Supramolecular Metal–Organic Frameworks of s- and f‑Block Metals: Impact of 1,8-Naphthalimide Functional Group

The new ligand 5-(1,8-naphthalimido)­isophthalate (L 135 2– ), containing two carboxylate donor groups and the 1,8-naphthalimide supramolecular tecton, has been used under solvothermal conditions to prepare a series of group 2, lanthanide, and actinide metal complexes: [Ca4(L 135 )4­(H2O)8]­·(H2O)9.5­(DMF)2.6 (1), Ba­(L 135 )­(H2O)1.5­(DMF)0.5 (2), La2(L 135 )3­(DMF)4 (3), Ce2(L 135 )3­(DMF)4 (4), Eu2(L 135 )3­(DMF)4 (5), Tb2(L 135 )3­(DMF)4 (6), [UO2(L 135 )­(DMF)]­·(py)0.5­(EtOH)0.5 (7), and Th­(L 135 )­(NO3)2­(DMF)2]­·(DMF)2 (8). The solid state structure of the calcium complex 1 is based on helical rod-shaped secondary building-units (SBUs) of edge-shared polyhedra bridged by oxygen atoms from the carboxylate groups. The crystals are racemic, with the one-dimensional (1D) helical rods organized by π···π stacking interactions of the naphthalimide group into a three-dimensional (3D) supramolecular metal-organic framework (SMOF) structure. Although the structure of the barium complex 2 also contains rod-shaped SBUs, the rods are linked through the aryl backbone of the ditopic L 135 2– ligands into two-dimensional (2D) sheets. The sheets are further engaged in naphthalimide π···π stacking interactions to build a 3D SMOF. The lanthanide­(III) complexes 3–6 are isostructural, based on binuclear SBUs linked through the ligands into a square-shaped, 2D grid pattern, with π-stacking interactions linking adjacent sheets to generate a 3D SMOF. The uranium­(VI) complex 7 contains 7-coordinate pentagonal bipyramidal uranyl cations bridged through the ligands into 1D ribbons. The solid state structure of the thorium­(IV) complex 8 consists of 10-coordinate thorium cations, also bridged through the ligands into 1D ribbons. Both of these actinide structures are organized into 2D supramolecular sheets by π-stacking interactions. Compounds 1, 2, 3, 6, and 8 exhibit solid-state luminescence dominated by the naphthalimide chromophore in the ligand. The group 2 complexes are slightly red-shifted, and the lanthanum complex 3 and the thorium complex 8 are slightly blue-shifted with respect to the ligand. The terbium compound, 6, is greatly blue-shifted by ∼75 nm, and naphthalimide sensitization of the metal emission occurs for the europium complex 5. The cerium­(III) and uranyl­(VI) compounds 4 and 7 have no solid state emission.