Hydrothermal synthesis, structure, Raman spectroscopy, and self-irradiation studies of 248Cm(IO3)3

The study of curium iodate, Cm(IO3)3, was undertaken as part of a systematic investigation of the 4f- and 5f-elements' iodates. The reaction of 248CmCl3 with aqueous H5IO6 under mild hydrothermal conditions results in the reduction of IO65- to IO3- anions, and the subsequent formation of Cm(IO3)3 single crystals. Crystallographic data are: (193K, MoKα, λ=0.71073A): monoclinic, space group P21/c, a=7.2014(7)A, b=8.5062(9)A, c=13.4622(14)A, β=100.142(2)o, V=811.76(14), Z=4, R(F)=2.11%, Rw(Fo2)=4.43% for 119 parameters with 1917 reflections with I>2σ(I). The structure consists of Cm3+ cations bound by iodate anions to form [Cm(IO3)8] units, where the local coordination environment around the curium centers can be described as a distorted dodecahedron. There are three crystallographically unique iodate anions within the structure; two iodates bridge between three Cm centers, and one iodate bridges between two Cm centers and has a terminal oxygen atom. The bridging of the curium centers by the iodate anions creates a three-dimensional structure. Three strong Raman bands with comparable intensities were observed at 846, 804, and 760cm-1 and correspond to the I-O symmetric stretching of the three crystallographically distinct iodate ions. The Raman profile suggests a lack of inter-ionic vibrational coupling of the I-O stretching, while intra-ionic coupling provides symmetric and asymmetric components that correspond to each iodate site. Repeated collection of X-ray diffraction data for a crystal of Cm(IO3)3 over a period of time revealed a gradual expansion of the unit cell from self-irradiation. After 71 days, the new parameters were: a=7.2132(7)A, b=8.5310(8)A, c=13.505(1)A, β=100.021(2)o, V=818.3(2)