Homochiral BINAPO-Based Metal–Organic Frameworks for Luminescence Sensing of Phenylglycinol Enantiomers

Chiral metal–organic frameworks (CMOFs) with luminescent properties are promising enantioselective sensors for important chiral molecules. Herein, we report the synthesis and characterization of four CMOFs, Cu-L, Zn-L, Cd-L, and Mn-L, based on the BINAP oxide (BINAPO) ligand R-2,2′-Bis(diphenylphosphoryl)-1,(1′-binaphthyl)-4,4′-bis(4-carboxyphenyl) (H2L). In the isostructural Cu-L and Zn-L MOFs, the metal cations coordinate with carboxylate groups and solvent molecules to form paddle-wheel shaped secondary building units (SBUs). These SBUs are further connected by the ligands as 4-connected nodes, resulting in square lattice (sql) networks. The metal centers in Cd-L and Mn-L coordinate with phosphine oxides and carboxylates, with each Mn cation additionally coordinating to one aqua molecule. The resulting frameworks adopt 2D and 3D networks of fes and qtz-h topologies, respectively. At a ligand concentration of 28 μM, the fluorescence of an H2L solution in acetonitrile was quenched by R-phenylglycinol (R-PG) and S-PG, with Stern–Völmer constants (Ksv) of 69.6 ± 1.0 and 34.2 ± 0.5 M–1, respectively. At the same ligand concentration, a Zn-L suspension in acetonitrile exhibited slightly lower quenching efficiencies, with Ksv values of 16.2 ± 0.3 M–1 for R-PG and 27.5 ± 0.4 M–1 for S-PG. In tetrahydrofuran, Zn-L was quenched by R-PG and S-PG with Ksv values of 44.5 ± 0.7 and 21.7 ± 0.4 M–1, respectively, and H2L exhibited lower quenching efficiencies. The reversed enantioselectivity observed in Zn-L in acetonitrile, compared to H2L, suggests the presence of distinct chiral recognition sites, potentially influenced by solvent effects on the coordinated BINAPO ligand within the MOF.