Hello everyone. I am running b3lyp/def2-TZVP (slightly higher quality than 6-311G**) geometry optimization calculations on a Nickel compound complexed with a bridged four-ring pentadentate ligand that has 5 coordinating Nitrogens. The SCF Energy is compared between this complex bound with either CO2, CO or MeCN. I also have a set of calculations with Nickel complexed to a bridged 3-ring tetradentate ligand (4 coordinating Nitrogens) and MeCN, along with either CO2or CO to complete the octahedral complex.
For each structure, I set the charge to either +1 or +2 and include the two likely Spin States for each charge. I am noticing that the calculated energies for a given complex are almost exactly the same, sometimes even within 1 Hartree of another. It's as if my designation of the charge and multiplicity were practically arbitrary. This has made me question:
What kind of role does the oxidation state of a metal play in coordination chemistry?
What kind of role does the spin state (doublet vs. quartet, singlet vs. triplet) play in coordination chemistry?
It also has me worried that my basis set is not accounting for the differences appropriately, but I can't really explore that possibility until I know what these differences might be. Links to further reading are always welcome. I had trouble finding anything beyond counting electrons and summaries of high spin vs low spin, but I might be using the wrong terms to search. I did read that high oxidation state is not conducive to coordination with strong pi acidic ligands, as pi-backbonding is not as favorable. I was hoping someone could enlighten me to other, possibly more general, implications.
Thank you very much for reading and any advice!