金基二元合金团簇Au_(12)M(M=Cu,Pt,Ni)催化水煤气变换反应的理论研究

利用密度泛函理论(DFT)对Au12M(M=Cu,Pt,Ni)3种合金团簇的结构稳定性、热力学稳定性和反应活性进行研究,并对金基二元合金团簇催化水煤气变换反应(WGSR)的反应机理进行探讨.研究发现,Au12Ni合金团簇的稳定性及电子活性最优.考察了WGSR在金基二元合金团簇上的氧化还原机理和羧基机理,表明Au12Cu合金团簇上WGSR按照氧化还原机理A进行,水解离后产生的OH*会继续解离为O*和H*(*代表吸附物质);Au12Pt及Au12Ni合金团簇上按照氧化还原机理B进行,2个OH*发生歧化反应.比较3种团簇上的最佳反应路径发现,Au12Cu团簇对WGSR表现出较好的催化活性.     

Au12M (M=Na,Mg, Al,Si, P,S, Cl)团簇的结构、稳定性和电子性质

采用基于密度泛函理论的第一性原理方法系统地研究了Au12M(M=Na,Mg,Al,Si,P,S,Cl)团簇的结构、稳定性和电子性质.对团簇的平均结合能、镶嵌能、垂直离化势、最高占据分子轨道(HOMO)和最低未占据分子轨道(LUMO)的能级差、电荷布居分析、自然键轨道(NBO)进行了计算和讨论.对于Au12M(M=Na,Mg,Al)团簇,它们形成了内含M原子的最稳定的笼状结构.然而对于Au12M(M=Si,P,S,Cl)团簇,它们却形成了以M元素为顶点的稳定锥形结构.在这些团簇中发现Au12S团簇相对是最稳定的,这是由于Au12S团簇形成了稳定的满壳层的电子结构.自然电荷布居分析表明:对于所有的Au12M(M=Na,Mg,Al,Si,P,S,Cl)团簇电荷总是从Au原子转向M原子.自然键轨道和HOMO分析表明Au12M团簇中发生了Au原子的s-d轨道和M原子的p轨道间的杂化现象.     

M0,±6(M=Os,Ir,Pt)团簇结构与性质的密度泛函理论研究

采用密度泛函理论(DFT)中的杂化密度泛函(B3LYP)方法,在LANL2DZ基组水平上对M06,±(M=Os,Ir,Pt)团簇的各种可能构型进行了几何结构优化,得出各团簇的最稳定构型,并对其能量、振动频率、热力学性质、核独立化学位移(NICS)和极化率进行了理论研究.结果表明,M06,±(M=Os,Ir)团簇的基态都是三棱柱结构,Pt-6团簇的基态是平面三角形结构;M06,±(M=Os,Ir,Pt)团簇生成焓都为负值,热力学上是稳定的;NICS值都为负值,表明M06,±(M=Os,Ir,Pt)团簇都具有芳香性,其中Os6-团簇的芳香性最强;从光谱分析来看,Os6的IR和Raman谱的较强吸收峰的个数最多,Ir6的IR和Raman谱的最强吸收峰都只有一个,IR最强吸收峰在137.O和143.5 cm-1之间,Raman谱最强的吸收峰位于169.5 cm-1处;Pt6的IR和Raman谱的最强吸收峰分别位于50.2和194.7 cm-1处.     

M_6~(0,±)(M=Os,Ir,Pt)团簇结构与性质的密度泛函理论研究

采用密度泛函理论(DFT)中的杂化密度泛函(B3LYP)方法,在LANL2DZ基组水平上对M06,±(M=Os,Ir,Pt)团簇的各种可能构型进行了几何结构优化,得出各团簇的最稳定构型,并对其能量、振动频率、热力学性质、核独立化学位移(NICS)和极化率进行了理论研究.结果表明,M06,±(M=Os,Ir)团簇的基态都是三棱柱结构,Pt-6团簇的基态是平面三角形结构;M06,±(M=Os,Ir,Pt)团簇生成焓都为负值,热力学上是稳定的;NICS值都为负值,表明M06,±(M=Os,Ir,Pt)团簇都具有芳香性,其中Os-6团簇的芳香性最强;从光谱分析来看,Os6的IR和Raman谱的较强吸收峰的个数最多,Ir6的IR和Raman谱的最强吸收峰都只有一个,IR最强吸收峰在137.0和143.5 cm-1之间,Raman谱最强的吸收峰位于169.5 cm-1处;Pt6的IR和Raman谱的最强吸收峰分别位于50.2和194.7 cm-1处.     

