why do t2g obitals lose energy when a ligand approaches?

and...

if CO is a strong fireld ligand, then y do elements show 0 oxidation state when they fom complex compounds with CO?

Dear student,

The valence atomic orbitals that are located on the transition-metal centre are the s, p, and d orbitals, which have A1g, T1u, and (Eg/T2g) symmetry, respectively. Ignoring any ligand π-orbitals, we have to consider only six linear combinations of atomic ligand σ-orbitals. In principle, we have three choices of ligand σ-orbitals: s-orbitals, pσ orbitals (those p orbitals that point directly towards the central atom), and the sp3 hybrid orbitals that point towards the metal centre. The latter mix hybridization, which is strictly based on VB theory, with MO theory and, therefore, we won’t use that description. The s orbitals of the ligands are usually too low in energy, since the ligating atom is usually more electronegative than the central atom; therefore, the pσ orbitals are the σ-orbitals of choice. On the right-hand side, the transition-metal valence orbitals are depicted together with the symmetry-adapted ligand orbital of appropriate symmetry.

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Sagar Singh

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