Curium compounds

When curium is heated with fluorine at 400°C, the product is CmF4, a tetravalent curium compound. However, heating with other halogens yields trivalent halides, CmXa. Similarly, when heated with hydrogen chloride gas at 500°C, the product is curium(lll) chloride, CmCls. 

Solid curium compounds are known, e.g., CmF3, CmF4, CmCl3, CmBr3, white Cm203 (mp 2265°C), and black Cm02. Where X-ray structural studies have been made— and these are difficult, since amounts of the order of 0.5 pg must be used to avoid fogging of the film by radioactivity and because of the destruction of the lattice by emitted particles—the compounds are isomorphous with other actinide compounds. 

To date, the hahdes represent by far the most extensively characterized class of curium compounds (refer to Table 9.2). The complete CmXs series (X = F, Q, Br, I), as well as CmF4 and several complex Cm(iv) fluorides, have been prepared and studied. Several reviews deal specifically with actinide halides and for further information (especially for cross-comparisons of Cm with other actinide halides) the reader is referred to these articles [2, 3, 58, 59]. 

In the actinides, the element curium, Cm, is probably the one which has its inner sub-shell half-filled and in the great majority of its compounds curium is tripositive, whereas the preceding elements up to americium, exhibit many oxidation states, for example -1-2, -1-3. -1-4, -1-5 and + 6, and berkelium, after curium, exhibits states of -1- 3 and -E 4. Here then is another resemblance of the two series. 

C22-0054. Identify the compound nucleus and final product resulting from each of the following nuclear reactions (a) carbon-12 captures a neutron and then emits a proton (b) the nuclide with eight protons and eight neutrons captures an a particle and emits a y ray and (c) curium-247 is bombarded with boron-11, and the product loses three neutrons. 

Some Compounds of Americium and Curium. Report UCRL-846 (1. Aug. 1950). 

Gonsidering the small amount of curium produced, a surprising number of compounds have been formed and identified. For example, there are two common oxides, curium dioxide (GmO ) and curium trioxide (Cm O ). Gurium also combines with other nonmetals such as the halogens as follows curium iodide (Cml ), curium bromide (CmBrp, and curium tetrafluo-ride (CmF ). 

Curium metal and its compounds are radioactive bone-seeking poisons that attack the skeletal system of humans and animals. Care must be used in handling them. 

Two other methods have been used successfully to prepare very pure Cm metal. A rather unique one is thermal decomposition of the intermetallic compound PtjCm produced by hydrogen reduction of curium oxide in the presence of Pt (36, 82). The second method, the method of choice for gram-scale preparations of very pure Cm metal, involves reduction of curium oxide with Th metal (8, 83) in an apparatus... 

Many compounds of curium are known. They include the oxides, Cm02 and Cm203, fluorides CmF4 and CmFs, other halides, CmXa hydroxide, Cm(OH)3, and oxalate Cm2(C204)3. The oxide, hydroxide, fluoride, and oxalate salts are insoluble in water and may be obtained by precipitation reactions. 

ACTINIDE CONTRACTION. An effect analogous to the Lanthanide contraction, which lias been found in certain elements of the Actinide series. Those elements from thorium (atomic number 90) to curium (atomic number 96) exhibit a decreasing molecular volume in certain compounds, such as those which the actinide tetrafluoiides form with alkali metal fluorides, plotted in Eig. 1. The effect here is due to the decreasing crystal radius of the tetrapositive actinide ions as the atomic number increases. Note that in the Actinides the tetravalent ions are compared instead of the trivalent ones as in the case of the Lanthanides, in which the trivalent state is by far the most common. 

The solubility properties of curium(111) compounds are in every way similar to those of Ihe other tripositive Actinide elements and the tnpositive Lanthanide elements. Thus the fluoride and oxalate tire insoluble in acid soluliun, while the nitrate, halides, sulfate, perchlorate, and sullide are all soluble. 

Curium was first isolated in Ihe form of a pure compound, the hydroxide, of curium—242 (produced by the neutron irradiation ol aincncium-241) hy Werner and Perlmun at the University of California in the autumn of 1947. Much of the earlier work wiili curium used the isotopes J Cm and wCm, but the heavier isotopes oiler greater advantages mainly because of llicir longer half-lives. The isotope obtainable in relatively high... 

The berkelium monopnictides have been prepared on the multimicrogram scale by direct combination of the elements (138). In all cases, the lattice constants of the NaCl-type cubic structures were smaller than those of the corresponding curium monopnictides but comparable to those of the corresponding terbium compounds. This supports the semimetallic classification for these compounds. One additional report of BkN has appeared (139). The lattice parameter derived from the sample exhibiting a single phase was 0.5010 0.0004 nm, whereas that extracted from the mixed-phase sample of BkN resulting from incomplete conversion of a hydride was 0.4948 0.0003 nm. Clearly, additional samples of BkN should be prepared to establish more firmly its lattice constant. 

Americium was isolated first from plutonium, then from lanthanum and other impurities, by a combination of precipitation, solvent extraction, and ion exchange processes. Parallel with the separation, a vigorous program of research began. Beginning in 1950, a series of publications (1-24) on americium put into the world literature much of the classic chemistry of americium, including discussion of the hexavalent state, the soluble tetravalent state, oxidation potentials, disproportionation, the crystal structure(s) of the metal, and many compounds of americium. In particular, use of peroxydisulfate or ozone to oxidize americium to the (V) or (VI) states still provides the basis for americium removal from other elements. Irradiation of americium, first at Chalk River (Ontario, Canada) and later at the Materials Testing Reactor (Idaho), yielded curium for study. Indeed, the oxidation of americium and its separation from curium provided the clue utilized by others in a patented process for separation of americium from the rare earths. 

A number of compounds of curium have been produced, including two forms of curium oxide (Cm203 and Cm02), two forms of curium fluoride (CmF3 and CmF4), curium chloride (CmCl3), curium bromide (CmBr3), and curium hydroxide (Cm(OH)3). 

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