Bonding in cationic MOH n + (M = K − La, Hf − Rn; n = 0–2): DFT performances and periodic trends

On the linear geometry of lanthanide hydroxide (Ln-OH, Ln = La–Lu)

Density functional theory predicts that lanthanide hydroxides are linear, with the lanthanide-hydroxide bond being characterized as a covalent triple bond.

Interaction of FeO- with water: anion photoelectron spectroscopy and theoretical calculations

The interactions of FeO^- with water molecules were studied by using photoelectron spectroscopy and density functional theoretical calculations. It is found that a dihydroxyl species, Fe(OH)₂^-/0, can be formed when FeO^-/0 interacts with the first water molecule. The complexes formed via the interactions between FeO^-/0 and n water molecules can be viewed as Fe(OH)₂(H₂O)_n-1^-/0, in which (n - 1)H₂O molecules interact with a Fe(OH)₂ core. For Fe(OH)₂^-/0 and Fe(OH)₂(H₂O)^-, the Fe(OH)₂ unit has two conformers with the two OH groups oriented differently. The vertical detachment energies (VDEs) of FeO₂H₂(H₂O)_n-1^- (n = 1-4) are measured to be 1.25 ± 0.04, 1.66 ± 0.04, 2.06 ± 0.04, and 2.37 ± 0.04 eV, respectively, by experiment. It is also worth mentioning that in the FeO₂H₂(H₂O)^- anion the water molecule interacts with the Fe(OH)₂ core by forming a hydrogen bond with one of the OH groups, while in neutral FeO₂H₂(H₂O), the water molecule interacts with the Fe atom of the Fe(OH)₂ core via its O atom.

Density Functional Theory Study of the Reaction between d0 Tungsten Alkylidyne Complexes and H2O: Addition versus Hydrolysis

The reactions of early-transition-metal complexes with H₂O have been investigated. An understanding of these elementary steps promotes the design of precursors for the preparation of metal oxide materials or supported heterogeneous catalysts. Density functional theory (DFT) calculations have been conducted to investigate two elementary steps of the reactions between tungsten alkylidyne complexes and H₂O, i.e., the addition of H₂O to the W≡C bond and ligand hydrolysis. Four tungsten alkylidyne complexes, W(≡CSiMe₃)(CH₂SiMe₃)₃ (A-1), W(≡CSiMe₃)(CH₂^tBu)₃ (B-1), W(≡C^tBu)(CH₂^tBu)₃ (C-1), and W(≡C^tBu)(O^tBu)₃ (D-1), have been compared. The DFT studies provide an energy profile of the two competing pathways. An additional H₂O molecule can serve as a proton shuttle, accelerating the H₂O addition reaction. The effect of atoms at the α and β positions has also been examined. Because the lone-pair electrons of an O atom at the α position can interact with the orbital of the proton, the barrier of the ligand-hydrolysis reaction for D-1 is dramatically reduced. Both the electronic and steric effects of the silyl group at the β position lower the barriers of both the H₂O addition and ligand-hydrolysis reactions. These new mechanistic findings may lead to the further development of metal complex precursors.

On the Activation of Methane and Carbon Dioxide by [HTaO](+) and [TaOH](+) in the Gas Phase: A Mechanistic Study

The thermal reactions of [Ta,O,H](+) with methane and carbon dioxide have been investigated experimentally and theoretically by using electrospray ionization mass spectrometry (ESI MS) and density functional theory calculations. Although the activation of methane proceeds by liberation of H2 , the activation of CO2 gives rise to the formation of [OTa(OH)](+) under the elimination of CO. Computational studies of the reactions of methane and carbon dioxide with the two isomers of [Ta,O,H](+) , namely, [HTaO](+) and [Ta(OH)](+) , have been performed to elucidate mechanistic aspects and to explain characteristic reaction patterns.

Unravelling Mechanistic Aspects of the Gas-Phase Ethanol Conversion: An Experimental and Computational Study on the Thermal Reactions of MO2 (+) (M=Mo, W) with Ethanol

The ion/molecule reactions of molybdenum and tungsten dioxide cations with ethanol have been studied by Fourier transform ion-cyclotron resonance mass spectrometry (FT-ICR MS) and density functional theory (DFT) calculations. Dehydration of ethanol has been found as the dominant reaction channel, while generation of the ethyl cation corresponds to a minor product. Cleary, the reactions are mainly governed by the Lewis acidity of the metal center. Computational results, together with isotopic labeling experiments, show that the dehydration of ethanol can proceed either through a conventional concerted [1,2]-elimination mechanism or a step-wise process; the latter occurs via a hydroxyethoxy intermediate. Formation of C2 H5 (+) takes place by transfer of OH(-) from ethanol to the metal center of MO2 (+) . The molybdenum and tungsten dioxide cations exhibit comparable reactivities toward ethanol, and this is reflected in similar reaction rate constants and branching ratios.

