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 th e reactions of UO3 with HF and homopiperazine (C5H12N2), pyridine, or pyraz ole at 180 degreesC in aqueous media. In all cases, the compounds were isol ated in high yield in the form of large single crystals. Single crystal X-r ay diffraction, elemental analysis, and fluorescence spectroscopy have been used to characterize these compounds. Each structure contains linear one-d imensional chains formed from edge-sharing [UO2F5] pentagonal bipyramids wi th substantial hydrogen-bonding occurring between the protonated organic ca tions and the anionic chains. AU1-4 and AU1-5 luminesce brightly when irrad iated with 365 nm UV light, while emission is considerably weaker from AU1- 3. An energy transfer mechanism between the pyridinium and pyrazolium catio ns and the UO22+ groups in AU1-4 and AU1-5, respectively, is proposed to ac count for some of these differences. Crystallographic data: AU1-3, triclini c, 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, orthor hombic, 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 4 4 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, be ta = 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 Pr ess.