Preparation and Crystal Structure Analyses of Compounds in the Systems HgO/ MX O 4 /H 2 O ( M = Co, Zn, Cd; X = S, Se)

During phase formation experiments under hydrothermal conditions (250 °C, 5d) in the systems HgO/ MX O 4 /H 2 O ( M = Co, Zn, Cd; X = S, Se), single crystals of the mercuric compounds (CdSO 4 ) 2 (HgO) 2 H 2 O (I), (CdSeO 4 ) 2 (HgO) 2 H 2 O (II), (CdSeO 4 )Hg(OH) 2 (III), (CoSO 4 ) 2 (HgO) 2 H 2 O (IV), (ZnSO 4 ) 2 (HgO) 2 H 2 O (V), (ZnSeO 4 ) 2 (HgO) 2 H 2 O (VI), and the mixed‐valent (ZnSe IV O 3 )(ZnSe VI O 4 )Hg I 2 (OH) 2 (VII) were obtained. The crystal structure determinations from X‐ray diffraction data revealed four unique structure types for these compounds. I and II crystallise isotypically in space group P 2/ n ( a ≈ 7.85, b ≈ 6.28, c ≈ 10.5Å, β ≈ 102°), compound III crystallises in space group C 2/ m ( a = 10.540(2), b = 9.0120(8), c = 6.1330(12)Å, β = 100.45(3)°), and the isotypic compounds IV, V and VI crystallise in space group Pbcm ( a ≈ 6.15, b ≈ 11.3, c ≈ 13.1Å). Common with these three structure types are distorted octahedral [ M O 6 ] and tetrahedral X O 4 building units which are organised in a layered assembly. Within the layers H bonding of OH groups or H 2 O molecules of the [ M O 6 ] octahedra leads to an additional stabilisation. Adjacent layers are separated by mercury atoms which are linearly bonded to two O atoms at short distances, forming either interconnecting [O‐Hg‐O] units which are part of [O‐Hg‐O] ∞ zig‐zag chains, or single [HO‐Hg‐OH] units (realised in compound III). VII is the only compound with mercury in oxidation state +1. It crystallises in space group C 2/ m ( a = 17.342(3), b = 6.1939(10), c = 4.4713(8)Å, β = 90.154(3)°) and is made up of Hg 2 2+ dumbbells, [ZnO 4 (OH) 2 ] octahedra, and statistically distributed Se VI O 4 and Se IV O 3 groups as the main building units.