Curium Compounds

Curium compounds are compounds containing the element curium (Cm). Curium usually forms compounds in the +3 oxidation state, although compounds with curium in the +4, +5 and +6 oxidation states are also known.

Oxides

Curium readily reacts with oxygen forming mostly Cm₂O₃ and CmO₂ oxides,Curium
(in German) but the divalent oxide CmO is also known.Holleman, p. 1972 Black CmO₂ can be obtained by burning curium oxalate (), nitrate (), or hydroxide in pure oxygen.Greenwood, p. 1268 Upon heating to 600–650 °C in vacuum (about 0.01 Pa), it transforms into the whitish Cm₂O₃:
: 4CmO2 ->Delta T2Cm2O3 + O2.

Or, Cm₂O₃ can be obtained by reducing CmO₂ with molecular hydrogen:
: 2CmO2 + H2 -> Cm2O3 + H2O

Also, a number of ternary oxides of the type M(II)CmO₃ are known, where M stands for a divalent metal, such as barium.

Thermal oxidation of trace quantities of curium hydride (CmH_2–3) has been reported to give a volatile form of CmO₂ and the volatile trioxide CmO₃, one of two known examples of the very rare +6 state for curium. Another observed species was reported to behave similar to a supposed plutonium tetroxide and was tentatively characterized as CmO₄, with curium in the extremely rare +8 state; but new experiments seem to indicate that CmO₄ does not exist, and have cast doubt on the existence of PuO₄ as well.

Halides

The colorless curium(III) fluoride (CmF₃) can be made by adding fluoride ions into curium(III)-containing solutions. The brown tetravalent curium(IV) fluoride (CmF₄) on the other hand is only obtained by reacting curium(III) fluoride with molecular fluorine:Morss, L. R.; Edelstein, N. M. and Fugere, J. (eds): ''The Chemistry of the Actinide Elements and transactinides'', volume 3, Springer-Verlag, Dordrecht 2006, .
: $\mathrm$

A series of ternary fluorides are known of the form A₇Cm₆F₃₁ (A = alkali metal).

The colorless curium(III) chloride (CmCl₃) is made by reacting curium hydroxide (Cm(OH)₃) with anhydrous hydrogen chloride gas. It can be further turned into other halides such as curium(III) bromide (colorless to light green) and curium(III) iodide (colorless), by reacting it with the ammonia salt of the corresponding halide at temperatures of ~400–450°C:
: $\mathrm$

Or, one can heat curium oxide to ~600°C with the corresponding acid (such as hydrobromic for curium bromide). Vapor phase hydrolysis of curium(III) chloride gives curium oxychloride:
: $\mathrm$

Chalcogenides and pnictides

Sulfides, selenides and tellurides of curium have been obtained by treating curium with gaseous sulfur, selenium or tellurium in vacuum at elevated temperature. Curium pnictides of the type CmX are known for nitrogen, phosphorus, arsenic and antimony. They can be prepared by reacting either curium(III) hydride (CmH₃) or metallic curium with these elements at elevated temperature.Lumetta, G. J.; Thompson, M. C.; Penneman, R. A.; Eller, P. G
Curium
, Chapter Nine in ''Radioanalytical Chemistry'', Springer, 2004, pp. 1420–1421. ,

Organocurium compounds and biological aspects

Organometallic complexes analogous to uranocene are known also for other actinides, such as thorium, protactinium, neptunium, plutonium and americium. Molecular orbital theory predicts a stable "curocene" complex (η⁸-C₈H₈)₂Cm, but it has not been reported experimentally yet.

Formation of the complexes of the type (BTP = 2,6-di(1,2,4-triazin-3-yl)pyridine), in solutions containing n-C₃H₇-BTP and Cm³⁺ ions has been confirmed by EXAFS. Some of these BTP-type complexes selectively interact with curium and thus are useful for separating it from lanthanides and another actinides. Dissolved Cm³⁺ ions bind with many organic compounds, such as hydroxamic acid, urea, fluorescein and adenosine triphosphate. Many of these compounds are related to biological activity of various microorganisms. The resulting complexes show strong yellow-orange emission under UV light excitation, which is convenient not only for their detection, but also for studying interactions between the Cm³⁺ ion and the ligands via changes in the half-life (of the order ~0.1 ms) and spectrum of the fluorescence.Bünzli, J.-C. G. and Choppin, G. R. ''Lanthanide probes in life, chemical, and earth sciences: theory and practice'', Elsevier, Amsterdam, 1989

Curium has no biological significance. There are a few reports on biosorption of Cm³⁺ by bacteria and archaea, but no evidence for incorporation of curium into them.

See also

* Berkelium compounds
* Californium compounds

References

{{Curium compounds

Curium
Curium compounds
Chemical compounds by element