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

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journal contribution
posted on 20.02.2015 by Vincent de Paul N. Nziko, Steve Scheiner
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···O chalcogen bond, sometimes augmented by CH···F or CH···O H-bonds. The strength of the intramolecular S···O bond is estimated to lie in the range between 3 and 6 kcal/mol. A secondary effect of the S···O chalcogen bond is elongation of the S–F bonds. Solvation of the molecule strengthens the S···O interaction. Addition of substituents to the phenyl ring has only modest effects upon the S···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.