Ge10 Clusters Research Articles

Systematic investigation of structure and optoelectronic properties of Gen (n = 3–20), MGe9 (M = Ga, Si, Sn, As) and GaxGe(10−x) (x = 1–10) Clusters: Computational approach

Herein, the structural, electronic, and optical properties of Gen (n = 3–20), mixed MGe9 (M = Ga, Si, Sn, As), and GaxGe(10−x) (x = 1–10) clusters using the density-functional theory (DFT) and the time dependent-DFT (TD-DFT) were systematically investigated. The calculated values of binding energies (Eb, eV/atom), second-order differences of total energies (Δ2E), and fragmentation energies (Efrg) for pristine Gen clusters demonstrated that the pristine Ge10 and Ge20 are the most stable structure of Gen clusters. Based on first-principles calculations, the properties of studied clusters are highly dependent on their composition. The electronic properties of Gen clusters reveal that, in general, the HOMO-LUMO energy gap decreases with increasing the cluster size. SiGe9 was found to be more thermodynamically and chemically stable than its parent. On the other hand, generally, the energy gap of mixed MGe9 clusters decreased compared with the pure Ge10 cluster. The calculated H-L energy gap of GaxGe(10−x) (x = 1–10) cluster with even/odd number of Ga atom is in the range of ~ 1.567–2.194 eV/1.153–1.297 eV. Based on TD-DFT calculations, with increasing the cluster size, the maximum wavelength for Gen (n = 3–20) clusters shifted towards higher values. Due to their significant optical HOMO-LUMO energy gap and maximum wavelength, these clusters could be potentially promising candidates for optoelectronic devices.

PKU-21: A Novel Layered Germanate Built from Ge7 and Ge10 Clusters for CO2 Separation.

The attractive properties of layered inorganic materials, which make them suitable for numerous applications in chemical industries and life sciences, originated from their crystalline framework structures. Here, we report a new layered germanate PKU-21, which was prepared by the hydrothermal synthesis method using 2-propanolamine (MIPA) as the structure-directing agent. The structure of PKU-21 was determined from synchrotron single-crystal X-ray diffraction and synchrotron powder X-ray diffraction data. It reveals a complicated framework structure containing 18 unique Ge atoms in the asymmetric unit. PKU-21 is the first layered germanate built from both Ge7 and Ge10 clusters, following the 3-dimensional germanate PKU-17. The preparation and structure of PKU-21 are discussed in comparison with PKU-17, which provides new insight into the formation mechanism of germanates. Gas sorption experiments indicate that the layered PKU-21 sample exhibits a better CO2 sorption selectivity over N2 and CH4 at 298 K than at 273 K, making it a promising candidate for CO2 separation.

Van der Waals Effects on semiconductor clusters.

Van der Waals (vdW) interactions play an important role on semiconductors in nanoscale. Here, we utilized first-principles calculations based on density functional theory to demonstrate the growth mode transition from prolate to multiunit configurations for Gen (n = 10-50) clusters. In agreement with the injected ion drift tube techniques that "clusters with n < 70 can be thought of as loosely bound assemblies of small strongly bound fragments (such as Ge7 and Ge10 )," we found these stable fragments are connected by Ge6 , Ge9 , or Ge10 unit (from bulk diamond), via strong covalent bonds. Our calculated cations usually fragment to Ge7 and Ge10 clusters, in accordance with the experiment results that the spectra Ge7 and Ge10 correspond to the mass abundance spectra. By controlling a germanium cluster with vdW interactions parameters in the program or not, we found that the vdW effects strengthen the covalent bond from different units more strikingly than that in a single unit. With more bonds between units than the threadlike structures, the multiunit structures have larger vdW energies, explaining why the isolated nanowires are harder to produce. © 2015 Wiley Periodicals, Inc.

Structures and stability of metal-doped GenM (n = 9, 10) clusters

The lowest-energy structures of neutral and cationic GenM (n = 9, 10; M = Si, Li, Mg, Al, Fe, Mn, Pb, Au, Ag, Yb, Pm and Dy) clusters were studied by genetic algorithm (GA) and first-principles calculations. The calculation results show that doping of the metal atoms and Si into Ge9 and Ge10 clusters is energetically favorable. Most of the metal-doped Ge cluster structures can be viewed as adding or substituting metal atom on the surface of the corresponding ground-state Gen clusters. However, the neutral and cationic FeGe9,10,MnGe9,10 and Ge10Al are cage-like with the metal atom encapsulated inside. Such cage-like transition metal doped Gen clusters are shown to have higher adsorption energy and thermal stability. Our calculation results suggest that Ge9,10Fe and Ge9Si would be used as building blocks in cluster-assembled nanomaterials because of their high stabilities.

