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

Abstract The crystal structures of B 9 Cl 9 and B 9 Br 9 have been determined with X-ray single crystal structure analysis (subcell: R 3 m (166); Z =6; a =1259.6(5) pm, c =1700.1(5)pm (B 9 Cl 9 ); a =1317.5(3) pm, c =1777.6(3) pm (B 9 Br 9 )). Both compounds are isotypic and consist of a tricapped trigonal B 9 prism (C 3 v ) 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 B 9 Br 2− 9 , B 8 Cl 2− 8 , H 2 B 9 Br 9 (three types), and B 10 H 14 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 2 e –3 c bonds play a dominant role in these polyhedral cages. The changes in bonding going from the non-Wade cluster B 9 Br 9 with 18 cluster electrons to the Wade cluster B 9 Br 2− 9 with 20 cluster electrons can be visualized by the ELF.