1,1'-Dimethyl-4,4'-bipyridinium as a multivalent structure-directing counterion to anionic uranyl ion polycarboxylate complexes

Seven uranyl ion complexes with polycarboxylates have been synthesized under solvo-hydrothermal conditions and in the presence of 1,1'-dimethyl-4,4'-bipyridinium (Me2bipy2+) as structure -directing counterion. Two complexes were obtained with phthalate (pht2-), [Me2bipy]2[(UO2)4(pht)4(O)2] (1), which is a discrete, bis(mu 3- oxo-bridged) tetranuclear species, and {[Me2bipy][(UO2)3(pht)4(H2O)]}n (2), which crystallizes as a monoperiodic coordination polymer. The complex obtained with citric acid (H4cit), {[Me2bipy][UO2(Hcit)]2 & sdot;H2O}n (3), assumes a well-known monoperiodic form. {[Me2bipy][(UO2)2(Hthftc)2]}n (4), obtained from tetrahydrofurantetracarboxylic acid (H4thftc), is also a monoperiodic polymer further assembled into layers through hydrogen bonding, the packing defining channels containing columns of stacked counterions. The previously reported {[Me2bipy][(UO2)2(tdc)3]}n (5), where tdc2- is 2,5-thiophenedicarboxylate, is a diperiodic hcb network, with the counterions crossing the hexanuclear rings. One experiment with pimelate (pim2-) gave the two complexes {[Me2bipy][(UO2)2(pim)3]}n (6) and {[Me2bipy][(UO2)4(pim)5(DMA)2]}n (7) (DMA = N,N-dimethylacetamide). Both 6 and 7 are diperiodic assemblies, but while 6 has the KIa topology previously found in other uranyl ion complexes with elongated dicarboxylate ligands, 7 is a very intricate and thick assembly with a packing displaying interdigitation. The weak interactions formed by the counterions are discussed through examination of Hirshfeld surfaces.