Nine-atom Clusters Research Articles

Crystal Structure of the Protonated Germanide Cluster [HGe9]3−

A single crystal X-ray diffraction study of the new compound [Rb([2.2.2]crypt)]2[Rb([18]crown−6)][HGe9]·4NH3 revealed the presence of the first protonated nine-atom germanide cluster [HGe9]3−. It forms from Rb4Ge9 in liquid ammonia, so that [Ge9]4− can be considered as the base and [HGe9]3− its formally conjugated acid. The H atom is attached to a germanium vertex atom of the basal square plane, as it is known for [RGe9]3− (R = C5H9, Mes, etc.) or [HE9]3− (E = Si, Sn). In addition, the proton could be located unambiguously in the Fourier difference map. [HGe9]3− also represents a nido cluster species with 22 cluster-bonding electrons, which can be considered the most stable structure for nine-atom cluster species for all group 14 elements.

(Me3 Si)Si]3 EtGe9 Pd(PPh3 ), a Pentafunctionalized Deltahedral Zintl Cluster: Synthesis, Structure, and Solution Dynamics.

The title compound, which has a ten-atom deltahedral cluster core of Ge9 Pd, was synthesized through insertion of Pd(PPh3 ) into the tetrasubstituted nona-germanium cluster [(Me3 Si)Si]3 EtGe9 through a reaction of the latter with Pd(PPh3 )4 . This first reaction of neutral tetrasubstituted nine-atom clusters shows that they retain reactivity despite their neutral charge. The Ge9 Pd core is the first that incorporates a 5-connected transition metal other than from Group VI, a noble metal in this case. Single-crystal X-ray diffraction shows that the ten-atom core is a closo-cluster with the expected shape of a bicapped square antiprism. (1) H and (13) C NMR spectroscopy show that, in contrast to the parent tetra-substituted [(Me3 Si)Si]3 EtGe9 , the new compound does not exhibit dynamics. Relativistic DFT calculations are used to explain the differences.

Nanocatalysts Reveal Structure Sensitivity

A combined molecular-beam and quantum-simulation study that explores the catalytic behavior of tiny platinum clusters calls into question a well-established precept regarding the influence of structure on the reactivity of solid catalysts (Nat. Commun. 2016, DOI: 10.1038/ncomms10389). Years of experiments have shown that platinum-catalyzed hydrogenation of ethylene to ethane does not depend on the surface structure of the platinum crystallites. This archetypal “structure-insensitive” reaction has long stood in contrast to structure-sensitive reactions, for example, ammonia synthesis on iron crystals. These classifications have influenced strategies for enhancing catalyst performance. Now, a team led by Ueli Heiz of the Technical University of Munich and Uzi Landman of Georgia Tech has shown that ethylene hydrogenation is indeed sensitive to the structure of platinum particles, if those particles lie at the low end of the nanoscale regime. By studying size-selected platinum clusters composed of nine to 13 atoms, they found that the nine-atom cluster

John D. Corbett (1926-2013)

John D. Corbett (1926-2013)

Mixed Si/Ge Nine-Atom Zintl Clusters: ESI Mass Spectrometric Investigations and Single-Crystal Structure Determination of Paramagnetic [Si9–xGex]3–

Mixed Si/Ge compounds are of special interest as potential materials for photovoltaic applications. In order to evaluate the usage of soluble precursor compounds, we investigated the synthesis of heteroatomic nine-atom clusters that consist of Si and Ge atoms through dissolution of the ternary Zintl phases K12Si(17-x)Ge(x) (x = 9, 12) and Rb12Si(17-x)Ge(x) (x = 9). Electrospray ionization (ESI) mass spectrometry demonstrates the presence of mixed Si(9-x)Ge(x) clusters in acetonitrile solution. From ammonia solutions of the ternary phases, four compounds that contain 3-fold negatively charged [Si(9-x)Ge(x)](3-) clusters are obtained. The paramagnetic behavior is confirmed by EPR spectroscopy. [E9](3-) Zintl clusters are considered as intermediate structures in the stepwise oxidation of [E9](4-) clusters to novel element allotropes (E = Si-Pb). The structure of Rb[Rb-crypt]2[Si2.3(1)Ge6.7(1)](NH3)7 and the isostructural structures of [Rb-crypt]3[Si2.2(1)Ge6.8(1)](NH3)8, [K-crypt]3[Si2.4(1)Ge6.6(1)](NH3)8.5, and [K-crypt]3[Si4.6(1)Ge4.4(1)](NH3)8.5 are investigated by single-crystal X-ray diffraction (crypt = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]-hexacosane). The Si/Ge ratio of the products correlates with the composition of the ternary precursor phases.

