engleski

Competition of halogen bonds in cocrystals of imines derived from o-vanillin

Halogen bonds (XB) are described as non-covalent interactions formed between polarizable and electron-deficient halogen atoms (Br, I) and electron-rich Lewis bases (nucleophilic atoms such as O, N, S, etc.), (Cavallo et al., 2016). In this work, we report XB cocrystals of four o-hydroxy imines with two XB donors, 1, 2-diiodotetrafluorobenzene (12tfib) and 1, 4-diiodotetrafluorobenzene (14tfib), prepared by both mechanochemical synthesis (liquid-assisted grinding) and conventional solution-based method. As XB acceptors we have used the imines derived from o-vanillin (ov) and four selected aromatic amines: 2-aminonaphthalene (2an), 3-aminoacetophenone (3aa), 4-aminoacetophenone (4aa) and 4-aminobenzonitrile (4abn). The selected imines have both a hydroxy and a methoxy group on the aldehyde moiety and an additional functional group on the amine moiety ; either a carbonyl, a nitrile group or no substituents. Thus, the functional groups are able to take part in different types of halogen and hydrogen bonding. In the crystal structures of all seven cocrystals the molecules are connected via halogen bonds. Crystal structure determination of cocrystals with imines derived from 2an, 3aa and 4aa revealed that they form various XB of I∙∙∙O type as well as the competition of XB acceptors (hydroxy, methoxy and carbonyl group). To the best of our knowledge, we report the first known cocrystals, (ov4aa)2(14tfib), (ov2an)2(14tfib) and (ov4aa)(12tfib) with a novel I∙∙∙O(hydroxy), methoxy XB motif, containing a bifurcated XB donor with hydroxy and methoxy groups. The I∙∙∙O(carbonyl) XB connects the molecules in the structure of (ov3aa)2(14tfib), one polymorph of (ov4aa)2(14tfib) and concomitantly with bifurcated XB in (ov4aa)(12tfib). In the crystal structures of cocrystals (ov4abn)2(14tfib) and (ov4abn)(12tfib), with imine derived from 4abn only the I∙∙∙N(nitrile) XB was found, demonstrating a competition between hydroxy/methoxy and nitrile groups as acceptors in favour of I∙∙∙N(nitrile) halogen bond.

1, 2-diiodotetrafluorobenzene ; 1, 4-diiodotetrafluorobenzene ; cocrystals ; halogen bond ; o-vanillaldimine ;

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