Coordination Chemistry

Complex ion in [brackets], counter-ions outside. Complex charge balances the counter-ions; then metal charge + Σ(ligand charges) = complex charge.

Cation first. Ligands alphabetical before the metal (ignore di/tri prefixes for ordering). Use bis/tris if the ligand name already has di/tri (ethylenediamine → bis). Anionic complex → metal takes -ate.

CN = total metal-ligand bonds (monodentate 1, bidentate like en/oxalate 2). CN 2 → linear; 4 → tetrahedral or square planar; 6 → octahedral.

Write the free-metal configuration, then remove electrons (4s before 3d) for the ion. Count d-electrons for CFT. Mn = [Ar]4s²3d⁵ → Mn³⁺ = [Ar]3d⁴.

Octahedral d⁴-d⁷: compare Δ_o with pairing energy P. Δ_o < P → high spin (fill e_g before pairing); Δ_o > P → low spin (pair in t2g first). d⁰-d³ and d⁸-d¹⁰ have only one filling.

Strong-field d⁸ ions (Pt²⁺, Pd²⁺, Ni²⁺) adopt square planar, with a distinct d-orbital splitting; the highest orbital (d_x²−y²) stays empty, giving a diamagnetic low-spin d⁸.

Any unpaired d-electrons → paramagnetic; all paired → diamagnetic. d³ octahedral (3 unpaired) and d⁸ octahedral (2 unpaired) are the same in either field strength.

Structural isomers (same formula, different connectivity): ionization and linkage. Stereoisomers (same connectivity, different arrangement): cis/trans (geometric) and non-superimposable optical isomers.

A = εcℓ: A absorbance (unitless), ε molar extinction coefficient (M⁻¹cm⁻¹), c concentration (M), ℓ path length (cm). ε is wavelength-specific.

Same compound, same ε and ℓ: A₁/A₂ = c₁/c₂, so c₂ = A₂c₁/A₁ (no need for ε).

For a diluted sample, apply M₁V₁ = M₂V₂ to get the diluted concentration BEFORE using A = εcℓ.