Showing papers by "Lester Andrews published in 2017"

Formation and Characterization of Homoleptic Thorium Isocyanide Complexes.

Abstract: Homoleptic thorium isocyanide complexes have been prepared via the reactions of laser-ablated thorium atoms and (CN)2 in a cryogenic matrix, and the structures of the products were characterized by infrared spectroscopy and theoretical calculations. Thorium atoms reacted with (CN)2 under UV irradiation to form the oxidative addition product Th(NC)2, which was calculated to have closed-shell singlet ground state with a bent geometry. Further reaction of Th(NC)2 and (CN)2 resulted in the formation of Th(NC)4, a molecule with a tetrahedral geometry. Minor products such as ThNC and Th(NC)3 were produced upon association reactions of CN with Th and Th(NC)2. Homoleptic thorium cyanide isomers Th(CN)x (x = 1–4) are predicted to be less stable than the corresponding isocyanides. The C–N stretches of thorium cyanides were calculated to be between 2170 and 2230 cm–1 at the B3LYP level, more than 120 cm–1 higher than the N–C stretches of isocyanides and with much weaker intensities. No experimental absorptions appea...

Properties of Lanthanide Hydroxide Molecules Produced in Reactions of Lanthanide Atoms with H2O2 and H2 + O2 Mixtures: Roles of the +I, +II, +III, and +IV Oxidation States

Abstract: The reactions of laser-ablated lanthanide metal atoms with hydrogen peroxide or hydrogen plus oxygen mixtures have been studied experimentally in a solid argon matrix and theoretically with the ab initio MP2 and CCSD(T) methods. The Ln(OH)3 and Ln(OH)2 molecules and Ln(OH)2+ cations are the major products, and the reactions to form those hydroxides are predicted to be highly exothermic at the CCSD(T) level. Vibronic interactions are hypothesized to contribute to the abnormalities in deuterium shifts for Ln–OH(D) stretching modes for several hydroxides, consistent with CASSCF calculations. Additional new absorptions were assigned as HLnO or LnOH and OLnOH molecules. The tetrahydroxides of Ce, Pr, and Tb have also been observed. These reactive intermediates were identified from their matrix infrared spectra by using D2O2, HD, D2, 16,18O2, and 18O2 isotopic substitution, by matching observed frequencies with values calculated by electronic structure methods, and by following the trends observed in frequencie...

Thorium and Uranium Hydride Phosphorus and Arsenic Bearing Molecules with Single and Double Actinide-Pnictogen and Bridged Agostic Hydrogen Bonds.

Abstract: Thorium atoms from laser ablation react with phosphine during condensation in excess argon to produce two new infrared absorptions at 1467.2 and 1436.6 cm–1 near weak bands for ThH and ThH2, which increase on annealing to 25 and 30 K, indicating spontaneous reactions. Analogous experiments with uranium produced two similar bands at 1473.4 and 1456.7 cm–1 above UH at 1423.8 cm–1 and another absorption at 1388.2 cm–1. Electronic structure calculations at the coupled cluster CCSD(T) for Th and density functional theory calculations for U as well as their proximity to other actinide hydride absorptions support assignments of these bands to the simplest molecules HP═ThH2, HP═UH2, and PH2–UH. Arsine gave the analogous products HAs═ThH2, HAs═UH2, and AsH2–UH. The HE═AnH2 molecules (E = P, As; An = Th, U) have strong agostic An–H(E) interactions with H–E–An angles in the range of 60–64°. The calculated agostic bond distances are 9% to 12% longer than terminal single An–H bonds, which suggests that these strong ag...

Infrared Spectroscopic and Theoretical Studies on the OMF2 and OMF (M = Cr, Mo, W) Molecules in Solid Argon

Abstract: Group 6 metal oxide fluoride molecules in the form of OMF2 and OMF (M = Cr, Mo, W) were prepared via the reactions of laser-ablated metal atoms and OF2 in excess argon. Product identifications were performed by using infrared spectroscopy, 18OF2 samples, and electronic structure calculations. Reactions of group 6 metal atoms and OF2 resulted in the formation of ternary OCrF2, OMoF2, and OWF2 molecules with C2v symmetry in which the tetravalent metal center is coordinated by one oxygen and two fluorine atoms. Both OCrF2 and OMoF2 are computed to possess triplet ground states, and a closed shell singlet is the ground state for OWF2. Triatomic OCrF, OMoF, and OWF molecules were also observed during sample deposition. All three molecules were computed to have a bent geometry and quartet ground state. A bonding analysis showed that the OMF2 molecules have highly ionic M–F bonds. 3OCrF2 and 3OMoF2 have an M–O double bond composed of a σ bond and a π bond. 1OWF2 has an M–O triple bond consisting of a σ bond, a π...

