Question
Determine the oxidation state of iron and the IUPAC name of .
Solution — Step by Step
Cyanide () has charge . There are of them, contributing total. The complex has overall charge . Let be the oxidation state of Fe:
Iron is in the state.
Order: ligand count (cyanido), then central metal name. For an anion, the metal name takes the “-ate” suffix. Fe in -ate form becomes “ferrate” (Latin root).
The IUPAC name: hexacyanidoferrate(II) or as an ion, hexacyanidoferrate(II) ion.
Final answer: Fe is in oxidation state ; the complex is hexacyanidoferrate(II).
Why This Works
Naming follows a strict order: number of ligands (di-, tri-, tetra-, …, hexa-), ligand name (cyanido in modern IUPAC, formerly cyano), then the central atom. For anionic complexes, use the Latin/Greek root + “-ate” (cuprate, ferrate, plumbate, argentate, aurate). For neutral or cationic complexes, the English name stays.
The oxidation state in roman numerals goes in parentheses after the metal name.
Alternative Method
Old IUPAC (pre-2005) used “cyano” instead of “cyanido”; you might see the old name “hexacyanoferrate(II)” in older textbooks. Both are still recognised by NCERT.
For neutral complexes (no overall charge), no “-ate” suffix. For cations, also no “-ate.” Only anionic complexes get the Latin-ate ending. JEE Advanced often tests this in Match-the-Column.
Common Mistake
Students often use “iron” in the name instead of “ferrate” for an anionic complex. Anions need the Latin-derived “-ate” form: ferrate, cuprate, argentate, aurate, plumbate, stannate. Memorise the metal-to-Latin map.