Propeller-like Hydrogen-Bonded Banana-Melamine Complexes Inducing Helical Supramolecular Organizations Joaquı ´n Barbera ´ , Laura Puig, Pilar Romero, Jose ´ Luis Serrano,* and Teresa Sierra* Contribution from Quı ´mica Orga ´ nica, Facultad de Ciencias, Instituto de Ciencia de Materiales de Arago ´ n, UniVersidad de Zaragoza-CSIC, 50009-Zaragoza, Spain Received December 16, 2005; E-mail: joseluis@unizar.es; tsierra@unizar.es Abstract: The results of the study presented here show a new example of the use of liquid crystals and the interactions involved in the mesomorphic state to build up complex molecular organizations. We have pursued a design strategy in which hydrogen bonding allows the combination of the π-stacking tendency of melamine and the lateral interaction capability of V-shaped molecules, which has been extensively demonstrated through nematic, smectic, or columnar mesophases. This combination addresses the formation of columnar arrangements with inherent helical organization. In this work, nonmesomorphic as well as mesomorphic V-shaped acids, with a structure similar to banana liquid crystals, have been complexed to a 2,4,6-triamino-1,3,5-triazine derivative in a proportion 3 to 1, respectively. Hydrogen-bonded supramol- ecules whose formation and stability in solution have been proven by infrared and NMR techniques have been thus obtained. DOSY experiments have allowed us to assess in solution the presence of the complexes and their tetrameric composition. All the complexes display mesogenic ability, and their mesomorphic organization has been studied by X-ray diffraction and CD spectroscopy. Results allow us to propose a helical columnar model for the mesophase originated from a propeller-like conformation of the supramolecular complexes. Introduction Building helical organizations with controlled structure, imitating nature, is a major point of interest in supramolecular chemistry and material science. Furthermore, if these organiza- tions are achieved by means of simple but unconventional molecular units, this study can attract interest from researchers on molecular materials. Hydrogen bonding and π-interactions are frequently employed as driving forces to give well-defined supramolecular architectures. 1 In this context, melamine and its derivatives, which can be involved in both types of interaction, have provided a variety of elegant approaches to new types of material through self-assembly. 2 A number of examples of these systems have been reported within the liquid crystals field. 3 In the work described here, we explored a new strategy to design columnar liquid crystalline organizations that employ both types of noncovalent interaction, which arise from a melamine derivative and from one of the newest types of mesogenic structure: banana-like molecules. The latter com- pounds promote the appearance of special classes of nematic, 4 smectic, or columnar 5 mesophases with unique molecular packing that comes from their peculiar V-shape. 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