Cux (x=1-4)团簇在CeO2(111)表面的吸附

用基于密度泛函理论的第一性原理方法研究了Cu团簇(Cu_x, x=1-4)在CeO₂(111)表面的吸附. 研究发现当团簇比较小时(x=2, 3), 倾向于平铺表面; 当x=4时, Cu团簇在CeO₂(111)表面以三维的四面体结构吸附较为稳定, 从Cu 3d到Ce 4f的电荷转移使Cu团簇带正电荷. 由二维的菱形结构到三维的四面体结构的转变势垒为1.05 eV, 并且其中一个Cu原子直接迁移到另外三个Cu原子的空位顶部的转变路径比较有利. 在Cu团簇与CeO₂的相互作用过程中, Cu-O和Cu-Cu相互作用的竞争最终决定了Cu团簇在CeO₂上的形貌. 这种CeO₂(111)负载的带正电的三维Cu团簇将对水分解, 进而对水煤气反应具有高的催化活性.     

双金属合金团簇M12Ni(M=Pt,Sn,Cu)催化甲烷干法重整反应的理论研究

利用密度泛函理论(DFT)研究了M₁₂Ni(M=Pt, Sn, Cu) 3种双金属合金团簇的电子活性和结构稳定性, 并探讨了甲烷干法重整反应(DRM)在M₁₂Ni双金属团簇表面的反应能量变化情况. 经比较发现甲烷脱氢和二氧化碳活化过程在Pt₁₂Ni团簇表面进行需克服的活化能垒最低, 反应最易进行. Sn₁₂Ni团簇上生成碳需要较高的活化能, 说明Sn₁₂Ni团簇能够有效抑制焦碳的生成, 一定程度上克服了碳沉积导致的催化剂失活现象, 并且Sn₁₂Ni团簇在C ^*和CH ^*氧化过程中表现出最佳的催化活性. Cu₁₂Ni团簇仅在甲烷脱氢过程中表现出较为优异的催化活性.     

Cu_nNi(n=2-13)团簇基态结构和电子特性的密度泛函研究

基于第一性原理,利用密度泛函理论中广义梯度近似(GGA)对团簇Cun-1Ni和Cun(n=3-14)进行了结构优化和能量计算,结果表明,单质Cu团簇不是以密实结构而是以类平面结构生长,但Ni的掺杂使得Cu团簇结构以二十面体为基础生长并且增加了团簇的稳定性;团簇结合能的二阶差分计算表明Cu3Ni,Cu7Ni和Cu9Ni结构最为稳定;在团簇的最稳定结构中Ni原子趋于占据团簇的中心位置和更多的Cu原子形成化学键;位于表面的Cu原子成为Mülliken电荷的接受体而带负电性,这也可能是Ni掺杂Cu合金耐腐蚀性增强的原因之一;Ni的掺杂使原来没有磁性的铜团簇显示了磁性且总自旋磁矩表现明显的奇偶振荡,为1或2μB,与团簇的尺寸无关.     

(BN)_n团簇的结构和稳定性

用HF方法、密度泛函理论的B3LYP以及微扰理论的MP2方法 ,在 6 3 1G(d)基组水平上 ,对 (BN) n(n =1～ 16)团簇的各种可能结构进行了优化 .讨论了环状与笼状稳定团簇的几何构型、自然键轨道 (NBO)、振动频率、结合能、核独立化学位移 (NICS)和能量二次差分 ,得到了 (BN) n(n =1～ 16)团簇结构的稳定性信息 .比较了HF ,B3LYP以及MP2三种理论方法对(BN) n 团簇的适应性所表现出的差异 .     

