Sn12(2-): stannaspherene

Stannaspherene. The Sn122- cluster is discovered to be a highly stable and highly symmetric icosahedral cage bonded by four delocalized radial pi bonds and nine delocalized on-sphere sigma bonds from the 5p orbitals of the Sn atoms. It has a diameter of 6.1 A, with a large empty interior volume, and can host most transition metal atoms inside, giving rise to a large class of endohedral chemical building blocks for cluster-assembled nanomaterials.     

锗分族元素二元团簇及其与Co形成的团簇离子

通过比较激光烧蚀E1/E2 (代表Ge/Sn， Ge/Pb和Sn/Pb) 和Co/E (E为Ge、Sn、Pb)混合样品形成的二元团簇负离子飞行时间质谱分布和谱峰的相对强度及形成的幻数团簇离子峰，发现E1/E2二元团簇离子中原子量大的锗分族元素在团簇离子中占主要组分，而原子量小的元素则少量掺杂，其组成和分布特点说明其结构和性质与纯E团簇离子相似，可能的结构为该类负离子团簇所有原子都在笼结构的骨架上；对于二元团簇离子GeSn9－、GePb9－和SnPb9－其结构可能是双帽反四棱柱构型，只是每个原子均为骨架的一部分.而对激光烧蚀过渡金属钴与锗分族元素的混合物的研究发现，反应形成了丰富的Co/E二元合金团簇负离子，分析发现该类簇离子为钴内包覆于E(锗分族元素)笼状结构.幻数离子CoGe10－、CoSn10－和CoPb10－可能具有双帽四角反棱柱结构，而CoPb12－可能具有二十面体构型，钴原子均为笼状结构的中心.     

5d过渡金属原子中心镶嵌Ag团簇M@Ag12(M＝Hf～Hg) Ih和Oh构型的密度泛函理论研究

采用相对论密度泛函理论方法对Ih和Oh构型M@Ag12 (M＝Hf～Hg)的几何和电子结构进行了系统的研究. 研究表明, 原子半径之和与团簇的电子结构共同决定了M—Ag键长的大小. M@Ag12的成键能来自中心原子的嵌入能和Ag12笼子的形变能. 最高占据轨道为成键轨道的团簇比反键轨道的团簇的稳定性强. 我们发现在此系列中, Ih构型不一定总比Oh构型稳定. Hf@Ag12, Ir@Ag12, Au@Ag12和Hg@Ag12的Oh构型比Ih构型稳定.     

Effect of charge and composition on the structural fluxionality and stability of nine atom tin-bismuth Zintl analogues

Synergistic studies of bismuth doped tin clusters combining photoelectron spectra with first principles theoretical investigations establish that highly charged Zintl ions, observed in the condensed phase, can be stabilized as isolated gas phase clusters through atomic substitution that preserves the overall electron count but reduces the net charge and thereby avoids instability because of coulomb repulsion. Mass spectrometry studies reveal that Sn(8)Bi(-), Sn(7)Bi(2)(-), and Sn(6)Bi(3)(-) exhibit higher abundances than neighboring species, and photoelectron spectroscopy show that all of these heteroatomic gas phase Zintl analogues (GPZAs) have high adiabatic electron detachment energies. Sn(6)Bi(3)(-) is found to be a particularly stable cluster, having a large highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap. Theoretical calculations demonstrate that the Sn(6)Bi(3)(-) cluster is isoelectronic with the well know Sn(9)(-4) Zintl ion; however, the fluxionality reported for Sn(9)(-4) is suppressed by substituting Sn atoms with Bi atoms. Thus, while the electronic stability of the clusters is dominated by electron count, the size and position of the atoms affects the dynamics of the cluster as well. Substitution with Bi enlarges the cage compared with Sn(9)(-4) making it favorable for endohedral doping, findings which suggest that these cages may find use for building blocks of cluster assembled materials.     

