A CRYSTAL-STRUCTURE DETERMINATION OF HGC2O4 FROM SYNCHROTRON X-RAY AND NEUTRON POWDER DIFFRACTION DATA

The crystal structure of mercury oxalate, HgC2O4 was solved from synch rotron X-ray and neutron powder diffraction patterns. The unit cell wa s obtained by auto-indexing of the X-ray powder pattern, and the posit ions of the atoms were found using the direct method program SIRPOW92. The structure was refined by Rietveld analysis of the neutron powder diffraction data. The unit cell is monoclinic, space group P2(1) with lattice parameters from the synchrotron refinement: a = 5.033(1) angst rom, b = 5.237(1) angstrom, c = 6.453(1) angstrom, beta = 108.74(1)-de grees, and Z = 2. The mercury atoms are bounded to the oxalate ions by two short mercury-oxygen bonds Hg-O3 = 2.10 angstrom and Hg-O2' = 2.1 2 angstrom, and six longer bonds in the range 2.63 angstrom to 2.83 an gstrom. The mercury-oxygen coordination polyhedron is a slightly defor med box.