Coordination Compounds short notes

Basics

• Werner's theory has primary (ionisable) and secondary (non-ionisable) valencies.
• Ligands donate electron pairs. They can be unidentate, didentate (en), or polydentate (EDTA, hexadentate).
• Chelate compounds are more stable than similar complexes with unidentate ligands.
• Coordination number is the number of donor atoms bound to the metal.

Naming

• Name the cation first, then the anion.
• Name ligands in alphabetical order before the metal, ignoring number prefixes.
• Anionic ligands end in -o, such as chlorido and cyanido. Water is aqua, and ammonia is ammine.
• Give the oxidation state in Roman numerals. An anionic complex ends in -ate.

Isomerism

• Structural: ionisation, linkage, coordination and solvate (hydrate).
• Stereo: geometrical (cis-trans, fac-mer) and optical.
• MA₂B₂ square planar complexes show cis-trans isomerism, but tetrahedral ones don't.

Bonding

• Valence bond theory: inner orbital complexes use (n − 1)d, and outer orbital complexes use nd.
• Crystal field theory: d orbitals split into t₂g and eg in an octahedral field.
• Tetrahedral splitting is smaller, and always forms high-spin complexes.
• Spectrochemical series, weak to strong field: I⁻ < Br⁻ < Cl⁻ < F⁻ < OH⁻ < H₂O < NH₃ < en < CN⁻ < CO.
• The colour of a complex comes from d-d transitions.

Splitting relation

Tetrahedral and octahedral

$\displaystyle \Delta_t = \frac49\Delta_o$

CFSE, octahedral

$\displaystyle \text{CFSE} = (-0.4\,x + 0.6\,y)\Delta_o$

x electrons in t₂g and y in eg, ignoring pairing energy.