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 dorbitals is called the crystal field splitting D.
In general, the crystal field splitting energy D corresponds to wavelength 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 the we see is complementry to the colour absorbed.
Different metal ion have different values of D, 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 H2O to NH3 to ethylenediamine, D for complexes increases. Accordingly, the electronic transition shifts to higher energy (shorter wavelength) as the ligand varies from H2O to NH3 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 and the spin pairing energy P. Small values favour high spin complexes, and large Dvalues favour low spin complexes.
Which of the following complexes are diamagnetic ? [Pt(NH3)4]2+ [Co(SCN)4]2- [Cu(en)2]2+ [HgI4]2-square planar tetrahedral square planar tetrahedral (i) (ii) (iii) (iv)
Correct answer is option 'C'. Can you explain this answer?