Electron diffraction investigation of the molecular structures of dimethylsilyl isocyanate and dimethylsilyl isothiocyanate

Abstract

The molecular structures of dimethylsilyl Isocyanate and dimethylsilyl Isothiocyanate have been determined by electron diffraction in the gas phase. For both molecules the data are consistent with the presence of a single conformer at room temperature, the NCX group eclipsing the Si–H bond of the dimethylsilyl group. The skeletal parameters found are (NCO, NCS; distances in pm, angles in degrees):r(Si–N)171.9(5),172.3(8);r(Si–C)185.8(3),185.0(5);r(NC)121.8(4), 121.2(5); r(CO)115.5(4); r(CS) 1 57.9(5); angle NSiC 111.2(25),109.7(9); angle CSiC 113.3(50),112.3(13); angle Si–NC 1 53.5(1 3), 1 54.7(22). The NCX groups are linear. The large apparent bond angles at nitrogen suggest that these molecules are pseudolinear, like the nonmethylated silyl Isocyanate, or truly linear like silyl Isothiocyanate, both of which show shrinkage effects of similar magnitude due to the effects of a very low-frequency, high-amplitude bending vibration. The results are compared with those for some related molecules.