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Isomerism in Benzenetricarboxylates: Variations in the Formation of Coordination Polymers with Uranyl Ion

Abstract : A series of uranyl ion complexes with fully or partially deprotonated 1,2,4-benzenetricarboxylic acid (H$_3$btc) and involving either organic countercations or additional metal cations has been synthesized under solvo-hydrothermal conditions. The complexes [PPh$_4$][UO$_2$(btc)] and [PPh$_4$]$_2$[(UO$_2$)2(Hbtc)$_3$]$\cdot$H$_2$O crystallize as monoperiodic coordination polymers, while [PPh$_3$Me][UO$_2$(btc)]$\cdot$H$_2$O is a diperiodic network with the fes topology. Monoperiodic organization is also found in [H$_2$DABCO][(UO$_2$)$_2$(btc)$_2$]$\cdot$2H$_2$O (DABCO = 1,4-diazabicyclo[2.2.2]octane), but [Hquin]$_2$[(UO$_2$)$_5$(btc)$_4$]$\cdot$2H$_2$O (5) (quin = quinuclidine) is a triperiodic framework. Incorporation of azamacrocyclic complexes of d-block metal cations gives [(UO$_2$)$_2$(btc)$_2$Ni(cyclam)] and [(UO$_2$)$_2$(btc)$_2$Cu(R,S-Me$_6$cyclam)] (cyclam = 1,4,8,11-tetraazacyclotetradecane, $R,S$-Me$_6$cyclam = 7($R$),14($S$)-5,5,7,12,12,14-hexamethylcyclam), two diperiodic networks with the same V$_2$O$_5$ topology, but differing in the diaxial bonding of the 3d metal cation, either to uranyl oxo groups or to carboxylato groups, respectively. Triperiodic polymerization occurs in [UO$_2$Ag$_2$(Hbtc)$_2$(H$_2$O)$_2$] and [(UO$_2$)$_2$Ag$_2$(btc)$_2$(CH$_3$CN)$_{1.5}$(H$_2$O)$_{0.43}$]$\cdot$ 1.5H$_2$O, with both oxo-and carboxylato-bonding of the bridging silver(I) cations. The isomorphous complexes [UO$_2$Rb(btc)(H$_2$O)] and [UO$_2$Cs(btc)(H$_2$O)] also crystallize as triperiodic frameworks with bonding of the alkali metal cations to oxo and carboxylato groups. In 10 and 11, uranyl cations and btc$^{3-}$ligands alone give a 2-fold interpenetrated triperiodic framework with utp topology. Emission spectra in the solid state display the usual vibronic fine structure for 1-5, 10 and 11, while uranyl emission is quenched in 7. Photoluminescence quantum yields range from 1.3 to 17.4%, less than that for solid UO$_2$(NO$_3$)$_2$$\cdot$6H$_2$O, except for 1 which has the unusually large value of 35%. Comparisons are drawn with previous studies of uranyl ion complexes of all known benzenetricarboxylate isomers.
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Submitted on : Monday, September 28, 2020 - 8:15:59 AM
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Pierre Thuery, Youssef Atoini, Jack Harrowfield. Isomerism in Benzenetricarboxylates: Variations in the Formation of Coordination Polymers with Uranyl Ion. Crystal Growth and Design, American Chemical Society, In press, ⟨10.1021/acs.cgd.0c01050⟩. ⟨cea-02950485⟩



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