COSMO default radius for 3rd row transition metals

[antti_karttunen]

Hi,

It seems that Cosmoprep does not have any default radius values for atoms Cs-Rn. Does anybody have suggestions on suitable radius values for 3rd row transition metals such as gold?

[diedenho]

Hi Antti,

Sorry, we don't have good radii for this metals.
There might be a couple of good choices dependent on the
problem you are modeling.
For naked metal cations it might be a good idea to include an implicit solvens shell for instance - at least for strongly coordinating solvents.
The normal cosmo radii are roughly 1.17*bondii radius. But as far as I know there are no bondii radii available for the metals you are interested in. Dependent on your molecule
there are two cases:

1) The metal has no (or nearly no) solvens accesable surface. In other words:  The ligands coordinate the metal in a way that the metal surface is perfectly screened. In this case any metal radius that defines a sphere smaller that the ligand sphere is OK.

2) If the metal surface is accessible, like in square planar complexes, you need to find a useful radius.
The optimized cosmo radii have been fitted to thermodynamic data. But this is not a simple straight forward procedure. Furthermore, exp. data is not available for many systems.
I would try some reasonable values like metal radius*1.17 and do some test calculations in order to get an impression of the sensitivity.

hope this helps a bit
michael

[antti_karttunen]

Thanks for the tips! The systems I'm currently studying are usually of the "no solvent accessible surface"-type, so the accuracy of the metal radius is probably not that critical. However, I'll run some calibration calculations for the radius as you suggested.