The closo-cluster triad: B9X9, [B9X9](center dot-), and [B9X9](2-) with tricapped trigonal prisms (X = Cl, Br, I). Syntheses, crystal and electronic structures

Halogenation of nido-B10H14 with C2H2Cl4, C2Cl6, Br-2, or I-2, produces by cluster degradation the (2 n)-closo-clusters B9X9 (X = Ck, Pr, I). The synt hesis of salts of the perhalogenated radical anions of the type (2 n + 1)-c loso-[B9X9](.-) and of the corresponding dianions (2 n + 2)-closo-[B9X9](2- ) from neutral B9X9 is described in is the number of cluster atoms; (2 n), (2 n + 1), and (2 n + 2) is the number of cluster electrons]. Molecular and crystal structures of B9Cl9, B9Br9, [(C6H5)(4)P][B9Br9]. CH2C l2, and [(C4H9)(4)N](2)[B9Br9]. CH2Cl2 have been determined via X-ray diffr action. All three oxidation states of the cluster retain the tricapped trig onal prism. The reduction of the clusters B9X9 was shown by cyclic voltammetry in CH2Cl 2 to proceed via two successive one electron reversible steps, separated by at least 0.4 V. The paramagnetic radical anions [B9X9](.-) (X = Cl, Pr) were further charac terized by magnetic susceptibility measurements of [Cp2Fe][B9X9] and [Cp2Co ][B9X9], respectively. The EPR spectra of [B9X9](.-) (X = Cl, Br, I) in glassy frozen CH2Cl2 solut ions showed increasing g anisotropy for the heavier halogen derivatives, il lustrating significant halogen participation at the singly occupied MO. The B-11 NMR spec tra of CD2Cl2 solutions of the neutral clusters B9X9 exhibit only one sharp resonance, indicating that the boron atoms are highly fluxi onal in solution. In contrast, two different boron resonances as expected f or a rigid tricapped trigonal prism are clearly observed for the [B9X9](2-) dianions in solutions and for solid B9Br9 in the B-11 MAS NMR spectra. Tem perature dependent B-11 MAS NMR experiments on B9Br9 and [B9Br9](2-) in the solid state show a reversible coalescence of the two resonances at higher temperature. B-11 MAS NMR spectra and DTA measurements of [B9Br9](2-) showe d a phase transition.