Intuitive Explanation for why more negative charge on ligand does not imply more splitting effect? I have studied coordination chemistry as part of my school curriculum and we covered Crystal Field Theory as our final theory, and the book says that Ligand Field Theory and Molecular Orbital Theory are used to explain the limitations of CFT but are beyond our scope of learning.
One of the limitations of CFT according to the book is that if the ligands are point charges then it should follow that an anionic ligand should exert more splitting effect but that is not the case as we see in the spectro-chemical series.
A good example would be $\ce{S^2-}$ &lt; $\ce{F-}$ &lt; $\mathrm{EDTA^{4-}}$ &lt; $\ce{CO}$
Also we can see that size is not the determining factor as then $\mathrm{EDTA^{4-}}$ wouldn't be so high as compared to $\ce{F-}$
Is there some intuitive explanation or logic for this which I can follow with my current knowledge till CFT without going too deep into MOT or LFT?
Crystal Field Theory assumes that all of the interactions occuring are purely electrostatic and only concern d-orbitals.  This is clearly not true when dealing with some ligands which create a covalent bond.
Most limitations of CFT all stem from the inability to explain non-electrostatic interactions.  For this reason, it works well when the electrostatic aspect is the dominant factor but it completely fails for some cases such as neutral CO ligands.  While you could easily argue electrostatic forces still exist in this situation, clearly they are not dominant and do not explain any observed behavior while still having an effect.