Trimetallic deltahedral Zintl ions [Sn9−m−nGemBin](4−n)−for n = 1–4 and m = 0–(9 − n): a theoretical survey with prediction and rationalization of the possible structures

The recent discovery of trimetallic deltahedral Zintl ions based on Sn, Ge, and Bi revealed the possibility to obtain such clusters with a variety of different Sn/Ge/Bi ratios. Although only the dimer [(BiSn(6)Ge(2))-(Ge(2)Sn(6)Bi)](4-) was structurally characterized, a number of other nine-atom clusters with various stoichiometries were detected by electrospray mass spectrometry. The lack of structural data for the latter persuaded us to use relativistic density functional calculations in order to determine and rationalize theoretically the most stable structure conformation of each cluster and the positional preferences for the different atoms in the series [Sn(9-m-n)Ge(m)Bi(n)]((4-n)-) where n = 1-4 and m = 0-(9 - n). The analysis revealed strong dependence of the cluster geometry on the cluster stoichiometry and revealed sites with significantly different charge distribution. In addition, we introduce a parameter ϕ based on certain angles in order to rationalize the obtained structures as monocapped square antiprisms (C(4v)), tricapped trigonal prisms (D(3h)), or intermediates (C(2v)).

Tri-metallic deltahedral Zintl ions: experimental and theoretical studies of the novel dimer [(Sn6Ge2Bi)2]4−

We report the synthesis, characterization, and computational rationalization of the first trimetallic deltahedral Zintl ions. The novel nine-atom clusters were structurally characterized as dimers of [(Sn(6)Ge(2)Bi)(2)](4-) with Ge-Ge intercluster bonds. They are synthesized either by reacting bimetallic clusters (Sn(9-x)Ge(x))(4-) with BiPh(3) or by direct extraction from precursors with nominal composition "K(4)Ge(4)Sn(4)Bi".

Addition of a Thallium Vertex to Empty and Centered Nine-Atom Deltahedral Zintl Ions of Germanium and Tin

Nickel atoms were inserted into nine-atom deltahedral Zintl ions of E(9)(4-) (E = Ge, Sn) via reactions with Ni(cod)(2) (cod = cyclooctadiene), and [Ni@Sn(9)](3-) was structurally characterized. Both the empty and the Ni-centered clusters react with TlCp (Cp = cyclopentadienyl anion) and add a thallium vertex to form the deltahedral ten-atom closo-species [E(9)Tl](3-) and [Ni@E(9)Tl](3-), respectively. The structures of [Ge(9)Tl](3-) and [Ni@Sn(9)Tl](3-) showed that, as expected, the geometry of the ten-atom clusters is that of a bicapped square antiprism where the Tl-atom occupies one of the two capping vertices. This illustrates that centering a nine-atom cluster with a nickel atom does not change its reactivity toward TlCp. All compounds were characterized by electrospray mass spectrometry.

Polyhedral nine-atom clusters of tetrel elements and intermetalloid derivatives

Homoatomic polyanions have the basic capability for a bottom-up synthesis of nanostructured materials. Therefore, the chemistry and the structures of polyhedral nine-atom clusters of tetrel elements [E(9)](4-) is highlighted. The nine-atom Zintl ions are available in good quantities for E = Si-Pb as binary alkali metal (A) phases of the composition A(4)E(9) or A(12)E(17). Dissolution or extraction of the neat solids with aprotic solvents and crystallization with alkali metal-sequestering molecules or crown ethers leads to a large variety of structures containing homoatomic clusters with up to 45 E atoms. Cluster growth occurs via oxidative coupling reactions. The clusters can further act as a donor ligand in transition metal complexes, which is a first step to the formation of bimetallic clusters. The structures and some nuclear magnetic resonance spectroscopic properties of these so-called intermetalloid clusters are reviewed, with special emphasis on tetrel clusters that are endohedrally filled with transition metal atoms.

