Given below are two statements Statements-I: The number of paramagnetic species among [CoF₆]³⁻$[CoF_6]^{3-}$, [TiF₆]³⁻$[TiF_6]^{3-}$, V₂O₅$V_2O_5$ and [Fe(CN)₆]³⁻$[Fe(CN)_6]^{3-}$ is 3. Statement-II: K₄[Fe(CN)₆] < K₃[Fe(CN)₆] < [Fe(H₂O)₆]SO₄ · H₂O < [Fe(H₂O)₆]Cl₃$K_4[Fe(CN)_6] < K_3[Fe(CN)_6] < [Fe(H_2O)_6]SO_4 \cdot H_2O < [Fe(H_2O)_6]Cl_3$ is the correct order in terms of number of unpaired electron(s) in the complexes. In the light of the above statements, choose the correct answer from the options given below.

Core Logic

This pathway corresponds to the standard confirmatory test for cobalt (Co²⁺$\mathrm{Co}^{2+}$) ions in qualitative inorganic analysis:

• CoS$\mathrm{CoS}$ dissolves in aqua regia to yield cobalt chloride (CoCl₂$\mathrm{CoCl}_2$):

• Treating this solution with potassium nitrite (KNO₂$\mathrm{KNO}_{2}$) in the presence of acetic acid (AcOH$\mathrm{AcOH}$) oxidizes Co²⁺$\mathrm{Co}^{2+}$ to Co³⁺$\mathrm{Co}^{3+}$, precipitating potassium cobaltinitrite as a characteristic yellow solid:

Pattern Recognition

A yellow precipitate formed specifically upon adding KNO₂$\mathrm{KNO}_2$ and acetic acid is a definitive signature of potassium cobaltinitrite, K₃[Co(NO₂)₆]$\mathrm{K}_3[\mathrm{Co}(\mathrm{NO}_2)_6]$. This confirms the starting sulfide was CoS$\mathrm{CoS}$.

Chapter Mix

Class 12 Chemistry: Coordination Compounds Class 11 Chemistry: Qualitative Analysis

Core Logic

An aqueous nickel (II) chloride solution contains the green hexaquarickel(II) complex, [Ni(H₂O)₆]²⁺$[\mathrm{Ni}(\mathrm{H}_{2}\mathrm{O})_{6}]^{2+}$. Ethane-1,2-diamine ('en') is a bidentate ligand that binds more strongly than water, shifting the crystal field splitting parameter (Δₒ$\Delta_o$) to higher energies as it replaces water molecules:

• Initial state:

• Adding 1 equivalent of 'en' forms a mono-en complex:

• Adding a 2nd equivalent forms a bis-en complex:

• Adding a 3rd equivalent forms the tris-en complex:

This progressive ligand replacement shifts the absorption spectrum, changing the solution's visible color from Green arrow$\rightarrow$ Pale Blue arrow$\rightarrow$ Blue arrow$\rightarrow$ Violet.

Pattern Recognition

Replacing weak-field ligands (like H₂O$\mathrm{H}_2\mathrm{O}$) with stronger bidentate chelating ligands (like 'en') increases crystal field splitting. For Ni²⁺$\mathrm{Ni}^{2+}$, this ligand substitution always follows the specific chromatic progression: Green arrow$\rightarrow$ Pale Blue arrow$\rightarrow$ Blue arrow$\rightarrow$ Violet.

Chapter Mix

Class 12 Chemistry: Coordination Compounds

Core Logic

Consider an octahedral coordination environment for a d⁴$d^4$ transition metal ion configuration:

• Weak Field Ligand (WFL):

The crystal field splitting energy is smaller than the pairing energy (Δₒ < P$\Delta_o < P$). Consequently, electrons prefer to occupy the higher-energy eg$e_g$ orbitals rather than pair up in the lower-energy t2g$t_{2g}$ orbitals. This leads to a high spin complex with the configuration:

• Strong Field Ligand (SFL):

The splitting energy is larger than the pairing energy (Δₒ > P$\Delta_o > P$). Electrons pair up in the t2g$t_{2g}$ orbitals before occupying the eg$e_g$ subshell, resulting in a low spin complex with the configuration:

Pattern Recognition

An electron occupying an eg$e_g$ orbital before the t2g$t_{2g}$ orbitals are fully paired requires a weak-field ligand. This configuration maximizes the number of unpaired electrons, which is the defining characteristic of a high-spin complex.

Chapter Mix

Class 12 Chemistry: Coordination Compounds

Related Formula

Core Logic

Since 1 mole of the complex yields 2 moles of AgCl(s)$AgCl_{(s)}$, there must be exactly 2 chloride ions outside the coordination sphere to undergo precipitation:

This dissociation produces a total of 3 moles of ions per mole of the complex, perfectly consistent with the problem constraints.

Pattern Recognition

Number of precipitated AgCl$AgCl$ moles directly equates to the count of counter-anions located outside the square brackets.

Chapter Mix

Class 12 Chemistry: Coordination Compounds

Related Formula

Coordination Number 6 corresponds to either d²sp³$d^2sp^3$ or sp³d²$sp^3d^2$ configuration templates. Coordination Number 4 corresponds to either sp³$sp^3$ or dsp²$dsp^2$ configuration templates.

Core Logic

Analyzing metal orbital dynamics under varying ligand fields:

• (A) [CoF₆]³⁻$[CoF_6]^{3-}$: Co³⁺$Co^{3+}$ (3d⁶$3d^6$) with a weak field ligand (F^-$F^-$) arrow$\rightarrow$ no pairing occurs arrow$\rightarrow$ utilizes outer orbitals arrow$\rightarrow$ sp³d²$sp^3d^2$.
• (B) [NiCl₄]²⁻$[NiCl_4]^{2-}$: Ni²⁺$Ni^{2+}$ (3d⁸$3d^8$) with a weak field ligand (Cl^-$Cl^-$) arrow$\rightarrow$ no pairing occurs arrow$\rightarrow$ tetrahedral profile arrow$\rightarrow$ sp³$sp^3$.
• (C) [Co(NH₃)₆]³⁺$[Co(NH_3)_6]^{3+}$: Co³⁺$Co^{3+}$ (3d⁶$3d^6$) with a strong field ligand (NH₃$NH_3$) arrow$\rightarrow$ electrons pair up arrow$\rightarrow$ inner orbital configuration arrow$\rightarrow$ d²sp³$d^2sp^3$.
• (D) [Ni(CN)₄]²⁻$[Ni(CN)_4]^{2-}$: Ni²⁺$Ni^{2+}$ (3d⁸$3d^8$) with a strong field ligand (CN^-$CN^-$) arrow$\rightarrow$ forced pairing opens a 3d$3d$ slot arrow$\rightarrow$ square planar geometry arrow$\rightarrow$ dsp²$dsp^2$.

Step 1: Final Pairing Match

The completed matching configuration aligns cleanly with: (A)-(III), (B)-(II), (C)-(I), (D)-(IV).

Pattern Recognition

Isolate coordination frameworks quickly:

• Nickel(II) with weak field ligands (Cl^-$Cl^-$) yields sp³$sp^3$, while with strong field ligands (CN^-$CN^-$) it yields dsp²$dsp^2$.
• Cobalt(III) with weak field ligands (F^-$F^-$) yields sp³d²$sp^3d^2$, while with strong field ligands (NH₃$NH_3$) it yields d²sp³$d^2sp^3$.

Chapter Mix

Class 12 Chemistry: Coordination Compounds