# How can I get create complex metal ion solution such that the majority of the central metal ions only have one specific ligand?

I'm looking for a way to have the ligand, Chloride ion, datively bond with Copper Sulphate.

I understand it is as simple as creating a solution of Hydrochloric Acid and dissolving Copper Sulphate inside it will produce tetrachlorocuprate(ii) ions, however there are still the presence of hexaaquacopper(ii) ions in the solution.

Is there any method to create a solution purely consisting of tetrachlorocuprate(ii) or at least make the amount of hexaaquacopper(ii) negligible?

1. Play by rules, add copper to a solution of $$\ce{HCl}$$ and $$\ce{H_2O_2}$$. The basic goal is to "eliminate" copper: $$\ce{Cu + H2O2 + 2HCl → CuCl2 + 2H2}$$ and then obtain your ion: $$\ce{CuCl2 + 2Cl^- <=> [CuCl_4]^2-}$$.
2. Risk. (It might not work). Use $$\ce{[Cu(H_2O)6]Cl2 + 2NaOH = [Cu(OH)_2(H_2O)_4]↓ + 2NaCl + 2H_2O}$$ (blue precipitate forms). I haven't seen evidence that $$\ce{NaOH}$$ reacts with $$\ce{[CuCl_4]^2-}$$, but this idea might be risky. It's always better to play by rules :)