The crystal structure of the decomposition product NH4HC2O4 from powder diffraction data

The crystal structure of anhydrous ammonium acid oxalate, NH4HC2O4, obtained from the thermal decomposition of the related hemihydrate has been determined from powder diffraction data collected with monochromatic laboratory X-rays, using the capillary technique. The crystal structure is monoclinic, P2(1)/c, Z = 4, a = 4.3629(1) Angstrom, b = 13.5657(1) Angstrom, c = 7.7100(1) Angstrom, = 102.602(1)degrees and V = 445.3(1) Angstrom(3). The structure has been solved with the direct methods and refined with the Rietveld method, from which the agreement factors R-wp = 8.19% and R-B = 5.18% have been obtained. The crystal structure consists of corrugated layers built from seven-fold ammonium coordination polyhedra and connected by oxalate groups. The hydrogen atom positions have been located and the hydrogen bond network is extensively discussed.