Abstract
Black prisms of Np3Q5 (Q = S, Se) have been synthesized by the stoichiometric reactions between Np and Q at 1173 K
in a CsCl flux. The structures of these compounds were characterized by single-crystal X-ray diffraction methods. The
Np3Q5 compounds are isostructural with U3Q5. The structure of Np3Q5 is constructed from layers of Np(1)Q8 distorted
bicapped trigonal prisms that share faces with each other on bc planes. Each Np(1)Q8 layer further shares Q(2) edges
with two adjacent identical neighbors to form a three-dimensional framework. The space inside each channel within
this framework is filled by one single edge-sharing Np(2)Q7 distorted 7-octahedron chain running along the b axis.
Magnetic susceptibility measurements show that Np3S5 and Np3Se5 have antiferromagnetic orderings at 35(1) and
36(1) K, respectively. Above the magnetic ordering temperatures, both Np3S5 and Np3Se5 behave as typical
Curie-Weiss paramagnets. The effective moments obtained from the fit of the magnetic data to a modified Curie-
Weiss law over the temperature range 70 to 300 K are 2.7(2) μB (Np3S5) and 2.9(2) μB (Np3Se5).