Coordination compounds
The coordination compounds are very important in biological systems (like human, plant and animal's body), metallurgy, analytical chemistry, medicine etc. Chlorophyll, Hemoglobin, vitamin B12 etc. are coordination compounds of various metals. They are also called complex compounds and formed by two main entities, metal and ligands. Some ligands are Poly-dentate, like EDTA, which is used in the estimation of hardness of water with Ca2+ and Mg2+ ions. Gold and silver make [Au(CN)2]− and [Ag(CN)2]− type complex ions in aqueous solution during extraction of metals. In photography, developing film form a complex ion [Ag (S2O3)2]3−. A complex compound of platinum (Pt), cis-platin is used in the treatment of cancer. Some metals can be refined by making their complex compounds, like impure Nickel is converted to [Ni(CO)4] complex. All these coordination compounds may be colored or colorless, paramagnetic or diamagnetic, low spin or high spin, and arranged in particular geometry and hybridization. Isomerism is shown by these complexes due to different arrangement of ligands around the central metal atom.
What is IUPAC name of the complex [Ag(S2O3)2]3-
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Dithiosulphatoargentate(I) ion
In naming a complex ion, anionic ligands end in “-o”: \( \ce{S2O3^{2-}} \) is thiosulphato and \( \ce{SO4^{2-}} \) is sulphato. In an anionic complex, the metal name ends in “-ate”, and silver takes its Latin name, argentate (as iron becomes ferrate).
In \( \ce{[Ag(S2O3)2]^{3-}} \) there are two thiosulphato ligands. For the oxidation state of silver:
\( \displaystyle x+2(-2)=-3\ \Rightarrow\ x=+1 \)
The complex is an anion, so silver is named argentate(I). The name is dithiosulphatoargentate(I) ion.
Why the other options are incorrect
Option (1) Dithiosulphatoargentate(II) ion — Incorrect. The ligand name is correct, but silver is in the +1 state here, not +2.
Option (2) Disulphatoargentate(I) ion — Incorrect. “Sulphato” is the name for the \( \ce{SO4^{2-}} \) ligand. The ligand here is \( \ce{S2O3^{2-}} \), which is thiosulphato.
Option (4) Disulphatoargentate(II) ion — Incorrect. Both the ligand name and the oxidation state are wrong.
NCERT (2026-27 edition):
Naming of Mononuclear Coordination Compounds – …
Naming of Mononuclear Coordination Compounds – “… (iii) Names of the anionic ligands end in –o, those of neutral and cationic ligands are the same except aqua for H2O, ammine for NH3, carbonyl for CO and nitrosyl for NO. While writing the formula of coordination entity, these are enclosed in brackets ( ).”