(4-Butyl-1-ethyl-1,2,4-triazol-5-yl-idene)[(1,2,5,6-η)-cyclo-octa-1,5-diene](tri-phenyl-phosphane)iridium(I) tetra-fluorido-borate.

The title compound, [Ir(C8H12)(C8H15N3)(C18H15P)]BF4, a new triazole-based N-heterocyclic carbene iridium(I) cationic complex with a tetra-fluorido-borate counter-anion, crystallizes with two cations and two anions in the asymmetric unit of space group Pc. The Ir centers of the cations have distorted square-planar conformations, formed by a bidentate (η2 + η2) cyclo-octa-1,5-diene (COD) ligand, an N-heterocyclic carbene and a tri-phenyl-phosphane ligand with the NHC carbon atom and P atom being cis. In the extended structure, non-classical C-H⋯F hydrogen bonds, one of which is notably short (H⋯F = 2.21 Å), link the cations and anions. The carbon atoms of one of the COD ligands are disordered over adjacent sites in a 0.62:0.38 ratio.

(4-Butyl-1-ethyl-1,2,4-triazol-5-yl-idene)[(1,2,5,6-η)-cyclo-octa-1,5-diene](tri-phenyl-phosphane)rhodium(I) tetra-fluorido-borate.

In the title triazole-based N-heterocyclic carbene rhodium(I) cationic complex with a tetra-fluorido-borate counter-anion, [Rh(C8H12)(C8H15N3)(C18H15P)]BF4, which crystallizes with two cations and two anions in the asymmetric unit, the Rh center has a distorted square-planar coordination geometry with expected bond distances. Several nonclassical C-H⋯F hydrogen-bonding inter-actions help to consolidate the packing. Two of the F atoms of one of the anions are disordered over adjacent sites in a 0.814 (4):0.186 (4) ratio.

[(1,2,5,6-η)-Cyclo-octa-1,5-diene](1-ethyl-4-isopropyl-1,2,4-triazol-5-yl-idene)(tri-phenylphos-phane)iridium(I) tetra-fluorido-borate di-chloro-methane sesquisolvate.

The synthesis and crystal structure of a new triazole-based N-heterocyclic carbene iridium(I) cationic complex with a tetra-fluorido-borate counter-anion and solvating di-chloro-methane, [Ir(C8H12)(C7H13N3)(C18H15P)]BF4·1.5CH2Cl2, is reported. The IrI center of the cationic complex has a distorted square-planar conformation, formed by a bidentate cyclo-octa-1,5-diene (COD) ligand, an N-heterocyclic carbene, and a triphenylphosphane ligand. There are weak hydrogen-bonding inter-actions between C-H groupings of the iridium complex and F atoms of the [BF4]- counter-ions. The atoms of the COD ligand are disordered over two sets of sites in a 0.65:0.35 ratio and two of the F atoms of the anion are disordered over adjacent sites in a 0.6:0.4 ratio. One of the di-chloro-methane solvent mol-ecules is disordered about an inversion center with 0.5 occupancy.

1-Ethyl-4-isopropyl-1,2,4-triazolium bromide.

An ionic compound consisting of a triazolium cation and bromide anion, C7H14N3 +·Br-, has been synthesized and structurally characterized using single-crystal X-ray diffraction and NMR. The compound crystallizes in the monoclinic space group P21/m with the non-hydrogen atoms of one cation lying on general positions and the others lying on a mirror plane. One bromide ion also lies on the mirror. The extended structure exhibits only weak inter-molecular inter-actions between heterocyclic C-H groups and Br- ions.

[(1,2,5,6-η)-Cyclo-octa-1,5-diene](4-isopropyl-1-methyl-1,2,4-triazol-5-yl-idene)(tri-phenyl-phos-phane)iridium(I) tetra-fluorido-borate di-chloro-methane 0.8-solvate.

