Question

Write the IUPAC names of the following coordinate compounds:
(i) [CrCl$_2$(en)]Cl
(ii) Cs[FeCl$_4$]
(iii) K$_3$[Co(C$_2$O$_4$)$_3$]
(iv) [CoCl$_3$(NH$_3$)$_3$]

Hint:

While naming coordination compounds: 1. Name ligands in alphabetical order before the metal.
2. Use oxidation state of metal in Roman numerals.
3. Anionic complexes end with "-ate" (e.g., ferrate, cobaltate).

Answer 1

(i) [CrCl$_2$(en)]Cl
- Central metal: Cr (oxidation state = +3).
- Ligands: 2 Cl$^-$ (chloro), 1 en (ethane-1,2-diamine, bidentate).
- Outside Cl$^-$ = counter ion.
\[ \text{IUPAC name: Dichlorido(ethane-1,2-diamine)chromium(III) chloride} \] (ii) Cs[FeCl$_4$]
- Central metal: Fe (oxidation state = +3).
- Ligands: 4 Cl$^-$ = tetrachlorido.
- Cs$^+$ = counter ion.
\[ \text{IUPAC name: Caesium tetrachloridoferrate(III)} \] (iii) K$_3$[Co(C$_2$O$_4$)$_3$]
- Central metal: Co (oxidation state = +3).
- Ligand: oxalato (C$_2$O$_4^{2-}$, bidentate).
- Three oxalato ligands.
\[ \text{IUPAC name: Potassium tris(oxalato)cobaltate(III)} \] (iv) [CoCl$_3$(NH$_3$)$_3$]
- Central metal: Co (oxidation state = +3).
- Ligands: 3 Cl$^-$ (chloro), 3 NH$_3$ (ammine).
\[ \text{IUPAC name: Triamminetrichloridocobalt(III)} \]