The oxidation of molybdenum hexacarbonyl, Mo(CO)(6), by antimony(V) fluoride, SbF5, at 60 degrees C in an excess of liquid SbF5, produces polymeric [{Mo(CO)(4)}(2)(cis-mu-F2SbF4)(3)](x)[Sb2F11](x) as the main product. Recrystallization from HF-SbF5 produces orange prismatic crystals, suitable for a single-crystal X-ray diffraction study. Crystals of [{Mo(CO)(4)}(2)(cis-mu-F2SbF4)(3)](x)[Sb2F11](x) are monoclinic, space group P2(1)/c (No. 14), a = 9.234(4) Angstrom, b = 13.858(3) Angstrom, c = 25.790(3) Angstrom, beta = 90.532(2)degrees, V = 3300.1(12) Angstrom(3), and Z = 4. The structure was solved by the Patterson method and refined with anisotropic thermal parameters to R = 0.048 and R-w = 0.047 (on F, 472 variables, 5116 observations with I greater than or equal to 3 sigma(I)). In the polymeric cation, two pyramidal Mo(CO)(4) groups are linked by bridging, iso-bidentate F2SbF4 groups first into eight-membered rings, which are then further linked into polymeric chains. The bridging F2SbF4 groups and the [Sb2F11](-) anion are involved in significant intermolecular and interionic F ... C contacts to the C atoms of the Mo(CO)(4) groups.