Integrating Compositional and Structural Diversity in Heterometallic Titanium Frameworks by Metal Exchange Methods.

Abstract

The increasing use of Metal-Organic Frameworks (MOFs) in separation, catalysis or storage is linked to the targeted modification of their composition or porosity metrics. While modification of pore shape and size necessarily implies the assembly of alternative nets, compositional changes often rely on post-synthetic modification adapted to the functionalisation or exchange of the organic linker, or the modification of the inorganic cluster by metal exchange methods. We describe an alternative methodology that enables the integration of both types of modification, structural and compositional, in titanium MOFs by metal exchange reaction of the heterometallic cluster Ti2 Ca2 . A systematic analysis of this reactivity with MUV-10 is used to understand which experimental variables are crucial to enable replacement of calcium only, or to integrate metal exchange with structural transformation. The isoreticular expanded framework MUV-30, is next used to template the formation of MUV-301, a titanium framework not accessible by direct synthesis that displays the largest mesoporous cages reported to date. Given that the interest of Ti MOFs in photoredox applications often meets the limitations imposed by the challenges of titanium solution chemistry to design concrete candidates, this soft strategy based on pre-assembled frameworks will help integrating specific combinations of metals into high porosity architectures.