Question

IUPAC name of $N{a_3}\left[ {Co{{\left( {N{O_2}} \right)}_6}} \right]$ is:
A. Sodium cobaltinitrite
B. Sodium hexanitrocobaltate(III)
C. Sodium hexanitrocobalt(III)
D. Sodium hexanitrocobaltate

Answer 1

Hint: We can deduce the name of a given coordination compound by following a set of given rules.

Complete step by step answer:
We have a different branch dedicated to coordination compounds, coordination chemistry. This indicates the significance of coordination compounds and so is their nomenclature. We have some given rules recommended by IUPAC for the nomenclature of coordination compounds which can be listed as follows:
In case both cation and anion are given, we would write the name of the cation first followed by that of the anion
First, name of the ligands are written in an alphabetical order followed by that of the central metal
The name of the central metal is followed by its oxidation state written in parenthesis by using Roman numerals
Now, in case the complex ion is positively charged or neutral, name of the central metal remains same but if it is negatively charged, we use suffix “–ate” with the name of the central metal
Finally, coming to the nomenclature of ligands, we have some more rules:
For neutral ligands, we use their common names mostly but there are some exceptions including: ${H_2}O$-aqua, $N{H_3}$-ammine, $NO$-nitrosyl and $CO$-carbonyl
For anionic ligands, their names end with suffix “-o”
We use Greek prefixes to indicate the number of ligand present such as “di- or tri-“ but in case the ligand already has a Greek prefix in its name, then different prefixes are used such as “bis- or tri-s” and their name is written in parenthesis
The prefixes are ignored while determining the alphabetical order
Now, let’s have a look at the given formula: $N{a_3}\left[ {Co{{\left( {N{O_2}} \right)}_6}} \right]$
Here, cations are sodium ions and anion is a complex ion. So, the name would start with “Sodium”. Now, only one type of ligands are attached to cobalt so no worries about the alphabetical order. The ligands are “nitro” and as six of them are present so we will use the prefix “hexa-” accordingly. The complex ion is an anion, so we will use cobaltate for the central metal. Now we have, “Sodium hexanitrocobaltate”.
We have to find the oxidation state of cobalt now as per the charge neutrality principle as follows:
$\begin{array}{c}
N{a_3}\left[ {Co{{\left( {N{O_2}} \right)}_6}} \right] = 0\\
\left\{ {3 \times \left( { + 1} \right)} \right\} + Co + \left\{ {6 \times \left( { - 1} \right)} \right\} = 0\\
 + 3 + Co - 6 = 0\\
Co = + 3
\end{array}$

Therefore, from the above explanation the correct option is (B).

Note:
We have to carefully follow all the recommended rules and write the names accordingly.