Two hydrate pseudopolymorphs of thi­amine pyrophosphate: a dihydrate and a trihydrate

Two hydrate pseudopolymorphs of 3-[(4-amino-2-methylpyrimidin-1-ium-5-yl)meth­yl]-4-methyl-1,3-thia­zol-3-ium-5-yl hydrogen pyrophosphate (TPP), viz. a dihydrate, C₁₂H₁₈N₄O₇P₂S·2H₂O, (I), and a trihydrate, C₁₂H₁₈N₄O₇P₂S·3H₂O, (II), were obtained during a structural study of vitamin B1 coenzyme. In both compounds, TPP is a neutral zwitterion, with its pyrophosphate group doubly deprotonated and its pyrimidine ring protonated, and it assumes the usual `F' conformation in terms of the two torsion angles about the bonds by which the methyl­ene group links the thia­zolium and pyrimidinium rings [1.1 (3) and 79.7 (3)° for (I), and 2.0 (3) and 75.5 (3)° for (II)]. In (I), two TPP mol­ecules are linked by a pair of O-H...O hydrogen bonds into a phosphate-pairing dimer. N-H...O hydrogen bonds connect the dimers into a sheet parallel to (101). In (II), the TPP mol­ecules are self-assembled solely by N-H...O hydrogen bonds, generating a tape structure along [001]. A comparison of the four known hydrate pseudopolymorphs of TPP shows that the phosphate-pairing dimers are basic building units for the formation of two-dimensional networks.