  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.
