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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.
