Does tris(ethylenediamine)iron(III) exhibit optical isomerism? [closed]








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I'm studying 12th. In my book they mentioned that $\ce{[Co(en)3]^3+}$ exhibits optical isomerism.


But in that same book, there is a question



> 
> Which of this doesn't exhibit isomerism?
> 
> 
> 


and the answer is $\ce{[Fe(en)3]^3+}.$ Since both complexes have the same structure, then why they are saying $\ce{[Fe(en)3]^3+}$ doesn't show isomerism?




I think the answer given in your textbook is either incorrect or a misprint. I let you find out the correct answer from given choices.


However, I'd like like to claim that the given answer is wrong because of following facts: 


* Tris(ethylenediamine) complexes of transition metals have been studied for more than 100 years and $\ce{M(en)3^3+}$ complexes are been considered chiral (*e.g.*, Ref.1 for studies on $\ce{Co(en)3^3+}$).
* The enanti­omeric nature of these complexes has been verified by X-ray crystallography (*e.g.*, Ref.2 for studies on $\ce{Co(en)3^3+}$).
* The crystal structures of the first-row transition-metal series of tris­­(ethyl­enedi­amine) di­acetate complexes have been recently studied (Ref.3) to show their chiral nature, and following common structure is given for the complexes with $\ce{M^2+}$ central metal:


[![tris­­(ethyl­enedi­amine) di­acetate complexes](https://i.stack.imgur.com/li3Uh.jpg)](https://i.stack.imgur.com/li3Uh.jpg)


The abstract states that:



> 
> The crystal structures of the first-row transition-metal series of tris­(ethyl­enedi­amine-$\kappa^2$*N,N′*)metal(II) di­acetate, $\ce{[M(C2H8N2)3](CH3CO2)2}$, with $\ce{M = Mn, Fe, Co, Ni, Cu,}$ and $\ce{Zn}$, are reported. The complexes are all isostructural, crystallizing in a centrosymmetric triclinic cell and possessing an asymmetric unit composed of one $\ce{[M(en)3]^2+}$ cation and two symmetrically independent acetate anions. In the unit cell, the two complex cations are inversion-generated enanti­omers, possessing the energetically favoured Δ(λλλ) and Λ(δδδ) configurations. The complex cations and acetate anions combine through a series of $\ce{N—H⋯O}$ hydrogen bonds to generate a three-dimensional network in the crystals. The other notable feature of the series is a significant Jahn–Teller distortion for the $\mathrm{d^9}$ $\ce{Cu^2+}$ complex.
> 
> 
> 


It is a fact that structures of these same first-row transition-metal series with 3+ oxidation state would give the same octahedral shapes, the cation of which are chiral (*e.g.*, Ref.1 and Ref.2). Examples of few are given below:


[![Metal 3+ Complexes](https://i.stack.imgur.com/J9POH.jpg)](https://i.stack.imgur.com/J9POH.jpg)


Overall, it is true that the $\ce{[Fe(en)3]^3+}$ cation is chiral.


**References:**


1. A. Werner, "Zur Kenntnis des asymmetrischen Kobaltatoms. V," *Berichte der deutschen chemischen Gesellschaft* **1912**, *45(1)*, 121-130 (<https://doi.org/10.1002/cber.19120450116>).
2. Y. Saito, K. Nakatsu, M. Shiro, H. Kuroya, "The first-row transition-metal series of tris­­(ethyl­enedi­amine) di­acetate Determination of the absolute configuration of optically active complex ion, $\ce{[Co(en)3]^3+}$, by means of X-rays," *Acta Crystallographica* **1955**, *8*, 729-730 (<https://doi.org/10.1107/S0365110X55002211>).
3. Duyen N. K. Pham, Mrittika Roy, James A. Golen, David R. Manke, "The first-row transition-metal series of tris­­(ethyl­enedi­amine) di­acetate complexes M(en)32 (M is Mn, Fe, Co, Ni, Cu, and Zn)," *Acta Crystallographica Section C* **2017**, *73(6)*, 442-446 (<https://doi.org/10.1107/S2053229617006738>).


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