Showing papers by "Lester Andrews published in 2011"
TL;DR: Infrared spectra of three new thorium oxide species have been obtained in argon and neon matrixes and it is predicted that Th(2)O(4) is predicted to have nonplanar C(2h) symmetry for its closed shell singlet ground state.
Abstract: Infrared spectra of three new thorium oxide species have been obtained in argon and neon matrixes. All of the products are experimentally characterized using isotopic oxygen samples with the aid of...
45 citations
TL;DR: This work shows that U and C atoms react spontaneously to form the uranium carbide U≡C and C≡U⩽C molecules with uranium-carbon triple bonds.
Abstract: Laser evaporation of carbon rich uranium/carbon alloy targets into condensing argon or neon matrix samples gives weak infrared absorptions that increase on annealing, which can be assigned to new uranium carbon bearing species. New bands at 827.6 cm−1 in solid argon or 871.7 cm−1 in neon become doublets with mixed carbon 12 and 13 isotopes and exhibit the 1.0381 carbon isotopic frequency ratio for the UC diatomic molecule. Another new band at 891.4 cm−1 in argon gives a three-band mixed isotopic spectrum with the 1.0366 carbon isotopic frequency ratio, which is characteristic of the anti-symmetric stretching vibration of a linear CUC molecule. No evidence was found for the lower energy cyclic U(CC) isomer. Other bands at 798.6 and 544.0 cm−1 are identified as UCH, which has a uranium-carbon triple bond similar to that in UC. Evidence is found for bicyclic U(CC)2 and tricyclic U(CC)3. This work shows that U and C atoms react spontaneously to form the uranium carbide U≡C and C≡U≡C molecules with uranium-car...
34 citations
TL;DR: The products reveal that C-H insertion by excited Au, Ag, and Cu readily occurs, and subsequent hydride-detachment or electron addition also follows, and each type of product has similar photochemical properties regardless of the metal.
Abstract: Methane activation by laser-ablated, excited Group 11 metal atoms has been carried out, leading to generation of CH3–MH, CH3–M, and CH3–MH−, which are identified in the product infrared spectra on the basis of isotopic shifts and correlation with DFT calculated frequencies. The products reveal that C–H insertion by excited Au, Ag, and Cu readily occurs, and subsequent hydride-detachment or electron addition also follows. Each type of product has similar photochemical properties regardless of the metal. DFT computed energies reveal facile hydride dissociation and high electron affinities for the insertion complexes. The methyl metal species have the shortest C–M bonds, consistent with their highest calculated effective bond order, and the CH3–MH complexes have higher electron affinities than the metal atoms.
31 citations
TL;DR: New infrared absorption bands are assigned to the oxidative addition product methylene lanthanide difluorides on the basis of deuterium substitution and vibrational frequency calculations with density functional theory (DFT).
Abstract: Laser-ablated lanthanide metal atoms were condensed with CH2F2 in excess argon at 6 K or neon at 4 K. New infrared absorption bands are assigned to the oxidative addition product methylene lanthanide difluorides on the basis of deuterium substitution and vibrational frequency calculations with density functional theory (DFT). Two dominant absorptions in the 500 cm−1 region are identified as lanthanide−fluoride stretching modes for this very strong infrared absorption. The predominantly lanthanide−carbon stretching modes follow a similar trend of increasing with metal size and have characteristic 30 cm−1 deuterium and 14 cm−1 13C isotopic shifts. The electronic structure calculations show that these CH2LnF2 complexes are not analogous to the simple transition and actinide metal methylidenes with metal−carbon double bonds that have been investigated previously, because the lanthanide metals (in the +2 or +3 oxidation state) do not appear to form a π-type bond with the CH2 group. The DFT and ab initio correl...
29 citations
TL;DR: Intrinsic reaction coordinate calculations indicate that conversion between the two products is feasible via the cyclic configuration, and density functional frequency calculations and D and (13)C isotopic substitutions substantiate the vibrational assignments.
