Solvent‐Triggered Reversible Phase Changes in Two Manganese‐Based Metal–Organic Frameworks and Associated Sensing Events

A flexible Mn‐based MOF, Mn‐sdc‐1, has been successfully synthesized by using the ligand 4,4′‐stilbenedicarboxylic acid (H 2 sdc). Attributed to the flexibility of the framework, Mn‐sdc‐1 can transform into a new phase (Mn‐sdc‐2) with completely different structural geometry; this is induced by trace levels of H 2 O at room temperature. Reversibly, the transformation from Mn‐sdc‐2 to Mn‐sdc‐1 can be triggered by DMF upon heating beyond 100 °C. These results inspired a study of the influences of temperature and H 2 O volume in the solid‐state transformation of two MOF phases and, for the first time, a phase diagram of MOFs has been depicted. This phase diagram reflects the gradual H 2 O‐/temperature‐dependent changes between Mn‐sdc‐1 and Mn‐sdc‐2, which is very meaningful in achieving the controllable synthesis of these two MOFs and lead to targeting the desired water‐stable structure. As a result, the obtained water‐stable Mn‐sdc‐2 can be developed as an excellent Pb 2+ sensor in aqueous solution through the luminescence quenching effect with a limit of detection of 31.4 n m .