- 2075 Baisakh · 2.5+2.5 marks
Magnetic difference of [Co(NH₃)₆]³⁺ and [CoF₆]³⁻
Short answer
[Co(NH3)6]3+ is low-spin d2sp3, octahedral, diamagnetic. [CoF6]3- is high-spin sp3d2, octahedral, paramagnetic with four unpaired electrons (4.90 BM). The difference is due to strong-field NH3 versus weak-field F-.
[Co(NH₃)₆]³⁺ and [CoF₆]³⁻ are both octahedral but show marked difference in their magnetic properties. Explain.
Co³⁺ has the configuration 3d⁶ in both. The difference comes from the strength of the ligands.
[Co(NH₃)₆]³⁺
NH₃ is a strong-field ligand. The 3d electrons pair up, leaving two 3d orbitals empty. d²sp³ hybridisation gives an octahedral inner orbital (low spin) complex.
3d: [↑↓][↑↓][↑↓][ ][ ] d²sp³
No unpaired electrons: diamagnetic (μ = 0).
[CoF₆]³⁻
F⁻ is a weak-field ligand and cannot force pairing. The 3d⁶ electrons remain with four unpaired electrons and the outer 4s, 4p and 4d orbitals are used (sp³d²). It is an octahedral outer orbital (high spin) complex.
3d: [↑↓][↑ ][↑ ][↑ ][↑ ] 4s 4p 4d: sp³d²
Four unpaired electrons: paramagnetic, μ = √(4×6) = 4.90 BM.
✓ Answer checked by Claude Opus 5.5 (high effort)
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