The Neat Ternary Solid K5−xCo1−xSn9with Endohedral [Co@Sn9]5−Cluster Units: A Precursor for Soluble Intermetalloid [Co2@Sn17]5−Clusters

Geometries, electronic structures, and bonding properties of endohedral Group-14 Zintl clusters TM@E10 (TM = Fe, Co, Ni; E = Ge, Sn, Pb)

The geometries, electronic structures, and bonding properties of the title endohedral Zintl clusters have been studied by using ab initio calculations. [Fe@Ge₁₀ ]^4- and [Co@Ge₁₀ ]^3- have D_5h -symmetric pentagonal prismatic structure and [Fe@Sn₁₀ ]^4- adopts the C_2v -symmetric structure as their ground-state structures, whereas all the other clusters possess D_4d bicapped square antiprismatic structures, in consistent with the experimental values when available. Natural bonding orbital and electron localization function disclosed that the negative charges are localized on the central atoms rather than the cages while the TME ionic bonding interactions increase in the order of Ge < Sn < Pb. The energy decomposition analysis revealed that the total bonding energy ∆E_int between central TM and E₁₀ cage is above 150 kcal/mol. The ionic bonding interaction termed as electrostatic interaction ∆E_elstat increases in the order of Ge < Sn < Pb and becomes higher than the covalent bonding interactions termed as total orbital interactions ∆E_orb . Among the total orbital interactions, the π back donations from the TM-d orbitals to the empty cage orbitals consisting of E-p orbitals, the magnitude of which is importantly affected by the cage symmetry, are dominant contributions.

[Co2@(Ge17Ni)]4-: the first edge-sharing double-cage endohedral germanide

We report here a new double-cage endohedral Ge cluster, [Co₂@(Ge₁₇Ni)]^4-, fused through two [Co@(Ge₉Ni)] moieties with a shared Ni-Ge edge. This ternary Co-Ge-Ni species not only represents the first double-cage example of an 18-vertex Zintl cluster, but also fills in the missing link of the edge fusion model in the double-cage systems.

High electron affinity triggered by lithium coordination: quasi-chalcogen properties of Li2Sn8Be

This work puts forward an unusual but rational strategy to design superatoms mimicking the properties of group VIA elements. A stable dianion with closo-configuration, namely Li2Sn8Be2−, has been obtained by...

Recent developments in germanium containing clusters in intermetallics and nanocrystals

Multimetallic clusters can be described as building blocks in intermetallics, compounds prepared from all metals and/or semi-metals, and in Zintl phases, a subset of intermetallics containing metals with large differences in electronegativity. In many cases, these intermetallic and Zintl phases provide the first clue for the possibilities of bond formation between metals and semi-metals. Recent advances in multimetallic clusters found in Zintl phases and nanoparticles focusing on Ge with transition metals and semi-metals is presented. Colloidal routes to Ge nanocrystals provide an opportunity for kinetically stabilized Ge-metal and Ge-semi-metal bonding. These routes provide crystalline nanoclusters of Ge, hereafter referred to as nanocrystals, that can be structurally characterized. Compositions of Ge nanocrystals containing transition metals, and the semi-metals, Sb, Bi, and Sn, whose structures have recently been elucidated through EXAFS, will be presented along with potential applications.

Filled trivacant icosahedra as building fragments in 17-atom endohedral germanides [TM2@Ge17]n- (TM = Co, Ni)

The syntheses and the characterization of two 17-atom endohedral Ge clusters, [Co₂@Ge₁₇]^6- (1a) and [Ni₂@Ge₁₇]^4- (2a), are reported. The anions 1a and 2a, which close the gap between the known 16- and 18-atom Ge clusters, are investigated by single crystal X-ray diffraction and by quantum chemical calculations. The structures mark a new example on the pathway for cluster growth towards larger clusters with icosahedral symmetry. Furthermore, the [Co@Ge₁₀]^3- anion (3a) is obtained from liquid ammonia.

Endohedral group-14-element clusters TM@E9 (TM = Co, Ni, Cu; E = Ge, Sn, Pb) and their low-dimensional nanostructures: a first-principles study

Endohedral group14-based clusters with the encapsulation of a transition metal, which are termed [TM@E_m]^n- (TM = transition metal and E = group-14 elements), have lots of potential applications and have been used as interesting building blocks in materials science. Nevertheless, their electronic structures and stability mechanism remain unclear. In this paper, we systematically study the geometries, electronic structures, and bonding properties of [TM@E₉]^n- clusters which are the smallest endohedral group-14-based clusters synthesized so far, by using density functional theory (DFT) calculations. The calculation results reveal the important role of TMs in affecting the structures and bonding interactions in the [TM@E₉]^n- cluster. In the presence of a TM, the cluster geometry could change from a monocapped square antiprism (C_4v) for empty [E₉]^4- cages to a tricapped trigonal prismatic geometry (D_3h) for [TM@E₉]^n-. By using the energy decomposition analysis (EDA) method, the bonding properties between the endohedral TM and E₉ cluster have been thoroughly investigated. It was found that the origin of stability of these clusters is from the large electrostatic attraction with significantly reduced Pauli repulsion. In the case of orbital interactions, the π back-donations from d orbitals of the TM to the cluster make important contributions. More interestingly, the 1D-chain and 2D-sheet nanostructures based on the [Ni@E₉] cluster have been theoretically predicted. The band structure and density of states analysis revealed that all of these nanostructures are metallic and their excellent thermodynamic stability has been confirmed by using ab initio molecular dynamics (AIMD) simulations.

