Tharanga K. Wijethunga

The structural landscape of heteroaryl-2-imidazoles: competing halogen- and hydrogen-bond interactions

In order to examine the competition between hydrogen bonds and halogen bonds when confronted with a probe molecule containing multiple potential acceptor sites and one hydrogen-bond donor, five heteroaryl-2-imidazoles were synthesized and subsequently co-crystallized with fifteen different halogen-bond donors. 30 of the 75 experiments resulted in the formation of co-crystals, and fifteen of these produced crystals were suitable for single-crystal X-ray diffraction analysis. A systematic analysis of the primary intermolecular interactions in these fifteen structures shows that the halogen bond is formed with the best acceptor site (as predicted by DFT molecular electrostatic potential surface calculations) demonstrating that a suitably activated iodine-based halogen-bond donor can compete with a strong hydrogen-bond donor in the directed assembly of molecular solid-state architectures.

Constructing molecular polygons using halogen bonding and bifurcated N-oxides

Bifurcated halogen bonds constructed from N-oxides and complementary halogen-bond donors provide the basis for a synthetic strategy for the deliberate assembly of molecular polygons in the solid state. The donor- and acceptor sites were located on different molecular components and a co-crystallization approach furnished the desired architectures.

Molecular electrostatic potential dependent selectivity of hydrogen bonding

A series of co-crystallizations between four biimidazole based compounds (1,1′-bis(pyridin-4-ylmethyl)-2,2′-biimidazole A1, 1,1′-bis(pyridin-3-ylmethyl)-2,2′-biimidazole A2, 1,1′-bis(pyridin-2-ylmethyl)-2,2′-biimidazole A3 and 1,1′-dibenzyl-2,2′-biimidazole A4) and nine symmetric aliphatic di-acids were carried out in order to determine if a ranking based on calculated molecular electrostatic potential surfaces (MEPS) can be used to effectively assign selectivity in hydrogen-bond based intermolecular interactions. Acceptors A1–A3 are asymmetric ditopic acceptors where two types of nitrogen atoms (pyridine and imidazole) are present, while A4 is a control molecule with only one type of acceptor to rule out any influence of steric factors in the observed structures. 28 of 36 experiments (78% yield) produced a co-crystal, as indicated by relevant changes in the corresponding infrared spectra. Twelve crystal structures of co-crystals of A1–A3 were obtained and every single one displayed primary OH⋯N hydrogens bonds that could be rationalized using the ranking based upon electrostatic potential maps. One crystal structure of A4 was obtained the result of which indicate that the patterns of behaviour established in this family of compounds is not a result of sterics or crystal packing; a simple electrostatic view of hydrogen-bond strength provides a reliable tool for predicting the most likely interactions in a competitive system.

A new tecton with parallel halogen-bond donors : a path to supramolecular rectangles

A new tecton, 1,8-diiodoethynylanthracene, with two halogen-bond donor sites was synthesized and characterized. This tecton is capable of forming two parallel halogen bonds at once, which makes it a useful building block for the construction of a variety of supramolecular squares and rectangles.