Showing papers by "Lester Andrews published in 2015"
TL;DR: For the first time the higher polyfluoride anion [F5 ](-) has been observed under cryogenic conditions in neon matrices at 850 cm(-1) .
Abstract: Polyfluoride anions have been investigated by matrix-isolation spectroscopy and quantum-chemical methods. For the first time the higher polyfluoride anion [F5 ](-) has been observed under cryogenic conditions in neon matrices at 850 cm(-1) . In addition, a new band for the Cs(+) [F3 ](-) complex in neon is reported.
45 citations
TL;DR: Structures, vibrational frequencies, and heats of formation were predicted for MX4 and both singlet and triplet states of MX2 using the Feller-Peterson-Dixon composite electronic structure approach based on coupled cluster CCSD(T) calculations extrapolated to the complete basis set limit with additional corrections including spin orbit effects.
Abstract: Structures, vibrational frequencies, and heats of formation were predicted for MX4 and both singlet and triplet states of MX2 (M = group 4, group 14, Ce, and Th; X = F and Cl) using the Feller–Peterson–Dixon composite electronic structure approach based on coupled cluster CCSD(T) calculations extrapolated to the complete basis set limit with additional corrections including spin orbit effects. The spin–orbit corrections are not large but need to be included for chemical accuracy of ±1 kcal/mol. The singlet–triplet splittings were calculated for the dihalides and all compounds have singlet ground states except for the dihalides of Ti, Zr, and Ce which have triplet ground states. The calculated heats of formation are in good agreement with the available experimental data. Our predictions suggest that the experimental heats of formation need to be revised for a number of tetrahalides: TiF4, HfF4, PbF4, PbCl4, and ThCl4 as well as a number of dihalides: GeF2, SnF2, PbF2, TiF2, and TiCl2. The calculated heats ...
41 citations
TL;DR: In this paper, the C2v-symmetrischen [F5]−-Komplex in Neon was beschrieben, and a sehr starke Bande bei 850 cm−1 auf.
Abstract: Polyfluoride wurden mittels Matrixisolationsspektroskopie und quantenchemischen Berechnungen auf Coupled-Cluster-Niveau untersucht. Erstmalig konnte ein hoheres Polyfluoridanion spektroskopisch in Neonmatrices bei 4 K nachgewiesen werden. Das C2v-symmetrische [F5]− weist eine sehr starke Bande bei 850 cm−1 auf. Daruber hinaus wird eine neue Bande fur den Cs+[F3]−-Komplex in Neon beschrieben.
25 citations
TL;DR: Reactions of laser-ablated U atoms with (CN)2 produce UNC, U( NC)2, and U(NC)4 as the major products, identified from their Ar matrix infrared spectra and precursors partially and fully substituted with (13)C and (15)N.
23 citations
TL;DR: In this article, an argon matrix infrared spectrum of strong N-C and U-H stretching modes at 2028 and 1417 cm-1 was used to identify the HUCN isomer.
Abstract: Reactions of laser-ablated U atoms with HCN produce HUNC, which is identified from its argon matrix infrared spectrum of strong N–C and U–H stretching modes at 2028 and 1417 cm–1. B3LYP calculations show that the unobserved HUCN isomer has a 6.3 kcal/mol higher energy, and its C–N stretching mode is about 125 cm–1 higher with more than an order of magnitude weaker intensity. Complementary experiments were done with thorium and group 4 metal atoms to form the analogous HMNC species for comparison and to demonstrate metal dependence for these new metal-bearing product absorptions.
11 citations
TL;DR: In this article, the reaction of laser-ablated scandium metal atoms with di-, tri-, and tetrahalomethanes were carried out in excess argon during condensation, and the matrix infrared spectra of products were investigated.
11 citations
TL;DR: In this article, the most stable components in the previously proposed reaction path for reactions of metal atoms with acetonitrile, in line with the observed products in other metal systems and DFT calculations.
