Question

The correct order for the wavelength of absorption in the visible region is
A. (a) `[Ni(NO_2)_6]^(4-)lt[NI(NH_3)_6]^(2+)lt[Ni(H_2O)_6]^(2+)`
B. (b) `[Ni(NO_2)_6]^(4-)lt[Ni(H_2O)_6]^(2+)lt[Ni(NH_3)_6]^(2+)`
C. (c) `[Ni(H_2O)_6]^(2+)lt[Ni(NH_3)_6]^(2+)lt[Ni(NO_2)_6]^(4-)`
D. (d) `[Ni(NH_3)_6]^(2+)lt[Ni(H_2O)_6]^(2+)lt[Ni(NO_2)_6]^(4-)`

Answer 1

Correct Answer - A
The absorption of energy or the observation of colour in a complex transition compound depends on the charge of the mtal ion and the nature of the ligands attached. The same metal ion with different ligands shows different absorption depending upon the type of ligand. The presence of weak field ligands make the central metal ion to absorb low energies, i.e., of higher wavelengths. The field strength of ligands can be obtained from spectrochemical series. i.e.
(weak field) `I^(-)Br^(-)ltS^(2-)ltCl^(-)ltNO_3^(-)ltF^(-)ltOH^(-)ltH_2OltNH_3ltNO_2^(-)ltCN^(-)ltCO`