Crystal Structure, Thermal Behavior, and Photochemical Reactivity of a Series of Co-Crystals of trans-1,2-Bis(4-pyridyl) Ethylene with Dicarboxylic Acids

A series of co-crystals of trans-1,2-bis(4-pyridyl) ethylene (bpe) with aliphatic saturated or unsaturated dicarboxylic acids, of the type [(bpe)(L)] (L = dicarboxylic acid), were prepared and characterized by single crystal X-ray crystallography. In all cases chains of the type acid···bpe···acid were formed via strong O–H···N hydrogen bonds. The chains were further linked between them by weak C–H···O hydrogen bonds, π–π and herringbone interactions to form three-dimensional structures. Thermal analysis showed considerable elevation of the melting/decomposition point of the co-crystals with respect either to both components or to bpe, ascribed to the formation of multiple complementary C–H···O bonds as well as to π–π interactions between the two conformer molecules. When L = fumaric acid, the two components stack separately with their C═C bonds strictly parallel between them at 3.83 Å from one another. However, photodimerization reaction takes place only between the olefin bonds of bpe. Photodimerization reaction between one C═C bond of the acid and that of bpe was also induced when L = trans,trans-muconic acid.