FULL PAPER DOI:10.1002/ejic.201402489 Combined Stabilizing Effects of Trifluoromethyl Groups and Semifluorinated Side Chains on the Thermotropic Liquid-Crystal Behavior of β-Enamino Ketone Ligands and Their Bischelate Pd II Complexes Alexander Martin, [a] Carolin Mügge, [a] Douglas L. Gin, [b] Bertrand Donnio,* [c,d] and Wolfgang Weigand* [a,e] Keywords: Metallomesogens / Palladium / Liquid crystals / Fluorinated ligands / Fluorophobic effects Several linear β-enamino ketone ligands and their corre- sponding bischelate Pd II complexes bearing various combi- nations of methyl and trifluoromethyl groups at the chelating center as well as peripheral hydrocarbon and perfluorinated side chains were prepared. The effect of these structural modifications on the thermotropic liquid-crystalline behavior of both the ligands and the corresponding metal complexes was studied. The relationships between the molecular struc- tures and the corresponding thermal properties are dis- Introduction The rational design of functional molecules [1] plays a cru- cial role in the development of new materials, such as the engineering of new mesomorphic materials for commercial applications. [2–5] One approach to partially achieve some of the demanding and specific requirements for the use of li- quid crystals as components in various types of devices is the introduction of local dipole moments into liquid-crystal (LC) systems. [2,6] The judicious incorporation of dipole mo- ments within calamitic mesogenic molecules strongly influ- ences their transition temperatures, the nature and stability of their mesophases, and some of their physical proper- [a] Institut für Anorganische und Analytische Chemie, Friedrich- Schiller-Universität Jena, Humboldtstraße 8, 07743 Jena, Germany E-mail: wolfgang.weigand@uni-jena.de http://www.uni-jena.de/Prof_W_Weigand.html [b] Department of Chemistry & Biochemistry, and Department of Chemical & Biological Engineering, University of Colorado, Boulder, Colorado 80309, USA [c] Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504 (CNRS-University of Strasbourg), 23 rue du Loess, BP 43, 67034 Strasbourg Cedex 2, France E-mail: bdonnio@ipcms.u-strasbg.fr http://www.ipcms.unistra.fr/?page_id=8049&lang=en [d] Complex Assemblies of Soft Matter Laboratory (COMPASS), UMI 3254 (CNRS-Solvay-University of Pennsylvania), CRTB, 350 George Patterson Boulevard, Bristol, PA 19007, USA [e] Jena Center for Soft Matter (JCSM), Philosophenweg 7, 07743 Jena, Germany Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejic.201402489. Eur. J. Inorg. Chem. 2014, 5609–5617 © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 5609 cussed. As expected, the persistence of liquid-crystalline be- havior was highly sensitive to both applied structural manipulations. On the one hand, increased steric congestion around the chelating moiety clearly appears detrimental to the retention of mesomorphism. On the other hand, per- fluorinated chains at the molecular extremity can occasion- ally restore it. Therefore, the regulation of the balance be- tween both structural parameters permits a precise control of the mesomorphic properties of the compounds. ties. [2] For instance, several studies have shown that the in- sertion of electron-withdrawing groups such as halide, cy- ano, hydroxy, or nitro groups into calamitic [2,6] and other [7] mesogenic structures often has a stabilizing effect on the structures and also influences the formation, the degree of order, and the symmetry of the liquid-crystalline phases. In addition, the integration of perfluorinated or semifluorin- ated alkoxy side chains into classical calamitic and discotic molecules is another means to drastically affect the LC properties, and this approach has been largely and success- fully exploited. [8] Indeed, it leads to enhanced microsegrega- tion, caused by the chemical incompatibility between the fluoroalkyl and alkyl chains (i.e., the fluorophobic effect), which often modifies the stability of the mesophase in com- parison with those of hydrocarbon analogs and, in some cases, gives rise to the emergence of new types of liquid- crystalline phases. [9–11] For metal-containing liquid crystals, [12] the effect of halo- genation, particularly fluorination, on the mesomorphic be- havior has been widely studied. [13] In contrast, metallome- sogens bearing perfluorinated chains are scarce, and only a few examples have been reported to date. Guillevic et al. synthesized mesomorphic Re I carbonyl complexes with benzaldimine-like ligands containing perfluoroalkyl side chains with different tail lengths. [14] In contrast to their n- alkyl parent compounds, which only exhibit a nematic phase, the Re I complexes bearing at least one perfluoro side chain show a smectic A (SmA) phase. The promotion of