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.     

Metal-substituted Ti8C12 metallocarbohedrynes: toward less reactive clusters as building blocks of cluster-assembled materials

To form cluster-assembled materials, the clusters should have low reactivity and be characterized by a closed-shell electronic configuration with a large gap between the highest occupied and the lowest unoccupied molecular orbitals (HOMO-LUMO). Using spin-polarized density functional theory calculations, we investigate the M-substituted Ti(8)C(12) metallocarbohedrynes to search for less reactive clusters as building blocks for cluster-assembled materials (M = Be, Mg, Ca, Sr, Ba and Sc, Y). The selected atoms in the correct stoichiometry would produce a metallocarbohedryne that is isoelectronic with the Ti(8)C(12)(2+), which has a closed-shell electronic configuration and an enhanced HOMO-LUMO gap of 1.735 eV. According to our results, the HOMO-LUMO gaps of the M-substituted Ti(8)C(12) metallocarbohedrynes are in the range of 0.715-0.979 eV for the case of Be, Mg, Ca, Sr and Ba and in the range of 0.865-1.294 eV for the case of Sc and Y. Among all the M-substituted metallocarbohedrynes we consider here, one of the isomers of Ti(6)Sc(2)C(12) is not only energetically more favorable but also exhibits a larger HOMO-LUMO gap of 1.294 eV. This result indicates that the Ti(6)Sc(2)C(12)(4) metallocarbohedryne should be less reactive than the Ti(8)C(12) metallocarbohedryne which has a narrow HOMO-LUMO gap of 0.146 eV. Moreover, we show that the intercluster interaction between two individual Ti(6)Sc(2)C(12)(4) metallocarbohedrynes is relatively weak compared to the Ti(8)C(12) dimer.     

Self-assembling endohedrally doped CdS nanoclusters: new porous solid phases of CdS

Hollow CdS nanoclusters were predicted to trap alkali metals and halogen atoms inside their cavity. Furthermore, electron affinities (EA) of endohedrally halogen doped clusters and ionization potentials (IE) of endohedrally alkali doped clusters were predicted to be very similar. This makes them suitable to build cluster-assembled materials, in the same vein as do related ZnO, ZnS and MgO nanoclusters, which yield porous solid materials. With this aim in mind, we have focused on the assembly of bare Cd(i)S(i) and endohedral K@Cd(i)S(i)-X@Cd(i)S(i) (i = 12, 16, X = Cl, Br) clusters in order to obtain solids with tailored semiconducting and structural properties. Since these hollow nanoclusters possess square and hexagonal faces, three different orientations have to be considered, namely, edge-to-edge (E-E), square-to-square (S-S) and hexagon-to-hexagon (H-H). These three orientations lead to distinct zeolite-like nanoporous bulk CdS solid phases denoted as SOD, LTA and FAU. These solids are low-density crystalline nanoporous materials that might be useful in a wide range of applications ranging from molecular sieves for heterogeneous catalysis to gas storage templates.     

Silica nanoarchitectures with tailored pores based on the hybrid three- and four-membered rings

Inspired by the recent developments in the controlled synthesis of porous materials, we present herein the structural prediction of silica nanoarchitectures by using the three- (3MRs) and four-membered rings (4MRs), which are more frequently found in the nanometer-sized particles than in the bulk form, as building blocks. The proposed models include the active molecular rings, thin nanowires, hollow nanotubes, discrete fullerene-like cages, and porous zeolite-like three-dimensional networks. Their geometrical and electronic structures and properties were studied by performing density functional calculations. These silica nanostructures were proved, using molecular dynamics simulations, to possess intrinsic structural stabilities with highly symmetrical geometries and regular nanochannels. These atomically well-defined clusters, (SiO)(n), are chemically more reactive than those proposed earlier and are energetically more favorable for n > 20 in high-level density functional calculations over the corresponding two-membered ring (2MR) chains and rings as well as the pure 3MR networks. The nanoparticles and nanodevices based on them are expected to have potential technological applications that mainly make use of their characteristic geometrical structures (nanosized pores) and novel electronic properties.     

