(a) What type of isomerism is shown by the complex `[Co(NH_(3))_(5)(SCN)]^(2+)`?
(b) Why is `[NiCl_(4)]^(2-)` paramagnetic while `[Ni(CN)_(4)]^(2-)` is diamagnetic ? (Atomic number of `Ni = 28`)
(c) Why are low spin tetrahedral complexes rarely observed?

Explanation

(a) Linkage isomerism is shown by complex `[Co(NH_(3))_(3)(SCN)]^(2+)`
(b) `[NiCl_(4)]^(2-)`
As `Cl^(-)` is weak ligand, hence, pairing of `e^(-)` does not take place. Hence, paramagnetic due to the presence of 2 unpaired `e^(-)s`.
ltBrgt as `CN^(-)` is strong ligand due to that, pairing of `e^(-)`s take place. Hence, no unpaired electrons due to that. It is diamagnetic in nature.
(c) In tetrahedral complexes, the splitting is much smaller than that is case of octahedral complexes, i.e., `Delta_(t)=(4)/(9)Delta_(o)`. This energy is so small, that it is unable to force the `e^(-)`s to pair up. Hence, low spin complexes of tetrahedral are rarely observed and they have high spin configuration.