配体稳定的二元过渡金属团簇[PdAu8(PR3)8]2+(R=Me,OMe,H,F,Cl,CN)的量子化学理论研究

采用从头计算MP2方法和密度泛函理论方法,对过渡金属团簇[PdAu8(PR3)8]2+(R=Me,OMe,H,F,Cl,CN)的几何结构、电子结构以及团簇各组成部分之间的结合能进行了研究.MP2方法和SVWN局域泛函能够对团簇的结构给予准确的描述,而离域泛函BP86,PBE,BLYP和杂化泛函B3LYP则过高地估计了团簇的几何结构参数.电子结构研究表明Pd,Au原子通过d电子的成键作用构成团簇内核[PdAu8]2+,[PdAu8]2+与PR3配体则通过"σ给予/π反馈"模式成键.PR3配体与[PdAu8]2+的结合能够加强Pd-Au之间的成键作用,增大前线轨道能级间隙,从而提高团簇的稳定性.PR3配体中 R 基团供、吸电能力的变化对[PdAu8(PR3)8]2+结构的影响较小,但对[PdAu8]2+ -pR3结合能的影响较大.能量分析显示不同PR3与[PdAu8]2+之间具有相近的轨道作用能,与R基团供、吸电能力相关的非轨道作用能成为影响两者连接牢同程度的决定因素.     

硅基稀土掺杂团簇MSi_7~q(M=Eu,Sm,Yb;q=0,-1)结构预测与光电子能谱研究

采用随机踢球模型结合密度泛函理论,在PBEPBE/RE/SDD/Si/6-311+G(d)水平下研究了中性和阴性的硅基稀土掺杂团簇MSi_7~q(M=Eu,Sm,Yb;q=0,-1)的几何结构、稳定性及电子和磁学性质.计算结果表明,阴性团簇的基态结构是在五角双锥的双锥侧面外法向方向加入一个Si原子而形成的3D结构,并且稀土原子M处于五角双锥的顶点;中性团簇的最低能结构是一个畸变的双帽八面体,并且M原子处于八面体的赤道面上.SmSi_7~-团簇在这3种稀土掺杂的团簇中具有最高的平均结合能和掺杂能,是这3种稀土掺杂团簇中最稳定的一种.Si_7团簇是非磁性团簇,但是当M原子(M=Eu,Sm,Yb)掺入其中时,由于镧系元素独特的原子磁性,使其变成了磁性团簇.此外,还模拟了各团簇前几种低能异构体的光电子能谱.     

Equilibrium geometries, stabilities, and electronic properties of the bimetallic M2-doped Au(n) (M = Ag, Cu; n = 1-10) clusters: comparison with pure gold clusters

The density functional method with relativistic effective core potential has been employed to investigate systematically the geometrical structures, relative stabilities, growth-pattern behaviors, and electronic properties of small bimetallic M(2)Au(n) (M = Ag, Cu; n = 1-10) and pure gold Au(n) (n ≤ 12) clusters. The optimized geometries reveal that M(2) substituted Au(n+2) clusters and one Au atom capped M(2)Au(n-1) structures are dominant growth patterns of the stable alloyed M(2)Au(n) clusters. The calculated averaged atomic binding energies, fragmentation energies, and the second-order difference of energies as a function of the cluster size exhibit a pronounced even-odd alternation phenomenon. The analytic results exhibit that the planar structure Ag(2)Au(4) and Cu(2)Au(2) isomers are the most stable geometries of Ag(2)Au(n) and Cu(2)Au(n) clusters, respectively. In addition, the HOMO-LUMO gaps, charge transfers, chemical hardnesses and polarizabilities have been analyzed and compared further.     

