What is the IUPAC name of the complex [Ni(H2O)4(H2NCH2CH2NH2)]SO4?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → tetraaqua(ethane-1,2-diamine)nickel(II) sulphate
The cation is named first, its ligands in alphabetical order before the metal, and the oxidation state of the metal in Roman numerals. The ending -ate is used only when the complex ion is an anion.
Complex ion: one \( \ce{SO4^2-} \) is outside the bracket, so \( \ce{[Ni(H2O)4(H2NCH2CH2NH2)]^2+} \) is a cation.
Oxidation state of Ni: \( \ce{H2O} \) and ethane-1,2-diamine are neutral, so x + 4(0) + 0 = +2 and x = +2, written (II).
Ligand names: four \( \ce{H2O} \) → tetraaqua; one \( \ce{H2NCH2CH2NH2} \) → (ethane-1,2-diamine), with no multiplying prefix.
Order: aqua (a) comes before ethane-1,2-diamine (e); the prefix tetra is not counted.
Metal in a cation: named as the element, nickel.
Why the other options are incorrect
Option (1) tetraaqua(ethane-1,2-diamine)nickelate(II) sulphate — Incorrect. “Nickelate” would mean a complex anion; here the complex ion is a cation.
Option (3) tetraaquabis(ethane-1,2-diamine)nickel(II) sulphate — Incorrect. “Bis” means two ethane-1,2-diamine ligands, but the formula has only one.
Option (4) (ethane-1,2-diamine)tetraaquanickel(II) sulphate — Incorrect. It names ethane-1,2-diamine before aqua, which breaks the alphabetical order.
NCERT (2026-27 edition):
5.3.2 Naming of Mononuclear Coordination Compounds – “(ii) The ligands are named in an alphabetical order before the name of the central atom/ion. …
(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. …”
“(vi) If the complex ion is a cation, the metal is named same as the element. …”