Question

Identify the complexes which are expected to be coloured. Explain

• A. $[Ti(N{O}_3{)}_4]$
• B. $[Cu(NCC{H}_3){]}^{+}B{F}_4$
• C. $[Cr(N{H}_3{)}_6]C{l}_3$
• D. $K_3[V{F}_6]$

Answer 1

Answer: (D)

Option (C), (D) are correct. $\left[Cr{\left(N{H}_3\right)}_6\right]C{l}_3$ and $K_3\left[V{F}_6\right]$ are coloured.
For the colouration of complexes, the complex must have unpaired electrons present in outer available d-orbitals.
(A) : $\left[Ti{\left(N{O}_3\right)}_4\right]$, titanium is in $T{i}^{4+}:[Ar]3d^{0}4s^0$ and has no unpaired electrons.
(B) : ${\left[Cu{\left(NCC{H}_3\right)}_4\right]}^{+}B{F}_4^{-}$; copper is in $C{u}^{+}:[Ar]3d^{10}4s^0$ and has no unpaired electrons.
(C) : $\left[Cr{\left(N{H}_3\right)}_6\right]C{l}_3;$ chromium is in $C{r}^{3+}:[Ar]3d^{3}4s^0$ has three unpaired electrons and thus it is coloured complex.
(D) : $K_3\left[V{F}_6\right]$; vanadium is in $V^{3+}:[Ar]3d^{2}4s^0$ has two unpaired electrons and thus it is coloured complex.