过渡金属异核原子簇化学键研究 1: Ⅷ-Ⅷ, ⅥB-Ⅷ族双金属原子簇电子结构研究

本文对18个Ⅷ族双金属四面体簇和16个ⅥB-Ⅷ异金属四核簇进行了量子化学研究, 用DV-Xα方法讨论了它们的化学键、电荷转移、能级态密度。计算结果表明: Ⅷ族四面体簇需36个金属电子, 其中12个形成6个金属簇骼轨道, 24个与配体成键; ⅥB-Ⅷ异金属簇核中, 因两金属能带、电负性差异, ⅥB原子易向Ⅷ原子转移电荷, 环戊二烯基配体促进这一过程; 异金属簇能级总价带比单金属簇收缩, 而d能带比单金属簇展宽。     

过渡金属异核原子簇化学键研究 1: Ⅷ-Ⅷ, ⅥB-Ⅷ族双金属原子簇电子结构研究

本文对18个Ⅷ族双金属四面体簇和16个ⅥB-Ⅷ异金属四核簇进行了量子化学研究,用DV-X_o方法计论了它们的化学键、电荷转移、能级态密度.计算结果表明:Ⅷ族四面体簇需36个金属电子,其中12个形成6个金属簇骼轨道,24个与配体成键;ⅥB-Ⅷ异金属簇核中,因两金属能带、电负性差异,ⅥB原子易向Ⅷ原子转移电荷,环戊二烯基配体促进这一过程;异金属簇能级总价带比单金属簇收缩,而d能带比单金属簇展宽.     

NO_x储存催化剂Pt/BaAl_2O_4-A1_2O_3的XAFS研究

采用共沉淀－浸渍法在不同载体焙烧温度下,制备了不同Ａｌ／Ｂａ原子比的Ｐｔ／ＢａＡｌ２Ｏ４－Ａ１２Ｏ３系列样品。用ＸＲＤ,ＸＡＮＥＳ,ＥＸＡＦＳ,以及ＮＳＣ（ＮＯ_ｘ　ｓｔｏｒａｇｅ ｃａｐａｃｉｔｙ）测定等手段对样品的微观结构和ＮＯ_ｘ储存性能进行了详细的表征．样品中Ｂａ物种是以ＢａＡｌ２Ｏ４和ＢａＣＯ３两种混合物相的形式存在,且伴随着载体焙烧温度和Ｂａ含量的降低,ＢａＡｌ２Ｏ４物相的分散度变高,ＮＯ_ｘ储存活性也随之提高,这表明ＢａＡｌ２Ｏ４相的分散度与样品的ＮＯ_ｘ储存性能密切相关,小颗粒的ＢａＡｌ２Ｏ４相是ＮＯ_ｘ的主要储存活性中心．在样品中,Ｐｔ物种以金属原子簇形式存在．分散度很高,其Ｐｔ—Ｐｔ壳层配位数较标样Ｐｔ粉有显著下降,Ｐｔ—Ｐｔ键长变短,出现了纳米收缩现象．高分散的小颗粒金属Ｐｔ原于簇为捕获和氧化ＮＯ_ｘ的主要活性中心．     

金属硼烷arachmo—P4M2B8和closo—MB10X2分子结构的键合研究

利用ＤＶ－Ｘα法计算了ａｒａｃｈｎｏ－（ＰＨ３）４Ｍ２Ｂ８Ｈ８（ｕ－Ｈ）２（Ｍ：Ｎｉ,Ｐｄ,Ｐｔ）和ｃｌｏｓｏ－（ＰＨ３）２ＭＢ１０Ｈ８Ｘ２（Ｍ：Ｆｅ,Ｒｕ,Ｏｓ;Ｘ：Ｃｌ,Ｂｒ,Ｉ,ＯＨ,Ｌｉ）系列分子的电子结构。结果表明在２类ａｒａｃｈｎｏ－Ｐ４Ｍ２Ｂ８和ｃｌｏｓｏ－ＭＢ１０Ｘ２主干结构中均有类似的２种Ｍ－－Ｂ键合：一是金属原子ｄ轨道相对配体原子轨道形成了全对称匹配分子轨道（ＭＯｓ）;二是部分     

CO_xM_(4—x)异金属四面体簇羰基化合物的量子化学研究

本文对十个CO_xM_(4-x)异金属四面体簇合物体系进行了量化计算(DV-X_a方法)。结果表明:CO_xM_(4-x)异金属簇与Co_4四面体簇化学键相似,但其他金属(M)的引入,使四面体簇价带收缩,Co的3d能级展宽,体系费米能级升高。在Co与Fe、Ru等ⅦB族元素形成的双金属簇中,Co在簇中所占比例愈大,贡献的电荷就愈多;而在Co与Mo、W等ⅥB族元素形成的四面体簇中,Mo、W为电荷主要提供者。     

