Explain the structure of diborane.

Explanation

Structure of diborane: Electron diffraction studies have shown that dibroane contains two coplanar `BH_(2)` groups. Its structure can be represented as

The four H atoms present in the `BH_(2)` groups are known as terminal hydrogen atoms. The remaining two H atoms are called Bridge hydrogens. the two bridge hydrogens lie in a plane per pendicular to the plane of the two `BH_(2)` groups. Out of the two bridge hydrogens, one H atoms lies above the plane and the ohter H atom lies below the plane. Orbital structural of Diborane:
In Diborane each boron atom undergoes `sp^(3)` hybridisation resulting in four equivalent `sp^(3)` hybrid orbitals. Three of these orbitals have one electron each and the fourth hybrid orbital is vacant. In the formation of B-H-B bridge `sp^(3)` hybrid orbital with one electron from one boron atom, 1s orbital of one bridge hydrogen and the vacant `sp^(3)` hybrid orbital of the second boron atom overlap as shown below.

The two B-H-B bridges present in Dibroran are abnormal bonds. They are considered as three centered two electron bonds. This type of bond is called banana bond or tau bond. In this type of bond a pair of electrons holds three atoms. In Diborane there are two such bridges. This Diborane structure can also be represented as shown here.