Crystal structure of a second modification of the mercury oxychloride Hg₃O₂Cl₂

Abstract

The crystal structure of a monoclinic mercury oxychloride of composition Hg₃ O₂ Cl₂ has been described. A crystallographically different mercury oxychloride of the same composition was reported. The crystal structure of this second modification, called the β-form, has been established through a single-crystal x-ray diffraction study. The β-form is also monoclinic, with space groupP2₁/c andZ = 8. The unit-cell at 25 ° C hasa = 10.826(5),b = 9.310(4),c = 11.5 15(5) Å and β = 71.04(8) °. The density is calculated to be 8.53 g cm⁻³, that observed by displacement being 8.53(2) g cm⁻³. Diffraction data were obtained using the θ-2θ scanning mode on a Picker four-circle automatic diffractometer with CuKα radiation. This apparently unsuitable radiation was chosen in order to test rigorously an absorption correction procedure. The structure was refined toR ₁ = 4.0% through conventional least-squares reduction basedF. The structure of β-Hg₃ O₂ Cl₂ is found to be markedly different from that of the earlier-determined α-Hg₃O₂Cl₂; distorted Hg₄O tetrahedra are linked into a three-dimensional array, terminated at four locations within the cell by covalent Hg-Cl bonds.