Precision of crystal structure derived from a synchrotron x-ray powder pattern. The structure of barium oxalate hydrate, BaC204*2H20

The crystal structure of barium oxalate hydrate, BaC204.2H20, was reinvestigated using a synchrotron X-ray powder pattern and a single crystal X-ray data set. The compound is monoclinic, a = 7.538(l), b = 11.062(l), c = 7.105(1) angstroms, beta = 105.42(l)“, space group P21/c, with Z = 4. The precision of the structure arrived at with the synchrotron X-ray powder pattern is not as high as that obtained with the single crystal X-ray data. The barium atoms are bonded to the. oxalate ions and to the water molecules with nine barium oxygen- bonds in the range 2.71(l)-2.97(l)angstroms. The structure has hydrogen bonds in the range 2.72(2)-2.91(2)angstroms, and the oxalate ion has only a minor deviation from planarity.