Synthesis, crystal-structure refinement and properties of bastnaesite-type PrF[CO3], SmF[CO3] and EuF[CO3]

By adding a hot aqueous solution containing KF and K2[CO3] to another hot aquatic brine of Pr[NO3]3 ⋅ 5 H2O, Sm[NO3]3 ⋅ 5 H2O or Eu[NO3]3 ⋅ 5 H2O with a 1.3 times excess of the anion-providing solution, amorphous water-insoluble powders of PrF[CO3], SmF[CO3] and EuF[CO3] can be obtained. Through hydrothermal treatment at 210 °C for five days crystalline powders could be synthesized and their crystal structure was refined with Rietveld methods based on PXRD data. The named compounds crystallize in the bastnaesite-type structure with a = 710.912(12) pm, c = 976.811(6) pm for the praseodymium, a = 704.77(2) pm, c = 971.83(4) pm for the samarium and a = 700.734(6) pm, c = 969.066(8) pm for the europium compound, all hexagonal with Z = 6. Upon heating them, the compounds lose CO2 and fluoride oxides REFO emerge. Thermogravimetric experiments with crystalline samples show thermal stability up to 420 °C for PrF[CO3], 400 °C for SmF[CO3] and 340 °C for EuF[CO3], but decomposition below 200 °C for the amorphous ones. Infrared spectroscopy confirms only marginal portions of [OH]− instead of F− anions in all cases. The RE 3+ cations are coordinated by 9 + 2 anions at distances between 236 and 254 pm plus 326 pm to F− anions and oxygen atoms bonded to carbon as oxocarbonate anions [CO3]2−. Triggered by ultraviolet radiation, the bulk sample of EuF[CO3] shows a poor red luminescence.

Synthesis, Crystal Structure and Fluorescence Property of Terbium Coordination Polymers with Pyridine-3.5-Dicarboxylic Acid

Rare-earth metal-organic frameworks [Tb2(pdc)3(H2O)9]n3nH2O, were synthesized and characterized by elemental analysis, IR spectra and single-crystal X-ray diffraction. The title compound consisted of one-dimensional dual-chains, in which each metal atom is nine-coordinated with oxygen atoms. The carboxylate groups of pdc provided two kinds of coordination ways as bidentate and monodentate. The solid-state photoluminescence measurement exhibited green light-emitting characteristic of terbium (III) coordination polymer, and the fluorescence intensities were stronger than that of the europium compound with the same ligand.