changes in bonding going from the non-Wade cluster B9Br9 with 18 cluster electrons to the Wade cluster B9Br92- with 20 cluster electrons can be visualized by the ELF. (C) 1997 Academic Press.