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

2,5-Thiophenedicarboxylic acid (H₂tdc) has been reacted with uranyl nitrate hexahydrate under solvo-hydrothermal conditions with N,N-dimethylacetamide (dma) as an organic cosolvent, giving the complex [UO₂(tdc)(dma)] (1), isomorphous to the previously reported [UO₂(tdc)(nmp)] (nmp = N-methyl-2-pyrrolidone). With tdc²⁻ adopting the bis(μ₂-κ¹O:κ¹O’)-bridging coordination mode, complex 1 crystallizes as a triperiodic framework with the point symbol {4².8⁴}. With acetonitrile as an organic cosolvent and in the presence of [Ni(PPh₃)₂Br₂], triphenylphosphine oxide is formed in situ and it binds to uranyl to give [UO₂(tdc)(OPPh₃)] (2). Complex 2 is also a triperiodic framework, with the point symbol {4.10²}₂{4².10⁴} and the dmd topological type with uranium as 3-coordinated (3-c) nodes and tdc²⁻ as either a 4-c node in its bis(μ₂-κ¹O:κ¹O’)-bridging mode, or a simple edge in the bis(κ²O,O’)-chelating mode. In both 1 and 2, as in the previously described nmp complex, but not in [UO₂(tdc)(dmf)] (dmf = N,N-dimethylformamide), coordination of a unidentate ligand disrupts the most common formation of diperiodic networks with tdc²⁻ 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 O₅ equatorial uranyl environment; the “hot band” observed at room temperature disappears at 77 K.