Molecular Coordinative Complexes by Ligand Fields Analysis

5 MOLECULAR COORDINATIVE COMPLEXES BY LIGAND FIELDS ANALYSIS 

In describing the crystal field and allied effects, one remark that the attractive forces of bonding were not even mentioned, while only the repulsive effects being invariable considered. 

To this aim, the ligand field theory comes to complete the presence of the attractive forces in chemical bonding, by combining the crystal field theory developed by Bethe and van Vleck (about 1930) with the contemporary theory of the valence bond of Pauling, which assumes the molecular complex formation as a reaction between the Lewis bases (ligands) and the Lewis acids (the metals or the metallic ions). 

This way the coordinative or dative covalent bond is resulting, likely as molecular orbitals ingredient of the crystal field theory. More specifically, the ligands treatment is supplemented with the molecular orbital picture, precisely by admitting both the terms and the orbitals rising from the hybridization of the ligand orbitals. 

Essentially, for the metal or the central ion its valence state is considered with the valence orbitals (s,p,d) written as prescribed by the separation of this type of orbital in the crystalline field the ligands, instead, are not anymore considered only as point charges, but they also achieve orbital identity, as s and p, for which there are also considered their hybridization, such as a and n. 

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