Die thermische zersetzung von [Mo(NO)2Cl2]n und seiner mit alkoholen und glykolen gebildeten derivate

The thermal decomposition of [Mo(NO)₂Cl₂]_n was studied. It was found that N₂ and MoOCl₄ were evolved at 340°C in an exothermic reaction and the solid residue was MoO₃. The Mo(NO)₂Cl₂L_n-type alcohol complexes are similary decomposed after the alcohol is split off in an endothermic process. The decomposition products of glycol derivatives are N₂, N₂O, CO, Cl₂, different organic carbonyl compounds and metallic molybdenum.     

Comparative Investigation of Mo(CO)6 Adsorption on Clean and Oxidized Si(111) Surfaces

Mo(CO)₆ adsorption on the clean, oxygen-precovered and deeply oxidized Si(111) surfaces was comparatively investigated by high-resolution electron energy loss spectroscopy. The downward vibrational frequency shift of the C-O stretching mode in adsorbed Mo(CO)₆ illustrates that different interactions of adsorbed Mo(CO)₆ occur on clean Si(111) and SiO₂/Si(111) surfaces, weak on the former and strong on the latter. The strong interac-tion on SiO₂/Si(111) might lead to the partial dissociation of Mo(CO)₆, consequently the formation of molybdenum subcarbonyls. Therefore, employing Mo(CO)₆ as the precursor, metallic molybdenum could be successfully deposited on the SiO₂/Si(111) surface but not on the clean Si(111) surface. A portion of the deposited metallic molybdenum is transformed into the MoO₃ on the SiO₂/Si(111) surface upon heating, and the evolved MoO₃ finally desorbs from the substrate upon annealing at elevated temperatures.     

Activation of the C-O bond on the surface of palladium: An <Emphasis Type="Italic">In situ</Emphasis> study by X-ray photoelectron spectroscopy and sum frequency generation

An in situ study of the adsorption of CO on atomically smooth and defect Pd(111) surfaces was performed over wide ranges of temperatures (200–400 K) and pressures (10^–6-1 mbar) by X-ray photoelectron spectroscopy and sum frequency generation. Both of the techniques indicated that CO was adsorbed as three-fold hollow, bridging, and terminal species to form well-known ordered structures on the surface. In the course of the in situ experiments, no signs of CO dissociation or of the formation of carbonyl structures (Pd(CO)_n, n > 1) were detected. The mechanism of C-O bond activation in the course of methanol decomposition on the surface of palladium was considered. It was found that the adsorption of methanol on the surface of palladium essentially depends on pressure. Along with the well-known reaction path of methanol dehydrogenation to CO and hydrogen, a slow process of methanol decomposition with C-O bond cleavage was observed at elevated pressures. In this case, the formation of carbon deposits finally resulted in the carbonization and complete deactivation of the surface. A mechanism for C-O bond activation on the surface of palladium was proposed; the geometry of adsorption complexes plays an important role in this mechanism.__________Translated from Kinetika i Kataliz, Vol. 46, No. 2, 2005, pp. 288–301.Original Russian Text Copyright © 2005 by Kaichev, Bukhtiyarov, Rupprechter, Freund.     

Adsorption of Propene on Neutral Gold Clusters in the Gas Phase

The adsorption of propene on neutral gold clusters is investigated in a collision cell under a few collision conditions. The adsorption reaction is studied by pressure‐dependent kinetic measurements and delayed unimolecular dissociation of the excited Au_n?propene complexes. The cluster size (n=9–25) and temperature (T=90–300 K) dependence of the propene adsorption is analyzed. Strong size dependences of the absorption reaction are observed; a larger propene adsorption probability was found for gold clusters composed of an even number of atoms. Propene binding energies are estimated by comparison of the temperature‐dependent unimolecular dissociation rates with rates obtained by using statistical RRKM modeling. The Au_n–propene binding energies decrease non‐monotonously with cluster size and are in the range of 1.2–0.85 eV for n=9–25. Finally, the bonding of C₃H₆ on Au_n is qualitatively described and similarities with the absorption of CO molecules on gold clusters are discussed.     

