Oxalic Acid Dihydrate - an Accurate Low-Temperature Structural Study using High-Resolution Neutron Powder Diffraction

Deuterated oxalic acid dihydrate, C2D2O4.2H2O, M=132.10, monoclinic, P21/n, Z=2,. At 100K, a=6.13338(6), b=3.50018(1), c=11.98334(3) Å, β=106.0599(2)0, V=247.218Å3, Dx=1.706 g cm-3, χ2. High-resolution neutron powder diffraction data have been recorded at temperatures of 15 and 100K on fully deuterated oxalic acid dihydrate, which has been widely used as a crystallographic standard, in order to assess the in particular the potential use of neutron powder diffraction data for charge-density studies. The accuracy and precision of the structural parameters obtained in the present powder study are found to be comparable to neutron and X-ray single-crystal results. The technique is therefore shown to have a useful role in providing reliable high-quality structural data in cases where single crystals are difficult to obtain