The oxidation number of the central atom in a complex is defined by considering the charge it would have if all ligands and shared electron pairs are removed. It is represented by a Roman numeral in parenthesis following the coordination ...

Homoleptic complexes, like [Co(NH₃)₆]³⁺, involve a metal bound to only one kind of donor group. Heteroleptic complexes, such as [Co(NH₃)₄Cl₂]⁺, feature a metal bound to more than one kind of donor group.

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.