title: Reinvestigation of Np2Se5: a clear divergence from Th2S5 and Th2Se5 in chalcogen-chalcogen and metal-chalcogen interactions.
abstract: Single crystals of Np2Se5 have been prepared through the reactions of Np and Se at 1223 K in an Sb2Se3 flux. The structure of Np2Se5, which has been characterized by single-crystal X-ray diffraction methods, crystallizes in the tetragonal space group P42/nmc. The crystallographic unit cell includes one unique Np and two Se positions. Se(1) atoms form one-dimensional infinite chains along the a and b axes with alternating intermediate Se-Se distances of 2.6489 (8) and 2.7999 (8) Å, whereas Se(2) is a discrete Se(2-) anion. Each Np is coordinated to 10 Se atoms and every NpSe10 polyhedron shares faces, edges, or vertices with 14 other identical metal polyhedra to form a complex three-dimensional structure. Np LIII-edge X-ray Absorption Near Edge Structure (XANES) measurements show a clear shift in edge position to higher energies for Np2Se5 compared to Np3Se5 (Np(3+)2Np(4+)Se(2-)5). Magnetic susceptibility measurements indicate that Np2Se5 undergoes a ferromagnetic-type ordering below 18(1) K. Above the transition temperature, Np2Se5 behaves as a paramagnet with an effective moment of 1.98(5) μB/Np, given by a best fit of susceptibilities to a modified Curie-Weiss law over the temperature range 50-320 K.
authors.affiliation: Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States. gjin@anl.gov
authors.forename: Geng Bang
authors.initials: GB
authors.lastname: Jin
authors.forename: Yung-Jin
authors.initials: YJ
authors.lastname: Hu
authors.forename: Brian
authors.initials: B
authors.lastname: Bellott
authors.forename: S
authors.initials: S
authors.lastname: Skanthakumar
authors.forename: Richard G
authors.initials: RG
authors.lastname: Haire
authors.forename: L
authors.initials: L
authors.lastname: Soderholm
authors.forename: James A
authors.initials: JA
authors.lastname: Ibers