Temperature-induced structural transformations accompanied by changes in magnetic properties of two copper coordination polymers

Abstract

The self-assembly reactions of 5-aminodiacetic isophthalic acid (H₄adip) ligands and Cu²⁺ ions at different temperatures to produce two one-dimensional (1D) coordination polymers (CPs), {[Cu(H₂adip)(H₂O)]·5H₂O}_n (1) and [Cu₂(adip)(H₂O)₃]_n (2) are reported. 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. However, CP 2 belonged to the triclinic P- space group, and two types of Cu²⁺ ions were linked through carboxylate groups to generate 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 form 3D supramolecular architectures through hydrogen bonds. Interestingly, the block crystal 1 can undergo structural transformation to form the sheet crystal 2 when 1 was heated and kept at 80 °C for 12 h, which represents a rare example of structural transformation 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.