Synthesis And Transformations Of Supramolecular Co-crystals In The Solid State

At present, to develop low-pollution or pollution-free products and processes has become a hot focus, in the sense that it not only pursuits the high efficiency and high selectivity, but also pursuits "green" in the reaction process. The solid-state synthesis, as an alternative "green" method, has attained increasing interest in recent years. This new green synthetic method, compared to the traditional solution method, has its unique advantages:(1) It is manipulated easily, quickly and quantitatively;(2) The material products are prepared without involving environmentally unfriendly solvents;(3) It may produce compounds which could not be prepared in their solution reactions.Using solid state synthesis method for preparation of supramolecular co-crystals is an important research field of green synthesis of supramolecular. The significant advantage is that the solid-state synthesis usually can obtain the desired co-crystals by controlling appropriate stoichiometric amounts of the co-crystal reactants, while the traditional solution method cannot. In the solid state synthesis process, the individual molecules of each reactants have to be freed from the original lattice and rearranged themselves with other molecules to form a crystal lattice in solid-state.In this paper, we have prepared two series of supramolecular co-crystalsby the solid-state grinding:(a) Urea-sulfosalicylic acid co-crystal and (b) Benzimidazole-sulfosalicylic acid co-crystal. We have obtained the following result and conclusions:(1) Grinding with the different stoichiometric of reactants can form1:1,1:2and2:1co-crystals AxBy (x,y=1,2), and some of these could not be obtained by the traditional solution method, although a variety of solvents or seeding method have been used.(2) These co-crystals were characterized by X-ray single-crystal diffraction, PXRD, thermogravimetric analysis and melting-point test.(3) We have studied systematically the hydrogen bond competitionin the Sulfosalicylic acid-Urea-Benzimidazole co-crystal system. (4) Especially,we monitored an interesting transformation process of these co-crystals, whichhas provided a good model for the study of the solid-state reaction mechanism.