Abstract
Zr2(OH)2(XO4)3·4H2O (X = S, Se), Zr(SO4)2·4H2O, and Zr(SeO3)2 were synthesized at low-hydrothermal conditions from mixtures of Zr2O2(CO3)(OH)2, the respective acids, and minor amounts of water. While Zr2(OH)2(XO4)3·4H2O (X = S, Se) and Zr(SO4)2·4H2O form crystals up to several tenths of a mm, Zr(SeO3)2 was mainly obtained as microcrystalline powder, single crystals rarely exceeded 10 μm in size. Samples were investigated by single-crystal X-ray techniques and in the case of Zr(SeO3)2 also by X-ray powder diffraction. The compounds Zr2(OH)2(XO4)3·4H2O (X = S, Se) crystallize in the Ce2(OH)2(SO4)3·4H2O structure type (C2/c, Z = 4, a = 13.034(2) / 13.308(3), b = 6.500(1) / 6.683(2), c = 15.056(3) / 15.383(4) Å, β = 96.27(1) / 96.81(1)°, V = 1267.9(4) / 1358.5(6) Å3 for X = S / Se, respectively). Tetragonal aniprisms Zr[8]O8 are edge-connected to dimers that share corners with XO4 tetrahedra forming a three-dimensional network. Zr(SO4)2·4H2O (Fddd, Z = 8, a = 5.498(1), b = 11.618(3), c = 25.893(6) Å, V = 1653.9(6) Å3) is isotypic with the respective selenate compound. Occasionally, pseudomerohedral twinning is observed, simulating a larger monoclinic C-centered unit cell. Again, tetragonal antiprisms Zr[8]O8 are formed; however, they are corner-linked with SO4 tetrahedra to Zr(SO4)2 layers interconnected solely by hydrogen bonds. Zr(SeO3)2 crystallizes in P21/c, Z = 2; a = 4.9724(3), b = 8.5992(5), c = 6.9447(3) Å, β = 110.128(3)°, V = 278.81(3) Å3 (unit cell from powder data) and belongs to the β-Sn(SeO3)2 structure type established further for Ti(SeO3)2 and Pb(SeO3)2. Isolated ZrO6 octahedra share corners with the selenite groups forming a three-dimensional network.Graphical abstract
Highlights
The presented work is part of long-term investigations on the crystal chemistry of zirconium oxysalts with (XO4)2− or (XO3)2− (X = S, Se) anions synthesized under mild-hydrothermal conditions below 250 °C
The zirconium atoms in the isotypic compounds Zr2(OH)2(XO4)3·4H2O (X = S, Se) are coordinated by eight oxygen atoms arranged in distorted tetragonal antiprisms
In the light of the present investigations on the crystal structure of Zr(SO4)2·4H2O with its remarkable twinning behavior, it seems very likely that crystals of α-Ce(SO4)2·4H2O might be twinned in the same way as described simulating a monoclinic C-centered previous description of Zr(SeO3)2 with orthorhombic symmetry from powder data [17] and the respective ICDD entry 50–0336 have to be revised
Summary
The compounds Z r2(OH)2(XO4)3·4H2O (X = S, Se) crystallize in the Ce2(OH)2(SO4)3·4H2O structure type (C2/c, Z = 4, a = 13.034(2) / 13.308(3), b = 6.500(1) / 6.683(2), c = 15.056(3) / 15.383(4) Å, β = 96.27(1) / 96.81(1)°, V = 1267.9(4) / 1358.5(6) Å3 for X = S / Se, respectively). Later on, [7] determined the crystal structure and refined this compound in space group Fddd but without locating hydrogen atoms.
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