GATE 2025 CY – Question 48

Inorganic Chemistry · Main Group Elements: Shapes and structures of molecules using VSEPR postulates, Hydrides, halides, oxides, oxoacids, nitrides, sulfides - shapes and reactivity. Structure and bonding of boranes, carboranes, silicones, silicates, boron nitride, borazine and phosphazenes: electron counting in polyhedral boranes, isolobal analogy. Allotropes of carbon, phosphorus and sulfur. Industrial synthesis of compounds of main group elements such as NH3, H2SO4 and HNO3. Chemistry of noble gases and interhalogen compounds. Acid-base concepts and principles (Lewis, Brønsted, HSAB and acid-base catalysis). · 2 marks · Multiple select

The compound(s) having structure similar to that of B2H6 is/are

$\mathrm{I_2Cl_6}$
$\mathrm{Si_2Cl_6}$
$\mathrm{Al_2Cl_6}$
$\mathrm{Cl_2O_6}$

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Correct answer: (A) $\mathrm{I_2Cl_6}$; (C) $\mathrm{Al_2Cl_6}$

Explanation

Diborane, $\text{B}_2\text{H}_6$, has a **bridged dimeric** structure: two $BH_2$ groups joined by two bridging H atoms (three-centre two-electron bonds), so each boron is surrounded by four hydrogens in a distorted tetrahedron.

Look for compounds whose two central atoms are joined by **two bridging atoms** in the same way:

**$\text{I}_2\text{Cl}_6$:** the dimer of $\text{ICl}_3$, with two bridging Cl atoms between two iodine atoms. ✓
**$\text{Si}_2\text{Cl}_6$:** two $\text{SiCl}_3$ groups joined by a **direct Si–Si bond**, no bridges. ✗
**$\text{Al}_2\text{Cl}_6$:** the dimer of $\text{AlCl}_3$ with two bridging chlorides. ✓
**$\text{Cl}_2\text{O}_6$:** exists as $[\text{ClO}_2]^+[\text{ClO}_4]^-$ in the solid, an ionic structure. ✗

Answer **A and C**.