Neptunium halides

Neptunium halides. Neptunium forms binary halides in the oxidation states of Np (III, IV, and VI). The trifluoride is prepared by hydrofiuorination of the dioxide, hydroxide, carbonate, oxalate, or nitrate in the presence of hydrogen ... 

Neptunium forms a number of halides in various oxidation states. These include tri-, tetra- and hexafluorides of compositions NpFs, NpF4, and NpFe, respectively trichloride, NpCF and tetrachloride, NpCh tribromide, NpBrs and the triiodide NpN. Neptunium fluorides are formed by heating neptunium dioxide at elevated temperatures with fluorine in the presence of hydrogen fluoride. The tetrachloride, NpCh is obtained similarly by heating the dioxide with carbon tetrachloride vapor at temperatures above 500°C. Neptunium tribromide and triiodide are prepared by heating the dioxide in a sealed vessel at 400°C with aluminum bromide and aluminum iodide, respectively. 

Answer 10.1 Early on in the series, as far as uranium, the maximum oxidation state corresponds to the total number of outer shell electrons. Uranium forms a hexachloride, in addition to the MEe also formed by Np and Pu. After uranium, neptunium forms the full range of tetrahalides, but, from plutonium onwards, the (-1-3) state dominates the chemistry of the binary halides, which strongly resemble those of the lanthanides. This may reflect decreased availability of 5f (and 6d ) electrons for bonding. As usual, F supports the highest oxidation states. 

Investigations of the solid-state chemistry of the americium oxides have shown that americium has properties typical of the preceding elements uranium, neptunium, and plutonium as well as properties to be expected of a typical actinide element (preferred stability of the valence state 3-j-). As the production of ternary oxides of trivalent plutonium entails considerable difficulties, it may be justified to speak of a discontinuity in the solid-state chemical behavior in the transition from plutonium to americium. A similar discontinuous change in the solid-state chemical behavior is certainly expected in the transition Am Cm. Americium must be attributed an intermediate position among the neighboring elements which is much more pronounced in the reactions of the oxides than in those of the halides or the behavior in aqueous solution. 

Tetrachloride and tetrabromide complexes are known for thorium, protactinium, uranium, neptunium, and plutonium. These are similarly produced by halide-based oxidation of metals or hydrides, or by halogenation of oxides. A common structural type is reported for most compounds. The reported structure of thorium tetrachloride reveals that the coordination geometry about the metal is dodecahedral.The compounds are generally volatile and can be sublimed. The gas-phase electron diffraction structure of suggests that the molecule is... 

Binary halides. A number of homoleptic halides of pentavalent protactinium, uranium, and neptunium have been reported. In particular, the fluoride complexes AnFs are prepared by high... 

With the exception of thorium, the actinides form trihalides. For uranium and neptunium, reduction of the MX4 compounds with hydrogen is necessary, but for the elements from plutonium onwards the action of the carbon tetrahalide or aluminium halide on the dioxide is usually employed. The trifluorides are insoluble but the rest dissolve to give solutions containing ions. 

Isomorphism among compounds of the actinides is common and only a few examples need be given. The dioxides, MO2, of thorium, uranium, neptunium, plutonium and americium all have a fluorite lattice. The trihalides of the transuranic elements are isomorphous not only with the corresponding trihalides of actinium and uranium but also with those of the lanthanides. Isomorphism is also exhibited in many complex halides thus thorium, ura-... 

Rand, M. H., Fuger, J., The thermodynamic properties of the transuranium halides Part 1, Neptunium and plutonium halides, ITU, European Commission Joint Research Centre report. Report 17332 EN, (2000). Cited on pages 500, 513, 522, 528, 546, 547. 

Micro techniques have been very useful in chemical studies of the actinide elements, and particularly so for the study of the halides. Historically, micro methods were required because of the very small amounts of the synthetic actinides originally available for experiment. However, even when large amounts of neptunium, plutonium, and other actinide elements became available, micro methods were found to offer many advantages, and they have therefore continued to be of great service to this day. W. H. Zachariasen was able to obtain and interpret X-ray diffraction patterns on samples of the order of a few micrograms and the... 

Bamberger also applied a similar metathesis reaction process to the synthesis of phosphates of uranium and neptunium, thus this represents a versatile and alternative synthesis method for the conversion of rare-earth oxides or halides to the phosphate form. 

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