The preferred conformation of the tetrafluoro-1,3-dithietaneisopropylamine complex as revealed by rotational spectroscopy.

The 1 : 1 intermolecular complex formed between tetrafluoro-1,3-dithietane and isopropylamine has been studied in a supersonic-jet using Fourier transform microwave spectroscopy. Two isomers, in which the isopropylamine monomer adopts the gauche or trans conformation, were experimentally observed. Isomer formed by gauche isopropylamine has a higher population than that formed by trans with a relative ratio of 3 : 2, contrary to the relative stability of the isopropylamine monomer. In both isomers, the two moieties are linked through a dominant SN chalcogen bond and cooperative secondary interactions. Natural bond orbital theory analysis confirms that the SN interaction formed by gauche isopropylamine is 3.4 kJ mol-1 stronger than that formed by the trans conformer. Symmetry-adapted perturbation theory energy decomposition analysis points out that the intermolecular interactions in the complex are dominated by electrostatics and remarkable charge transfer in the complexation.