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CSIR NET Chemical Sciences

Inorganic Chemistry

An octahedral d6complex has a single spin-allowed absorption band. The spin-only magnetic moment (B.M.) and the electronic transition for this complex

Question

An octahedral d⁶complex has a single spin-allowed absorption band. The spin-only magnetic moment (B.M.) and the electronic transition for this complex, respectively, are

$0 \text{ and } {}^1T_{1g} \leftarrow {}^1A_{1g}$

$4.9 \text{ and } {}^5T_{2g} \leftarrow {}^5E_g$

$4.9 \text{ and } {}^5E_{g} \leftarrow {}^5T_{2g}$

$0 \text{ and } {}^1T_{2g} \leftarrow {}^1A_{1g}$

Solution

Correct option is C

In a high spin octahedral complex of d⁶metal ion, the d orbitals split into t_2g (lower energy) and e_g orbitals (higher energy) as shown in figure

Transitions of unpaired electron from t_2g orbitals to e_g orbitals are restricted because there will be change in spin multiplicity that is these transitions are spin forbidden. Transition of that electron in t_2g orbital which is paired and has the opposite spin to all other electrons can occur because this transition is spin allowed. Since there is transition of only one electron, therefore, this transition is similar to transition in d¹ octahedral complexes.

The ground state term of d⁶ metal ion can be found as:

S=4(1/2)=2.

Spin multiplicity: 2S+1=2(2)+1=5

L=2 [+2+2+1+0-1-2]