Question

The compound(s) having structure similar to that of B\( _2 \)H\( _6 \) is/are

• A. I\( _2 \)Cl\( _6 \)
• B. Si\( _2 \)Cl\( _6 \)
• C. Al\( _2 \)Cl\( _6 \)
• D. Cl\( _2 \)O\( _6 \)

Hint:

Diborane (B\( _2 \)H\( _6 \)) is a classic example of electron-deficient bonding involving three-center two-electron (3c-2e) bonds in the bridging B-H-B units. Look for compounds that exhibit similar bridging through 3c-2e bonds with halogen atoms. Al\( _2 \)Cl\( _6 \) is a key example of such a compound.

Answer 1

The Correct Option is C

The structure of diborane (B₂H₆) is characterized by two bridging hydrogen atoms between the two boron atoms. This type of bonding is known as a three-center two-electron bond (3c-2e). The two boron atoms and the two bridging hydrogen atoms lie in one plane, while the four terminal hydrogen atoms are above and below this plane. The boron atoms are sp³ hybridized.

Let's examine the structures of the given compounds:

(A) I₂Cl₆: Iodine(III) chloride exists as a dimer, I₂Cl₆, in the solid state and in the gas phase at low temperatures. Its structure consists of two planar ICl₃ units linked by two bridging chlorine atoms. The iodine atoms are at the center of a square planar arrangement of chlorine atoms. The bridging involves two I–Cl–I three-center four-electron bonds (3c-4e), which is different from the bonding in diborane.

(B) Si₂Cl₆: Hexachlorodisilane has a structure analogous to ethane (C₂H₆), with two SiCl₃ tetrahedra linked by a Si–Si single bond. There are no bridging chlorine atoms or 3c-2e bonds.

(C) Al₂Cl₆: Aluminum(III) chloride exists as a dimer, Al₂Cl₆, in the vapor phase and in the solid state. Its structure consists of two AlCl₃ units linked by two bridging chlorine atoms. The aluminum atoms are four-coordinate, and the bridging involves Al–Cl–Al three-center two-electron bonds (3c-2e), similar to the B–H–B bonds in diborane. The aluminum atoms are sp³ hybridized.

(D) Cl₂O₆: Chlorine dioxide dimer exists as dichlorohexaneoxide. Its structure is O₂Cl–O–ClO₃, containing a Cl–O–Cl linkage and a perchlorate-like ClO₃ group. It does not have a structure similar to diborane with bridging halogen atoms through 3c-2e bonds.

Conclusion: Based on the structural similarities in bonding (bridging halogen atoms through 3c-2e bonds), Al₂Cl₆ has a structure most similar to that of B₂H₆.