Chemistry - Coordination Chemistry Question with Solution | TestHub

Explain Question:

Isomerism, magnetism, and color (CFSE) in Co(III) complexes.

Concept:

Crystal Field Theory & Stereoisomerism

Solution: Analyze the geometry for isomers, oxidation state for magnetism, and ligand field strength for absorption wavelength (λ ∝ 1/Δ₀ )

Calculation:

• Isomerism: $[\mathrm{Co}{\left(en)({\mathrm{NH}}_3\right)}_3({\mathrm{H}}_2\mathrm{O}){]}^{3+}$is type $\left[M\left(AA\right)a_{3}b].c\right]$It has 2 GIs (H₂O trans to 'en' or cis to 'en'). (Option 1 Correct).

• Ligand Replacement: Replacing 'en' with 2 CN⁻ gives $[\mathrm{Co}{\left(CN{)}_2({\mathrm{NH}}_3\right)}_3({\mathrm{H}}_2\mathrm{O})]$(type [Ma₃b₂c]). This typically forms 3 GIs (1 facial + 2 meridional). (Option 2 Correct).

Explanation

(A) Two G.I. of $[\mathrm{Co}({\mathrm{NH}}_3{)}_3({\mathrm{H}}_2\mathrm{O})(\mathrm{en}){]}^{3+}$

(B) Two G.I. of $[\mathrm{Co}({\mathrm{NH}}_3{)}_3({\mathrm{H}}_2\mathrm{O})(\mathrm{en}){]}^{3+}$

Magnetism: Co(III) (3d⁶ ) with Strong Field Ligands (en, NH₃ ) pairs all electrons t_2g⁶. It is Diamagnetic. (Option C Incorrect).

• Absorption: H₂O is a weaker ligand than NH₃ . The given complex has weaker field splitting  Δ₀ than $[\mathrm{Co}{\left(en)({\mathrm{NH}}_3\right)}_4{]}^{3+}$. Since Energy  ∝ 1/λ ,lower energy means longer wavelength. (Option D Correct).

Final Answer: Option (A, B, D)