Intermetallic phases meet intermetalloid clusters

In this article intermetalloid clusters of Cu-Zn, Cu-AI, Cu-Sn, and Cu-Pb are discussed. Intermetallic compounds based on these metal combinations are of the Hume-Rothery type with well-defined structures related to the valence electron count of the involved metals. Many Zintl-type and molecular clusters with these metals are known with remarkable structural parallels to the respective solid-state phases. On several examples, this article discusses intermetalloid clusters in terms of their metal core structures and relates them to structural principles in intermetallic solid-state phases. Also the syntheses of such clusters are addressed. Zintl-type and molecular clusters are most generally accessible from organometallic precursor complexes with redox processes between the different metals as an underlying synthesis concept.

Metallocages for Metal Anions: Highly Charged [Co@Ge9 ]5- and [Ru@Sn9 ]6- Clusters Featuring Spherically Encapsulated Co1- and Ru2- Anions

Endohedral clusters count as molecular models for intermetallic compounds-a class of compounds in which bonding principles are scarcely understood. Herein we report soluble cluster anions with the highest charges on a single cluster to date. The clusters reflect the close analogy between intermetalloid clusters and corresponding coordination polyhedra in intermetallic compounds. We now establish Raman spectroscopy as a reliable probe to assign for the first time the presence of discrete, endohedrally filled clusters in intermetallic phases. The ternary precursor alloys with nominal compositions "K5 Co1.2 Ge9 " and "K4 Ru3 Sn7 " exhibit characteristic bonding modes originating from metal atoms in the center of polyhedral clusters, thus revealing that filled clusters are present in these alloys. We report also on the structural characterization of [Co@Ge9 ]5- (1a) and [Ru@Sn9 ]6- (2a) obtained from solutions of the respective alloys.

Synthesis and structure of a family of rhodium polystannide clusters [Rh@Sn10]3-, [Rh@Sn12]3-, [Rh2@Sn17]6- and the first triply-fused stannide, [Rh3@Sn24]5

Through relatively subtle changes in reaction conditions, we have been able to isolate four distinct Rh/Sn cluster compounds, [Rh@Sn10]3-, [Rh@Sn12]3-, [Rh2@Sn17]6- and [Rh3@Sn24]5-, from the reaction of K4Sn9 with [(COE)2Rh(μ-Cl)]2(COE = cyclooctene). The last of these has a hitherto unknown molecular topology, an edge-fused polyhedron containing three Rh@Sn10 subunits, and represents the largest endohedral Group 14 Zintl cluster yet to have been isolated from solution. DFT has been used to place these new species in the context of known cluster chemistry. ESI-MS experiments on the reaction mixtures reveal the ubiquitous presence of {RhSn8} fragments that may play a role in cluster growth.

Structural isomerism in the [(Ni@Sn9)In(Ni@Sn9)]5− Zintl ion

A new Zintl cluster, [(Ni@Sn₉)In(Ni@Sn₉)]⁵⁻, has been isolated in two distinct isomeric forms, one where both Ni@Sn₉ units are coordinated to the bridging indium atom in an η³- mode, the other where one is η³- and the other η⁴-.

Recent developments in Zintl cluster chemistry

Zintl anions have been known for more than a century and were studied systematically by Eduard Zintl in the 1930s. Since then, they have been investigated for their interesting structures, bonding, and physical properties - in solid Zintl phases, in solvate salts, and in solution. While their popularity remained limited for several decades, Zintl ion chemistry has recently experienced a renaissance as a result of breakthroughs regarding their modifications into multinary anions that include transition metal atoms, their organic derivatization, and their oxidative linkage. A plethora of reports from the past two decades - demonstrating the ever growing variety of Zintl ion chemistry - have been since summarized in several review articles. Herein, we intend to present the most recent developments, which also shed light on Zintl anions and clusters as useful precursors for materials development, as illustrated by one recent example.

