Reinvestigation Of Np2se5: A Clear Divergence From Th2s5 And Th2se5 In Chalcogen-Chalcogen And Metal-Chalcogen Interactions

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 P4(2)/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) angstrom, whereas Se(2) is a discrete Se2- 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 L-III-edge X-ray Absorption Near Edge Structure ()CANES) measurements show a clear shift in edge position to higher energies for Np2Se5 compared to Np3Se5 (Np23+Np4+Se52-). 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) mu(B)/Np, given by a best fit of susceptibilities to a modified Curie-Weiss law over the temperature range 50-320 K.