配体保护下的Au_(20)团簇吸附和活化CO的理论研究

用密度泛函理论方法计算了CO分子吸附在有机配体聚乙烯吡咯烷酮poly(N-vinyl-2-pyrrolidone)(PVP)保护下的Au20团簇上的稳定构型的结构和性质。配体PVP通过物理吸附主要作用于Au20团簇的顶点位置。与Au20比较,配体的存在有利于CO的吸附和活化,其根本原因是PVP和CO在Au20表面分别作为供电子和吸电子基团产生的协同效应。中性及阴离子Au20团簇对配体和CO的吸附强度不同,前者对PVP吸附作用较强,后者对CO的吸附和活化作用较强。     

TDDFT studies of electronic structure and first hyperpolarizability of terta-nuclear cubane-like transition metal clusters

The TDDFT method is first applied in a series of tetra-nuclear transition metal clusters studies for nonlinear optical properties. The results indicate that the charge transfer inside the metal core [MCu3X4] (M=W, Mo; X=S, O, Cl, Se, Br) makes contribution to the optical nonlinearity. It is possible to enhance the hyperpolarizability by substituting the ligands of the clusters.     

Electron correlation effects in ionic hydrogen clusters

We employ density functional, post‐Hartree–Fock, and quantum Monte Carlo methods to study the electronic structure, geometries, and behavior of positively charged H_m⁺ clusters with m=3,5,…,17. Their structure consists of a tightly bound H₃⁺ core ion surrounded by successive solvation shells of H₂ molecules. For the largest clusters, we propose new geometries. We find that correlated methods yield the stepwise decrease of enthalpies for dissociation of H₂ from the clusters observed in experiments. Our best results are obtained by the diffusion Monte Carlo method, and by including finite temperature entropic effects, we are able to reproduce the experimental dissociation enthalpies with an unprecedented accuracy of less than 0.5 kcal/mol. These benchmark results contrast with erroneous predictions discovered in the density functional approaches. Finally, our analysis of the cluster energy surfaces indicates that under quantum and thermal fluctuations, the outer solvation shells will exhibit pronounced fluctional behavior. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 83: 86–95, 2001     

Density functional study of AgnPd and AgnPdH clusters

Small Ag_nPd (n = 5) clusters and their hydrides Ag_nPdH (n = 5) have been studied by density functional theory calculations. For bare clusters, the structures in which the Pd atom has a maximum number of neighboring Ag atoms tend to be energetically favorable. Hydrogen prefers binding to Ag? Pd bridge site of Ag_nPd clusters except for Ag₅Pd. The binding energy has a strong odd–even oscillation. The electron transfers are from Ag atoms to Pd in bare clusters and are from metal clusters to H in cluster hydrides. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

The mechanism of transition metal catalyzed carbonylation of allyl halides: A theoretical investigation

The mechanism of the carbonylation reaction of allyl halides catalyzed by nickel (Ni(CO)₄) and palladium (Cl₂Pd(PPh₃)₂) complexes is theoretically investigated at the DFT level using the hybrid B3LYP functional. The favored reaction path to carbonylation corresponds, for both catalysts, to a direct attack of the halogen on the metal. This affords η¹ intermediates that can undergo the final carbonylation step. It is also possible to obtain the acyl product (β,γ-unsaturated acyl halides) from η² and/or η³ intermediates. However, in this case, the barrier of the rate-determining step to carbonylation is much higher. Since a channel on the potential surface connects rather easily the η² or η³ intermediates to the η¹ intermediates, an alternative and competitive path leading to the acyl products can originate from the η² or η³ intermediates, follow the η²/η³ → η¹ transformation, then undergo the final carbonylation step.     

