hide
Free keywords:
-
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.
