In the cupper complexes Ia , b , c , the homologue with a larger alkoxy chain 10 carbon atoms was the unique derivative which displays mesomorphic behaviour.
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Probably, the length of the terminal chain increase of the complex flexibility, futhermore, the lateral interactions are an influence on mesophase arrangement, favoring the formation of the smectic phase. In the case of the palladium complexes, the three homologues IIa,b,c show liquid crystalline properties with a broad mesomorphic range. Probably, the palladium complexes have a major anisotropy of the polarizability, than the corresponding cupper complexes. So, the palladium in the complexes introduces the best mesomorphic properties.
The transition temperatures and the thermal degradation temperatures of the metallomesogens are given in table 1 and 2 , respectively. The mesophases exhibited by these metallomesogens were identified according to their optical textures which were observed by optical microscopy, using the clasification system reported by Sackmann and Demus, Gray and Goodby.
The nematic phase showed the typical nematic droplets near of clearing point, the smectic C mesophase was identified by the appearance of broken fan shaped texture. A graphical representation of the mesomorphic behaviour as a function of the number of carbon atoms in the lateral chain for the palladium metallomesogens IIa , b , c , is given in figure 4.
The same mesomorphic behaviour of the pure ligands was observed in the metallomesogens 6 , the compounds with length alkoxy chain of 5 and 6 carbon atoms display nematic and smectic C mesomorphism.
Metallomesogens synthesis properties and applications
The liquid crystalline properties showed by complexes are due to of anysommetric arrangement of the molecule, the complexes with an alkoxy chain in the 4-position of the phenyl ring favour a calamitic geometry in which the length of the molecule is major in comparison with its diameter. However, the diameter of the molecule increases when the substitution is in the 5-position of the aromatic ring, leading to a complete loss of liquid cystalline properties.
On the other hand the heterocycles in the central core of calamitic molecules play an important role in the mesomorphism. The oxadiazole ring produces a deviation from the typical rod-like mesogen symmetry towards one with an average nonlinear shape, explaining the suppression of the mesomorphic behaviour of these metallomesogens 7. The transition temperatures and textures of the mesophases were determined by optical microscopy using an Ortholux Pol BKII polarizing microscope equipped with a Mettler FP hot stage.
The apparatus was calibrated with indium.
The thermogravimetric analysis were carried out with an instrument STA , model Found: C, 66,97; H, 7,85; Cu, 5, Found: C, 61,95; H, 7,45; Pd, 9, Found: C, 62,16; H, 7,37; Pd, 9, Found: C, 64,90; H, 7,24; Pd, 8, Gallardo, R. Magnago, A. Bortoluzzi, Liq.
Diaz, N. Valdebenito Liq. Giround-Godquin, P. Maitlis, Angew. Espinet, M. Esteruelas, L Oro, J.
Serrano, Coord. Hudson, P. Maitlis, Chem. Ghedini, Mol. Cryst, liq. Marcos, M. Ros, J.
Book Metallomesogens Synthesis Properties And Applications 2014
Serrano, Liq. Levelut, 6 Liq. Polischchuk, T. First published: 14 December About this book Research on metal-containing liquid crystals is a rapidly expanding, multidisciplinary field with new materials continually being synthesized and novel applications being developed. It is an indispensable guide to experienced researchers in coordination and organometallic chemistry as well as in liquid-crystal and materials science.
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Metallomesogens: synthesis, properties, and applications
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