Heteroatomic Deltahedral Zintl Ions of Group 14 and their Alkenylation

Reported is the synthesis of Ge(9-x)Sn(x) heteroatomic deltahedral Zintl ions and their alkenylation by reactions with alkynes. The nine-atom clusters are made either by extraction from mixed Ge/Sn precursors with nominal composition K(4)Ge(9-x)Sn(x) or by dissolution of mixtures of the corresponding binary precursors K(4)Ge(9) and K(4)Sn(9) in solvents with high dielectric constants such as DMF, DMSO, and acetonitrile. Reactions of the heteroatomic clusters with alkynes such as Me(3)SiC[triple bond]CSiMe(3), HC[triple bond]CCpr (Cpr = cyclopropyl), and HC[triple bond]CPh in ethylenediamine resulted in the following structurally characterized compounds with alkenylated heteroatomic clusters: [K-(2,2,2-crypt)](3)[GeSn(8)-CH=CH(2)].en.tol (1), triclinic, P1, a = 13.9220(3) A, b = 14.9788(3) A, and c = 21.5892(5) A, alpha = 94.2580(10) degrees , beta = 98.5210(10) degrees , and gamma = 98.4890(10) degrees , V = 4382.31(16) A(3), Z = 2; [K-(2,2,2-crypt)](4)[Ge(2)Sn(7)(CH=CH(2))(2)](2).en (2), monoclinic, P2(1)/c, a = 48.1883(15) A, b = 12.1551(4) A, and c = 21.4824(7) A, beta = 90.052(2) degrees , V = 12583.0(7) A(3), Z = 4; [K-(2,2,2-crypt)](3)[GeSn(8)-CH=CHCpr].en (3), monoclinic, P2(1)/c, a = 17.9132(9) A, b = 22.7967(11) A, and c = 21.6922(12) A, beta = 98.409(2) degrees , V = 8763.0(8) A(3), Z = 4; [K-(2,2,2-crypt)](3)[Ge(2)Sn(7)-CH=CHPh].2en (4), monoclinic, P2(1)/n, a = 13.2583(5) A, b = 47.0565(17) A, and c = 15.9978(6) A, beta = 111.536(2) degrees , V = 9284.1(6) A(3), Z = 4. The potassium countercations of the divinyl-substituted cluster in 2 were exchanged for tetrapropylammonium cations, and the resulting compound was also crystallized and structurally characterized: [Pr(4)N](4)[Ge(2)Sn(7)(CH=CH(2))(2)](2) (5), triclinic, P1, a = 11.6757(8) A, b = 18.8150(16) A, and c = 21.0608(17) A, alpha = 112.327(3) degrees , beta = 91.550(3) degrees , and gamma = 91.892(3) degrees , V = 4273.5(6) A(3), Z = 2. All clusters were also characterized in solution by electrospray mass spectrometry.

Polyhedral structures with an odd number of vertices: nine-atom clusters and supramolecular architectures

The geometries of metal clusters and supramolecular architectures that contain nine metal atoms are analyzed within the framework of continuous shape measures (CShM). The most common polyhedra in nine coordinate complexes, the capped square antiprism and the tricapped trigonal prism, are also found among these families of compounds, even if much more scarcely. In addition, a variety of new shapes, not found among coordination polyhedra, can be identified and their proximity to the ideal geometries quantified. These include a linear chain, two types of trigonal columns, the planar regular enneagon, two-dimensional hexagonal and square grids, fragments of a close-packed structure, the triangular cupola, the tridiminished icosahedron or different fragments of the icosahedron. Among the nine-atom boranes and related clusters of the groups 13 and 14 elements, those having between 18 and 20 framework electrons present the structure of the tricapped trigonal prism, the expected closo structure. However, clusters with 21 and 22 framework electrons present a variety of structures with geometries covering nearly all the path that takes one from the capped square antiprism (nido form) to the tricapped trigonal prism (closo form).