Icosahedral gold cage clusters: M@Au12- (M=V, Nb, and Ta)

We report the observation and characterization of a series of stable bimetallic 18-valence-electron clusters containing a highly symmetric 12-atom icosahedral Au cage with an encapsulated central heteroatom of Group VB transition metals, M@Au(12) (-) (M=V,Nb,Ta). Electronic and structural properties of these clusters were probed by anion photoelectron spectroscopy and theoretical calculations. Characteristics of the M@Au(12) (-) species include their remarkably high binding energies and relatively simple spectral features, which reflect their high symmetry and stability. The adiabatic electronic binding energies of M@Au(12) (-) were measured to be 3.70+/-0.03, 3.77+/-0.03, and 3.76+/-0.03 eV for M=V, Nb, and Ta, respectively. Comparison of density-functional calculations with experimental data established the highly symmetric icosahedral structures for the 18-electron cluster anions, which may be promising building blocks for cluster-assembled nanomaterials in the form of stoichiometric [M@Au(12) (-)]X(+) salts.     

用密度泛函理论研究纳米级的硼簇Bn（n=13～20）的物理和化学性质

采用密度泛函理论B3LYP与6—311＋＋G方法研究了硼簇Bn（n=13～20）的电子和几何结构、总能量、结合能、谐波频率、点对称性、电荷分布、偶极矩、化学键以及最高分了占据轨道和最低分子占轨道能量差．此外,借助第一和第二能级差确定最稳定的硼簇尺寸．研究表明硼簇几乎所有的物理性质有尺寸依赖性,双环管状结构的B20具有最高平均结合能．内有一原子的二十面体结构的B13不具有稳定构型,这种结构转变为开放式笼状．B20出现二维到三维的结构转变．Mulliken分析表明电荷分布有x-z和y-z平面对称．硼簇的平面稳定性可以通过离域键（π键和σ键）以及多中心键来解释．     

Formation,growth mechanism and packing sequences of binary alloy cluster anions from laser ablation of mixtures of lead and transition metals

By using laser ablation of the mixtures of a transition metal (M: Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, Ag) plus lead, M/Pb binary cluster anions were observed except for Zn, and the number of transition metal atoms contained in the binary clusters is at most 4. This behavior is different from that reported previously for M/Ge binary clusters. The experiments indicate that it is also very difficult to form Al/Pb clusters. The distribution patterns of M/Pb binary alloy cluster anions are remarkably similar to those of pure Pb clusters, consistent with a formation mechanism in which transition metal atoms are sequentially attached to [M(x-1)Pb(y)](-) clusters and thus form [M(x)Pb(y)](-) clusters by a simple condensation process. As the number of transition metal atoms increases, the intensities of binary clusters gradually decrease. It is proposed that [MPb(4)](-) and [MPb(5)](-) cluster anions might be the unit building blocks of M/Pb binary cluster anions, and the layer packing sequences for magic clusters are predicted on this basis. The [M(x)Pb(y)](-) binary clusters containing 13 atoms (x + y = 13; x not equal 0) are proposed to have an icosahedral structure.     

Structural and electronic properties of Al12X+ (X=C, Si, Ge, Sn, and Pb) clusters

Using the first-principles method with the generalized gradient approximation, the authors have studied the structural and electronic properties of Al(12)X(+) (X=C, Si, Ge, Sn, and Pb) clusters in detail. The ground state of Al(12)C(+) is a low symmetry C(s) structure instead of an icosahedron. However, the Si, Ge, Sn, and Pb atom doped cationic clusters favor icosahedral structures. The ground states for Al(12)Si(+) and Al(12)Ge(+) are icosahedra, while the C(5nu) structures optimized from an icosahedron with a vertex capped by a tetravalent atom have the highest binding energy for Al(12)Sn(+) and Al(12)Pb(+) clusters. The I(h) structure and the C(5nu) structure are almost degenerate for Al(12)Ge(+), whose binding energy difference is only 0.03 eV. The electronic properties are altered much by removing an electron from the neutral cluster. The binding strength of a valence electron is enhanced, while the binding energy of the cluster is reduced much. Due to the open electronic shell, the band gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital are approximately 0.3 eV for the studied cationic clusters.     