A new triazole-based N-heterocyclic carbene iridium(I) cationic complex with a tetra-fluorido-borate counter-anion, [Ir(C8H12)(C18H15P)(C6H11N3)]BF4·0.8CH2Cl2, has been synthesized and structurally characterized. The central IrI atom of the cationic complex has a distorted square-planar coordination environment, formed by a bidentate cyclo-octa-1,5-diene (COD) ligand, an N-heterocyclic carbene, and a tri-phenyl-phosphane ligand. The crystal structure comprises C-H⋯π(ring) inter-actions that orient the phenyl rings; non-classical hydrogen-bonding inter-actions between the cationic complex and the tetra-fluorido-borate anion are also present. The complex crystallizes in a triclinic unit cell with two structural units and an incorporation of di-chloro-methane solvate mol-ecules with an occupancy of 0.8.

[(1,2,5,6-η)-Cyclo-octa-1,5-diene](4-isopropyl-1-methyl-1,2,4-triazol-5-yl-idene)(tri-cyclo-hexyl-phosphane-κP)iridium(I) tetra-fluorido-borate di-chloro-methane monosolvate.

The title compound, [Ir(C8H12)(C6H11N3)(C18H33P)]BF4·CH2Cl2, a triazole-based N-heterocyclic carbene iridium(I) cationic complex with a tetra-fluorido-borate counter-anion, crystallizes with one di-chloro-methane solvent mol-ecule per formula unit. The IrI atom of the cationic complex has a distorted square-planar coordination environment, defined by a bidentate cyclo-octa-1,5-diene (COD) ligand, an N-heterocyclic carbene, and a tri-cyclo-hexyl-phosphane ligand. The complex crystallizes in a C-centered monoclinic unit cell and has an unusually high number of eight formula units.

(4-Butyl-1-methyl-1,2,4-triazol-5-yl-idene)[(1,2,5,6-η)-cyclo-octa-1,5-diene](tri-phenyl-phosphane)iridium(I) tetra-fluorido-borate.

A new triazole-based N-heterocyclic cationic carbene iridium(I) complex with a tetra-fluorido-borate counter-anion, [Ir(C8H12)(C7H13N3)(C18H15P)]BF4, has been synthesized and structurally characterized. The IrI atom of the cationic complex has an expected square-planar coordination environment with unexceptional bond lengths. There are several close F⋯H contacts between the cations and the anions in the range 2.36-2.58 Å, stabilizing the orientation of the out-sphere [BF4 -] counter-anion. In the crystal, C-H⋯π(ring) inter-actions are observed that orient the phenyl rings of the tri-phenyl-phosphane ligands.

(4-Benzyl-1-methyl-1,2,4-triazol-5-yl-idene)[(1,2,5,6-η)-cyclo-octa-1,5-diene](tri-phenyl-phosphane-κP)iridium(I) tetra-fluorido-borate.

A new triazole-based N-heterocyclic carbene iridium(I) cationic complex with a tetra-fluorido-borate counter-anion, [Ir(C10H11N3)(C8H12)(C18H15P)]BF4, has been synthesized and structurally characterized. The cationic complex exhibits a distorted square-planar environment around the IrI ion. One significant non-standard hydrogen-bonding inter-action exists between a hydrogen atom on the N-heterocyclic carbene ligand and a fluorine atom from the counter-ion, BF4 -. In the crystal, π-π stacking inter-actions are observed between one of the phenyl rings and the triazole ring. Both inter-molecular and intra-molecular C-H⋯π(ring) inter-actions are also observed.

(Chlorido/bromido)[(1,2,5,6-η)-cyclo-octa-1,5-diene](4-isopropyl-1-methyl-1,2,4-triazol-5-yl-idene)rhodium(I).