A new 19-metal-atom cluster [(Me2PhP)10Au12Ag7(NO3)9] with a nearly staggered-staggered M5 ring configuration

New mixed metal clusters with M19 metal frameworks have been synthesized by NaBH4 reduction of Au(NO3)(PMe2Ph) together with AgNO3 in ethanol. Single crystal X-ray diffraction has revealed Au12Ag7 and Au17Ag2 metal skeletons for these clusters, which are best described in terms of bicapped pentagonal antiprismatic cages with a staggered-staggered M(5) ring configuration. These clusters connect the missing link between M13 icosahedral and M25 biicosahedral clusters providing a view of the cluster growth process. A TEM image of this cluster has been observed, which has clearly demonstrated single-sized nano-particles of less than 1.0 nm.     

Enhanced stability by three-dimensional aromaticity of endohedrally doped clusters X(10)M(0/-) with X = Ge, Sn, Pb and M = Cu, Ag, Au

The group 14 clusters encapsulated by coinage metals in neutral and anionic states X(10)M(0/-) (X = Ge, Sn, Pb and M = Cu, Ag, Au) are investigated using quantum chemical calculations with the DFT/B3LYP functional and coupled-cluster CCSD(T) theory. Addition of transition metals into the empty cages forms high symmetry endohedral structures, except for Ge(10)Ag(0/-). In agreement with experiments available for X(10)Cu, the D(4d) global minima of the anions are calculated to be magic clusters with large frontier orbital gaps, high vertical and adiabatic detachment energies, and large embedding energies and binding energies as compared to those of the empty cages X(10)(2-). The enhanced stability of these magic clusters can be rationalized by the three-dimensional aromaticity.     

Electronic Structures of Copper(I) and Silver(I) beta-Diketonate Complexes

The valence electronic structures of [Cu(hfac)L] (hfac = CF(3)C(O)CHC(O)CF(3); L = PMe(3), CNMe), [Ag(hfac)(PMe(3))], and [Ag(fod)(PEt(3))] (fod = t-BuC(O)CHC(O)C(3)F(7)) have been studied by recording their photoelectron spectra and by performing Xalpha-SW calculations on the model compounds [M(dfm)(PH(3))] (dfm = HC(O)CHC(O)H; M = Cu, Ag) and [Cu(dfm)(CNH)]. For the copper complexes, the spectra were recorded between 21 and 160 eV using He I, He II and synchrotron radiation; while, for the silver complexes, He I and He II, spectra were recorded. Assignments were made by comparison of experimental and calculated values of band energies, and, for the copper complexes, by similar comparison of experimental and theoretical branching ratios as a function of photon energy. For the silver complexes, a more limited comparison of band intensities in the He I and He II spectra was made. In analogous compounds, it is shown that the binding energies follow the sequence Ag 4d > Cu 3d, with an energy difference of almost 2 eV.     

Zwitterionic metalates of group 11 elements and their use as metalloligands for the assembly of multizwitterionic clusters

Reaction of RNHC(S)PPh2NPPh2C(S)NR (HRSNS; R = Me, Et) with M(I) (M = Cu, Ag, Au) salts afforded zwitterionic complexes of the general formula [M(RSNS)] (M = Cu, Ag, Au). The ligand was found in the solid state in S,S-kappa2 and S,N,S-kappa3 coordination fashions. [Cu(RSNS)] and [Ag(RSNS)] can be used as metalloligand building blocks for the assembly of pentanuclear multizwitterionic Cu5, Cu3Ag2 and Ag5 core clusters of the general formula [M'2{M(RSNS)}3]2+ (M = Cu, M' = Cu, Ag; M = M' = Ag) upon reaction with suitable M' salts. The crystal structures of the most significant compounds are reported herein. Compound [Ag2{Ag(RSNS)}2(OTf)2] was also isolated and structurally characterized, representing a model for the intermediate species of the aforementioned assembly.     

