Polyhedral Clusters Research Articles

Synthesis and Structure of Five Sc3CuyZn18‐y‐Type Compositions (0 ≤ y ≤ ≈2.2), 1/1 Crystalline Approximants of a New Icosahedral Quasicrystal. Direct Example of Tuning on the Basis of Size Effects and Hume—Rothery Concepts.

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Boron Clusters Come of Age

Polyhedral clusters containing boron, alone or in combination with other elements, have been known for nearly a century, and intensive studies of their structures, bonding, and reactivity have been...

Twin Boundaries in Zinc Oxide with Additions of Gallium Oxide

Twin boundaries (TBs) in ZnO sintered with small additions of Ga2O3 have been characterized with advanced methods of transmission electron microscopy (TEM). The TBs and accompanying inversion domain boundaries are on {011¯3} planes of ZnO. The Ga content of the TB corresponds to an effectively half occupied {011¯3} plane determined from compositional maps calculated from electron spectroscopic images using electron filtering TEM. The structure of the TBs were investigated by high-resolution TEM, and images of focus series were used to reconstruct the complex electron wave. Simulated electron waves based on structure models of the TB were quantitatively compared with the reconstructed wave to identify and to refine atom positions. The twins can be considered to be created by a mirror operation on a {011¯3} plane of ZnO, and two alternating closed-packed polyhedral clusters of oxygen ions can be identified as building units of the TB structure. Unit 1 is occupied with Zn2+ by simply continuing ZnO4 tetrahedra of the same type from both crystals to the TB. Using arguments of local charge balance unit 2 can only be occupied with the trivalent Ga3+ ion. The Ga3+ position was refined with high precision (±5 pm), and the resulting polyhedron is a GaO5 square pyramid. The pyramids form densely occupied columns parallel to the twin axis [21¯1¯0]. The analysis of the TB structure yields a fractional occupancy of the boundary plane by Ga of 0.5, which is in good agreement with the result of the chemical composition measurement with energy filtered TEM.

Synthesis and structure of five Sc3CuyZn18-y-type compositions (0 < or = y < or = approximately 2.2), 1/1 crystalline approximants of a new icosahedral quasicrystal. Direct example of tuning on the basis of size effects and Hume-Rothery concepts.

The newly reported icosahedral quasicrystalline phase approximately Sc(3)Cu(2.1)Zn(12.9) was approached through four synthetic, structural, and EDX analyses of the range of approximants formed by systematic substitutions of 0-4 Zn by Cu in the reported Sc(3)Zn(17) as well as for the corrected Sc(3)Zn(18) (ScZn(6)) composition. Structures of high yield products of the 0, 1, 2, 3 Cu atom steps all refined as isotypic Sc(3)Cu(y)Zn(18-y) phases (Im(-)3, Z = 8, a = 13.8311(5) to 13.7528(5) A for 0 < or = y < or =2.2), basically isostructural with RCd(6) phases known for many rare-earth elements. The present phases all exhibit the novel feature of disordered zinc tetrahedra in the center of four concentric polyhedral clusters: pentagonal dodecahedron (Zn/Cu), icosahedron (Sc), icosidodecahedron (Zn), and triacontahedron (Zn). The Cu tuning process reduces both the average electron count per atom (e/a) to 2.04 and the average atom size until major amounts of the zinc-poorer quasicrystal separate along with the present normal crystalline phase near four added Cu. The Cu is an important neighbor to the disordered Zn atoms. The approximant structure repeatedly exhibits components with pseudo-icosahedral symmetry.

Radiobromination of monoclonal antibody using potassium [ 76Br] (4 isothiocyanatobenzyl-ammonio)-bromo-decahydro -closo-dodecaborate (Bromo-DABI)

The use of charged linkers in attaching radiohalogens to tumor-seeking biomolecules may improve intracellular retention of the radioactive label after internalization and degradation of targeting proteins. Derivatives of polyhedral boron clusters, such as closo-dodecaborate (2-) anion, might be possible charged linkers. In this study, a bifunctional derivative of closo-dodecaborate, (4-isothiocyanatobenzyl-ammonio)-undecahydro -closo-dodecaborate (DABI) was labeled with positron-emitting nuclide 76Br (T = 16.2 h) and coupled to anti-HER2/neu humanized antibody Trastuzumab. The overall labeling yield at optimized conditions was 80.7 ± 0.6%. The label was proven to be stable in vitro in physiological and a set of denaturing conditions. The labeled antibody retained its capacity to bind to HER-2/neu antigen expressing cells. The results of the study demonstrated feasibility for using derivatives of closo-dodecaborate in indirect labeling of antibodies for radioimmunoPET.

ＩＶ族多面体結晶の構造と物性

Researches of crystals consisting of IVth group element (C, Si, Ge and Sn) polyhedra are described. Fundamental concept for understanding the structure and the electronic properties of the polyhedral clusters and crystals is given. The different structure of the crystals of C and Si is emphasized focusing on van der Waals and covalent characters. Applications of cluster crystals colored by elemental isotopes are also demonstrated in connection to materials science and future electronic devices.