Continuation calculations of boron- (aluminum-, titanium-, and nickel-) doped La13 clusters

In this work, we have calculated boron-, aluminum-, titanium-, and nickel-doped La13 clusters by DMOL method based on the density-functional theory. Two doping modes are employed: surface and center doping. The boron, aluminum, and nickel atoms prefer to occupy the surface sites while the titanium atom prefers to occupy the center site. The doped La13 clusters with these four kinds of atoms have lower binding energy than pure La13 clusters. The icosahedral isomers are of lower binding energy than cubotahedral and decahedral isomers for La12B(-1), La12Al(-1), and La12Ni, while doping makes the cubotahedral La12Ti stable with a binding energy a little lower than icosahedral La12Ti. There are electronic shell effects in icosahedral La12B(-1) and La12Al(-1). The icosahedral La12B(-1) is promising to be formed during the doped process experimentally. Furthermore, we have also discussed the distorted structures of center doping by bond lengths, density of states, and charge transfers.     

A highly distorted open-shell endohedral Zintl cluster: [Mn@Pb12]3-

Reaction of an ethylenediamine (en) solution of K(4)Pb(9) and 2,2,2-crypt (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) with a tetrahydrofuran (THF) solution of Mn(3)(Mes)(6) (Mes = 2,4,6-trimethylphenyl) yielded the anionic cluster [Mn@Pb(12)](3-). This species was observed in the positive and negative ion-mode electrospray mass-spectra of the crude reaction mixture. The crystalline samples obtained from such solutions allowed us to confirm the composition of the sample as [K(2,2,2-crypt)](3)[Mn@Pb(12)]·1.5en (1). Because of numerous issues related to crystal sample quality and crystallographic disorder a high-quality crystal structure solution could not be obtained. Despite this, however, the data collected permit us to draw reasonable conclusions about the charge and connectivity of the [Mn@Pb(12)](3-) cluster anion. Crystals of 1 were further characterized by elemental analysis and electron paramagnetic resonance (EPR). Density Functional Theory (DFT) calculations on such a system reveal a highly distorted endohedral cluster anion, consistent with the structural distortions observed by single crystal X-ray diffraction. The cluster anions are considerably expanded compared to the 36-electron closed-shell analogue [Ni@Pb(12)](2-) and, moreover, exhibit significant low-symmetry distortions from the idealized icosahedral (I(h)) geometry that is characteristic of related endohedral clusters. Our computations indicate that there is substantial transfer of electron density from the formally Mn(-I) center to the low-lying vacant orbitals of the [Pb(12)](2-) cage.     

Comprehensive analysis of chemical bonding in boron clusters

We present a comprehensive analysis of chemical bonding in pure boron clusters. It is now established in joint experimental and theoretical studies that pure boron clusters are planar or quasi-planar at least up to twenty atoms. Their planarity or quasi-planarity was usually discussed in terms of pi-delocalization or pi-aromaticity. In the current article, we demonstrated that one cannot ignore sigma-electrons and that the presence of two-center two-electron (2c--2e) peripheral B--B bonds together with the globally delocalized sigma-electrons must be taken into consideration when the shape of pure boron cluster is discussed. The global aromaticity (or global antiaromaticity) can be assigned on the basis of the 4n+2 (or 4n) electron counting rule for either pi- or sigma-electrons in the planar structures. We showed that pure boron clusters could have double (sigma- and pi-) aromaticity (B3-, B4, B5+, B6(2+), B7+, B7-, B8, B(8)2-, B9-, B10, B11+, B12, and B13+), double (sigma- and pi-) antiaromaticity (B6(2-), B15), or conflicting aromaticity (B5-,sigma-antiaromatic and pi-aromatic and B14, sigma-aromatic and pi-antiaromatic). Appropriate geometric fit is also an essential factor, which determines the shape of the most stable structures. In all the boron clusters considered here, the peripheral atoms form planar cycles. Peripheral 2c--2e B--B bonds are built up from s to p hybrid atomic orbitals and this enforces the planarity of the cycle. If the given number of central atoms (1, 2, 3, or 4) can perfectly fit the central cavity then the overall structure is planar. Otherwise, central atoms come out of the plane of the cycle and the overall structure is quasi-planar.     

