Three New Sodium Neptunyl(V) Selenate Hydrates: Structures, Raman Spectroscopy, and Magnetism
详细信息 查看全文
- 作者：Geng Bang Jin ; S. Skanthakumar ; L. Soderholm
- 刊名：Inorganic Chemistry
- 出版年：2012
- 出版时间：March 5, 2012
- 年：2012
- 卷：51
- 期：5
- 页码：3220-3230
- 全文大小：619K
- 年卷期：v.51,no.5(March 5, 2012)
- ISSN：1520-510X
文摘
Green crystals of Na(NpO2)(SeO4)(H2O) (1), Na3(NpO2)(SeO4)2(H2O) (2), and Na3(NpO2)(SeO4)2(H2O)2 (3) have been prepared by a hydrothermal method for 1 or evaporation from aqueous solutions for 2 and 3. The structures of these compounds have been characterized by single-crystal X-ray diffraction. Compound 1 is isostructural with Na(NpO2)(SO4)(H2O) (4). The structure of 1 consists of ribbons of neptunyl(V) pentagonal bipyramids, which are decorated and further connected by selenate tetrahedra to form a three-dimensional framework. The resulting open channels are filled by Na+ cations and H2O molecules. Within the ribbon, each neptunyl polyhedron shares corners with each other solely through cation鈥揷ation interactions (CCIs). The structure of 2 adopts one-dimensional [(NpO2)(SeO4)2(H2O)]3鈥?/sup> chains connected by Na+ cations. Each NpO2+ cation is coordinated by four monodentate SeO42鈥?/sup> anions and one H2O molecule to form a pentagonal bipyramid. The structure of 3 is constructed by one-dimensional [(NpO2)(SeO4)2]3鈥?/sup> chains separated by Na+ cations and H2O molecules. These chains have two configurations resulting in two disordered orientations of the Se(2)O42鈥?/sup> tetrahedra. Each NpO2+ cation is coordinated by one bidentate Se(1)O42鈥?/sup> and three monodentate Se(2)O42鈥?/sup> anions to form a pentagonal bipyramid. Raman spectra of 1, 2, and 4 were collected on powder samples. For 1 and 4, the neptunyl symmetric stretch modes (670, 676, 730, and 739 cm鈥?) shift significantly toward lower frequencies compared to that in 2 (773 cm鈥?), and there are several asymmetric neptunyl stretch bands in the region of 760鈥?20 cm鈥?. Magnetic measurements obtained from crushed crystals of 1 are consistent with a ferromagnetic ordering of the neptunyl(V) spins at 6.5(2) K, with an average low temperature saturation moment of 2.2(1) 渭B per Np. Well above the ordering temperature, the susceptibility follows Curie鈥揥eiss behavior, with an average effective moment of 3.65(10) 渭B per Np and a Weiss constant of 14(1) K. Correlations between lattice dimensionality and magnetic behavior are discussed.