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, H4L, incorporating the (S)-(+)-2-methylpiperazine
moiety in its middle, solvothermally forms
a homochiral Cu­(II) framework, {[Cu2(L)­(H2O)2]·(4DMF)­(4H2O)}n (LCu). It forms a non-interpenetrated
structure consisting of [Cu2(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 (Ec) of ∼12 kV cm–1 with a distinct
electric hysteresis loop. Dielectric studies of LCu reveal
almost frequency-independent behavior with a dielectric constant (εr) of ∼42 and a low dielectric loss (tan δ) of
∼0.04 up to 106 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.