Activation of dimethyl ether with barium and strontium atoms

Organometallic compounds are produced when barium and strontium atoms are cocondensed with dimethyl ether at ?196°C; hydrolysis of the cocondensation products from both reactions yields mainly C₁—C₈ alkanes, alkenes, and alkynes.     

Minimal-basis-adapted pseudopotentials for transition metal atoms

A pseudopotential technique is presented to be used with a single function constructed from the three primitive GTOs for the representation of d orbitals of transition-metal atoms. Applied to Cu, CU₂, and CuF, it has permitted a reduction in the number of 3d-type GTO primitives without reducing the quality of the results.     

Temperature dependence of the rate coefficients for the reactions of Br atoms with dimethyl ether and diethyl ether

The rate constants for the reactions of atomic bromine with dimethyl ether and diethyl ether were measured from approximately 300 to 350 K using the relative rate method. Both isooctane and isobutane were used as the reference reactants, and the rate constants for the reactions of these hydrocarbons were measured relative to each other over the same temperature range. The kinetic measurements were made by photolysis of dilute mixtures of bromine, the reference reactant, and the test reactant in mixtures of argon and oxygen at a total pressure of 1 atm. The resulting ratios of rate constants were combined with the absolute rate constant as a function of temperature for the reference reaction of Br with isobutane to calculate absolute rate constants for the reactions of Br with isooctane, dimethyl ether, and diethyl ether. The absolute rate constant, in the units cm3 molecule(-1) s(-1), for the reaction of Br with dimethyl ether was given by k = (3.8 +/- 2.4) x 10(-10) exp(-(3.54 +/- 0.21) x 10(3)/T) while for the reaction of Br with diethyl ether the rate constant is given by k = (2.8 +/- 2.7) x 10(-10) exp(-(2.44 +/- 0.32) x 10(3)/T). On the same basis, the rate constant for the reaction of Br with isooctane is given by k = (3.34 +/- 0.59) x 10(-12) exp(-(1.80 +/- 0.11) x 10(3)/T). In each case, the activation energy of the reaction is significantly smaller than the endothermicity of the reaction. This is discussed in terms of a complex mechanism for these reactions.     

Matrix infrared spectroscopic and theoretical studies on the reactions of scandium, yttrium, and lanthanide metal atoms with dimethyl ether

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(CH(3)OCH(3)) and CH(3)OMCH(3) (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(CH(3)OCH(3)) complexes spontaneously on annealing, which isomerize to the CH(3)OMCH(3) insertion products with visible irradiation. Density functional calculations reveal that the M(CH(3)OCH(3)) complexes possess C(2v) symmetry with metal atoms bound to the oxygen side of dimethyl ether, and bent geometries are found for the inserted CH(3)OMCH(3) 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(CH(3)OCH(3)) complex is predicted to be a stable molecule, it is not observed in the experiment due to the low energy barrier for the subsequent C-O bond insertion reaction.     

CNDO bonding parameters in transition metal atoms

The method of calculating CNDO bonding parameters developed recently is extended to transition metal atoms. It is shown that one of the approximations introduced earlier can also be deduced by a more complete treatment of the imbalance problem in CNDO-MO theory. The conventionally calibrated bonding parameters indirectly incorporate important contributions from two-particle interactions. The parameters developed are used to compute the coefficients of metal-to-ligand transfer of spin in many hexafluro metallate ions of transition metals. The results are compared with those obtained by conventional CNDO-MO calculation. Comparison of the computed bonding parameters with other available values is also made.     

Shock‐tube studies on the reactions of dimethyl ether with oxygen and hydrogen atoms

The reactions of dimethyl ether (CH₃OCH₃, DME) with O(³P) and H atoms have been studied at high temperatures by using a shock tube apparatus coupled with atomic resonance absorption spectroscopy (ARAS). The rate coefficients for the reactions CH₃OCH₃ + O(³P) → CH₃OCH₂ + OH (1) and CH₃OCH₃ + H → CH₃OCH₂ + H₂ (2) were experimentally determined from the decay of O(³P) and H atoms as: These results show that DME can react with O(³P) atoms more easily than with H atoms. By combining these results with the previous lower temperature data, we obtained the following modified Arrhenius expressions applied over the wide temperature range between 300 and 1500 K: Both reactions of DME are faster than those of ethane, because the dissociation energy of the C? H bond in DME is smaller. Furthermore, the rate coefficients for reactions ( 1 ) and ( 2 ) were calculated with the transition‐state theory (TST). Structural parameters and vibrational frequencies of the reactants and the transition states required for the TST calculation were obtained from the MP2(full)/6‐31G(d) ab initio molecular orbital (MO) calculation. The energy barrier, E^?₀, was adjusted until the TST rate coefficient most closely matched the observed one. The fitting results of E(1) = 23 kJ mol^?1 and E(2) = 34 kJ mol^?1 were in agreement with the G2 energy barriers, within the expected uncertainty, demonstrating that the experimentally determined rate coefficients were theoretically valid. © 2006 Wiley Periodicals, Inc. 39: 97–108, 2007     

Polyoxometalates containing late transition and noble metal atoms

This review describes the state of the art in the field of polyoxometalates containing noble metal atoms (ruthenium, rhodium, palladium, silver, osmium, iridium, platinum and gold). The structures of the various species are listed together with their applications (mainly in catalysis).     

