3D Zinc–Organic
Frameworks Based on Mixed Thiophene
Dicarboxylate and 4‑Amino-3,5-bis(4-pyridyl)-1,2,4-triazole
Linkers: Syntheses, Structural Diversity, and Single-Crystal-to-Single-Crystal
Transformations
posted on 2023-12-27, 00:03authored byShreya Mahajan, Manu Lahtinen
In this study, for
the first time two new interpenetrated
3D pillared-layer
metal–organic frameworks (MOFs), namely, {[Zn(bpt)(tdc)]·dmf}n (MOF-1-Zn) and {[Zn2(bpt)(tdc)2]·2(dmf)}n (MOF-2-Zn), as well as a homochiral 3D framework {[Zn(bpt)(tdc)(H2O)]·dmf}n (MOF-3-Zn), were prepared under different synthesis conditions (bpt = 4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole,
H2tdc = 2,5-thiophenedicarboxylic acid, and dmf = N,N′-dimethylformamide). Synthesis
products were thoroughly characterized by single-crystal and powder
X-ray diffraction and thermoanalytical methods. Remarkably, in the
case of MOF-2-Zn, dmf molecules in the voids can be exchanged
for different solvents, e.g., chloroform, methanol, ethanol, isopropyl
alcohol, acetonitrile, acetone, tetrahydrofuran, 1,4-dioxane, and
cyclohexane in a single-crystal-to-single-crystal (SCSC) manner. With
different solvent types, the bpt ligands adapted slightly different
conformations by adjusting the orientation of the NH2-triazole
core unit and the tilting of the pyridyl groups. In comparison, most
changes for planar tdc ligands were observed on the dihedral angles
of the adjacent thiophene rings (e.g., 69.5 vs 78.5° for MOF-2-Zn and 2-CHCl3, respectively). Desolvation
of the MOF illustrated systematic structural adaptability of {Zn2}-“paddlewheel” in SCSC fashion, and the MOF’s
crystallinity and 3D networked structure were preserved even after
vacuum and heat-assisted desolvation. Finally, preliminary CO2 adsorption tests for MOFs were conducted utilizing a custom-built
fixed-bed adsorption/desorption device, resulting in about 0.1 mmolCO2/gsorbent at 400–4000 ppmv
CO2 and about 1 mmolCO2/gsorbent at 15 vol % CO2.