JEE Main · 2005 · 08 May 2005 · Offline · Coordination Compounds

Optical isomerism needs a complex with no plane of symmetry, one not superimposable on its mirror image. $[\mathrm{Cr}(\mathrm{C}{}_2\mathrm{O}{}_4){}_3]{}^{3-}$ is octahedral with three bidentate oxalate ligands wrapped around the metal like a three-bladed propeller, a chiral arrangement existing as non-superimposable $\Delta$ and $\Lambda$ forms. The others each possess a symmetry plane, the square-planar $[\mathrm{Cu}(\mathrm{NH}{}_3){}_4]{}^{2+}$, the tetrahedral $[\mathrm{ZnCl}{}_4]{}^{2-}$ and the octahedral $[\mathrm{Co}(\mathrm{CN}){}_6]{}^{3-}$ with their simple monodentate ligands, so only the tris-oxalato chromium complex is optically active.