Robust Barium Phosphonate Metal–Organic Frameworks Synthesized under Aqueous Conditions

Abstract

The design and discovery of three-dimensional crystalline metal–organic frameworks (MOFs) from linkers with phosphonate coordinating groups and even alkaline earth metals is largely undeveloped. Herein, we report a strategy for realizing new, stable, and robust barium phosphonate MOFs, termed Empa-1 and Empa-2. The two-dimensional (2D) Empa-1 or three-dimensional (3D) Empa-2 could be realized by way of systematically modulating the ratio of Ba2+ with a tetratopic phosphonate-based linker that was crafted to incorporate nitrogen-rich triazine units bridged by a fixed piperazine core. In addition to this synthetic approach, temperature-dependent synchrotron-radiation powder X-ray diffraction analysis demonstrated that the 2D Empa-1 undergoes an irreversible phase transition upon heating and subsequent dehydration to form the 3D Empa-2. Given the presence of uncoordinated phosphonic acid moieties within the structure of 3D Empa-2, the CO2 sorption capabilities are reported. We believe our ability to link the alkaline earth metal barium with a novel tetratopic phosphonate linker, as evidenced by the robust structures of Empa-1 and -2, paves the way for further exploration and discovery of new crystalline, porous frameworks with greater structural diversity, stability, and wide-scale practical applicability.

Elucidating phase transformation of Eu-based metal organic framework with intermediate isolation and theoretical calculations

“…25–27 Because the functions of MOFs highly depend on their crystalline phases, understanding conditions that drive phase transformation in MOFs represents an alternative rational approach to modulate the properties of MOFs without changing the chemical constituents. 28–32…”

“…[25][26][27] Because the functions of MOFs highly depend on their crystalline phases, understanding conditions that drive phase transformation in MOFs represents an alternative rational approach to modulate the properties of MOFs without changing the chemical constituents. [28][29][30][31][32] In recent years, studies on MOF phase transformation have been growing and spark off more follow-up investigations on how to control this process. [33][34][35] The phase transformation of MOFs may take place under the action of external stimuli (e.g., temperature, pressure, and irradiation) by one parameter or interplay between them.…”