Showing papers by "Lester Andrews published in 2005"
TL;DR: The computed structure shows considerable agostic bonding distortion of the CH2 and ThH2 subunits in the simple actinide methylidene dihydride CH2=ThH2 molecule, which is similar to the transition metal analogue,CH2=HfH2.
Abstract: The actinide methylidene CH2=ThH2 molecule is formed in the reaction of laser-ablated thorium atoms with CH4 and trapped in a solid argon matrix The five strongest infrared absorptions computed by density functional theory (two ThH2 stretches, C=Th stretch, CH2 wag, and ThH2 bend) are observed in the infrared spectrum The computed structure shows considerable agostic bonding distortion of the CH2 and ThH2 subunits in the simple actinide methylidene dihydride CH2=ThH2 molecule, which is similar to the transition metal analogue, CH2=HfH2
63 citations
TL;DR: In this paper, the authors used a large basis set with polarization functions to predict a C1 symmetry structure with agostic C−H-ZrH-1 bonding and distance of 2.5 cm-1.300 A.
Abstract: Reaction of laser-ablated Zr with CH4 (13CH4, CD4, and CH2D2) in excess neon during condensation at 5 K forms CH2ZrH2, the simplest alkylidene hydride complex, which is identified by infrared absorptions at 1581.0, 1546.2, 757.0, and 634.5 cm-1. Density functional theory electronic structure calculations using a large basis set with polarization functions predict a C1 symmetry structure with agostic C−H- - -Zr bonding and distance of 2.300 A. Identification of the agostic CH2ZrH2 methylidene complex is confirmed by an excellent match of calculated and observed isotopic frequencies particularly for the four unique CHDZrHD isotopic modifications. The analogous reactions in excess argon give two persistent photoreversible matrix configurations for CH2ZrH2. Finally, methane activation by CH2ZrH2 gives the new (CH3)2ZrH2 molecule.
62 citations
TL;DR: The computed planar structure for singlet ground-state CH2=TiH2 shows CH2 distortion and evidence for agostic bonding (H-C-Ti, 91.4 degrees), which is supported by the spectra for CHD=TiHD.
Abstract: Laser-ablated titanium atoms react with methane to form the insertion product CH3TiH, which undergoes a reversible photochemical α-H transfer to give the methylidene complex CH2TiH2. On annealing a second methane activation occurs to produce (CH3)2TiH2. These molecules are identified from matrix infrared spectra by isotopic substitution (CH4, 13CH4, CD4, CH2D2) and comparison to DFT frequency calculations. The computed planar structure for singlet ground-state CH2TiH2 shows CH2 distortion and evidence for agostic bonding (H−C−Ti, 91.4°), which is supported by the spectra for CHDTiHD.
58 citations
TL;DR: These simple methyl, methylidene, and methylidyne molybdenum hydride molecules are reversibly interconverted by alpha-H transfers upon visible and ultraviolet irradiations.
Abstract: Reaction of laser-ablated Mo atoms with CH4 in excess argon forms the CH3−MoH, CH2MoH2, and CH⋮MoH3 molecules, which are identified from infrared spectra by isotopic substitution and density functional theory frequency calculations. These simple methyl, methylidene, and methylidyne molybdenum hydride molecules are reversibly interconverted by α-H transfers upon visible and ultraviolet irradiations. The methylidene dihydride CH2MoH2 exhibits CH2 and MoH2 distortion and agostic interaction to a lesser degree than CH2ZrH2. Molybdenum methylidyne trihydride CH⋮MoH3 is a stable C3v symmetry molecule.
44 citations
TL;DR: Matrix infrared spectra and DFT/B3LYP calculations show that CH[triple bond]WH3 is a stable molecule with C3v symmetry, but other levels of theory were required to describe agostic distortion for CH2=WH2.
Abstract: Laser-ablated W atoms react with CH4 in excess argon to form the CH3−WH, CH2WH2, and CH⋮WH3 molecules with increasing yield in this order of product stability. These molecules are identified from m...
42 citations
TL;DR: In this article, the authors used infrared spectra to identify the methylidene complex CH2HfH2 and showed that it is more stable than the symmetrical nonagostic structure.
42 citations
TL;DR: The bonding and electronic interactions in these molecules are discussed on the basis of the observed aromatic C-C breathing modes activated in the complexes.
