Inducing Reactivity by Cluster Strain in Titanium Frameworks

TL;DR

Researchers showed that distorting titanium clusters in a framework can boost their reactivity for CO2 conversion.

Contribution

A new strategy for inducing reactivity in titanium frameworks through cluster strain engineering is demonstrated.

Findings

Replacing Ca2+ with larger cations in MUV-10 causes predictable distortions in Ti2M2 clusters.

Cluster strain enhances charge transfer and generates Ti3+ sites, improving CO2 methanation.

The Goldschmidt tolerance factor explains the distortion trend in reticular frameworks.

Abstract

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.

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