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]·0.5DMF·H₂O (<b>1</b>; 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 <b>1</b> 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 <b>1</b>, and the sensing event was operating repeatedly. The three-dimensional framework of <b>1</b> with 3-fold interpenetration is uniquely converted to the two-dimensional Cu phase with no interpenetration, reflecting a drastic dimensionality variation