ic500181t_si_001.cif (19.64 kB)
Expansion of the Rich Structures and Magnetic Properties of Neptunium Selenites: Soft Ferromagnetism in Np(SeO3)2
dataset
posted on 2014-07-21, 00:00 authored by Kariem Diefenbach, Jian Lin, Justin N. Cross, Naresh S. Dalal, Michael Shatruk, Thomas E. Albrecht-SchmittTwo new neptunium selenites with
different oxidation states of
the metal centers, NpIV(SeO3)2 and
NpVIO2(SeO3), have been synthesized
under mild hydrothermal conditions at 200 °C from the reactions
of NpO2 and SeO2. Np(SeO3)2 crystallizes as brown prisms (space group P21/n, a = 7.0089(5) Å, b = 10.5827(8) Å, c = 7.3316(5) Å,
β = 106.953(1)°); whereas NpO2(SeO3) crystals are garnet-colored with an acicular habit (space group P21/m, a =
4.2501(3) Å, b = 9.2223(7) Å, c = 5.3840(4) Å, β = 90.043(2)°). Single-crystal X-ray
diffraction studies reveal that the structure of Np(SeO3)2 features a three-dimensional (3D) framework consisting
of edge-sharing NpO8 units that form chains that are linked
via SeO3 units to create a 3D framework. NpO2(SeO3) possesses a lamellar structure in which each layer
is composed of NpO8 hexagonal bipyramids bridged via SeO32– anions. Bond-valence sum calculations
and UV-vis-NIR absorption spectra support the assignment of tetravalent
and hexavalent states of neptunium in Np(SeO3)2 and NpO2(SeO3), respectively. Magnetic susceptibility
data for Np(SeO3)2 deviates substantially from
typical Curie–Weiss behavior, which can be explained by large
temperature-independent paramagnetic (TIP) effects. The NpIV selenite shows weak ferromagnetic ordering at 3.1(1) K with no detectable
hysteresis, suggesting soft ferromagnetic behavior.