The reaction of suitable organic groups in combination with well defined inorganic silsequioxane cores leads to covalently bound organic-inorganic hybrid materials, which exhibit nematic and smectic C phase behaiour close to room temperature.
New derivatives of hexamethyldisilazanelithium of the general formula [X−Me2Si−N−SiMe2−X]2Li2 (X = Ph (2), C4H3S (3), NMe2 (4), NEt2 (5), N(H)iPr (6), OPh (7), OSiMe3 (8), C4H3O (9)) have been synthesized and characterized by spectroscopic means. All compounds except 3 have been subjected to X-ray structure determinations which reveal a common polycyclic arrangement with a central Li2N2 four-membered ring to which four similar LiNSiY rings are annealed along a common Li−N edge (Y can either be a carbon atom of a π-system (2, 3), nitrogen (4−6) or oxygen (7−9)). The common four-membered polycyclic skeleton Li2N2Si4Y4 has a point symmetry of approximately D 2 (222) of which only C 2 (2) symmetry is retained in the crystals of 4, 5, 6, and 9, whereas all other derivatives have point symmetry C 1 (1). One of the compounds crystallizes in one enantiomeric form (4) in an acentric structure. All other compounds crystallize in centrosymmetric structures with the two enantiomers present in the crystal. The lithium atoms in 2−9 are present in a distorted tetrahedral environment constituted by two nitrogen and two Y atoms. From molecular mass determinations, the compounds seem to retain their dimeric nature in benzene, the NMR patterns being nevertheless more simple than expected from the crystal structures and indicate a dynamic behavior in solution. None of these compounds, so far, shows lithium motion in the solid state up to room temperature, although phase transitions seem to occur in compound 8 at higher temperatures (13C SPE/MAS NMR evidence). Li−N distances in the central Li2N2 ring depend on the nature of donor groups Y: short Li−N bonds (2.024 Å) are found for the lithium atoms coordinated by organic π-systems together with relatively long Li−C bonds (2.53 Å in 2), whereas longer Li−N bonds (2.07−2.085 Å) are encountered for the nitrogen donors with short Li−N “donor” bonds (2.157 (4), 2.163 (5), 2.121 Å (6)). If the donor atom (Y) is oxygen, the Li−O bonds can be either shorter than the Li−N bonds (7, Li−N 2.073, Li−O 1.978 Å; 9, Li−N 2.076, Li−O 1.977 Å) or slightly longer (8, Li−N 2.021, Li−O 2.077 Å). It is remarkable that in the trimethylsilyloxy case 8 the Li−N distances are not equal within their standard deviations as observed in the other cases: two distances (average 1.96 Å) on opposite sides of the Li2N2 ring are much shorter than the remaining two (average 2.08 Å).
The controlled synthesis of nematic nanophase‐separated materials poses an attractive synthetic challenge. The use of carbosilazane multipodes and dendrimers (such as 1) in conjunction with laterally attached mesogens allows the systematic investigation of the structure–property relationships of room‐temperature nematic liquid crystals.
A novel family of air-stable dendrimers with a N−Si−C framework has been prepared up to the fourth generation. The divergent synthesis starts with the hydrosilylation of the trisilazane N(SiMe2vinyl)3 [0-G(vinyl)] by HSiMe2Cl, which gives the three-directional core molecule N(SiMe2CH2CH2SiMe2Cl)3 [0-G(Cl)]. A 1-to-2 branching achieved by reacting the core molecule [0-G(Cl)] with 3 equiv of KN(SiMe2vinyl)2 affords the first generation dendrimer [1-G(vinyl)]. By repeating the above two steps, the second [2-G(vinyl)], third [3-G(vinyl)], and fourth generation [4-G(vinyl)] can be obtained. The compounds have been characterized by 1H, 13C, and 29Si NMR spectroscopy, by elemental analysis, and up to the third generation by MALDI-TOF mass spectrometry. Gel permeation chromatography was used to prove the fourth generation [4-G(vinyl)].
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.