Coordination Compounds and d-Block Elements
Coordination Compounds and d-Block Elements tests ligand nomenclature, coordination number, isomerism, crystal-field splitting, magnetic moments, and the characteristic properties of transition metals.
Core rules
- In a complex, the coordination number is the number of donor atoms bonded to the metal.
- Oxidation state is found by summing ligand charges and setting the total equal to the complex charge.
- Strong-field ligands such as CN− and CO cause large splitting and low-spin complexes; weak-field ligands such as H2O and Cl− favor high-spin complexes.
- Magnetic moment: μ = sqrt(n(n+2)) BM, where n is the number of unpaired electrons.
- Transition metals show variable oxidation states, catalytic activity, colored ions, and paramagnetism due to partially filled d orbitals.
- Lanthanoid contraction explains the similar radii of Zr and Hf.
Worked example
Find the magnetic moment of [Fe(CN)6]3−. The complex charge is −3; six CN− ligands contribute −6; therefore Fe is +3. Fe3+ is d5. CN− is a strong-field ligand, so the five d electrons pair as t2g5, leaving one unpaired electron. μ = sqrt(1 × 3) = 1.73 BM. A weak-field d5 complex such as [Fe(H2O)6]3+ would have five unpaired electrons and μ ≈ 5.92 BM.
Traps
Do not count ligands instead of donor atoms when finding coordination number. Do not forget the overall complex charge when assigning oxidation state. Do not use the spin-only formula for f-block ions without care. Do not assume every d-block ion is colored; d0 and d10 ions are usually colorless.