ZnS bubble clusters with onion-like structures

Following recent studies which showed that the most stable structures for (ZnS)(n) clusters (n= 10-47) are the so-called "bubble clusters", in which all the atoms are three-coordinated, we have used simulated annealing techniques to find the most stable structure for a larger cluster, (ZnS)(60). We find an onion-like structure, with one small cluster enclosed inside a bigger one. The inner cluster has the structure of a sodalite cage. Bonding between the inner and the outer clusters creates a network of four-coordinated atoms.     

Analysis of why boron avoids sp2 hybridization and classical structures in the BnHn+2 series

We performed global minimum searches for the B(n) H(n+2) (n=2-5) series and found that classical structures composed of 2c-2e B-H and B-B bonds become progressively less stable along the series. Relative energies increase from 2.9?kcal?mol(-1) in B(2) H(4) to 62.3?kcal?mol(-1) in B(5) H(7). We believe this occurs because boron atoms in the studied molecules are trying to avoid sp(2) hybridization and trigonal structure at the boron atoms, as in that case one 2p-AO is empty, which is highly unfavorable. This affinity of boron to have some electron density on all 2p-AOs and avoiding having one 2p-AO empty is a main reason why classical structures are not the most stable configurations and why multicenter bonding is so important for the studied boron-hydride clusters as well as for pure boron clusters and boron compounds in general.     

Structural, energetic, and electronic properties of hydrogenated titanium clusters

Hydrogen undergoes dissociative chemisorption on small titanium clusters. How the electronic structure of the cluster changes as a function of the number of adsorbed hydrogen atoms is an important issue in nanocatalysis and hydrogen storage. In this paper, a detailed theoretical investigation of the structural, energetic, and electronic properties of the icosahedral Ti13 cluster is presented as a function of the number of adsorbed hydrogen atoms. The results show that hydrogen loaded Ti13H20 and Ti13H30 clusters are exceptionally stable and are characterized by hydrogen multicenter bonds. In Ti13H20, the dissociated hydrogen atoms are bound to each of the 20 triangular faces of Ti13, while in Ti13H30, they are bound to the 30 Ti-Ti edges of Ti13. Consequently, the chemisorption and desorption energies of the Ti13H20 (1.93 eV, 3.10 eV) are higher than that of Ti13H30 (1.13 eV, 1.95 eV). While increased hydrogen adsorption leads to an elongation of the Ti-Ti bonds, there is a concomitant increase in the electrostatic interaction between the dissociated hydrogen atoms and the Ti13 cluster. This enhanced interaction results from the participation of the subsurface titanium atom at higher hydrogen concentrations. Illustrative results of hydrogen saturation on the larger icosahedral Ti55 cluster are also discussed. The importance of these results on hydrogen saturated titanium clusters in elucidating the mechanism of hydrogen adsorption and desorption in titanium doped complex metal hydrides is discussed.     

