Triperiodic frameworks in the uranyl–2,5-thiophenedicarboxylate system: Effect of unidentate auxiliary ligands

Two triperiodic frameworks are formed when 2,5-thiophenedicarboxylate complexes the uranyl ion in the presence of N,N -dimethylacetamide or triphenylphosphine oxide as unidentate coligands. Both assemblies display channels accommodating the latter coligands. 2,5-Thiophenedicarboxylic acid (H 2 tdc) has been reacted with uranyl nitrate hexahydrate under solvo-hydrothermal conditions with N,N -dimethylacetamide (dma) as an organic cosolvent, giving the complex [UO 2 (tdc)(dma)] ( 1 ), isomorphous to the previously reported [UO 2 (tdc)(nmp)] (nmp = N -methyl-2-pyrrolidone). With tdc 2− adopting the bis(μ 2 -κ 1 O :κ 1 O’ )-bridging coordination mode, complex 1 crystallizes as a triperiodic framework with the point symbol {4 2 .8 4 }. With acetonitrile as an organic cosolvent and in the presence of [Ni(PPh 3 ) 2 Br 2 ], triphenylphosphine oxide is formed in situ and it binds to uranyl to give [UO 2 (tdc)(OPPh 3 )] ( 2 ). Complex 2 is also a triperiodic framework, with the point symbol {4.10 2 } 2 {4 2 .10 4 } and the dmd topological type with uranium as 3-coordinated (3-c) nodes and tdc 2− as either a 4-c node in its bis(μ 2 -κ 1 O :κ 1 O’ )-bridging mode, or a simple edge in the bis(κ 2 O , O’ )-chelating mode. In both 1 and 2 , as in the previously described nmp complex, but not in [UO 2 (tdc)(dmf)] (dmf = N,N -dimethylformamide), coordination of a unidentate ligand disrupts the most common formation of diperiodic networks with tdc 2− and tris-chelated uranyl, and promotes formation of frameworks in which channels accommodate the pendant, unidentate ligands. Complex 2 has a photoluminescence quantum yield of 3 % in the solid state, and its emission spectrum displays the typical vibronic progression with peak positions in the range usual for complexes with an O 5 equatorial uranyl environment; the “hot band” observed at room temperature disappears at 77 K.