title: Predominantly sigma-bonded metal carbonyl cations (sigma-carbonyls): new synthetic, structural, and bonding concepts in metal carbonyl chemistry.
abstract: Predominantly sigma-bonded metal carbonyl cations (sigma-carbonyls) are conveniently generated in the Lewis superacid SbF(5) or the conjugate Brønsted-Lewis superacid HFbondSbF(5), primarily by solvolytic or reductive carbonylations. Thermally stable salts are formed with the fluoroantimonate(V) ions [SbF(6)](-) and [Sb(2)F(11)](-). The salts are characterised by analytical, structural, spectroscopic and computational methods. Most homoleptic carbonyl cations have very regular geometries, comensurate with their d-electron configurations: linear (d(10)), square planar (d(8)) or octahedral(d(6)). The cations with metals in oxidation states of +2 or +3 are termed "superelectrophilic". Extended molecular structures form by significant interionic C-F contacts with electrophilic carbon as acceptor. To account for all experimental observations, a conceptually simple synergetic bonding model is proposed. An outlook at anticipated future developments based on very recent results is provided.
authors.affiliation: Fakultät 4, Anorganische Chemie, Gerhard Mercator Universität, Lotharstr. 1, 47048 Duisburg, Germany. willner@uni-duisburg.de
authors.forename: Helge
authors.initials: H
authors.lastname: Willner
authors.forename: Friedhelm
authors.initials: F
authors.lastname: Aubke