Two Sets of Metal Organic Frameworks along the Lanthanide Series Constructed by 2,3-Dimethylsuccinate: Structures, Topologies, and Strong Emission without Ligand Sensitization

Reactions in aqueous solution under hydrothermal conditions between (±)-2,3-dimethylsuccinic acid and lanthanide chlorides lead to two different isostructural types with chemical formulas [Ln2­(C6H8­O4)3­(H2O)2] Ln­(III) = Pr–Eu (except Pm) (Type I, compounds 1–4) and [Ln2­(C6H8­O4)3] Ln­(III) = Tb–Yb (except Tm) (Type II, compounds 5–9). The crystal structure has been solved for the Pr (1)-, Sm (3)-, and Ho (7)-containing compounds by means of single-crystal XRD methods, whereas powder XRD Rietveld refinement was used for the rest of the MOFs. Compounds 1–4 crystallize in the triclinic space group P1̅, whereas compounds 5–9 belong to the tetragonal space group P43212. Type I and II compounds are 3D frameworks consisting of chains of [LnO8­(H2O)] or [LnO8] polyhedra, respectively, linked by dimethylsuccinate anions, giving rise to I1O2 connectivity. All the compounds were characterized by X-ray diffraction, variable-temperature Fourier transform infrared spectroscopy, and thermal analysis. An exhaustive topological study was performed in comparison with other related compounds. The photoluminescent (PL) properties for compounds 3, 4, and 5 have been also explored, indicating that a metal-centered luminescent process takes place.