[hongyeus]

I've seen posts about specific things being insoluble or not, but my question is what property determines if something can form a complex ion? For example, Zinc²⁺ ion can form Zn(OH)₄^2- in excess hydroxide but on the other hand, iron and copper ions cannot? Is there any way for someone to determine whether something can form a complex ion or not? What specific properties of the metal do we look at to explain why some can complex while others can't? For example why does copper ion complex with ammonia to form Cu(NH3)₄²⁺ while iron ion doesn't?

[Ari Ben Canaan]

Maybe electrode potentials ?