The prefixes mono-, di-, tri-, tetra-, penta-, and hexa- are used to denote the number of simple ligands.
The prefixes bis-, tris-, tetrakis-, etc., are used for more complicated ligands or ones that already contain di-, tri-, etc.
The oxidation state of the central metal ion is designated by a Roman numeral in parentheses.
When more than one type of ligand is present, they are named alphabetically. Prefixes do not affect the order.
If the complex ion has a negative charge, the suffix –ate is added to the name of the metal.
Sometimes the Latin name is used to identify the metal.
Latin Names for Some Metal Ions Found in Anionic Complex Ions
In the case of complex-ion isomerism the names cis, trans, fac, or mer may precede the formula of the complex-ion name to indicate the spatial arrangement of the ligands. Cis means the ligands occupy adjacent coordination positions, and trans means opposite positions just as they do for organic compounds. The complexity of octahedral complexes allows for two additional geometric isomers that are peculiar to coordination complexes. Fac means facial, or that the three like ligands occupy the vertices of one face of the octahedron. Mer means meridional, or that the three like ligands occupy the vertices of a triangle one side of which includes the central metal atom or ion.
Examples of rules:
[CrCl2(OH2)4]+tetraaquadichlorochromium (III) ion
[CrCl4(OH2)2]-diaquatetrachlorochromate (III) ion
[Cr(OH2)(NH3)5]3+pentaammineaquachromium (III) ion
[Ga(OH)Cl3]-trichlorohydroxogallate (III) ion
cis-[PtBrCl(NO2)2]2-cis-bromochlorodinitroplatinate (II) ion
trans-[Co(OH)Clen2]+chlorobis(ethylenediamine)-trans-hydroxo cobalt (III) ion
[Mn(CO)3(C6H6)]+benzenetricarbonvlmanganese (I) ion
NH4[AuCl4]ammonium tetrachloroaurate (I)
Because ligands can coordinate in various ways and in different arrangements profound differences are seen in the chemical properties of compounds with identical composition. The ordering and connectivity yield unique physical and chemical properties for each isomer. The structure, or molecular geometry, also yields dramatic differences in the chemical properties of coordination complexes. Tetrahedral compounds behave differently than square planar compounds containing exactly the same metal atom and the same ligands with the same ordering and connectivity. Typical geometries for the most common coordination numbers are listed in Table 3.