The Amine Group as Halogen Bond Acceptor in Cocrystals of Aromatic Diamines and Perfluorinated Iodobenzenes

Abstract

In order to study the proclivity of primary amine groups to act as halogen bond acceptors, three aromatic diamines (p-phenylenediamine (pphda), benzidine (bnzd) and o-tolidine (otol)) were cocrystallised with three perfluorinated iodobenzenes (1,4-tetrafluorodiiodobenzene (14tfib), 1,3-tetrafluorodiiodobenzene (13tfib) and 1,3,5-trifluorotriiodobenzene (135tfib)) as halogen bond donors. Five cocrystals were obtained: (pphda)(14tfib), (bnzd)(13tfib)2, (bnzd)(135tfib)4, (otol)(14tfib) and (otol)(135tfib)2. In spite of the variability of both stoichiometries and structures of the cocrystals, in all the prepared cocrystals the amine groups form exclusively I···N halogen bonds, while the amine hydrogen atoms participate mostly in N–H⋯F contacts. The preference of the amine nitrogen atom toward the halogen bond, as opposed to the hydrogen bond (with amine as a donor), is rationalised by means of computed hydrogen and halogen bond energies, indicating that the halogen bond energy between a simple primary amine (methylamine) and a perfluorinated iodobenzene (pentafluoroiodobenze ne) is ca. 15 kJ mol−1 higher than the energy of the (H)NH∙∙∙NH2 hydrogen bond between two amine molecules.

Halogen Bonding in N-Alkyl-3-halogenopyridinium Salts

“…To date, various Lewis bases (neutral molecules or charged species) have been employed as halogen bond acceptors in constructing halogenbonded supramolecular assemblies. These have most commonly been organic [13,14] and metal-organic [15] molecules containing electron-rich nitrogen [16][17][18][19][20][21][22][23][24][25][26] and oxygen atoms [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41], as well as inorganic anions such as halogenides [42][43][44][45][46][47][48][49][50][51][52][53][54]. The most commonly used halogen bond donors have traditionally been neutral organic molecules where a halogen atom is bonded to electron-withdrawing molecular residues.…”

Evaluation of Halogenopyridinium Cations as Halogen Bond Donors

“…To date, most commonly used halogen bond donors have been perfluorinated iodo- or/and bromohydrocarbons, − where the electronegative fluorine substituents on the hydrocarbon skeleton act as electron-withdrawing fragments. Other electron-withdrawing substituents, such as cyano and nitro groups, can also be employed. − Halogenoethyne derivatives were also successfully used as halogen bond donors, as there the large positive potential of the σ-hole is ensured by the electron-withdrawing properties of the C–C triple bond. − Alternatively, halogen atoms can be directly bonded to a (more electronegative) heteroatom, such as nitrogen in ( N -halogeno)­imidesa strategy that has yielded some of the strongest organic halogen bond donors studied to date. − Another approach is using hypervalent halogens such as in iodine­(I) and iodine­(III) compounds.…”

Editorial: Advanced Research in Halogen Bonding

“…V. Stilinović, D. Cinčić and co-workers evaluate the tautomeric equilibrium of an asymmetric β-diketone in halogen-bonded cocrystals with perfluorinated iodobenzenes [8]. The behavior of the amine group as a halogen-bond acceptor in cocrystals formed by aromatic diamines and perfluorinated iodobenzenes is reported by V. Stilinović, D. Cinčić et al [9] In agreement with the calculated halogen and hydrogen bond energies, these crystals show a preferable formation of the halogen N•••I bonds as opposed to hydrogen bonds (with amine as a donor). The competition and cooperation of halogen and hydrogen bonds is also explored in the halogen-bonding-driven self-assembly of tetrabromoterephthalic solvates by K. Chainok et al [10] In comparison, C.E.…”