Solution stoichiometry determines crystal stoichiometry in halogen-bonded supramolecular complexes

The behavior of the methylisonicotinate (MINC) building block as halogen bonding-acceptor module has been investigated in the solid state. Both the N and the O atoms of MINC interact with the iodine atoms of 1,4-diiodotetrafluorobenzene (DITFB) giving rise to N…I and O…I interactions. Hierarchy between these interactions allows the control of the composition and thus the structure of the supramolecular complex, according to the composition of the reaction mixture. A structure based on an infinite chain and a trimeric supermolecule have been obtained starting from a 1 : 1 MINC/DITFB stoichiometry or by using a large excess of MINC, respectively. While the former structure shows simultaneous N…I and O…I halogen bonds, only N…I interactions are present in the latter one. The results also elicit some general considerations based on the rare chain morphology shown by the 1 : 1 complex.