<h2>Introduction</h2> <p>Coordination compounds are one of the most scoring chapters in NEET Inorganic Chemistry. Werner's coordination theory, IUPAC naming, isomerism, bonding theories, and colour/magnetism typically yield 2–3 direct NEET questions.</p> <h2>Key Terminology</h2> <ul> <li><strong>Central metal ion:</strong> Transition metal accepting electron pairs (Lewis acid)</li> <li><strong>Ligands:</strong> Ions/molecules donating electron pairs (Lewis base)</li> <li><strong>Coordination number:</strong> Number of coordinate bonds to central metal</li> <li><strong>Coordination sphere:</strong> Central metal + ligands (written in square brackets)</li> </ul> <h2>Types of Ligands</h2> <ul> <li><strong>Monodentate:</strong> Cl⁻, NH₃, H₂O, CN⁻, CO (one donor atom)</li> <li><strong>Bidentate:</strong> en (ethylenediamine), oxalate C₂O₄²⁻</li> <li><strong>Polydentate:</strong> EDTA (hexadentate, 6 donor atoms)</li> <li><strong>Ambidentate:</strong> Can bond via two different atoms — NO₂⁻ (N or O), SCN⁻ (S or N)</li> </ul> <h2>IUPAC Naming Rules</h2> <ol> <li>Cation named before anion</li> <li>Inside bracket: ligands (alphabetical, with prefixes di, tri…) then metal with oxidation state in Roman numerals</li> <li>Anionic complex ends in -ate; use Latin names for Fe (ferrate), Cu (cuprate), Pb (plumbate)</li> </ol> <p>Example: [Co(NH₃)₄Cl₂]Cl → tetraamminedichloridocobalt(III) chloride</p> <h2>Isomerism</h2> <p><strong>Structural isomers:</strong></p> <ul> <li>Linkage: [Co(ONO)(NH₃)₅]²⁺ vs [Co(NO₂)(NH₃)₅]²⁺</li> <li>Ionisation: [Co(SO₄)(NH₃)₅]Br vs [Co(Br)(NH₃)₅]SO₄</li> <li>Coordination: [Co(NH₃)₆][Cr(CN)₆] vs [Cr(NH₃)₆][Co(CN)₆]</li> </ul> <p><strong>Stereoisomers:</strong></p> <ul> <li>Geometric (cis-trans): square planar MA₂B₂ or octahedral MA₄B₂</li> <li>Optical: chiral complexes with no plane of symmetry (e.g., [Co(en)₃]³⁺)</li> </ul> <h2>Crystal Field Theory (CFT)</h2> <p>In an octahedral field, d-orbitals split into t₂g (lower, dx²-y², dz²) and eg (higher). Δo = Crystal Field Splitting Energy.</p> <ul> <li><strong>Strong field ligands</strong> (CN⁻, CO, en): large Δo → low spin, fewer unpaired e⁻, diamagnetic/less paramagnetic</li> <li><strong>Weak field ligands</strong> (F⁻, Cl⁻, H₂O): small Δo → high spin, more unpaired e⁻, paramagnetic</li> </ul> <p><strong>Spectrochemical series (partial):</strong> I⁻ < Br⁻ < Cl⁻ < F⁻ < OH⁻ < H₂O < en < CN⁻ < CO</p> <h2>Colour in Coordination Compounds</h2> <p>Colour arises from d-d transition. The complementary colour of absorbed light is observed. Complexes with d⁰ (no d electrons, e.g. TiO₂) or d¹⁰ (Cu⁺) are colourless.</p> <h2>Valence Bond Theory</h2> <p>Hybridisation determines geometry: sp³ (tetrahedral), dsp² (square planar, inner orbital), sp³d² (octahedral outer), d²sp³ (octahedral inner).</p>