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Abstract

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 synthesis of salts of the perhalogenated radical anions of the type (2 n + 1)-closo-[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]. CH2Cl2, and [(C4H9)(4)N](2)[B9Br9]. CH2Cl2 have been determined via X-ray diffraction. All three oxidation states of the cluster retain the tricapped trigonal prism. The reduction of the clusters B9X9 was shown by cyclic voltammetry in CH2Cl2 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 characterized by magnetic susceptibility measurements of [Cp2Fe][B9X9] and [Cp2Co][B9X9], respectively. The EPR spectra of [B9X9](.-) (X = Cl, Br, I) in glassy frozen CH2Cl2 solutions showed increasing g anisotropy for the heavier halogen derivatives, illustrating 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 fluxional in solution. In contrast, two different boron resonances as expected for 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. Temperature 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-) showed a phase transition.