Neptunium complexes

Purex process, 6, 951 Neptunium complexes, 3, 1131-1215 cupferron, 2, 510 Neptunium dioxide ions disproportionation Purex process, 6, 950... 

Neptunium, complexes (continued) stability constants, enthalpies,... 

A significant amount of structural information has been gathered on neptunium complexes. For the main, they resemble corresponding U and Pu complexes. However, an EXAFS study of alkaline solutions of Np " found evidence for a trans dioxo ion of the type P4p02(OH)4(OH2)]i-. 

Neptunium complex with pyridine [Np02(CH3C(0)CHC(0)CH3)2(Py)] (27) is described in the work [84]. The equatorial plane of Np atom is formed by four oxygen atoms of anions and nitrogen atom of pyridine. The Np-0 distances are equal to 2.333-2.372 A, while Np-N bond is longer, 2.564 A. The equatorial surrounding is near planar, the deviation of atoms does not exceed 0.088 A. At... 

Naphthoic acid, 3-hydroxy-7-sulfonato-metal complexes structure, 482 1,8-Naphthyridine metal complexes, 92,93 Neoeupferron metd complexes, 509-512 Neptunium complexes cupferron, 510 Neutron diffraction hydrates... 

A lot of new coordination Np(V) complexes are still synthesized and several types of a novel CCB network have been found in their crystal structure [58-61]. Magnetic study is also performed about some neptunyl(+l) complexes [62], but there is no application of Np Mossbauer spectroscopy to them. Np Mossbauer spectroscopy is a very powerful and indispensable tool to study the electronic and the magnetic properties of neptunium complexes and will give several important information that cannot be provided with the magnetization measurement. Now Np Mossbauer spectroscopy is hardly performed due to the severe restrictions in handling transuranic materials and the output in this field is markedly reduced [63] however, many unsolved problems in this field that one should work on are left uncompleted. 

The hydrolysis of Np " appears to be very similar to that of though Np " is an appreciably weaker acid [41] (Table 21.2). From the actinide contraction (see, for example, ref. 261, p. 466) the opposite trend would rather be expected. This unexpected relation between the stabilities of corresponding uranium and neptunium complexes is a general feature, found for both the tetravalent and hexavalent states. Evidently, the strength of the complex formation is not governed exclusively by simple electrostatic interaction. 

The authors have concluded that hexaphyrin in its oxidized, aromatic form is capable of complexing actinide ions, specifically uranyl (U02 ) and nep-tunyl (Np02 ) neptunyl represents the first crystalographically characterized neptunium complex. The complex is very stable and the authors believe that the system could see application in remediation of radioactive waste. ... 

That magnetic measurements often raise more problems than they solve, is demonstrated for the indicated compound. We prepared a series of [ (C2H5N] i,An(NSC) e compounds (An = Th, U, Np, Pu) with cubic coordination of the actinide ion. We derived a consistent interpretation of the magnetic and optical properties of the uranium and the neptunium compounds (6 ). In the case of Pu we expect an isolated T1 ground state and a first excited state at about 728 cm-1. To our surprise we found a magnetic ground state much more pronounced than in the case of the hexachloro-complex, Fig. 4. 

The Table shows a great spread in Kd-values even at the same location. This is due to the fact that the environmental conditions influence the partition of plutonium species between different valency states and complexes. For the different actinides, it is found that the Kd-values under otherwise identical conditions (e.g. for the uptake of plutonium on geologic materials or in organisms) decrease in the order Pu>Am>U>Np (15). Because neptunium is usually pentavalent, uranium hexavalent and americium trivalent, while plutonium in natural systems is mainly tetravalent, it is clear from the actinide homologue properties that the oxidation state of plutonium will affect the observed Kd-value. The oxidation state of plutonium depends on the redox potential (Eh-value) of the ground water and its content of oxidants or reductants. It is also found that natural ligands like C032- and fulvic acids, which complex plutonium (see next section), also influence the Kd-value. 

Considering the anion concentration ranges in natural waters (Table II) and the magnitude of the corresponding plutonium stability constants (Table III), the chemistry of plutonium, as well as that of uranium and neptunium, is almost entirely dominated by hydroxide and carbonate complexation, considering inorganic complexes only (41, 48, 49). ... 

Thorium(III) and protactinium(III) complexes are unknown, and relatively few uranium(III), neptunium(III) and plutonium(III) compounds have been described. This is mainly because of the ease of oxidation to the +4 state in all three cases, accentuated for plutonium(III) by the oxidizing nature of the a-radiolysis products formed in solutions. 

Because of the ease of oxidation of protactinium(IV) and uranium(IV), peroxides and peroxo complexes are limited to their higher oxidation states. The compounds M04"JcH20 precipitated from dilute acid solutions of neptunium(IV) and plutonium(IV) by hydrogen peroxide appear to be actinide(IV) compounds. Soluble intermediates of the type [Pu( U-02)2Pu]4+ are formed at low hydrogen peroxide concentrations. 

The coordination geometry in anhydrous Th(CF3COCHCOMe)4 is a 1111 ( )4-422) antiprism 74 the structure of the monohydrate has been discussed earlier (p. 1144). Th[CF3COCHCO(2-C4H3S)]4 is isostructural with the cerium(IV), uranium(IV) and plutonium(IV) analogues. The coordination polyhedron is a distorted dodecahedron in which the four ligands span the two perpendicular trapezoids of the dodecahedron.75 In the complexes M(n-C3F7COCHCOBut)4, the thorium(IV), uranium(IV) and neptunium(IV) compounds are isomorphous, but the plutonium compound is not. 

The basic structure of the hydrated oxalato complex, NaNpC CyiVSPkO, is made up of infinite chains of composition [Np02C2O4(H2O)]" connected by Na+ ions and H20 molecules in a three-dimensional network. The neptunium atom is at the centre of a pentagonal bipyramid, coordinated to four O atoms from two C204 groups and a fifth from the water molecule in the equatorial plane.17915... 

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