Question

Which one of following complex has the highest magnitude of crystal field splitting energy $\left(\Delta_{o}\right)$ ?

• A. $\left[ Co \left( H _{2} O \right)_{6}\right]^{3+}$
• B. $\left[ Co \left( NH _{3}\right)_{6}\right]^{3+}$
• C. $\left[ Co \left( C _{2} O _{4}\right)_{3}\right]^{3-}$
• D. $\left[ CoF _{6}\right]^{3-}$

Answer 1

Answer: (B)

The crystal field splitting, i.e. $\Delta_{o}$, depends upon the field produced by the ligand and charge on the metal ion.

So, ligands can be arranged in a series in the order of increasing field strength. This series is known as spectrochemical series.

e.g., $I ^{\ominus}< Br ^{\ominus}< SCN ^{\ominus}< Cl ^{\ominus}< F ^{\ominus}< OH ^{\ominus}< C _{2} O _{4}^{2-}$

$< H _{2} O < NCS ^{\ominus}< EDTA ^{4-}< NH _{3}< en < CN ^{\ominus}< CO \because$

Among the given options, ligand $\left( NH _{3}\right)$ has highest magnetic field therefore, it has maximum value for $\Delta_{o}$.