The reactions of either bis(mu-chloro)tetracarbonyldirhodium(I), [Rh(CO)(2()mu-Cl)](2), or chlorotricarbonyliridium(I), [Ir(CO)(3)Cl](n), in the conjugate Bronsted-Lewis superacid HF-SbF5 and in a CO atmosphere, produce [Rh-(CO)(5)Cl][Sb2F11](2) or [Ir(CO)(5)Cl][Sb2F11](2), respectively. In these oxidative carbonylation reactions, antimony(V) fluoride functions as an oxidizing agent. The reduced product is identified as 6SbF(3). 5SbF(5). [Rh(CO)(5)Cl][Sb2F11]2 is obtained in the form of single crystals. Crystal data: monoclinic, space group P2(1) (No. 4); a = 9.721(1), b = 12.602(1), c = 10.538(1) Angstrom; beta = 106.51(1)degrees; V = 1237.7(2) Angstrom(3); Z = 2; T = 300 K; R-1 [I > 3 sigma(r)] = 0.0367, wR(2) = 0.0739. Single crystals of [Ir(CO)(5)Cl][Sb2F11](2) are produced in small amounts from a solution of mer-Ir(CO)(3)-(SO3F)(3) in magic acid, HSO3F-SbF5. The possible source of chlorine will be discussed. Crystal data for [Ir-(CO)(5)Cl][Sb2F11](2): monoclinic; space group P21 (No. 4); a = 9.686(2), b = 12.585(2), c = 10.499(2) Angstrom; beta 106.59(2)degrees; V = 1226.5(4) Angstrom(3); Z = 2; T = 294 K; R-1[I > 3 sigma(1)] = 0.032, R-w = 0.031. The bond lengths and bond angles are nearly identical in the two isostructural salts; however, the cell volume of [Ir(CO)(5)Cl][Sb2F11](2) is slightly smaller than that of [Rh(CO)(5)Cl][Sb2F11](2). The cations (point group C-4v) feature unusually long M-C bonds (M = Rh, Ir) and correspondingly short CO bonds, as well as high CO stretching wavenumbers and high CO stretching force constants. The [Sb2F11](-) anions are not symmetry related, and their dihedral and bridge angles differ slightly in both salts. There are significant interionic contacts in [Ir(CO)(5)Cl][Sb2F11](2) exclusively of the C-F type (about 2 for each C atom of the five carbonyl groups) resulting in extended structures. The vibrational spectra for both [M(CO)(5)Cl](2+) cations (M = Rh, Ir) are assigned with the help of density functional calculations, which also provide intensities for IR and Raman bands. While [Rh(CO)(5)Cl](2+) is the first cationic carbonyl derivative of Rh(III), the vibrational and structural parameters for [Ir(CO)(5)Cl](2+) are compared to data for [Ir(CO)(6)](3+) and mer-Ir(CO)(3)(SO3F)(3).