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

A series of uranyl ion complexes with fully or partially deprotonated 1,2,4-benzenetricarboxylic acid (H₃btc) and involving either organic countercations or additional metal cations has been synthesized under solvo-hydrothermal conditions. The complexes [PPh₄]­[UO₂(btc)] (1) and [PPh₄]₂[(UO₂)₂(Hbtc)₃]·H₂O (2) crystallize as monoperiodic coordination polymers, while [PPh₃Me]­[UO₂(btc)]·H₂O (3) is a diperiodic network with fes topology. Monoperiodic organization is also found in [H₂DABCO]­[(UO₂)₂(btc)₂]·2H₂O (4) (DABCO = 1,4-diazabicyclo[2.2.2]­octane), but [Hquin]₂[(UO₂)₅(btc)₄]·2H₂O (5) (quin = quinuclidine) is a triperiodic framework. Incorporation of azamacrocyclic complexes of d-block metal cations gives [(UO₂)₂(btc)₂Ni­(cyclam)] (6) and [(UO₂)₂(btc)₂Cu­(R,S-Me₆cyclam)] (7) (cyclam = 1,4,8,11-tetraazacyclotetradecane, R,S-Me₆cyclam = 7­(R),14­(S)-5,5,7,12,12,14-hexamethylcyclam), two diperiodic networks with the same V₂O₅ 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 [UO₂Ag₂(Hbtc)₂(H₂O)₂] (8) and [(UO₂)₂Ag₂(btc)₂(CH₃CN)_1.5(H₂O)_0.43]· 1.5H₂O (9), with both oxo and carboxylato bonding of the bridging silver­(I) cations. The isomorphous complexes [UO₂Rb­(btc)­(H₂O)] (10) and [UO₂Cs­(btc)­(H₂O)] (11) 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 UO₂(NO₃)₂·6H₂O, 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.