Abstract: The H2CCN and H2CNC radicals are observed in matrix IR spectra from acetonitrile exposed to radiation from laser ablation of transition metals, whereas cyc-H2CCN, another plausible isomer, is not. ...
24 citations
TL;DR: In this paper, deuterium substitution and density functional theory frequency calculations were used to identify metal-fluorine stretching modes for fluoromethylene lanthanide difluoride complex.
22 citations
TL;DR: CH(2)-LnHF does not form a π-bond between Ln and C and is best described as a LnHF-substituted CH(3) radical, with an unpaired p electron on C weakly interacting with the unpaired f electrons on the Ln.
Abstract: Lanthanide metal atoms, produced by laser ablation, were condensed with CH3F in excess Ar at 8 K. New infrared absorption bands are assigned to the first insertion CH3LnF and oxidative addition methylene lanthanide hydride fluoride CH2LnHF products on the basis of 13C and deuterium substitution and density functional theory calculations of the vibrational frequencies. It is also possible to observe the cationic species CH3LnF+ for some Ln. For Ln = Eu and Yb, only CH3LnF is observed. CH3LnF in the Ln formal +2 state is predicted to be more stable than CH2LnHF with the Ln in the formal +3 oxidation state. CH3-LnF forms a single bond between Ln and C and is a substituted methane. Similar to CH2-LnF2, CH2-LnHF does not form a π-bond between Ln and C and is best described as a LnHF-substituted CH3 radical, with an unpaired p electron on C weakly interacting with the unpaired f electrons on the Ln. The calculated potential energy surface for the CH3F + La → CH3-LaF/CH2-LaHF shows a number of intermediates and ...
22 citations
TL;DR: The assignment of strong M-H as well as C≡C bond stretching product absorptions suggests oxidative C-H insertion during reagent codeposition and subsequent photolysis of ethynyl metal hydride molecules.
Abstract: The ethynyl metal hydride molecules (HM–C≡CH) are identified in the matrix infrared spectra from reactions of laser-ablated Mn and Re atoms with acetylene using D and 13C isotopic substitution and ...
21 citations
TL;DR: It is shown that atomic Rh can convert acetylene to the simple Rh vinylidene complex, analogous to that found for ligand-supported Rh complexes.
Abstract: Laser-ablated Rh atoms react with C2H2 upon co-condensation in excess argon and neon to form the insertion product HRhCCH, the alkyne RhCCH, the vinylidene RhCCH2, and the metallacycle complex Rh-η2-(C2H2). These species are identified through 13C2H2, C2D2, and mixed C2HD isotopic substitutions and density functional theory isotopic frequency calculations. The HRhCCH molecule is characterized by the CH stretching mode at 3306.2 cm−1 (Ar) and 3310.9 cm−1 (Ne), the Rh—H stretching mode at 2090.8 cm−1 (Ar) and 2111.0 cm−1 (Ne), and two CCH deformation modes at 584.3 and 573.3 cm−1 (Ar) and 587.1 and 580.3 cm−1 (Ne). The absorptions for the vinylidene RhCCH2 complex are observed at 3150.9 (Ar), 3147.2 (Ne) (CH stretching), 1690.1 (Ar), 1694.3 (Ne) (CC stretching), and 804.9 (Ar), 810.5 cm−1 (Ne) (CCH deformation). The metallacycle Rh-η2-(C2H2) complex is also identified through CC stretching and CCH deformation modes. The insertion reaction of ground Rh atom to the C—H bond is spontaneous on the basis of the ...
19 citations
TL;DR: The products in the infrared spectra identified reveal that M-F insertion by the coinage metals and H atom release readily occur, and that F bonded to Au contracts the gold 5d orbitals for better overlap with the carbon 2p orbital for π bonding.
