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Sunday, August 25, 2019

Factor's affecting magnitude of crystal field stabilisation energy (CFSE): MAGNITUDE OF CFSE:


Magnitude of CFSE depends upon the following factors.
(1) Nature of central metal cation: the the value of CFSE depends other following factors of central metal cation as given as
(a) For the Complex having same geometry and same ligands but having different numbers of d-electrons then CFSE decrease on increasing number of d-electrons in the central metal cation.
(b) When numbers of d-electrons are same then CFSE increasing on increasing Oxidation number.
(c) For same Ligand, Oxidation state, same d-electrons, CFSE increasing on increasing principle quantum Number of d- orbitals like 3d < 4d < 5d etc.
Thus the elements of the second and third transition series have greater tendency to form low spin complexes than the first transition series. It is possible to arrange the metals according to a spectrochemical series as well. The approximate order is
(2) Nature of ligands: the magnitude of CFSE varies from stronger ligand to weaker ligands it meant CFSE increasing on increasing of splitting power of ligands and decreasing on decreasing of splitting power of ligands.

Splitting power of ligands decide according to spectrochemical series.

(3) Geometry of the Complex: the value of CFSE will change with geometry of Complexes. It is estimated that CFSE of tetrahedral Complexes is approximately 50% as large as that of octahedral Complexes.

Illustrative example (1)
Which of the Complex of the following pairs has the largest value of CFSE?
(1) [Co(CN)6]3-  and [Co(NH3)6]3+
(2) [Co(NH3)6]3+ and [CoF6]3-
(3) [Co(H2O)6]3+  and [Rh(H2O)6]3+
(4) [Co(H2O)6]2+ and [Co(H2O)6]3+


(1)  CN is the stronger ligand than NH3 therefore CFSE of [Co(CN)6]3-  will be more than  [Co(NH3)6]3+
(2) NH3 is stronger ligand than F therefore CFSE of [Co(NH3)6]3+ will be more than [CoF6]3- .
(3) Co belong to 3d series whereas The Rh belong to 4d series. More the value of n more is CFSE therefore CFSE of  [Rh(H2O)6]3+  is more than [Co(H2O)6]3+ .
(4) Oxidation number of Co in [Co(H2O)6]3+ is more than the Oxidation number of [Co(H2O)6]2+  therefore, CFSE of [Co(H2O)6]3+ is more than  [Co(H2O)6]2+ .

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