CCL:G: Calculation of Redox Potentials

[Tobias Kraemer <tobiask * chem.gla.ac.uk>]

 Sent to CCL by: Tobias Kraemer [tobiask|chem.gla.ac.uk]
 Hi....
I'm trying to get experience in calculating some redox potentials of
 copper complexes to refer these data to experimental values.
 I have done a number of initial calculations on a test set of
 organometallic molecules, to get used to the method, using B3LYP/6-31G*
 and the default PCM model as implemented in Gaussian with methanol as
 solvent. As expected, deviations from experiment are big
 (in order of a few hundreds of millivolts). I also applied this
 protocol
 to the copper complexes I'm interested in and in a next step increased
 the
 basis set to TZVP for copper and ligating atoms, and SVP for remaining
 ligand atoms. I observed a big difference in the computed value for the
 redox potential, going from
 -0.12 (B3LYP/6-31G*) to +0.35 (B3LYP/TZVP). This is surely not so
 unexpected.  There are significant changes in the solvation energy
 for  the reduced form of the complex, Cu(I), whereas the solvation
 energy of the oxidised form, Cu(II), is uneffected. Also, significant
 changes in the relative energies of the
 structures in gas phase contribute to the change in the reduction
 potential.
 After reading some papers about the topic, I feel that the use of
 Jaguar
 for calculations of this type is preferred.  This causes some
 difficulty
 in reproducing results, as I'm using
 Gaussian. So, in order to design some further test calculations, I
 would
 like to ask for some advise from people that have experience with this
 type of calculations using Gaussian and the
 solvent models therein. Maybe there is some further literature, which
 would help me as well, that report benchmark calculations using
 Gaussian.
 I would especially like to know, if it is advisable to do full
 optimisations in solvent, to improve the results, and which solvent
 models yield good results, although
 I'm aware, that this strongly depends on the system that is being
 investigated.
 Your comments are much appreciated.
 Thanks
 Tobi
 --
 ____________________________________
  dipl.-chem. tobias kraemer
  westCHEM, department of chemistry
  university of glasgow
  joseph black building
  university avenue
  glasgow G12 8QQ
  scotland, uk
  |phone| +44 (0)141 330 8121
  |email| tobiask=chem.gla.ac.uk
 ____________________________________