Competition between Methoxy-Based and Pyrazine-Based Synthons in Methoxy-Substituted Distyrylpyrazines

Abstract

Four new methoxy-substituted derivatives of E,E-2,5-bis(2-phenylethenyl)pyrazine have been synthesized. The supramolecular structures of the resulting set of five polymorphs have been studied using single-crystal X-ray diffraction to gauge the influence of the position of the methoxy groups on the organization of the molecules in the solid state, as part of an attempt to dispense with the particular polymorphism of the parent compound. The crystal packing patterns were analyzed in terms of the two pyrazine-based synthons found in the parent compound’s crystal structure, the πpyrazine···πphenyl stacking synthon, and the pyrazine hydrogen-bonded synthon, as well as in terms of weak intermolecular interactions such as CH···O, CH···N, and CH···π. The analysis shows that the introduction of methoxy groups in positions other than only the para position of the peripheral benzene rings successfully switches off the two synthons seen in the parent compound and that the new compounds adopt other packing strategies, based on methoxy···methoxy and −OCH3···π contacts. Polymorphism, however, remains.