A new triazole-based neutral RhI complex, [Rh(Cl0.846Br0.154)(C6H11N3)(C8H12)], has been synthesized and structurally characterized. The RhI atom has a distorted square-planar coordination environment, formed by a bidentate cyclo-octa-1,5-diene (COD) ligand, an N-heterocyclic carbene and a halide ligand that shows substitutional disorder (Cl:Br = 0.846:0.154). No significant inter-molecular inter-actions other than van der Waals forces are found in the crystal structure. Diffraction data indicated a two-component inversion twin with a ratio of 0.95 (5):0.05 (5).

High intensity vacuum ultraviolet and extreme ultraviolet production by noncollinear mixing in laser vaporized media.

A method is described for generating intense pulsed vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) laser radiation by resonance enhanced four-wave mixing of commercial pulsed nanosecond lasers in laser vaporized mercury under windowless conditions. By employing noncollinear mixing of the input beams, the need of dispersive elements such as gratings for separating the VUV/XUV from the residual UV and visible beams is eliminated. A number of schemes are described, facilitating access to the 9.9-14.6 eV range. A simple and convenient scheme for generating wavelengths of 125 nm, 112 nm, and 104 nm (10 eV, 11 eV, and 12 eV) using two dye lasers without the need for dye changes is described.

Crossed molecular beams studies of phenyl radical reactions with propene and trans-2-butene.

The reactions of phenyl radicals with propene have been studied at collision energies of 84 and 108 kJ/mol using the crossed molecular beams technique. The branching ratios between methyl radical elimination forming C8H8 and H-atom elimination forming C9H10 were found to be 10 ± 1:1 at 84 kJ/mol and 3 ± 1:1 at 108 kJ/mol. By using "soft" 9.9 eV vacuum ultraviolet photoionization for product detection, we were able to observe both product channels with negligible fragmentation of C9H10 to C8H8(+). Our finding that CH3 elimination is dominant is consistent with conclusions from a recent study employing a pyrolysis molecular beam reactor using photoionization detection. However, our C8H8/C9H10 branching ratios are significantly larger than inferred from previous CMB experiments and RRKM calculations. For comparison, we have also studied the reactions of phenyl radicals with trans-2-butene at Ecoll = 97 kJ/mol. In this case, the symmetry of trans-2-butene makes both alkene addition sites chemically equivalent. The intermediate formed in the reaction with trans-2-butene is similar to the 2-carbon addition intermediate in the reaction with propene. We observed only methyl elimination in the reaction with trans-2-butene, with no evidence for H-atom elimination, consistent with conclusions that C-C bond fission is the most favorable channel in these systems. Analogies between phenyl radical reactions with propene and trans-2-butene are used to provide insight into the mechanisms in the propene reaction.

High-intensity coherent vacuum ultraviolet source using unfocussed commercial dye lasers.

Using two or three commercial pulsed nanosecond dye lasers pumped by a single 30 Hz Nd:YAG laser, generation of 0.10 mJ pulses at 125 nm (6 × 10(13) photons∕pulse) has been demonstrated by resonance enhanced four-wave mixing of collimated (unfocussed) laser beams in mercury (Hg) vapor. Phase matching at various vacuum ultraviolet (VUV) wavelengths is achieved by tuning one laser in the vicinity of the 6 (1)S0 → 6 (3)P1 resonance near 253.1 nm. A number of different mixing schemes are characterized. Our observations using broadband lasers (~0.15 cm(-1) bandwidths) are compared to previous calculations pertaining to four-wave mixing of low intensity narrowband laser beams. Prospects for further increases in pulse energies are discussed. We find that VUV tuning curves and intensities are in good agreement with theoretical predictions. The utility of the VUV light source is demonstrated by "soft universal" single-photon VUV ionization in crossed molecular beam studies and for generation of light at 130.2 nm for oxygen atom Rydberg time-of-flight experiments.

Studies of bimolecular reaction dynamics using pulsed high-intensity vacuum-ultraviolet lasers for photoionization detection.

