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Standard XII
Chemistry
Crystal Field Theory
Question

When degenerate d-orbitals of an isolated atom/ion come under influence of magnetic field of ligands, the degeneracy is lost. The two set $$t_{2g}(d_{xy}, d_{yz}, d_{xz})$$ and $$e_{g}(d_{g^{2}}, d_{x^{2} - y^{2}})$$ are either stabilized or destabilized depending upon the nature of magnetic field. It can be expressed diagrammatically as:
Value of $$CFSE$$ depends upon nature of ligand and a spectrochemical series has been made experimentally, for tetrahedral complexes, $$\triangle$$ is about $$4/9$$ times to $$\triangle_{0} (CFSE$$ for octahedral complex). This energy lies in visible region and i.e., why electronic transition are responsible for colour. Such transitions are not possible with $$d^{0}$$ and $$d^{10}$$ configuration.
$$Ti^{3+}(aq.)$$ is purple while $$Ti^{4+}(aq.)$$ is colourless because

A
There is no crystal field effect in $$Ti^{4+}$$
B
$$Ti^{4+}$$ is very small in comparison to $$Ti^{3+}$$ and hence does not absorb any radiation
C
The energy difference between $$t_{2g}$$ and $$e_{g} Ti^{4+}$$ is quite high and does not fall in the visible region
D
$$Ti^{4+}$$ has $$d^{0}$$ configuration
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Solution
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Correct option is C. $$Ti^{4+}$$ has $$d^{0}$$ configuration

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Similar Questions
Q1
When degenerate d-orbitals of an isolated atom/ion come under influence of magnetic field of ligands, the degeneracy is lost. The two set $$t_{2g}(d_{xy}, d_{yz}, d_{xz})$$ and $$e_{g}(d_{g^{2}}, d_{x^{2} - y^{2}})$$ are either stabilized or destabilized depending upon the nature of magnetic field. It can be expressed diagrammatically as:
Value of $$CFSE$$ depends upon nature of ligand and a spectrochemical series has been made experimentally, for tetrahedral complexes, $$\triangle$$ is about $$4/9$$ times to $$\triangle_{0} (CFSE$$ for octahedral complex). This energy lies in visible region and i.e., why electronic transition are responsible for colour. Such transitions are not possible with $$d^{0}$$ and $$d^{10}$$ configuration.
$$Ti^{3+}(aq.)$$ is purple while $$Ti^{4+}(aq.)$$ is colourless because

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Q2

When degenerate d-orbitals of an isolated atom/ion come under influence of the magnetic field of ligands, the degeneracy is lost. The two set t2g(dxy,dyz,dxz) and (d2z,dx2−y2) are either stabilized or destabilized depending upon the nature of magnetic field. It can be expressed diagrammatically as :
The value of CFSE depends upon the nature of the ligand and a spectrochemical series has been made experimentally, for tetrahedral complexes. Δ is about 4/9 times to Δ0 (CFSE for octahedral complex). This energy lies in the visible region and i.e., why the electronic transition is responsible for colour. Such transitions are not possible with d0 and d10 configuration.

Crystal field stabilization energy for [CoF6]3− in terms of parameter Dq is - (Δ=10Dq)
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Q3
Reason
In octahedral complexes, the three $$d-$$ orbitals $$(d_{xy}, d_{yz}, d_{zx})$$ experience less repulsion from the ligands while two $$d-$$ orbitals $$(d_{x^2-y^2}, d_{z^2})$$ experience more repulsion from the ligands due to their shapes.
Assertion
In octahedral complexes, the three orbitals $$(d_{xy}, d_{yz}, d_{zx})$$ are stable and of low energy while the two orbitals $$(d_{x^2-y^2}, d_{z^2})$$ are unstable and have high energy.
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Q4
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 metal ion d-orbitals
In this 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 two d-orbitals is called crystal field splitting $$ \Delta $$.

In general, the crystal field splitting energy $$ \Delta $$ corresponds to wavelengths of light in the visible region of the spectrums and colores of the complexes can be attributed to electronic transition between the lower and higher energy sets of d-orbitals.

In general, the colour that we see is complementary to the colour absorbed.
Different metal ions have different values of $$ \Delta $$ which explains why their complexes with the same ligand have a different colour.

Similarly, the crystal field splitting also depends on the nature of ligands and as ligands for the same metal varies from $$ H_{2}O $$ to $$ NH_{3} $$ to ethylenediamine, $$ \Delta $$ for complexes increases. Accordingly, the electronic transition shifts to higher energy (shorter wavelength) as the ligand varies from $$ H_{2}O,\ $$ $$ NH_{3} $$ 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.

Which of the following statement is incorrect?
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