Identify the correct IUPAC name for the complex.
\([Co(H_2NCH_2CH_2NH_2)_3]_2 (SO_4)_3\)
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → tris (ethane-1,2-diamine) cobalt(III) sulphate
In naming a coordination compound, the cation is named first, the ligands are given with prefixes for their number, and the metal’s oxidation state follows in Roman numerals. When the ligand name already contains a number, as ethane-1,2-diamine (en) does, the prefixes bis, tris, tetrakis are used instead of di, tri, tetra.
The oxidation state of cobalt: three \( \ce{SO4^{2-}} \) ions balance two complex cations, so each cation is \( \ce{[Co(en)3]^{3+}} \); en is neutral:
\( \displaystyle 2n = 3 \times 2 \;\Rightarrow\; n = +3; \qquad x + 3(0) = +3 \;\Rightarrow\; x = +3 \)
So the name is tris(ethane-1,2-diamine)cobalt(III) sulphate.