The IUPAC name for following complex compound
\(K[Au(Br)(ONO)(SO_4)(NH_3)]\) is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Potassium amminebromidonitrito-O-sulphatoaurate (III)
IUPAC rules for naming a coordination compound: the cation is named first; the ligands are named in alphabetical order before the metal; anionic ligands end in -o (bromido, sulphato); \( \ce{NH3} \) is “ammine”; an ambidentate ligand shows its donor atom (nitrito-O for –ONO); in a complex anion the metal name ends in -ate, using the Latin name where there is one (gold → aurate); the oxidation state follows in Roman numerals.
In \( \ce{K[Au(Br)(ONO)(SO4)(NH3)]} \) the complex ion carries a charge of −1 (balanced by \( \ce{K^{+}} \)):
\( x + (-1) + (-1) + (-2) + 0 = -1 \;\Rightarrow\; x = +3 \)
The ligands in alphabetical order are ammine, bromido, nitrito-O, sulphato. So the name is potassium amminebromidonitrito-O-sulphatoaurate(III).
Why the other options are incorrect
Option (1) Potassium aminebromido-O-nitritosulphatogoldate (III) — Incorrect. \( \ce{NH3} \) as a ligand is “ammine” (two m), and the anion of gold is “aurate”, not “goldate”.
Option (2) Potassium amminebromido-O-nitritosulphatoaurate (III) — Incorrect. The donor atom of the ambidentate ligand is written after its name, nitrito-O; written before it, the “O” reads as part of bromido.
Option (3) Potassium amminebromidonitrito-O-aurate (III) — Incorrect. The sulphato ligand is missing, so the name does not describe the compound.
NCERT (2026-27 edition):
Naming of Mononuclear Coordination Compounds – …
