d- and f-Block Elements and Coordination Compounds
d- and f-Block Elements and Coordination Compounds
Questions test electronic configurations, oxidation states, magnetic and colour properties, and the nomenclature, isomerism and bonding of complexes.
Core rules
- The 3d series fills after 4s; ions lose 4s electrons first (Fe: [Ar]3d⁶4s²; Fe³⁺: [Ar]3d⁵).
- Common oxidation states: Mn +2 to +7, Cr +3 and +6, Fe +2 and +3. Lanthanoids are mainly +3; Ce⁴⁺ and Eu²⁺ are notable.
- Lanthanoid contraction explains the similar radii of Zr and Hf.
- Magnetic moment μ=√(n(n+2)) BM, where n is the number of unpaired electrons.
- CFT: strong-field ligands (CN⁻, CO) give low-spin, large Δ₀; weak-field ligands (Cl⁻, H₂O) give high-spin.
- Naming: ligands alphabetically; anionic complexes end in -ate.
Worked example [Fe(CN)₆]³⁻: Fe is +3, d⁵. CN⁻ is strong field, so t₂g⁵ eg⁰: one unpaired electron. μ=√(1×3)=1.73 BM; the complex is low-spin and paramagnetic. [Fe(H₂O)₆]³⁺ is high-spin d⁵ with five unpaired electrons, μ=5.92 BM.
Traps
- Counting 4s electrons in transition-metal ions.
- Assuming tetrahedral complexes can be low-spin; they cannot.
- Ignoring linkage isomerism with NO₂⁻ or SCN⁻.