A comparative study of the structural, electrochemical and magnetic properties of Copper(II)-squarate coordination frameworks

Abstract

Three new copper(II)–squarate coordination polymers, 1-D double-chain {Cu(C₄O₄)(H₂O)₂(DMF)}_n (1) ( = dianion of 3,4-dihydroxy-3-cyclobuten-1,2-dione), 3-D network {[Cu(C₄O₄)(H₂O)₂]·0.33H₂O}_n (2), and 3-D network {[Cu(C₄O₄)(H₂O)₂]·0.33CH₃OH}_n (3), have been synthesized and characterized structurally. The complexes show altered assembly behavior in different solvent systems, which can further affect the physical properties of the frameworks. Cyclic voltammetry experiments show that 1, 2, and 3 have rich redox activities and both Cu(II) ions and squaric acid ligands are involved in redox process. Magnetic characterization on 3 shows the effect of weak antiferromagnetic exchange.

Perspective view of the 3-D cage-like network of {[Cu(C₄O₄)(H₂O)₂]·0.33H₂O}_n (2). View of voids in the framework with van der Waals spheres (mean diameters 1.5 nm) inside.

Keywords:

• Squaric acid
• Copper
• Crystal structure
• Redox properties
• Magnetism

Additional information

Funding

This work was supported by the National Science Foundation of China [grant number 21301194]; the Recruitment Program of Global Youth Experts, and Research Fund for the Doctoral Program of Higher Education of China [grant number 20130162120031].