Structural Studies of New Sulfito Mercurates(II) with General Formula xM[XHgSO₃]middot;yHgX₂.zMX.nH₂O (M = NH₄, K; X = Cl, Br)

Abstract

Several solid phases with the general formula xM[XHgSO₃].yHgX₂.zMX.nH₂O were obtained from aqueous solutions during phase formation studies in the systems M₂SO₃/HgX₂ (M = NH₄, K; X = Cl, Br). All phases were structurally characterized on the basis of single crystal X-ray diffraction data and adopt new structure types. Compounds with x, y, z = 1 and n = 0 are isostructural (structure type I) and crystallise with two formula units in space group P21/m and lattice parameters of a 9.7, b 6.2, c 10.4Å, 111°. Compounds with x, y = 1 and z, n = 0 (structure type II) crystallize in space group Cmc2₁ with four formula units and lattice parameters of a 5.9, b 22.0, c 6.9Å. The structures with x = 2, y, z = 1 and n = 0 are likewise isostructural (stucture type III) and consist of four formula units in space group Pnma with lattice parameters of a 22.2, b 6.1, c 12.4Å. K[HgSO₃Cl].KCl.H₂O is the only representative where x = 1, y = 0, z = 1 and n = 1 (structure type IV). It is triclinic (space group) with four formula units and lattice parameters of a = 6.1571(8), b = 7.1342(9), c = 10.6491(14) Å, α = 76.889(2), β = 88.364(2), γ = 69.758(2)°. Characteristic for all structures types is the segregation of the M⁺ cations and the anions and/or HgX₂ molecules into layers. The [XHgSO₃]⁻ anions are present in all structures and have m symmetry, except for K[HgSO₃Cl].KCl.H₂O with 1 symmetry (but very close to m symmetry). The different [XHgSO₃] units exhibit very similar Hg-S distances (average 2.372Å) and are more or less bent with (X-Hg-S) angles ranging from 159.7 to 173.7°. The molecular HgX₂ entities present in structure types I-III deviate only slightly from linearity with (X-Hg-X) angles ranging from 174 to 179°. The structures are stabilised by interaction of the K⁺ or NH₄⁺ cations that are located between the anionic layers or in the vacancies of the framework, by K-O contacts or, in case of ammonium compounds, by medium to weak hydrogen bonding interactions of the type N-H...O.