Summary & Master Memory Capsule

The Whole Chapter in One Glance

Coordination compounds have a central metal bonded to ligands. Werner's primary/secondary valencies became oxidation state and coordination number. We name them by IUPAC rules, classify their isomerism, and explain bonding by VBT (hybridisation, inner/outer orbital) and CFT (d-orbital splitting, spectrochemical series, high/low spin, colour). Carbonyls bond synergically; chelates are extra-stable.

Slot every fact into one of these branches.

Master Facts Sheet

Werner: primary valency = oxidation state (ionisable); secondary valency = coordination number (directional).

Terms: ligand denticity - unidentate, bidentate (en, oxalate), hexadentate (EDTA), ambidentate (NO2-, SCN-).

Nomenclature: ligands first (alphabetical), -o for anionic ligands, aqua/ammine/carbonyl for neutral, oxidation state in Roman numerals, -ate for anionic complexes (ferrate, cuprate).

Isomerism: structural (linkage, coordination, ionisation, solvate) and stereo (geometrical cis-trans/fac-mer, optical enantiomers). Tetrahedral shows no geometrical isomerism.

VBT: $sp^3$ tetrahedral; $dsp^2$ square planar; $sp^3d^2$ outer octahedral (high spin); $d^2sp^3$ inner octahedral (low spin). $\mu = \sqrt{n(n+2)}$ BM.

CFT: octahedral $t_{2g}$ (-0.4) / $e_g$ (+0.6), gap $\Delta_o$; tetrahedral $\Delta_t = \tfrac{4}{9}\Delta_o$ (high spin). Strong field ($\Delta_o > P$) -> low spin. Spectrochemical: I- < Cl- < H2O < NH3 < en < CN- < CO.

Colour: d-d transition; $d^0$/$d^{10}$ colourless. Carbonyls: synergic ($\sigma$ + $\pi$ back-bond). Chelate effect: entropy-driven extra stability.

Quick Comparison Tables

VBT vs CFT

Feature	VBT	CFT
Bond model	Covalent (hybrid orbitals)	Electrostatic (ionic)
Explains geometry	Yes	Yes
Explains colour	No	Yes
Inner/outer or high/low spin	Inner/outer orbital	High/low spin

High spin vs Low spin (octahedral)

Feature	High spin	Low spin
Ligand field	Weak	Strong
delta o vs P	delta o < P	delta o > P
Unpaired electrons	More	Fewer
Hybridisation (VBT)	sp3d2 (outer)	d2sp3 (inner)

Last-Minute Memory Hooks

• Werner: primary = oxidation state, secondary = coordination number.
• Coordination number: count donor atoms - bidentate counts as 2 (e.g. [Co(en)3]3+ = 6).
• Naming: ligands alphabetical, ammine (two m's) for NH3, -ate for anionic complexes.
• Tetrahedral = no geometrical isomerism; cis chelate complexes are usually optically active.
• VBT geometries: sp3 -> tetrahedral, dsp2 -> square planar, sp3d2 -> octahedral (outer/high spin), d2sp3 -> octahedral (inner/low spin).
• The classic pair: [NiCl4]2- (tetrahedral, 2 unpaired, paramagnetic) vs [Ni(CN)4]2- (square planar, 0 unpaired, diamagnetic).
• CFT: strong field (CN-, CO, NH3) -> large delta o -> low spin; weak field (H2O, F-, Cl-) -> high spin.
• Colour = d-d transition; d0 and d10 are colourless. Stronger field -> larger delta o -> shorter-wavelength absorption.
• Chelate effect (entropy) makes en/EDTA complexes very stable. Carbonyl bonding is synergic.

One-line revision flow: Werner -> terms/ligands -> nomenclature -> isomerism (structural + stereo) -> VBT -> CFT (splitting, spectrochemical, spin) -> colour -> carbonyls/stability/applications.