Which one of the following complexes is not expected to exhibit isomerism? [JEE Main 2020, 2 Sep (Shift 2)]

\( \left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{4}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]^{2+} \)

\( \left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\right] \)

\( \left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\right] \)

\( \left[\mathrm{Ni}(e n)_{3}\right]^{2+} \)