Chalcogen versus Dative Bonding in [SF] Lewis Acid-Base Adducts: [SF(NCCH)], [SF(NCH)], and [SF(phen)] (phen = 1,10-phenanthroline).

The Lewis-acid behavior of [SF][MF] (M = Sb, As) salts toward mono- and bidentate nitrogen bases was explored. Reactions of [SF][MF] with excesses of CHCN and CHN yielded [SF(L)] (L = CHCN, CHN) salts, whereas the reaction of [SF][SbF] with equimolar 1,10-phenanthroline (phen) in CHCN afforded [SF(phen)][SbF]·2CHCN. Salts of these cations were characterized by low-temperature X-ray crystallography and Raman spectroscopy in the solid state as well as by F NMR spectroscopy in solution. In the solid state, the geometries of [SF(NCH)] and [SF(phen)] are square pyramids with negligible cation-anion contacts, whereas the coordination of CHCN and [SbF] to [SF] in [SF(NCCH)][SbF] results in a distorted octahedral coordination sphere with a minimal perturbation of the trigonal-pyramidal SF moiety. F NMR spectroscopy revealed that [SF(L)] is fluxional in excess L at -30 °C, whereas [SF(phen)] is rigid in CHCl at -40 °C. Density functional theory (DFT-B3LYP) calculations suggest that the S-N bonds in [SF(NCH)] and [SF(phen)] possess substantial covalent character and result in a regular AXE VSEPR geometry, whereas those in [SF(NCCH)] are best described as S···N chalcogen-bonding interactions via σ-holes on [SF], which is consistent with the crystallographic data.