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Coordination Compounds
Question
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A solution of [Ni (H2O)6]2+ is green but a solution of [Ni(CN)4]2– is colourless. Explain. 

Answer

Ni(CN)42– has no unpaired electron in its d sub shell and thus d - d transition is not possible whereas Ni(H2O)62+ has compaired electron in its d-subshell which give rise to d - d transition to impart colour.

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Some More Questions From Coordination Compounds Chapter

Explain on the basis of valence bond theory that [Ni(CN)4]2–  ion with square planar is diamagnetic and the [NiCl4]2– ion with tetrahedral geometry is paramagnetic.

Predict the number of unpaired electrons in the square planar [Pt(CN)4,]2– ion.

The hexaquo manganese(II) ion contains five unpaired electrons, while the hexacynoion contains only one unpaired electron. Explain using crystal field theory.

Calculate the overall complex dissociation equilibrium constant for the Cu(NH3)42+ion, given β4 for this complex is 2.1 x 1013.

Identify the ligands from the following coordination compounds:
(a)    [Co(en)2Cl(NO2)2]
(b)    K[Co(CN)(CO2)(NO)]
(c)    K3[Al(OH)6]
(d)    [Co(H2O)2(NH3)4](OH)3

Write IUPAC name of the following complexes:
(a)    [Fe(H2O)6]SO4
(b)    [Cu(en)2(NO3)2

Give IUPAC name of the following complexes:
(i) Na2[Fe(CN)5(NO)],       (ii) K2[Zn(CN)4]