Kinetic and thermochemical characteristics of the dissociation of Mo(CO)6 and W(CO)6

The thermal dissociation of gaseous Mo(CO)₆ and W(CO)₆ in an argon carrier gas, Mo(CO)₆ → Mo(CO)₅ + CO (1) and W(CO)₆ → W(CO)₅ + CO (2), is studied over temperature ranges of ∼585–685 K for (1) and ∼690−810 K for (2) at a total gas concentrations of 4 × 10⁻⁶ and 4 × 10⁻⁵ mol/cm³ by using the shock tube technique in conjunction with absorption spectrophotometry. The measured rate constants are extrapolated to the high-pressure limit by means of a newly developed procedure, with the resultant expressions for the indicated temperature ranges reading as k_d1,∞(T),[s⁻¹] = 10^{16.12 ± 0.68}exp[(−148.8 ± 8.1 kJ/mol)/RT] and k_d2,∞(T),[s⁻¹] = 10^{15.93 ± 0.63}exp[(−171.7 ± 8.9 kJ/mol)/RT]. Comparison of the high-pressure dissociation rate constants with the published data revealed a considerable discrepancy, a tentative explanation of which is given. Based on the obtained high-pressure dissociation rate constants and the available data on the high-pressure room-temperature rate constants for the reverse reaction of recombination, the first bond dissociation energies for these molecules are evaluated and compared with previous determinations, both theoretical and experimental. The enthalpies of formation of Mo(CO)₅ and W(CO)₅ are determined: Δ_fH°(Mo(CO)₅, g, 298.15 K) = −644.1 ± 5.6 kJ/mol and Δ_fH°(W(CO)₅, g, 298.15 K) = −581.9 ± 6.6 kJ/mol. Based on the enthalpies of formation of Mo(CO)₅, W(CO)₅, Mo(CO)₆, and W(CO)₆, and the published molecular parameters of these four species, their thermochemical functions are calculated and presented in the form of NASA seven-term polynomials.     

Mechanochemical Palladium-Catalyzed Carbonylative Reactions Using Mo(CO)6

Esters and amides were mechanochemically prepared by palladium-catalyzed carbonylative reactions of aryl iodides by using molybdenum hexacarbonyl as a convenient solid carbonyl source and avoiding a direct handling of gaseous carbon monoxide. Real-time monitoring of the mechanochemical reaction by in situ pressure sensing revealed that CO is rapidly transferred from Mo(CO)₆ to the active catalytic system without significant release of molecular carbon monoxide.     

Transition Metal Complexes with more than one Dihydrogen Ligand: Structure and Bonding of M(CO)6–x(H2)x (M = Cr,Mo, W; x = 1, 2, 3) [1]

Quantum mechanical ab initio calculations at the MP2 and CCSD(T) level of theory have been used to investigate the geometries and bond energies of the complexes M(CO)_6–x(H₂)_x (M = Cr, Mo, W; x = 1, 2, 3). The theoretically predicted M(CO)₅–(H₂) bond dissociation energies are in excellent agreement with experimental values. The M–(H₂) dissociation energies of the bis- and tris-dihydrogen complexes are very similar to the values for the mono-dihydrogen complexes. In M(CO)₅(H₂) the dihydrogen ligand prefers an eclipsed conformation relative to the equatorial carbonyl groups. For M(CO)₄(H₂)₂ the cis and trans isomers are nearly equal in energy for M = W, while a cis configuration is favoured for M = Cr. For M(CO)₃(H₂)₃ the facial configurations are more stable than the meridial structures for all three metals M. The charge decomposition analysis (CDA) classifies dihydrogen as a donor ligand with moderate acceptor properties. In trans-M(CO)₄(H₂)₂ back donation is increased and the M–(H₂) bonds are stronger than in M(CO)₅–(H₂). Back donation in M(CO)₃(H₂)₃ is slightly weaker than in the mono-dihydrogen complexes M(CO)₅(H₂).     

Density functional calculations on CO attached to PtnRu(10−n) (n = 6–10) clusters

B3LYP and SCF‐Xα calculations have been performed on Pt_nRu_(10−n)CO (n = 6–10) clusters. The work aims to simulate the adsorption of CO on the (111) surface of platinum metal and to examine the electronic effects that arise when some Pt atoms are replaced with Ru. Adsorption energies and Pt C and C O stretching frequencies have been calculated for each cluster. Ru does affect the electronic structure of the clusters, the calculated adsorption energies, and frequencies, the Pt C frequency more than the C O. The donation‐backbonding mechanism that accompanies the shift in CO stretching frequency that occurs when CO adsorbs on platinum does not explain the differences in frequency shift observed in CO on various Pt/Ru surfaces. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 589–598, 2000     

Metallorganische Chemie mit P/N-Chelatliganden. I. Molybdän- und Eisen(0)-Verbindungen des 2-Diphenylphosphinomethylpyridins

