Complexes of O=C=S with Nitrogen Bases: Chalcogen Bonds, Tetrel Bonds, and Other Secondary Interactions

다국어 초록 (Multilingual Abstract)

Ab initio MP2/aug’‐cc‐pVTZ calculations have been carried out to investigate chalcogen‐bond formation through the σ‐hole at S and tetrel‐bond formation through the π‐hole at C in complexes of OCS with a series of nitrogen bases. The binding energies of chalcogen‐ and tetrel‐bonded complexes with the sp‐hybridized bases correlate exponentially with the N−S and N−C distances, respectively. The presence of secondary interactions between an N−H or C−H group of an sp2‐hybridized base and OCS in chalcogen‐bonded complexes decreases the correlation between binding energies and the N−S distance. These secondary interactions are stronger in the tetrel‐bonded complexes with the sp2 bases, particularly in the isomers of OCS:imidazole and OCS : N2H2, where they may be described as distorted N−H⋅⋅⋅O or N−H⋅⋅⋅S hydrogen bonds. Charge‐transfer interactions are consistent with the nature of the primary and secondary interactions in these complexes. The in‐plane OCS bending frequencies are blue‐shift in the chalcogen‐bonded complexes, and red‐shifted in the tetrel‐bonded complexes. EOM‐CCSD spin‐spin coupling constants 1cJ(N4−S) across chalcogen bonds have absolute values less than 9.0 Hz, while the two‐bond coupling constants 2cJ(N4−C) do not exceed 4.0 Hz. These are greater in absolute value that the one‐bond coupling constants 1tJ(N4−C) across tetrel bonds that are less than 0.5 Hz at much shorter N−C distances.
Ab initio calculations have been carried out to investigate chalcogen‐ and tetrel‐bonded complexes of OCS with nitrogen bases. Binding energies correlate with N−S and N−C distances in complexes with sp nitrogen bases but not with sp2 bases, due to the presence of secondary interactions. The nature of charge‐transfer is consistent with the primary and secondary interactions in these complexes. OCS inplane bending frequencies and spin‐spin coupling constants across intermolecular bonds also characterize these bonds.