← Labs|Coordination Chemistry — Build Complex · Geometry · Isomerism
Central Metal Ion
Ligands (CN=6/8)
← weak ···················· strong →
I⁻
1D
0
Br⁻
1D
0
Cl⁻
1D
0
F⁻
1D
0
H₂O
1D
0
NH₃
1D
6
en
2D
0
NO₂⁻
1D
0
CN⁻
1D
0
CO
1D
0
EDTA⁴⁻
6D
0
ox²⁻
2D
0
[Co(NH₃×6)]2+
Geometry
Octahedral
Hybridization
d²sp³ (inner)
Charge
+2
Spin
Low Spin
CFSE
-2.4Δo
Unpaired e⁻
0
μ (BM)
0.00
EAN
37
3D Geometry
NH₃NH₃NH₃NH₃NH₃NH₃MOctahedral
d-Orbital Splitting — d6 Low Spin
eg +0.6Δ↑↓↑↓↑↓t2g −0.4ΔΔo
t2g: [2,2,2]eg: [0,0]Strong field → pair first
EAN / 18-electron
Metal e⁻25
Ligand donate+12
Total (EAN)37
Not 36/54/86
CO complexes obey 18e: Ni(CO)₄ (36), Fe(CO)₅ (36), Cr(CO)₆ (36)
Isomerism:
Same bonds but different spatial arrangement (cis/trans, fac/mer). NOT interconvertible without bond breaking.
cis-[Pt(NH₃)₂Cl₂] cisplatin (anticancer!)
⇌
trans-[Pt(NH₃)₂Cl₂] transplatin (inactive)
cis: same groups adjacent. ONLY cisplatin is pharmacologically active — it cross-links DNA. A classic JEE example.
cis-[Co(en)₂Cl₂]⁺ violet
⇌
trans-[Co(en)₂Cl₂]⁺ green
en is bidentate — forces cis-like arrangement. trans has both Cl 180° apart.
fac-[Co(NH₃)₃Cl₃] facial (3 same on one triangular face)
⇌
mer-[Co(NH₃)₃Cl₃] meridional (3 same in a plane)
Octahedral MA₃B₃: fac and mer are distinct isomers. fac has C₃ symmetry, mer has no C₃.
When does geometric isomerism arise?
Square planar: MA₂B₂, MABCD, MA₂BC types
Octahedral: MA₄B₂, MA₃B₃, MA₂B₂C₂ types
Tetrahedral: MA₂B₂ does NOT show geometric isomerism
cis = same side; trans = opposite sides
Key Concepts
Werner's Theory
Primary valency = ox. state (ionisable) Secondary valency = CN (non-ionisable) Secondary must always be satisfied
Chelate Effect
Bidentate/polydentate ligands: more stable than equivalent monodentate Reason: +ΔS (entropy) on releasing multiple H₂O EDTA: log K ≈ 18; NH₃: log K ≈ 4
Spectrochemical Series
Weak: I⁻<Br⁻<Cl⁻<F⁻<OH⁻<H₂O<NH₃<en<NO₂⁻<CN⁻<CO :Strong Strong field → Low spin, large CFSE
IUPAC Naming
1. Cation before anion 2. Ligands alphabetically 3. Metal name last (ox. state) 4. Anionic complex: metal+ate Ex: potassium hexacyanoferrate(III)
Trans Effect
Ligands that weaken the bond trans to themselves: High: CO > CN⁻ > NO > Cl⁻ Low: OH⁻ < NH₃ Used to synthesise cis/trans Pt²⁺ complexes
Stability of Complexes
log K increases with: • Higher charge on metal • Smaller metal ion (higher charge density) • More donation by ligand • Chelate effect (bidentate > monodentate)