Question

Identify the complexes which are expected to be coloured. Explain.

(i) [Ti(NO₃)₄]

(ii) [Cu(NCCH₃)]⁺BF₄

(iii) [Cr(NH₃)₆]³⁺3Cl^-

(iv) K₃[VF₆]

Answer 1

(i) In [T(NO₃)₄], O.N. of Ti is + 4. 

Hence, in Ti (IV) (1s², 2s² 2p⁶, 3s²3p⁶) 

incomplete d-orbital is not present. so it is colourless. 

(ii) In [cu (NCCH₃)]⁺BF^-, O.N. of cu is + 1. 

Hence, in Cu (I) (1s², 2s²2p⁶, 3s²3p⁶3d¹⁰] 

incomplete d-orbital is not present, so it is also colourless. 

(iii) In [Cr(NH₃)₆]³⁺3Cl^- , O.N of Cr is + 3. 

Hence, in Cr (III) (1s²,2s²2p⁶, 3s²3p⁶3d³) 

incomplete d-orbitals are present, so it is coloured. 

(iv) In K₃[VF₆], O.N. of V is + 3. 

Hence, V(III) (1s², 2s²2p⁶, 3s²3p⁶ 3d²) 

incomplete d-orbital is present, so it is coloured.