Which of the following is not a correct match between complex and its IUPAC name?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → [Pt(en)2Cl2](NO3)2-----Dichloridobis(ethane-1,2-diamine) platinate(IV) nitrate
The IUPAC rules for naming coordination compounds that decide this question are:
The cation is named first, then the anion, whether or not the complex is the cation.
Inside the complex, ligands are named first in alphabetical order (with prefixes di-, tri-, or bis-, tris- for ligands like ethane-1,2-diamine), then the metal, with its oxidation state in Roman numerals.
In a complex anion, the metal name ends in -ate (aluminate, cobaltate, ferrate, platinate). In a complex cation or a neutral complex, the metal keeps its ordinary name (platinum, cobalt, iron).
In \( \ce{[Pt(en)2Cl2](NO3)2} \), the two \( \ce{NO3^{-}} \) ions lie outside the bracket, so the complex ion is a cation, \( \ce{[Pt(en)2Cl2]^{2+}} \). Its oxidation state (en is neutral, \( \ce{Cl^{-}} \) is −1):
\( \displaystyle x+2(0)+2(-1)=+2\quad\Rightarrow\quad x=+4 \)
Since the metal is in a cation, it must be named platinum, not platinate. The correct name is dichloridobis(ethane-1,2-diamine)platinum(IV) nitrate.
Option (1) Li[AlH4] — Lithium tetrahydridoaluminate(III) — A correct match. \( \ce{Li^{+}} \) is the cation; in the anion \( \ce{[AlH4]^{-}} \), x + 4(−1) = −1 gives Al(+3). \( \ce{H^{-}} \) is named hydrido, and the metal in an anion becomes aluminate.
Option (2) Hg[Co(SCN)4] — Mercury(I) tetrathiocyanato-S-cobaltate(III) — A correct match (as named in the book). The option copies the name the NCERT book gives for this compound: \( \ce{SCN^{-}} \) bound through sulphur is thiocyanato-S, and the metal in a complex anion becomes cobaltate.
Option (3) Fe4[Fe(CN)6]3 — Iron(III) hexacyanidoferrate(II) — A correct match. Four \( \ce{Fe^{3+}} \) ions (total +12) balance three \( \ce{[Fe(CN)6]^{4-}} \) ions (total −12); in the anion, x + 6(−1) = −4 gives Fe(+2), named ferrate(II).
Option (4) [Pt(en)2Cl2](NO3)2 — Dichloridobis(ethane-1,2-diamine) platinate(IV) nitrate — Not a correct match. The platinum is in a complex cation, so it must be named platinum(IV), not platinate(IV).
Note: The NCERT book names Hg[Co(SCN)4] as mercury (I) tetrathiocyanato-S-cobaltate(III), and Option (2) copies that name. The compound actually contains Hg2+ and the [Co(SCN)4]2− ion (mercury(I) exists as Hg22+, not as Hg+), so its name should read mercury(II) tetrathiocyanato-S-cobaltate(II).
NCERT (2026-27 edition):
Naming of Mononuclear Coordination Compounds – …
