Ionisation isomerism occurs when the counter ion in a complex salt becomes a ligand. In [Co(NH₃)₅(SO₄)]Br, SO₄ displaces a ligand, while in [Co(NH₃)₅Br]SO₄, Br⁻ becomes the ligand. This is similar to ‘hydrate isomerism’ when water is involved as a solvent.

Optical isomers are mirror images that cannot be superimposed, known as enantiomers. Enantiomers are chiral and rotate the plane of polarized light either to the right (dextro – d) or to the left (laevo – l) in a polarimeter.

In octahedral coordination entities like [Co(NH₃)₃(NO₂)₃], if ligands occupy adjacent positions at the corners of an octahedral face, it is the facial (fac) isomer. When they are around the meridian, it is the meridional (mer) isomer.

Geometrical isomerism occurs in complexes of the formula [MX₂(L–L)₂] when didentate ligands like ethane-1,2-diamine (en) are present.

In [MX₂L₂], square planar complexes, the ligands X can be arranged adjacent (cis) or opposite (trans). Such isomerism is not possible in tetrahedral geometry. Octahedral complexes [MX₂L₄] also exhibit similar cis-trans isomerism.

Stereoisomerism in heteroleptic complexes arises from different geometric arrangements of ligands. Examples occur in coordination numbers 4 and 6, such as square planar complexes [MX₂L₂] and octahedral complexes [MX₂L₄].

Isomers are compounds with the same chemical formula but different atom arrangements. Stereoisomers have the same chemical bonds but differ in spatial arrangement, while structural isomers have different bonds.

It is named diamminesilver(I) dicyanidoargentate(I). The Roman numerals indicate the oxidation state of silver, which is +1. The name also reflects the ligands present in the complex cations.

The name is tris(ethane-1,2–diamine)cobalt(III) sulphate. The oxidation state of cobalt is deduced from the charge on the complex cation, which is +3, as three sulphates are needed to balance two complex cations.

It is named as triamminetriaquachromium(III) chloride. The ligands are arranged alphabetically, and the oxidation number of chromium is calculated from the charge on the complex ion, which is +3 due to the three chloride ions.