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Water Vapor Single-Gas Selectivity via Flexibility of Three Potential Materials for Autonomous Indoor Humidity Control

: Tsobnang, P.K.; Hastürk, E.; Fröhlich, D.; Wenger, E.; Durand, P.; Ngolui, L.J.; Lecomte, C.; Janiak, C.


Crystal growth and design 19 (2019), No.5, pp.2869-2880
ISSN: 1528-7483
ISSN: 1528-7505
Journal Article
Fraunhofer ISE ()
Gebrauchsdaueranalyse und Materialcharakterisierung; Gebäudeenergietechnik; Energieeffiziente Gebäude; Lüftungs- und Klimatechnik

Two new isostructural porous supramolecular materials {[Cu2(amp)4Cl][M(C2O4)3]·6H2O}n (amp = 2-aminomethylpyridine), designated as II and III for M = Cr(III) and M = Fe(III) respectively, have been synthesized by a self-assembly process of two ionic complexes [Cu2(amp)4Cl]3+ and [M(C2O4)3]3–, M = Fe(III) and Cr(III). They build heterometallic hydrogen-bonded-, oxalato- and chlorido-bridged zigzag chains with interchain hydrogen bonds and π–π interactions. This results in supramolecular potentially porous architectures exhibiting large channels filled with hexameric water clusters. Their activated phases, II′ and III′, can readsorb the water molecules to regenerate the initial materials which are stable for many water adsorption and desorption cycles like that of their homologous catena-{[(Co(amp)3][Cr(C2O4)3]·6H2O} (I′). The three materials I′, II′, and III′ exhibit water adsorption and desorption isotherms having a sigmoidal shape and resulting in the combination of a type I(b) profile followed by an S-shaped type V isotherm with hysteresis. At 20 °C, the steep water sorption of the S-shaped isotherm occurs at 0.1P/P0 for II′ and III′. This water sorption behavior is quite different from the related compound I′, where a gate opening and closure process is involved, giving a type V isotherm with a pronounced H1-type hysteresis loop with parallel and steep adsorption (at 0.25P/P0) and desorption branches (at 0.17P/P0). The water adsorption capacities of the three materials I′, II′, and III′ are 17, 12, and 11 wt %, respectively. Temperature does not have a great effect on their water sorption properties, and they all exclude N2 and CO2 gases in the low pressure range. Compounds II′ and III′ are classified among the materials for which the dehumidification and the humidification trigger points are the same or too close (10% relative humidity (r.H.) in their case), while I′ shows a good potential to be used for automatic indoor control in the range of 15–25% r.H. recommended for many activities. All the differences observed in the water sorption properties of the three materials are related to (i) the type of water cluster which is built in each material, (ii) the strength of the hydrogen bonds within each water cluster and between the clusters and its host, and (iii) the strength of the intrahost interactions which keep the pores of the material closed.