The title compound, C18H3ON4O12, exists as an unsymmetrical tri-zwitte
rion. The protonated N atoms form intramolecular hydrogen bonds to car
boxylate O atoms. The molecules are linked by strong intermolecular hy
drogen bonds formed by three COOH groups at one end of the molecule an
d three carboxylates at the negative ends of the two nearest neighbors
[O ... H 1.45(3) <Angstrom]. The C-N bond lengths are clearly differe
ntiated with respect to the charge on the N atom [C-N 1.459(6) and C-N
H+ 1.502(9) Angstrom].