Bis(2,4,6-tri­amino-1,3,5-triazin-1-ium) 2-[bis­(carboxyl­atometh­yl)aza­nium­yl]acetate trihydrate

The title compound, 2C(3)H(7)N(6) (+)·C(6)H(7)NO(6) (2−)·3H(2)O, was obtained by mixing melamine and nitrilo­tri­acetic acid in aqueous solution. There is proton transfer from the nitrilo­triacteic acid to melamine to produce two melaminium cations and an inter­nal proton transfer to generate the [HN(CH(2)COO)](2−) zwitterion. The melaminium cations are arranged in hydrogen-bonded tapes formed by N—H⋯N inter­actions. These tapes extend parallel to the [010] direction and are stacked parallel to the a axis at a mean separation of 3.3559 (11) Å. Between these tapes lie the anions and lattice water mol­ecules. Further O—H⋯O and N—H⋯O hydrogen bonds exist between the water mol­ecules, the anions, and the melaminium cations, generating a three-dimensional array. The crystal examined was found to be twinned by a twofold rotation about the direct lattice direction [100]. The two twin components were present in the ratio 0.5918:0.4082 (14).