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

Abstract

A flexible Mn-based MOF, Mn-sdc-1, has been successfully synthesized by using the ligand 4,4'-stilbenedicarboxylic acid (H 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 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 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 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 sensor in aqueous solution through the luminescence quenching effect with a limit of detection of 31.4 nm.

Controlled dye release from a metal–organic framework: a new luminescent sensor for water

“…The structural and physical nature of the two Mn-MOFs has been reported before, 30 hence, a brief structural depiction of the MOFs is presented. Mn-sdc-1, formulated as Mn 3 (sdc) 3 (H 2 O) 2 ·DMF, belongs to the trigonal space group R 3̄, each sdc 2− ligand coordinates with two trinuclear Mn 3 (RCOO) 6 secondary building units (SBUs) extending the hexagonal structure to form a two-dimensional layer.…”

“…This suggests that the dye R6G has been encapsulated into the MOFs. Besides it is interesting to notice that the transformation temperature for obtaining pure Mn-sdc-2 starts at 100 C, 30 but for R6G@Mn-sdc-2, the temperature decreased to 60 C (Fig. S5 †), which indicates that the dye R6G signicantly promotes the transformation process.…”

“…Herein, based on solvent-triggered reversible phase change MOFs that have been reported earlier by our group, 30 we synthesized these two flexible MOFs, namely, Mn-sdc-1 and Mn-sdc-2 (H 2 sdc = 4,4′-stilbenedicarboxylic acid), separately. Mn-sdc-2 has large 1D channels along the c axis while Mn-sdc-1 has relatively smaller pores.…”

Coordination Polymers Based on Highly Emissive Ligands: Synthesis and Functional Properties

“…The water-stable MOF [Mn(sdc)(H 2 O) 2 ] n was employed as a luminescent sensor for Pb 2+ ions in water, with the detection limit of 31.4 nM. The luminescence quenching was explained by binding between Pb 2+ ions and the framework, confirmed by XPS [100].…”

“…Huang et al studied the reversible phase transitions in two manganese based coordination polymers [100]. By adjusting the temperature and water content in the solvent mixture it was possible to selectively isolate [Mn 3 (sdc) 3 (H 2 O) 2 ] n and [Mn(sdc)(H 2 O) 2 ] n .…”