${\left[Ni{\left(CN\right)}_4\right]}^{2-}$ is a low spin complex. Oxidation state of $Ni$ in ${\left[Ni{\left(CN\right)}_4\right]}^{2-}$ is $+2$ .

$Ni=\left[Ar\right]3d^8 4s^2$

$N{i}^{2+}=\left[Ar\right]3d^8$



$C{N}^{-}$ being strong field ligand causes pairing of $3d$ -electrons. Thus, one of the $3d$ orbital becomes empty for $C{N}^{-}$ ion.

Here, the complex formed involves the inner $\left(n-1\right)d$ orbitals for hybridisation. So, the complex is called inner orbital complex.