Morphology and magnetism ofFenclusters(n=1–9)supported on a Pd(001) substrate

We present a detailed ab initio density-functional study of the morphology and magnetic and electronic properties of small ${\mathrm{Fe}}_{n}$ $(n=1--6,9)$ clusters and Fe monolayers supported on a Pd(001) substrate. Our focus is on the variation of the cluster moments with the size and shape of the cluster and on the induced magnetization of the substrate. For the smallest clusters, the magnetic moments of the Fe atoms are strongly enhanced compared to bulk Fe. With increasing size of the cluster, the moment decreases linearly with the number of Fe nearest neighbors. The magnetic moment of the adsorbed cluster induces a substantial magnetization of the substrate. The induced magnetic moments are largest on the Pd atoms binding to the cluster atoms, increasing with the number of Fe neighbors. The induced magnetic polarization is quite long ranged, and the enhanced magnetic moments of the Fe atoms and the induced magnetization of the substrate add up to a ``giant effective moment'' per Fe atom ranging between $7.6\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{B}$ for an isolated adatom and $4.6\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{B}$ for a nine-atom cluster. Relaxation of the cluster structure reduces the Fe moments but enhances the induced moments. Orbital moments induced by spin-orbit coupling have been determined via self-consistent relativistic calculations for an isolated Fe adatom. Due to the strong hybridization, the orbital moment on the Fe atom remains rather modest, but a much higher ratio of orbital and spin moments is found for the Pd atoms of the substrate. Relativistic effects also lead to a substantial anisotropy of the induced spin and orbital moments, which makes a significant contribution to the magnetic anisotropy energy.

Ligand‐Free Deltahedral Clusters of Silicon in Solution: Synthesis, Structure, and Electrochemistry of Si92‐.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Ligand-Free Deltahedral Clusters of Silicon in Solution: Synthesis, Structure, and Electrochemistry of Si92-

Deltahedral nine-atom clusters of silicon, Si(9)(2-), were synthesized by mild oxidation of a liquid ammonia solution of K(12)Si(17) with Ph(3)GeCl in the presence of 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) or 2,2,2-crypt (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane). The clusters were structurally characterized in [K(18-crown-6)](2)Si(9).C(5)H(5)N (yellow; orthorhombic, Pnma; a = 14.013(1), b = 18.108 (1), c = 18.320 (1) A; Z = 4) crystallized from a pyridine solution of the product of the aforementioned reaction in liquid ammonia. Si(9)(2-) is the first unequivocally characterized nine-atom cluster of group 14 with a charge of 2-. In addition to pyridine, the product from the reaction in liquid ammonia is also soluble in DMF, and the Si(9)(2-) clusters were characterized by mass spectrometry in such a solution. The more reduced clusters Si(9)(3-) have also been crystallized from pyridine solution. Cyclic voltammetry in both pyridine and DMF solutions clearly shows the Si(9)(2-)/Si(9)(3-) redox couple as one-electron reversible process. The structural similarities and differences between Si(9)(3-) and Si(9)(2-) are discussed herein.

Ge(9)=Ge(9)=Ge(9)](6-): a linear trimer of 27 germanium atoms.

The title anion was synthesized by oxidation of nido-Ge94- with Ph3P or Ph3As in ethylenediamine solution. It was structurally characterized in the compound (Rb-2,2,2-crypt)6[Ge9=Ge9=Ge9].3en (2,2,2-crypt = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) crystallized from the solution. The anion is a linear trimer of nine-atom clusters with the shape of tricapped trigonal prisms elongated along two of the three prismatic edges. Each pair of clusters is connected by two exo-bonds.

Heteroatomic deltahedral clusters of main-group elements: synthesis and structure of the Zintl ions [In4Bi5]3-, [InBi3]2-, and [GaBi3]2-.

