Synthesis and spectra of Np(V) γ-Octamolybdates of the composition M6[(NpO2)2(Mo8O28)]·2H2O (M = NH4, K, Rb, Cs, Tl)

Abstract

Previously unknown Np(V) compounds with γ-octamolybdate anions are reported. A series of complexes of the general composition M 6 [(NpO 2 ) 2 (Mo 8 O 28 )]·2H 2 O (M = NH 4 , K, Rb, Cs, Tl) were synthesized by the hydrothermal method from aqueous solutions. The composition and crystal structure of the compounds were determined by single crystal X-ray diffraction. All the compounds contain the NpO 2 + dioxocations, (Mo 8 O 28 ) 8anions, M + cations, and water molecules of crystallization. The Np atoms have the pentagonal bipyramidal oxygen surrounding, with five O atoms of three different octamolybdate ions arranged in the equatorial plane of the dioxocation. The complexes with the NH 4 , K, Rb, and Tl cations are isostructural (space group P1), whereas the complex with the Cs cation crystallizes in another space group (P2 1 /n). The structure of the centrosymmetric octamolybdate ions (Mo 8 O 28 ) 8is similar in all the compounds. The oxygen surrounding of the outer-sphere cations is characterized by a large scatter of the interatomic distances, and both the main and additional coordination numbers of the cations can be considered. The electronic and vibrational absorption spectra of the synthesized Np(V) octamolybdate complexes were measured and analyzed. The influence of the structural features of the complexes and of the kind of the outer-sphere cation on the spectral pattern is discussed.

Structural and Morphological Influences on Neptunium Incorporation in Uranyl Molybdates

“…A more likely explanation for the 28 nm peak shift is strong ligand complexation between Np­(V) and Mo­(VI) through a shared oxygen atom. Similarly large shifts have been reported for Np­(V) compounds of pertechnetate, chromate, and vanadate as well as molybdate all in the absence of CCIs. − …”

Mixed-Valence NpV/AnVI Molybdate Complexes with Single-Charge Outer-Sphere Cations

“…The spectrum of 5 also shows a band with a maximum at 957 cm –1 , which can be attributed to stretching vibrations of bridge bonds ν 1 (Mo–O–Mo). Similar frequencies are observed for compounds containing condensed molybdenum–oxygen groups. − As mentioned above, structure 5 contains “double” molybdate ions, which can be considered as transitional to the Mo 2 O 8 4– anion.…”

A Novel Family of Np(VI) Oxysalts: Crystal Structures, Calorimetry, Thermal Behavior, and Comparison with U(VI) Compounds

“…Although Np is a radioactive element, the structures of about 550 compounds are known to date (Cambridge Structural Database, Version 5.39; and Inorganic Crystal Structure Database, Version 2018.1). Among them, Np 5+ -bearing compounds (for example, see refs − ) are the most common, whereas the number of Np 6+ compounds reported to date is much smaller. − The electronic structures of U 6+ and Np 6+ differ, especially in the presence of a 5f electron in the case of Np 6+ , and this may result in different stereochemistries of their compounds. It is therefore interesting to compare phase formation processes involving these ions within chemically similar systems.…”