Violation of the isolated square rule for group 13-15 oligomers: theoretical prediction of a new class of inorganic polymers

It is widely thought that the oligomer compounds [RMYR]n (M-group 13, Y-group 15 element) should obey the isolated square rule found for the boron-nitrogen cages. In contrast to these expectations, the needle-shaped oligomers, which violate this rule, are more stable compared to the cage (fullerene-like) oligomers for all MY pairs (M = B, Al, Ga, In; Y = N, P, As). The stability of the needle-shaped clusters improves with increasing oligomerization degree. Thus, the isolated square rule, which is analogous to the isolated pentagon rule widely applied for fullerenes, should not serve as the basis for searches for the most stable structures of the inorganic oligomers. Generation of the needle-shaped oligomers from the group 13 and 15 hydrides is thermodynamically favorable. A synthesis of novel inorganic polymers, formed by fusion of trimeric M3Y3 rings, is expected to be viable.     

Endohedral zintl ions: intermetalloid clusters

Tetrels can be regarded as most promising candidates for the construction of larger clusters. Recent examples have shown that larger clusters are particularly stable if they contain interstitial atoms (e.g. [Pt@Pb12]2-). Many salts of the polyhedral anions are soluble, but a number of examples-usually those with higher charges-occur only as quasi-discrete units in saltlike crystals (Zintl phases) or as building blocks in intermetallic phases. In this Minireview, the chemistry of intermetalloid clusters is reviewed with reference to the endohedral Zintl ions, Zintl phases, and polyhedral building blocks of intermetallic compounds, including heteroatomic species in the gas phase. We focus on selected examples and discuss the new findings in the context of recent advances in the field of metalloid clusters and (endohedral) fullerenes and fullerides.     

Structures and stabilities of small lead oxide clusters PbmOn (m=1-4,n=1-2m)

The structures and stabilities of small lead oxide clusters PbmOn with m=1-4, n=1-2m are systematically studied using density functional theory. It is found that the lowest-energy structures of all these clusters can be obtained by the sequential oxidation of small "core" lead clusters. For Pb-rich clusters (oxygen-to-lead ratio<1), oxygen atoms favor bridge sites for Pb2On and Pb3On and surface sites for Pb4On. The lead-monoxide-like clusters (PbO)i (i=1-4) have great stability because of their significant dissociation energies and highest occupied molecular orbital-lowest unoccupied molecular orbital gaps. This suggests that they could be adopted as the building blocks of cluster-assembled materials. For O-rich clusters (oxygen-to-lead ratio>1), the grouping of oxygen atoms usually appears. It is found that the structures with a grouping of more than two oxygen atoms are unstable.     

Growth pattern and electronic properties of acetonitrile clusters: a density functional study

We report a systematic theoretical study on the growth pattern and electronic properties of acetonitrile clusters [(CH(3)CN)(n) (n = 1, 9, 12)] using density functional approach at the B3LYP6-31++G(d,p) level. Although we have considered a large number of configurations for each cluster, the stability of the lowest energy isomer was verified from the Hessian calculation. It is found that the lowest energy isomer of the dimer adopts an antiparallel configuration. For trimer and tetramer, cyclic ring structures were found to be favored over the dipole stabilized structure. In general, it is found that the intermolecular CH...N interactions play a significant role in the stabilization of the cyclic layered geometry of acetonitrile clusters. A critical comparison between trimer and tetramer clusters suggests that the three member cyclic ring is more stable than four member rings. The growth motif for larger clusters (n = 5-9, 12) follows a layered pattern consisting of three or four membered rings, which, in fact, is used as the building block. Based on the stability analysis, it is found that clusters with an even number of molecular entities are more stable than the odd clusters, except trimer and nonamer. The exceptional stability of these two clusters is attributed to the formation of trimembered cyclic rings, which have been found to form the building blocks for larger clusters.     

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.     

氮笼N12的量子化学研究

采用量子化学从头算方法研究了7个氮笼N₁₂,其中包括以前文献中研究过的两个氮笼N₁₂.在RHF/6-31G^*理论水平下进行全构型优化、振动频率分析和热化学计算.计算结果表明,7个结构均是势能面上的局域极小点.N₁₂(D_3d)是所有7个笼状异构体中最稳定的.能量分析表明,如果这些分子能够被合成,将会成为潜在的高能量密度材料.     