Abstract: Reactions of laser-ablated, excited group 11 metal atoms with CH3F isotopomers have been carried out, leading to the generation of CH3–MF and CH2F–M complexes for Cu, Ag, and Au in addition to smaller complexes for gold. The products in the infrared spectra identified on the basis of their frequencies, isotopic shifts, and correlation with DFT calculated frequencies reveal that M–F insertion by the coinage metals and H atom release readily occur. The relatively low dissociation energies of CH3–AuF to give several smaller Au complexes are consistent with the observation of these fragments. The C–Au bonds of CF–AuH and CH2–AuF exhibit considerable π character, and the methylidene CH2–AuF contains a true double bond. In contrast, the bond orders of CH2–Au and CH2–AuH are lower, indicating that F bonded to Au contracts the gold 5d orbitals for better overlap with the carbon 2p orbital for π bonding.
18 citations
TL;DR: In this article, small manganese insertion (CX3−MnX) and methylidene (cX2═Mnx2) complexes, carrying the highest multiplicities (sextet and quartet) among the analogous group 3−12 metal complexes, are produced in the USA.
TL;DR: The reaction mechanism for formation of the Ru═C═CH(2) complex was investigated by B3LYP internal reaction coordinate calculations, and the hydrido-alkyny complex is the rate-determining step.
Abstract: Laser-ablated ruthenium atoms undergo reaction with acetylene during condensation in excess neon and argon matrices to form a metallacycle complex, insertion into the C–H bond, and rearrangement to...
TL;DR: The structures and reactions of different rhodium oxides and dioxygen complexes with RhO4 stoichiometry were investigated by matrix isolation infrared spectroscopy and quantum chemical calculations.
Abstract: The structures and reactions of different rhodium oxides and dioxygen complexes with RhO4 stoichiometry were investigated by matrix isolation infrared spectroscopy and quantum chemical calculations. The inserted RhO2 molecule reacted with dioxygen upon sample annealing to form the [(η1-O2)RhO2] complex, which can further isomerize to the known [(η2-O2)RhO2] complex via infrared irradiation. Both experimental and theoretical studies suggest that the [(η1-O2)RhO2] complex has a doublet ground state with non-planar C
s symmetry in which the O2 ligand is end-on bonded to the rhodium centre. Although rhodium tetroxide is predicted to be a stable molecule with D
2d symmetry at different level of theory, no evidence is found for the formation of this Rh(VIII) species in noble gas matrices. Our experiments also suggest the formation of a new peroxo [Rh(η2-O2)2] complex, which is calculated to have a doublet ground state with D
2d symmetry. This peroxo complex undergoes isomerization to the known superoxo [Rh(η2-O2)2] complex via the rotation of the dioxygen ligand under infrared irradiation.
TL;DR: Although the CH(3)LnOH molecules are predicted to be more stable than the O-H bond insertion products, formation of the C-O bond insertion isomers is kinetically prohibited as revealed by calculated potential energy surfaces.
Abstract: The reactions of laser-ablated late lanthanide atoms and methanol were studied using matrix isolation infrared spectroscopy and electronic structure calculations at the density functional theory level. Both terbium and lutetium atoms react with methanol spontaneously to form the CH3OTbH and CH3OLuH insertion products, which react further with another methanol molecule to give the Tb(OCH3)2 and Lu(OCH3)2 products as found previously for uranium. The reactions of Dy through Yb and methanol first produce Ln(CH3OH) complexes during sample annealing, which isomerize to the CH3OLnH insertion products on visible irradiation. The Ln–H stretching frequencies of the CH3OLnH molecules exhibit a unique trend from Tb to Lu, which is also reproduced by theoretical calculations at the B3LYP level of theory. Although the CH3LnOH molecules are predicted to be more stable than the O–H bond insertion products, formation of the C–O bond insertion isomers is kinetically prohibited as revealed by calculated potential energy su...
TL;DR: Reactions of laser-ablated uranium atoms and methanol are investigated in solid argon using matrix isolation and infrared spectroscopy and four new product molecules are identified with the help of isotopically substituted meethanol as well as density functional frequency calculations.
