Connection Note — Linking CFT, Colour, Magnetism, and Stability — Notes

How the four major properties of coordination compounds are all connected through CFT:

Ligand Field Strength (Spectrochemical Series)
        │
        ▼
   Crystal Field Splitting ($\Delta o$)
        │
   ┌────┴────┐
   │         │
$\Delta o$ > P     $\Delta o$ < P
   │         │
Low Spin   High Spin
   │         │
More paired  More unpaired
   │         │
   ▼         ▼
Lower μ    Higher μ
(diamagnetic (paramagnetic
 if all paired)  if unpaired)
   │
   ▼
CFSE (Crystal Field Stabilisation Energy)
   │
   ▼
Thermodynamic stability of complex
   │
   ▼
Spectrochemical Series determines what colour is absorbed
(Energy of absorbed photon = $\Delta o$)
Complementary colour is observed

Connecting example — [Fe(CN)_{6}]^{4-} vs [ $FeF_{6}$ ]^{3-}:

Property	[Fe(CN)_{6}]^{4-}	[ $FeF_{6}$ ]^{3-}
Metal oxidation state	$Fe^{2+}$ ( $d^{6}$ )	$Fe^{3+}$ ( $d^{5}$ )
Ligand field	$CN^{-}$ (very strong)	$F^{-}$ (very weak)
Spin state	Low spin	High spin
Unpaired electrons	0	5
μ (BM)	0 (diamagnetic)	5.92
Absorbed colour	Red-orange (high $\Delta o$ )	UV/low energy (low $\Delta o$ )
Observed colour	Pale yellow	Pale violet