JEE Advanced · 2021 · 03 Oct 2021 · Paper 2 · Coordination Compounds

The pair(s) of complexes wherein both exhibit tetrahedral geometry is(are)
(Note: py = pyridine
Given: Atomic numbers of

Fe, Co, Ni

and Cu are 26, 27, 28 and 29, respectively)

Answer: (A), (B), (D)

Solution

Tetrahedral geometry occurs with weak-field ligands or when the d-electron configuration favors it. (A)

[FeCl_{4}]^{-}

: Fe³⁺ (d⁵) with weak-field Cl⁻ → tetrahedral.

[Fe (CO)_{4}]^{2 -}

: Fe²⁻ (d¹⁰) → tetrahedral. (B)

[Co (CO)_{4}]^{-}

: Co⁻ (d¹⁰) → tetrahedral.

[CoCl_{4}]^{2 -}

: Co²⁺ (d⁷) with weak-field Cl⁻ → tetrahedral. (C)

[Ni (CO)_{4}]

: Ni⁰ (d¹⁰) → tetrahedral.

[Ni (CN)_{4}]^{2 -}

: Ni²⁺ (d⁸) with strong-field CN⁻ → square planar (dsp² hybridization). (D)

[Cu (py)_{4}]^{+}

: Cu⁺ (d¹⁰) → tetrahedral.

[Cu (CN)_{4}]^{3 -}

: Cu⁺ (d¹⁰) → tetrahedral. Options (A), (B), and (D) have both complexes tetrahedral.

JEE Advanced · 2021 · 03 Oct 2021 · Paper 2 · One or more correct options