Question

What is the true IUPAC name of \( \mathrm{Hg_2[Co(SCN)_6]} \) coordination compound?

• A. Mercury (I) tetraisothiocyanato - S - cobaltate (III)
• B. Mercury (II) tetraisothiocyanato - N - cobaltate (III)
• C. Mercury (I) tetrathiocyanato - S - cobalt (III)
• D. Mercury (I) tetrathiocyanato - N - cobalt (III)

Hint:

SCN is an ambidentate ligand: bonding through N gives isothiocyanato, through S gives thiocyanato. Always check charge to decide “cobalt” or “cobaltate”.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
In coordination nomenclature, we name the cation first, then the ligands in alphabetical order, followed by the central metal of the complex anion with the suffix "-ate."
Step 2: Formula Application:
In $\mathrm{Hg[Co(SCN)_4]}$, Mercury is the cation ($Hg^{2+}$). The complex anion is $[Co(SCN)_4]^{2-}$. Let $x$ be the oxidation state of Cobalt: $x + 4(-1) = -2 \implies x = +2$.
Step 3: Explanation:
The ligand $SCN$ is named "thiocyanato-S" because it is linked through the Sulfur atom. Since the complex is an anion, Cobalt becomes "cobaltate."
Step 4: Final Answer:
The IUPAC name is Mercury (II) tetrathiocyanato - S - cobaltate (II).