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Functionalized Aromatic Dicarboxylate Ligands in Uranyl–Organic Assemblies: The Cases of Carboxycinnamate and 1,2-/1,3-Phenylenedioxydiacetate

Pierre Thuéry 1, * Youssef Atoini 2 Jack Harrowfield 2
* Corresponding author
1 LCMCE - Laboratoire de Chimie Moléculaire et de Catalyse pour l'Energie (ex LCCEF)
NIMBE UMR 3685 - Nanosciences et Innovation pour les Matériaux, la Biomédecine et l'Energie (ex SIS2M)
Abstract : 2-Carboxycinnamic acid (ccnH$_2$) and the isomeric 1,2-and 1,3-phenylenedioxydiacetic acids (1,2-and 1,3-pddaH$_2$) have been used to synthesize eight uranyl ion complexes under solvo-hydrothermal conditions. In the four complexes [PPh$_4$]$_2$[UO$_2$(ccn)(NO$_3$)]$_2$, [PPh$_4$]$_2$[UO$_2$(ccn)(dibf)]$_2$ , [UO$_2$(ccn)(bipy)]$_2$, and [Ni(R,S-Me$_6$cyclam)][UO$_2$(ccn)(HCOO)]$_2$ , the ccn$^{2-}$ dianion retains a nearly planar geometry, which favors the formation of the centrosymmetric [UO2(ccn)]2 dimeric unit. Additional terminal ligands, either neutral (bipy = 2,2ʹ-bipyridine) or anionic (nitrate, dibf-= 1,3-dihydro-3-oxo-1-isobenzofuranacetate, and formate, the two latter formed in situ) complete the uranyl coordination sphere, leading in all cases to discrete, dinuclear species. Sodium(I) bonding to the carboxylate/ether O$_4$ site of the 1,2-pdda$^{2-}$ dianion in the two complexes [UO$_2$Na(1,2-pdda)(OH)] and [(UO$_2$)$_2$Na$_2$(1,2-pdda)$_2$(C2O$_4$)] results in this ligand being planar. Further lateral coordination to uranyl and sodium bonding to a uranyl oxo group allow formation of heterometallic diperiodic networks containing monoperiodic uranyl-only subunits. In the absence of Na$^+$ cations, 1,2-pdda$^{2-}$ adopts a conformation in which one carboxylate group is tilted out of the ligand plane in [UO$_2$(1,2-pdda)$_2$Ni(cyclam)], and diaxial carboxylato bonding to nickel(II) unites uranyl-only monoperiodic subunits into a diperiodic network. The 1,3-pdda$^{2-}$ ligand in [UO$_2$(1,3-pdda)(H$_2$O)] is also non-planar with one tilted carboxylate group, and the bridging bidentate nature of both carboxylate groups allows formation of a triperiodic framework in which both metal and ligand are four-coordinated nodes. While the emission spectra of complexes 1 and 5 display the vibronic progression considered typical of uranyl ion, those of complexes 2, 4 and 8 show broad emission bands which in the case of complex 4 completely replace the uranyl emissions and which appear to be ligand-centred. The low energy of these broad bands can be rationalized in terms of the close association of certain ligand pairs within the structures.
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Pierre Thuéry, Youssef Atoini, Jack Harrowfield. Functionalized Aromatic Dicarboxylate Ligands in Uranyl–Organic Assemblies: The Cases of Carboxycinnamate and 1,2-/1,3-Phenylenedioxydiacetate. Inorganic Chemistry, American Chemical Society, In press, 59, pp.2923-2936. ⟨10.1021/acs.inorgchem.9b03273⟩. ⟨cea-02485715⟩

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