Single-crystal-to-single-crystal (SCSC) transformation and dissolution–recrystallization structural transformation (DRST) among three new copper(II) coordination polymers

In this work, water- and temperature-induced single-crystal-to-single-crystal (SCSC) transformation and dissolution–recrystallization structural transformation (DRST) are observed among three new copper(II) coordination polymers, {[Cu5(μ3-OH)2(MIPA)4(4,4′-bpy)2]·2H2O}n (1), {[Cu(H2O)2(MIPA)(4,4′-bpy)0.5]·H2O}n (2) and {[Cu2(H2O)2(MIPA)2(4,4′-bpy)(μ2-H2O)]·3H2O}n (3) (MIPA = 4-methoxyisophthalic acid, 4,4′-bpy = 4,4′-bipyridine). The 3D framework of 1 experienced an intensive DRST process to form the 1D intermediate of 2, followed by a unique SCSC process to transform it into the 2D network of 3. Nevertheless, compound 3 can be obtained from compound 1 directly via another DRST. That is to say, a DRST process could be achieved by the combination of another DRST process and an SCSC process. To the best of our knowledge, this type of study is still scarce. And it provides a convenient strategy to investigate the mechanism of crystal transformation and construct advanced crystalline materials. Results have been characterized by single crystal X-ray diffraction and powder X-ray diffraction (PXRD). Significant structural alterations were observed and these changes could be analyzed from the properties of center Cu(II) ions and the switch of chelating-bridging modes of MIPA. Magnetic susceptibility measurements indicate that 1 and 3 exhibit antiferromagnetic interaction between adjacent Cu(II) centers. Additionally, complexes 1–3 have been characterized by thermogravimetric analysis and infrared and PXRD studies.