CRYSTAL STRUCTURE DETERMINATION OF BARIUM OXALATE,BaC₂O₄*3.5H₂O/D₂O. A. Norlund Christensen, Department of Inorganic Chemistry, Aarhus University, DK-8000 Aarhus C, Denmark, Reinhard B. Neder, Institute of Crystallography and Mineralogy, University of München, D-80333 München, Germany

The crystal structure of barium oxalate hydrate, BaC₂O₄ 3.5H₂O, was solved using synchrotron X-ray powder diffraction data, neutron powder diffraction data of BaC₂O₄ 3 5D₂O, and synchrotron X-ray single crystal diffraction data, measured on a microcrystal. The compound is monoclinic, a = 13.489(1), b = 7.663(1), c = 15.085(1) Å, [[beta]] = 1l3.569(5)deg., from the neutron data, space group C2/c, No. 15, Z = 4. The precision of the structure arrived at with the synchrotron X-ray single crystal data is higher than that obtained with the neutron powder diffraction data. The barium atoms are bonded to the oxalate ions and to the water molecules with ten barium oxygen bonds in the range 2.704(3) to 2.974(3) Å. The structure has hydrogen bonds in the range 2.732(4) to 2.855(5) Å, and the oxalate ion is planar.