[Co@Sn6 Sb6 ]3- : An Off-Center Endohedral 12-Vertex Cluster

We report on the asymmetric occupation of a 12-vertex cluster centered by a single metal atom. Three salts of related intermetalloid cluster anions, [Co@Sn₆ Sb₆ ]^3- (1), [Co₂ @Sn₅ Sb₇ ]^3- (2), and [Ni₂ @Sn₇ Sb₅ ]^3- (3) were synthesized, which have pseudo-C_4v -symmetric or pseudo-D_4h -symmetric 12-vertex Sn/Sb shells and interstitial Co^- ions or Ni atoms. Anion 1 is a very unusual single-metal-"centered" 12-atom cluster, with the inner atom being clearly offset from the cluster center for energetic reasons. Quantum chemistry served to assign atom types to the atomic positions and relative stabilities of this cluster type. The studies indicate that the structures are strictly controlled by the total valence electron count-which is particularly variable in ternary intermetalloid cluster anions. Preliminary ¹¹⁹ Sn NMR studies in solution, supported by quantum-chemical calculations of the shifts, illustrate the complexity regarding Sn:Sb distributions of such ternary systems.

Synthesis of a Cyclic Co2Sn2 Cluster Using a Co- Synthon

[Ar'SnCo]2 (1, Ar' = C6H3-2,6{C6H3-2,6- iPr2}2), a rare metal-metal bonded cobalt-tin cluster with low-coordinate tin atoms, was prepared by the reaction of [K(thf)0.2][Co(1,5-cod)2] (cod = 1,5-cyclooctadiene) with [Ar'Sn(μ-Cl)]2. This reaction illustrates a promising synthetic strategy to access uncommon metal clusters. The structure of 1 features a rhomboidal Co2Sn2 core with strong metal-metal bonds between tin and cobalt and a weaker tin-tin interaction. Reaction of 1 with white phosphorus afforded [Ar'2Sn2Co2P4] (2), the first molecular cluster compound containing phosphorus, cobalt and tin.

Switching the Structure Type upon Ag Substitution: Synthesis and Crystal as well as Electronic Structures of Li12AgGe4

Li-rich compounds of metals and semimetals are interesting candidates for anode materials for rechargeable batteries. The investigation of the Li-rich part of the Li-Ag-Ge phase diagram led to the discovery of the new compound Li12AgGe4, which represents the Li-richest phase in the ternary phase system. The phase-pure compound is synthesized by high-temperature reaction of Li with stoichiometric amounts of premelted reguli of Ag and Ge. The structure was determined by single-crystal X-ray diffraction. Li12AgGe4 crystallizes in the Li13Si4 structure type in the space group Pbam (no. 55) with lattice parameters of a = 8.0420(2) Å, b = 15.1061(4) Å, and c = 4.4867(1) Å and exhibits the unique Zintl anion [AgGe2](7-)-iso(valence) electronic to the CO2 molecule-and Ge2 dumbbells. Li12AgGe4 adopts the atom packing of the lighter homologue Li13Si4 and not that of Li13Ge4 by the selective substitution of one out of seven Li positions by Ag. The calculation of the electronic structure indicates metallic property and the presence of strong covalent bonds between Ag and Ge in the linear triatomic Ge-Ag-Ge unit as well as π character between the Ge atoms of the dumbbells. The Ag-Ge bond order of the linear AgGe2 unit reaches its maximum at EF of Li12AgGe4 with full occupancy of all atomic positions (in contrast to the related Li12Ag1-xSi4), indicating that the formation of covalent Ag-Ge bonds is the driving force for the formation of the structure type.

A niobium-necked cluster [As3Nb(As3Sn3)]3− with aromatic Sn32−

A new Zintl cluster [As₃Nb(As₃Sn₃)]³⁻ was synthesized and characterized, in which an As₃ triangle and a bowl-type As₃Sn₃ ligand are bridged by a niobium atom. The Sn₃ ring is found to have σ-aromaticity featured by a delocalized Sn–Sn–Sn σ orbital.

'Pd20Sn13' revisited: crystal structure of Pd6.69Sn4.31

The crystal structure of the title compound was previously reported with composition 'Pd20Sn13' [Sarah et al. (1981 ▸). Z. Metallkd, 72, 517-520]. For the original structure model, as determined from powder X-ray data, atomic coordinates from the isostructural compound Ni13Ga3Ge6 were transferred. The present structure determination, resulting in a composition Pd6.69Sn4.31, is based on single crystal X-ray data and includes anisotropic displacement parameters for all atoms as well as standard uncertainties for the atomic coordinates, leading to higher precision and accuracy for the structure model. Single crystals of the title compound were obtained via a solid-state reaction route, starting from the elements. The crystal structure can be derived from the AlB2 type of structure after removing one eighth of the atoms at the boron positions and shifting adjacent atoms in the same layer in the direction of the voids. One atomic site is partially occupied by both elements with a Pd:Sn ratio of 0.38 (3):0.62 (3). One Sn and three Pd atoms are located on special positions with site symmetry 2. (Wyckoff letter 3a and 3b).