含手性膦配体2-MBPA铂(Ⅱ)配合物的2DNMR

利用一维和二维ＮＭＲ技术,对含有手性膦配体的铂配合物ｃｉｓ－〔Ｐｔ（２－ＭＢＰＡＨ）２Ｃｌ２〕（１）,ｔｒａｎｓ－〔Ｐｔ（２－ＭＢＰＡＨ）２Ｃｌ２〕（２）,ｃｉｓ－〔Ｐｔ（２－ＭＢＰＡ）２〕（３）和ｃｉｓ－〔Ｐｔ（２－ＭＢＰＡ）（２－ＭＢＰＡＨ）Ｃｌ〕（４）进行１Ｈ和１３ＣＮＭＲ谱分析,区分了化合物（３）和（４）,归属了糖苷部分的１Ｈ和１３ＣＮＭＲ谱线,并根据磷和铂及磷与磷的偶合常数确定化合物（３）和（４）是顺式构型     

金属硼化物结构与稳定性的理论研究

用ＨＦ／３－２１Ｇａｂｉｎｉｔｉｏ法对金属硼化物ＭＢ２／ＭＢ２（Ｍ＝Ｌｉ，Ｎａ，Ｂｅ，Ｍｇ，Ａｌ）的７５个电子态结构进行能量梯度法优化，再用大基组二次且上互作用ＱＣＩＳＤ（Ｔ）／６－３１１Ｇ进行单点计算，得到了结构参数总能量，为了考察各原子簇的稳定性，还对２４个碎片的７０多个电子态，求得相应的ＱＣＩＳＤ（Ｔ）能量，在此基础上计算了原子化能、电离能、离解通道和碎片化能，得到了原子簇的稳定性规律。     

簇电荷对金属—金属键影响的量子化学研究

在探讨过渡金属原子簇化合物的金属——金属键的本质时,簇电荷的影响已引起人们的注意。簇电荷对金属——金属键的作用比较复杂,其中有价电子的成键效应和金属原子氧化数变化所产生的电荷效应。键长与簇电荷之间很难找到简单的关系。Cotton等曾对此问题做过初步讨论,但尚缺定量或半定量的理论计算依据,本文采用改进的电荷自洽EHMO程序(MAD—SCCO-EHMO)计算一系列Mo,Tc,Ru,Rh,和Re等二核簇的电子结构,根据M(?)lliken重迭集居分析,讨论簇电荷对金属——金属键的影响。     

金属羰基络合物制备的Pt-Re/Al2O3催化剂的性能Ⅱ.不同方法制备的Pt-Re/Al2O3催化剂的物化性质表征

采用ＴＰＲ，Ｈ２化学吸附，ＴＰＤ，ＴＥＭ和ＤＲＳ等方法对一组组成相同制法不同的Ｐｔ－Ｒｅ／Ａｌ２Ｏ３催化剂进行了表征。ＴＰＲ，Ｈ２化学吸附等结果表明，Ｐｔ－Ｒｅ／Ａｌ２Ｏ３催化剂中Ｒｅ是通过与ＰＴ的相互作用形成有高温吸附Ｈ２中心及抗积炭能力的Ｐｔ－Ｒｅ集团，从而提高了重整催化剂的活性和稳定性。制备方法的不同对催化剂活性表面的形成及铂铼相互作用有重要影响。以羰基金属原子簇化合物制备的Ｐｔ２Ｒ３２催化     

铝与氧、硫、磷、砷、碳形成的二元原子簇负离子的质谱研究

以脉冲激光束真空溅射的方式,产生了铝与多种非金属元素—氧、硫、磷、砷、碳等形成的二元原子簇负离子的离子束,记录了它们的飞行时间质谱。质谱分析的结果显示,这些彼此分离的气相簇离子的结构与键型,随着成簇的非金属元素的改变和成簇原子数的增加而有规律地变化:当簇离子中的非金属元素从ⅥA族改变至ⅥA族以至ⅣA族时。其键型也从离子型向共价型改变。     

MULTIPLE CENTER d-β ORBITALS AND CHARGE TRANSFER OF HETERONUCLEAR COUSTERS WITH CUBANE TYPE (Mo_3S_4)_xM~n+ (x=1, 2, M = Cu, W, Ni, Sb. Mo, Sn, Cu_2; n = 4,8)

<正> In this work, with the analysis on MO and electronic structure for a series of heteronuclear cluster with cubane type (Mo4S1 )xMn1(x=1.2. M = Cu, W, Ni, Sb, Mo, Sn, Cu2) we found that it is with the multiple center d-pir orbitals that the ligand Mo3S44+ bonds to the M atom to form these class clusters. It is revealed that the charges transfer from the M atom to Mo atom of the ligand Mo3S44+ and its relationship with the MC (multiple center) d-pπ orbitals. Based on the charge transfer the electronic spectrum and the magnetic property of some cubane clusters have been discussed.     

