Structure of the Mercury(II) Chromate(III) HgCr2O4 and Lattice Constants of the Isotypic Mercury(I) Compounds Hg2MoO4 and Hg2WO4

The previously reported cubic compound HgCr2O4 was prepared by thermal decomposition of Hg2CrO4 at 400 °C in evacuated, sealed silica tubes. Its structure was determined by a Rietveld analysis of powder diffractometer data. It is of spinel type (a = 865.8(1) pm), and it was refined to a profile residual of Rp = 0.092. The Guinier powder patterns of the isotypic yellow compounds Hg2MoO4 and Hg2WO4 were indexed with the parameters of a monoclinic C-centered lattice (Hg2MoO4: a = 873.7(1) pm, b = 1155.1(1) pm, c = 493.17(4) pm, and β = 115.24(1)°; Hg2WO4: a = 73.4(2) pm, b = 1148.3(2) pm, c = 493.16(7) pm, and β = 114.87(1)°).