A chalcogen-bonded complex (CH3)3N•••S=C=O characterised by rotational spectroscopy

Rotational spectra of 5 isotopologues of (CH3)(3)N center dot center dot center dot S=C=O were observed by chirped-pulse, Fourier-transform microwave spectroscopy. Spectroscopic constants B-0, D-J, D-JK and the N-14 nuclear quadrupole coupling constant chi(aa)(N-14) determined for the symmetric-top isotopologues (CH3)(3)N center dot center dot center dot S=C=O, (CH3)(3)N center dot center dot center dot S-34=C=O, (CH3)(3)N center dot center dot center dot S=C-13=O, (CD3)(3)N center dot center dot center dot S=C=O and ((CH3)-C-12)(2)((CH3)-C-13)N-14 center dot center dot center dot S=C=O show that the intermolecular binding involves a chalcogen bond to S rather than O. Changes in various properties (the distance r(N center dot center dot center dot S) and the force constants k(sigma) and k(theta theta) associated with intermolecular stretching and angular oscillation theta of the trimethylamine subunit, respectively) from those of H3N center dot center dot center dot S=C=O allow for the effect of complete methylation of NH3 on the chalcogen bond to be assessed.