title: Gas-phase reaction studies of dipositive hafnium and hafnium oxide ions: generation of the peroxide HfO2(2+).
abstract: Fourier transform ion cyclotron resonance mass spectrometry was used to characterize the gas-phase reactivity of Hf dipositive ions, Hf(2+)and HfO(2+), toward several oxidants: thermodynamically facile O-atom donor N(2)O, ineffective donor CO, and intermediate donors O(2), CO(2), NO, and CH(2)O. The Hf(2+) ion exhibited electron transfer with N(2)O, O(2), NO, and CH(2)O, reflecting the high ionization energy of Hf(+). The HfO(2+) ion was produced by O-atom transfer to Hf(2+) from N(2)O, O(2), and CO(2), and the HfO(2)(2+) ion by O-atom transfer to HfO(2+) from N(2)O; these reactions were fairly efficient. Density functional theory revealed the structure of HfO(2)(2+) as a peroxide. The HfO(2)(2+) ion reacted by electron transfer with N(2)O, CO(2), and CO to give HfO(2)(+). Estimates were made for the second ionization energies of Hf (14.5 ± 0.5 eV), HfO (14.3 ± 0.5 eV), and HfO(2) (16.2 ± 0.5 eV), and also for the bond dissociation energies, D[Hf(2+)-O] = 686 ± 69 kJ mol(-1) and D[OHf(2+)-O] = 186 ± 98 kJ mol(-1). The computed bond dissociation energies, 751 and 270 kJ mol(-1), respectively, are within these experimental ranges. Additionally, it was found that HfO(2)(2+) oxidized CO to CO(2) and is thus a catalyst in the oxidation of CO by N(2)O and that Hf(2+) activates methane to produce a carbene, HfCH(2)(2+).
authors.affiliation: Centro de Química Estrutural, Instituto Superior Técnico, Universidade Técnica de Lisboa, Lisboa, Portugal.
authors.forename: Célia
authors.initials: C
authors.lastname: Lourenço
authors.forename: Maria del Carmen
authors.initials: Mdel C
authors.lastname: Michelini
authors.forename: Joaquim
authors.initials: J
authors.lastname: Marçalo
authors.forename: John K
authors.initials: JK
authors.lastname: Gibson
authors.forename: Maria Conceição
authors.initials: MC
authors.lastname: Oliveira
mesh_terms: D002248:Carbon Monoxide / Q000737:chemistry; D002384:Catalysis; D005740:Gases / Q000737:chemistry*; D006195:Hafnium / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D016877:Oxidants / Q000737:chemistry; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D010545:Peroxides / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D005740:Gases; D016877:Oxidants; D010087:Oxides; D010545:Peroxides; C545179:hafnium oxide; D002248:Carbon Monoxide; D006195:Hafnium