Three Acentric Cu(II) D-(–)-quinate Complexes: Solvent-Dependent Assemblies, Magnetic and Ferroelectric Properties

Abstract

Reaction of copper salts and D-(–)-quinic acid (H5L) yielded three complexes, [Cu(H2O)(H3L)]2·2H2O 1, [Cu(H2O)(H4L)(NO3)]n·(H2O)n 2, and [Cu(H2O)(H4L)(ClO4)]n·(2H2O)n 3. An interesting law was observed that solvent selection influenced the structural assemblies, namely, in an aqueous solution utilizing CuCl2·2H2O/Cu(NO3)2·6H2O/Cu(ClO4)2·6H2O and D-(–)-quinic acid only obtained [Cu(H2O)(H3L)]2·2H2O 1, while the environment was replaced by an alcoholic system, afforded three polymers: [Cu(H2O)(H4L)Cl]n·(H2O)n 4, [Cu(H2O)(H4L)(NO3)]n·(H2O)n 2, and [Cu(H2O)(H4L)(ClO4)]n·(2H2O)n 3, respectively. Complex 1 crystallizes in the polar monoclinic C2 space group, while complexes 2 and 3 in the nonpolar orthorhombic space group P212121. In compound 1, the binuclear Cu(II) units are assembled into 3D network through hydrogen bonds and the overall topology can be described as a 7-connected dinodal net topology of (36·48·57) with the Schläfli symbol of (3.3.3.3.3.3.4.4.4.4.4.4.4.4.5.5.5.5.52.52.52). In 2 and 3, the D-(–)-quinic acid anions are function as tetradentate ligands bridging Cu(II) ions to build up 3D metal-organic frameworks (MOFs) with {103} topological representation. The polar complex 1 displays a promising ferroelectricity with a remnant polarization (Pr) of ca. 0.07 μC/cm2, coercive field (Ec) of ca. 2.43 kV/cm, and saturation of the spontaneous polarization (Ps) of ca. 0.128 μC/cm2. The magnetic behavior of 1 suggests significant antiferromagnetic coupling interactions between Cu(II) ions bridged by carboxylic groups, while considerable ferromagnetic coupling interactions in complexes 2 and 3. Furthermore, the title complexes 1–3 were subjected to microelement analyses, IR spectroscopic measurements, and thermal analyses.