It is well known that 1,10-phenanthroline (Phen) ligand forms more stable complex with Co(3+) than Co(2+) and Fe(2+) than Fe(3+). This has been attributed to their low spin t2g6 configuration what can be the reason for this enhanced stability how it can be explored computationally?
Probably you can do an energetic study, also with simple DFT study with a B3LYP functional, changing the number of electrons in the overall molecule ( that is easy to do because you change the charge and the spin state) ( not only on the metal itself, because i suppose this kind of complexes have a good degree of delocalization on the ligands, that can be the reason of this bigger stability respect to the other electronic configurations). If you calculate the energy of the optimized geometry, you could identify a bigger stability (more negative energy) in the complexes that are experimentally more stable. I suppose that the electron correlation is important in those sistems for their charge-transfer nature, so a HF level is not so appropriate to make this study.
Emanuele Priola
Thanks Priola half part of your answer i have already done by calculating free energies in two oxidation states. yes these systems have electron delocalization or charge transfer from metal to phen ligand point is how to probe that and how to quantify that the degree of charge transfer is different in two oxidation states.
I expect that answers can be obtained by the HOMO components of specific atomic orbitals in the different cases. I think this can be done visually by Gaussview if you use Gaussian or other programs that visualize electronic MO, but in the imput part you can find also the electronic function and the orbitals involved in MO; if you find the HOMO you should find also the components of the delocalized orbital, and the percentage of the MO that isn't 3d orbital of metal atom is a rought measure of the delocalization of the electrons involved.
Emanuele Priola
May be it happaned becouse of d6 configuration of these complexes, low spin with Fe2+ and Co3+. This configuration is stable, non-degenerate electron ground state (all the levels with the same namber of electrons). For octahedral geometric straucture with the ligand phen - ligand high field. So we get this configuration with Fe2+ and Co3+ metals ion and not with Fe3+ and Co2+, becouse of electronic configuration (d6 - low spin) .
May be it happaned becouse of d6 configuration of these complexes, low spin with Fe2+ and Co3+. This configuration is stable, non-degenerate electron ground state (all the levels with the same namber of electrons). For octahedral geometric straucture with the ligand phen - ligand high field. So we get this configuration with Fe2+ and Co3+ metals ion and not with Fe3+ and Co2+, becouse of electronic configuration (d6 - low spin) .
Mr. Rizvi,
You need thermodynamics and NBO analysis, which can be done by quantum chemistry. Suitable program-package is Gaussian (www.gaussian.com).
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