Rare Earth pcu Metal–Organic Framework Platform Based on RE4(μ3-OH)4(COO)62+ Clusters: Rational Design, Directed Synthesis, and Deliberate Tuning of Excitation Wavelengths

The T d point group symmetry of rare earth (RE 3+ ) metal clusters RE 4 (μ 3 -OH) 4 (COO) 6 2+ makes them attractive building blocks for creating metal–organic frameworks (MOFs) with controllable topologies. Herein, we describe the design and synthesis of a series of isoreticular MOFs featuring pcu topology [ MOF-1114(RE) and MOF-1115(RE) ] with variable rare earth metal ions (RE 3+ = Y 3+, Sm 3+, Eu 3+, Gd 3+, Tb 3+, Dy 3+, Ho 3+, Er 3+, Tm 3+, Yb 3+ ) and linear amino-functionalized dicarboxylate linkers of different lengths. In total, we report 22 MOFs that vary in both composition and structure yet share the same RE 4 (μ 3 -OH) 4 cluster motif. We demonstrate that these pcu MOFs are cationic and that anion exchange can be used to affect the MOF properties. We also investigate the luminescence properties of a representative member of this MOF series [ MOF-1114(Yb) ] that exhibits near-infrared emission. We show that the excitation energy for Yb 3+ sensitization can be carefully adjusted to lower energy via covalent postsynthetic modification at the amino group sites within the MOF.