Question

What is the structure of diborane:
A. four $2c - 2e$ bonds four $3c - 2e$bonds
B. two $2c - 2e$ bonds and two $3c - 2e$ bonds
C. two $2c - 2e$ bonds and four $3c - 2e$bonds
D. four $2c - 2e$ bonds and two $3c - 2e$bonds

Answer 1

Diborane consists of boron and hydrogen elements with the molecular formula ${B_2}{H_6}$ . It is a colourless gas with a sweet odour.

Complete step by step answer: In Diborane, four terminal hydrogens and bridging hydrogens between the borons are present.

The bonds between the terminal hydrogens and boron is $2 - Center,2 - electron$ covalent bond.
Whereas, the bonds between boron and the bridging hydrogens are different. Each Boron atom uses its two electrons in bonding with the terminal hydrogen. The remaining one valence electron participates in bridging. The Boron and bridging hydrogen provide one electron each and form a$B{}_2{H_2}$ ring, held by four electrons forming two $3-$Centre$- 2$ electron
So, the correct answer is “Option D”.

Additional Information: The length of the B (terminal) bond is $1.19{\text{ }}A$, whereas the length of the $B - H$(Bridges) Bond is $1.33A$. Due to difference in bond length, bond strength is also different. The $B - H$(Bridge) bond is relatively weaker than the $B - H$(terminal) bond.

Note: This type of bond is known as "Banana bond". Gallium also forms a similar compound $G{a_2}{H_6}$ , known as "digauane".