[SadBloke]

I'm having some trouble calculating the Ligand Field Stabilizing Energies of transition metals. The first thing I do is determine the oxidation state of the metal and then I input it in this equation:

LFSE = (# of t_2g electrons)(.4) - (# of e_g electrons)(.6)

Sometimes this works, like when I use it for Fe²⁺ when it is bound to a weak field ligand and creates a high spin complex.

I get:  LFSE = (4 t_2g electrons)(.4) - (2 e_g electrons)(.6) = .4

It doesn't work for other atoms, like Co³⁺. When I use it for Co³⁺ (in a low spin state) I get 2.4 because there are no electrons in the e_g orbitals. When I look it up in my book, the correct LFSE is 2.4-2P.

I know 2P is related to the energy pairing of electrons that destabilize the configuration but I don't know how it factors into the equation or how to calculate any LFSE that contains a 'P' term.

How do I know when to include a P term?

[SadBloke]

I think I understand a little more, now. For every pair of electrons, I need to subtract P (or so it seems).