Disodium D-3-Phosphoglycerate (a Reinvestigation at 80 K) and Bis(cyclohexylammonium) D-3-Phosphoglycerate Dihydrate at 85 K

The structure of the D-3-phosphoglycerate dianion in the disodium salt 2Na⁺.C₃H₅O₇P²⁻ [Na₂H(3-PGA), (I)], and the hydrated bis(cyclohexylammonium) salt 2C₆H₁₄N⁺.C₃H₅O₇P²⁻.2H₂O [(CHA)₂H(3-PGA)·2H₂O, (II)] [H(3-PGA) = ⁻HO₃POCH₂CH(OH)COO⁻, CHA = C₆H₁₁NH₃⁺] has been determined by X-ray analyses at 80 and 85 K, respectively. A room-temperature study of (I) was previously desribed by Fewster & Fenn [Acta Cryst. (1982), B38, 282–284]. The dianions in (I) and (II) differ in the orientations of the carboxylate and phosphate groups with respect to the carbon backbone. The P-O ester bond lengths are 1.606 (2) and 1.608 (2) Å in (I) and (II), respectively. The crystal structure of (I) is governed by Na...O interactions. The two crystallographically independent Na⁺ cations are seven- and six-coordinate, respectively, with Na...O distances in the range 2.275 (2)–2.822 (2) Å. The crystal structure of (II) is stabilized by hydrogen bonds which utilize all N and O atoms.

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