Butterflies and bridges
15 Nov 2011



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.

​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.

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​