Experimental study on high-pressure adsorption of hydrogen on activated carbon

A systematic measurement of H2 adsorption on activated carbon over a wide scope of conditions was completed for the first time using a novel cryostat developed by the present authors. The equilibrium temperatures covered 77-298 K with the space of about 20 K, and the equilibrium pressures increased from 0 to about 7MPa. A set of adsorption/desorption isotherms was obtained by a standard volumetric method. This set of experimental data was fitted to all the well-known models of type-I isotherms, and Dubinin-Astakhov (D-A) equation was found to be the best-fit one On the basis of D-A model one can predict adsorption with relative error of ±4%. A 3-dimensional adsorption surface was also constructed, and the isosteric heat of adsorption was analytically determined. Except in the low pressure area, the calculated values agreed well with the experimental ones. Finally, the troubles encountered in applying D-A equation to supercritical adsorption is discussed.     

Interaction of NO molecules with Pd clusters: Ab initio density–functional study

The adsorption of NO molecules on small Pd_n (n = 1?6) clusters has been studied using first‐principles density‐functional theory. Three adsorption sites were considered: vertex (on–top), bridge, and hollow. Adsorption is strong, ranging from 2 to 3 eV. In all cases NO adsorbs in a bent configuration. Calculated shifts in N–O bond vibration frequencies (with anharmonic corrections) agree very well with available experimental data. In contrast to metallic Pd surfaces, adsorption of NO on palladium clusters causes considerable changes in geometry around adsorption site because palladium d‐orbitals rehybridize to maximize the overlap with NO orbitals (mainly the antibonding π*). Thus, the overall energetic effect of NO adsorption is the result of two competing processes: lowering of the total energy through tighter bonding with NO and rising the energy due to cluster deformation. The Pd_n–NO bond creation is governed by electron transfer from Pd–d orbitals into the NO π*. As a result, the Pd cluster becomes locally demagnetized (with total magnetic moment of 1 μ_B located at Pd atoms not connected to NO) and the NO molecule is activated: the N–O bond length is increased and the vibration frequency is redshifted. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Erratum: Separability between valence and conduction bands in transition metal clusters

Density Functional Theory (DFT) and direct ab initio molecular dynamics (MD) calculations were applied to the hydrogen molecule trapped in a water cluster composed of 12 water molecules (H₂O)₁₂. The static DFT calculation showed that the H₂ molecule is trapped in the center of mass of (H₂O)₁₂. The vibrational frequency of the H–H stretching mode of the H₂ molecule trapped in the water cluster was blueshifted from that in vacuo. On the other hand, the vibrational frequency of H₂ in water‐hydrogen 1:1 complex (H₂O–H₂) was redshifted. A direct ab initio MD calculation of H₂(H₂O)₁₂ at 50 K indicated that the H₂ molecule is rotated freely around the center of mass of the water cluster. The origin of the spectral shift of H₂ in water ice is discussed on the basis of the theoretical results. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Adsorption of carbon monoxide and oxygen on transition metal surfaces: A comparative study of the results from electron spectroscopy and theoretical calculations

Results of investigations on the adsorption of CO andO ₂ on transition metal surfaces by employinguv and x-ray photoelectron spectroscopy and electron energy loss spectroscopy (eels) are presented. Results of molecular orbital calculations on adsorbed CO and O₂ are also discussed. Some of the interesting aspects discussed are, satellites in the O(ls) region due to adsorbed CO, vibrationaleels of adsorbed O₂ and dissociation energy profiles of adsorbed O₂ on clean surfaces as well as surfaces covered with potassium or presorbed atomic oxygen. Contribution No 245 from the Solid State and Structural Chemistry Unit.     

Applications of transition metal complexes containing aminophosphine ligand to transfer hydrogenation of ketones

