complex ions

When NH3(aq) is added to Cu2+(aq), then a pale blue gelatinous precipitate [Cu(OH)2(s) copper(II) hydroxide] will form.
2OH-(aq) + Cu2+(aq) → Cu(OH)2(s)
When excess NH3(aq) is added to Cu(OH)2(s), then the pale blue solution redissovles to give a deep blue solution. It is tetraamminecopper(II) ion.
Cu(OH)2(s) + 4NH3(aq) → [Cu(NH3)4]2+(aq) + 2OH-(aq)

That's the case. Some of the metal hydroxide can redissolve in excess NaOH(aq) or NH3(aq).
For instance, the following metal hydroxide can redissolve in both excess NH3(aq) and NaOH(aq)
Zn(OH)2(s)
→ [Zn(OH)4]2-(aq) [colourless zincate ion, in the case of NaOH(aq)]
→ [Zn(NH3)4]2+(aq) [colourless tetraamminezinc(II) ion, in the case of NH3(aq)]
The following metal hydroxides can redissolve in excess NH3(aq)
Cu(OH)2(s)
Ag2O(s) + 4NH3(aq) + H2O(l) → 2[Ag(NH3)2]+(aq) + 2OH-(aq) [colourless diamminesilver(I) ion] [Ag2O is the formed when silver ion is added to OH-(aq)]

The following metal hydroxides can redissolve in excess NaOH(aq)
Al(OH)3(s) → [Al(OH)4]-(aq) [colourless aluminate ion]
Pb(OH)2(s) → [Pb(OH)4]2-(aq) [colourless plumbate ion]

Name: Copper (II) tetrahydroxide

Formula: [Cu(OH)4]2-