Deconstructing and Rationalizing Interpenetration in Pillar-Layered Metal–Organic Frameworks

Structural interpenetration, a prevalent phenomenon in crystalline networks assembled from molecular building blocks, exerts a profound impact on the stability, porosity, flexibility, and functionality of the materials. However, the rational design and construction of crystalline architectures with tailorable interpenetration remains elusive, and the interpretation of the underlying self-assembly mechanism is largely underexplored. Here, we report precise control and molecular-level understanding of interpenetration within pillar-layered frameworks built on an 8-connected hexanuclear Co₆(μ₃-OH)₆(COO)₆N₆ inorganic node, a 3-connected tricarboxylate linker, and a 2-connected bipyridine pillar. Isoreticular expansion along horizontal or vertical directions affords a family of six distinct structures exhibiting varying degrees of interpenetration. Our findings reveal that the degrees of interpenetration generally correlate with the length of the lateral ligands, whereas the specific interpenetration mode is governed by the size compatibility between the individual net and its intrinsic pore aperture. Density functional theory calculations further corroborate the thermodynamic advantages associated with interpenetrated structures. Furthermore, we elucidate the pivotal role of interpenetration in dictating the porosity, stability, and benzene/cyclohexane adsorption of these materials.