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Shivani Kumari posted an Question
June 11, 2020 • 21:05 pm 95 points
  • IIT JAM
  • Chemistry (CY)

Which of the following complexes are chiral? (a) [cr(ox)3] 3–; (b) cis‐[ptcl2(en)]; (c) cis‐[rhcl2(nh3)4] + ; (d) [ru(bipy)3] 4+; (e) [co(edta)]– ; (f) f

Which of the following complexes are chiral? (a) [Cr(ox)3] 3–; (b) cis‐[PtCl2(en)]; (c) cis‐[RhCl2(NH3)4] + ; (d) [Ru(bipy)3] 4+; (e) [Co(edta)]– ; (f) fac‐[Co(NO2)3(dien)]; (g) mer‐ [Co(NO2)3(dien)]. Identify the enantiomers as chiral and achiral complexes.

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  • Suman Kumar best-answer

    Ans. (a) [Cr(ox)3] 3–    It is definitely chiral; two chelating ligands on an octahedral framework are sufficient do impart chirality to the complex. The two enantiomers provide the left and right of a plane of reflection. (b) cis‐[PtCl2(en)]  This molecule would be chiral because of the twist in the en ligand. However, ring inversion in chelate complexes of this type (as in cyclopentane) is very fast at room temperature and well below, so that enantiomers cannot be isolated, and the complex is normally considered to be achiral. (c)  cis‐[RhCl2(NH3)4] + This complex is achiral.  It has  C2v symmetry, and thus has two internal mirror planes, which can be clearly seen in the picture of the molecule, one virtical and one horizontal to the page.  Note that the symmetry requires the ammine ligands to be in a specific orientation.   In practice, the Rh—N bonds rotate sufficiently fast that the ammine ligands are effectively spherical, so the molecule definitely acts as a C2v species.

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