# 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.

## Key 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.