Inducing Reactivity by Cluster Strain in Titanium Frameworks

Despite their potential to control charge separation and redox activity, deliberate strategies to distort metal-oxo clusters in molecular frameworks remain limited. Here we present a proof-of-concept for cluster strain engineering using the titanium-organic framework MUV-10 as a model. Replacing Ca²⁺ with larger alkaline-earth cations (Sr²⁺, Ba²⁺) induces predictable distortions of Ti₂M₂ clusters and a cubic-to-tetragonal cell transformation while preserving the overall connectivity. This local strain alters Ti-O coordination geometry, enhances ligand-to-metal charge transfer, and promotes the photogeneration of Ti³⁺ sites, as validated by photocatalytic CO₂ methanation under standardized conditions. Importantly, the extent of distortion follows the trend anticipated from the Goldschmidt tolerance factor, a classical descriptor from perovskite chemistry, that we repurpose here to rationalize strain in reticular frameworks. Taken together, these findings establish a conceptual link between oxide catalysis and reticular chemistry, highlighting cluster strain as a potential structural switch to modulate redox reactivity in molecular solids.