Synthesis, structure, and spectroscopic properties of Am(IO 3)3 and the photoluminescence behavior of Cm(IO 3)3

We have prepared Am(IO3)3 as a part of our continuing investigations into the chemistry of the 4f- and 5f-elements' iodates. Single crystals were obtained from the reaction of Am3+ and H 5IO6 under mild hydrothermal conditions. Crystallographic data on an eight-day-old crystal are (21°C, Mo Kα, λ = 0.71073 Å): monoclinic, space group P21/c, a = 7.2300(5) Å, b = 8.5511(6) Å, c = 13.5361(10) Å, β = 100.035(1)°, V = 824.06(18), Z = 4. The structure consists of Am3+ cations bound by iodate anions to form [Am(IO3)8] units, where the local coordination environment around the americium centers is a distorted dodecahedron. There are three crystallographically unique iodate anions within the structure that bridge in both bidentate and tridentate fashions to form the overall three-dimensional structure. Repeated collection of X-ray diffraction data with time for a crystal of 243Am(IO3)3 revealed an anisotropic expansion of the unit cell, presumably from self-irradiation damage, to generate values of a = 7.2159(7) Å, b = 8.5847(8) Å, c = 13.5715(13) Å, β = 99.492(4)°, V = 829.18(23) after approximately five months. The Am(IO3)3 crystals have also been characterized by Raman spectroscopy and the spectral results compared to those for Cm(IO3)3. Three strong Raman bands were observed for both compounds and correspond to the I-O symmetric stretching of the three crystallographically distinct iodate anions. The Raman profile suggests a lack of interionic vibrational coupling of the I-O stretching, while intraionic coupling provides symmetric and asymmetric components that correspond to each iodate site. Photoluminescence data for both Am(IO3)3 and Cm(IO3)3 are reported here for the first time. Assignments for the electronic levels of the actinide cations were based on these photoluminescence measurements and indicate the presence of vibronic coupling between electronic transitions and IO 3- vibrational modes in both compounds. © 2005 American Chemical Society.