Empty versus filled polyhedra: 11 vertex bare germanium clusters

The structures and energetics of centered 10-vertex Ge@Ge₁₀(z) (z = -4, -2, 0, +2, +4) clusters have been investigated by density functional theory (DFT) for comparison with the previously studied isomeric empty 11-vertex Ge₁₁(z) clusters. For the cationic species (z = +2, +4) such centered Ge@Ge₁₀(z) structures are shown to be energetically competitive (within ∼1 kcal mol⁻¹) to the lowest energy isomeric empty Ge₁₁(z) structures. These Ge@Ge₁₀(z) structures can be derived from the lowest energy empty 10-vertex Ge₁₀(z-4) structures by inserting a Ge⁴⁺ ion in the center. The outer 10-vertex polyhedron in the lowest energy Ge@Ge₁₀²⁺ dication structure is the most spherical D(4d) bicapped square antiprism, which is also the lowest energy structure of the empty Ge₁₀²⁻ dianion, as expected from the Wade-Mingos skeletal electron counting rules. For the tetracationic Ge₁₁⁴⁺ /Ge@Ge₁₀⁴⁺ system the lowest energy centered Ge@Ge₁₀⁴⁺ structure can be obtained by inserting a Ge⁴⁺ ion in the center of a C(3v) deltahedral empty Ge10 cluster. Centered 10-vertex polyhedral Ge@Ge₁₀(z) structures were also found for the neutral (z = 0) and dianionic (z = -2) systems but at significantly higher energies than the lowest energy isomeric empty Ge₁₁(z) structures.

Solving complex open-framework structures from X-ray powder diffraction by direct-space methods using composite building units

The crystal structure of a novel open-framework gallogermanate, SU-66 {|(C6H18N2)18(H2O)32|[Ga4.8Ge87.2O208]}, has been solved from laboratory X-ray powder diffraction (XPD) data by using a direct-space structure solution algorithm and local structural information obtained from infrared (IR) spectroscopy. IR studies on 18 known germanates revealed that the bands in their IR spectra were characteristic of the different composite building units (CBUs) present in the structures. By comparing the bands corresponding to Ge—O vibrations in the IR spectra of SU-66 with those of the 18 known structures with different CBUs, the CBU of SU-66 could be identified empirically as the Ge10(O,OH)27 cluster (Ge10). The unit cell and space group (extinction symbol P--a; a = 14.963, b = 31.593, c = 18.759 Å) were determined initially from the XPD pattern and then confirmed by selected-area electron diffraction. The structure of SU-66 was solved from the XPD data using parallel tempering as implemented in FOX [Favre-Nicolin &amp; Černý (2002). J. Appl. Cryst. 35, 734–743] by assuming P21 ma symmetry and two Ge10 clusters in the asymmetric unit. Rietveld refinement of the resulting structure using synchrotron XPD data showed the framework structure to be correct and the space group to be Pmma. The framework has extra-large (26-ring) one-dimensional channels and a very low framework density of 10.1 Ge/Ga atoms per 1000 Å3. SU-66, with 55 framework atoms in the asymmetric unit, is one of the more complicated framework structures solved from XPD data. Indeed, 98% of the reflections were overlapping in the XPD pattern used for structure solution. Tests on other open-framework germanates (SU-62, SU-65, SU-74, PKU-12 and ITQ-37) for which the XPD data, unit cell, space group and IR spectra were available proved to be equally successful. In a more complex case (SU-72) the combination of FOX and powder charge flipping was required for structure solution.

Complex Open-Framework Germanate Built by 8-Coordinated Ge10 Clusters

A novel open-framework germanate |(C5H14N2)2(C5H12N2)0.5(H2O)2.5|[Ge12.5O26(OH)2] with three-dimensional 10- and 11-ring channels, denoted as SU-67, has been synthesized under hydrothermal conditions using 2-methylpiperazine (MPP) as the structure-directing agent (SDA). The synthesis is intimately related to that of JLG-5, a tubular germanate built from Ge7 clusters. The influences of synthesis parameters are discussed. A strong influence of the hydrofluoric acid quantity on the resulting cluster building units can be concluded. The framework of SU-67 is based on an elaborate topological pattern of connected Ge10 clusters forming intersecting 10- and 11-ring channels and has a low framework density (12.4 Ge atoms per 1000 Å(3)). We have discovered that the topology of SU-67 is a new 8-connected nce-8-I41/acd net. Strong hydrogen bonding among the organic SDAs, water molecules, and Ge10 clusters resulted in helical networks in SU-67.

Two Open-Framework Germanates with Nickel Complexes Incorporated into the Framework

Two open-framework germanates, SUT-1 and SUT-2, have been synthesized under hydrothermal conditions using ethylenediamine (en, H(2)NCH(2)CH(2)NH(2)) as templates and Ni(NO(3))(2)·6H(2)O as the transition-metal source. Their frameworks are built with Ge(10) clusters and [Ni(en)(2)](2+) complexes. In both structures, Ge(10) clusters form square nets in the a-c plane, while the [Ni(en)(2)](2+) complexes bridge the square nets via Ni-O-Ge bonds to form 3D networks. They present the first examples to incorporate Ni(2+) complexes into the germanate frameworks. In SUT-2, additional linkages by Ge(2)O(7) clusters between the square nets generate a new type of topology.

