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 <b>1</b>–<b>4</b>) and [Ln₂­(C₆H₈­O₄)₃] Ln­(III) = Tb–Yb (except Tm) (Type II, compounds <b>5</b>–<b>9</b>). The crystal structure has been solved for the Pr (<b>1</b>)-, Sm (<b>3</b>)-, and Ho (<b>7</b>)-containing compounds by means of single-crystal XRD methods, whereas powder XRD Rietveld refinement was used for the rest of the MOFs. Compounds <b>1</b>–<b>4</b> crystallize in the triclinic space group <i>P</i>1̅, whereas compounds <b>5</b>–<b>9</b> belong to the tetragonal space group <i>P</i>4₃2₁2. 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 <b>3</b>, <b>4</b>, and <b>5</b> have been also explored, indicating that a metal-centered luminescent process takes place