(Benzene-1,2,4,5-tetrayl)tetrakis(3-(1-carboxylatomethylpyridinium)), a novel uranyl-complexing tetrazwitterion

Abstract

The tetrazwitterionic, tetracarboxylate (benzene-1,2,4,5-tetrayl)tetrakis(3-(1-carboxylatomethylpyridinium)) (L) has been synthesized and used as a ligand in mixed-ligand complexes of the uranyl cation involving anionic carboxylates. {[(UO2)2(tdc)2(L)]·2H2O}n (1), where tdc2– is 2,5-thiophenedicarboxylate, crystallizes as a monoperiodic, ladder-like coordination polymer in which two UO2(tdc) rows are bridged by L ligands with monodentate carboxylate groups. {[(UO2)2(OH)4(L)]·2H2O}n (2) is a diperiodic polymer in which the dinuclear (UO2)2(OH)22+ units are the nodes of a square lattice (sql) network and L being bound by its four monodentate carboxylate groups. The positional isomer (benzene-1,2,4,5-tetrayl)tetrakis(4-(1-carboxylatomethylpyridinium)) (L′) undergoes decarboxylation during synthesis under solvo-hydrothermal conditions, giving tetracationic (benzene-1,2,4,5-tetrayl)tetra{4-(N-methylpyridinium)} (btp4+) included as a counterion in [btp][(UO2)4(O)2(pht)4]·1.5H2O (3), where pht2– is phthalate. The discrete, tetranuclear complexes in 3 are of the usual form with two μ3-oxo bridges and rows of alternating anions and cations linked through π–π interactions arranged into layers.