Explain the structure of diborane.

Explanation

Diborane is an electron deficient compound. It has .12. valency electrons for bonding purpose instead of .14. electrons.
In diborane each boron atom undergoes `sp^3` hybridization out of the four hybrid orbitals one is vacant.
Each boron forms two, `sigma` - bonds (2 centred - 2 electron bonds) bonds with two hydrogen atoms by overlapping with their .1s. orbital.
The remaining hybrid orbitals of boran used for the formation of B-H-B bridge bonds.
In the formation of B-H-B. bridge, half filled `sp^3` hybrid ofbital of one boron atom and vacant `sp^3` hybrid orbital of second boron atom overlap with 1s orbital of H-atom.
These three centred two electron bonds are also called as banana bonds. These bonds are present above and below the plane of `BH_2` units.
Diborane contains two coplanar `BH_2` groups. The four hydrogen atoms are called terminal hydrogen atoms and the remaining two hydrogens are called bridge hydrogen atoms.