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 center dot center dot center dot I and O center dot center dot center dot 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 center dot center dot center dot I and O center dot center dot center dot I halogen bonds, only N center dot center dot center dot 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.