Cyanogen isocyanate and dicyanoether: ab initio studies of geometries and electronic structures

Complete geometry optimizations, employing a minimal STO-3G basis set, have been applied to the recently-prepared cyanogen isocyanate [NCNCO] and to the isomeric dicyanoether [NCOCN]. Cyanogen isocyanate is found to be a rather flexible molecule with the computed barrier to inversion about the central nitrogen being ~5 k cal mol^?1. In addition, the inversion motion is found to be coupled to the bending of the NCN and OCN linkages away from colinearity. On the other hand, dicyanoether is predicted to be a fairly rigid molecule, with no important inversion motions. Both molecules are predicted to have planar trans bent equilibrium structures similar to that found for the simpler HNCO-HOCN isomers. Cyanogen isocyanate is predicted to be the more stable isomer. Electronic structures of these molecules are discussed in the light of the results of a Mulliken population analysis.