Question

IUPAC name of $\left[ CrC{{l}_{2}}{{\left( N{{H}_{3}} \right)}_{4}} \right]N{{O}_{3}}$ is:
A. tetraamminedichlorochromium (I) nitrate
B. dichloro tetraamine chromium (III) nitrate
C. tetraamminedichlorochromium (IV) nitrate
D. tetraamminedichlorochromium (III) nitrate

Answer 1

Hint: Try to recall that if the coordination compound contains a complex ion, name the cation first, followed by the anion name. Now, by using this you can easily find the correct option from the given options.

Complete step by step answer:
The nomenclature system given by IUPAC for naming the coordination compounds is as follows:
- Ordering of naming ions: In ionic complexes, the cation is named first and then the anion.
So, in this case, the coordination complex will be named first and then the nitrate ion.
- Naming the coordination entity: In naming the coordination entity, the ligands are named first and then the central metal ion.
So, in the coordination complex, the names of the ligands chloro and ammine will come before the chromium atom will be named.

- Order of naming ligands: When more than one type of ligands are present, they are named in alphabetical order of preference without any consideration of charge.
So, here, the ammine ligand will be mentioned before the chloro ligand since ‘a’ comes alphabetically before ‘c’.
- Numerical prefix to indicate the number of ligands: When more than one ligand of particular kind are present in the complex, the prefix di-, tri- ,etc. are used to indicate their number.
Here, 4 amine ligands and 2 chloro ligands are present. So, the name we have up until now is:
Tetraamminedichlorochromium nitrate.

- Ending of names: When the complex is anionic, the number of the central metal atom ends in –ate. For cationic and neutral complexes, the name of the metal is written without any characteristic ending.
Here, the complex is cationic, the name of the metal atom will stay chromium and will not be changed to chromate.
- Oxidation state of central metal ion: The oxidation state of the central metal atom ion is designated by a Roman numeral (such as II, III, IV) in the brackets at the end of the name of complex without a gap between the two.
In this complex, the oxidation number of chromium turns out to be +3. We can calculate this using the charges present on the ligands and the overall charge of the complex.
So, by following above rules, the IUPAC name of $\left[ CrC{{l}_{2}}{{\left( N{{H}_{3}} \right)}_{4}} \right]N{{O}_{3}}$ is tetraamminedichlorochromium (III) nitrate
So, the correct answer is “Option D”.

Note: It should be remembered to you that when the name of ligand, includes the numerical prefix (di, tri, tetra), then the prefixes bis, tris, tetrakis are used for two, three, four ligands, respectively. Such ligands are called complex ligands.