Refinement of the crystal structure of sinigrin

The crystal structure of sinigrin (potassium myronate), KC_(10)H_(16)NO_9S_2. H_2O, has been refined on the basis of three-dimensional intensity data collected on an automated diffractometer. The final agreement index is 0·056 for 1906 reflections, and the estimated standard deviations in the atomic coordinates of the C, N, and 0 atoms are about 0·004 Å. The absolute configuration of the anion was confirmed from anomalous dispersion effects. The crystals are orthorhombic with space group P212121. The unit-cell dimensions of a new crystal are ɑ = 8·265 (1), b = l1·440(3), and c = 17·757 (3)A. An appreciable increase in the length of the c axis occurred during irradiation of the crystal. In addition, the vinyl group of the myronate ion appears to undergo large thermal motions. The distances between vinyl groups of adjacent myronate ions are such that a photopolymerization reaction between them would be possible, which might explain these two observations.