Diborane contains a D2h structure containing four terminal and two bridging hydrogen atoms.
The bonds between boron and the terminal hydrogen atoms are conventional 2-centre, 2-electron covalent bonds.
The bridging hydrogen atoms lie above and below the plane. The two bridges B−H− B bonds are unusual three centred two-electron bonds.
Thus, there are two terminal hydrogen atoms with one boron atom (total 4) and two hydrogen atoms are bridged between two boron atoms.