Synthesis and structure of cuboctahedral and anticuboctahedral cages containing 12 quadruply bonded dimolybdenum units

The syntheses and structures of two clusters containing 12 Mo-Mo quadruple bonds, [Mo(24)(C(12)H(12)O(4))(24)](C(5)H(5)N)(12) and Mo(24)(C(8)H(4)O(4))(24), are reported. The 12 paddlewheel building blocks and 24 ligands self-assemble into cuboctahedral and anticuboctahedral polyhedra, respectively, depending on the manner in which the two halves of the cluster are aligned. These clusters contain twice as many dimolybdenum units as any previously reported cluster. Possible assembly mechanisms are also proposed.     

Templated assembly of polymer particles into mesoscopic clusters with well-defined configurations

We report on the fabrication of colloidal clusters through the combination of spherical particles. Polystyrene latex particles bearing amino groups on their surface were used as building blocks of the clusters. Packing of these particles with diameters of 91 and 154 nm into assemblies with defined configurations was accomplished using narrow dispersed emulsion droplets as templates. The building blocks of the clusters adhered to the oil–water interphase due to the Pickering effect. Subsequent evaporation of the dispersed phase forced them to pack into small clusters. Addition of the particles via the dispersed phase led to higher yields of clusters than if the building blocks were added via the continuous phase. All clusters had well-defined configurations. Because the dimensions of these clusters were below 400 nm, the colloidal assemblies underlay Brownian motion, which resulted in stable suspensions. The number and yields of different species could be controlled via the concentration of the building blocks and surfactant within the emulsions. Moreover, the nature of the dispersed phase itself had a strong impact on the cluster formation. When cyclohexane was used as the dispersed phase, predominately, particle doublets and triplets were obtained. The use of toluene-in-water emulsions resulted into a broader spectrum of clusters of up to 12 constituents. Such clusters could satisfy the demand for particles with complex but defined shapes and special symmetries for the fabrication of novel hierarchically organized materials.     

Orientation transition of nanorods induced by polymer brushes

Coarse-grained molecular dynamics simulations are used to explore the spatial orientations and conformational transitions of nanorods (NRs) within semiflexible polymer brushes. The orientations of the NR clusters are controlled by the competition between the entropy cost for NRs infiltrated into the polymer brushes and the attractive energy between NRs and polymer brushes. By reducing the grafting density or enhancing the number of NRs, the NR cluster experiences an orientation transition from the vertical direction to the horizontal direction. The semiflexible polymer brushes are regarded as the soft confinements for the NRs, and the soft confinements can induce the formation of the NR aggregation under the effect of the depletion attractions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

INORGANIC RINGS AND CLUSTERS AS SINGLE-SOURCE PRECURSORS TOWARD STOICHIOMETRY CONTROLLED SYNTHESIS OF MATERIALS: GAS PHASE CHEMISTRY IN COMMAND

Potential of the inorganic rings and clusters as single-source precursors to 13–15 binary materials and composites is examined employing quantum-chemical methods. Importance of the gas phase association reactions during MOCVD processes from organometallic and hydride precursors is emphasized. Generation of the gas phase [HMYH]_n clusters (M = Al,Ga,In; Y = N,P,As) with large oligomerization degree (n ≥ 30) is thermodynamically favorable even at high temperature conditions (1000 K) for all M,Y pairs. High stability of the N-containing clusters makes mixed metal oligomer imidometallanes excellent single-source precursors for the stoichiometry-controlled MOCVD of 13–15 composites.     

Modification of gold nanorods using phosphatidylcholine to reduce cytotoxicity

Hexadecyltrimethylammonium bromide (CTAB), which is necessary for the preparation of gold nanorods (NRs), was extracted from a NR solution into a chloroform phase containing phosphatidylcholine (PC). After three extractions, the zeta potential of the NRs remained positive, but its magnitude decreased from +67 +/- 1 to +15 +/- 1 mV. Transmission electron microscopy and energy-dispersive X-ray analysis indicated that the NRs were passivated with PC. The PC layer on the NR surface contributed to the prevention of NR aggregation. The PC-passivated NRs showed low cytotoxicity in comparison with twice-centrifuged NRs. It was shown that a negligible amount of CTAB was dispersed in the NR solution after the extraction. The extraction using a chloroform phase containing PC was found to be a convenient way of replacing the CTAB with alternative capping agents such as PC. This is a key technique for preparing functional NRs that can have practical applications.     