Al7Ag and Al7Au clusters with large highest occupied molecular orbital-lowest unoccupied molecular orbital gap

The candidate structures for the ground-state geometry of the Al(7)M (M = Li, Cu, Ag, and Au) clusters are obtained within the spin-polarized density functional theory. Absorption energy, vertical ionization potential, vertical electron affinity, and the energy gap between the highest occupied molecular orbital (HOMO) level and the lowest unoccupied molecular orbital (LUMO) level have been calculated to investigate the effects of doping. Doping with Ag or Au can lead to a large HOMO-LUMO gap, low electron affinity, and increased ionization potential of Al(7) cluster. In the lowest-energy structure of the Al(7)Au cluster, the Al atom binding to the Al(6)Au acts monovalent and the other six Al atoms are trivalent. Thus, the Al(7)Au cluster has 20 valence electrons, and its enhanced stability may be due to the electronic shell closure effect.     

CO adsorption on pure and binary-alloy gold clusters: a quantum chemical study

We performed density-functional theory analysis of nondissociative CO adsorption on 22 binary Au-alloy (Au(n)M(m)) clusters: n=0-3, m=0-3, and m+n=2 (dimers) or 3 (trimers), M=Cu/Ag/Pd/Pt. We report basis-set superposition error corrections to adsorption energies and include both internal energy of adsorption (DeltaU(ads)) and Gibbs free energy of adsorption (DeltaG(ads)) at standard conditions (298.15 K and 1 atm). We found onefold (atop) CO binding on all the clusters except Pd2 (twofold/bridged), Pt2 (twofold/bridged), and Pd3 (threefold). In agreement with the experimental results, we found that CO adsorption is thermodynamically favorable on pure Au/Cu clusters but not on pure Ag clusters and also observed the following adsorption affinity trend: Pd>Pt>Au>Cu>Ag. For alloy dimers we found the following patterns: Au2>M Au>M2 (M=Ag/Cu) and M2>M Au>Au2 (M=Pd/Pt). Alloying Ag/Cu dimers with (more reactive) Au enhanced adsorption and the opposite effect was observed for PdPt dimers. The Ag-Au, Cu-Au, and Pd-Au trimers followed the trends observed on dimers: Au3>M Au2>M2Au>M3 (M=Ag/Cu) and Pd3>Pd2Au>PdAu2>Au3. Interestingly, Pt-Au trimers reacted differently and alloying with Au systematically increased the adsorption affinity: PtAu2>Pt2Au>Pt3>Au3. A strikingly different behavior of Pt is also manifested by the triplet spin state and onefold (atop) binding in Pt3-CO which is in contradiction with the singlet spin state and threefold binding in Pd3-CO. We found a linear correlation between CO binding energy (BE) and elongation of the CO bond. For Ag-Au and Cu-Au clusters, the increase in CO BE (and elongation of the C-O bond which is probably due to the back donation) is accompanied by the decrease in the cluster-CO distance suggesting that the donation (from 5sigma highest occupied molecular orbital in CO to cluster lowest unoccupied molecular orbital) mechanism also contributes to the BE. For Pd-Au clusters, the cluster-CO distance (and CO bond length) increases with increase in the BE, suggesting that the donation mechanism may not be important for those clusters. No clear trend was observed for Pt-Au clusters.     

Electronic structures and nonlinear optical properties of trinuclear transition metal clusters M-(mu-S)-M' (M = Mo,W; M' = Cu,Ag, Au)

A series of trinuclear metal clusters MS4(M'PPh3)2(M'PPh3) (M = Mo, W; M' = Cu, Ag, Au) have been studied using the density functional theory (DFT) method. The static polarizabilities and hyperpolarizabilities of the model clusters have been calculated using the finite-field (F-F) method. The model clusters, divided into two groups, are alike in the structure of two fragments of rhombic units M-(mu-S)2-M' (M = Mo, W; M' = Cu, Ag, Au), perpendicular to each other, which are joined by sharing the bridge metal M. It is the charge transfer from one of these moieties to the other in these characteristic sulfido-transitional metal cores that is responsible for the polarizabilities and hyperpolarizabilities. This kind of electronic delocalization, different from that of the planar pi-system, is interesting and warrants further investigation. The structural effects on properties are important. In these models, considerable third-order nonlinearities are exhibited. The element substitution effect of Mo and W is weak, while that of Cu and Ag is relatively substantial. An overall order is gamma xxxx(Mo-Ag) > gamma xxxx(W-Ag) > gamma xxxx(Mo-Au) > gamma xxxx(W-Au) > gamma xxxx (Mo-Cu) > gamma xxxx(W-Cu) and gamma av(Mo-Ag) approximately gamma av(W-Ag) > gamma av(Mo-Au) approximately gamma av(W-Au) approximately gamma av (Mo-Cu) approximately gamma av(W-Cu).     