Unsaturated platinum-rhenium cluster complexes. Synthesis, structures and reactivity

Two new compounds PtRe3(CO)12(PBut3)(micro-H)3, 9, and PtRe2(CO)9(PBut3)(micro-H)2, 10, were obtained from the reaction of Pt(PBut3)2 with Re3(CO)12(micro-H3), 8, at room temperature. Compound 9 contains a butterfly cluster of four metals formed by the insertion of the platinum atom from a Pt(PBut3) group into one of the hydride-bridged metal-metal bonds of 8. The three hydrido ligands are bridging ligands across each of three new Pt-Re bonds. Compound 10 contains a triangular PtRe2 cluster with two hydrido ligands; one bridges a Pt-Re bond, and the other bridges the Re-Re bond. The new compound Pt2Re2(CO)7(PBut3)2(micro-H)2, 11, was obtained from the reaction of 8 with Pt(PBut3)2 in hexane at reflux. Compound 11 was also obtained from 10 by reaction with an additional quantity of Pt(PBut3)2. Compound 11 contains a tetrahedral cluster of four metal atoms with two dynamically active hydrido ligands. A CO ligand on one of the two platinum atoms also exchanges between the two platinum atoms rapidly on the NMR time scale. Compound 11 is electronically unsaturated and was found to add hydrogen at room temperature to form the tetrahydrido cluster complex, Pt2Re2(CO)7(PBut3)2(micro-H)4, 12. Compound 12 has a structure similar to 11 but contains one triply bridging hydrido ligand, two edge bridging hydrido ligands, and one terminal hydrido ligand on one of the two platinum atoms. A kinetic isotope effect D/H of 1.5(1) was determined for the addition of H2 to 11. Hydrogen can be eliminated from 12 by heating to 97 degrees C or by the application of UV-vis irradiation at room temperature. Compound 12 adds CO at room temperature to yield the complex Pt2Re2(CO)8(PBut3)2(micro-H)4, 13, which contains a planar cluster of four metal atoms with a Pt-Pt bond and four edge bridging hydrido ligands. Compounds 11 and 12 react with Pt(PBut3)2 to yield the known five metal cluster complexes Pt3Re2(CO)6(PBut3)3(micro-H)2, 14, and Pt3Re2(CO)6(PBut3)3(micro-H)4, 15, respectively. Density functional calculations confirm the hydride positions in the lowest energy structural isomers of 11 and 12 and suggest a mechanism for H2 addition to 11 that occurs on the Pt atom with the lower coordination number.     

过渡金属异核原子簇化学键研究 2: IB-Ⅷ, IB-ⅥB族金属四核原子簇电子结构研究

我们选择了14个IB-Ⅷ, IB-ⅥB族异金属四核簇合物, 用DV-Xα方法研究它们的成键规律、配体效应及能级变化。计算表明: 它们按构型可分为三类: 三角锥、蝶型、平面四边形、金属簇骼轨道分别为6个、5个、4个, 稳定性也依次降低。文中还讨论了三苯基膦等配体在合成IB簇合物中的作用和异核簇中d能带的变化对吸附的影响。     

Geometric, electronic, and bonding properties of AuNM (N = 1-7, M = Ni, Pd, Pt) clusters

Employing first-principles methods, based on density functional theory, we report the ground state geometric and electronic structures of gold clusters doped with platinum group atoms, Au(N)M (N = 1-7, M = Ni, Pd, Pt). The stability and electronic properties of Ni-doped gold clusters are similar to that of pure gold clusters with an enhancement of bond strength. Due to the strong d-d or s-d interplay between impurities and gold atoms originating in the relativistic effects and unique properties of dopant delocalized s-electrons in Pd- and Pt-doped gold clusters, the dopant atoms markedly change the geometric and electronic properties of gold clusters, and stronger bond energies are found in Pt-doped clusters. The Mulliken populations analysis of impurities and detailed decompositions of bond energies as well as a variety of density of states of the most stable dopant gold clusters are given to understand the different effects of individual dopant atom on bonding and electronic properties of dopant gold clusters. From the electronic properties of dopant gold clusters, the different chemical reactivity toward O(2), CO, or NO molecule is predicted in transition metal-doped gold clusters compared to pure gold clusters.     

