Contributions to the stereochemistry of zirconium oxysalts-part I: syntheses and crystal structures of novel Zr(SeO4)(2)center dot H2O and Zr(SeO4)(2)center dot 4H(2)O

摘要

The new compounds Zr(SeO4)(2)center dot H2O and Zr(SeO4)(2)center dot 4H(2)O were synthesized at low-hydrothermal conditions (teflon-lined steel vessels, 220 A degrees C) from mixtures of Zr2O2(CO3)(OH)(2), H2SeO4, and minor contents of water. Colorless single crystals up to 0.2 mm in length, obtained within 1 week, were studied by single-crystal X-ray techniques. Zr(SeO4)(2)center dot H2O crystallizes in the monoclinic space group P2(1)/n (no. 14), with a = 5.332(1) , b = 7.962(2) , c = 16.256(3) , beta = 92.19(1)A degrees, V = 689.6(3) (3), Z = 4, and R1 = 0.0195. Zr(SeO4)(2)center dot H2O represents a new structure type built from isolated ZrO7 pentagonal dipyramids, further cornerlinked via SeO4 groups to a three-dimensional framework. One H2O group acts as a ligand of the ZrO7 coordination. Zr(SeO4)(2)center dot 4H(2)O [orthorhombic, space group Fddd (no. 70), with a = 5.651(1) , b = 11.964(3) , c = 26.611(6) , V = 1799.1(4) (3), Z = 8, and R1 = 0.0177] is isotypic with the compounds M(SO4)(2)center dot 4H(2)O; M = Zr, Hf, Ce, and Pu. The structure is built up by sheets within (001), linked by hydrogen bonds only. The zirconium atom is 8-coordinated to oxygen atoms of four H2O molecules and of SeO4 tetrahedra, forming a distorted tetragonal antiprism. For both structures, mean cation-oxygen bond lengths are in accordance with the literature: Zr-[7]: 2.137 , Zr-[8]: 2.188 , and Se-[4]: 1.631-1.635 . Observed hydrogen bonds show donor-acceptor distances within the range of 2.65-2.79 .