Coordination compounds are formulated and named according to the system set up by the Inorganic Nomenclature Committee of the International Union of Pure and Applied Chemistry (IUPAC). It is called the IUPAC System of Nomenclature.
The following rules are applied while writing the formulas:
(i) The formula of the cation whether simple or complex is written first followed by that of the anion.
(ii) The coordination entity is written in square brackets.
(iii) The sequence of symbols within the coordination entity is: first the symbol of the central metal atom followed by ligands in alphabetical order. According to the latest IUPAC recommendations, the placement of a ligand in the list does not depend on its charge. The ligands in the coordination entity are arranged as:
(a) The different ligands are arranged alphabetically according to the first symbol of their formulae. For example, H2O, NH3, NO3–, SO42– and OH–, etc. are cited at H, N, N, S, and O. The ligands containing carbon and hydrogen are cited only under C.
When the SCN− ligand is bound to the central atom through nitrogen, the ligand is named
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Thiocyanato-N
The thiocyanate ion, \( \ce{SCN^-} \), is an ambidentate ligand: it can bind to the metal through sulphur or through nitrogen. Its name follows two rules:
Anionic ligand: the name ends in –o, so \( \ce{SCN^-} \) is thiocyanato (“thio” marks the sulphur atom).
Donor atom: for an ambidentate ligand the symbol of the bonding atom is added after the name, as in nitrito-N (\( \ce{NO2^-} \) bound through N) and thiocyanato-S (\( \ce{SCN^-} \) bound through S).
Bound through nitrogen, the ligand is therefore thiocyanato-N.
Why the other options are incorrect
Option (2) Thiocyanato-S — Incorrect. This name is used when the ligand is bound through sulphur, not nitrogen.
Option (3) Cyanato-N — Incorrect. “Cyanato” names the cyanate ion, \( \ce{OCN^-} \), which has oxygen, not sulphur; the “thio” part is missing.
Option (4) Cyanato-S — Incorrect. It drops “thio” and also names the wrong donor atom (S instead of N).
NCERT (2026-27 edition):
5.2 Definitions of Some Important Terms Pertaining to Coordination Compounds – “… Ligand which has two different donor atoms and either of the two ligetes in the complex is called ambidentate ligand. Examples of such ligands are the NO2– and SCN– ions. NO2– ion can coordinate either through nitrogen or through oxygen to a central metal atom/ion. Similarly, SCN– ion can coordinate through the sulphur or nitrogen atom.”
Example 5.2 – “Write the IUPAC names of the following coordination compounds: … (a) [Pt(NH3)2Cl(NO2)] … (e) Hg[Co(SCN)4]
(a) diamminechloridonitrito-N-platinum(II) …
(e) mercury (I) tetrathiocyanato-S-cobaltate(III)”