A non-porous Fe(II) complex for the colorimetric detection of hazardous gases and the monitoring of meat freshness

From a mononuclear FeIIL2 complex to a spin crossover FeII4L6 cage by symmetric ligand architecture modification: insights into the ammonia gas sensing mechanism

“…2), suggesting a high thermal stability compared to the reported Fe II -based sensors with coordinated H 2 O molecules (around 470 K). [26][27][28][29][30] No solvent loss was observed, which matches well with CHN results and single crystal XRD analysis. The FT-IR spectrum of 1 shows a typical stretching of pyridyl-imine groups at 1584 cm À1 , while the peaks near 1056 and 1014 cm À1 are attributed to the vibration of BF 4…”

“…Thus, the sensing mechanism of 1 was ascribed to partial substitution of L1 by the analyte NH 3(g) leading to a spin state conversion and partial oxidation from Fe II to Fe III ions. This suggests that the FeN 4 O 2 coordination mode provided by the multidentate ligand L1, instead of classic water molecules, [26][27][28][29][30] can also undergo substitution by NH 3(g) molecules, due to the small radius and electronegativity of the nitrogen atom compared to the oxygen atom. In order to obtain a crystal structure after NH 3(g) adsorption, we tried to perform sensing experiments with single crystals of 1, but without success owing to crystals fragmentation.…”

“…4d). We also attempted to complete the desorption process with a dilute hydrochloric acid solution, which has been reported to regenerate Fe II sensors, 26,27 but 1@NH 3 dissolved directly.…”

“…25 Recently, our group developed three Fe II mononuclear complexes (Scheme 1), which were able to colorimetric detect various toxic volatile chemicals under ambient conditions, but with a slow response to NH 3(g) due to non-porosity. [26][27][28][29][30] The discoloration mechanism is ascribed to the substitution of coordinated water by guest NH 3(g) molecules leading to a change in the Fe II spin state from complete HS to a mixed HS/LS situation. [26][27][28][29][30] Notably, insight into the structural changes of the sensor from the perspective of the sensing mechanism and thus its cyclability could provide ideas for designing NH 3(g) sensors with different applications, for example as an element of a disposable colorimetric sensor array (structural irreversibility) or as a commercial sensor for longterm use (structural reversibility).…”

“…[26][27][28][29][30] The discoloration mechanism is ascribed to the substitution of coordinated water by guest NH 3(g) molecules leading to a change in the Fe II spin state from complete HS to a mixed HS/LS situation. [26][27][28][29][30] Notably, insight into the structural changes of the sensor from the perspective of the sensing mechanism and thus its cyclability could provide ideas for designing NH 3(g) sensors with different applications, for example as an element of a disposable colorimetric sensor array (structural irreversibility) or as a commercial sensor for longterm use (structural reversibility). In addition, as an applicable solid state gas sensor material, good permeability is crucial, since it determines the response time and reversibility.…”