Strongly bound noncovalent (SO3)n:H2CO complexes (n = 1, 2)

Abstract

The potential energy surfaces (PES) for the SO₃:H₂CO and (SO₃)₂:H₂CO complexes were thoroughly examined at the MP2/aug-cc-pVDZ computational level. Heterodimers and trimers are held together primarily by S⋯O chalcogen bonds, supplemented by weaker CH⋯O and/or O⋯C bonds. The nature of the interactions is probed by a variety of means, including electrostatic potentials, AIM, NBO, energy decomposition, and electron density redistribution maps. The most stable dimer is strongly bound, with an interaction energy exceeding 10 kcal mol⁻¹. Trimers adopt the geometry of the most stable dimer, with an added SO₃ molecule situated so as to interact with both of the original molecules. The trimers are strongly bound, with total interaction energies of more than 20 kcal mol⁻¹. Most such trimers show positive cooperativity, with shorter S⋯O distances, and three-body interaction energies of nearly 3 kcal mol⁻¹.