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)·H2O (7; e-urea = ethyleneurea), [Nd2(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).