Two complexes $\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right] \mathrm{Cl}_{3}$ (A) and $\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{6}\right] \mathrm{Cl}_{3}$ (B) are violet and yellow coloured respectively. The incorrect statement regarding them is

(A) $\Delta_{0}$ values of (A) and (B) are calculated from the energies of violet and yellow light, respectively.

(C) both absorbs energies corresponding to their complementary colours

(D) $\Delta_{0}$ value for (A) is less than that of (B)

JEE Main · 2019 · 09 Jan 2019 · Shift 1 · Coordination Compounds

Two complexes

[Cr (H_{2} O)_{6}] Cl_{3}

(A) and

[Cr (NH_{3})_{6}] Cl_{3}

(B) are violet and yellow coloured respectively. The incorrect statement regarding them is

(A) $Δ_{0}$ values of (A) and (B) are calculated from the energies of violet and yellow light, respectively.✓ Correct
(B)both are paramagnetic with three unpaired electrons
(C)both absorbs energies corresponding to their complementary colours
(D) $Δ_{0}$ value for (A) is less than that of (B)

Answer: (A)

Solution

Both complexes hold

Cr X^{3 +}

(

d^{3}

), so both are paramagnetic with three unpaired electrons, and each absorbs the complement of the colour it shows: the violet complex absorbs yellow light and the yellow complex absorbs violet light. Because

NH X_{3}

is a stronger-field ligand than

H X_{2} O

, the splitting

Δ_{0}

is larger for the ammine complex. The flawed statement is the one claiming that

Δ_{0}

of the violet and yellow complexes is read from the energies of violet and yellow light respectively, since

Δ_{0}

is set by the absorbed light, which is the reverse pairing.

JEE Main · 2019 · 09 Jan 2019 · Shift 1 · Single correct option

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JEE Main · 2019 · 09 Jan 2019 · Shift 1 · Coordination Compounds

Solution

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