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 [Ln(2)(C6H8O4)(3)(H2O)(2)] Ln(III) = Pr-Eu (except Pm) (Type I, compounds 1-4) and [Ln(2)(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 P (1) over bar, whereas compounds 5-9 belong to the tetragonal space group P(4)2(1)2. Type I and II compounds are 3D frameworks consisting of chains of [LnO(8)(H2O)] or [LnO(8)] polyhedra, respectively, linked by dimethylsuccinate anions, giving rise to (IO2)-O-1 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.