Solvent-Effected Coordination Variation of Flexible Ligands to Cu(II) for the Formation of 1D and 2D Secondary Building Units for Metal–Organic Frameworks

Producing more than one structure from the same set of metal and ligand precursors will grant structural diversity in metal–organic framework (MOF) systems. One of the biggest obstacles of getting structural diversity for the late transition metals is that the coordination mode is pretty much fixed by nature. Herein, we show that two different coordination modes to Cu­(II) are possible for flexible ligands containing hydrophilic terminal groups through solvent guidance. It is demonstrated that trans,trans-muconic acid (H₂muco) ligands coordinate to Cu­(II) to form Cu­(II) muconate MOFs having a 1D chain structure and a 2D plane structure in water-rich and DMF-rich water–DMF mixed solvent systems, respectively. It is suggested that the interaction between ligands and solvent is responsible for the selective coordination. A similar result was observed from the attempts using the fumaric acid ligand. Our results provide a new direction to obtain diverse secondary building units for the construction of diverse MOFs.