From a mononuclear FeIIL2 complex to a spin crossover FeII4L6 cage by symmetric ligand architecture modification: insights into the ammonia gas sensing mechanism
(2023) Journal of Materials Chemistry C — Vol. 11, n° 11, p. 11175-11184 (2023)
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- Abstract
- The occurrence of spin crossover usually induces different outputs, one of which is the colour change, an essential parameter for a colorimetric sensor. Herein, by symmetric modification of the ligand architecture, two complexes: a FeII(L1)2 mononuclear high-spin (HS) complex (1) and a FeII4(L2)6 tetranuclear spin crossover cage (2) were constructed as colorimetric NH3(g) sensors, operating in the solid state. The sensing process is accompanied by a remarkable colour change from reddish brown (1) or light purple (2) to dark grey at room temperature. 2 presents a shorter response time (90 s) to NH3(g) compared to 1 (8 min) due to its empty cage structure, as revealed by single crystals X-ray diffraction, and large specific surface area increasing the adsorption rate of NH3(g). 57Fe Mössbauer spectroscopy was employed to investigate the sensing mechanism around the metal centre. A conversion of 33% FeII ions to the low-spin (LS) state was observed in 1@NH3, after the substitution of NH3(g) molecules, leading to FeN6 sites. The sensing mechanism of 2 also involves a HS to LS transition of FeII ions induced with a new FeN6 centre, but non-coordinated BF4− anions also react with NH4+ to form NH4BF4. These findings provide a foundation for exploring FeII-based coordination complexes as potential NH3 gas sensors towards high nuclearity as well as tuneable porosity.
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Li, W., Rotaru, A., Wolff, M., Demeshko, S., Meyer, F., & Garcia, Y. (2023). From a mononuclear FeIIL2 complex to a spin crossover FeII4L6 cage by symmetric ligand architecture modification: insights into the ammonia gas sensing mechanism. Journal of Materials Chemistry C, 11(11), 11175-11184. https://doi.org/10.1039/D3TC02231E (Original work published 2023)