Ni2 ions can be either four coordinate or six coordinate a w

Ni²⁺ ions can be either four coordinate or six coordinate. (a) which one is more likely to be a red compound (b) which is likely to be a blue compound?

Solution

As CFSE of octahedral complexes is always greater than tetrahedral complexes. And CFSE is inversely proportional to the wavelength of absorption.

As Nickel hexacoordinated complex has more CFSE and hence less wavelength of absorption than Nickel tetra-coordinated complex.

We see only complimentary colour.

Thus, according to VIBGYOR, the wavelength of red is highest.

(a) hexacoordinated complexes of nickel are red (because absorb less wavelength and emit the colour of the higher wavelength)

(b) the tetra-coordinated complex of nickel would be blue in colour ( because of less CFSE absorb the higher wavelength and emit the colour of lesser wavelength.)