Question

Write the formula of the following complex:
Pentaamine carbonate chromium (III) chloride

Answer 1

Hint: Coordination compounds are neutral substances having a metal with one or more ligands. The ligands may be anionic, cationic or neutral. The charge must be balanced on the complex. There are certain rules provided by IUPAC for their naming.

Complete step by step answer:
As per the IUPAC nomenclature rule, for naming a coordination compound, ligands are first numbered and then mention the metal name with the oxidation state in brackets. For ligands naming such as ionic ligands: chloride is chloride, sulphate is sulphate, nitrate is nitrate, carbonate is carbonate etc. whereas for neutral ligands like water is aqua, carbon monoxide is carbonyl, ammonia is ammine, etc.
Next is to mention the number and for it, numerical prefixes are used i.e. 1 for mono, 2 for di, 3 for tri, 4 for tetra, 5 for penta, 6 for hexa and so on. If the overall complex is negatively charged then the metal’s name ends with ‘ate’. For example, iron as ferrate, copper as cuprate, platinum as platinate, gold as aurate, etc. but in case of neutral or positively charged complexes, the metal’s name remains as it is. Such as cobalt will be cobalt in tris(ethane-1,2-diamine) cobalt(III) sulphate where the oxidation state of copper is +3.
If in the complex, the ligand name has some prefix like di, tri, tetra, then to mention their number prefixes, we use bis for two, tris for three, terakis for four, etc.
The compound given is Pentaamine carbonate chromium (III) chloride. It tells us that five amine groups are present along with one carbonate group to the central metal atom. The central metal atom is chromium having one more ligand namely chloride but it is not attached directly to the metal. So, it will not be included in the square bracket. The central atom has +3 charge on it, that is why its name remains as it is.

Therefore, the formula of the coordination compound Pentaamine carbonate chromium (III) chloride is \[[Cr{(N{H_3})_5}C{O_3}]Cl\].

Note:
 There are more rules for nomenclature such as for bridging ligands, \[\mu \] is used as a prefix. The directly attached ligands are always placed before the metal ion. If more than one ligand is present, then they are named in alphabetical order.