Rapid, Ambient Temperature Synthesis of Imine Covalent Organic Frameworks Catalyzed by Transition-Metal Nitrates

Abstract

Covalent\norganic frameworks (COFs) are crystalline, porous organic\nmaterials that are promising for applications including catalysis,\nenergy storage, electronics, gas storage, water treatment, and drug\ndelivery. Conventional solvothermal synthesis approaches require elevated\ntemperatures, inert environments, and long reaction times. Herein,\nwe show that transition-metal nitrates can catalyze the rapid synthesis\nof imine COFs under ambient conditions. We first tested a series of\ntransition metals for the synthesis of a model COF and found that\nall transition-metal nitrates tested produced crystalline COF products\neven in the presence of oxygen. Fe­(NO₃)₃·9H₂O was found to produce the most crystalline product, and crystalline\nCOFs could be produced within 10 min by optimizing the catalyst loading.\nFe­(NO₃)₃·9H₂O was further tested\nas a catalyst for six different COF targets varying in linker lengths,\nsubstituents, and stabilities, and it effectively catalyzed the synthesis\nof all imine COFs tested. This catalyst was also successful in the\nsynthesis of 2D imine COFs with different geometries, 3D COFs, and\nazine-linked COFs. This work demonstrates a simple, low-cost approach\nfor the synthesis of imine COFs and will significantly lower the barrier\nfor the development of imine COFs for applications.