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

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.

本研究合成了E,E-2,5-双(2-苯乙烯基)吡嗪的4种新型甲氧基取代衍生物。针对该系列共5种多晶型物，我们采用单晶X射线衍射技术对其超分子结构展开研究，旨在探究甲氧基取代位置对固态分子排布的影响，以此作为消除母体化合物特定多晶型现象的研究尝试。分析过程中，我们以母体化合物晶体结构中发现的两种吡嗪基超分子合成子——吡嗪环-苯环π堆积合成子与吡嗪氢键合成子为基础，同时结合CH···O、CH···N、CH···π等弱分子间相互作用，对晶体堆积模式进行了剖析。结果表明，若在外围苯环的对位以外的位置引入甲氧基，可有效阻断母体化合物中的两种超分子合成子，新型衍生物转而采用基于甲氧基-甲氧基相互作用与-OCH3···π接触的新型堆积策略。但多晶型现象仍未被消除。