FULL PAPER DOI: 10.1002/ejoc.200700725 New H-Bonded Complexes and Their Supramolecular Liquid-Crystalline Organizations Ana Pérez, [a] Nélida Gimeno, [a] Francisco Vera, [a] M. Blanca Ros,* [a] José Luis Serrano, [a] and M. Rosario De la Fuente [b] Keywords: Supramolecular chemistry / Hydrogen bond / Liquid crystals / Bent-core liquid crystals Different approaches to the design of liquid crystals by using H-bonds were analyzed. A selection of stilbazoles and pyr- idine compounds, with one or two chelating positions, were used as H-acceptors in mixtures with carboxylic acids. The noncovalent complexes in question afforded calamitic meso- morphism (N, SmA and SmC) as well as a lamellar meso- phase (SmCP). Additionally, the liquid crystalline behaviour of the new 2-hydroxy- and 2-aminopyridine compounds as pure materials is also discussed. Useful results concerning Introduction Supramolecular chemistry has found in hydrogen bonds an extraordinary tool to generate many original and attract- ive architectures and functionalities. Furthermore, the use of appropriate H-donor and H-acceptor structures enables numerous calamitic and columnar liquid-crystalline me- sophases to be stabilized [1] (Figure 1). These soft materials have broadened the possibilities for structural design and macroscopic arrangement through this noncovalent interac- tion. One particularly attractive possibility is the use of nonmesomorphic single components to form such liquid- crystalline systems. In recent years, a new type of mesogenic material has emerged in this field, the so-called banana-shaped liquid crystal. [2] This name comes from the bent-shape of the molecules involved in generating these new phases. Through a compact arrangement that restricts their rotational free- dom, these molecules offer new types of mesophases and phenomena that are attracting the interest of chemists and physicists. A large variety of columnar and lamellar molec- ular packing arrangements, some of which exhibit supra- molecular chirality, have been reported since the pioneering results of Niori et al. [3] [a] Química Orgánica, Facultad de Ciencias – Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza – C.S.I.C. 50009-Zaragoza, Spain Fax: +34-976761209 E-mail: bros@unizar.es [b] Departamento de Física Aplicada II, Facultad de Ciencias y Tecnología,Universidad del País Vasco Apdo. 644, Bilbao, Spain Supporting information for this article is available on the WWW under http://www.eurjoc.org/ or from the author. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Eur. J. Org. Chem. 2008, 826–833 826 the design and stability of noncovalent calamitic and bent- core liquid crystals are reported. To induce the bent-core li- quid crystalline order, the conformational flexibility around the H-bond must be controlled. The new liquid crystals were characterized by IR spectroscopy, optical microscopy, calo- rimetry, X-ray diffraction and dielectric spectroscopy. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) Figure 1. Different liquid crystals generated by using H-bonds. Current research in this new field is focused on numerous areas. Some examples concern the characterization and un- derstanding of the new types of liquid crystalline phases, their physical properties, the exploration of their practical applications and, of particular interest to chemists, how to control all of these properties through suitable molecular design. In this respect, hydrogen bonding has proved to be a use- ful tool to tailor properties. The use of carboxylic acids and stilbazoles I and II (Figure 2), which act as H-donor and H-acceptor, respectively, has afforded bent-shaped com- plexes that arrange in these new mesophases, even with side-chain bent-shaped liquid-crystal polymers. [4,5] The SmCP phases are the most common and widely studied of this new type of mesophase. This phase is characterized by its tilted lamellar and polar packing. Depending on the di- rection of polarization in adjacent layers, the mesophase can have either a ferro- and/or antiferroelectric ground state. On the other hand, depending on the tilt sense of the molecules in adjacent layers, this supramolecular arrange-