Modulation of the Dynamics of a Two-Dimensional Interweaving Metal–Organic Framework through Induced Hydrogen Bonding

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.


S2. Single-crystal X-ray diffraction
Crystallographic data for TMU-27-op, TMU-27-cp and TMU-27-NH2-act were collected at 100K on the XALOC beamline at ALBA synchrotron (l = 0.82653 Å). 1 Data from TMU-27-op were indexed, integrated, and scaled using the XDS 2 and iMOSFLM 3 programs, whereas TMU-27cp and TMU-27-NH2-act data were indexed, integrated, and scaled using the Xia2 package. 4bsorption correction was not applied.Single-Crystal X-Ray Diffraction (SC-XRD) for TMU-27-NH2 was collected at 293 K on a Bruker AXS SMART Apex diffractometer, using graphite monochromated Mo-Ka radiation (l = 0.71073 Å), and were corrected for Lorentz and polarisation effects.The frames were integrated with the Bruker SAINT 5 software package.Absorption corrections were applied using the program SADABS 6 , giving max./min.transmission factors of 1.000/0.4760.The structures were solved by direct methods and subsequently refined by correction of F 2 against all reflections, using SHELXS2013 7 and SHELXL2013 8 within the WinGX package (for TMU-27-NH2 and TMU-27 op) 9 and Olex2 package (for TMU-27-cp and TMU-27-NH 2-act) 10 All non-hydrogen atoms were refined with anisotropic thermal parameters by full-matrix least-squares calculations on F 2 , using the program SHELXL2013.Hydrogen atoms were inserted at calculated positions and constrained with isotropic thermal parameters, except for the hydrogen atoms of the NH and NH2 groups in TMU-27-NH2 and TMU-27-NH2-act, which were located from the difference Fourier map.In TMU-27-NH2, the oxygen atom of the carbonyl group is distorted in two positions, at 70% and 30% occupancy.The contributions of two DMF molecules in TMU-27-NH2 (302 electrons per unit cell) to the diffraction pattern could not be rigorously included in the model and thus, were consequently removed with the SQUEEZE routine of PLATON.

S3. Powder X-ray diffraction
Figure S4.Experimental PXRD pattern for as-synthesised TMU-27-NH2 (top, blue) and its corresponding simulated PXRD pattern (purple, bottom).The additional peak at 8.943º (identified with the asterisk) corresponds to DMF molecules trapped inside the framework that is not present in the simulated pattern as the structure was squeezed during the refinement.

S7. Unit Cells comparison
For comparison, the unit cell of Open-Pore (OP) phase TMU-27 was transformed into a triclinic lattice.For valid crystallographic information, the Single Crystal X-Ray Diffraction data for these materials can be found in Table S1.
Table S2.Comparison of the unit cell parameters of TMU-27 in Open-Pore (OP) phase and Closed-Pore (CP) phase.

Figure S2 .
Figure S2.(a) Ortep diagram depicting the coordination motif between the metal node and the ligands.The ellipsoids are drawn at the 50% probability level.Hydrogen atoms are omitted and only the coordination environment of Zn(II) has been labelled for the sake of clarity.(b) Single layer.(c) Interwoven layers of TMU-27 and TMU-27-NH2 and (d) underlying sql topology, where Zn(II) is highlighted in green.
Powder X-Ray Diffraction patterns for the simulated Open-Pore (OP) phase of TMU-27 (bottom, black), as-synthesised TMU-27 (second to bottom, light grey), activated Closed-Pore (CP) phase of TMU-27 (second to top, orange), and after immersion of the activated crystal in DMF for 2 h (top, red).