Reversible Structural Flexibility and Sensing Properties of a Zn(II) Metal-Organic Framework: Phase Transformation between Interpenetrating 3D Net and 2D Sheet

A three-dimensional Zn(II) framework, [Zn4O(L)(3)(DMF)(2)]center dot 0.5DMF center dot H2O (1; H2L = 3,3'-dimethoxybiphenyl-4,4'-dicarboxylic acid) was prepared under a solvothermal reaction in DMF. The structure reveals that the 3-fold interpenetration is stabilized in the framework with a distinct secondary building unit of the formula [Zn4O(R-CO2)(6)(DMF)(2)], slightly different from that of MOF-5. Phase transformations in 1 occur reversibly via two pathways of solvent exchange/resolvation and activation/resolvation, which is indicative of the presence of extensive structural flexibility. Nitrobenzene among tested solvents is selectively detected by 1, and the sensing event was operating repeatedly. The three-dimensional framework of 1 with 3-fold interpenetration is uniquely converted to the two-dimensional Cu phase with no interpenetration, reflecting a drastic dimensionality variation.