Infrared Spectroscopic and Electronic Structure Investigations of Beryllium Halide Molecules, Cations, and Anions in Noble Gas Matrices

Abstract: Laser-ablated Be atoms, cations, and electrons were reacted with F2, ClF, Cl2, NF3, CCl4, CF2Cl2, HCl, DCl, and SiCl4 diluted in noble gases. The major products were the dihalides BeF2, BeClF, BeCl2, and the hydride chloride HBeCl, whose identities were confirmed by comparison with previous evaporative work, deuterium substitution, and vibrational frequency calculations. The matrix-isolated fundamental frequency of the BeF molecule is higher, and the frequency of BeCl is lower, than that determined for the gas-phase molecules. The BeF+ and BeCl+ cations formed strong dipole-induced dipole complexes in solid Ne, Ar, Kr, and Xe with stepwise increase in computed noble gas dissociation energies. Going down the family NgBeF+ and NgBeCl+ series (Ng = Ne, Ar, Kr, Xe) the Mulliken charges q(Be) decrease, while q(Ng) increases, and the dipole moments decrease, which suggests covalent bonding in the xenon species. We find that the largest intramatrix shift is Ne to Ar which follows the largest factor increase for ...

Matrix Infrared Spectra of Manganese and Iron Isocyanide Complexes

Abstract: Mono and diisocyanide complexes of manganese and iron were prepared via the reactions of laser-ablated manganese and iron atoms with (CN)2 in an argon matrix. Product identifications were performed based on the characteristic infrared absorptions from isotopically labeled (CN)2 experiments as compared with computed values for both cyanides and isocyanides. Manganese atoms reacted with (CN)2 to produce Mn(NC)2 upon λ > 220 nm irradiation, during which MnNC was formed mainly as a result of the photoinduced decomposition of Mn(NC)2. Similar reaction products FeNC and Fe(NC)2 were formed during the reactions of Fe and (CN)2. All the product molecules together with the unobserved cyanide isomers were predicted to have linear geometries at the B3LYP level of theory. The cyanide complexes of manganese and iron were computed to be more stable than the isocyanide isomers with energy differences between 0.4 and 4 kcal/mol at the CCSD(T) level. Although manganese and iron cyanide molecules are slightly more stable a...

Observation and Characterization of CH3CH2-MH, (CH2)2-MH2, CH2═CH-MH3, and CH3-C≡MH3- Produced by Reactions of Group 5 Metal Atoms with Ethane.

Abstract: The primary products in reactions of laser-ablated group 5 metal atoms with ethane were identified in argon matrix IR spectra and characterized via density functional theory computations. The second- and third-row transition metals Nb and Ta produced insertion, metallacyclopropane, vinyl trihydrido, and anionic ethylidyne complexes (CH3CH2–MH, (CH2)2–MH2, CH2═CH–MH3, and CH3C≡MH3–), while the first-row transition metal V yielded only the insertion and metallacyclopropane products. The energetically higher ethylidenes and neutral ethylidynes (CH3CH═MH2 and CH3C≐MH3) were not detected. The unique anionic ethylidynes are the most stable anionic species in the Nb and Ta systems. Evidently back-donation from the metal center to the C–C π* orbital is stronger than that in the group 6 metal analogue but weaker than that in the corresponding group 4 metal complex. The C–M bond for the Nb and Ta ethylidyne anions is a true triple bond.

Double and Triple Si–H–M Bridge Bonds: Matrix Infrared Spectra and Theoretical Calculations for Reaction Products of Silane with Ti, Zr, and Hf Atoms

Abstract: Infrared spectra of matrix isolated dibridged Si(μ-H)2MH2 and tribridged Si(μ-H)3MH molecules (M = Zr and Hf) were observed following the laser-ablated metal atom reactions with SiH4 during condensation in excess argon and neon, but only the latter species was observed with titanium. Assignments of the major vibrational modes, which included terminal MH, MH2 and hydrogen bridge Si–H–M stretching modes, were confirmed by the appropriate SiD4 isotopic shifts and density functional vibrational frequency calculations (B3LYP and BPW91). The Si–H–M hydrogen bridge bond is calculated as weak covalent interaction and compared with the C–H···M agostic interaction in terms of electron localization function (ELF) analysis and noncovalent interaction index (NCI) calculations. Furthermore, the different products of Ti, Zr, and Hf reactions with SiH4 are discussed in detail.

Matrix Infrared Spectra of Insertion and Metallacyclopropane Complexes [CH3CH2-MH and (CH2)2-MH2] Prepared in Reactions of Laser-Ablated Group 3 Metal Atoms with Ethane.

Abstract: CH3CH2–MH and (CH2)2–MH2 were identified in the matrix IR spectra from reactions of laser-ablated group 3 metal atoms with ethane, and they were characterized via theoretical investigations. The observed products are the most stable in the proposed reaction path. Because of the small number of valence electrons, the group 3 metal high oxidation-state complexes are less stable. The C–C insertion product [(CH3)2M], which was predicted to be more stable than the observed ones, was not observed probably because of the high energy barrier and a likely slower rate for insertion into one C–C bond than one of six C–H bonds. The C–C bond of the metallacyclopropanes is the shortest among the early transition-metal analogues, and its stretching frequencies are the highest, revealing the weakest interaction between the metal dihydride and ethylidene groups. The undetected ethylidene is not agostic, parallel to the previously examined methylidene.