A Series of Four-Connected Entangled Metal–Organic Frameworks Assembled from Pamoic Acid and Pyridine-Containing Ligands: Interpenetrating, Self-Penetrating, and Supramolecular Isomerism

Five novel compounds, {[Ni(PA)(bpe)(H2O)2]·DMF}n (1), {[Zn(PA)(bpe)]·DMF}n (2), {[Zn(PA)(bpe)]·2DMF·CH3OH}n (3), {[Cd2(PA)2(bpe)2(H2O)]·3.5H2O}n (4), {[Ni2(PA)2(bpp)2(H2O)3]·2DMF}n (5), based on pamoic acid (H2PA) (bpe = 1,2-bi(4-pyridyl)ethane, bpp = 1,3-bi(4-pyridyl)propane) have been synthesized. In such a system, both the PA2– anion ligand and dipyridyl ligands act as bipodal linkers, connecting the metal centers in square or tetrahedral geometries into 4-connected topologies with different entangled modes: 3-fold interpenetrating CdSO4 net (65.8) (1), roto-translational [2 + 2] interpenetrating diamond pseudosupramolecular isomers (2 and 3), 3-fold interpenetrating (6.74.8)(64.7.8) (4) and (6.85)(64.82) net with both 2-fold interpenetrating and self-penetrating characters (5), respectively. The formation of unique penetrating frameworks was investigated in detail. Gas adsorption and photoluminescent properties of the compounds have also been explored.