Hypercloso-type boron subhalides

Most boron clusters follow Wade's rules of electron count and have closo structures for 2n + 2 cage bonding electrons. Boron subhalides of type B_nX_n (X = Hal, n = 6,8-12) are an exception. They possess only 2n electrons in the cluster framework, but still show closo structures (hypercloso-clusters).
Electrochemical investigations show that B_nX_n clusters with n = 6 (X = Cl, Br, I), 8 (X = Cl), 9 (X = Cl), and 10 (X = Cl,Br) show uncomplicated stepwise two-electron reduction to the closo dianions B_nX_n^2- via the radical anions B_nX_n^•-. In fact the radical anions are very stable with respect to disproportionation, as follows from the formal potentials of the two steps. Furthermore, the experiments suggest that the neutral clusters undergo very easily a spontaneous reduction to the radical anions in organic solvents.

Coworkers in this project:

Carsten Tittel, Tina Wizemann and Marc Würde

This project is based on a cooperation with Wolfgang Einholz. We thank W. Preetz, Kiel, for samples of B₆X₆^2- salts.

Oral presentations:

Bernd Speiser at the

59th ISE Annual Meeting, Sevilla/Spain, Sept. 7-12, 2008, keynote lecture

Publications from this project:

B. Speiser, T. Wizemann und M. Würde, Inorg. Chem., 42, 4018 - 4028 (2003); Two-Electron-Transfer Redox Systems. Part 7. Two-Step Electrochemical Oxidation of the Boron Subhalide Cluster Dianions B₆X₆^2- (X = Cl, Br, I).

W. Einholz, K. Vaas, C. Wieloch, B. Speiser, T. Wizemann, M. Ströbele und H.-J. Meyer, Z. anorg. allgem. Chem., 628, 258 - 268 (2002); Zweielektronentransfer-Redoxsysteme, Teil 5. Chemische und cyclovoltammetrische Untersuchung der Redoxreaktionen der Decahalogendecaborate closo-[B₁₀X₁₀]^2- und hypercloso-[B₁₀X₁₀]^•- (X = Cl, Br). Kristallstrukturanalyse von Cs₂[B₁₀Br₁₀] ^. 2 H₂O.

B. Speiser, C. Tittel, W. Einholz und R. Schäfer, J. Chem. Soc., Dalton Trans., 1999, 1741 - 1751; Two-Electron-Transfer Redox Systems. Part 2. Redox Reactions of the Boron Subhalide Clusters B_nCl_n^0/•-/2- (n = 8,9) Investigated by Electrochemical and Spectroscopic Methods.