Hydrogen transfer reduction processes are attracting increasing interest from synthetic chemists in view of their operational simplicity. Reaction of [Ph₂PNHCH₂‐C₄H₃S] with [Ru(η⁶‐benzene)(µ‐Cl)Cl]₂, [Rh(µ‐Cl)(cod)]₂ and [Ir(η⁵‐C₅Me₅)(µ‐Cl)Cl]₂ gave a range of new monodendate complexes [Ru(Ph₂PNHCH₂‐C₄H₃S)(η⁶‐benzene)Cl₂], 1, [Rh(Ph₂PNHCH₂‐C₄H₃S)(cod)Cl], 2, and [Ir(Ph₂PNHCH₂‐C₄H₃S)(η⁵‐C₅Me₅)Cl₂], 3, respectively. All new complexes were fully characterized by analytical and spectroscopic methods. ¹H? ³¹P NMR, ¹H? ¹³C HETCOR or ¹H? ¹H COSY correlation experiments were used to confirm the spectral assignments. 1–3 are suitable catalyst precursors for the transfer hydrogenation of acetophenone derivatives. Notably [Ru(Ph₂PNHCH₂‐C₄H₃S)(η⁶‐benzene)Cl₂], 1, acts as an excellent catalyst, giving the corresponding alcohols in 98–99% yields in 30 min at 82 °C (TOF ≤200 h^?1) for the transfer hydrogenation reaction in comparison to analogous rhodium or iridium complexes. This transfer hydrogenation is characterized by low reversibility under these conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

Ethylene addition to group-6 transition metal oxo complexes - A theoretical study

Quantum chemical calculations using density functional theory (B3LYP) were carried out to elucidate the reaction pathways for ethylene addition to the chromium and molybdenum complexes CrO(CH₃)₂(CH₂) (Cr1) and MoO(CH₃)₂(CH₂) (Mo1). The results are compared with previously published results of the analogous tungsten system WO(CH₃)₂(CH₂) (W1). The comparison of the group-6 elements shows that the molybdenum and tungsten compounds Mo1 and W1 have a similar reactivity while the chromium compound has a more complex reactivity pattern. The kinetically most favorable reaction pathway for ethylene addition to Mo1 is the [2+2]_Mo,C addition across the MoCH₂ double bond which has an activation barrier of only 8.4 kcal/mol. The reaction is slightly exothermic with ΔE_R = −0.6 kcal/mol. The [2+2]_Mo,O addition across the MoO double bond and the [3+2]_C,O addition have much higher barriers and are strongly endothermic. The thermodynamically mostly favored reaction is the [1+2]_Mo addition of ethylene to the metal atom which takes place after prior rearrangement of the Mo(VI) compound Mo1 to the Mo(IV) isomer Mo1g. The reaction is −19.2 kcal/mol exothermic but it has a large barrier of 34.5 kcal/mol. The kinetically and thermodynamically most favorable reaction pathway for ethylene addition to the chromium homologue Cr1 is the multiple-step process with initial rearrangements Cr1 → Cr1c → Cr1g which are followed by a [1+2]_Cr addition yielding an ethylene π complex Cr1g + C₂H₄ → Cr1g-1. The highest barrier comes from the first step Cr1 → Cr1c which has an activation energy of 14.2 kcal/mol. The overall reaction is exothermic by −26.3 kcal/mol.     

Boundary effect on the adsorption properties of H2 on charged MgCaHb complex

In this article, the equilibrium structure, binding energy, and electronic structure for charged Mg coated C_aH_b (a = 6, b = 6; a = 14, b = 10; a = 22, b = 14; a = 24, b = 14; a = 54, b = 18) are investigated by using all electrons density‐functional calculations. The boundary effect for the adsorption property of H₂ on charged MgC_aH_b complex is investigated by using several structures based on benzene ring molecules. A method for calculating the pathways for the synthesis of MgC_aH_bⁿ⁺ is presented here, and also the kinetic stability of these charged hydrogen‐covered MgC_aH_bⁿ⁺ complexes is also discussed. We find that the Mg doped complex with appropriate charge can enhance adsorption of hydrogen molecular. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Adsorption of CO on oxygen preadsorbed neutral and charged gas phase Pd4 clusters: A density functional study

We present the results of a density functional calculation on adsorption of O₂, CO, and their coadsorption at various sites of neutral, cationic, and anionic Pd₄ clusters. For all the clusters, the dissociative adsorption of oxygen sitting on Pd bridge sites is found to be preferable. Both O₂ and CO binding energies are found to be higher for the anionic Pd₄ cluster followed by cationic and neutral cluster. However, binding energies of O₂ or CO in the coadsorption complexes follow the trend: anionic > neutral > cationic. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Theoretical characterization of H2 adsorption on AuPt clusters

