Counterion-Controlled Formation of an Octanuclear Uranyl Cage with cis-1,2-Cyclohexanedicarboxylate Ligands
Abstract
$cis$-1,2-Cyclohexanedicarboxylic acid ($c$-chdcH$_2$) was reacted with uranyl nitrate under (solvo-)hydrothermal conditions in the presence of different possible counterions. Two neutral complexes of 1:1 stoichiometry were obtained, [UO$_2$(c-chdc)(DMF)] (1) and [UO$_2$($c$-chdc)(H$_2$O)] (2), which crystallize as two-dimensional coordination polymers and do not include the additional cations present in solution.
In contrast, the complex [NH$_4$][PPh$_4$][(UO$_2$)$_8$($c$-chdc) $_9$(H$_2$O)$_6$]·3H$_2$O (3) crystallized in the presence of PPh$_4$Br, ammonium cations being generated $in\ situ$ from acetonitrile hydrolysis. This complex of 8:9 uranium:ligand stoichiometry contains an octanuclear anionic cage of $D_3$ symmetry with a pseudo-cubic arrangement of uranium atoms. The ammonium cation is held within the cage through four hydrogen bonds with uranyl oxo groups directed inwards. This cage complex is luminescent, although with a low quantum yield of 0.06, indicating some potential as a photo-oxidant of included species.
Origin : Files produced by the author(s)
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