Question

Among the following, the compound that is both are diamagnetic and colored is- 1) K2Cr2O7 (2) (NH4)2 [TiCl6] (3) VOSO4 (4)K3[Cu(CN)4] ((please solve with details ))

Answer 1

Answer on Question # 73503 - Chemistry - Inorganic Chemistry

Among the following, the compound that is both are diamagnetic and colored is- 1) K2Cr2O7 (2) (NH4)2 [TiCl6] (3) VOSO4 (4)K3[Cu(CN)4] ((please solve with details))

Solution

Diamagnetic compounds have only paired d-electrons of the central atom (transition metal). The electron configurations of the central atoms are:

$\mathrm{Cr}^{+6}$ [Ar] $3\mathrm{d}^0$ $4\mathrm{s}^0$

$\mathrm{Ti}^{+4}$ [Ar] $3\mathrm{d}^0$ $4\mathrm{s}^0$

$\mathrm{V}^{+4}$ [Ar] $3\mathrm{d}^1$ $4\mathrm{s}^0$

$\mathrm{Cu}^{+1}$ [Ar] $3\mathrm{d}^9$ $4\mathrm{s}^0$

Since $\mathrm{V}^{+4}$ and $\mathrm{Cu}^{+1}$ ions have odd number of electrons, these compounds are paramagnetic, whereas $\mathrm{Cr}^{+6}$ and $\mathrm{Ti}^{+4}$ are diamagnetic.

The partially full d-orbitals in transition metals have energy splittings that happen to lie in the visible range and are colored. However, the compounds of $\mathrm{Cr}^{+6}$ and $\mathrm{Ti}^{+4}$ is not the case, d-orbitals of these ions are empty. Therefore, if we consider d-d transitions only, the both should be colorless. Although it is known that $\mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7$ forms a colored solution, in this compound oxygen has extra lone pairs to donate to chromium so there is actually charge transferred spectra and not d-d transition.

Answer: $\mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7$