Butterflies and bridges

Molecular structure of (μ-D)2(Eind)11B11B(Eind).

Molecular structure of (μ-D)2(Eind)11B11B(Eind) determined using single-crystal neutron diffraction (50% probability ellipsoids). Eind is a large hydrocarbon molecule used to stabilise the compound.
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While covalent bonds are usually formed by sharing two electrons between two atoms, some compounds contain B–H–B bonds in which an electron pair is distributed over three sites.

The electron-deficient nature of these ‘3-center, 2-electron’ bonds can give rise to various distinct chemical structures, some of which have only been predicted theoretically.

 We have isolated the stable diborane(4), [B2H4]2-, with butterfly-shaped B–H–B bonds and a boron-boron link with triple-bond character. Neutron data were collected on a large-size single
crystal of 11B-labeled and deuterated diborane(4) using the SXD neutron diffractometer. The two bridging deuterium (μ-D) atoms are found to be located over two positions, which have been refined with occupancy factors of 0.5. An extraordinarily short B-B distance of 1.483(3) Å is comparable to computational predictions of B-B triple bonds. These structural features indicate that the chemical bonding at the B atoms can be described in terms of sp-hybridization.

Y Shoji, T Matsuo, D Hashizume, K Tamao (RIKEN), H Fueno, K Tanaka (Kyoto University), MJ Gutmann (ISIS)

Research date: August 2011

Further Information

Contact: Dr T Matsuo, matsuo@riken.jp
Further reading: Y Shoji et al., J. Am. Chem. Soc. 133 (2011) 11058

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