Hypercoordinate carbon in polyhedral organic structures

Carbon holds a unique position among the elements. It forms more than 14 millions of currently known organic compounds, structural organization of which is governed by the beautifully simple principles of tetravalence and tetrahedral stereochemical configuration. In the past decades, the edifice of the classical structural theory of organic compounds has been complemented with new approaches allowing a rational design of polyhedral clusters with hypercoordinate carbon centres.

Ligand and Metal Effects on the Formation of Main‐Group Polyhedral Clusters

Ligand and Metal Effects on the Formation of Main‐Group Polyhedral Clusters

Ligand and Metal Effects on the Formation of Main‐Group Polyhedral Clusters

Ligand and Metal Effects on the Formation of Main‐Group Polyhedral Clusters

Application of database methods to the prediction of B3LYP-optimized polyhedral water cluster geometries and electronic energies

A method is described for a rapid prediction of B3LYP-optimized geometries for polyhedral water clusters (PWCs). Starting with a database of 121 B3LYP-optimized PWCs containing 2277 H-bonds, linear regressions yield formulas correlating O–O distances, O–O–O angles, and H–O–H orientation parameters, with local and global cluster descriptors. The formulas predict O–O distances with a rms error of 0.85 pm to 1.29 pm and predict O–O–O angles with a rms error of 0.6° to 2.2°. An algorithm is given which uses the O–O and O–O–O formulas to determine coordinates for the oxygen nuclei of a PWC. The H–O–H formulas then determine positions for two H’s at each O. For 15 test clusters, the gap between the electronic energy of the predicted geometry and the true B3LYP optimum ranges from 0.11 to 0.54 kcal/mol or 4 to 18 cal/mol per H-bond. Linear regression also identifies 14 parameters that strongly correlate with PWC electronic energy. These descriptors include the number of H-bonds in which both oxygens carry a non-H-bonding H, the number of quadrilateral faces, the number of symmetric angles in 5- and in 6-sided faces, and the square of the cluster’s estimated dipole moment.

Theoretical Studies of Monosubstituted and Higher Phenyl-Substituted Octahydrosilsesquioxanes

The electronic and structural properties of molecules (octahydrosilsesquioxane, H 8Si8O12), the monosubstituted and higher phenyl-substituted octahydrosilsesquioxanes (PhH7Si8O12 ,P h 2H6Si8O12, (Ph-Ph)H7Si8O12, and Ph8Si8O12), and crystals (H8Si8O12 and octa(phenylsilsesquioxane) acetone solvate (C48H40O12Si8‚C3H6O)) have been studied using plane-wave (PW), pseudo-potential (PP), and density functional theory and the generalized gradient approximation (DFT-GGA) methods. The results show that the orbitals near the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) (inclusive) for the phenylsubstituted polyhedral oligomeric silsesquioxane clusters and crystal are localized on the phenyl functional groups, whereas for both isolated molecular and crystalline H8Si8O12, the HOMO is that with the lone pair on the O atoms.

Ligand and metal effects on the formation of main-group polyhedral clusters.

The reaction of AlMe3 or ZnMe2 with hppH (hppH = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) and then with tBuLi affords [Li8(H)m(hpp)6]n+[X] -n, X = [ZntBu3], m = n = 1 (the cation core of which is shown); X = [Li(Me2AltBu2)2, m = 0, n = 2, as the major product in each case. These data reveal that non-aromatic heterocycle hppH and ZnMe2 can be employed to generate novel hydride-encapsulation main-group-metal clusters, and that related polylithium architectures can also incorporate a central void.

Ligand and Metal Effects on the Formation of Main‐Group Polyhedral Clusters

Ein Lithiumcluster mit eingeschlossenem Hydridion, [Li8(H)m(hpp)6]n+[X]−n, entsteht als Hauptprodukt bei der Umsetzung des nichtaromatischen Heterocyclus 1,3,4,6,7,8-Hexahydro-2H-pyrimido[1,2-a]pyrimidin (hppH) mit ZnMe2 (m=n=1, X=[ZntBu3]; Kation siehe Bild). Ähnliche Strukturen könnten auch in anderen Polylithium-Architekturen vorliegen. Ersetzt man ZnMe2 durch AlMe3, so erhält man ein Produkt ohne Hydrideinschluss (m=0, n=2, X=[Li(Me2AltBu2)2]).

Template‐Assisted Self‐Assembly of Spherical Colloids into Complex and Controllable Structures

AbstractColloidal aggregates with well‐controlled sizes, shapes, and structures have been fabricated by dewetting aqueous dispersions of monodispersed spherical colloids across surfaces patterned with two‐dimensional arrays of relief structures (or templates). The capability and feasibility of this approach have been demonstrated with the organization of polymer latex or silica beads into homo‐aggregates, including circular rings; polygonal and polyhedral clusters; and linear, zigzag, and spiral chains. It was also possible to generate hetero‐aggregates in the configuration of HF and H2O molecules that contained spherical colloids of different sizes, compositions, densities, functions, or a combination of these features. These uniform, well‐defined aggregates of spherical colloids are ideal model systems to investigate the aerodynamic, hydrodynamic, and optical properties of colloidal particles characterized by non‐spherical shapes and/or complex topologies. They can also serve as a new class of building blocks to generate hierarchically self‐assembled structures that are expected to exhibit interesting features valuable to areas ranging from condensed matter physics to photonics.

