Intramolecular S center dot center dot center dot O Chalcogen Bond as Stabilizing Factor in Geometry of Substituted Phenyl-SF3 Molecules

摘要

Density functional methods are used to examine the geometries and energetics of molecules containing a phenyl ring joined to the trigonal bipyramidal SF3 framework. The phenyl ring has a strong preference for an equatorial position. This preference remains when one or two ether -CH2OCH3 groups are added to the phenyl ring, ortho to SF3, wherein an apical structure lies nearly 30 kcal/mol higher in energy. Whether equatorial or apical, the molecule is stabilized by a S center dot center dot center dot O chalcogen bond, sometimes augmented by CH center dot center dot center dot F or CH center dot center dot center dot O H-bonds. The strength of the intramolecular S center dot center dot center dot O bond is estimated to lie in the range between 3 and 6 kcal/mol. A secondary effect of the S center dot center dot center dot O chalcogen bond is elongation of the SF bonds. Solvation of the molecule strengthens the S center dot center dot center dot O interaction. Addition of substituents to the phenyl ring has only modest effects upon the S center dot center dot center dot O bond strength. A strengthening arises when an electron-withdrawing substituent is placed ortho to the ether and meta to SF3, while electron-releasing species produce an opposite effect.