Overview
This lecture covers the fundamentals of coordination compounds, including their types, key terminology, theories of bonding, isomerism, preparation, identification, and organometallic chemistry.
Introduction to Coordination Compounds
- Coordination compounds form due to transition metals' tendency for complex formation.
- Addition compounds are classified as double salts (unstable in solution) and coordination/complex compounds (retain identity in solution).
- Double salts dissociate into constituent ions in water, while complex compounds do not.
Types of Coordination Compounds
- Classified based on cation/anion complexity: simple cation/complex anion, complex cation/simple anion, both complex, or neutral.
- Based on stability: perfect complexes (highly stable), imperfect complexes (less stable).
Key Terminologies
- Central metal atom/ion accepts electron pairs from ligands to form coordinate bonds.
- Ligands are electron pair donors (Lewis bases) and can be anionic, neutral, or cationic, and mono- to hexadentate.
- Chelating ligands form rings with the metal, increasing complex stability.
- Coordination number: number of donor atoms bonded to metal.
- Coordination sphere includes the central metal and attached ligands (in square brackets).
- Oxidation number: effective charge on metal after ligand removal; found by charge balance.
- Effective Atomic Number (EAN): atomic number adjusted for electrons lost/gained in complex formation.
Formula and Nomenclature
- Cation is written before anion; complex part in brackets.
- Ligands listed in alphabetical order before metal in IUPAC names; anionic ligands end with -o, and special names are given to some neutral ligands.
- Prefixes indicate number of each ligand; bis/tris/tetrakis used for ligands with internal numerical prefixes.
- Metal is named based on charge and whether the complex is cationic, anionic, or neutral.
Isomerism in Coordination Compounds
- Structural isomerism: different connectivity (ionization, hydrate, linkage, polymerization, coordination, and position isomerism).
- Stereoisomerism: same bonds, different spatial arrangement (geometrical and optical isomerism).
- Geometrical isomers: cis (adjacent ligands) and trans (opposite ligands) forms.
- Optical isomers: non-superimposable mirror images (dextro, laevo forms).
Preparation and Identification
- Complexes prepared by substitution, combination, or redox reactions.
- Identified by changes in solubility, conductivity, chemical properties, color, pH, EMF, or magnetic properties.
Theories of Bonding
- Werner's theory distinguishes primary (ionizable) and secondary (coordination number) valencies.
- Valence Bond Theory: metal orbitals hybridize to accommodate ligand electron pairs; predicts geometry and magnetism.
- Crystal Field Splitting Theory: ligand field splits d-orbital energies, explaining color, magnetism, and stability.
- Spectrochemical series ranks ligands by their field strength.
Organometallic Compounds
- Compounds with metal–carbon bonds, classified as covalent or ionic.
- Sigma- and pi-bonded complexes, including metal carbonyls and sandwich compounds (e.g., ferrocene).
- Bonding involves both σ-donation and π-backbonding.
- Synthesized by direct combination, alkylating agents, or reactions yielding Grignard reagents.
Key Terms & Definitions
- Coordination compound — Compound with a central metal atom/ion bonded to ligands.
- Ligand — Ion/molecule donating electron pairs to a metal.
- Chelation — Binding of a metal ion by a polydentate ligand forming a ring.
- Coordination number — Number of ligand donor atoms attached to the metal.
- Isomerism — Same formula, different structures or spatial arrangements.
- Spectrochemical series — Ranking of ligands by crystal field splitting strength.
- Crystal Field Splitting — Separation of d-orbital energies in a ligand field.
Action Items / Next Steps
- Review and practice IUPAC nomenclature for given complexes.
- Solve problems related to isomerism and bonding theories.
- Prepare for upcoming homework or quizzes on coordination chemistry concepts.