Abstract: Laser-ablated Hf and Ti atoms produce M–η2-(NC)–CH3, CH3–MNC, and CH2=M(H)NC in reactions with acetonitrile, parallel to the earlier Zr results, based on isotopic substitution and frequencies computed by DFT. These products are the most stable components in the previously proposed reaction path for reactions of metal atoms with acetonitrile, in line with the observed products in other metal systems and DFT calculations. Other plausible products [CH3CN–M and CH≡M(H2)NC] are energetically too high to be generated in reactions of the group 4 metals. The group 4 metals form strong π complexes with the nitrile group as they do with acetylene and ethylene. The methylidenes are slightly more agostic due to the metal-containing conjugation system than those produced from small alkanes and methyl halides. Relativistic contraction is also evident in that the Hf bonds are shorter than the Zr bonds.
8 citations
TL;DR: Metal reaction products reacted with laser-ablated vanadium, niobium, and tantalum atoms were reacted with CH2X2, CHX3, and CX4 molecules in condensing argon, and the products were investigated by matrix isolation infrared spectroscopy.
Abstract: Laser-ablated vanadium, niobium, and tantalum atoms were reacted with CH2X2, CHX3, and CX4 (X = F and Cl) molecules in condensing argon, and the products were investigated by matrix isolation infrared spectroscopy. The major reaction products are new CH2-MX2, CHX-MX2, HC-MX3, and XC-MX3 complexes. These reactive species were identified by comparing their matrix infrared spectra with frequencies, intensities, and isotopic shifts from density functional theory calculations. Product structures and energies from these calculations are also presented. Results from previously studied Group 4 and 6 metal reaction products are compared. Little change is found in the calculated metal-carbon bond lengths in the early first row CH2═MF2 methylidene σ(2)π(2) series; however, the methylidyne complexes HC{}MF3 show considerable increase in bond strength for the nominally σ(2)π(1)π(1)(Ti), σ(2)π(2)π(1)(V), and σ(2)π(2)π(2)(Cr) carbon{}metal bonds left to right. The Group 5 HC{}MF3 complexes have only a plane of symmetry whereas the Group 4 and 6 analogues have 3-fold symmetry.
7 citations
TL;DR: The HF reaction provides a lower concentration of F in the system and thus simplifies the fluorine chemistry relative to similar U atom reactions with F2, and the new matrix identification of UF here is consistent with recent high level calculations on UF.
Abstract: Reactions of laser-ablated U atoms with HF produce HUF as the major product and UH and UF as minor products, which are identified from their argon and neon matrix infrared spectra. Our assignment of HUF is confirmed by the observation of DUF and close agreement with observed and calculated vibrational frequencies and deuterium shifts in the vibrational frequencies. Our previous observation of the UH diatomic molecule from argon matrix experiments with H2, HD, and D2 as reagents is confirmed through its present observation with HF and DF, and with recent higher level quantum chemical calculations. The HF reaction provides a lower concentration of F in the system and thus simplifies the fluorine chemistry relative to similar U atom reactions with F2, and the new matrix identification of UF here is consistent with recent high level calculations on UF. In addition, we find evidence for the higher oxidation state secondary reaction products UHF2, UHF3, and UH2F2.
7 citations
TL;DR: In this paper, the reaction products of laser ablated thorium atoms with HF were reported and a discussion of the bonding in HThF and higher oxidation state molecules were discussed.
6 citations
TL;DR: In this article, the matrix infrared spectra from reactions of laser-ablated Fe and Os atoms with acetylene isotopomers was used to identify the π- and C H insertion products (M-η 2 -C 2 H 2 and HM CCH).
TL;DR: In this article, photoisomers of CH2Cl2 and CH2Br2 were identified in the matrix IR spectra from the precursors exposed to plume radiation of a laser-ablated transition metal.
Abstract: CH2Cl–Cl and CH2Br–Br, photoisomers of CH2Cl2 and CH2Br2 , were identified in the matrix IR spectra from the precursors exposed to plume radiation of a laser-ablated transition metal. On the other hand, the corresponding photoisomers of CH2F2 and CH2FCl (CH2F–F, CH2F–Cl, and CH2Cl–F) were not observed because of their instabilities. The CX bond of the product is unusually strong, leading to a high CX stretching frequency. Natural bond orbital (NBO) analysis reveals that it is a true carbon–halogen double bond; in contrast, the XX bond is largely ionic (H2CXδ+ ∙∙∙Xδ− ), similar to the previously studied analogs from tri- and tetrahalomethanes. Intrinsic reaction coordinate (IRC) computation reproduces the smooth interconversion between the precursor and the energetically higher photoisomer, consistent with the disappearance of the product during visible photolysis.