The structure of [WOF4](4) has been reinvestigated by low-temperature X-ray crystallography and DFT (MN15/def2-SVPD) studies. Whereas the W4F4 ring of the tetramer is planar and disordered in the solid state, the optimized gas-phase geometry prefers a disphenoidally puckered W4F4 ring and demonstrates asymmetric fluorine bridging. Dissolution of MOF4 (M = Mo, W) in SO2 and SF(4 )results in the formation of MOF4 (OSO) and [SF3]-[M2O2F9], respectively. Both SO2 adducts and [SF3][Mo2O2F9] have been characterized by X-ray crystallography. The crystal structure of [SF3][Mo2O2F9] reveals dimerization of the ion pair that results in a rare heptacoordinate sulfur center. Optimization of the {[SF3][M2O2F9]}(2) dimers in the gas phase, however, results in the elongation of one contact such that the sulfur centers are effectively hexacoordinate. Meanwhile, the crystal structure of [SF3][W2O2F9].HF instead demonstrates hexacoordinate sulfur centers and a highly unusual coordination to [SF3](+) from [W2O2F9](-) through an oxido ligand. While [SF3] [W2O2F9] does not decompose at ambient temperature, MOF4 (OSO) and [SF3][Mo2O2F9] are unstable toward evolution of SO2 or SF4. Computational studies reveal that the monomerization of [WOF4](4) in the gas phase at 25 degrees C is thermodynamically unfavorable using SO2, but favorable using SF4, consistent with the relative thermal stabilities of WOF4 (OSO) and [SF3][W2O2F9].