A new magic titanium-doped gold cluster and orientation dependent cluster-cluster interaction

The stability and structures of titanium-doped gold clusters Au(n)Ti (n=2-16) are studied by the relativistic all-electron density-functional calculations. The most stable structures for Au(n)Ti clusters with n=2-7 are found to be planar. A structural transition of Au(n)Ti clusters from two-dimensional to three-dimensional geometry occurs at n=8, while the Au(n)Ti (n=12-16) prefer a gold cage structure with Ti atom locating at the center. Binding energy and second-order energy differences indicate that the Au(14)Ti has a significantly higher stability than its neighbors. A high ionization potential, low electron affinity, and large energy gap being the typical characters of a magic cluster are found for the Au(14)Ti. For cluster-cluster interaction between magic transition-metal-doped gold clusters, calculations were performed for cluster dimers, in which the clusters have an icosahedral or nonicosahedral structure. It is concluded that both electronic shell effect and relative orientation of clusters are responsible for the cluster-cluster interaction.     

Evolution of the structural stability of large Cu,Ni, Pd,and Ag clusters with size: An analysis within the embedded atom method

A study of the structural stability of clusters made up of a single component has been carried out within the Embedded Atom Method. Perfect icosahedral and cuboctahedral Cu, Ni, Pd, and Ag clusters with up to 5083 atoms have been compared. The icosahedron is found to be the stable structure for small clusters, and a change of structure from icosahedral to cuboctahedral is found as the cluster size increases. A contraction of the interatomic distances results when the cluster size decreases.     

Synthesis of stable crystals of a self-assembled centered icosahedral samarium cluster formed by bis(L-prolinato)nickel(II) ligands

A centered icosahedral 12-coordinate samarium cluster formed by six bis(L-prolinato)nickel(II) ([Ni(pro)2]) ligands, [Sm(Ni(pro)2)6]3+, was prepared. The reaction of Sm with [Ni(pro)2] in a small excess (a 2-fold excess) and also in a large excess (even a 10-fold excess) of the latter produced the cluster. Therefore, this system is a self-assembly. In the cluster, each nickel atom is surrounded by six atoms: two amino nitrogens, two carboxylate oxygens which form chelate rings with the nitrogen atoms, and two carboxylate oxygen atoms which link the neighboring nickel atoms. The samarium atom is coordinated by six [Ni(pro)2] ligands, and the metal is in an icosahedral environment formed by 12 oxygen atoms. The icosahedral geometry is almost ideal. Crystals of [Sm(Ni(pro)2)6](ClO4)3.6MeOH, which were prepared from a methanol solution, immediately decompose after filtration because of loosely trapped MeOH molecules in the crystal lattice. Therefore, crystals without MeOH molecules, which must be stable, were prepared by recrystallization from acetonitrile with tetramethylammonium perchlorate (TMAP). According to the X-ray crystal analysis, the cluster is TMA[Sm(Ni(pro)2)6](ClO4)4, cubic of space group F23, with a = 21.273(9) A, V = 9626(1) A3, and Z = 4; R = 0.053 (Rw = 0.049) for 1296 reflections. In addition, several crystals of cluster salts that have different counteranions, i.e., tetrafluoroborate (BF4-), hexafluorophosphate (PF6-), iodide (I-), and nitrate (NO3-), were prepared. The order of increasing ease of crystallization of the cluster salts was I- > PF6- approximately ClO4- > BF4- > NO3-. The cluster structure is retained in alcohol and acetonitrile solutions; the UV-vis spectra of the solutions are perfectly consistent with the powder diffuse reflection spectrum. Cyclic voltammograms of [Sm(Ni(pro)2)6]3+ in acetonitrile proved that the structure of [Sm(Ni(pro)2)6]3+ is retained in the redox process and that the nickel atoms electrochemically interact with one another. Thermal analysis of the cluster salts with different counteranions was investigated. The results imply that the cluster is very stable until bis(L-prolinato)nickel(II) ligands, which form the cage structure, disintegrate and that the thermal decomposition processes of the cluster salts depend on their counteranions.     

