Lanthanide-thiophene-2,5-dicarboxylate frameworks: ionothermal synthesis, helical structures, photoluminescent properties, and single-crystal-to-single-crystal guest exchange.

Eight three-dimensional lanthanide-thiophene-2,5-dicarboxylate frameworks, [Ln(TDC)(2)]·(choline) (1-6; Ln = Gd, Nd, Eu, Er, Tb, Dy; TDC = thiophene-2,5-dicarboxylate), [Yb(TDC)(2)(e-urea)]·(choline)·H(2)O (7; e-urea = ethyleneurea), [Nd(2)(TDC)(3)(e-urea)(4)]·3(e-urea) (8) have been successfully prepared in deep eutectic solvents (choline chloride/e-urea), respectively. Compounds 1-7 are anionic frameworks with 8-connected bcu topology, while compound 8 features a neutral 6-connected rob-type framework with guest e-urea molecules. In these structures, lanthanide ions show dicapped trigonal prism, pentagonal bipyramid, and tricapped trigonal prism coordination configurations, respectively, and the TDC ligands exhibit different coordination modes. Versatile helical substructures are presented in these compounds. The photoluminescent properties of compounds 3 (Eu) and 8 (Nd) were studied. Moreover, compound 8 can perform single-crystal-to-single-crystal guest exchange. The ethanol-exchange mechanism of 8 can be ascribed to the kinetically controlled flexibility (KCF).