VBT and CFT of Coordination compounds

p-Block Elements: Coordination compounds


Valence bond theory (VBT) Crystal field theory (CFT)
Provides chemical bonding of atoms in a molecule in ionic and covalent structures. Provides the only electronic structure of coordinate complex where the bonding is purely ionic
Explains the formation of a covalent bond via hybridization of atomic orbitals. Explains the breaking of degeneracies of electron orbitals due to the electrostatic field produced by a surrounding anion or anions explanation
It assumes that more overlap increases the strength of an orbital. It assumes that a central atom is surrounded by ligands that are point charge or point dipole.
Based on the overlapping of orbitals to form a chemical bond It assumes that is no interaction between metal orbitals and ligand orbitals. And splitting of d orbital occurs due to ligands. It disregards covalent bonding and orbital overlap in metal complexes
Can show the shape but not the geometry of the molecules. The σ bonds for liner and π bonds for parallel overlap are applicable Cannot predict the shape of the complexes
Indicates the type of bonding present between atoms Indicates the spectroscopy, magnetism, and reactivity trends of d-block compounds
The metal atom or ion under the influence of ligands can use (n-1)d, ns, np or ns, np, nd, nf orbital for hybridization to yield a set of equivalent orbitals of definite geometry such as octahedral, tetrahedral, square planar and so on All the five d-orbitals are degenerate (same energy) in the isolated, gaseous metal ion.
It does not give a quantitative interpretation of the magnetic spin of the electrons or explain the colour exhibited by various forms of coordination compounds with the same molecular formula. Since the CF model is an ionic model based on the electrostatic effect of the ligands on the energies of the metal ion d orbitals, it is surprising to find that anionic ligands such as Br, F and OH should be weaker-field than neutral ligands such as CO, NH3 and PR3. This anomaly arises because the CFA model does not take account of covalence in metal-ligand bonding.
It does not make exact predictions especially for the tetrahedral and square planar structures in the case of 4-coordinate complexes. Shows exact structural representation of tetrahedral splitting and square planar splitting
It does not distinguish between weak and strong ligands. Ligand strength: (Weak) I< F< H2O < NH3< CN (Strong)

Metal strength: (Weak) Mn2+< Ni2+< Co2+< Fe2+< V2+< Fe3+< Cr3+< V3+< Co3+< Mn3+< Mo3+< Rh3+< Ru3+< Pd4+< Ir3+< Pt4+ (Strong)

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