I am interested in terminal metal-oxo complexes and their electronic structure, specifically those with coordination numbers of 6, including the oxo ligand.
I know that Fe(IV)-oxo complexes tend to exhibit the 1+2+1+1 $d$-orbital energy scheme shown in the 3rd complex below. With this, I have two questions. Let's consider an Fe(IV) center for consistency.
Is there any way to predict, without performing calculations, what might occur if the ligands are not all identical? Does that change the likelihood of a 1+2+1+1 arrangement?
How does one account for the presence of dative bonds (e.g. if two of the equatorial ligands form dative bonds whereas the rest form traditional covalent bonds)?