Organometallic Chemistry with P/N-Chelating Ligands. I. Molybdenum and Iron(0) Compounds of 2-Diphenylphosphinomethylpyridine The reaction of 2-diphenylphosphinomethylpyridine 1 (PN) with norbornadiene-tetracarbonylmolybdenum gives (PN)Mo(CO)₄ 2 in good yield. The acetonitrile ligands in (π-C₃H₅)Mo(CO)₂(CH₃CN)₂Br 3 are easily exchanged by 1 . The thus formed complex (π-C₃H₅)(PN)Mo(CO)₂Br 4 undergoes a reductive deallylation with further 1 to afford cis-(PN)₂Mo(CO)₂ 6 . Deallylation of 3 by triphenylphosphine and subsequent reaction with 1 yields the complex cis-(CO)₂-trans-(PPh₃)₂Mo(PN) 7 . Ligand 1 displays a chelating function in all of the molybdenum complexes. The structures of the (PN)-complexes are deduced mainly from the nmr data. The initial product of the photochemical reaction of 1 with ironpentacarbonyl is (PN)Fe(CO)₄ 8 , followed by trans-(PN)₂Fe(CO)₃ 9 . In both cases 1 is bonded via the phosphorus atom only. Prolonged irradiation affords the chelated tricarbonyl (PN)Fe(CO)₃ 10 . The thermal reaction of 1 with Fe₂(CO)₉ is different in that the first product is a sensitive red compound 11 , which still contains bridging carbonyl groups and has to be formulated as (PN)Fe₂(CO) 7 . Longer reaction times, but also the reaction of 8 with Fe₂(CO)₉ finally give a new type of complex, (PN)Fe₂(CO)₆ 12 , without bridging carbonyls.     

Density functional study of carbon monoxide adsorption on small cationic,neutral, and anionic aluminum nitride clusters

CO adsorption on small cationic, neutral, and anionic (AlN)_n (n = 1–6) clusters has been investigated using density functional theory in the generalized gradient approximation. Among various possible CO adsorption sites, an N on‐top (onefold coordinated) site is found to be the most favorable one, irrespective of the charge state of the clusters. The adsorption energies of CO on the anionic (AlN)_nCO (n = 2–4) clusters are greater than those on the neutral and cationic complexes. The adsorption energies on the cationic and neutral complexes reflect the odd–even oscillations, and the adsorption energies of CO on the cationic (AlN)_nCO (n = 5, 6) clusters are greater than those on the neutral and anionic complexes. The adsorption energies for the different charge states decrease with increasing cluster size. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Ab‐Initio calculations of the CO adsorption and dissociation on substitutional Fe–Cu surface alloys relevant to Fischer–Tropsch Synthesis: bcc‐(Cu)Fe(100) and fcc‐(Fe)Cu(100)

Direct CO dissociation is seen the main path of the first step in the Fischer–Tropsch Synthesis (FTS) on the reactive iron surfaces. Cu/Fe alloy film is addressed with various applications over face‐centered‐cubic (fcc)‐Cu and body‐centered‐cubic (bcc)‐Fe in the FTS, i.e. preventing iron carbide formation (through direct CO dissociation) by moderating the surface reactivity and facilitating the reduction of iron surfaces, respectively. In this study by density functional theory, the stable configurations of CO molecule on various Cu/Fe alloys over fcc‐Cu(100) and bcc‐Fe(100) surfaces with different CO coverage (25% and 50%) have been evaluated. Our results showed that the ensemble effect plays a fundamental role to CO adsorption energy on the surface alloys over bcc‐Fe(100); on the other hand, the ligand effect determines the CO stability on the fcc‐Cu(100) surface alloys. CO dissociation barrier was also calculated on the surface alloys that showed although the CO dissociation process is thermodynamically possible on the more reactive surface alloys, but according to their high barrier, CO dissociation does not occur directly on these surfaces. Copyright © 2013 John Wiley & Sons, Ltd.     

The chemisorption of hydrogen on Cu(111): A dynamical study

Ab initio band-structure calculations within a density functional formalism were performed to compute the binding energy curves of atomic hydrogen with the high-symmetry adsorption sites of the (111) surface of copper. For a two-layer slab of Cu atoms and H coverage equal to 0.25, the binding energies are 2.25, 3.12, and 3.24 eV, for on-top, bridge, and threefold sites, so that the chemisorption of H₂ on Cu(111) is exothermic for threefold and bridge sites, but endothermic for on-top sites. Starting from these results, an LEPS potential for the interaction of H₂ with the Cu(111) surface was built. In this model potential, the most favored approaches correspond to a H₂ molecule parallel to the Cu surface, and for them, the activation barrier is located at the corner between the entrance and the exit channels of the reaction, and its lowest value is 0.6 eV. The LEPS potential was used in quasi-classical trajectories calculations to simulate the adsorption of a beam of H₂ molecules on Cu(111). The results show that (a) when H₂ is in the ground vibrational state the dissociative adsorption probability P_a increases from 0 to .90 along a roughly sigmoidal curve by increasing the collision kinetic energy from 0.4 to 1.3 eV, and (b) the vibrational energy can be as effective as the translational one in promoting dissociative chemisorption, in agreement with the experimental results. © 1994 John Wiley & Sons, Inc.     

