Explain ,Why NH4+ ion doesnot form complexes?

NH₄⁺ Ion does not act as ligand because nitrogen atom has no lone pair of
electrons which it can donate to metal atom.

Complexes are generally formed by donation of a pair of electrons from the
ligand to metal; as NH3 with a lone pair on nitrogen can form complexes but NH₄⁺ does not have it.So,it can''t.

or

Proton spin lattice relaxation by NH₄⁺ ion motions and spin diffusion in some ammonium compounds

Approved

Ammonia is a good Lewis Base, has a tendency to donate electrons. Ammonia has free lone pair, it can form stable complex by donating the electrons while ammonium ion do not have free lone pair to donate, so not form complex ions.