Chiral Motifs in Highly Interpenetrated Metal–Organic Frameworks Formed from Achiral Tetrahedral Ligands

• Published in: Chemistry : a European journal 2022-09, Vol.28 (54), p.e202201108-n/a
• Main Authors: Wen, Qiang, Gregorio, Maria Chiara, Shimon, Linda J. W., Pinkas, Iddo, Malik, Naveen, Kossoy, Anna, Alexandrov, Eugeny V., Proserpio, Davide M., Lahav, Michal, Boom, Milko E.
• Format: Article
• Language: English
• Subjects: Cell size; Channels; Chemistry; Chirality; Coordination; Crystals; diamondoid networks; Diamonds; Dichlorides; Interpenetrating networks; interpenetration; Ligands; Metal-organic frameworks; symmetry breaking; Unit cell
• ISSN: 0947-6539; 1521-3765; 1521-3765
• DOI: 10.1002/chem.202201108

Formation of highly interpenetrated frameworks is demonstrated. An interesting observation is the presence of very large adamantane‐shaped cages in a single network, making these crystals new entries in the collection of diamondoid‐type metal–organic frameworks (MOFs). The frameworks were constructed by assembling tetrahedral pyridine ligands and copper dichloride. Currently, the networks’ degree of interpenetration is among the highest reported and increases when the size of the ligand is increased. Highly interpenetrated frameworks typically have low surface contact areas. In contrast, in our systems, the voids take up to 63 % of the unit cell volume. The MOFs have chiral features but are formed from achiral components. The chirality is manifested by the coordination chemistry around the metal center, the structure of the helicoidal channels, and the motifs of the individual networks. Channels of both handednesses are present within the unit cells. This phenomenon shapes the walls of the channels, which are composed of 10, 16, or 32 chains correlated with the degree of interpenetration 10‐, 16‐, and 32‐fold, respectively. By changing the distance between the center of the ligand and the coordination moieties, we succeeded in tuning the diameter of the channels. Relatively large channels were formed, having diameters up to 31.0 Å×14.8 Å. Tetrahydral achiral ligands and copper ions assemble into a record number of interpenetrating diamondoid networks. The networks intertwine akin to strands of a molecular rope to shape the chiral channels. The design of the ligand “arms” allows modulating their degree of interpenetration and the channel properties. The concurrent presence of such numerous interpenetrated networks and porosity is unprecedented for metal–organic frameworks.