Assessment of relative stabilities of positional isomers of polyhedral heteronuclear clusters via a simplified method of bond energy calculations based on tight-binding approach and adjacent matrix method: applications to binary icosahedral clusters

A new and simple method for assessing the relative stabilities of various positional isomers of a given heteronuclear cluster is described. The method is based on a tight-binding approach in conjunction with an adjacent matrix methodology (TBAM). The usefulness of the method is illustrated by bond energy calculations of a number of binary icosahedral clusters, including noncentered icosahedral A(n)B(12)(-)n clusters comprising main-group elements B, C, N, and S as well as B- and A-centered icosahedral A(n)B(13)(-)n clusters that consist of transition metals, Au, Ag, Ni, and Pt atoms. The latter results are compared with the previously reported molecular mechanics calculations based on Lennard-Jones potential and with experimental results, whenever possible. The trends of the total bond energies obtained by the two methods are nearly parallel in all cases, indicating that the relative stabilities predicted by the two methods follow the same order. The TBAM approach provides a simple and efficient way of predicting the relative stabilities of various positional isomers of a given cluster, particularly for clusters where the number of positional isomers is so large that it cannot be handled manually. The total bond energies exhibit a stepwise progression. Each step is characterized by a set of A-A, B-B, and A-B bonds which uniquely determines the total bond energy and, hence, the stability. The step formation implies that positional isomers of a given cluster geometry can be categorized by sets of numbers of A-A, B-B, and A-B bonds, or simply the numbers of the minority (either A-A or B-B) bonds. Three site preference rules, the strong-bond rule, the heterobond rule, and the big-hole rule, were formulated based on these model calculations. These rules are useful in rationalizing and/or predicting the relative stabilities of various positional isomers of a given cluster geometry.     

Elongation of planar boron clusters by hydrogenation: boron analogues of polyenes

Dihydrogenated boron clusters, H(2)B(n)(-) (n = 7-12), were produced and characterized using photoelectron spectroscopy and computational chemistry to have ladderlike structures terminated by a hydrogen atom on each end. The two rows of boron atoms in the dihydrides are bonded by delocalized three-, four-, or five-center σ and π bonds. The π bonding patterns in these boron nanoladders bear similarities to those in conjugated alkenes: H(2)B(7)(-), H(2)B(8), and H(2)B(9)(-), each with two π bonds, are similar to butadiene, while H(2)B(10)(2-), H(2)B(11)(-), and H(2)B(12), each with three π bonds, are analogous to 1,3,5-hexatriene. The boron cluster dihydrides can thus be considered as polyene analogues, or "polyboroenes". Long polyboroenes with conjugated π bonds (analogous to polyacetylenes), which may form a new class of molecular wires, should exist.     

Heteroatomic deltahedral clusters: synthesis and structures of closo-[Bi3Ni(4)(CO)6]3-, closo-[Bi4Ni4(CO)6]2-, the open cluster [Bi3Ni6(CO)9]3-, and the intermetalloid closo-[Nix@[Bi6Ni6(CO)8)]4-

Reactions of ethylenediamine solutions of K4Bi5 with Ni(PPh3)2(CO)2 yielded four novel hetero-atomic Bi/Ni deltahedral clusters. Three of them, the 7-atom pentagonal bipyramidal [Bi3Ni4(CO)6]3-, the 8-atom dodecahedral [Bi4Ni4(CO)6]2-, and the Ni-centered or empty 12-atom icosahedral [Nix@[Bi6Ni6(CO)8]4-, are closo-species according to both electron count and shape. The centered icosahedral cluster resembles packing in intermetallic compounds and belongs to the emerging class of intermetalloid clusters. The shape of the fourth cluster, [Bi3Ni6(CO)9]3-, can be derived from the icosahedral Ni-centered [Ni@[Bi6Ni6(CO)8]4- by removal of three Bi- and one Ni-atoms of two neighboring triangular faces. The clusters were structurally characterized by single-crystal X-ray diffraction in compounds with potassium cations sequestered by 2,2,2-crypt or 18-crown-6 ether. They were also characterized in solution by electrospray mass spectrometry.