Abstract: Vanadium, niobium, and tantalum metal atoms, produced by laser ablation, are reacted with benzene vapor diluted in argon and codeposited onto a 7 K CsI window. The resulting reaction products are trapped, and the M(C6H6) and M(C6H6)2 complexes are identified by benzene isotopic substitution (C6H6, 13C6H6, C6D6). Density functional theory (DFT) frequency calculations are used to support molecular complex assignments. On the basis of the computed energies and a comparison of calculated and observed vibrational isotopic shifts, the ground electronic states and geometries are predicted. The bonding and electronic interactions in these molecules are discussed on the basis of the observed aromatic C-C breathing modes activated in the complexes.
39 citations
TL;DR: Infrared spectroscopy, isotopic substitution, and density functional theoretical frequency calculations confirm the identification of this methylidene complex as the major product observed and trapped in solid argon.
Abstract: Laser-ablated thorium atoms react with methyl fluoride to give the CH2=ThHF molecule as the major product observed and trapped in solid argon. Infrared spectroscopy, isotopic substitution, and density functional theoretical frequency calculations confirm the identification of this methylidene complex. The four strongest computed absorptions (Th-H stretch, Th=C stretch, CH2 wag, and Th-F stretch) are the four vibrational modes observed. The CH2=ThHCl and CH2=ThHBr species formed from methyl chloride and methyl bromide exhibit the first three of these modes in the infrared spectra. The computed structures (B3LYP and CCSD) show considerable agostic interaction, similar to that observed for the Group 4 CH2=MHX (M = Ti, Zr, Hf) methylidene complexes, and the agostic angle and C=Th bond length decrease slightly in the CH2=ThHX series (X = F, Cl, Br).
39 citations
38 citations
TL;DR: Reactions of laser-ablated Mg, Ca, Sr, and Ba atoms with O2 and H2 in excess argon give new absorptions in the O-H and O-M-O stretching regions, which increase together upon UV photolysis and are due to the M(OH)2 molecules.
Abstract: Reactions of laser-ablated Mg, Ca, Sr, and Ba atoms with O2 and H2 in excess argon give new absorptions in the O−H and O−M−O stretching regions, which increase together upon UV photolysis and are d...
38 citations
TL;DR: The simple methylidene and Grignard-type and dimethyl dihalide complexes are produced by reaction of methyl chloride and bromide with laser-ablated Ti atoms and isolated in a solid Ar matrix and form a persistent photoreversible system via alpha-hydrogen migration between the carbon and titanium atoms.
Abstract: The simple methylidene (CH2=TiHX) and Grignard-type (CH3TiX) complexes are produced by reaction of methyl chloride and bromide with laser-ablated Ti atoms and isolated in a solid Ar matrix, and they form a persistent photoreversible system via alpha-hydrogen migration between the carbon and titanium atoms. The Grignard-type product is transformed to the methylidene complex upon UV (240 nm 530 nm) irradiation. More stable dimethyl dihalide complexes [(CH3)2TiX2] are also identified, whose relative concentration increases upon annealing and at high methyl halide concentration. The reaction products are identified with three different groups of absorptions on the basis of the behaviors upon broadband photolysis and annealing, and the vibrational characteristics are in a good agreement with DFT computation results.
TL;DR: The Group 4 tetravalent HM(O)OH isomer reported here are the first examples of pure metal tetrahydroxide molecules.
Abstract: Hafnium and zirconium atoms react with H(2)O(2) molecules and with H(2) + O(2) mixtures to form M(OH)(2) and M(OH)(4) molecules, which are trapped in solid argon and identified from isotopic shifts in the infrared spectra. Electronic structure calculations at the MP2 level converge to almost linear M(OH)(2) and tetrahedral M(OH)(4) molecules and predict vibrational frequencies for mixed isotopic molecules of lower symmetry that are in excellent agreement with experimental measurements, thus substantiating the identification of hafnium and zirconium dihydroxide and tetrahydroxide molecules. Titanium atoms react to give the same product molecules, but Ti(OH)(4) has an S(4) structure with bent Ti-O-H bonds, Ti(OH)(2) appears to be nearly linear, and the more stable tetravalent HM(O)OH isomer is more prominent for Ti. The Group 4 tetrahydroxides reported here are the first examples of pure metal tetrahydroxide molecules.