Effects of composition on catalytic activities of molybdenum doped platinum nanoparticles

The physical and chemical properties of bimetallic nanoparticles can be optimized by tuning the particle composition. In this study, we identified CO adsorption and dissociation energetics on five Pt-Mo nanoparticles at different concentrations, the lowest energy Pt₇, Pt₆Mo, Pt₅Mo₂, Pt₄Mo₃, and Mo₇ clusters. We have shown that the CO adsorption and dissociation energies and preferred CO adsorption sites are largely dependent on the composition of the nanoparticles. As the Mo concentration increases, the strength of the C-O internal bond in the adsorption complex decreases, as indicated by a decrease in the C-O stretching frequency. Also, more Mo sites in the nanoparticle become available for CO adsorption, and the preferred CO adsorption site switches from Pt to Mo. For these reasons, dissociation of CO is energetically favorable on Pt₄Mo₃ and Mo₇. On both compositions, we have shown that the dissociation paths begin with CO adsorbed on a Mo site in a multifold configuration, in particular in a tilted configuration. These findings provide insight on the effects of the composition on the chemical and catalytical properties of Pt-Mo nanoparticles, thereby guiding future experiments on the synthesis of nanoparticles, especially those that may be suitable for various desired applications containing CO.     

Near Ambient Pressure Adsorption of Nickel Carbonyl Contaminated CO on Cu(111) Surface

Formation of volatile nickel carbonyls with CO in catalytic reaction is one of the mechanisms of catalyst deactivation. CO is one of the most popular probe molecules to study the surface properties in model catalysis. Under ultra-high vacuum (UHV) conditions, the problem of nickel carbonyl impurity almost does not exist in the case that a high purity of CO is used directly. While in the near ambient pressure (NAP) range, nickel carbonyl is easily found on the surface by passing through the Ni containing tubes. Here, the NAP techniques such as NAP-X-ray photoelectron spectroscopy and NAP-scanning tunneling microscopy are used to study the adsorption of nickel carbonyl contaminated CO gas on Cu(111) surface in UHV and NAP conditions. By controlling the pressure of contaminated CO, the Ni-Cu bimetallic catalyst can form on Cu(111) surface. Furthermore, we investigate the process of CO adsorption and dissociation on the formed Ni-Cu bi-metal surface, and several high-pressure phases of CO structures are reported. This work contributes to understanding the interaction of nickel carbonyl with Cu(111) at room temperature, and reminds the consideration of CO molecules contaminated by nickel carbonyl especially in the NAP range study.     

Effects of coverage and solvent on H2S adsorption on the Cu(100) surface: A DFT study

Density functional theory is used to investigate the effects of coverage and solvent on the adsorption of H₂S on the Cu(100) surface. In this work, the adsorption energies, structural parameters and Mulliken charges of the adsorbed H₂S are calculated. The results show that when the coverage of H₂S is high (1 ML), H₂S molecule cannot adsorb on the Cu(100) surface spontaneously, and the decomposition of H₂S preferentially occurs at the bridge site. When the coverage decreases to 1/4 ML coverage, H₂S molecule does not exhibit the decomposition, but bonds to the top Cu atom with the tilted adsorption. Furthermore, when the coverage is 1/9, 1/16 and 1/25 ML, H₂S adsorption remains stable. In addition, the stability of H₂S adsorption on the Cu(100) surface improves rapidly when the solvent dielectric constant (ε) increases from 1 to 12.3 corresponding to the vacuum and pyridine, respectively. For the higher ε (≥24.3), the effect of the solvent on the H₂S adsorption was greatly reduced. In this work, both coverage and solvent are shown to have an important effect on the H₂S adsorption on the Cu(100) surface, which might be useful to improve the future similar simulations. Copyright © 2015 John Wiley & Sons, Ltd.     

