CBSE · Class 12 · Chemistry · Chapter 5

Coordination Compounds — Formula Sheet

Board Formulas

10 formulas

1.Werner's Primary and Secondary Valency
$Primary valency = oxidation state (ionisable); Secondary valency = coordination number (non-ionisable)$
Primary valency = charge on metal, satisfied by anions in the ionisation sphere. Secondary valency = number of ligand-metal bonds inside coordination sphere.
2.Oxidation State of Central Metal★
$Charge on complex = OS_{M} + \sum (ligand charges)$
$OS_{M}$ : Oxidation state of the central metal · $ligand charge$ : Formal charge on each coordinated ligand
Solve for OS_M knowing overall charge and each ligand's charge. NH₃, H₂O, CO, en = 0; Cl⁻, CN⁻, OH⁻ = −1; O²⁻, ox²⁻ = −2.
3.Coordination Number★
$CN = total donor atoms bonded to central metal$
Monodentate contributes 1, bidentate 2, EDTA⁴⁻ (hexadentate) 6 per molecule. Common CNs: 2, 4, 6.
4.Spin-Only Magnetic Moment★
$μ = n (n + 2) BM$
$n$ : Number of unpaired electrons · $μ$ : Magnetic moment (Bohr magnetons, BM)
n = number of unpaired electrons in the metal ion's d-orbitals. BM = Bohr Magneton.
5.Crystal Field Splitting (Octahedral)★
$Δ_{o} = E (e_{g}) - E (t_{2 g}), E (t_{2 g}) = - 0.4 Δ_{o}, E (e_{g}) = + 0.6 Δ_{o}$
In an octahedral field, five d-orbitals split into lower t₂g (3) and upper eg (2). Splitting energy Δ_o (also written 10Dq).
6.Crystal Field Stabilisation Energy (CFSE)
$CFSE = [(- 0.4) n_{t_{2 g}} + (+ 0.6) n_{e_{g}}] Δ_{o} + P$
$n_{t_{2 g}}$ : Electrons in t₂g set · $n_{e_{g}}$ : Electrons in eg set · $Δ_{o}$ : Octahedral crystal field splitting (units of energy) · $P$ : Pairing energy (added for each extra pair)
Sum of contributions from t₂g and eg electrons. Include pairing energy P if number of pairs in complex exceeds that in free ion.
7.High-Spin vs Low-Spin Condition
$Δ_{o} < P \Rightarrow high-spin; Δ_{o} > P \Rightarrow low-spin$
Weak-field ligands (small Δ) leave electrons unpaired (high-spin). Strong-field ligands (large Δ) force pairing (low-spin).
8.Tetrahedral Splitting
$Δ_{t} = \frac{4}{9} Δ_{o}$
Tetrahedral splitting is smaller and INVERTED (e below t₂). All tetrahedral complexes are high-spin because Δ_t < P.
9.IUPAC Nomenclature Rule (order)★
$[Cation] [Anion] : ligands (alphabetical, with di/tri or bis/tris) + metal(OS in Roman)$
Anionic complex ends in '-ate' (ferrate, cuprate, argentate). Use bis/tris for ligands whose names already contain di/tri (e.g. bis(ethylenediamine)).
10.Effective Atomic Number (EAN)
$EAN = Z - OS_{M} + 2 \times CN$
Sidgwick's rule: stable complex often has EAN equal to the next noble gas. E.g. [Fe(CN)₆]⁴⁻: EAN = 26 − 2 + 12 = 36 (Kr).