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

Abstract

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.

Synthesis of 1,2-Disubstituted Adamantane Derivatives by Construction of the Adamantane Framework

“…To date, mostly 1,3-disubstituted achiral adamantane derivatives, utilized as rigid spacers, have been reported. The properties of chiral derivatives can then be exploited in applications where chirality plays a role, such as enantioselective catalysis [30][31][32], the synthesis of enantiopure compounds [33,34], interactions of enantiopure compounds with material [35,36] or light [37], and other physical, chemical, or biological applications [38][39][40]. The low stability of the adamant-1-ene molecule, which has a rather biradical character, does not allow the use of classical alkene chemistry for the formation of 1,2-disubstituted adamantane compounds [41][42][43].…”

“…Molecules 2023, 28, x FOR PEER REVIEW 2 of 30 enantiopure compounds [33,34], interactions of enantiopure compounds with material [35,36] or light [37], and other physical, chemical, or biological applications [38][39][40]. The low stability of the adamant-1-ene molecule, which has a rather biradical character, does not allow the use of classical alkene chemistry for the formation of 1,2-disubstituted adamantane compounds [41][42][43].…”

Spontaneous resolution of two chiral metal–organic frameworks through local geometric and lattice frustration effects

“…9,25,26 The synthesis of chiral MOFs (CMOFs) from achiral precursors is perhaps less well understood due to their unpredictable formation pathways. Two regimes have been identified as possible justifications for producing chiral forms from achiral reagents: (1) subcomponent self-assembly into chiral superstructures, 27,28 and (2) asymmetric metal coordination modes that lead to chiral-at-metal "symmetrybreaking". 14,16 In both instances, local chiral secondary building units that appear due to specific ligand geometries (e.g., twisted or concave/bowl-shaped conformations) and/or supramolecular interactions can transmit their chiral information to the long-range structure.…”