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

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. Although the uses of uranium in the nuclear industry are well known, the element has a remarkably varied chemistry, exploited, for example, in photooxidation catalysis for the destruction of environmental pollutants. To this end, it is desirable to have compounds in the highest oxidation state of uranium, +VI, 'uranyl' complexes, that are luminescent and insoluble but porous, ideally containing cavities that generate selectivity with regard to absorbed species. Coordination polymers continue to be developed as materials that may provide such properties. (Image credit: Pierre Thuéry.) [ABSTRACT FROM AUTHOR]