Heteroorganic betaines 2. X-ray diffraction study of betaines containing the P+-C-Si-S- fragment

The structures of three silicon-containing organophosphorus betaines contai ning the P+-C-Si-S- fragment were established by X-ray diffraction study. D ue to the attractive electrostatic interaction between the anionic and cati onic centers, the main chain adopts a gauche conformation, whereas this cha in in the S-ethyl derivative of the phosphonic salt [Ph3P+-CMe2-SiMe2SEt]Br - adopts a trans conformation. The changes in the geometric parameters of b etaines depending on the substituents at the phosphorus, carbon, and silico n atoms were analyzed. The P-S bond can in principle be formed, resulting i n the closure of the four-membered ring provided that additional steric hin drances at the silicon atom occur.