Framework Flexibility and Hysteretic Adsorption

An interesting feature of adsorption on MOFs is that some materials have framework flexibility and structural change may occur during the 

Structural change without bond breaking occurs with a scissoring motion leading to an increase in crystallographic cell volume of ethanol and methanol templated phases E and M of Ni2(bpy)3.(N03)4 during adsorption of the templates. Hysteretic adsorption was observed 

Llewellyn et al. have developed the MIL series of MOFs where the changes in structure during adsorption are much larger. Thermodynamic and structural studies of nanoporous metal benzenedicarboxylate, M(0H)(02CCgH4C02), MIL-53(Cr) suggest that a minimum hydrocarbon adsorption enthalpy of 20 kj moH in the initial large pore structure is required to induce the structural transition to narrow pore structure. MIL-53(A1) exhibits a reversible structural transition 

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