This article describes recent progress on the development and application of pulsed high-intensity (~0.1 mJ per pulse) vacuum-ultraviolet (VUV) radiation produced by commercial tabletop lasers for studies of gas phase chemical reaction dynamics involving polyatomic free radicals. Our approach employs near-triply resonant four-wave mixing of unfocussed nanosecond dye lasers in an atomic gas as an alternative to the use of synchrotron light sources for sensitive universal soft photoionization detection of reaction products using a rotatable source crossed molecular beams apparatus with fixed detector. We illustrate this approach in studies of the reactions of phenyl radicals with molecular oxygen and with propene. Future prospects for the use of tabletop laser-based VUV sources for studies of chemical reaction dynamics are discussed.

Photodissociation dynamics of gaseous CpCo(CO)2 and ligand exchange reactions of CpCoH2 with C3H4, C3H6, and NH3.

The photodissociation dynamics of CpCo(CO)(2) was studied in a molecular beam using photofragment translational energy spectroscopy with 157 nm photoionization detection of the metallic products. At 532 and 355 nm excitation, the dominant one-photon channel involved loss of a single CO ligand producing CpCoCO. The product angular distributions were isotropic, and a large fraction of excess energy appeared as product vibrational excitation. Production of CpCO + 2CO resulted from two-photon absorption processes. The two-photon dissociation of mixtures containing CpCo(CO)(2) and H(2) at the orifice of a pulsed nozzle was used to produce a novel 16-electron unsaturated species, CpCoH(2). Transition metal ligand exchange reactions, CpCoH(2) + L → CpCoL + H(2) (L = propyne, propene, or ammonia), were studied under single-collision conditions for the first time. In all cases, ligand exchange occurred via 18-electron association complexes with lifetimes comparable to their rotational periods. Although ligand exchange reactions were not detected from CpCoH(2) collisions with methane or propane (L = CH(4) or C(3)H(8)), a molecular beam containing CpCoCH(4) was produced by photolysis of mixtures containing CpCo(CO)(2) and CH(4).

Improved piezoelectric actuators for use in high-speed pulsed valves.

We describe the assembly of piezoelectric actuators suitable for use in Proch-Trickl pulsed gas valves employed in pulsed molecular beam experiments. In their simplest form, these actuators have performance equal to and resistance to chemical attack far superior to the recently discontinued commercial actuator around which the valve was originally designed. New actuators have been designed employing several different dual piezo configurations. The dual piezo design reliably produces shorter pulses than the original actuator, resulting in reduced gas consumption and lower average source chamber pressures for a given backing pressure and pulse rate. By electrically isolating the actuator assembly, active adjustment of the closed position may be achieved by simple addition of a continuous voltage bias.

Collisions of DCl with a solution covered with hydrophobic and hydrophilic ions: tetrahexylammonium bromide in glycerol.

Gas-liquid scattering experiments are used to investigate interfacial interactions of gaseous DCl with liquid glycerol containing 0.03 M tetrahexylammonium bromide (THABr), an ionic surfactant composed of hydrophobic THA(+) and hydrophilic Br(-) ions. Surface tension and argon scattering measurements indicate that the surface of this solution is dominated by the hexyl chains of the THA(+) ion. The hydrocarbon character of the surface is further explored by comparing Ar and DCl scattering from the THABr solution and liquid squalane. We find that the addition of THABr to glycerol alters the reactivity of DCl in two ways: DCl molecules that land on the surface are more likely to desorb when THA(+) and Br(-) are present and are less likely to dissolve, but they are also more likely to undergo rapid, interfacial DCl --> HCl exchange. Similar trends are observed when THA(+) ions are replaced by Na(+) ions in a 2.7 M NaBr solution, even though THA(+) interacts weakly with glycerol OH groups and Na(+) binds strongly to them. These observations suggest that the THA(+) hexyl chains do not physically block DCl entry and that interfacial cation-OH bonding is not essential for promoting rapid D --> H exchange when Br(-)-OH bonding also occurs. The use of THABr confirms that ions in the top few monolayers, and not those deeper in solution, control DCl entry and rapid D --> H exchange.