Crystal field stabilisation energy (CFSE)

Crystal field stabilisation energy (CFSE)-

·       The splitting of the degenerate orbitals due to the presence of ligands in a definite geometry is known as crystal field splitting and the difference between two sets of degenerate orbitals as a result of crystal field splitting is known as crystal field stabilisation energy

·       It is denoted by Δ_o (the subscript o stands for octahedral) and Δ_t (the subscript t stand for tetrahedral.

·       The splitting is much smaller in tetrahedral than that in case of octahedral complexes. Thus the difference of energy, represented by Δ_t = 4/9 Δ_o.

Factors affecting the magnitude of CFSE(Δ )-

a.     Oxidation state of metal ion- higher the oxidation state of central ion, larger the value of Δ.

b.     Nature of the metal ion- in block elements, within the same group, as we move from 3d to 4d to 5d the value of Δ increases and the tendency to form low spin complexes increases. So 4d and 5d series element have high tendency to form low spin complexes than 3d series.

c.     Nature of the ligand -for the same metal ion, splitting is much smaller (Δ) in presence of weak ligand than that in case of strong ligand defined in spectrochemical series.

d.     Geometry of complex ion- in octahedral, splitting is larger that in case of tetrahedral i.e Δ will be higher in case of octahedral complexes.   

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