The kinetics of the reactions of O(3P) atoms with dimethyl ether and methanol

The kinetics of the reaction of O + CH₃OCH₃ were investigated using fast-flow apparatus equipped with ESR and mass-spectrometric detection. The concentration of O(³P) atoms to CH₃OCH₃ was varied over an unusually large range. The rate constant for reaction was found to be k = (5.0 ± 1.0) × 10¹² exp [(?2850 ± 200/RT)] cm³ mole^?1 sec^?1. The reaction O + CH₃OH was studied using ESR detection. Based on an assumed stoichiometry of two oxygen atoms consumed per molecule of CH₃OH which reacts, we obtain a value of k = (1.70 ± 0.66) × 10¹² exp [(?2,280 ± 200/RT)] cm³ mole^?1 sec^?1 for the reaction The results obtained in this study are compared with the results from other workers on these reactions. The observation of essentially equal activation energies in these two reactions is indicative of approximately equal C? H bond strengths in CH₃OCH₃ and CH₃OH. This is in agreement with recent measurements of these bond energies.     

State-dependent photoionization cross-sections of 3d transition metal atoms

Using the saturation method, we measured the absolute photoionization cross-sections of several excited states of titanium, vanadium, chromium, iron, and cobalt. These results are reported for the first time in this paper. The measured values range from 0.4 ± 0.1 Mb to 6.9 ± 2.0 Mb. The results show that the photoionization cross-section depends on the atomic state and not just on the electronic configuration.     

Approximate STO functions for the first-row transition metal atoms

Slater type orbital (STO) basis sets for the atoms Sc-Zn have been derived using a technique based on the distance between subspaces. The accuracy for several properties of these basis sets has been tested. Basis sets studied are of both single- and double-zeta sizes, although this technique can be generalized for any size. Uniform quality criteria through the series of atoms Sc-Zn are difficulty to establish due to the varying number of d electrons. A comparative study at the atomic level of the quality of STO basis sets (both the two new basis sets and Clementi's basis sets) for the first-row transition elements has been carried out. Results show that the new basis sets provide better simulation for several properties. Molecular calculations on compounds with these atoms using a Gaussian expansion fitted according to the new values of optimized STOs are also included. The results obtained are similar to those reported when STO-3G basis set is used.     

New relativistic ANO basis sets for transition metal atoms

New basis sets of the atomic natural orbital (ANO) type have been developed for the first, second, and third row transition metal atoms. The ANOs have been obtained from the average density matrix of the ground and lowest excited states of the atom, the positive and negative ions, and the atom in an electric field. Scalar relativistic effects are included through the use of a Douglas-Kroll-Hess Hamiltonian. Multiconfigurational wave functions have been used with dynamic correlation included using second order perturbation theory (CASSCF/CASPT2). The basis sets are applied in calculations of ionization energies, electron affinities, and excitation energies for all atoms and polarizabilities for spherically symmetric atoms. These calculations include spin-orbit coupling using a variation-perturbation approach. Computed ionization energies have an accuracy better than 0.2 eV in most cases. The accuracy of computed electron affinities is the same except in cases where the experimental values are smaller than 0.5 eV. Accurate results are obtained for the polarizabilities of atoms with spherical symmetry. Multiplet levels are presented for some of the third row transition metals.     

Valence 4p functions for the first-row transition metal atoms

For the valence 4p orbitals of the first-row transition metal atoms Sc through Zn, Gaussian-type basis functions are developed referring to excited 3d ^m 4s ¹4p ¹ electronic configurations. Molecular tests of the present work 4p sets are performed for the Cu atom, the diatomic Cu₂ molecule, and Cu₉ and Cu₁₃ clusters, and the results are compared with those from two literature sets. Received: 17 January 2000 / Accepted: 30 May 2000 / Published Online: 11 September 2000     

High-temperature pyrolysis of dimethyl ether

The kinetics of pyrolysis of dimethyl ether wexre studied in an adiabatic flow reactor at temperatures between 790 and 950°C. The unimolecular rate constant for the initiating step CH₃OCH₃ = CH₃O + CH₃ was found to be k₁ = 2.16 × 10¹⁵e^?76,600/RTsec^?1. Aspects of the kinetic mechanism are discussed and a system postulated to account for the high-temperature products.     

