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Agonistic-antagonistic effects of multiple halogen bonding in the cocrystals of polytopic donors and acceptors

Halogen bond (XB) is a much-studied interaction in the solid state nowadays, [1, 2] mainly in the context of crystal engineering. However, its coupling to the neighbouring interactions in the crystals is investigated only on few examples [3] and is still not sufficiently understood. In this work, six cocrystals of XB donors and acceptors (showed in figure) were synthesized and characterized by SCXRD. Although the reactants were mixed in the molar ratio of 1:1 in each synthesis, the cocrystals displayed stoichiometric diversity, having schematic formulas (14)×(SB1)2, (14)×(SB2), (13)2×(SB1), (13)3×(SB2), (135)2×(SB1) and (135)4×(SB2). In the cocrystals with 14 only the C–I···Npyridine halogen bonds are present, while 13 and 135 formed the C–I···Nimine and C–I···I (orthogonal to the C–I···Npyridine) halogen bonds as well. QM calculations were used to estimate the relative strengths of the observed XBs, which showed that the C–I···I bond is the weakest, but electron density deformation (EDD) analysis showed that the C–I···Npyridine bond is its agonist. The EDD analysis also showed that C–I···Npyridine is the antagonist for polytopic halogen bonding of all used donors. This effect was much larger for 13 and 135 then for 14 donor. [1] V. Stilinović, G. Horvat, T. Hrenar, V. Nemec, D. Cinčić, Chem. Eur. J. 23 (2017) 5244. [2] V. Nemec, D. Cinčić, CrystEngComm 18 (2016) 7425. [3] A. Regier Voth, P. Khuu, K. Oishi, P. Shing Ho, Nat. Chem. 1 (2009) 74.

cocrystals ; electron density deformation analysis ; halogen bonding ; solution crystallization

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