Question

IUPAC name of $N{a}_3\left[Co\right(ONO{)}_6]$ is :

• A. Sodium hexanitrito-O cobalt(III)
• B. Sodium hexanitrito-O cobaltate(III)
• C. Sodium hexanitrocobalt(III)
• D. Sodium hexanitrocobaltate(II)

Answer 1

The correct option is B Sodium hexanitrito-O cobaltate(III)

The names of coordination compounds are derived by the following principles of nomenclature,
1. The cation is named first in both positively and negatively charged coordination entities.
2. The ligands are named in an alphabetical order before the name of the central atom/ion.

$3N{a}^{+}\left[Co\right(ONO{)}_6{]}^{3-}$ is a anionic complex.
By first law, the IUPAC name starts as 'Sodium'

Ligands:
$ONO\to \text{Negative ambidentate ligand and it named as 'O-nitrito'}$ sonce it is binding through oxygen atom to the metal.
Since, it is a anionic complex, the name of central metal atom ends with 'ate'.
There are six $ONO$ ligands so its prefix will be 'hexa'
The oxidation state of $Co$ in this complex is
$x+(-1\times 6)=-3x=-3+6x=+3$

Hence, according to above rules the IUPAC name is Sodium hexanitrito-O cobaltate(III). Thus, option (b) is correct.