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.

Keywords:

• syntheses
• crystal structure
• topology
• magnetic properties
• ferroelectric properties
• solvent influence

Funding

This project was supported by the Open Foundation from Application of nonlinear Science and Technology in the Most Important Subject of Zhejiang (Grant No. xkzl2006). The honest thanks are also extended to K. C. Wong Magna Fund in Ningbo University.