Question

The IUPAC name of compound \[N{{a}_{3}}[Co{{(ONO)}_{6}}]\] will be
(A) Hexanitriticobalt (III) sodium
(B) Sodium cobalt nitrite
(C) Sodium hexanitrocobalt (III)
(D) Sodium hexanitrocobaltate (III)

Answer 1

Hint: A compound and any salt are always formulated with cation in the first position and then followed by anion. In the given compound sodium is a cation and another part is an anion (non-ionizable or a complex). According to IUPAC naming, always naming of a cation takes place and then the name of the anion. As the anionic part contains ligand and metal atoms, thus, the naming of ligand takes place first then the naming of metal along with its oxidation state.

Complete Step by Step Solution:
In a given coordinated complex, sodium (\[N{{a}_{3}}\]) is a cation, and another part that is non-ionizable (\[\left[ Co{{\left( ONO \right)}_{6}} \right]\]) is an anion (complex anion). As per the IUPAC naming rule, the naming of cation takes place first which is sodium for Na3, and then the naming of the anionic part takes place which contains a central metal, cobalt (Co), and six ligand (\[{{\left( ONO \right)}_{6}}\]) bonded with coordinate bonds, ligands are donating pair of electron.

The naming of the ligand of an anionic complex is done by replacing ide or e with o. Thus, nitrite, ONO changed to nitrito in naming. Also, prefixes, di, tri, tetra, and so on indicate the number of ligands used before the name of ligands such as hexanitrito as there are six nitrites. And the naming of central metal (if an anionic complex is present)takes place by adding the suffix ‘ate’ at the end of the metal name such as cobaltate along with its oxidation state.

Suppose oxidation state of cobalt say x, charge on NO2 is -1 and charge on complex anion is -3 (cross multiply by 3, number of sodium atoms) such as
x + 6(-1) = -3
x – 6 = -3
x = -3 + 6
x = +3
Thus, the correct name is given as Sodium hexanitritocobaltate (III).
Thus, the correct option is D.

Note: In a coordinate complex, one cation and one anion are present. Now in coordinate complex, the cation can be in complex form (non-ionizable) and the anion can be in complex form (non-ionizable). But the naming of the coordinate complex remains the same in terms of its pattern to give name first to cation and then anion. The major difference is in the naming of complex ions (could be cation or anion). In naming metal of cation complex, the naming of metal is simple (does not end with suffix ate) which is not the case with the metal of anionic complex.