Can anyone explain to me how exactly EDTA forms 1:1 complexes with any metal ion despite their charge?? I know that it forms a ring with the metal cation, but I can't seem to figure out how something with a Charge of 4- only reacts once with a metal cation no matter its charge. Can someone please enlighten me???

i believe that the reason for this is that hydrogen bonds to all the negative areas that the cation does not bond to

EDTA is a fairly large molecule, and it is also fairly flexible. It wraps around the metal ion so that its six binding sites are all in contact, and in a tetrahedral geometry.

 

As a general answer to the charge question, the electronic structure of transition metals allows them to form fairly stable ions.