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Budantseva, N. A.; Федосеев, А. М.; Lapitskaya, T. S.

doi:10.1023/a:1026268127421

Cited by 3 publications

(5 citation statements)

References 3 publications

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“…Presumably, these vibrations are responsible for the band at approximately 830 cm -1 , manifested in the experimental spectra as a shoulder on the long-wave side of the strong band in the spectra of triclinic octamolybdates. This frequency is close to those reported previously for other Np(V) molybdates [30]. In the spectrum of Cs 6 [(NpO 2 ) 2 (Mo 8 O 28 )]·2H 2 O, we failed to reveal a similar vibration.…”

Section: Absorption Spectrasupporting

confidence: 90%

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

2015

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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.

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Section: Absorption Spectrasupporting

confidence: 90%

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

2015

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“…As shown previously [1], crystalline phases of the zeolite type with the composition (AlO 2 ) 2 (SiO 2 ) 4 . 7H 2 O similar to faujasite mineral (as judged from the X-ray diffraction patterns) are formed at 80 3100oC from alkaline solutions with [OH 3 ] of approximately 2 M at the Si : Al molar ratio varied from 2 to 6.…”

Section: Resultssupporting

confidence: 75%

“…The experimental conditions were the same as in [1]. A solution of Np(VI) purified by anion exchange was used as the initial solution.…”

Section: Methodsmentioning

confidence: 99%

“…We studied previously [1] the Pu(VI) sorption on aluminosilicates of the zeolite type, whose spontaneous formation is possible in prolonged storage of alkaline radioactive wastes containing silicate and aluminate ions at elevated temperature. It was shown that Pu(VI) existing in strong alkalis in the form of anionic hydroxo complexes hampers crystallization of aluminosilicate, but in the case of formation of a solid phase it is partially sorbed on its surface.…”

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Interaction of Np(V), (VI), and (VII) with Aluminosilicates in Alkaline Medium

et al. 2005

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The behavior of Np in higher oxidation states in alkaline solution containing silicate and aluminate ions was studied. In formation of a crystalline aluminosilicate in a solution, Np(V), (VI), and (VII) are not incorporated into its crystal structure but hamper formation of the solid phase. The possibility of sorption of Np on various aluminosilicates is primarily governed by its oxidation state. Np(V) and Np(VII) are not sorbed from strong alkali. Np(VI) is retained by aluminosilicate materials to various extents depending on the surface characteristics and surface area of these materials. On heating, the degree of Np(VI) sorption decreases, which suggests the physical nature of the process.We studied previously [1] the Pu(VI) sorption on aluminosilicates of the zeolite type, whose spontaneous formation is possible in prolonged storage of alkaline radioactive wastes containing silicate and aluminate ions at elevated temperature. It was shown that Pu(VI) existing in strong alkalis in the form of anionic hydroxo complexes hampers crystallization of aluminosilicate, but in the case of formation of a solid phase it is partially sorbed on its surface. The sorption capacity of crystalline aluminosilicates is low (approximately 6 mg per gram of the sorbent), which apparently reflects the ratio of neutral hydroxo complexes PuO 2 (OH) 2 (H 2 O) 2 and negatively charged complexes [PuO 2 (OH) n (H 2 O) 4 3n ] 2 3n existing in alkaline solution, among which PuO 2 (OH) 4 23 predominates at [OH 3 ] > 1 M. Highly charged ionic species are less sorbable because of electrostatic repulsion from the negatively charged aluminosilicate surface [2]. Almost quantitative sorption of Pu(VI) with natural montmorillonite is caused by reduction of Pu(VI) to Pu(IV), which is well retained by many materials.No less interesting is the behavior of long-lived radionuclide 237 Np, which can be present in alkaline wastes in oxidation state +5 and, under certain conditions, +6, since Np(IV) under these conditions is unstable and is oxidized to Np(V) even with atmospheric oxygen. The hydrolytic behavior of Np(V) and Np(VI) is different. Np(VI) can be expected to be similar to Pu(VI) in the hydrolytic behavior, although there are no published data on the speciation of Np(VI) in strong alkalis. Pentavalent neptunium is subject to hydrolysis to a lesser extent than Np(VI); in addition, it shows a weaker tendency to form polymeric species [3,4]. It was assumed [5,6] that, at relatively high concentration of hydroxide ions in a solution, the major ionic Np(V) species are [NpO 2 (OH) 2 ] 3 , [NpO 2 (OH) 3 ] 23 , and [NpO 2 (OH) 3 (H 2 O)] 23 . In this study we examined the reaction of Np(V) and Np(VI) with various aluminosilicates at [OH 3 ] of approximately 2 M. Under the same conditions, we also studied the behavior of Np(VII), which, as known, exists in alkaline solutions as a highly charged anion NpO 4 (OH) 2 33 [7, 8] and is highly soluble in alkalis. In addition, attention should be given to the possibility of disproportionation of Np(VI) in alkali...

