Question

Write down the IUPAC name of the following complex:
(i) ${\text{[Cr(N}}{{\text{H}}_{\text{3}}}{{\text{)}}_{\text{2}}}{\text{C}}{{\text{l}}_{\text{2}}}{\text{(en)]Cl}}$ (en = ethylenediamine)
(ii) Write the formula for the following complex:
pentammminentrito-o-cobalt(III)

Answer 1

Use the IUPAC naming rules of coordination compounds. Using the charges of ligands determine the oxidation state of the metal ion.

Complete step by step answer:
(i) The given complex is: ${\text{[Cr(N}}{{\text{H}}_{\text{3}}}{{\text{)}}_{\text{2}}}{\text{C}}{{\text{l}}_{\text{2}}}{\text{(en)]Cl}}$
IUPAC naming rules of coordination compounds.
The ligands are named first and the central metal atom is named last.
Name the ligand in alphabetical order.
Negative ligands are named as ending O. Positively charged ligands have suffix –ium.
Neutral ligands are given their usual name, with some exception.
Use Greek prefix di, tri for multiple monodentate ligands and use prefix bis, tris for multiple polydentate ligands.
Use the Roman numeral in parentheses to indicate the oxidation state of the metal ion.
Use the suffix-ate for the central metal atom if the complex is an anion.
In this complex the central metal is ${\text{Cr}}$ and ligands are ${\text{N}}{{\text{H}}_{\text{3}}}$, and ${\text{en}}$.
Name of ligand ${\text{N}}{{\text{H}}_{\text{3}}}$= ammine
As there are two amine ligands in this complex so diammine.
Name of ligand ${\text{C}}{{\text{l}}^{\text{ - }}}$ = Chloro
As there are two Chloro ligands in this complex so the name is dichloro.
Name of ligand en = ethylenediamine
One Cl outside the square bracket indicates this is a cationic complex with a +1 charge on it. Ligands ammine and ethylenediamine are neutral ligands and chloro is a negatively charged ligand with -1 charge on it so the charge on the metal Cr is +3.
So, the name of the complex is Diamminedichloride ethylenediamine chromium (III) chloride.
(ii) Name of complex given is : pentammminentrito-o-cobalt(III)
The name of the complex indicates that there are two types of ligands present in the complex.
Ammine = ${\text{N}}{{\text{H}}_{\text{3}}}$
Ntrito = ${\text{ON}}{{\text{O}}^ - }$
There are 5 neutral amine ligands, one ${\text{ON}}{{\text{O}}^ - }$ ligand and metal cobalt (Co) has oxidation state +3. So, the charge on the complex is +2.
So, the formula of the complex
is ${{\text{[Co(N}}{{\text{H}}_{\text{3}}}{{\text{)}}_5}{\text{ONO]}}^{{\text{2 + }}}}$.

Note: The oxidation state of the metal ion is determined using the charges on ligands. Alphabetical order of ligands does not depend on the prefix di, tri etc.