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Q.
Identify the complexes which are expected to be coloured. Explain
IIT JEEIIT JEE 1994Coordination Compounds
Solution:
Option (C), (D) are correct. $\left[ Cr \left( NH _{3}\right)_{6}\right] Cl _{3}$ and $K _{3}\left[ VF _{6}\right]$ are coloured.
For the colouration of complexes, the complex must have unpaired electrons present in outer available d-orbitals.
(A) : $\left[ Ti \left( NO _{3}\right)_{4}\right]$, titanium is in $Ti ^{4+}:[ Ar ] 3 d ^{0} 4 s ^{0}$ and has no unpaired electrons.
(B) : $\left[ Cu \left( NCCH _{3}\right)_{4}\right]^{+} BF _{4}^{-}$; copper is in $Cu ^{+}:[ Ar ] 3 d ^{10} 4 s ^{0}$ and has no unpaired electrons.
(C) : $\left[ Cr \left( NH _{3}\right)_{6}\right] Cl _{3} ;$ chromium is in $Cr ^{3+}:[ Ar ] 3 d ^{3} 4 s ^{0}$ has three unpaired electrons and thus it is coloured complex.
(D) : $K _{3}\left[ V F _{6}\right]$; vanadium is in $V ^{3+}:[ Ar ] 3 d ^{2} 4 s ^{0}$ has two unpaired electrons and thus it is coloured complex.