Structure and bonding of diborane

Abstract

Diborane played a key role in the development of our understanding of the bonding in electron deficient compounds. Although it was first isolated and characterized by Stock in 1912,¹ and recognized from its molecular formula as posing something of a valence problem, the distribution of its valence electrons in the molecule could not of course be determined until the positions of the atomic nuclei were known. The elucidation of its structure proved no easy task, and 30 years were to elapse before spectroscopic techniques were developed sufficiently for convincing evidence to be obtained that its structure was the bridged structure shown in Fig. 1-1, first suggested in 1921 by Dilthey,² rather than the ethane-like alternative shown in Fig. 1-2. The steps by which it was finally possible to distinguish between these structures reveal both the power and limitations of various methods of structure determination, and are briefly outlined in the following section.