Identify the homoleptic complexes with odd number of d electrons in the central metal. (A) [FeO4]2- (B) [Fe(CN)6]3- (C)…

🧠 Two Filters: Homoleptic + Odd d-electrons

Homoleptic = all ligands identical. d-electron count must be odd (1, 3, 5, 7, 9).

🗺️ Evaluate Each

| # | Complex | Metal/OS | d-electrons | Homoleptic? | Odd d? | Both? | |---|---|---|---|---|---|---| | (A) | $[\mathrm{FeO_4}]^{2-}$ | Fe(VI) | d² | ✓ (all O) | ✗ (even) | ✗ | | (B) | $[\mathrm{Fe(CN)_6}]^{3-}$ | Fe(III) | d⁵ | ✓ (all CN⁻) | ✓ | ✓ | | (C) | $[\mathrm{Fe(CN)_3 NO}]^{2-}$ | Fe(I)/(II)/(III) (depends on NO) | varies | ✗ (mixed CN + NO) | — | ✗ | | (D) | $[\mathrm{CoCl_4}]^{2-}$ | Co(II) | d⁷ | ✓ (all Cl⁻) | ✓ | ✓ | | (E) | $[\mathrm{Co(H_2O)_3}]_3$ | unclear cluster | unclear | unclear | — | ✗ |

So (B) and (D) match both criteria.

🗺️ (A) Verification

$[\mathrm{FeO_4}]^{2-}$ is ferrate(VI). Charge balance: $x + 4(-2) = -2 \Rightarrow x = +6$. Fe(VI) d² (even). Homoleptic but even.

🗺️ (D) Verification

$[\mathrm{CoCl_4}]^{2-}$: Co(II) d⁷. All 4 ligands are Cl⁻ → homoleptic. d⁷ is odd.

⚡ Homoleptic Definition

A coordination compound is homoleptic if all ligands are of the same kind (same chemical species). Heteroleptic = mixed ligands.

⚠️ Watch for Mixed-Ligand Traps

$[\mathrm{Fe(CN)_3 NO}]^{2-}$ has both CN⁻ and NO ligands → heteroleptic, fails the homoleptic filter.

$\boxed{\text{Answer: (1) (B) and (D) only}}$