Complexes

Nomenclature





Nomenclature for complexes

Nomenclature for complexes is fairly simple, compared to the other nomenclatures. For complexes you write the complex former first and the ligands afterwards, when writing the formula. Formally, naming is the other way around. The ligand and the number of these is mentioned first, and after that, the complex former, along with its oxidation step, if relevant, is mentioned, e.g.

Ag(NH3)2+: diamminesilver(I) ion
Cu(NH3)2+: diamminecopper(I) ion
Cu(NH3)42+: tetraamminecopper(II) ion

Informally you say the name as it written, without mentioning the oxidation step, i.e.

Ag(NH3)2+: silver diamine complex
Cu(NH3)2+: copper diamine complex
Cu(NH3)42+: copper tetramine complex


If the ligand is negatively charged, the name is changed to end with an o (unless it already ends on an o like cyano), following the rules -ide becomes -o, -ate becomes -ato, and -ite becomes -ito. Chloride thus becomes chloro, hydroxy becomes hydroxo etc. If the resulting charge of the complex is negative, the name of the complex ends with -ate, e.g.

Zn(OH)42−: tetrahydroxo zincate(II) ion
Al(Br)4: tetrabromo aluminate(II) ion
Fe(CN)64−: hexacyano ferrate(II) ion
Fe(CN)63−: hexacyano ferrate(III) ion

Notice that sometimes the Latin names are used, especially for the metals, like ferrum instead of iron and cuprum instead of copper, but only sometimes, and you can encounter both ways of naming the component. For water you always use the Latin word aqua. So, the copper(II) complex with water, [Cu(H2O)6]2+, becomes the copper(II) hexaaqua complex. The reason for using both Latin and English names appears to be historical.


The exceptions

Of course there is exceptions to these rules. They occur when the complexes are not well defined, e.g. the I/starch complex used for iodometric titration, and the particular type of complexes called flocculations. In this case you just mention the components in the complex.