Ionic bonding crystal field theory

Historically, crystal field theory was the first theoretical model (11, 86, 101, 123) used to explain d-d transition energies in metal complexes. Its usefulness is restricted to those complexes whose bonding is largely ionic, and its mqjor deficiency arises from its inability to account for charge transfer transitions. The iterative extended Hiickel and the ab initio, limited basis set, Hartree-Fock calculations are capable of de-... 

In this chapter, we discuss mostly the bonding in mononuclear homoleptic complexes ML using two simple models. The first, called crystal field theory (CFT), assumes that the bonding is ionic i.e., it treats the interaction between the metal ion (or atom) and ligands to be purely electrostatic. In contrast, the second model, namely the molecular orbital theory, assumes the bonding to be covalent. A comparison between these models will be made. 

Interpretations of the crystal chemistry of transition metal ions by crystal field theory are based on a predominatly ionic model of the chemical bond. As... 

The directionality in the bonding between a d-block metal ion and attached groups such as ammonia or chloride can now be understood in terms of the directional quality of the d orbitals. In 1929, Bethe described the crystal field theory (CFT) model to account for the spectroscopic properties of transition metal ions in crystals. Later, in the 1950s, this theory formed the basis of a widely used bonding model for molecular transition metal compounds. The CFT ionic bonding model has since been superseded by ligand field theory (LFT) and the molecular orbital (MO) theory, which make allowance for covalency in the bonding to the metal ion. However, CFT is still widely used as it provides a simple conceptual model which explains many of the properties of transition metal ions. 

In 1951, chemists trying to make sense of metal complex optical spectra and color returned to an emphasis on the ionic nature of the coordinate covalent bond. Coordination chemists rediscovered physicists Hans Bethe s and John van Vleck s crystal field theory (CFT),... 

Hans Bethe (1906- ) and J. H. van Vleck (1899-1980) developed the crystal field theory between 1919 and the early 1930s. It was not widely used, however, until the 1950s. In its original form, it assumed that the bonds between ligand and metal were completely ionic. 

Modern ligand field theory is based on crystal field theory. It attributes partial covalent character and partial ionic character to bonds. It is a more sophisticated theory, beyond the scope of this text. 

Crystal field theory A theory of bonding in transition metal complexes in which ligands and metal ions are treated as point charges a purely ionic model. Ligand point charges represent the crystal (electric) field perturbing the metal s d orbitals that contain nonbonding electrons. 

An Ionic Bonding Model - Introducing Crystal Field Theory... 

Crystal field theory can deal with the observed splitting between the d-orbital sets increasing with increasing oxidation state of the central metal atom. Since the ionic radius of an ion decreases as ionic charge (which equates with oxidation state for a metal ion) increases, the surface charge density increases, metal-ligand bond distances (r) decrease and the splitting A 0 (which varies with r-5) increases. However, CFT has some obvious limitations, which led to development of alternate models. It cannot easily explain why A0... 

The crystal field theory (CFT), an ionic bonding model, is focused on the d-orbital set and the way this degenerate set of five orbitals on the bare metal ion is split in the presence of a set of ligands into different energy levels. It provides a fair understanding of spectroscopic and magnetic properties. 

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