New Reticular Chemistry of the Rod Secondary Building Unit: Synthesis, Structure, and Natural Gas Storage of a Series of Three-Way Rod Amide-Functionalized Metal-Organic Frameworks

摘要

Reticular chemistry and methane storage materials have been predominately focused on finite metal-cluster-based metal-organic frameworks (MOFs). In contrast, MOFs constructed from infinite rod secondary building units (SBUs), i.e., rod MOFs, are less developed, and the existing ones are typically built from simple one-way helical, zigzag, or (mixed)polyhedron SBUs. Herein, inspired by a recent unveiled structure of Zn_6(H_2O)_3(BTP)_4 and by means of an amide-functionalized preliminary single tricarboxylate, a subsequent mixed tricarboxylate, and dicarboxylate linkers, an intricate three-way rod MOF and the next three isoreticular three-way rod MOFs have been successfully realized, namely, 3W-ROD-1 and 3W-ROD-2-X (X = -OH, -F, and -CH_3), respectively. The structural analyses disclosed that the four compounds were constructed from unprecedented three-way invariant nonintersecting trigonal rod-packing SBUs cross-linked via the noncovalent-interaction-driven self-assembly of pseudo hexacarboxylates with the original tricarboxylate or different functional ditopic linkers, resulting in cage-like pore geometries accessible via ultramicroporous apertures concomitant with the complex topology transitivity, namely, 18 42 and 18 44. Sorption studies show that the apparent surface areas of these materials are among the most highly porous materials for rod MOFs. Due to the presence of favorable pocket sites created by X, ketone, and proximal amide groups as revealed by Monte Carlo molecular dynamics (MCMD) computational calculations, the MOFs exhibit impressive methane storage working capacities, outperforming the well-known rod Ni-MOF-74 and representing the highest values among rigid rod MOFs.