Self-Assembly of Fluorinated Boronic Esters and 4,4′-Bipyridine into 2:1 N→B Adducts and Inclusion of Aromatic Guest Molecules in the Solid State: Application for the Separation of o,m,p-Xylene

A series of 2:1 fluorinated arylboronic ester adducts with 4,4'-bipyridine sustained by N -> B dative bonds have been synthesized. The degree of fluorination in the arylboronic esters derived from catechol is shown to modulate the molecular conformation of the coordinated boronic ester moieties and the intermolecular interactions by means of C-H center dot center dot center dot F and F center dot center dot center dot F contacts that sustain the crystal lattices. The adduct derived from the catechol ester of 2,4-difluorophenylboronic acid was chosen to examine the formation of inclusion complexes with a large number of aromatic guests, affording solvates, cocrystals, and a cocrystal solvate. Six different crystal structure types with 1:1, 1:2, and 1:2:2 N -> B adduct-guest ratios were observed, whose supramolecular organization is strongly influenced by the formation of sandwich-type complexes between the host and guest molecules. The host-guest interactions involve pi center dot center dot center dot pi interactions with the bipyridine linkers and additional contacts with the catecholate and B-aryl(F) substituents, indicating a large flexibility of the N -> B adducts to adapt to the guest stereochemistry. The versatility of the crystallization system was employed to isolate o-xylene from an equimolar mixture of o-, m-, and p-xylene.