Si modified Ge10 cluster: the preparation and characterization of single crystal Na4(Ge,Si)9O20

AbstractA Si modified Ge10 cluster with structure Na4(Ge,Si)9O20 (denoted as HUT‐1) was synthesized by hydrothermal synthesis at 160 °C with a sodium silicate source. The compound was characterized by single crystal, powder X‐ray diffraction and TGA‐DSC analysis. HUT‐1 crystallizes in space group I41 (80) with calculated unit cell (a=14.966(5) Å, c=7.343(2) Å, V=1644.8(9) Å3), which has the same structure as Na4Ge9O20. HUT‐1 has a high Si/Ge ratio with an approximate formula of Na4Ge7.68Si1.32O20. Single crystal X‐ray structure refinements together with results from X‐ray powder diffraction (XRPD) confirm the occupancy of Si at two tetrahedral sites. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

An Open-Framework Silicogermanate with 26-Ring Channels Built from Seven-Coordinated (Ge,Si)10(O,OH)28 Clusters

We report a new open-framework silicogermanate SU-61 containing 26-ring channels with a low framework density. It can be seen as a crystalline analogue to the mesoporous silica MCM-41. The structure is built from the assembly of (Ge,Si)10(O,OH)28 clusters. It is the first time that silicon has been successfully introduced in the Ge10 cluster in significant amounts ( approximately 21% of the tetrahedral sites). Five- and six-coordinated Ge10 clusters have previously been observed in other germanate compounds leading to either dense or open structures. In SU-61, the seven-coordinated clusters fall onto yet another underlying net, the osf net. SU-61, along with other Ge10 based frameworks, shows the versatility of the germanate system to adopt defined topologies playing on the connectivity of the clusters following the principles of net decoration and scale chemistry.

Na6[Ge10{Fe(CO)4}8]⋅18 THF: A Centaur Polyhedron of Germanium Atoms

Mythological figure: The reaction of GeBr with Na2[Fe(CO)4] yields the polyhedral Ge10 cluster compound Na6[Ge10{Fe(CO)4}8]⋅18 THF. The arrangement of the 10 germanium atoms (blue spheres in figure) in the cluster core can be described as a centaur polyhedron and therefore represents a new structural motif in germanium cluster chemistry.

A Theoretical Study on Growth Patterns of Ni-Doped Germanium Clusters

Ni-doped germanium clusters have been systematically investigated by using the density functional approach. The growth-pattern behaviors, stabilities, charge transfer, and polarities of these clusters are discussed in detail. Obviously different growth patterns appear between small-sized Ni-doped germanium clusters and middle- or larger-sized Ni-doped germanium clusters. The Ni-convex or substituted Ge(n) frames for small-sized clusters as well as Ni-concaved or encapsulated Ge(n) frames for middle- or large-sized clusters are dominant growth patterns. The calculated fragmentation energies manifest that the magic numbers of stabilities are 5, 8, 10, and 13 for Ni-doped germanium clusters; the obtained relative stabilities exhibit that the Ni-encapsulated Ge(10) cluster is the most stable species of all different-sized clusters, which is in good agreement with available experimental observations of CoGe(10)(-). Natural population analysis shows that different charge-transfer phenomena depend on the sizes of the Ni-doped Ge(n) clusters. Additionally, the properties of frontier orbitals and the polarities of Ni-doped Ge(n) clusters are also discussed.

A computational investigation of copper-doped germanium and germanium clusters by the density-functional theory

The geometries, stabilities, and electronic properties of Ge(n) and CuGe(n) (n = 2-13) clusters have been systematically investigated by using density-functional approach. According to optimized CuGe(n) geometries, growth patterns of Cu-capped Ge(n) or Cu-substituted Ge(n+1) clusters for the small- or middle-sized CuGe(n) clusters as well as growth patterns of Cu-concaved Ge(n) or Ge-capped CuGe(n-1) clusters for the large-sized CuGe(n) clusters are apparently dominant. The average atomic binding energies and fragmentation energies are calculated and discussed; particularly, the relative stabilities of CuGe10 and Ge10 are the strongest among all different sized CuGe(n) and Ge(n) clusters, respectively. These findings are in good agreement with the available experimental results on CoGe10- and Ge10 clusters. Consequently, unlike some transition metal (TM)Si12, the hexagonal prism CuGe12 is only low-lying structure; however, the basket-like structure is located as the lowest-energy structure. Different from some TM-doped silicon clusters, charge always transfers from copper to germanium atoms in all different sized clusters. Furthermore, the calculated highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO) gaps are obviously decreased when Cu is doped into the Ge(n) clusters, together with the decrease of HOMO-LUMO gaps, as the size of clusters increases. Additionally, the contribution of the doped Cu atom to bond properties and polarizabilities of the Ge(n) clusters is also discussed.

Stable Structures for Ge10 Cluster and Comparative Study with Si10 Cluster

Full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO MD) calculations have been performed to investigate the structures and energies of small cluster Ge10. We get twenty three stable structures for Ge10. The results suggest that only five structures are stable among the six structures proposed before, the remainder undergoes a distortion to another more stable form. Making comparison with the structures of Si10 cluster, we find that there are much in common between them. But their ground state structures are different.

Stable Structures for Ge10 Cluster and Comparative Study with Si10 Cluster

Stable Structures for Ge10 Cluster and Comparative Study with Si10 Cluster