Abstract: Reactions of laser-ablated uranium atoms and methanol are investigated in solid argon using matrix isolation and infrared spectroscopy. Four new product molecules are identified with the help of isotopically substituted methanol as well as density functional frequency calculations. Uranium atoms react spontaneously with methanol on annealing to form the U(II) insertion product CH3OUH, which has a quintet ground state with strong C—O and U—H stretching vibrations. Further sample annealing allows the reaction of CH3OUH and another methanol molecule to eliminate H2 and give the U(OCH3)2 product. Near-UV–vis irradiation isomerizes the CH3OUH molecule to the 32 kcal/mol lower energy U(IV) CH3U(O)H isomer and the U(OCH3)2 molecule to the 28 kcal/mol lower energy CH3OU(O)CH3 isomer. Both U(IV) products have triplet ground states, U═O double bonds, and pyramidal skeletal structures.
TL;DR: Reactions of laser-ablated thorium and uranium atoms with dimethyl ether were investigated using matrix isolation infrared spectroscopy and four types of reaction products for both uranium and thorium were identified using deuterium substituted samples as well as density functional frequency and energy calculations.
Abstract: Reactions of laser-ablated thorium and uranium atoms with dimethyl ether were investigated using matrix isolation infrared spectroscopy. Four types of reaction products for both uranium and thorium were identified using deuterium substituted samples as well as density functional frequency and energy calculations. Ground state uranium and thorium atoms react with dimethyl ether spontaneously to give the M(CH3OCH3) complexes (M = Th, U) on annealing, which are predicted to have C2v symmetry with triplet (Th) and quintet (U) ground states. Subsequent visible irradiation produces the divalent CH3OThCH3 and CH3OUCH3 insertion products with singlet and quintet states lowest in energy. Further UV irradiation induces isomerization of the CH3OMCH3 molecules to the (CH3)2MO isomers with MO double bonds and pyramidal structures. In the presence of another dimethyl ether reagent, evidence for (CH3O)2M(CH3)2 molecules is also produced upon UV irradiation.
TL;DR: In the matrix near-UV irradiation destroys the CH(3)OCH(2) radical with the formation of HCO radical and CH(4), which is different from the decomposition mechanism of CH( 3)O CH( 2) radical to H (2)CO and CH (3) radical proposed for the gas phase process.
Abstract: The methoxymethyl radical, CH(3)OCH(2), is prepared via hydrogen photodissociation from dimethyl ether during codeposition of CH(3)OCH(3) in excess argon at 4 K with laser-excited metal plume radiation. The spectrum of this radical is characterized by four infrared absorptions at 1468.1, 1253.9, 1226.6, and 944.4 cm(-1), which are assigned by deuterium substitution as well as frequency and intensity calculations using density functional theory. The O-CH(2) bond length is calculated to be 0.07 A shorter than the CH(3)-O bond due to additional π bonding interactions. In the matrix near-UV irradiation destroys the CH(3)OCH(2) radical with the formation of HCO radical and CH(4), which is different from the decomposition mechanism of CH(3)OCH(2) radical to H(2)CO and CH(3) radical proposed for the gas phase process.
TL;DR: In this paper, a detailed analysis of the bonding in US2 and SUO molecules is provided and compared to the better known UO2 molecule, which exhibits similar multireference character with the UO stretching mode at 857.1 cm-1 in solid argon.
Abstract: US2 and SUO molecules have been prepared by laser ablation of the solid materials and reaction of the elements during condensation in solid argon, which give the same absorptions as earlier U atom reactions with sulfur vapor and sulfur dioxide. The antisymmetric stretching mode of US2 shifts from 438.7 cm–1 in solid argon to 442.3 cm–1 in solid neon, which shows that the same electronic state is trapped in both matrix environments. Density functional calculations find a bent (3B2) ground state for the US2 molecule, and CASSCF/CASPT2 calculations reveal a multiconfigurational mixture of (5fφ)1(5fδ)1-type states, whereas the most stable state for UO2 is a linear structure of the (5fφ)(7s) type. The bent triplet ground state SUO molecule exhibits similar multireference character with the U–O stretching mode at 857.1 cm–1 in solid argon. The linear SUO molecule computed at the CASPT2 level is only 2 kcal/mol above the bent structure. A detailed analysis of the bonding in US2 and SUO is provided and compared to the better known UO2 molecule.
