Question

Given below are two statements:
Statement-I : $[\text{Fe}(\text{ox})_3]^{3-}$ is chiral.
Statement-II : trans-$[\text{Cr}(\text{H}_2\text{O})_2(\text{ox})_2]^-$ is chiral.
(Given : \(\text{oxH}_2 = \text{HOOC}-\text{COOH}\))
In light of the above statements, choose the most appropriate answer from the options given below:

• A. Statement-I is incorrect but Statement-II is correct
• B. Both Statement-I and Statement-II are correct
• C. Both Statement-I and Statement-II are incorrect
• D. Statement-I is correct but Statement-II is incorrect

Hint:

For octahedral complexes with bidentate ligands: - All tris-chelated complexes like $[\text{M}(\text{AA})_3]$ are always chiral. - For bis-chelated complexes like $[\text{M}(\text{AA})_2\text{B}_2]$: the cis-isomer is always chiral, while the trans-isomer contains planes of symmetry and is always achiral.

Answer 1

The Correct Option is D

Step 1: Recall the test for chirality.
A complex is chiral (optically active) only if it has no plane of symmetry and no centre of inversion, so its mirror image cannot be superimposed. Oxalate (ox) is a symmetric bidentate ligand forming five-membered rings.
Step 2: Look at Statement-I, \([Fe(ox)_3]^{3-}\).
This is a tris-chelate octahedron of the type \(M(AA)_3\). Such propeller-shaped complexes have no mirror plane and exist as two non-superimposable \(\Delta\) and \(\Lambda\) forms. So it is chiral, and Statement-I is correct.
Step 3: Look at Statement-II, trans-\([Cr(H_2O)_2(ox)_2]^-\).
Here two oxalates and two water ligands sit in a trans arrangement, with the two \(H_2O\) on opposite poles of the octahedron.
Step 4: Find the symmetry of the trans isomer.
In the trans form the two water ligands and the two oxalate rings lie so that the molecule has a plane of symmetry passing through the axial waters. A plane of symmetry makes the mirror image superimposable.
Step 5: Decide on Statement-II.
Because the trans isomer has that mirror plane, it is achiral. So Statement-II, which calls it chiral, is incorrect. (Only the cis form of this complex is chiral.)
Step 6: Combine the verdicts.
Statement-I correct, Statement-II incorrect, which is option 4.
\[ \boxed{\text{Statement-I is correct but Statement-II is incorrect}} \]