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Cooperativity of halogen bonds in cocrystals of 4-halogenoanilines and 1, 4- diiodotetrafluorobenzene

One of the most notable features of halogen bonding [1] is that it involves halogen atoms that are electrophilic species, but that can also be nucleophilic due to induced electron density anisotropy [2]. When considering interactions between two halogen species, it is necessary to differentiate between two types: type I, which arise from close packing requirements, and type II, which represent the interaction between the nucleophilic area of one halogen and the electrophilic area of another halogen and are therefore considered halogen bonding motifs [3]. Our goal in this work was to explore the possibilities in halogen bonding involving halogenated anilines, seeing as halogen atoms and ligands are known halogen bond acceptors [1, 3] and as their amine functional group is also a potential halogen bond acceptor [4]. We selected structurally equivalent reactants, 4-chloroaniline (4ClA), 4-bromoaniline (4BrA) and 4-iodoaniline (4IA), so as to study the effects on the supramolecular interactions on crystal packing. First, we performed mechanochemical and solution based synthesis, reacting each 4-halogenoaniline with 1, 4- diiodotetrafluorobenzene (14tfib) in a 2:1 molar ratio. Products were characterized by means of powder X-ray diffraction and by single crystal X-ray diffraction. The three obtained products are isostructural. In all three cases 14tfib forms remarkably similar halogen bonds only with the amine group (d(I···N) = 3.000 - 2.996 Å, (C–I···N) = 178 – 177 °), leaving the halogen atom of the 4-halogenoanilines to participate as both a halogen bond donor and acceptor in a type II contact. The geometry of the observed type II contacts is shown to be only slightly dependent on the donor capabilities of the halogen atom (d(I···I) = 3.892 Å, (C–I···I) = 169 ° ; d(Br···Br) = 3.666 Å, (C–Br···Br) = 165 ° ; d(Cl···Cl) = 3.623 Å, (C–Cl···Cl) = 165 °). The combination of halogen bonding and type II contacts leads to the formation of layers which are then further stacked into 3D.

halogen bond ; cocrystals ; halogenoanilines ; 1, 4- diiodotetrafluorobenzene

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