TL;DR: A new class of very high electron affinity neutral molecules, (F(2))MF(2) fluorine metal difluoride molecules, in solid argon and neon, are identified through matrix IR spectra containing new antisymmetric and symmetric M-F stretching modes.
Abstract: Electron-deficient group 13 metals react with F2 to give the compounds MF2 (M = B, Al, Ga, In, Tl), which combine with F2 to form a new class of very high electron affinity neutral molecules, (F2)MF2, in solid argon and neon. These (F2)MF2 fluorine metal difluoride molecules were identified through matrix IR spectra containing new antisymmetric and symmetric M−F stretching modes. The assignments were confirmed through close comparisons with frequency calculations using DFT methods, which were calibrated against the MF3 molecules observed in all of the spectra. Electron affinities calculated at the CCSD(T) level fall between 7.0 and 7.8 eV, which are in the range of the highest known electron affinities.
TL;DR: The vanadium dihydride hydrogen complex, VH(2)(H( 2)), is identified, while the niobium and tantalum tetrahydrides, NbH( 4) and TaH(4,) with D(2d) symmetry structures are confirmed.
Abstract: Laser ablated V, Nb, and Ta atoms react with molecular hydrogen in excess neon at 4 K to give vanadium, niobium, and tantalum dihydrides that further react with H2 to form VH2(H2), NbH4, and TaH4. The reaction products are identified by deuterium and deuterium hydride isotopic substitution. DFT and CCSD theoretical calculations are used to predict energies, geometries, and vibrational frequencies for these novel metal hydrides complex and molecules. The vanadium dihydride hydrogen complex, VH2(H2), is identified, while the niobium and tantalum tetrahydrides, NbH4 and TaH4, with D2d symmetry structures are confirmed. Reactions of group 5 metal atoms with H2 condensing in solid hydrogen gave VH2(H2) and the higher tetrahydride–hydrogen complexes NbH4(H2)4 and TaH4(H2)4.
TL;DR: Reactions of laser-ablated scandium, yttrium, lanthanum, and several lanthanide metal atoms with dimethyl ether have been studied using matrix isolation infrared spectroscopy and density functional calculations reveal that the M(CH( 3)OCH(3)) complexes possess C(2v) symmetry with metal atoms bound to the oxygen side ofDimethyl ether.
Abstract: Reactions of laser-ablated scandium, yttrium, lanthanum, and several lanthanide metal atoms with dimethyl ether have been studied using matrix isolation infrared spectroscopy. Identifications of the major products, M(CH3OCH3) and CH3OMCH3 (M = Sc, Y, La, Ce, Gd, Tb, Yb, and Lu), are supported by experiments with deuterium substitution as well as theoretical calculations. It is found that most ground-state metal atoms react with dimethyl ether to give the M(CH3OCH3) complexes spontaneously on annealing, which isomerize to the CH3OMCH3 insertion products with visible irradiation. Density functional calculations reveal that the M(CH3OCH3) complexes possess C2v symmetry with metal atoms bound to the oxygen side of dimethyl ether, and bent geometries are found for the inserted CH3OMCH3 molecules with direct M–O and C–O bonds. All of these products have the same ground states as their corresponding metal atoms except for Tb. Although the Lu(CH3OCH3) complex is predicted to be a stable molecule, it is not observ...
TL;DR: The linear title molecule forms by reactions of laser-ablated U atoms with N2 and H2 mixtures upon codeposition in excess Ar at 5 K as mentioned in this paper, where Ar is the number of U atoms.
Abstract: The linear title molecule forms by reactions of laser-ablated U atoms with N2 and H2 mixtures upon codeposition in excess Ar at 5 K.
TL;DR: In this article, neutral adduct molecules (F2) were defined by reaction of laser-ablated group 13 metal atoms with F2 in excess Ar and Ne during condensation at 5 K.
Abstract: The new class of neutral adduct molecules (F2)MF2 (M: B, Al, Ga, In, Tl) forms by reaction of laser-ablated group 13 metal atoms with F2 in excess Ar and Ne during condensation at 5 K.