Question

Explain the structure and bonding of diborane.

Answer 1

1. Electronic configuration of boron is 1s² 2s² 2p¹. Thus, it has only three valence electrons.
2. In diborane, each boron atom is sp³ hybridized. Three of such hybrid orbitals are half-filled while the fourth sp³ hybrid orbital remains vacant.
3. The two half-filled sp³ hybrid orbitals of each B atom overlap with 1s orbitals of two-terminal H atoms and form four B – H covalent bonds. These bonds are also known as two-centered-two-electron (2c-2e) bonds.
4. When ‘1s’ orbital of each of the remaining two H atoms simultaneously overlap with the half-filled hybrid orbital of one B atom and the vacant hybrid orbital of the other B atom, it produces two three-centered-two electron bonds (3c-2e) or banana bonds.
5. Hydrogen atoms involved in (3c-2e) bonds are the bridging H atoms i.e., H atoms in two B – H – B bonds.
6. In diborane, two B atoms and four-terminal H atoms lie in one plane, while the two bridging H atoms lie symmetrically above and below this plane.
   
          Bonding and structure of diborane