The calculated spin-only magnetic moments of K₃[Fe(OH)₆]$K_{3}[Fe(OH)_{6}]$ and K₄[Fe(OH)₆]$K_{4}[Fe(OH)_{6}]$ respectively are: (1) 4.90 and 4.90 B.M. (2) 5.92 and 4.90 B.M. (3) 3.87 and 4.90 B.M. (4) 4.90 and 5.92 B.M.

Core Logic

A complex is homoleptic if the metal is bound to only one kind of donor ligand group.

• (A) [FeO₄]²⁻$[FeO_4]^{2-}$ is homoleptic, but Fe⁺⁶$Fe^{+6}$ corresponds to a 3d²$3d^2$ (even) electronic configuration.
• (B) [Fe(CN)₆]³⁻$[Fe(CN)_6]^{3-}$ is homoleptic. Fe⁺³$Fe^{+3}$ corresponds to a 3d⁵$3d^5$ (odd) configuration.
• (C) [Fe(CN)₅NO]²⁻$[Fe(CN)_5NO]^{2-}$ is heteroleptic (contains two types of ligands).
• (D) [CoCl₄]²⁻$[CoCl_4]^{2-}$ is homoleptic. Co⁺²$Co^{+2}$ corresponds to a 3d⁷$3d^7$ (odd) configuration.
• (E) [Co(H₂O)₃F₃]$[Co(H_2O)_3F_3]$ is heteroleptic.

Pattern Recognition

Filter by 'homoleptic' first to instantly eliminate multi-ligand mixed structures like options (C) and (E).

Chapter Mix

Class 12 Chemistry: Coordination Compounds

Core Logic

From the given list, the complexes exhibiting a distinct yellow color are K₃[Co(NO₂)₆]$K_{3}[Co(NO_{2})_{6}]$ and K₄[Fe(CN)₆]$K_{4}[Fe(CN)_{6}]$.

Let's calculate the spin-only magnetic moments for these low-spin configurations:

• For K₃[Co(NO₂)₆]$K_{3}[Co(NO_{2})_{6}]$, cobalt is in +3$+3$ oxidation state (Co³⁺ = 3d⁶$Co^{3+} = 3d^{6}$).

In the presence of the strong ligand field (NO₂^-$NO_2^-$), all six electrons pair up completely in the t2g$t_{2g}$ orbitals:

• For K₄[Fe(CN)₆]$K_{4}[Fe(CN)_{6}]$, iron is in +2$+2$ oxidation state (Fe²⁺ = 3d⁶$Fe^{2+} = 3d^{6}$).

In the strong field of cyanide ligands (CN^-$CN^-$), pairing is complete:

Therefore, the sum of their spin-only magnetic moments is 0 + 0 = 0$0 + 0 = 0$.

Pattern Recognition

Low-spin d⁶$d^6$ octahedral complexes always yield a fully closed-shell t2g⁶$t_{2g}^6$ arrangement with zero unpaired electrons, leading deterministically to a magnetic moment of 0 BM.

Chapter Mix

Class 12 Chemistry: Coordination Compounds

Core Logic

Nickel (Ni²⁺$\mathrm{Ni}^{2+}$) exhibits a d⁸$d^8$ electronic profile. In regular octahedral complex splits: t2g⁶ eg²$t_{2g}^6 e_g^2$ Because the lower t2g$t_{2g}$ subshell is fully paired and the higher eg$e_g$ contains exactly 2 electrons matching Hund's rules, this orbital distribution remains configurationally identical under both strong-field and weak-field environments. Additionally, Ni²⁺$\mathrm{Ni}^{2+}$ compounds produce a characteristic violet bead during hot cycles in a non-luminous flame within the qualitative borax matrix.

Pattern Recognition

Sees: Configuration invariant to ligand strength + qualitative test combination. Shortcut: A d⁸$d^8$ structure in octahedral splitting always stays high-spin/low-spin identical, pointing strictly to Ni²⁺$\mathrm{Ni}^{2+}$.

Chapter Mix

Class 12 Chemistry: Coordination Compounds Class 12 Chemistry: The d-and f-Block Elements

Related Formula

The energy of light absorbed is inversely proportional to the wavelength absorbed:

Core Logic

All complexes share the same central metal ion, Co³⁺$\text{Co}^{3+}$. The magnitude of the crystal field splitting energy (Δₒ$\Delta_o$) depends exclusively on the relative ligand field strength listed in the spectrochemical series:

Step 1: Ordering Energies and Wavelengths

The splitting energy order is:

Inverting this sequence to match absorption wavelength values yields:

Pattern Recognition

Shortcut: Stronger field ligand $\implies$ larger splitting gap $\implies$ high photon energy $\implies$ shorter absorbed wavelength. Since CN^-$\text{CN}^-$ is a strong field ligand, complex C must absorb the shortest wavelength, putting it at the very end.

Chapter Mix

Class 12 Chemistry: Coordination Compounds