Syntheses, molecular structures, and vibrational spectra of chloropentacarbonylrhodium(III) and -iridium(III) undecafluorodiantimonate(V), [Rh(CO)5Cl][Sb2F11]2 and [Ir(CO)5Cl][Sb2F11]2: an experimental and density functional study.

Abstract

The reactions of either bis(mu-chloro)tetracarbonyldirhodium(I), [Rh(CO)2(mu-Cl)]2, or chlorotricarbonyliridium(I), [Ir(CO)3Cl]n, in the conjugate Brønsted-Lewis superacid HF-SbF5 and in a CO atmosphere, produce [Rh(CO)5Cl][Sb2F11]2 or [Ir(CO)5Cl][Sb2F11]2, respectively. In these oxidative carbonylation reactions, antimony(V) fluoride functions as an oxidizing agent. The reduced product is identified as 6SbF3.5SbF5. [Rh(CO)5Cl][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) A; beta = 106.51(1) degrees; V = 1237.7(2) A3; Z = 2; T = 300 K; R1 [I > 3 sigma (I)] = 0.0367, wR2 = 0.0739. Single crystals of [Ir(CO)5Cl][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)5Cl][Sb2F11]2: monoclinic, space group P2(1) (No. 4); a = 9.686(2), b = 12.585(2), c = 10.499(2) A; beta = 106.59(2) degrees; V = 1226.5(4) A3; Z = 2; T = 294 K; R1[I > 3 sigma (I)] = 0.032, Rw = 0.031. The bond lengths and bond angles are nearly identical in the two isostructural salts; however, the cell volume of [Ir(CO)5Cl][Sb2F11]2 is slightly smaller than that of [Rh(CO)5Cl][Sb2F11]2. The cations (point group C4v) 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)5Cl][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)5Cl]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)5Cl]2+ is the first cationic carbonyl derivative of Rh(III), the vibrational and structural parameters for [Ir(CO)5Cl]2+ are compared to data for [Ir(CO)6]3+ and mer-Ir(CO)3(SO3F)3.