|Title: ||The search for nematic lanthanide mesogens: a surprising outcome|
|Authors: ||Van Deun, Rik|
Van Hecke, Kristof
Van Meervelt, Luc
Donnio, Bertrand #
|Issue Date: ||2003 |
|Conference: ||8th International Symposium on Metallomesogens (ISM2003) location:Namur (Belgium) date:28-31 May 2003|
|Article number: ||O5|
|Abstract: ||Calamitic lanthanide mesogens have been thoroughly studied since their discovery by Galyametdinov and coworkers in 1991 [1-11]. Because of the ionic nature of these compounds, all calamitic lanthanide complexes that are known exibit SmA phases. This is due to the strong electrostatic interactions between different molecules in the mesophase. One main disadvantage of smectic mesophases is their relatively high viscosity in comparison to the nematic phase. This high viscosity hampers the use of smectic mesogens in devices which need high switching speeds. Therefore, it would be extremely promising to make nematic lanthanide mesogens, because of the combination of the characteristic properties of the lanthanides (paramagnetism, the potential high magnetic anisotropy and the bright photoluminescence of high colorimetric purity) with the high switching speeds that can be obtained in nematic phases.
That is exactly what must have inspired Kumar and Pisipati in 2000, when they reported for the first time a series of nematic lanthanide complexes . In this paper, hydrazide ligands were used to form complexes with La, Pr and Nd. The resulting complexes had stoichiometry [Ln(habbe)2Cl2)Cl.2H2O] and were said to exibit nematic and smectic C phases. Stimulated by the work of Kumar and Pisipati, we undertook an attempt to synthesize lanthanide complexes with the habbe ligands to check whether this new class of nematic lanthanide mesogens could be expanded further. We synthesized four different chain lengths for R : C4H9, C8H17, C12H25 and C16H33 and adopted the synthetic procedure described by Kumar and Pisipati to form lanthanide complexes. The resulting compounds were analysed with NMR, DSC, CHN elemental analysis, mass spectrometry and single crystal X-ray crystallography. Soon it became clear that the compounds were not lanthanide complexes, but that decomposition of the habbe ligands had occurred. The lanthanum ion catalyses the decomposition of the ligand in a symmetrical azine. Lanthanides are known to catalyse many organic reactions. Samarium has been reported to cleave the N-N bond in substituted hydrazines . The azines we obtained all showed mesomorphism: the shortest were only nematic mesogens, the longest had a smectic A phase.
In this oral contribution, the results of the different techniques that were used in the search for the nematic liquid crystals, will be displayed. These will include structural and thermal data (crystal structure, structure of the mesophases, phase behaviour, optical textures, …).
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|Description: ||oral presentation by Rik Van Deun|
|Publication status: ||published|
|KU Leuven publication type: ||IMa|
|Appears in Collections:||Molecular Design and Synthesis|
Chemistry - miscellaneous
Biochemistry, Molecular and Structural Biology Section