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https://chem.libretexts.org/Core/Inorganic_Chemistry/Coordination_Chemistry/Properties_of_Coordination_Compounds/Isomers/Stereoisomers%3A_Geometric_Isomers_in_Transition_Metal_Complexes

In example 1.1, it is written that en which occupy only adjacent positions.....is it true for any bidendate for octahedral isomer?

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    $\begingroup$ It surely depends on the size of the specific ligand. Big floppy ligands might well be able to occupy opposite positions. $\endgroup$ – matt_black Dec 12 '17 at 15:26
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Its not impossible to have a trans-spanning ligand, but they seem to be rarer than cis-ligands due to their increased length and greater potential for steric strain. While en is too small of a ligand to reach trans-positions, it is possible with significantly longer ligands.

It seems octahedral ones are even rarer than their square planar counterparts, but there has been at least one reported synthesis of a trans-spanned octahedral$^1$ that I could find. In the linked paper, they report the synthesis of trans-$\ce{[Ru(Cl)(trpy)(C3SPAN)]}$ where trpy = 2,2:6,2-terpyridine and C3SPAN=$\ce{Ph2PC6H4CH2O(CO)(CH2)3(CO)OC6H4PPh2}$.

$\hspace{25ex}$trans-spanned ruthenium complex

  1. C. Bessel, et al. Chem. Soc., Dalton Trans., 1999, 2281–2292
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  • $\begingroup$ Interesting, but isn't that for square-planar? Or does it apply to octahedral as well? $\endgroup$ – gilleain Dec 12 '17 at 15:27
  • $\begingroup$ @gilleain good catch, I jumped on that too quickly. It seems to also be possible for octahedral as well. I will try to link to a paper. $\endgroup$ – Tyberius Dec 12 '17 at 15:31
  • $\begingroup$ So the question was solved on the basis of assumption or taking the case which is more bound to happen? $\endgroup$ – Hydrous Caperilla Dec 12 '17 at 16:01
  • $\begingroup$ @HydrousCaperilla for the example you gave, it could only be cis because the en ligand is too small to be trans-spanning. $\endgroup$ – Tyberius Dec 12 '17 at 16:12
  • $\begingroup$ can en liagand be trans spanning in any other case? $\endgroup$ – Hydrous Caperilla Dec 12 '17 at 17:22

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