Showing papers by "Lester Andrews published in 2012"
TL;DR: Matrix-isolation experiments and quantum-chemical calculations have led to the characterization of two new compounds, namely first open-shell binary gold fluoride, AuF(2), and a NeAuF complex.
Abstract: Noble with a difference: Matrix-isolation experiments and quantum-chemical calculations have led to the characterization of two new compounds, namely first open-shell binary gold fluoride, AuF(2), and a NeAuF complex. Moreover, ArAuF, AuF(3), Au(2)F(6), and monomeric AuF(5) have been produced and identified under cryogenic conditions in neon and argon matrices.
54 citations
TL;DR: In this paper, the matrix IR spectra from reactions of laser-ablated Th and U atoms with acetonitrile was analyzed, and the N-coordination and methylidyne products (M←NCCH3 and HCM(H)2NC) were observed.
28 citations
TL;DR: The weak O-F bond in OF(2) as well as the strong U-O, U-F and Th-O , Th-F bonds make reaction to form the OUF (2) and OThF( 2) molecules highly exothermic.
Abstract: The terminal oxo species OUF2 and OThF2 have been prepared via the spontaneous and specific OF2 molecule reactions with laser ablated uranium and thorium atoms in solid argon and neon. These isolated molecules are characterized by one terminal M-O and two F–M–F (M = U or Th) stretching vibrational modes observed in matrix isolation infrared spectra, which are further supported by density functional frequency calculations and CASPT2 energy and structure calculations. Both molecules have pyramidal structures with singlet (Th) and triplet (U) ground states. The molecular orbitals and metal–oxygen bond lengths for the OUF2 and OThF2 molecules indicate triple bond character for the terminal oxo groups, which are also substantiated by NBO analysis at the B3LYP level and by CASPT2 molecular orbital calculations. Dative bonding involving O2p → Th6d and Udf interactions is clearly involved in these oxoactinide difluoride molecules. Finally, the weak O–F bond in OF2 as well as the strong U–O, U–F and Th–O, Th–F bon...
27 citations
TL;DR: The formation of group 4 OMF(2) molecules is highly exothermic due to the weak O-F bonds in OF(2), as well as the strong new MO and M-F bond formed.
Abstract: The isolated group 4 metal oxydifluoride molecules OMF2 (M = Ti, Zr, Hf) with terminal oxo groups are produced specifically on the spontaneous reactions of metal atoms with OF2 through annealing in solid argon. The product structures and vibrational spectra are characterized using matrix isolation infrared spectroscopy as well as B3LYP density functional and CCSD(T) frequency calculations. OTiF2 is predicted to have a planar structure while both OZrF2 and OHfF2 possess pyramidal structures, all with singlet ground states. Three infrared absorptions are observed for each product molecule, one M–O and two M–F stretching modes, and assignments of these molecules are further supported by the corresponding 18O shifts. The molecular orbitals of the group 4 OMF2 molecules show triple bond character for the terminal oxo groups, which are also supported by an NBO analysis. These molecular orbitals include a σ bond (O2p + Tisd hybrid), a normal electron pair π bond (O2p + Tid), and a dative π bond arising from O lone pair donation to the overlapping Ti d orbital. The M–O bond dissociation energies for OMF2 are comparable to those in the diatomic oxide molecules. The OTiF intermediate is also observed through two slightly lower frequency bond stretching modes, and its yield is increased in complementary TiO + F2 experiments. Finally, the formation of group 4 OMF2 molecules is highly exothermic due to the weak O–F bonds in OF2 as well as the strong new MO and M–F bonds formed.
24 citations
TL;DR: Infrared spectra of the matrix isolated OMS, OM(η(2)-SO), and OM (M = Ti, Zr, Hf) molecules were observed following laser-ablated metal atom reactions with SO(2) during condensation in solid argon and neon.
Abstract: Infrared spectra of the matrix isolated OMS, OM(η(2)-SO), and OM(η(2)-SO)(η(2)-SO(2)) (M = Ti, Zr, Hf) molecules were observed following laser-ablated metal atom reactions with SO(2) during condensation in solid argon and neon. The assignments for the major vibrational modes were confirmed by appropriate S(18)O(2) and (34)SO(2) isotopic shifts, and density functional vibrational frequency calculations (B3LYP and BPW91). Bonding in the initial OM(η(2)-SO) reaction products and in the OM(η(2)-SO)(η(2)-SO(2)) adduct molecules with unusual chiral structures is discussed.
24 citations
TL;DR: Results reveal that coordination of group 3 metal atoms to the acetylene π-bond and H-migration from C to M readily occur during codeposition and photolysis afterward.
Abstract: The major HM-C≡CH and M-η(2)-C(2)H(2) products are observed in the matrix infrared spectra from reactions of laser-ablated group 3 metal atoms with acetylene, while the vinylidene product is not detected. These results reveal that coordination of group 3 metal atoms to the acetylene π-bond and H-migration from C to M readily occur during codeposition and photolysis afterward. The product absorption assigned to the La-vinylidene complex in a previous study is reassigned to one of the absorptions of La-η(2)-C(2)H(2)···C(2)H(2). Two strong Sc-H stretching absorptions are assigned to the free HSc-CCH(-) anion, in accord with a previous study, but a lower frequency counterpart is reassigned to HSc-CCH(-) coordinated to acetylene based on the increasing relative intensity of the low-frequency component at higher acetylene concentration. The group 3 metals evidently form weaker π-complexes than the group 4 metals. The addition of an electron to HM-CCH elongates the M-H and M-C bonds in the anionic species due to the lower ionic contributions to the bonding.
