posted on 2012-09-05, 00:00authored byIonut Mihalcea, Natacha Henry, Till Bousquet, Christophe Volkringer, Thierry Loiseau
Four uranyl-organic framework-type compounds have been
hydrothermally
synthesized with different ditopic aromatic dicarboxylates. The use
of 1,4-benzenedicarboxylate (noted 1,4-bdc), 4,4′-biphenyldicarboxylate
(noted 4,4′-bpdc), 4,4′-azobenzenedicarboxylate (noted
4,4′-adc), and 1,3-benzenedicarboxylate (noted 1,3-bdc) gave
rise to the crystallization of a series of phases UO2(L)
(L = 1,4-bdc (1), 4,4′-bpdc (2),
4,4′-adc (3), or 1,3-bdc (4)), which
exhibited 6-fold coordinated uranyl centers as monomeric square bipyramidal
unit. The crystal structures showed that the para position of the
carboxylate groups favored the formation of layered extended assemblies
in 1–3, whereas the meta isomer isophthalate
induced the formation of a three-dimensional framework. In situ X-ray
diffraction of the thermal behavior indicated the decomposition of
the different networks in the range 360–420 °C, successively
followed by the crystallization of the uranium oxide U3O8.