Observation of resonance effects in the relative partial photoionization cross sections of the d bands of M(CO)6, M = Cr,Mo and W

Relative partial photoionization cross sections as a function of photon energy, over the range 20–110 eV, have been measured for the valence bands of Cr(CO)₆, Mo(CO)₆ and W(CO)₆. All three t_2g⁻¹ bands show a very pronounced increase in intensity at photon energies (hv) corresponding to np resonant absorption (Cr(CO)₆, hv = 52.5 eV, n = 3; Mo(CO)₆,hv = 48 eV, n = 4; W(CO)₆, hv = 44 and 53 eV, n = 5). The other valence bands show a small intensity increase at similar energies. Observation of such resonant photoemission provides an unambiguous method for assignment of nd bands in the photoelectron spectra of gas-phase molecules.     

cis‐Tetracarbonylbis(tricyclohexyl­phosphine)molybdenum(0) and pentacarbonyl(tricyclohexylphos­phine)molybdenum(0)

In the present redetermination of the complex cis‐tetra­carbonyl­bis­(tri­cyclo­hexyl­phosphine)molybdenum(0), (I), [Mo(C₁₈H₃₃P)₂(CO)₄] or cis‐{η¹‐[P(C₆H₁₁)₃]₂}Mo(CO)₄, the Mo atom has a distorted octahedral geometry with a large P—Mo—P angle of 104.8 (1)°. A strong trans influence on the carbonyls in (I) is seen in a shortening of the Mo—C and a lengthening of the C—O distances opposite the phosphines compared with those that are cis. This influence is greatly diminished in the complex penta­carbonyl­(tri­cyclo­hexyl­phosphine)­molyb­denum(0), (II), [Mo(C₁₈H₃₃P)(CO)₅] or {η¹‐[P(C₆H₁₁)₃]}­Mo(CO)₅, the core of which has a slightly distorted C_4v geometry.     

First-principles study of O2 adsorption and dissociation on the CuCr2O4 (100) surface

The adsorption and dissociation of molecular oxygen on spinel CuCr₂O₄ (100) surface were carried out by first-principles calculations based on density functional theory (DFT). The calculated results indicate that the Cr site is most favorable for atomic oxygen adsorption, with an adsorption energy of 402.8 kJ/mol. For molecular oxygen adsorption, there are three types of favorable interaction modes: O₂ forms bonds with the Cu site or O₂ binds to two Cr sites or O₂ interacts with both Cu and Cr sites simultaneously. The lowest activation energy (E_a = 35.4 kJ/mol) was found through exploring possible reaction pathways for O₂ dissociation. The relationship between E_a and reaction enthalpy (ΔH) for O₂ dissociation adsorption reactions fits Brønsted-Evans-Polanyi (BEP) behavior.     

水在HfO2(111)和(110)表面的吸附与解离

运用广义梯度近似密度泛函理论方法(GGA-PW91)结合周期平板模型, 研究水分子在二氧化铪(111)和(110)表面不同吸附位置在不同覆盖度下的吸附行为. 通过比较不同吸附位的吸附能和几何构型参数发现:(111)和(110)表面铪原子(top 位)是活性吸附位. 水分子与表面的吸附能值随覆盖度的变化影响较小. 在(111)和(110)表面, 水分子都倾向以氧端与表面铪原子相互作用. 同时也计算了羟基、氧和氢在表面的吸附, Mulliken 电荷布居, 态密度及部分频率. 结果表明, 在两种表面羟基以氧端与表面铪相互作用, 氧原子与表面铪和氧原子同时成键, 而氢原子直接与表面氧原子相互作用形成羟基. 通过过渡态搜索, 水分子在(111)和(110)表面发生解离, 反应能垒分别为9.7和17.3 kJ·mol^-1, 且放热为59.9和47.6 kJ·mol^-1.     

Electron spectroscopic studies of the adsorption and decomposition of methanol on transition metals. A review

Results of investigations of the adsorption and decomposition of methanol on the surface of transition metals such as Fe, Ni, Cu, Pd, Ag, Mo, W and Pt byuv and x-ray photoelectron spectroscopy, electron energy loss spectroscopy, Auger electron spectroscopy and thermal desorption spectroscopy have been reviewed. The first step in the decomposition of CH₃OH on these metal surfaces is the formation of the methoxy species, OCH₃ radical. In the case of Fe, Mo and W, complete decomposition of CH₃OH occurs leaving CO(β), H₂ and CH₄ on the surface. Dissociation proceeds upto CO(α) and H₂ on the surface of Ni, Pd and Pt whereas on Ag and Cu, selective oxidation of CH₃OH to H₂CO is preferred. The difference in the reactivity of metals towards CH₃OH is rationalised from the heats of adsorption of O₂, CO and H₂ on these metals. Contribution No. 253 from the Solid State and Structural Chemistry Unit.