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.