Imaging the quantum-state specific differential cross sections of HCl formed from reactions of chlorine atoms with methanol and dimethyl ether

Center-of-mass frame scattering angle distributions obtained directly from crossed molecular beam velocity map images are reported for HCl formed in different rotational levels of its vibrational ground state by reaction of Cl atoms with CH3OH and CH3OCH3. Products are observed to scatter over all angles, with peaks in the distribution in the forward and backward directions (theta = 0 and 180 degrees with respect to the relative velocity vectors of the Cl atoms). Products of both reactions exhibit differential cross sections that vary with the rotational quantum number of the HCl, with a greater propensity for forward scatter for J = 2, shifting to more pronounced backward scatter for J = 5. This trend is, however, more evident for reaction of dimethyl ether than for methanol. The mean fractions of the available energy channeled into product kinetic energy vary with scattering angle, but the angle-averaged fractions are, respectively, 0.37 and 0.42 for the methanol and dimethyl ether reactions. On average, 46% or more of the available energy of the reactions becomes internal energy of the radical co-product. Results are interpreted with the aid of computed energies of transition states and molecular complexes along the reaction pathways, and comparisons are drawn with recent measurements of the scattering distributions and energy release for reactions of Cl atoms with small alkanes.     

Chemical syntheses with metal atoms

Metal evaporation syntheses of [Cr(C₇H₇)(C₇H₁₀)], [Cr(C₇H₈)(PF₃)₃], metal carbonyls, and anhydrous metal acetylacetonates are described.     

Investigation of structures of mono- and diorgano-substituted oligosiloxanes containing transition metal atoms

Oligomeric linear copper-containing diorganosiloxanes with a variable Cu : Si ratio and branched Cu- and Ni-containing organosiloxanes containing the γ-aminopropyl group at the Si atom were investigated. IR spectroscopic studies demonstrated that the distribution of metal atoms throughout the metallosiloxane chain in compounds with a high metal content (M : Si≥2) is rather uniform. According to the data from electronic spectroscopy, compounds under study are complexes of metal ions characterized by d-d transitions and an octahedral configuration of the coordination units. The Cu^II and Ni^II ions are coordinated by the NH₂ groups primarily through interchain interactions. ESR spectroscopic studies demonstrated that the Cu^II ions are located predominantly in the main chain to form −O−Cu−O− fragments. The coordination polyhedron changes from a nearly planar square (in the solid phase) to an elongated tetragonal bipyramid (in solution). The spectral parameters of the Cu-containing oligomer containing the γ-aminopropyl group at the Si atom indicate that the N atoms of the amino groups are located in the equatorial plane of the Cu-containing coordination polyhedron. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1813–1817, October, 2000.     

Selective ion-molecule reactions of lactams with dimethyl ether ions

The ion-molecule reactions of dimethyl ether ions CH₃OCH₃ ⁺ and (CH₃OCH₃)H⁺, and four- to seven-membered ring lactams with methyl substituents in various positions were characterized by using a quadrupole ion trap mass spectrometer and a triple-quadrupole mass spectrometer. In both instruments, the lactams were protonated by dimethyl ether ions and formed various combinations of [M + 13] ⁺, [M + 15] ⁺, and [M + 45] ⁺ adduct ions, as well as unusual [M + 3] ⁺ and [M + 16] ⁺ adduct ions. An additional [M + 47] ⁺ adduct ion was formed in the conventional chemical ionization source of the triple-quadrupole mass spectrometer. The product ions were isolated and collisionally activated in the quadrupole ion trap to understand formation pathways, structures, and characteristic dissociation pathways. Sequential activation experiments were performed to elucidate fragment ion structures and stepwise dissociation sequences. Protonated lactams dissociate by loss of water, ammonia, or methylamine; ammonia and carbon monoxide; and water and ammonia or methylamine. The [M + 16] ⁺ products, which are identified as protonated lactone structures, are only formed by those lactams that do not have an N-methyl substituent. The ion-molecule reactions of dimethyl ether ions with lactams were compared with those of analogous amides and lactones.     

Magnetic enhancement and magnetic reduction in binary clusters of transition metal atoms

Electronic and magnetic properties of small binary clusters containing one or two transition metal atoms are investigated using ab initio calculations with a view to explain the experimentally observed magnetic enhancement/reduction in these systems. As the present investigations do not rely on spin-orbit effects, our results reveal the enhancement or reduction in the magnetic moment to depend on two main factors; namely geometry and, most importantly, the d-band filling. The results can be used as a guide in the experimental synthesis of high density magnetic grains.     

Encapsulation of transition metal atoms into carbon nanotubes: a supramolecular approach

A functionalised fullerene incorporating a double-chelating group binds transition metal cations and acts as an effective vehicle for delivering metals into carbon nanotubes.