TL;DR: Density functional theory and MP2 calculations reproduce the IR spectra of the M(OH)2 molecules and show that the Group 2 dihydroxide molecules are more ionic.
Abstract: Laser-ablated zinc and cadmium atoms were mixed uniformly with H2 and O2 in excess argon or neon and with O2 in pure hydrogen or deuterium during deposition at 8 or 4 K. UV irradiation excites metal atoms to insert into O2 producing OMO molecules (M = Zn, Cd), which react further with H2 to give the metal hydroxides M(OH)2 and HMOH. The M(OH)2 molecules were identified through O-H and M-O stretching modes with appropriate HD, D2, (16,18)O2, and (18)O2 isotopic shifts. The HMOH molecules were characterized by O-H, M-H, and M-O stretching modes and an M-O-H bending mode, which were particularly strong in pure H2/D2. Analogous Zn and Cd atom reactions with H2O2 in excess argon produced the same M(OH)2 absorptions. Density functional theory and MP2 calculations reproduce the IR spectra of these molecules. The bonding of Group 12 metal dihydroxides and comparison to Group 2 dihydroxides are discussed. Although the Group 12 dihydroxide O-H stretching frequencies are lower, calculated charges show that the Group 2 dihydroxide molecules are more ionic.
TL;DR: In this paper, the authors show that one α-H is distorted toward the metal atom, which provides evidence of strong agostic interaction in the methylidene ground state molecules.
TL;DR: In this paper, density functional theory calculations show that one of the alpha-hydrogen atoms of the carbene complex is considerably bent toward the metal atom (angle-spherical HCMo=84.5 degrees ), which provides evidence of a strong agostic interaction in the triplet ground state.
Abstract: Simple molybdenum methyl, carbene, and carbyne complexes, [CH3--MoF], [CH2=MoHF], and [CH[triple chemical bond]MoH(2)F], were formed by the reaction of laser-ablated molybdenum atoms with methyl fluoride and isolated in an argon matrix. These molecules provide a persistent photoreversible system through alpha-hydrogen migration between the carbon and metal atoms: The methyl and carbene complexes are produced by applying UV irradiation (240-380 nm) while the carbyne complex is depleted, and the process reverses on irradiation with visible light (lambda>420 nm). An absorption at 589.3 cm(-1) is attributed to the Mo--F stretching mode of [CH3--MoF], which is in fact the most stable of the plausible products. Density functional theory calculations show that one of the alpha-hydrogen atoms of the carbene complex is considerably bent toward the metal atom (angle-spherical HCMo=84.5 degrees ), which provides evidence of a strong agostic interaction in the triplet ground state. The calculated C[triple chemical bond]Mo bond length in the carbyne is in the range of triple-bond values in methylidyne complexes.
TL;DR: Atomic mercury in solid hydrogen reacts when subjected to mercury arc irradiation to form the linear HgH2 molecule with strong IR absorptions at 1902 and 1905, characterized by strong IR absorption at 1802, 739 and 673 cm(-1) and by decomposition at 150-170 K.
Abstract: Atomic mercury in solid hydrogen reacts when subjected to mercury arc irradiation to form the linear HgH2 molecule with strong IR absorptions at 1902.3 and 772.8 cm−1. Annealing leads to HgH2 dimer and trimer and warming above 7 K allows hydrogen to sublime and solid HgH2 to form. This covalent molecular solid is characterized by strong IR absorptions at 1802, 739 and 673 cm−1 and by decomposition at 150–170 K. Solid para-hydrogen gives sharper HgH2 absorptions at 1905.8 and 774.3 cm−1 and forms a more amorphous HgH2 solid with bands at 1813, 741 and 683 cm−1.
TL;DR: Density functional theory (DFT) calculations at the B3LYP level agree well with experiment and support the formation of 1:1 complexes of Pccp/base and distinct changes were observed in ring modes as well as CCl and CCl2 modes.
Abstract: Hydrogen-bonded complexes of pentachlorocyclopropane with the bases acetonitrile, ammonia, monomethylamine, and dimethylamine have been isolated and characterized for the first time in argon matric...