(a) What type of isomerism is shown by the complex ${\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_5\left(\mathrm{SCN}\right)\right]}^{2+}$ ?
(b) Why is ${\left[{\mathrm{NiCl}}_4\right]}^{2-}$ paramagnetic while ${\left[\mathrm{Ni}(\mathrm{CN}{)}_4\right]}^{2-}$ is diamagnetic ? (Atomic number of Ni = 28)
(c) Why are low spin tetrahedral complexes rarely observed

a) The given complex shows linkage isomerism
(b) CN is a strong field ligand while Cl is a weak field ligand. Strong filed ligand forces the Electrons to get paired. Therefore ${\left[{\mathrm{NiCl}}_4\right]}^{2-}$ is paramagnetic and ${\left[\mathrm{Ni}(\mathrm{CN}{)}_4\right]}^{2-}$ is diamagnetic.
(c) The energy gap between e_g and t₂g energy level of tetrahedral complex is low due to which, low spin complexes are rarely observed.