INFLUENCE OF VALENCE ENVIRONMENT ON THE O-]SI BOND IN PENTACOORDINATED SILICON-COMPOUNDS .2. CRYSTAL-STRUCTURE OF 3 O-]SI TRIFLUOROSILANES

We have determined crystal structures of three pentacoordinated silico n compounds: 3-(trifluorosilyl)-2-cyanoethylpropionate (I), N-methyl-N -(trifluorosilylmethyl)acetamide (II), and methyl-N-(trifluoro-silylme thyl)trifluoroacetamide (III). The coordination O-->Si bond length is 2729 and 2.668(5) in I (for two independent molecules), 1.879(1) in II , and 1.942(2) angstrom in III. We concluded that mutual orientation o f the carboxyl group and the = O-->Si bond has a strong effect on the length of the latter. In the molecular packing of I, there is a struct ural motif of rows of close-packed SiF3 fragments.