Synthesis of a NbO Type Homochiral Cu(II) Metal–Organic Framework: Ferroelectric Behavior and Heterogeneous Catalysis of Three-Component Coupling and Pechmann Reactions

A chiral tetracarboxylic acid ligand, H 4 L, incorporating the ( S )-(+)-2-methylpiperazine moiety in its middle, solvothermally forms a homochiral Cu(II) framework, {[Cu 2 ( L )(H 2 O) 2 ]·(4DMF)(4H 2 O)} n ( LCu ). It forms a non-interpenetrated structure consisting of [Cu 2 (COO) 4 ] paddle-wheel secondary bonding units (SBUs) with NbO topology. Interestingly, the framework LCu exhibits excellent ferroelectric properties. It shows a remnant polarization (Pr) of ∼3.5 μC cm –2 and a coercive field ( E c ) of ∼12 kV cm –1 with a distinct electric hysteresis loop. Dielectric studies of LCu reveal almost frequency-independent behavior with a dielectric constant (ε r ) of ∼42 and a low dielectric loss (tan δ) of ∼0.04 up to 10 6 Hz, for potential use in high-frequency applications. In addition, activated framework LCu′ having uncoordinated metal sites acts as an efficient heterogeneous catalyst in the three-component coupling of amines, aldehydes, and alkynes, as well as in Pechmann reactions of phenols with β-ketoesters.