Neutron Structure Determination of Monosodium Acetylide, NaC2H, at 293 and 5°K
Abstract
A neutron powder-diffraction study of monosodium acetylide has been carried out. The intensity data were deduced from a number of repeated measurements in order to attain a high statistical accuracy. The resultant structure confirms the previously reported unit cell and space group determined by the x-ray powder method. Regarding the atomic parameters, the neutron values obtained using the least squares method are of considerably higher accuracy than x ray's and hence enable us to interpret the structure features to a much greater extent. The structure is tegragonal (D4h7-P4/nmm) and exhibits a large anisotropic thermal expansion as indicated by a = 3.813 (2) and c = 8.104 (3) Å at 293°K and a = 3.764 (2) and c = 8.062 (2) Å at 5°K. The unit cell contains two NaC2H units. The interatomic configuration and the thermal libration modes support the conception that the negative formal charge is virtually localized on one carbon as represented by Na+C-≡ CH. The C-≡ C distance corrected for a large precessionlike libration is 1.27 (2) Å which is considerably longer than 1.204 Å in acetylene. The equilibrium bond angle, ∠ C-≡ CH, is likely 180° and the C-H distance is 1.07 (3) Å.
- Publication:
-
Journal of Chemical Physics
- Pub Date:
- May 1972
- DOI:
- 10.1063/1.1676972
- Bibcode:
- 1972JChPh..56.4947A