engleski

Halogen bonding of N-bromophthalimide via grinding and solution crystallization

N-haloimides (particularly N-halosuccinimides) are commercially available compounds commonly used as halogenation agents in organic synthesis. As the halogen atoms in these molecules are extremely polarised, they are potentially extremely strong halogen bond donors [1]. Also, they are potentially strong hydrogen bond acceptors considering that they possess carbonyl groups. In spite of this, they have not yet been fully recognised and studied as potential halogen bond donors, although they have the potential to be both excellent halogen bond donors, and are more environmentally friendly than the more usually employed perfluorinated compounds [2]. In this work we report the first known cocrystals of N-bromophthalimide (nbf) prepared by both mechanochemical synthesis (liquid-assisted grinding) and conventional solution-based method. As halogen bond acceptors we have used pyridine derivatives with a wide range of nitrogen atom basicity (pKa from 1.4 to 7.5) containing additional functional groups which may be hydrogen bond donors or acceptors. For all 10 cocrystals, molecules are connected via a Br∙∙∙N halogen bond between nbf and pyridine nitrogen. The Br∙∙∙N distances are from 2.38 Å to 2.51 Å and are considerably less than the sum of the van der Waals radii, 3.4 Å. For all cocrystals the N–Br bond in nbf molecules is extended in comparison with that observed for the pure nbf crystal (up to 0.1 Å) which indicates charge transfer in complexes and partially covalent character of the halogen bond. All supramolecular complexes nbf-pyridine are connected into a 3D network via C–H∙∙∙O hydrogen bonds between pyridine aromatic rings and carbonyl oxygen atoms of nbf.

N-bromophthalimide ; cocrystals ; halogen bond ; mechanochemistry ; pyridine derivatives

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