Coordination compounds
Class 12 · Updated 2026-10-03. Published for practice.
Terms and Werner theory
Central metal ion (usually transition metal), ligands (Lewis bases: NH3, H2O, Cl-, CN-), coordination number = number of donor atoms bonded to metal.
Primary valence (ionisable, e.g. Cl- outside brackets) vs secondary valence (non-ionisable bonds to ligands). Counter-ion balance gives the salt formula ([Co(NH3)6]Cl3 example pattern).
IUPAC naming
Ligands named before metal; alphabetical order of ligand names (ignore prefixes di-, tri- for ordering). Anionic ligands end in -o (chloro, cyano). Neutral: aqua, ammine, carbonyl.
Metal oxidation state in Roman numerals after name. Anionic complex: -ate suffix (ferrate, cuprate). Cationic: metal name as element.
Isomerism
Structural: ionisation (swap inside/outside), linkage (SCN- vs NCS-), coordination (swap ligands between cation and anion in salts).
Stereoisomerism: geometrical (cis/trans in square planar MA2B2 or octahedral; fac/mer in MA3B3). Optical isomerism when non-superimposable mirror images exist (common in octahedral chelates).
VBT, CFT, colour
VBT: ligand lone pair donated to empty metal orbital; hybridisation explains geometry (sp3, dsp2, d2sp3, sp3d2 — match to CN and common complexes your table lists).
CFT: d orbitals split in ligand field (octahedral Δ_o, tetrahedral smaller split). Colour from d–d transitions when partially filled d; weak field vs strong field affects pairing (high-spin vs low-spin).