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

Abstract

The study of curium iodate, Cm(IO 3) 3, was undertaken as part of a systematic investigation of the 4 f- and 5 f-elements’ iodates. The reaction of 248CmCl 3 with aqueous H 5IO 6 under mild hydrothermal conditions results in the reduction of IO 6 5− to IO 3 − anions, and the subsequent formation of Cm(IO 3) 3 single crystals. Crystallographic data are: (193 K, Mo Kα, λ = 0.71073 Å ): monoclinic, space group P2 1/ c, a = 7.2014 ( 7 ) Å , b = 8.5062 ( 9 ) Å , c = 13.4622 ( 14 ) Å , β = 100.142 ( 2 ) ° , V = 811.76 ( 14 ) , Z = 4 , R ( F ) = 2.11 % , R w ( F o 2 ) = 4.43 % for 119 parameters with 1917 reflections with I>2σ( I). The structure consists of Cm 3+ cations bound by iodate anions to form [Cm(IO 3) 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 760 cm −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(IO 3) 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 ) Å , b = 8.5310 ( 8 ) Å , c = 13.505 ( 1 ) Å , β = 100.021 ( 2 ) ° , V = 818.3 ( 2 ) .