Question

What are the main features of the ligand field theory?

Answer 1

A coordination complex is made up of a core atom or ion called the coordination centre, which is generally metallic, and a surrounding array of bonded molecules or ions called ligands or complexing agents. Coordination complexes are found in many metal-containing compounds, particularly those containing transition metals (d block elements).

Complete answer:
The bonding, orbital arrangement, and other properties of coordination complexes are described by Ligand Field Theory (LFT). It shows how molecular orbital theory may be used to transition metal complexes. Five nd, one (n+1)s, and three (n+1)p orbitals make up a transition metal ion's valence atomic orbitals. These orbitals have the right energy to create ligand-bonding interactions. The geometry of the complex affects the LFT analysis, although most explanations start with octahedral complexes, which have six ligands that coordinate to the metal. Crystal field theory may be used to describe other complexes. The molecular orbitals generated by coordination in an octahedral complex may be regarded as the consequence of each of six -donor ligands donating two electrons to the metal's d-orbitals. Because ligands approach the x, y, and z axes in octahedral complexes, their $\sigma$-symmetry orbitals create bonding and antibonding combinations with the$d{z^2}$and ${d_{{x^2}{y^2}}}$orbitals. The non-bonding orbitals dxy, dxz, and dyz remain. There are also weak bonding (and antibonding) interactions with the metal's s and p orbitals, for a total of 6 bonding (and antibonding) molecular orbitals.
In octahedral complexes, bonding happens in two ways: via any ligand p-orbitals that aren't being used for bonding, and via any $p,\pi$ or $\pi *$ molecular orbitals on the ligand.
The p-orbitals of the metal are utilised for bonding (and have the incorrect symmetry to overlap with the ligand $p,\pi$ or$\pi *$ orbitals anyhow), thus interactions are carried out using the appropriate metal d-orbitals, i.e. dxy, dxz, and dyz. When just bonding occurs, these are the orbitals that are non-bonding.

Note:
The Ligand Field Theory (LFT) covers coordination complex bonding, orbital arrangement, and other properties. It shows how molecular orbital theory may be used to transition metal complexes. Five nd, one (n+1)s, and three (n+1)p orbitals make up the valence atomic orbitals of a transition metal ion.