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“…The vibrations of bridging molybdate ions and NpO 2 groups are manifested in a narrow frequency range, 920 3780 cm !1 , which leads to partial overlap of the corresponding absorption bands. Based on the previous IR data for some Np(V) molybdates [14], the doublet with maxima at 830 and 820 cm !1 should be assigned to the neptunyl(V) stretching vibrations n 3 (NpO 2 + ). The other five observed bands correspond to stretching vibrations of distorted tetrahedral ions MoO 4 2!…”

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confidence: 97%

Structure and Some Properties of a Double Neptunyl(V) Cesium Molybdate, Cs[NpO2MoO4(H2O)]

et al. 2005

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A double neptunyl(V) cesium molybdate, Cs[NpO 2 MoO 4 (H 2 O)], was studied by single crystal X-ray diffraction. Crystal data: rhombic system, a = 9.478(2), b = 7.900(1), c = 10.499(2) ); space group Pnna, Z = 4, d = 5.05 g cm !3 , R = 0.030. The compound has a framework structure; the coordination polyhedron of the Np atom is a distorted pentagonal bipyramid with the equatorial positions occupied by four O atoms of four molybdate groups and an O atom of the coordinated water molecule. The IR and visible absorption spectra of this compound and of Cs 2 [(NpO 2 ) 2 Mo 2 O 8 ] whose structure had been determined previously were measured. The NpO 2 + stretching vibration frequencies in the IR spectra of these compounds virtually coincide. Incorporation of the O atom of the Mo!O!Mo bridge into the first coordination sphere of the neptunyl(V) ion in Cs 2 [(NpO 2 ) 2 Mo 2 O 8 ] exerts the same disturbing effect on the electronic absorption spectrum as does the cation!cation interaction with one of the O atoms acting as a bridge between two Np atoms.The previously studied Np(V) molybdate compounds showed certain unexpected features concerning the structure of the coordination polyhedra (CPs) of the Np and Mo atoms and the spectra [133]. Here we report on a single crystal X-ray diffraction study of a double Cs neptunyl (V) molybdate, Cs[NpO 2 MoO 4 . (H 2 O)] (I), and on the IR and visible spectra of this compound and of Cs 2 [(NpO 2 ) 2 Mo 2 O 8 ] (II) formed under similar conditions. The structure of Cs 2 [(NpO 2 ) 2 Mo 2 O 8 ] was described previously [3]. This complex is isostructural to synthetic anhydrous analogs of carnotite, K 2 [(UO 2 ) 2 . V 2 O 8 ] and Cs 2 [(UO 2 ) 2 V 2 O 8 ] [4]. The structure of II contains anionic layers of the composition [(NpO 2 ) 2 . Mo 2 O 8 ] n 2n! , in which the CPs of the Np atoms (distorted pentagonal bipyramids) are combined in pairs, sharing a common equatorial edge. Furthermore, each CP shares two common vertices with the CPs of two adjacent pairs. The centrosymmetrical anions Mo 2 O 8 4!in the structure of II are tetragonal bipyramids linked in pairs, sharing a common base edge (CN of Mo atoms 5). EXPERIMENTAL Double neptunyl(V) cesium molybdates I and IIwere prepared by the procedure described in detail in [3] in the form of fairly large crystals, which can be readily separated from a small amount of finely crystalline impurities by washing with water. The yields of I and II pass through a maximum at similar temperatures (180 and 200oC, respectively); therefore, in all the syntheses we obtained two-phase products with the ratio of I to II strongly depending on temperature. For spectroscopic studies, the crystals of complexes were separated manually using a binocular magnifier.The IR and visible spectra were taken from samples suspended in mineral oil and applied as a thin layer onto polished plates from molten NaCl. The spectra were recorded on Specord M80 and Shimadzu UV-3100 spectrometers.Single crystal X-ray diffraction analysis. For the X-ray structural study of I, we chos...

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Cited by 3 publications

References 3 publications

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

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

Interaction of Np(V), (VI), and (VII) with Aluminosilicates in Alkaline Medium

Structure and Some Properties of a Double Neptunyl(V) Cesium Molybdate, Cs[NpO2MoO4(H2O)]

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