Tetrahedrally Substituted Tribenzosilatranes:  Mesomorphic Properties and Structures

Abstract

The tribenzosilatrane moiety has been substituted with four long paraffinic chains. The physicochemical properties (optical microscopy, differential scanning calorimetry) of the condensed phases have been determined as a function of the chain length. Several crystalline or mesomorphic phases have been characterized by X-ray diffraction. In some cases, original layered structures have been found with a hexagonal order within the lamellae. However, none of the mesophases can be attributed to the class of plastic crystals. A globularity criterion has been defined which relates the shape of the molecular unit with the type of arrangement in the mesophases.

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“…If the aromatic cores are non-linear, then other organisations can occur within the layers. So, in the aromatic layers of the smectic phases of the tribenzosilatranes 34 141 and the triptycenes 35, 142 the C 3 -symmetric cores are organised in two-dimensional hexagonal lattices (Sm h phases).…”

6 Non-conventional soft matter

“…compound 10 70 ), octahedral tris(1,3-diketonates) of Fe, Co, Mn and Cr 427,428 (e.g. compound 120), square antiprismatic Zr tetrakis-1,3-diketonates) 121, 429 tetrahedral copper(I) complexes of multichain pyridine ligands 303,430 like 122, 431 the C 3 symmetric tribenzosilatranes 123 432 and triptycenes 124. 433 In dependence on the number of chains with respect to the core size, micellar cubic mesophases (compounds 8 62 and 10 70 ), columnar mesophases (compounds 120-122) and smectic phases (compounds 123 and 124) have been obtained with such materials.…”

“…Within the aromatic layers the molecules are organised in a two-dimensional hexagonal lattice (Sm h phase). 432 In some respects the ionic 1,4-diazabicyclooctane derived amphiphiles 128, which contain only two alkyl chains, can also be included in this group of mesogenic materials. 437 Here, the spherical diazabicyclooctane cores and counter-ions are organised within polar layers in tetragonal 2D-lattices (Sm t phase) (Fig.…”