Mild Periodic Acid Flux and Hydrothermal Methods for the Synthesis of Crystalline f-Element-Bearing Iodate Compounds

f-element-bearing iodate compounds are a large family mostly synthesized by hydrothermal reactions starting with actinide/lanthanide ions and iodic acid or iodate salt. In this work, we introduce melting periodic acid flux as a new reaction medium and provide a safe way for single-crystal growth of a series of new f-element iodate compounds including UO2(IO3)(2)center dot H2O (1), UO2(IO3),(H2O)center dot HIO3 (2), alpha-Th(IO3)(2)(NO3)(OH) (3), beta-Th(IO3)(2)(NO3)(OH) (4), and (H3O)(9)Nd-9(IO3)(36)center dot 3HIO(3) (5). The structures of these compounds deviate from those afforded from hydrothermal reactions. Specifically, compounds 1 and 2 exhibit pillared structures consisting of uranyl pentagonal bipyramids and iodate trigonal pyramids. Compounds 3 and 4 represent two new thorium iodate compounds that are constructed from subunits of thorium dimers. Compound 5 exhibits a flower shaped trivalent lanthanide iodate structure with HIO3 molecules and H3O+ cations filled in the channels. The aliovalent replacement off elements in 5 is available from a hydrothermal process, further generating compounds of Th-2(IO3)(8)(H2O) (6) and Ce-2(IO3)(8)(H2O) (7). The distinct absorption features are observed in isotypic compounds 5-7, where 7 shows typical semiconductor behavior with a band gap of 2.43 eV. Remarkably, noncentrosymmetric 1, 6, and 7 exhibit strong second-harmonic-generation efficiencies of 1.3, 3.2, and 9.2 times, respectively, that of the commercial material KH2PO4. Additionally, the temperature-dependent emission spectra of 1 and 2 were also collected showing typical emission features of uranyl units and a negative correlation between the intensities of the emissions with temperature. Clearly, the presented low-temperature melting inorganic acid flux synthesis would provide a facile and effective strategy to produce a large new family of structurally versatile and multifunctional f-element inorganic compounds.