Identify the homoleptic complexes with odd number of d electrons in the central metal. (A) \(\left[\mathrm{FeO}_{4}\right]^{2-}\) (B) \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}\) (C) \(\left[\mathrm{Fe}(\mathrm{CN})_{5} \mathrm{NO}\right]^{2-}\) (D) \(\left[\mathrm{CoCl}_{4}\right]^{2-}\) (E) \(\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{3} \mathrm{~F}_{3}\right]\) Choose the correct answer from the options given below :

JEE Main · 2025 · 29 Jan 2025 · Shift 2 · Coordination Compounds

Identify the homoleptic complexes with odd number of d electrons in the central metal.
(A)

[FeO_{4}]^{2 -}

(B)

[Fe (CN)_{6}]^{3 -}

(C)

[Fe (CN)_{5} NO]^{2 -}

(D)

[CoCl_{4}]^{2 -}

(E)

[Co (H_{2} O)_{3} F_{3}]

Choose the correct answer from the options given below :

(A)(B) and (D) only✓ Correct
(B)(C) and (E) only
(C)(A), (B) and (D) only
(D)(A), (C) and (E) only

Answer: (A)

Solution

A homoleptic complex carries only one kind of ligand, so

[F e (C N)_{5} N O]^{2 -}

and

[C o (H_{2} O)_{3} F_{3}]

are eliminated outright. In

[F e O_{4}]^{2 -}

, oxygen contributes

- 2

each, giving iron an oxidation state of

+ 6

;

F e^{6 +}

has configuration

3 d^{2}

— an even number of d-electrons. In

[F e (C N)_{6}]^{3 -}

, iron is

+ 3

(

3 d^{5}

);

C N^{-}

is a strong-field ligand, forcing a low-spin

t_{2 g}^{5}

arrangement with one unpaired electron — an odd count. In

[C o C l_{4}]^{2 -}

, cobalt is

+ 2

(

3 d^{7}

);

C l^{-}

is weak-field and the geometry is tetrahedral, so no pairing occurs, leaving three unpaired electrons — also odd. The homoleptic complexes with an odd number of d-electrons are

[F e (C N)_{6}]^{3 -}

and

[C o C l_{4}]^{2 -}

JEE Main · 2025 · 29 Jan 2025 · Shift 2 · Single correct option

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JEE Main · 2025 · 29 Jan 2025 · Shift 2 · Coordination Compounds

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