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Acta Cryst. (2013). E69, o1674-o1675
[ doi:10.1107/S1600536813028250 ]

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

K. Hoxha and T. J. Prior

Abstract: The title compound, 2C3H7N6+·C6H7NO62-·3H2O, 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(CH2COO)]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).

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