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Crystal field theory views the bonding in complexes as arising from electrostatic interaction and considers the effect of the ligand charges on the energies of the metal ion d-orbitals In this theory, a ligand lone pair is modelled as a point negative charge that repels electrons in the d-orbitals of the central metal ion.The theory concentrated on the resulting splitting of the d-orbitals in two groups with different energies and used that splitting to rationalize and correlate the optical spectra,thermodynamic stability, and magnetic properties of complexes.This energy splitting between the two sets of d-orbitals is called the crystal field splitting Delta. In general, the crystal field splitting energy Delta corresponds to wavelenght of light in visible region of the spectrum, and colours of the complexes can therefore be attributed to electronic transition between the lower and higher energy sets of d-orbitals. In general, the colour that we see is complementry to the colour absorbed. Different metal ions have different value of Delta, which explains why their complexes with the same ligand have different colour. Similarly the crystal field splitting also depends on the nature of ligands and as the ligand for the same metal varies from H_2O to NH_3 to ethylenediamine, Delta for complexes increase.Accordingly, the electronic transition shifts to higher energy (shorter wavelength) as the ligand varies from H_2O from NH_3 to en, thus accounting for the variation in colour. Crystal field theory accounts for the magnetic properties of complexes in terms of the relative values of Delta and the spin pairing energy P. Small Delta values favour high spin complexes, and large Delta values favour low spin complexes. The [Ti(NCS)_6]^(3-) ion exhibits a single absorption band at 544 nm.What will be the crystal field splitting energy (in kJ mol^(-1)) of the complex ? (h=6.626xx10^(-34) J.s, C=3.0xx10^5 m//s, N_A=6.02xx10^23 ions/mole. |
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Answer» 240 `=(3.65xx10^(-19)"J/ion")xx(6.02xx10^(23)"ions/mole")=(21.973xx10^(4))/1000"KJ mol"^(-1) =219.73 "kJ mol"^(-1)` |
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