Density functional theory study of trans-dioxo complexes of iron, ruthenium, and osmium with saturated amine ligands, trans-[M(O) 2(NH3)2(NMeH2)2] 2+ (M = Fe, Ru, Os), and detection of [Fe(qpy)(O)2] n+ (n = 1, 2) by high-resolution ESI mass spectrometry

Abstract

Density functional theory (DFT) calculations on trans-dioxo metal complexes containing saturated amine ligands, trans-[M(O)2(NH 3)2-(NMeH2)2]2+ (M = Fe, Ru, Os), were performed with different types of density functionals (DFs): 1)pure generalized gradient approximations (pure GGAs): PW91, BP86, and OLYP; 2) meta-GGAs: VSXC and HCTH407; and 3) hybrid DFs: B3LYP and PBE1PBE. With pure GGAs and meta-GGAs, a singlet d2 ground state for trans-[Fe(O) 2(NH3)2(NMeH2)2] 2+ was obtained, but a quintet ground state was predicted by the hybrid DFs B3LYP and PBE1PBE. The lowest transition energies in water were calculated to be at λ ≈ 509 and 515 nm in the respective ground-state geometries from PW91 and B3LYP calculations. The nature of this transition is dependent on the DFs used: a ligand-to-metal charge-transfer (LMCT) transition with PW91, but a π(Fe-O)→π*-(Fe-O) transition with B3LYP, in which it and π* are the bonding and antibonding combinations between the dπ(Fe) and Pπ(O2-) orbitais. The FeVI/V reduction potential of trans-[Fe(O)2-(NH 3)2(NMeH2)2]2+ was estimated to be +1.30 V versus NHE based on PW91 results. The [Fe(qpy)(O) 2]n+ (qpy = 2,2′:6′,2″:6″, 2‴:6‴,2-quinque-pyridine; N = 1 and 2) ions, tentatively assigned to dioxo iron(V) and dioxo iron(VI), respectively, were detected in the gas phase by high-resolution ESI-MS spectroscopy. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.