Molecular Structure of Isocyanic Acid, HNCO, the Imide of Carbon Dioxide

Isocyanic
acid, HNCO, the imide of carbon dioxide, was prepared
by reaction of stearic acid and potassium cyanate (KOCN) at 60 °C
in a sealed, thoroughly dried reactor. Interestingly, its crystal
structure, solved by X-ray single crystal diffraction at 123(2) K,
shows a group–subgroup relation for the NCO– anion to carbon dioxide: (for CO2, cP12, Pa3̅, a = 5.624(2) Å,
150 K, C–O 1.151(2) Å; for HNCO, oP16, Pca21, a = 5.6176(9), b = 5.6236(8), c = 5.6231(7) Å, 123(2)
K). Precise positions of H, N, C, and O were determined by DFT calculations
with WIEN2k leading to interatomic distances C–O 1.17, C–N
1.22, N–H 1.03, and −N–H···N 2.14
Å, and the interatomic angle N–C–O 171°.