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

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 pi (*)-pi (*)stacking interactions to form a 3D (3,4,6)-connected supramolecular architecture with the Schafli symbol of (4(4)center dot 6(2))(4(4)center dot 6(6)center dot 8(5))(6(3))(2). Complex 2 crystallizes in a noncentrosymmetric space group P2(1) 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 (P (r)) of ca. 0.09 mu C 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 (P (s)) of 0.22 mu C cm(-2). Furthermore, permittivity property measurements reveal a dielectric constant (epsilon (r)) 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.