posted on 2024-03-14, 22:14authored byPilar Fernández-Seriñán, Kornel Roztocki, Vahid Safarifard, Vincent Guillerm, Sabina Rodríguez-Hermida, Judith Juanhuix, Inhar Imaz, Ali Morsali, Daniel Maspoch
Inducing, understanding, and controlling the flexibility
in metal–organic
frameworks (MOFs) are of utmost interest due to the potential applications
of dynamic materials in gas-related technologies. Herein, we report
the synthesis of two isostructural two-dimensional (2D) interweaving
zinc(II) MOFs, TMU-27 [Zn(bpipa)(bdc)] and TMU-27-NH2 [Zn(bpipa)(NH2-bdc)], based on N,N′-bis-4-pyridyl-isophthalamide
(bpipa) and 1,4-benzenedicarboxylate (bdc) or 2-amino-1,4-benzenedicarboxylate
(NH2-bdc), respectively. These frameworks differ only by
the substitution at the meta-position of their respective bdc groups:
an H atom in TMU-27 vs an NH2 group in TMU-27-NH2. This difference strongly influences their respective responses
to external stimuli, since we observed that the structure of TMU-27
changed due to desolvation and adsorption, whereas TMU-27-NH2 remained rigid. Using single-crystal X-ray diffraction and CO2-sorption measurements, we discovered that upon CO2 sorption, TMU-27 undergoes a transition from a closed-pore phase
to an open-pore phase. In contrast, we attributed the rigidification
in TMU-27-NH2 to intermolecular hydrogen bonding between
interweaving layers, namely, between the H atoms from the bdc-amino
groups and the O atoms from the bpipa-amide groups within these layers.
Additionally, by using scanning electron microscopy to monitor the
CO2 adsorption and desorption in TMU-27, we were able to
establish a correlation between the crystal size of this MOF and its
transformation pressure.