Compositional dependence of anomalous thermal expansion in perovskite-like ABX3 formates

TL;DR

This study investigates how the thermal expansion behavior of 19 perovskite-like MOFs varies with composition, revealing that cation sizes and anisotropy influence the magnitude and direction of framework flexibility.

Contribution

It provides a systematic analysis of compositional effects on thermal expansion in metal-organic frameworks, highlighting the roles of cation radii and molecular shape.

Findings

Thermal expansion magnitude depends on A and M cation sizes.

Flexibility is maximized with large M and small A cations.

AI shape influences the direction of framework hingeing.

Abstract

The compositional dependence of thermal expansion behaviour in 19 different perovskite-like metal-organic frameworks (MOFs) of composition [AI][MII(HCOO)3] (A = alkylammonium cation; M = octahedrally-coordinated divalent metal) is studied using variable-temperature X-ray powder diffraction measurements. While all systems show essentially the same type of thermomechanical response-irrespective of their particular structural details-the magnitude of this response is shown to be a function of AI and MII cation radii, as well as the molecular anisotropy of AI. Flexibility is maximised for large MII and small AI, while the shape of AI has implications for the direction of framework hingeing.