On the Mechanisms of Hydrogen-Atom Transfer from Water to the Heteronuclear Oxide Cluster [Ga2 Mg2 O5 ](.+) : Remarkable Electronic Structure Effects

Mechanistic insight into the homolytic cleavage of the O-H bond of water by the heteronuclear oxide cluster [Ga2 Mg2 O5 ](.+) has been derived from state-of-the-art gas-phase experiments in conjunction with quantum chemical calculations. Three pathways have been identified computationally. In addition to the conventional hydrogen-atom transfer (HAT) to the radical center of a bridging oxygen atom, two mechanistically distinct proton-coupled electron-transfer (PCET) processes have been identified. The energetically most favored path involves initial coordination of the incoming water ligand to a magnesium atom followed by an intramolecular proton transfer to the lone-pair of the bridging oxygen atom. This step, which is accomplished by an electronic reorganization, generates two structurally equivalent OH groups either of which can be liberated, in agreement with labeling experiments.

Ionic liquids as solvents of polar and non-polar solutes: affinity and coordination

Evolution of H₂O and CO₂ interactions with an ionic liquid (IL) from gas phase to IL phase is described. Affinity is lost and coordination patterns vary in the process, favouring H₂O–anion and CO₂–cation interactions.

Isomer-selective thermal activation of methane in the gas phase by [HMO]+ and [M(OH)]+ (M=Ti and V)

Methane scrabble: To have the right elements is sometimes just not sufficient, as shown by [M(OH)](+) (M=Ti, V), which do not react with methane. However, reshuffling of the "tiles" to [HMO](+) changes the reactions behavior completely, leading to the first example of C-H bond activation of methane by an early first-row transition-metal cation.

Gas-phase reactions of cationic vanadium-phosphorus oxide clusters with C2H(x) (x=4, 6): a DFT-based analysis of reactivity patterns

The reactivities of the adamantane-like heteronuclear vanadium-phosphorus oxygen cluster ions [V(x)P(4-x)O(10)](.+) (x=0, 2-4) towards hydrocarbons strongly depend on the V/P ratio of the clusters. Possible mechanisms for the gas-phase reactions of these heteronuclear cations with ethene and ethane have been elucidated by means of DFT-based calculations; homolytic C-H bond activation constitutes the initial step, and for all systems the P-O(.) unit of the clusters serves as the reactive site. More complex oxidation processes, such as oxygen-atom transfer to, or oxidative dehydrogenation of the hydrocarbons require the presence of a vanadium atom to provide the electronic prerequisites which are necessary to bring about the 2e(-) reduction of the cationic clusters.

Theoretical approaches to estimating homolytic bond dissociation energies of organocopper and organosilver compounds

Although organocopper and organosilver compounds are known to decompose by homolytic pathways among others, surprisingly little is known about their bond dissociation energies (BDEs). In order to address this deficiency, the performance of the DFT functionals BLYP, B3LYP, BP86, TPSSTPSS, BHandHLYP, M06L, M06, M06-2X, B97D, and PBEPBE, along with the double hybrids, mPW2-PLYP, B2-PLYP, and the ab initio methods, MP2 and CCSD(T), have been benchmarked against the thermochemistry for the M-C homolytic BDEs (D(0)) of Cu-CH(3) and Ag-CH(3), derived from guided ion beam experiments and CBS limit calculations (D(0)(Cu-CH(3)) = 223 kJ·mol(-1); D(0)(Ag-CH(3)) = 169 kJ·mol(-1)). Of the tested methods, in terms of chemical accuracy, error margin, and computational expense, M06 and BLYP were found to perform best for homolytic dissociation of methylcopper and methylsilver, compared with the CBS limit gold standard. Thus the M06 functional was used to evaluate the M-C homolytic bond dissociation energies of Cu-R and Ag-R, R = Et, Pr, iPr, tBu, allyl, CH(2)Ph, and Ph. It was found that D(0)(Ag-R) was always lower (~50 kJ·mol(-1)) than that of D(0)(Cu-R). The trends in BDE when changing the R ligand reflected the H-R bond energy trends for the alkyl ligands, while for R = allyl, CH(2)Ph, and Ph, some differences in bond energy trends arose. These trends in homolytic bond dissociation energy help rationalize the previously reported (Rijs, N. J.; O'Hair, R. A. J. Organometallics2010, 29, 2282-2291) fragmentation pathways of the organometallate anions, [CH(3)MR](-).

Chemistry with methane: concepts rather than recipes

Four seemingly simple transformations related to the chemistry of methane will be addressed from mechanistic and conceptual points of view: 1) metal-mediated dehydrogenation to form metal carbene complexes, 2) the hydrogen-atom abstraction step in the oxidative dimerization of methane, 3) the mechanisms of the CH(4)→CH(3)OH conversion, and 4) the initial bond scission (C-H vs. O-H) as well as the rate-limiting step in the selective CH(3)OH→CH(2)O oxidation. State-of-the-art gas-phase experiments, in conjunction with electronic-structure calculations, permit identification of the elementary reactions at a molecular level and thus allow us to unravel detailed mechanistic aspects. Where appropriate, these results are compared with findings from related studies in solution or on surfaces.