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: Identify the complex ion.
The given compound is \( \mathrm{Hg_2[Co(SCN)_6]} \). The complex part is \( \mathrm{[Co(SCN)_6]} \). Since it is inside square brackets, it is a coordination complex.
Step 2: Determine oxidation state of cobalt.
Each \( \mathrm{SCN^-} \) ligand carries a charge of \(-1\). There are 6 such ligands, so total ligand charge is \(-6\).
Let oxidation state of Co = \(x\)
\[ x - 6 = -3 \Rightarrow x = +3 \] So cobalt is in \(+3\) oxidation state.
Step 3: Identify bonding mode of SCN ligand.
The ligand \( \mathrm{SCN^-} \) is ambidentate. If it is attached through nitrogen, it is called isothiocyanato - N.
Step 4: Naming the complex.
Since the complex ion is negative, cobalt will be named as cobaltate (III). The ligand name becomes isothiocyanato - N.
The cation is mercury in +2 oxidation state.
Step 5: Conclusion.
Thus, the correct IUPAC name is Mercury (II) tetraisothiocyanato - N - cobaltate (III).
Final Answer:Mercury (II) tetraisothiocyanato - N - cobaltate (III).