Electronic and Geometric Structure of Bimetallic Clusters: Density Functional Calculations on [M(4){Fe(CO)(4)}(4)](4-) (M = Cu, Ag, Au) and [Ag(13){Fe(CO)(4)}(8)](n)(-) (n = 0-5)

The results of all-electron density functional calculations on the bimetallic cluster compounds [M(4){Fe(CO)(4)}(4)](4-) (M = Cu, Ag, Au) and on the corresponding naked species M(4)Fe(4) are reported. The trends within the triad have been investigated. The bare metal clusters exhibit a strong magnetization which is quenched on addition of CO ligands. The bonding in the bare clusters is different for the silver derivative compared to that of copper and gold, resulting in comparatively weaker Ag-Fe and Ag-Ag bonds. This can be rationalized in terms of the different d-sp mixing, which for Cu and Au is larger than for Ag. Relativistic effects act to increase the 4d-5s mixing in Ag and to strengthen the intermetallic bond with Fe. In the carbonylated clusters a charge transfer from the metal M (M = Cu, Ag, or Au) to the Fe(CO)(4) groups occurs so that the atoms M can be considered in a formal +I oxidation state, rationalizing the nearly square-planar geometry of the metal frame. In fact, the local coordination of the M atoms is almost linear, as expected for complexes of M(I). The addition of extra electrons results in a stabilization of the clusters, indicating the electron-deficient nature of these compounds. Similar features have been found for the largest cluster synthesized so far for this class of compounds, [Ag(13){Fe(CO)(4)}(8)](n)(-), (n = 0-5). The nature and localization of the unpaired electron in the tetraanion is also discussed.     

Heterovalent Au(III)-M(I) (M=Cu, Ag, Au) complexes derived from incorporation of [Au(tdt)2]- (tdt = toluene-3,4-dithiolate) with [M2(dppm)2]2+ (dppm = Bis(diphenylphosphino)methane)

Polynuclear heterovalent Au(III)-M(I) (M = Cu, Ag, Au) cluster complexes [Au(III)Cu(I)8(mu-dppm)3(tdt)5]+ (1), [Au(III)3Ag(I)8(mu-dppm)4(tdt)8]+ (2), and [Au(III)Au(I)4(mu-dppm)4(tdt)2]3+ (3) were prepared by reaction of [Au(III)(tdt)2]- (tdt = toluene-3,4-dithiolate) with 2 equiv of [M(I)2(dppm)2]2+ (dppm = bis(diphenylphosphino)methane). Complex 3 originates from incorporation of one [Au(III)(tdt)2]- with two [Au(I)2(dppm)2]2+ components through Au(III)-S-Au(I) linkages. Formation of complexes 1 and 2, however, involves rupture of metal-ligand bonds in the metal components and recombination between the ligands and the metal atoms. The Au(tdt)2 component connects to four M(I) atoms through Au(III)-S-M(I) linkages in syn and anti conformations in complexes 1 (M = Cu) and 3 (M = Au), respectively, but in both syn and anti conformations in complex 2 (M = Ag). The tdt ligand exhibits five types of bonding modes in complexes 1-3, chelating Au(III) or M(I) atoms as well as bridging Au(III)-M(I) or M(I)-M(I) atoms in different orientations. Although complexes 1 and 2 are nonemissive, Au(III)Au(I)(4) complex 3 shows room-temperature luminescence with emission maximum at 555 nm (tau(em) = 3.1 micros) in the solid state and at 570 nm (tau(em) = 1.5 micros) in acetonitrile solution.