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Halogen bond hierarchy in cocrystals of N-haloimides and halogenated pyridine derivatives

It is usual (and relatively justified) to expect halogen bonds (XB) with inorganic donors as stronger than their counterparts involving organic donors. This is due to the larger polarisation of the halogen atom in dihalogen molecules, interhalogen compounds etc., as compared to that in commonly employed organic halogen donors (usually perhalogenated hydrocarbons). Recently however, N-halogenated succinimides have also been marked as extremely strong halogen donors [1]. Employing different imides can change the potential of forming other interactions – when N- halogenated phthalimides are used as XB donors, weak hydrogen bonds form which might complement, or compete with, the primary halogen bond formed by the imide and a XB acceptor [2]. The main emphasis of this presentation will be on introduction of hierarchy oh halogen bond donors and acceptors by adding halogen atoms on the pyridine molecule. The halogen atom of the N- haloimide binds preferentially to the pyridine nitrogen, while the halogen of the pyridine ring forms only substantially longer halogen bond with the N-haloimide oxygen atoms, other halogen atoms, or π-systems. This hierarchy is maintained even if the N-haloimide halogen is a lighter one than the one on the pyridine ring following the molecular electrostatic potential ; the highest positive values of ESP being associated with the best XB- donor atoms. [1] V. Stilinović, G. Horvat, T. Hrenar, V. Nemec, D. Cinčić, Chem. Eur. J. 23 (2017) 5244. [2] D. Cinčić, M. Eraković, T. Lež, I. Porupski, V. Nemec, V. Stilinović, 2nd International Symposium on Halogen Bonding, 6- 10.6.2016, Goteborg.

N-halogenated succinimides, cocrystals, halogen bond, pyridine derivatives

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