Linear and triangular AuPt_n cluster reactions with H₂ are studied theoretically, using ab initio multiconfiguration self-consistent field (MC-SCF) calculations, followed by extensive multireference configuration interaction (MR-CI) variational and perturbative. Both the linear dimer and the triangular trimers capture the hydrogen molecule by the Pt cluster side and by the Au cluster side. Gold has an electronic effect on the Pt activity, more important than a geometrical one, poisoning the Pt activity to dissociate H₂ and lowering the adsorption heats. This effect is stronger in the AuPt dimer, where the H₂ capture occurs only at the molecular level, without showing hydrogen bond dissociation. The trimers look more active, relaxing the H(SINGLE BOND)H bond until breakage. No activation barriers are observed in all the cases considered. The hydrogen molecule is not able to cross the clusters due to the large barriers present. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 399–409, 1998     

A theoretical study on the pure and doped ZnO nanoclusters as effective nanobiosensors for 5-fluorouracil anticancer drug adsorption

The electronic sensitivity and effectiveness of the pristine, Fe,- Mg-, Al- and Ga-doped ZnO nanoclusters interacted with 5-fluorouracil (5-FU) anticancer drug are theoretically investigated in the gas phase using the B3LYP/wB97XD density functional theory calculations with LANL2DZ basis set. It is concluded that 5-FU adsorption on the doped nanoclusters has relatively higher adsorption energy as compared with the pristine zinc oxide. A number of thermodynamic parameters, such as band gap energy (E_g), adsorption energy (E_ad), molecular electrostatic potential, global hardness (η) and density of electronic states, are attained and compared. Also, calculated geometrical parameters and electronic properties for the studied systems indicate that Mg- and Ga-doped Zn₁₂O₁₂ present higher sensitivity to 5-FU compared with the pristine nanocluster. Theoretical results reveal that adsorption of 5-FU on the doped nanoclusters is influenced by the electronic conductance of the nanocluster. Therefore, Mg- and Ga-doped ZnO can be considered as promising nanobiosensors for detection of 5-FU in medicine.     

Synthesis,structures, photophysical properties,and catalytic characteristics of 2,9-dimesityl-1,10-phenanthroline (dmesp) transition metal complexes

The syntheses of the 2,9-dimesityl-1,10-phenanthroline ( dmesp ) metal complexes, [Cu(dmesp)(MeCN)]PF₆ ( 1 ), [Cu(dmesp)₂]PF₆ ( 2 ), Fe(dmesp)Cl₂ ( 3 ), Co(dmesp)Cl₂ ( 4 ), Ni(dmesp)Cl₂ ( 5 ), Zn(dmesp)Cl₂ ( 6 ), Pd(dmesp)MeCl ( 7 ), Cu(dmesp)Cl ( 8 ), and Pd(dmesp)₂Cl₂ ( 9 ), in good to high yields are described. These complexes were characterized by ¹H and ¹³C NMR spectroscopy, HR–MS (ESI and/or APPI), and elemental analysis (CHN). The solid-state structures of complexes 1 – 8 were determined by single-crystal X-ray analysis and their photophysical properties were also characterized. To demonstrate the versatility of this new platform, complexes 3 – 5 , 8 , and 9 were employed in the catalytic oligomerization of ethylene using modified methyl aluminoxane (MMAO) as the cocatalyst, where Co(II) and Ni(II) complexes ( 4 and 5 , respectively) were found to exhibit moderate selectivity for catalytic dimerization of ethylene to butenes over tri- or tetramerization. Complex 8 is an effective catalyst of both the commonly encountered “click” reaction and amine arylation chemistries. Complexes 6 and 9 were found to be excellent catalysts for Friedel-Crafts alkylation and Suzuki-Miyaura coupling, respectively.