Crystal structures, magnetic, dielectric and ferroelectric properties of two copper(II) complexes with m-nitrobenzoic acid

Abstract

Reactions of CuCl2, m-nitrobenzoic acid (HNBA) and NaOH with 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) in aqueous ethanol afforded two Cu(II) complexes Cu(bpy)(NBA)2, 1, and [Cu(phen)(H2O)2(NBA)](NBA), 2. The monomolecular Cu(bpy)(NBA)2 moieties are both bridged by hydrogen bonding interactions and interlayer π*–π*stacking interactions to form a 3D (3,4,6)-connected supramolecular architecture with the Schafli symbol of (44·62)(44·66·85)(63)2. Complex 2 crystallizes in a noncentrosymmetric space group P21 where all molecules show the same orientation along the polar b axis. Preliminary investigations suggest that 2 exhibits ferroelectric hysteresis loops at room temperature with remanent polarization (Pr) of ca. 0.09 μC cm−2 and coercive electric fields of 2.53 kV cm−1, respectively. It may be a potential ferroelectric with a relatively large spontaneous polarization (Ps) of 0.22 μC cm−2. Furthermore, permittivity property measurements reveal a dielectric constant (er) of 6.36. Variable-temperature (2–300 K) magnetic susceptibility measurements showed the presence of weak ferromagnetic interactions between the Cu(II) ions for both 1 and 2.