GATE 2000
Which one of the following octahedral complexes shows Jahn-Teller distortion?
Correct Answer: (A) [Cr(H2O)6]2+
(B) [Cr(H2O)6]3+: Cr3+ is a d3 system.
(C) [Mn(H2O)6]2+: Mn2+ is a d5 system.
(D) [Fe(H2O)6]3+: Fe3+ is a d5 system.
Explanation:
(A) [Cr(H2O)6]2+: Cr2+ is a d4 system.(B) [Cr(H2O)6]3+: Cr3+ is a d3 system.
(C) [Mn(H2O)6]2+: Mn2+ is a d5 system.
(D) [Fe(H2O)6]3+: Fe3+ is a d5 system.
H2O is a weak field ligand, so high-spin configurations are formed. Jahn-Teller Distortion occurs when there is asymmetric filling of degenerate orbitals.
In [Cr(H2O)6]2+; d4, the configuration is t2g3 eg1. The single electron can occupy either the dx2-y2 or dz2 orbital, creates a strong distortion.
Other complexes (B), (C), and (D) have half-filled or empty subshells that are symmetrically occupied, resulting in no distortion.