Solveeit Logo
Login

Question

Question: Total number of space (stereo) isomers of complex ion $[Cr(gly)(en)_2]^{2+}$ are ____....

Total number of space (stereo) isomers of complex ion [Cr(gly)(en)2]2+[Cr(gly)(en)_2]^{2+} are ____.

Answer

3

Explanation

Solution

The complex ion is [Cr(gly)(en)2]2+[Cr(gly)(en)_2]^{2+}. Here, Cr is the central metal ion. gly (glycinate ion, NH2−CH2−COO−NH_2-CH_2-COO^-) is an unsymmetrical bidentate ligand, coordinating through one Nitrogen (N) atom and one Oxygen (O) atom. We can denote it as AB. en (ethylenediamine, NH2−CH2−CH2−NH2NH_2-CH_2-CH_2-NH_2) is a symmetrical bidentate ligand, coordinating through two Nitrogen (N) atoms. We can denote it as AA.

The coordination number of Cr is 2×2(from two en)+2×1(from one gly)=62 \times 2 (\text{from two en}) + 2 \times 1 (\text{from one gly}) = 6. So, it is an octahedral complex. The complex is of the type [M(AA)2(AB)][M(AA)_2(AB)].

For an octahedral complex of the type [M(AA)2(AB)][M(AA)_2(AB)], there are two possible geometrical isomers:

  1. trans-isomer: In this isomer, the two symmetrical bidentate ligands (en) are arranged in a 'trans' fashion relative to each other. This means their 'planes' are parallel and they are on opposite sides of the central metal ion.

    • Let's visualize this. Imagine the two en ligands occupying positions such that they are opposite to each other. For example, if one en occupies the top-front and top-back positions, the other en would occupy the bottom-front and bottom-back positions.
    • The gly ligand (N, O) would then occupy the remaining two adjacent positions.
    • This trans isomer possesses a plane of symmetry (passing through the Cr atom and bisecting the two en ligands, and containing the gly ligand). Therefore, the trans isomer is optically inactive (it is a meso compound).
    • Number of stereoisomers for the trans form = 1.

  2. cis-isomer: In this isomer, the two symmetrical bidentate ligands (en) are arranged in a 'cis' fashion relative to each other. This means their 'planes' are not parallel, and they are on the same side of the central metal ion, or at least not directly opposite.

    • This cis isomer lacks a plane of symmetry and is chiral. Therefore, it exists as a pair of enantiomers (non-superimposable mirror images).
    • Number of stereoisomers for the cis form = 2 (dextro and levo forms).

Total number of space (stereo) isomers = (Number of trans-isomers) + (Number of cis-enantiomers)

Total number of space (stereo) isomers = 1 (trans) + 2 (cis-enantiomers) = 3.

Therefore, there are 3 possible space (stereo) isomers for the complex ion [Cr(gly)(en)2]2+[Cr(gly)(en)_2]^{2+}.