THE GENERATION OF UNUSUAL NOBLE-METAL CATIONS IN FLUORO ACIDS AND SUPER ACIDS, AND THEIR SPECTROSCOPIC PROPERTIES

Two types of highly electrophilic cations, 'bare' M(2+) or carbonyl cations, formed by the noble metals palladium and platinum (Group 10) and silver and gold (Group 11) in low oxidation states (+1 or +2) are generated in highly acidic media. The acidic media consists of: the Bronsted superacid HSO3F; the Lewis superacid SbF5; and the conjugate superacid HSO3F-SbF5. Derived from these superacids are the very weakly nucleophilic anions SO3F- or Sb2F11- as counterions to stabilize the cations in solids. Finally, stabilization of the highly electrophilic cations by coordination to CO leads to isolable complexes, unprecedented in transition-metal chemistry in their structural, spectroscopic and bonding characteristics. The cations discussed include, in addition to 'bare' M(2+) (M=Ag or Au): linear [M(CO)(n)](+), M=Ag or Au, n=1 or 2; cyclic [Pd-2(mu-CO)(2)](2+); square-planar [M(CO)(4)](2+); the fluorosulfate derivatives cis-M(CO)(2)(SO3F)(2), M=Pd or Pt; and Ir(CO)(3)(SO3F)(3). Recently, the first post-transition-metal carbonyl cations, [Hg-n(CO)(2)](2+), n=1 or 2, have been obtained, stabilized by Sb2F11-. Characterization of these species by magnetochemical methods, vibrational and C-13 NMR spectroscopy, and single-crystal X-ray diffraction is discussed.