Electronic structures of size-selected single-layered platinum clusters on silicon(111)-7x7 surface at a single cluster level by tunneling spectroscopy

Tunneling spectra of size-selected single-layered platinum clusters (size range of 5-40) deposited on a silicon(111)-7x7 surface were measured individually at a temperature of 77 K by means of a scanning tunneling microscope (STM), and the local electronic densities of states of individual clusters were derived from their tunneling spectra measured by placing an STM tip on the clusters. In a bias-voltage (V(s)) range from -3 to 3 V, each tunneling spectrum exhibits several peaks assignable to electronic states associated with 5d states of a constituent platinum atom and an energy gap of 0.1-0.6 eV in the vicinity of V(s)=0. Even when platinum cluster ions having the same size were deposited on the silicon(111)-7x7 surface, the tunneling spectra and the energy gaps of the deposited clusters are not all the same but can be classified in shape into several different groups; this finding is consistent with the observation of the geometrical structures of platinum clusters on the silicon(111)-7x7 surface. The mean energy gap of approximately 0.4 eV drops to approximately 0.25 eV at the size of 20 and then decreases gradually as the size increases, consistent with our previous finding that the cluster diameter remains unchanged, but the number density of Pt atoms increases below the size of 20 while the diameter increases, but the density does not change above it. It is concluded that the mean energy gap tends to decrease gradually with the mean cluster diameter. The dependence of the mean energy gap on the mean Pt-Pt distance shows that the mean energy gap decreases sharply when the mean Pt-Pt distance exceeds that of a platinum metal (0.28 nm).     

Synthesis and structural analysis of the first nanosized platinum-gold carbonyl/phosphine cluster, Pt13[Au2(PPh3)2]2(CO)10(PPh3)4, containing a Pt-centered [Ph3PAu-AuPPh3]-capped icosahedral Pt12 cage

The preparation and molecular structure of the initial nanosized platinum-gold carbonyl cluster, Pt(13)[Au(2)(PPh(3))(2)](2)(CO)(10)(PPh(3))(4) (1), are described. A comparative analysis reveals its pseudo-D(2)(h) geometry, consisting of a centered Pt(13) icosahedron encapsulated by two centrosymmetrically related bidentate [Ph(3)PAu-AuPPh(3)]-capped ligands along with 4 PR(3) and 10 CO ligands, to be remarkably similar to that of the previously reported Pt(17)(mu(2)-CO)(4)(CO)(8)(PEt(3))(8) (2). Reformulation of 2 as Pt(13)[(PtPEt(3))(2)(mu(2)-CO)](2)(CO)(10)(PEt(3))(4) emphasizes the steric/electronic resemblance of the bulky-sized bidentate [Ph(3)PAu-AuPPh(3)] and [(PtPEt(3))(2)(mu(2)-CO)] capping ligands in 1 and 2, respectively, as well as their identical electron counts of 162 cluster valence electrons for a centered Pt(13) icosahedron. We hypothesize that analogous steric effects of their ligand polyhedra in 1 and 2 play a crucial role along with electronic effects in the formation and stabilization of these two nanosized clusters that contain an otherwise unknown centered icosahedron of platinum atoms.     

Preparation of polymer-protected gold/platinum bimetallic clusters and their application to visible light-induced hydrogen evolution

The dispersions of polymer-protected gold/platinum bimetallic clusters were easily and reproducibly prepared by refluxing the mixed solutions of tetrachloroaureic(III) acid and hexachloroplatinic(IV) acid in ethanol/water (1/1) at 90 ∼ 95 °C for 2 h in the presence of a protective polymer such as poly(N-vinyl-2-pyrrolidone) (PVP). The gold/platinum bimetallic clusters thus obtained were very small, well dispersed and very stable. The UV-Vis spectra and the transmission electron micrographs have indicated that each bimetallic particle has an alloy structure consisting of both gold and platinum atoms, and that the surface of the cluster particle is rich in platinum atoms and the inner core in gold atoms. The gold/platinum bimetallic clusters were used as the multi-electron redox catalysts for visible light-induced hydrogen evolution from water. The rate of hydrogen evolution depended on the mole ratio of the gold/platinum bimetallic clusters. The bimetallic clusters at the mole ratio of Au/Pt = 2/3 were the most active catalyst. The in-situ UV-Vis spectra during the reaction have indicated that the order of the aggregation in the two kinds of metal atoms is very important for structure determination of the Au/Pt bimetallic clusters. The protective polymer PVP plays a role not only in protecting hydrophobic colloidal particles in an aqueous solution, but also in determining the metal composition of the cluster surface.     