Geometric and electronic structures of (BeO)(N) (N = 2-12, 16, 20, and 24): rings, double rings, and cages

The structure of (BeO)(N) clusters (N = 2-12, 16, 20, and 24) are investigated using the method combining the genetic algorithm with density function theory. Benchmark calculation indicates that THSSh functional is reliable to predict the structures of (BeO)(N) cluster. The global minimum structures of (BeO)(N) clusters are rings up to N = 5, double rings at N = 6 and 7 and cages at N ≥ 8. Besides, almost all of the structures of (BeO)(N) cluster are aromatic according to the NICS criterion. Adaptive natural density partitioning analysis reveals that C(6), (BN)(3), and (BeO)(3) rings (C(24) and (BeO)(12) fullerenes) are similar in bonding patterns. The building-up principle of (BeO)(N) is different from that of covalent (BN) and ionic (LiF and MgO) clusters.     

Understanding the "tailoring synthesis" of CdS nanorods by O2

Parameters such as solution concentrations and composition of the ambient atmosphere are known to be important in phase and morphology control in the solvothermal synthesis of CdS semiconductor nanorods (NRs), but a clear understanding of the underlying mechanisms involved is lacking. In this work, a series of experiments were performed to demonstrate that the key factor affecting the phase and morphology of CdS NRs is the amount of O(2) in the space above the reaction solution in the sealed vessel relative to the amount of precursors in solution: O(2)-depleted conditions resulted in more cubic phase CdS and thick polycrystalline NRs with an aspect ratio usually less than 3, which have small blue shifts in band-edge emission and little surface trap emission, while O(2)-rich conditions resulted in more hexagonal-phase CdS and slim single-crystal NRs, which have significantly blue shifted band-edge emission and relatively strong surface trap emission. Thus, increasing the amount of solution in the vessel, changing the ambient atmosphere from air to N(2), and increasing the reagent concentration all lower the molar ratio of O(2) to reagents and lead to more cubic phase and thicker NRs. The results indicate that the composition of the "empty" section of the reaction vessel plays as important a role as the composition of the liquid in determining the phase and morphology, something that has been overlooked in earlier work. A mechanism to explain the effect of oxygen on the nucleation and growth stages has been proposed on the basis of those results and further supported by shaking experiments and ZnS NR synthesis manipulation. The CdS NRs synthesized under different conditions showed obvious differences in photocatalytic activity, which indicated that controlling the synthetic process can lead to materials with tailored photocatalytic activity.     

Abnormal coordination of Arduengo's carbene upon reaction with M(3)(CO)(12) (M = Ru, Os)

The first examples of abnormal coordination of Ardeungo's carbene, 1,3-bis-adamantylimidazol-2-ylidene, have been isolated and structurally characterised following reaction of the free carbene with the trinuclear clusters M(3)(CO)(12) (M = Ru, Os).     

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.     

First-principles study of hydrogen storage on Li12C60

Solid state materials capable of storing hydrogen with high gravimetric (9 wt %) and volumetric density (70 g/L) are critical for the success of a new hydrogen economy. In addition, an ideal storage system should be able to operate under ambient thermodynamic conditions and exhibit fast hydrogen sorption kinetics. No materials are known that meet all these requirements. While recent theoretical efforts showed some promise for transition-metal-coated carbon fullerenes, later studies demonstrated that these metal atoms prefer to cluster on the fullerene surface, thus reducing greatly the weight percentage of stored hydrogen. Using density functional theory we show that Li-coated fullerenes do not suffer from this constraint. In particular, we find that an isolated Li(12)C(60) cluster where Li atoms are capped onto the pentagonal faces of the fullerene not only is very stable but also can store up to 120 hydrogen atoms in molecular form with a binding energy of 0.075 eV/H(2). In addition, the structural integrity of Li(12)C(60) clusters is maintained when they are allowed to interact with each other. The lowest energy structure of the dimer is one where the Li atom capped on the five-member ring of one fullerene binds to the six-member ring of the other. The binding of hydrogen to the linking Li atom and the potential of materials composed of Li(12)C(60) building blocks for hydrogen storage are discussed.