Hydrothermal syntheses, structures, and fluorescence spectroscopy of new one-dimensional uranium oxyfluorides built from edge-sharing [UO2F5] pentagonal bipyramids

Three new one-dimensional uranium oxyfluorides, (C5H14N2) U2O4F6 (AU1-3), (C5H6N)UO2F3 (AU1-4), and (C3H5N2) UO2F3 (AU1-5), have been prepared from the reactions of UO3 with HF and homopiperazine (C5H12N2), pyridine, or pyrazole at 180 degreesC in aqueous media. In all cases, the compounds were isolated in high yield in the form of large single crystals. Single crystal X-ray diffraction, elemental analysis, and fluorescence spectroscopy have been used to characterize these compounds. Each structure contains linear one-dimensional chains formed from edge-sharing [UO2F5] pentagonal bipyramids with substantial hydrogen-bonding occurring between the protonated organic cations and the anionic chains. AU1-4 and AU1-5 luminesce brightly when irradiated with 365 nm UV light, while emission is considerably weaker from AU1-3. An energy transfer mechanism between the pyridinium and pyrazolium cations and the UO22+ groups in AU1-4 and AU1-5, respectively, is proposed to account for some of these differences. Crystallographic data: AU1-3, triclinic, space group P (1) over bar, a = 7.328(2) Angstrom, b = 9.488(3) Angstrom, c = 11.106(4) Angstrom, alpha = 94.65(3)degrees, beta = 106.47(3)degrees, gamma = 107.79(2)degrees, Z = 2, MoK alpha, lambda = 0.71073, R(F) = 5.02% for 173 parameters with 1977 reflections with O>2 sigma (1); AU1-4, orthorhombic, space group Imma, a = 6.793(2) Angstrom, b = 7.232(2) Angstrom, c = 17.094(7) Angstrom, Z = 4, MoK alpha, lambda = 0.71073, R(F) = 3.14% for 44 parameters with 412 reflections with I>2 sigma (I); AU1-5, monoclinic C2/m, a = 17.011(7) Angstrom, b = 6.708(3) Angstrom, c = 7.213(2) Angstrom, beta = 113.31(3)degrees, Z = 4, MoK alpha, lambda = 0.71073, R(F)= 3.76% for 65 parameters with 664 reflections with O>2 sigma (I). (C) 2000 Academic Press.