Q7(c)(i). [CoF₆]³⁻ paramagnetic, [Co(CN)₆]³⁻ diamagnetic
On the basis of Crystal Field Theory, account for the following statement: while [CoF₆]³⁻ is paramagnetic, [Co(CN)₆]³⁻ is diamagnetic.
Answer in brief
Both contain Co³⁺ (d⁶) in an octahedral field; F⁻ is weak-field (Δo < P), giving high-spin t2g⁴eg², four unpaired electrons, paramagnetic; CN⁻ is strong-field (Δo > P), giving low-spin t2g⁶, diamagnetic.
Part of VKC Basic
Read the key points and the full model answer with VKC Basic
VKC Basic (₹999 for 6 months) opens every solved answer, the notes, the handbook and the daily answer archive. Every Mains test series includes it.
The full model answer
As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.
How to plan and write this answer: book source, keyword map and model answer →
Topic notes: crystal field theory, with every Civil Services, IFoS and Geo-Scientist PYQ →
Coverscrystal field theoryhigh spin and low spinspectrochemical seriespairing energymagnetic momentCo(III) complexes
All parts of Question 7
- 7(a) Splitting of d orbitals in a square-planar field10 marks
- 7(b)(i) M–C and C–O bond orders in Ni(CO)₄, [Co(CO)₄]⁻ and [Fe(CO)₄]²⁻10 marks
- 7(b)(ii) Identify A, B and C5 marks
- 7(c)(i) [CoF₆]³⁻ paramagnetic, [Co(CN)₆]³⁻ diamagnetic10 marks
- 7(c)(ii) Structures and magnetic behaviour of Co₂(CO)₈15 marks