Questions
3–5 questions per paper
Difficulty
Medium-Hard
Importance
Core — high scoring, never skip
Overview
Coordination compounds are complex molecules formed by the combination of central metal ions with ligands via coordinate bonds. They are a cornerstone of inorganic chemistry, frequently appearing in board and competitive exams due to their unique structural and electronic properties. Mastering this topic requires a firm grasp of IUPAC naming rules, bonding theories, and electronic configuration.
Werner's Theory
Alfred Werner's coordination theory explains the dual valence of metal atoms: primary and secondary. It provides the foundational understanding of how ligands are arranged around a central metal ion to form complex structures.
- Primary valency corresponds to the oxidation state of the metal.
- Secondary valency corresponds to the coordination number.
- Secondary valencies are non-ionizable and directed in space.
- Metal-ligand bonds are coordinate covalent in nature.
IUPAC Nomenclature
Naming coordination compounds follows strict systematic rules based on IUPAC guidelines. Precise application of these rules is essential for scoring full marks in descriptive sections.
- Ligands are named alphabetically followed by the metal name.
- Ligands ending in -ide change to -o; -ite and -ate become -ito and -ato.
- Use Greek prefixes (di, tri, tetra) for multiple ligands.
- Roman numerals indicate the oxidation state of the central metal.
Crystal Field Theory (CFT)
CFT treats the interaction between metal and ligands as purely electrostatic, ignoring covalent character. It effectively explains the color and magnetic properties of coordination complexes through d-orbital splitting.
- Octahedral splitting results in t2g and eg orbital sets.
- Tetrahedral splitting energy is approximately 4/9 of octahedral splitting.
- Strong field ligands (e.g., CN-) cause larger splitting leading to low spin complexes.
- Weak field ligands (e.g., I-) result in small splitting and high spin complexes.
- Color arises from d-d transitions when electrons absorb specific wavelengths.
Formula Sheet
Delta_o = (4/9) * Delta_t
Spin-only magnetic moment: mu = sqrt(n(n+2)) BM
Coordination Number = Total number of sigma bonds formed by ligand with metal
Exam Tip
Always verify the coordination number and oxidation state before calculating magnetic moments or determining hybridization, as these are the most common source of calculation errors.
Common Mistakes
- Miscalculating the oxidation state of the central metal atom during nomenclature.
- Ignoring the correct order of naming ligands alphabetically regardless of quantity prefixes.
- Confusing t2g and eg splitting patterns between octahedral and tetrahedral geometries.
More Revision Notes
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