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Abstract Supramolecular chemistry can transform organic synthesis by revealing that crystalline materials are not static but rather dynamic environments for controlled covalent bond formations and manipulations. This review focuses on how supramolecular chemistry can be developed to direct molecular synthesis in the organic solid state, directing reliable C─C bond formations to enable transformations difficult or impossible in solution. Special attention is given to postsynthetic modifications that serve to broaden the functional scope of solid‐state reactivity allowing organic crystals to be developed as molecular flasks and a form of supramolecular matter. 

Abstract The exploitation of noncovalent bonding in the solid state is attractive to generate one‐dimensional (1D) wire‐like assemblies of metals and uncover dynamic and physical properties of such intriguing structures. Herein, we describe a metal‐organic crystal based on Ag(I) ions that assemble to be organized into 1D wire‐like assemblies maintained by argentophilic interactions. UV‐light irradiation of the crystal composed of the 1D structures results in a single‐crystal‐to‐single‐crystal (SCSC) photodimerization that transforms the 1D periodic metal arrays to isolated metal dimers. The structural reconfiguration creates small voids in the crystal and the resulting solids exhibit a substantial increase in softness up to 60%. 

Abstract An application of multi‐component milling is described to achieve a decolorization by dismantling the orange‐red zwitterionic cocrystal (PDA)∙(APAP) (wherePDA= 2,4‐pyridinedicarboxylic acid,APAP= acetaminophen) usingn,n′‐BPE(BPE=trans‐1,2‐bis(n‐pyridylethylene and forn=n′ = 3 or 4). Each ofn,n′‐BPEforms a colorless hydrogen‐bonded cocrystal withPDA. 

Abstract Methods to separate molecules (e.g., petrochemicals) are exceedingly important industrially. A common approach for separations is to crystallize a host molecule that either provides an enforced covalent cavity (intrinsic cavity) or packs inefficiently (extrinsic cavity). Here we report a self-assembled molecule with a shape highly biased to completely enclose space and, thereby, pack efficiently yet hosts and allows for the separation of BTEX hydrocarbons (i.e., benzene, toluene, ethylbenzene, xylenes). The host is held together by N → B bonds and forms a diboron assembly with a shape that conforms to a T-shaped pentomino. A T-pentomino is a polyomino, which is a plane figure that tiles a plane without cavities and holes, and we show the molecule to crystallize into one of six polymorphic structures for T-pentomino tiling. The separations occur at mild conditions while rejecting similarly shaped aromatics such as xylene isomers, thiophene, and styrene. Our observation on the structure and tiling of the molecular T-pentomino allows us to develop a theory on how novel synthetic molecules that mimic the structures and packing of polyominoes can be synthesized and—quite counterintuitively—developed into a system of hosts with cavities used for selective and useful separations. 

Abstract Mechanochemistry afforded a photoactive cocrystal via coexisting (B)O−H⋅⋅⋅N hydrogen bonds and B←N coordination. Specifically, solvent‐free mechanochemical ball mill grinding and liquid‐assisted grinding of a boronic acid and an alkene resulted in mixtures of hydrogen‐bonded and coordinated complexes akin to mixtures of noncovalent complexes that can be obtained in solution in equilibria processes. The alkenes of the hydrogen‐bonded assembly undergo an intermolecular [2+2] photodimerization in quantitative conversion, effectively reporting the outcome of the self‐assembly processes. Our results suggest that interplay involving noncovalent bonds subjected to mechanochemical conditions can lead to functional solids where, in the current case, the structure composed of the weaker hydrogen bonding interactions predominates. 

Competitive milling (CM) and stability milling (SM) mechanochemical reactions are used to comprehensively assess the relative thermodynamic stabilities and cocrystallization affinities of three pharmaceutical cocrystals (PCCs) of fluoxetine HCl ( X ) with three different pharmaceutically acceptable coformers (PACs, i.e. , benzoic acid ( B ), fumaric acid ( F ), and succinic acid ( S )). CM reactions, which involve milling X in the presence of two or more different PACs, were used to determine cocrystallization affinities, whereas SM reactions, which involve milling a PCC of X with a different coformer, were used to determine relative thermodynamic stabilities. In certain cases, SM reactions exhibited a remarkable solid-state exchange of coformers, yielding new cocrystalline forms. 35 Cl (spin I = 3/2) SSNMR is used as the primary probe of the products of CM and SM reactions, providing a reliable means of identifying and quantifying chloride ions in unique hydrogen bonding environments in each reaction mixture ( 13 C SSNMR spectra and pXRD patterns are used in support of these data). On the basis of these reactions and data, the PAC cocrystallization affinities with X are B > F ≈ S (most to least preferred), and the PCC stabilities are XB > X 2 F ≈ X 2 S (most to least preferred), corresponding to enthalpies of cocrystallization ranked as Δ H CCXB < ≈ . PAC affinities and PCC stabilities were found to be the same for products of analogous slow evaporation experiments and mechanochemical reactions with extended milling times ( i.e. , 90 minutes). Preliminary plane-wave DFT-D2* calculations are supportive of cocrystal formation; however, challenges remain for the quantification of relative enthalpies of cocrystallization. This work demonstrates the great potential of CM and SM reactions for providing pathways to the rational design, discovery, and manufacture of new cocrystalline forms of APIs.