Preparation and Crystal Structures of the Isotypic Compounds

Colourless single crystals of the compounds CdXO4 · 2 HgO (X = S, Se) were obtained under hydrothermal conditions (250 ◦C, 5 d), starting from stoichiometric amounts of HgO, CdSO4 ·7H2O and CdSeO4 ·2H2O, respectively. The crystal structures were determined from X-ray diffraction data sets. The CdXO4 · 2HgO compounds crystallise isotypically with two formula units in space group P1̄ (# 2) [CdSO4 ·2HgO (CdSeO4 ·2HgO): a = 6.793(2) (6.9097(5)) Å, b = 7.205(2) (7.1786(6)) Å, c= 7.359(2) (7.4556(6)) Å, α = 73.224(6) (74.586(2))◦, β = 66.505(6) (68.229(1))◦, γ = 63.054(5) (63.886(1))◦, 1670 (1786) structure factors, 92 parameters, R[F2 > 2σ(F2)] = 0.0379 (0.0244)] and are made up from zig-zag [O-Hg-O]∞ chains with very short bonds of d̄(Hg-O) 2.025 Å, distorted [CdO6] octahedra (d̄(Cd-O)= 2.297 Å), and XO4 tetrahedra (d̄(S-O)= 1.458 Å, d̄(Se-O)= 1.633 Å) as the main building blocks. The CdXO4 ·2HgO compounds reveal no structural relationship with the corresponding HgXO4 ·2HgO phases.