Translocation and Confinement of Tetraamines in Adaptable Microporous Cavities

Metal-Organic Frameworks can be grafted with amines by coordination to metal vacancies to create amine-appended solid adsorbents, which are being considered as an alternative to using aqueous amine solutions for CO2 capture. In this study, we propose an alternative mechanism that does not rely on the use of neutral metal vacancies as binding sites but is enabled by the structural adaptability of heterobimetallic Ti2Ca2 clusters. The combination of hard (Ti4+) and soft (Ca2+) metal centers in the inorganic nodes of the framework enables MUV-10 to adapt its pore windows to the presence of triethylenetetramine molecules. This dynamic cluster response facilitates the translocation and binding of tetraamine inside the microporous cavities to enable the formation of bis-coordinate adducts that are stable in water. The extension of this grafting concept from MUV-10 to larger cavities not restrictive to CO2 diffusion will complement other strategies available for the design of molecular sorbents for decarbonization applications. We introduce an alternative to the use of open metal vacancies in the design of amine-appended adsorbents based on the use of secondary building units combining of hard and soft metal sites. This endows MUV-10 with a flexible response to the uptake of tetraamines that facilitates their translocation into the microporous cavities of the framework to form stable bis-coordinate adducts that can remain stable in water. image