A chalcogen-bonded complex H₃N⋯S=C=S formed by ammonia and carbon disulfide characterised by chirped-pulse, broadband...

Ground-state rotational spectra were observed for ten symmetric-top isotopologues H₃N⋯S=C=S, H₃N⋯³⁴S=C=S, H₃N⋯S=C=³⁴S, H₃N⋯S=¹³C=S, H₃ ¹⁵N⋯S=C=S, H₃ ¹⁵N⋯³⁴S=C=S, H₃ ¹⁵N⋯S=C=³⁴S, H₃ ¹⁵N⋯S=¹³C=S, H₃ ¹⁵N⋯³³S=C=S, and H₃ ¹⁵N⋯S=C=³³S, the first five in their natural abundance in a mixture of ammonia and carbon disulphide in argon and the second group with enriched ¹⁵NH₃. The four asymmetric-rotor isotopomers H₂DN⋯S=C=S, H₂DN⋯³⁴S=C=S, H₂DN⋯S=C=³⁴S, and HD₂N⋯S=C=S were investigated by using a sample composed of ND₃ mixed with CS₂. Rotational constants, centrifugal distortion constants, and ³³S nuclear quadrupole coupling constants were determined from spectral analyses and were interpreted with the aid of models of the complex to determine its symmetry, geometry, one measure of the strength of the intermolecular binding, and information about the subunit dynamics. The complex has C_3v symmetry, with nuclei in the order H₃N⋯S=C=S, thereby establishing that the non-covalent interaction is a chalcogen bond involving the non-bonding electron pair of ammonia as the nucleophile and the axial region near one of the S atoms as the electrophile. The small intermolecular stretching force constant k_σ = 3.95(5) N m^-1 indicates a weak interaction and suggests the assumption of unperturbed component geometries on complex formation. A simple model used to account for the contribution of the subunit angular oscillations to the zero-point motion leads to the intermolecular bond length r(N⋯S) = 3.338(10) Å.