The complex having highest $∆$ value

${∆}_{\mathrm{sp}} > {∆}_{\circ } > {∆}_{\mathrm{f}} ; {∆}_{\mathrm{sp}} \approx 1.3 {∆}_{\circ }$

Therefores CFSE value of $[\mathrm{Ni}{\left(\mathrm{CN}\right)}_4{]}^{2-}$ is greater than $[\mathrm{Ni}{\left(\mathrm{en}\right)}_3{]}^{++}$ or $[\mathrm{Ni}{\left({\mathrm{NH}}_3\right)}_6{]}^{++}$ or ${\left[{\mathrm{NiCl}}_4\right]}^{2-}$ Also ${\mathrm{CN}}^{-}$ is very strong liquid.