Question

Which of the following coordination entities should be expected to absorb light of lowest frequency?

• A. $\left[ Cr ( en )_{3}\right]^{3+}$
• B. $\left[ CrCl _{6}\right]^{3-}$
• C. $\left[ Cr \left( NH _{3}\right)_{6}\right]^{3+}$
• D. $\left[ Cr ( CN )_{6}\right]^{3-}$

Answer 1

The Correct Option is B

The coordination entity, for which crystal field splitting is smaller, absorbs light of lowest frequency. Weaker the ligand field strength, smaller will be the crystal field splitting. The order of field strength of various ligands is as $CN > en > NH _{3}> Cl$ Hence, $\left[ CrCl _{6}\right]^{3-}$ due to the presence of $Cl ^{-}$ ligand absorbs light of lowest frequency.