Reported are the first heteroatomic deltahedral Zintl ions made of elements differing by more than one group, indium or gallium and bismuth. Nine-atom clusters [In4Bi5]3- are characterized in two different compounds, (Na-crypt)3[In4Bi5] (4, P2(1)/n, a = 23.572(6) A, b = 15.042(4) A, c = 24.071(4) A, beta = 106.00(3) degrees, Z = 4) and (K-crypt)6[In4Bi5][In4Bi5].1.5en.0.5tol (5, P2(1)/c, a = 28.532(2) A, b = 23.707(2) A, c = 28.021(2) A, beta = 93.274(4) degrees, Z = 4). Tetrahedra of [InBi3]2- or [GaBi3]2- are found in (K-crypt)2[InBi3].en (1, P2(1), a = 12.347(4) A, b = 20.884(4) A, c = 12.619(7) A, beta = 119.02(4) degrees, Z = 2) and in the isostructural (Rb-crypt)2[InBi3].en (2, a = 12.403(8) A, b = 20.99(1) A, c = 12.617(9) A, beta = 118.83(4) degrees) and (K-crypt)2[GaBi3].en (3, a = 12.324(5) A, b = 20.890(8) A, c = 12.629(5) A, beta = 118.91(3) degrees). All compounds are crystallized from ethylenediamine/crypt solutions of precursors with nominal composition "A5E2Bi4" where A = Na, K, or Rb and E = Ga or In. The cluster in 4 is a well-ordered monocapped square antiprism with the four indium atoms occupying the five-bonded positions. Compound 5 contains two independent [In4Bi5]3- clusters; one is the same as the cluster in 4, while the other is a tricapped trigonal prism with two elongated prismatic edges. All compounds are EPR-silent and therefore diamagnetic.

Magnetic order and defect structure ofFexAl1−xalloys aroundx=0.5: An experimental and theoretical study

High-field ${}^{57}\mathrm{Fe}$ M\ossbauer investigations up to 13.5 T on a series of ${\mathrm{Fe}}_{x}{\mathrm{Al}}_{1\ensuremath{-}x}$ alloys around $x=0.5$ and magnetic measurements on a 51.8% sample are performed between 4.2 and 295 K. The experimental results are complemented with augmented spherical-wave (ASW) and linear augmented plane-wave (LAPW) band structure as well as thermodynamic model calculations. For ideally ordered FeAl $(B2$ structure) both types of band-structure calculations yield ${\ensuremath{\mu}}_{\mathrm{Fe}}=0.71{\ensuremath{\mu}}_{B}.$ The ferromagnetic ground state is 0.7 mRy per formula unit below the nonmagnetic state. In experiment it was found that only approximately 25% of the Fe atoms carry a magnetic moment. This discrepancy can be explained if noncollinear spin ordering is allowed and a high density of defects is taken into account, which is typical for real alloys and destroys translational periodicity. Experimentally magnetic moments are only observed for Fe antistructure atoms and their eight Fe neighbors. This nine-atom cluster has a mean moment of $0.4{\ensuremath{\mu}}_{B}$ per atom, which is in fair agreement with the results from supercell (16 and 54 atoms) calculations $(0.6{\ensuremath{\mu}}_{B}).$ For the M\ossbauer analysis four subspectra are used, which are allocated to (i) Fe in the completely ordered $B2$ structure, (ii) Fe antistructure atoms, and (iii) their nearest Fe neighbors, as well as (iv) Fe atoms around a vacancy in the Fe sublattice. This analysis allows us to obtain simultaneously the concentration of both the Fe vacancies and the Fe antistructure atoms. The derived temperature dependence for both defect types corresponds well with thermodynamic model calculations, which account for all possible kinds of point defects.