Theoretical study of a series of alkyllithium clusters

The structural and energetic properties of a series of alkyllithium clusters (methyl, ethyl, n, iso-propyl, n, sec, tert-butyl) have been studied using density functional theory. Geometries and binding energies have been determined using the B3LYP functional and a polarised double zeta basis set. Geometries are found in good agreement with the available experimental data when the corresponding crystals are built from non-interacting clusters. The polyhedral hexameric clusters appear to be the most stable structures except for tert-butyllithium for which the polyhedral tetramer is favored. This behaviour is related to the high steric hindrance in the tert-butyllithium hexamers and the apolar character of their Li–alkyl bonds.

Novel metal-encapsulated caged clusters of silicon and germanium

We report the recent findings of metal (M) encapsulated clusters of silicon from computer experiments based on ab initio total energy calculations and a cage shrinkage and atom removal approach. Our results show that using a guest atom, it is possible to wrap silicon in fullerenelike (f) structures, as sp2 bonding is not favorable to produce empty cages unlike for carbon. Transition M atoms have a strong bonding with the silicon cage that are responsible for the compact structures. The size and structure of the cage change from 14 to 20 Si atoms depending upon the size and valence of the M atom. Fewer Si atoms lead to relatively open structures. We find cubic, f, Frank-Kasper (FK) polyheral type, decahedral, icosahedral and hexagonal structures for M@Sin with n = 12-16 and several different M atoms. The magic behavior of 15 and 16 atom Si cages is in agreement with experiments. The FK polyhedral cluster, M@Si16 has an exceptionally large density functional gap of about 2.35 eV calculated within the generalized gradient approximation. It is likely to give rise to visible luminescence in these clusters. The cluster-cluster interaction is weak that makes such clusters attractive for cluster assembled materials. Further studies to stabilize Si20 cage with M = Zr, Ba, Sr, and Pb show that in all cases there is a distortion of the f cage. Similar studies on M encapsulated germanium clusters show FK polyhedral and decahedral isomers to be more favorable. Also perfect icosahedral M@Ge12 and M@Sn12 clusters have been obtained with large gaps by doping with divalent M atoms. Recent results of the H interaction with these clusters, hydrogenated silicon fullerenes as well as assemblies of clusters such as nanowires and nanotubes are briefly presented.

Polyhedral boron-containing cluster chemistry: Aspects of architecture beyond the icosahedron

Abstract For the structural extent of the polyhedral molecular chemistry of boron to rival that of the organic chemistry of the carbon hydrides, (a) the individual boron-containing polyhedra need to be fused together to make larger contiguous covalent assemblies, and (b) an intermolecular chemistry needs to be developed. Contemporary examples are given that illustrate novel chemistry in both these areas and that may point the way to some future developments.

Ab initio molecular-orbital calculations for dodecahedral water clusters including rare-gas atoms

Dodecahedral water clusters including rare-gas atoms and molecules are considered to play an important role in the beginning of the formation of gas hydrates in solutions. To investigate their stability, ab initio molecular-orbital calculations were performed at the MP2/6-311G(d,p)//HF/6-311G(d,p) level. In He, Ne, Ar, and Kr, the cohesive energies of the 12-hedral water clusters including each rare-gas atom were negative, whereas in Xe they were positive. Neon in the dodecahedral cluster was almost as stable as Ar and Kr in the dodecahedral clusters; the latter two are known as clathrate-forming gases. This suggests the probability of the existence of Ne clathrate hydrate, which is generally considered to be impossible. The chemical shifts of Xe incorporated in polyhedral water clusters were computed for the first time. The computed values qualitatively agree with the experimental results. PACS Nos.: 31.15Ar, 31.15Md, 31.15Ne, 36.40Cg, 36.40Mr

Polyol-mediated synthesis of polyhedral silver clusters

Besides the spheres, polyhedral silver nanoclusters were prepared by the polyol process with 3-aminopropyl triethoxysilane (APTES). In the process, APTES acts as not only the stabilizer but also the template.

Polyhedral water clusters, I: Formal consequences of the ice rules

Polyhedral water clusters (PWCs) are (H 2O) n clusters in which every oxygen is 3-coordinated. An analog of the Bernal–Fowler ice rules, when combined with graph-theoretic facts about polyhedra, leads to a rich variety of mathematical relationships regarding structural descriptors of PWCs. These relationships are developed and rigorously proved. The emphasis is on relationships involving four structural parameters which are correlated with the electronic energy of PWCs. Principal results are the recognition of the importance of three levels of information in the H-bonding pattern of a PWC; the definition and classification of the ‘F-components’ and ‘L-components’ of a PWC; a method for generating all PWCs obeying the ice rules for a given polyhedral pattern; and a method based on the four-color theorem for producing low energy PWCs that have a property called ‘contiguity two’.