Binary clusters AuPt and Au6Pt: structure and reactivity within density functional theory

Within density functional theory with the general gradient approximation for the exchange and correlation, the bimetallic clusters AuPt and Au(6)Pt have been studied for their structure and reactivity. The bond strength of AuPt lies between those of Au(2) and Pt(2), and it is closer to that of Au(2). The Pt atom is the reactive center in both AuPt and AuPt(+) according to electronic structure analysis. AuPt(+) is more stable than AuPt. Au(6)Pt prefers electronic states with low multiplicity. The most stable conformation of Au(6)Pt is a singlet and has quasi-planar hexagonal frame with Pt lying at the hexagonal center. The doping of Pt in Au cluster enhances the chemical regioselectivity of the Au cluster. The Pt atom essentially serves as electron donor and the Au atoms bonded to the Pt atom acts as electron acceptor in Au(6)Pt. The lowest triplet of edge-capped rhombus Au(6)Pt clusters is readily accessible with very small singlet-triplet energy gap (0.32 eV). O(2) prefers to adsorb on Au and CO prefers to adsorb on Pt. O(2) and CO have stronger adsorption on AuPt than they do on Au(6)Pt. CO has a much stronger adsorption on AuPt bimetallic cluster than O(2) does. The adsorption of CO on Pt modifies the geometry of AuPt bimetallic clusters.     

Electronic and geometric stabilities of clusters with transition metal encapsulated by silicon

Silicon clusters mixed with a transition metal atom, MSin, were generated by a double-laser vaporization method, and the electronic and geometric stabilities for the resulting clusters with transition metal encapsulated by silicon were examined experimentally. By means of a systematic doping with transition metal atoms of groups 3, 4, and 5 (M = Sc, Y, Lu, Ti, Zr, Hf, V, Nb, and Ta), followed by changes of charge states, we explored the use of an electronic closing of a silicon caged cluster and variations in its cavity size to facilitate metal-atom encapsulation. Results obtained by mass spectrometry, anion photoelectron spectroscopy, and adsorption reactivity toward H2O show that the neutral cluster doped with a group 4 atom features an electronic and a geometric closing at n = 16. The MSi(16) cluster with a group 4 atom undergoes an electronic change in (i) the number of valence electrons when the metal atom is substituted by the neighboring metals with a group 3 or 5 atom and in (ii) atomic radii with the substitution of the same group elements of Zr and Hf. The reactivity of a halogen atom with the MSi(16) clusters reveals that VSi(16)F forms a superatom complex with ionic bonding.     

镍族金属团簇在催化加氢过程中的应用

Nanoparticles of precious metals play an important role in many heterogeneous catalytic reactions due to their excellent catalytic performance. As an idealized model, gas phase metal clusters have been extensively utilized to understand catalytic mechanisms at a molecular level. Here we provide an overview of our recent studies on H₂ dissociative chemisorption on nickel family clusters. The structure evolution and the stability of the metal clusters were first compared. H₂ dissociation on the clusters was then carefully addressed to understand the capability of metal clusters to break the H-H bond. Two key parameters, the dissociative chemisorption energy (ΔE_CE) and the H sequential desorption energy (ΔE_DE), were employed to characterize the catalytic activity of metal clusters. Our results show that both ΔE_CE and ΔE_DE decline significantly as the H coverage increases. Since the catalyst is in general covered entirely by H atoms and H₂ molecules in a typical hydrogenation process, and maintained at a pre-determined pressure of H₂ gas, we can rationally use the calculated ΔE_CE and ΔE_DE values at full H saturation to address the activity of metal clusters. Our results suggest that at full H coverage, each Pt atom is essentially capable of adsorbing 4 H atoms, while each Ni or Pd atom can only accommodate 2 H atoms. Considering the similar values of H desorption energies on Pt and Pd clusters, the higher average H capacity per Pt atom could probably lead to a faster reaction rate because more active H atoms are produced on the Pt catalyst particles in the hydrogenation process. Finally, the charge sensitivity of the key catalytic properties of Pt clusters for hydrogenation was systematically evaluated. The results show that the dissociation of H₂ and H desorption are strongly correlated to the charge state of the Pt clusters at low H coverage. However, at high H-capacities, both ΔE_CE and ΔE_DE fall into a narrow range, suggesting that the charge can be readily dispersed and that the Pt-H bonds average the interaction between clusters and H atoms. As a result, the H-capacities on charged clusters were found to be similar as the cluster size increased; in case of sufficiently large clusters, the reactivity of a fully saturated cluster was no longer sensitive to its charge state.