Synthesis and Structure of Isolated Silicon Clusters of Nine Atoms

We have discovered and structurally characterized the first “naked” silicon clusters larger than four atoms, Si9, in the compound Rb12Si17. Silicon is of unparalleled importance for many electronic applications, and the research associated with it spans over many different areas of science: chemistry, physics, surface science, materials processing, etc. In addition to the extensively studied silicon clusters in the gas phase,1 much interest has been focused lately on silicon nanoparticles and porous silicon due to their valuable optical properties.2 Recently, the first synthesis of such Si and Ge nanoparticles in liquid medium was reported.3 This approach utilizes a metathesis reaction (comproportionation) between the negatively charged silicon or germanium in the solids KSi or NaGe, respectively, and the corresponding positively charged ions in the tetrachlorides. Perhaps a better approach to the synthesis of such nanoparticles is to use premade silicon clusters in the solid state, extract them intact into a solution, and then use a metathesis reaction. Unfortunately, the only known such species, Si4 tetrahedra in A4Si4 (A ) alkali metal)4 and some lithium-stabilized planar silicon formations,5 cannot be extracted, apparently due to the large charge per atom ratio.6 The same is true for the tetrahedra of the other tetrels (tetrel ) a group 14 element), Ge4, Sn4, and Pb4. On the other hand, nine-atom clusters of germanium, tin, and lead have been identified in solutions made by dissolving the corresponding alkali-metal tetrelides in ethylenediamine or liquid ammonia.7 Such clusters with different shapes and charges have also been crystallized from the corresponding solutions and have been structurally characterized.6 It should be pointed out that in all reports the tetrelide precursors for such solutions have been labeled either “alloys” or “melts”, i.e., substances with no particular structure and without defined cluster formations. Hence, the current understanding on the formations of the clusters in solution is that they do not exist in the precursors but are rather assembled somehow during the process of dissolution.6 However, our recent studies of the systems alkali-metal-tetrel show that clusters of Ge9 and Pb9 exist in the compounds Cs4Ge9 and K4Pb9, respectively.8 Similarly, recent Raman studies of these and other alkali-metal-tetrel systems also suggest the existence of such clusters.9 The same clusters most likely existed in the precursors for the solution studies. The new compound, Rb12Si17, contains isolated nine-atom silicon clusters, Si9, and is a potential candidate for a precursor for silicon clusters in solution. The compound is made at 900 °C (kept for 1 h at that temperature and then slowly cooled with a rate of 5°/h) by direct synthesis from the pure elements sealed in niobium containers and jacketed in evacuated ampules of fused-silica. The same approach also yields the isostructural K12Sn17 (the phase which most likely “produces” the Sn9 in solution) and (KxRb1-x)12Si17. Furthermore, phases with the same or very similar structures and stoichiometries seem to exist in the systems Cs-Si, Cs-Sn, RbSn, Cs-Pb, and Rb-Pb, according to their X-ray diffraction powder patterns.

Ab initio calculations on CO4 centers in silicon dioxide

Ab initio SCF-MO Hartree–Fock calculations were performed using the STO-3G, 6-31G, and 6-31G* basis sets to model hypothetical substitutional carbon impurities in silicon dioxide. We utilized nine-atom clusters, [C(OH)4]qt, with charge number qt = 0 and + 1. The positions of the C and O atoms were varied to achieve minimum total energies, while the fixed protons served to simulate the rigid crystal surroundings. In the optimized configuration of the neutral cluster, the CO bond lengths are appreciably longer than typical CO bonds, indicating relatively weak bonds for a carbon impurity at a silicon site. For comparison, the relative positions of all nine atoms in the [C(OH)4]0 model were allowed to vary. This unconstrained model yielded more normal bond lengths and was lower in energy than the fixed-proton model by 6.80 eV with the 6-31G* basis set. The free-H model compared favorably with the x-ray diffraction data for an analogous orthocarbonate. Our results are in concert with the lack of reports of any substitutional carbon impurity in α-quartz. In the fixed-H models, the twofold local symmetry was found to be retained when qt is 0 but not when qt is + 1. For the latter ion, the unrestricted H-F calculations indicate that this paramagnetic center has its spin population almost entirely on one oxygen ion and is high in energy (5.31 eV with 6-31G) compared to the diamagnetic neutral one. Conclusions reached with the nine-atom clusters were confirmed by a series of calculations on the extended model [C(OSiH3)4]0.

NQR and Low-Field NMR of 181Ta in the Low-Temperature CDW State of 2 H-TaS2

Abstract NQR and low-field NMR spectra of 181 Ta are reported to probe the electronic environment of inequivalent tantalum sites in the low-temperature CDW state of a layered compound 2H-TaS2 . The overall features are found to be consistent with the structure consisting of nine-atom snowflake clusters in a locally commensurate CDW state.