$\endgroup$ – M.A.R. $\begingroup$ @Lord The first paper Ron linked to speaks about diborane (4), while I'm looking for the diborane (6) "version". Chemical bonding - Chemical bonding - Boranes: The electron-deficient compound diborane, B2H6, as noted earlier, can be regarded as a cluster of atoms held together by pairs of delocalized electrons that extend their binding influence over all electrons in the molecule. Bonding diagram of diborane (B 2 H 6) showing with curved lines a pair of three-center two-electron bonds, each of which consists of a pair of electrons bonding three atoms, two boron atoms and a hydrogen atom in the middle. In B2H6 two type H bond is present 1- FOUR TERMINAL HYDROGEN BOND-Each terminal B–H bond is a standard two-electron two center bond. The bonding in diborane is unique as it involves two 3c-2e bonds. The structure of diborane has D 2h symmetry. Diborane is an electron deficient molecule. A well-studied example is the 2-norbornyl cation (below). In simple molecular orbital theory of covalent bonding two atomic orbitals of the same symmetry and similar energy linearly combine with each other resulting in the formation of two molecular orbitals by the LCAO method. The bridging hydrogen atoms lie above and below this plane. These four terminal B -H bonds are regular 2-centered- 2 electron bonds. The 3-centre 2-electron bond, first identified in diborane, is probably also found in the cation intermediates formed during certain SN 1-reaction mechanisms. There's some info here . Jun 10 '15 at 19:16 Most books show the overlapping as between two sp3 orbitals of B atoms and s orbital of H atom.But the bond angle between the terminal H atoms and central B atom is 120, as if the B atom were sp2 hybrid. The bonding in diborane may be explained on the basis of an idea of three centre-two electron, BーHーB types of bond. The interesting part is that in computing molecular mass, it takes both HCl and B2H6 into account. The unusual feature of diborane is the existence of B―H―B bridges as part of the cluster. Four hydrides are terminal, while two bridge between the boron centers. Structure of B2H6 Boron is sp3 hybridised but the BH bonds are not all equal. The two boron atoms and the four terminal hydrogen atoms of the molecule are all in the same plane.