Structural transformation and hysteretic sorption of light hydrocarbons in a flexible Zn-pyrazole-adenine framework.

A three-dimensional metal-organic framework (MOF) was synthesized by combining 4-pyrazolecarboxylic acid and adenine. This MOF exhibits reversible flexibility and breathing adsorption behaviors in response to light hydrocarbons, with high capacity. The flexibility of the structural transitions was studied on the molecular scale by obtaining the crystal structures at 303, 353 and 373 K. The bridging nitrogen atoms of the pyrazolate rings act as a "kneecap" around the M⋅⋅⋅M axis, which causes the rotation of ligands around the M⋅⋅⋅M axis in response to external stimulus, thus giving rise to the deformation of the framework structure.