Give correct IUPAC names for the compounds below: Explain
(1) K3 [Fe(C2O4)3]-3H20
(2) K[Cu(C2O4)2]·2H2O
(3) K3[Cr(C2O4)3]-3H20
(4) K[Al(C2O4)3]-3H20
(5a) cis-K[Cr(C204)2(H2O)2]-2H2O
(5b) trans-K[Cr(C2O4)2(H20)2]·2H20
The correct answer and explanation is :
Correct IUPAC Names and Explanation
- Potassium tris(oxalato)ferrate(III) trihydrate
Formula: K₃[Fe(C₂O₄)₃]·3H₂O
- The central metal ion is iron (Fe³⁺).
- Oxalate (C₂O₄²⁻) is a bidentate ligand.
- The oxidation state of Fe is +3, determined by:
[
3K^+ + \text{Fe} + 3(C_2O_4^{2-}) = 0
]
Solving for Fe: Fe³⁺. - Since the complex is an anion, it ends with “-ate”, hence ferrate(III).
- Potassium bis(oxalato)cuprate(II) dihydrate
Formula: K[Cu(C₂O₄)₂]·2H₂O
- Copper (Cu²⁺) has an oxidation state of +2.
- Since the complex is anionic, “-ate” is used for the metal, forming cuprate(II).
- Potassium tris(oxalato)chromate(III) trihydrate
Formula: K₃[Cr(C₂O₄)₃]·3H₂O
- Chromium (Cr³⁺) has an oxidation state of +3.
- The complex is anionic, so chromate(III) is used.
- Potassium tris(oxalato)aluminate(III) trihydrate
Formula: K₃[Al(C₂O₄)₃]·3H₂O
- Aluminum (Al³⁺) oxidation state is +3.
- The complex is anionic, so aluminate(III) is used.
5a. cis-Potassium diaquabis(oxalato)chromate(III) dihydrate
Formula: cis-K[Cr(C₂O₄)₂(H₂O)₂]·2H₂O
- Chromium (Cr³⁺) oxidation state is +3.
- The complex has two oxalate ligands and two water ligands in a cis-configuration.
5b. trans-Potassium diaquabis(oxalato)chromate(III) dihydrate
Formula: trans-K[Cr(C₂O₄)₂(H₂O)₂]·2H₂O
- Chromium (Cr³⁺) oxidation state is +3.
- The complex has two oxalate ligands and two water ligands in a trans-configuration.
Explanation (300 Words)
The nomenclature of coordination complexes follows IUPAC rules, where the cation (potassium in this case) is named first, followed by the anionic coordination complex. The ligands are named in alphabetical order, and their quantity is specified using prefixes like bis- (2), tris- (3), tetra- (4), etc..
Oxalate (C₂O₄²⁻) is a bidentate ligand, meaning it coordinates through two oxygen atoms. Since these complexes are anionic, the metal names end in “-ate” (e.g., ferrate, cuprate, chromate, aluminate). The oxidation state of the metal is determined by balancing the charge of the complex.
For cis-trans isomerism in (5a) and (5b), the cis-form has the two water molecules adjacent, while in the trans-form, they are opposite. This affects properties like stability, reactivity, and color.
The presence of crystal water (trihydrate, dihydrate, etc.) is explicitly stated after the complex name, as it influences solubility and crystal structure.