Coordination Compounds
Coordination Compounds tests Werner's theory, IUPAC nomenclature, isomerism, valence bond theory, crystal field theory, stability and applications.
Core rules
- Ligands are named alphabetically before the metal; anionic complexes end in -ate.
- Coordination number is the number of donor atoms bonded to the metal.
- Isomerism includes geometrical (cis/trans), optical, ionisation, hydrate, linkage and coordination isomerism.
- VBT: strong-field ligands give inner-orbital (low-spin) complexes; weak-field ligands give outer-orbital (high-spin) complexes.
- CFT: Δo splitting; strong field gives low spin, weak field high spin. [Ni(CN)4]2- is square planar and diamagnetic; [NiCl4]2- is tetrahedral and paramagnetic.
Worked example
Describe [Co(NH3)6]3+. Co3+ is d6. NH3 is a strong-field ligand, so the six d electrons pair in t2g, leaving no unpaired electrons; the complex is low-spin, inner-orbital, octahedral and diamagnetic. Reasoning: strong field favours pairing because Δo exceeds the pairing energy.
Traps
Forgetting the charge on the complex ion when naming, counting ligands instead of donor atoms, and calling [Ni(CN)4]2- tetrahedral. In CFT, do not confuse Δo with pairing energy; their relative size decides high or low spin.