Polymorphism of molecules and complex ions in oxygen compounds of silicon and phosphorus. Communication 4. Phase transitions and conformations of the octamethylcyclotetrasiloxane molecule [OSi(CH3)2]4
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The phase transition in crystalline octamethylcyclotetrasiloxane is due to transition of the molecules from Ci to S4 symmetry. During melting, a further change in the structure of the molecule occurs; in the liquid phase it apparently possesses C4 symmetry, which is also preserved in the gas phase.
The transformations of the molecule [OSi(CH3)2]4 consist of a change in the conformation of ring and do not lead to any significant change in the bond lengths and valence angles in the ring. A vital role in the mechanism of the molecular rearrangement is played by the lability of the SiOSi angle-thermal excitation of the nonplanar deformational vibrations of the siloxane ring.
KeywordsOxygen Silicon Phosphorus Phase Transition Liquid Phase
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