Crystal and molecular structures of silyl isocyanate (at –135 °C) and of germyl isocyanate (at –95 °C)

Abstract

Crystals of the title compounds are orthorhombic, space group Pnma, with Z= 4. For silyl isocyanate, a= 7.96, b= 6.52, and c= 7.10 Å(at –135 °C), while for germyl isocyanate a= 8.01, b= 6.67 and c= 6.97 Å(at –95°C); 0.3% estimated standard deviations are assumed. Crystals have been grown ‘in situ’ on a Weissenberg goniometer fitted with low-temperature equipment, and microdensitometer intensities obtained from films exposed using Cu-K_α radiation. The structures have been refined to R= 0.034 over 329 reflections for silyl isocyanate, and R= 0.049 over 266 reflections for germyl isocyanate. The compounds have similar crystal structures, involving crystallographic C_s(m) molecular symmetry and bent (zigzag) heavy-atom skeletons. Important molecular parameters are: for silyl isocyanate, Si–N 1.720(6)Å, Si–N–C 158.4(5), and N–C–O 176.4(6)°; for germyl isocyanate, Ge–N 1.856(8)Å, Ge–N–C 147.0(7) and N–C–O 173.8(9)°. Both structures contain M ⋯ N and M ⋯ O intermolecular interactions. The nitrogen interactions result in linear N ⋯ M–N groupings and may be responsible for an apparent increase in the M–N bond length as compared with molecules in the gas phase. A quantitative method for estimating the increases to M–N bond lengths is described in the Appendix.