Explain structure of Diborane.

In diboranefour terminal B-H bonds are two centre- two electron bonds. Two bridge B − H − B bonds are three centre - two electron bonds
Bonds between boron and terminal hydrogen are 2-electron covalent bonds.
The bond between boron and hydrogen are held together by four electrons (each boron has 1 valence electron from 1 from hydrogen) forms 3-centre-2-electron bonding. It is also called banana bond.
The bond length of B-H(bridge) and B-H(terminal) is 1.22 A and 1.19 A. The B-H(bridge) bond is weaker compared to B-H(terminal).