Fixing CO2 under Atmospheric Conditions and Dual Functional Heterogeneous Catalysis Employing Cu MOFs: Polymorphism, Single-Crystal-to-Single-Crystal (SCSC) Transformation and Magnetic Studies

New copper compounds, [Cu(C₁₄H₈O₆)(C₁₀H₈N₂)(H₂O)] (1), [Cu(C₁₄H₈O₆)(C₁₀H₈N₂)(H₂O)]·(C₃H₇ON)₂ (2), [Cu(C₁₄H₈O₆)(C₁₀H₈N₂)(H₂O)₂]·(C₃H₇ON) (3), [Cu(C₁₄H₈O₆)(C₁₀H₈N₄)] (4), and [Cu(C₁₄H₈O₆)(C₁₀H₈N₄)]·(H₂O) (5), were prepared employing 2,5-bis(prop-2-yn-1-yloxy)terephthalic acid (2,5-BPTA) as the primary ligand and 4,4'-bipyridine (1-3) and 4,4'-azopyridine (4-5) as the secondary ligands. Single-crystal studies indicated that compounds 1-4 have two-dimensional layer structures and compound 5 has a three-dimensional structure. Compounds 1-3 were isolated from the same reaction mixture but by varying the time of reaction. The framework structures of compounds 1-3 are similar and may be considered as polymorphic structures. Compounds 4 and 5 can also be considered polymorphic with a change in dimensionality of the structure. Compounds 1-3 can be formed through a single-crystal-to-single-crystal transformation under a suitable solvent mixture. The Cu center was explored for the Lewis acid-catalyzed cycloaddition reaction of epoxide and CO₂ under ambient conditions in a solventless condition and also for the synthesis of propargylamine derivatives by three-component coupling reactions (A³ coupling) in a DCM medium. The Lewis basic functionality of the MOF (-N═N- group) has been explored for the Henry reaction (aldol condensation) in a solventless condition. In all of the catalytic reactions, good yields and recyclability were observed. The magnetic studies indicated that compounds 1 and 4 have antiferromagnetic interactions and compound 5 has ferromagnetic interactions. The present studies illustrated the rich diversity that the copper-containing compounds exhibit in extended framework structures.