Temperature-Induced Structural Transformations Accompanied by Changes in Magnetic Properties of Two Copper Coordination Polymers

The self-assembled reactions of 5-aminodiacetic isophthalic acid (H4adip) ligands and Cu2+ ions under different temperatures to produce two one-dimensional (1D) coordination polymers (CPs), {[Cu(H2adip)(H2O)]•5H2O}n (1) and [Cu2(adip)(H2O)3]n (2). The structures and chemical compositions of both CPs were characterized by using single-crystal X-ray diffraction and other methods. Structural analyses revealed that CP 1 crystallized in the monoclinic C2/c space group, and two crystallographically independent Cu2+ ions were interconnected by H4adip ligands to give a 1D zigzag chain. Whereas CP 2 belonged to the triclinic P-1 space group, two types of Cu2+ ions were linked through carboxylate groups to generate the dinuclear units, which were bridged by H4adip ligands to give a 1D double chain. Moreover, the adjacent chains in both 1 and 2 could be further stacked to present the 3D supramolecular architectures through hydrogen bonds. Interestingly, the block crystal 1 can undergo structural transformation to form the sheet crystal 2 when heated and held 1 at 80˚C for 12 h, which represents the rare example of structural transformations resulting from the coordination modes of organic ligands triggered by temperature. Both CPs 1 and 2 exhibited ferromagnetic coupling interactions between Cu2+ ions, and the magnetic results also supported the presence of structural transformation processes.