4-fluoro-2-(phosphonomethyl)-benzenesulfonic acid monohydrate

The title compound, C7H8FO6PS . H2O, contains both phosphonic and sulfonic acid functionalities. An extensive network of O-H ... O hydrogen bonds is p resent in the crystal structure. The three acidic protons are associated wi th the phosphonate group. Two protons experience typical hydrogen-bond cont acts with the sulfonate-O atoms, while the third has a longer covalent bond of 1.05 (3) Angstrom to the phosphonate-O atom and a short hydrogen-bond c ontact of 1.38 (3) Angstrom to the water O atom (all O-H ... O angles are i n the range 162-175 degrees). The sulfonate group is positioned so that one S-O bond is nearly coplanar with the phenyl ring [torsion angle O-S-C-C -8 .6(2)degrees]. The phosphonate group is oriented approximately perpendicula r to the ring [torsion angle P-C-C-C 99.2 (2)degrees] with one P-O bond ant i to the benzyl C-C bond. The molecules pack in layers in the b-c plant wit h the water molecules in between adjacent pairs of inverted layers.