Question

Write IUPAC name of the complex,\[{{\left[ CoC{{l}_{2}}{{\left( en \right)}_{2}} \right]}^{+}}\]

Answer 1

Hint: The IUPAC naming for the given compound is done taking into account the set rules for coordination compound/complexes. The coordination compound has a cation and anion part out of which at least one is a complex ion and the cation is always named before the anion part.

Complete step by step answer:
- We will use the rules set for the IUPAC naming of coordination complexes where the ligands such as \[\text{chloro, }C{{l}^{-}}\text{ and ethylenediamine}\left( en \right)\] are named before the metal ion. Here we have a complex cation with cobalt as the central metal.
- Then, the ligands are further written in the order of negative ions, neutral molecules and positive ions which are further named in alphabetical order, if multiple ligands of the same charge are present. The \[C{{l}^{-}}\]is a negative monodentate ligand and \[\left( en \right)\]is a neutral bidentate ligand which has two donor atoms of nitrogen that binds to the metal atom or ion at two points.
- The monodentate ligands are named di-, tri- or tetra- according to the occurrence of the ligands. Whereas, the polydentate ligands are named bis-, tris-, tetrakis- etc. So, the ligands in the given complex are named as di-chloro and bis-(ethylenediamine) respectively.
- The central metal atom/ions named as its elemental form if the complex is neutral or cation, whereas the anion complex is named in Latin form (except mercury) and ends with -ate. Thus, having a cation complex, the metal name is simply Cobalt.
- The oxidation state of the metal is also written in Roman numerals (or 0) in parentheses. The oxidation state of the metal ion is calculated as follows:
Let the oxidation state of metal be \[\text{X}\].
The \[\left( en \right)\]being a neutral ligand has zero charge and the\[C{{l}^{-}}\]a negative ion ligand has \[\left( -1 \right)\]charge. Also, the overall charge of the complex is \[\left( +1 \right)\]. Therefore, the equation will be
\[\overset{\text{charge of metal ion}}{\mathop{\text{X}}}\,+\overset{\text{charge of chloride ion}}{\mathop{2\left( -1 \right)}}\,+\overset{\text{charge of }\left( \text{en} \right)\text{ ligand}}{\mathop{\text{2}\left( \text{0} \right)}}\,=\overset{\text{charge of complex ion}}{\mathop{\left( +1 \right)}}\,\]
Then, \[\text{X=}+3\]


Thus, the IUPAC name of the complex is Dichlorobis(ethylenediamine)cobalt (III) ion.


Note: While writing the IUPAC name, the charge on the metal ion, ligands and complexes must be taken into account carefully which further helps in determining the order of naming and the oxidation state of metal.