Ab initio investigations of some molecular complexes containing hydrogen cyanide: hydrogen-bonded or donor–acceptor?

The structures, interaction energies and vibrational spectra of some molecular complexes of hydrogen cyanide with several oxygen, nitrogen and halogen compounds have been studied at the correlated level, using a triple zeta basis set with diffuse and polarization functions on all atoms. The partner molecules were chosen in order to investigate whether the structures of the complexes were of the hydrogen-bonded type, in which hydrogen cyanide acts as the proton donor, or of the electron donor–acceptor type, in which it plays the rôle of the electron donor. The computed properties of the complexes have been correlated with the nature of the partner molecule and are shown to form a consistent set of data which successfully describes the perturbations of the properties of the hydrogen cyanide monomer species as it undergoes formation of molecular complexes with other small molecules.