K+[Pb(OH)3]− is the SALT of potassium ion, K+, and the complex ion, [Pb(OH)3]−. I do not know whether this ion has been actually isolated and characterized; [Pb(OH)4]2− is better known. In either case, we could potentially exchange the potassium cation for other cations such as Na+ or Li+, but probably not for NH+4, why not?