23 citations
22 citations
TL;DR: In this article, it was shown that the Agostic interaction in the methylidene complex is apparently insignificant and this rare observation of a methylidyne product with Re reflects that H migration in the isocyanide system is less favorable than those in the hydride and halide analogues.
15 citations
14 citations
TL;DR: The previous and present experimental and computational results indicate that the higher oxidation state complexes become less favored with increasing atomic mass in groups 14 and 15, which is opposite the general trend found for transition metals.
Abstract: Methane activation has been carried out by laser-ablated Sn, Pb, Sb, and Bi atoms. All four metals generate the insertion complex (CH3–MH), but subsequent H-migration from C to M to form CH2–MH2 and CH–MH3 complexes is not observed. Our previous and present experimental and computational results indicate that the higher oxidation state complexes become less favored with increasing atomic mass in groups 14 and 15, which is opposite the general trend found for transition metals. The C–H bond insertion evidently occurs during reaction on sample condensation, and the product dissociates on broad-band photolysis afterward. The insertion complex contains a near right angle C–M–H moiety because of high p contribution from the metal center to the C–M and M–H bonds unlike many transition-metal analogues. The computed methylidene structures for these main group metals are not agostic possibly because of the absence of valence d-orbitals.
14 citations
TL;DR: In annealing, the π complex is produced, and it converts to the insertion product during photolysis with no trace of the vinylidene product, consistent with the considerably higher activation energy to H(2)CCM than that to HM-CCH in the previously proposed reaction path.
Abstract: The π and C–H insertion complexes (M-η2-C2H2 and HM-C≡CH) are identified in the matrix infrared spectra from reactions of laser-ablated Group 6 metal atoms with acetylene. In annealing, the π complex is produced, and it converts to the insertion product during photolysis with no trace of the vinylidene product. This observation is consistent with the considerably higher activation energy to H2CCM than that to HM-CCH in the previously proposed reaction path, whereas the three plausible products are in fact energetically comparable. The back-donations in the Group 6 metal π complexes are evidently weaker than those in the Groups 3–5 metal analogues but still stronger than those in the main group and Group 7–10 metal systems. The insertion complexes have bent CMH moieties in contrast with the linear Mn complex.
TL;DR: In this article, the M←NCCH3, η2-M(NC)-MNC, CH3, CH2 M(H)2NC, and HC W(H)-2X complexes are produced by reactions of laser-ablated Group 6 metal atoms with acetonitrile and identified from the matrix IR spectra through isotopic substitution and comparison to frequencies calculated by density functional theory.
TL;DR: Density functional calculations suggest it is highly exothermic for fluorine transfer from OF( 2) to scandium, which favors the formation of the OScF(2) radical species as well as the O ScF molecule after fluorine loss.
Abstract: The scandium oxydifluoride free radical, OScF(2), is produced by the spontaneous, specific reaction of laser ablated Sc atoms with OF(2) in solid argon and characterized by using matrix infrared spectroscopy and theoretical calculations. The OScF(2) molecule is predicted to have C(2v) symmetry and a (2)B(2) ground state with an unpaired electron located primarily on the terminal oxygen atom, which makes it a scandium difluoride molecule coordinated by a neutral oxygen atom radical in forming the Sc-O single bond. The closed shell singlet OScF molecule with an obtuse bent geometry has a much shorter Sc-O bond of 1.682 A than that of the OScF(2) radical (1.938 A) on the basis of B3LYP calculations. The Sc-O bond in OScF consists of two covalent bonds and a dative bond in which the oxygen 2p(π) lone pair donates electron density into an empty Sc 3d orbital thus forming a triple oxo bond. Density functional calculations suggest it is highly exothermic for fluorine transfer from OF(2) to scandium, which favors the formation of the OScF(2) radical species as well as the OScF molecule after fluorine loss.
TL;DR: In this article, the reaction of ThO molecules and CH4 have been investigated in solid argon near 4 K. The CH3Th(O)H molecule is produced when the sample is exposed to UV irradiation.
Abstract: Reactions of ThO molecules and CH4 have been investigated in solid argon near 4 K. The CH3Th(O)H molecule is produced when the sample is exposed to UV irradiation. Identification of this new interm...
TL;DR: In this article, the oxidifluoride molecules, OYF2 and OLaF2, are produced via the reactions of laser ablated metal atoms with OF2 in solid argon.
Abstract: The oxidifluoride molecules, OYF2 and OLaF2, are produced via the reactions of laser ablated metal atoms with OF2 in solid argon. The product structures are characterized using matrix isolation inf...
TL;DR: In this paper, a reaction mechanism of the possible reaction paths for these reactions is discussed, and the reaction products have been identified by isotopic substitutions as well as density functional theoretical frequency calculations.
TL;DR: In this article, the title molecules were prepared by reaction of OF2 molecules with laser ablated uranium and thorium atoms in solid argon and neon, and they were shown to be stable.
Abstract: The title molecules are prepared by reaction of OF2 molecules with laser ablated uranium and thorium atoms in solid argon and neon.
TL;DR: The first open-shell AuII fluoride AuF2 and a NeAuF complex were described in this paper. But they were derived using matrix-isolation experiments and quantum-chemical calculations.
Abstract: Matrix-isolation experiments and quantum-chemical calculations lead to the characterization of two new compounds, the first open-shell AuII fluoride AuF2 and a NeAuF complex.
TL;DR: In this paper, a weak Van der Waals interaction between rhC and matrix atoms was found in the matrix IR spectra of solid argon and neon, which is supported by carbon-13 substitution and B3LYP density functional frequency calculations.