The curium aqua ion

The coordination environment of the hydrated Cm3+ ion is probed both in the solid state and in solution. The analysis of single-crystal X-ray diffraction data from [Cm(H2O)(9)](CF3SO3)(3) determines that the Cm species is surrounded by nine coordinating waters with a tricapped-trigonal-prismatic geometry involving six short Cm-O distances at 2.453(1) angstrom and three longer Cm-O distances at 2.545(1) angstrom. The Cm nona-aqua triflate is isostructural with the series of lanthanide and actinide [R(H2O)(9)](CF3SO3)(3) (R = La-Lu, Pu) compounds. A similar nona-aqua geometry is seen for the coordination environment of Cm in aqueous solution, as probed by high-energy X-ray scattering and extended X-ray absorption fine structure spectroscopy, although the splitting in the first coordination shell is increased from 0.092(2) in the solid to 0.16(2) angstrom in solution. This increase in splitting of the Cm-water distances in the first coordination sphere is discussed in terms of its potential relevance to the previously observed decrease in coordinating waters with decreasing ionic radius about the f-ion in solution.