MOLECULAR CONFORMATION AND SUPRAMOLECULAR STRUCTURE OF CARBOSILANE, PRECURSOR OF LIQUID CRYSTALLINE PHASE. K.Yu. Suponitskii, T.V.Timofeeva, K.A. Lyssenko, N.N.Makarova Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow, Vavilov St., 28, 117813, Russia

Several years ago a series of dihydroxitetraalkyldisiloxanes has been studied by physical methods in order to find the structure-property relations for these compounds, which form termothropic liquid crystalline phases. It was found that liquid crystalline properties are due to the formation of one-dimensional columnar hydrogen bonded associates in crystal and mesophase. These associates have pseudo-hexagonal packing in crystal and form mesophase with hexagonal type of columnar packing.

In order to find other compounds inclined to form mesophases of the same type we performed conformational calculations and molecular modeling of molecular associates of dihydroxycarbosilanes and dihydroxydisiltianes. It was shown that conformational properties and associate formation for dihydroxycarbosilanes and dihydroxidisiloxanes is very close, but they are not the same for dihydroxydisiltianes.

To support the close supramolecular structure of siloxane and carbosilane derivatives crystallization and X-ray analysis of dihydroxitetra-methyldicarbosalan was performed. The one-dimensional columnar associate in this crystal was found to be nearly the same as for disiloxane. DSC and multitemperature powder X-ray data are discussed together with the data on single crystal structure.