Crystal polymorphism of sodium benzene-1,3-dicarboxy-5-sulfonate monohydrate

Two different crystal forms of sodium 5-sulfoisophthalate monohydrate have been found and structurally characterized by X-ray diffraction and FT-IR spectroscopic methods. Polymorph I is monoclinic, P21/n, and polymorph II is triclinic, P1. The analysis of the crystal structures reveals that the connectivity patterns in both polymorphs are different. Two of the sulfonate oxygen atoms (sites) interchange their function and are used to accept two hydrogen bonds in the first polymorph or to donate two bonds toward the metal ion in the second polymorph. Consequently the hydrogen-bonded anionic subnetwork reduces from two-dimensional in I to one-dimensional in II. The FT-IR spectra correlate well with the structural peculiarities of the crystals and reflect the variation of hydrogen-bonded networks in them.