Cage Clusters Research Articles

Modulated synthesis of cesium phosphomolybdate encapsulated in hierarchical porous UiO-66 for catalysing alkene epoxidation.

The hybrid composite of cesium phosphomolybdate (CsPM) encapsulated in hierarchical porous UiO-66 (HP-UiO-66) was synthesized using a modulated solvothermal method. A variety of characterization results demonstrated that the pore size distribution of CsPM@HP-UiO-66 is broader than traditional microporous CsPM@UiO-66 and cesium phosphomolybdate clusters are uniformly distributed in the octahedral cages of HP-UiO-66. The catalytic properties of the hybrid composite were investigated in alkene epoxidation reaction with tert-butyl hydroperoxide (t-BuOOH) as an oxidant. CsPM@HP-UiO-66 showed much higher catalytic activity for the alkene epoxidation reaction in comparison with the reference catalysts and could be easily reused by centrifugation and recycled for at least ten runs without significant loss in catalytic activity. The superior catalytic activity and stability of the hybrid composite CsPM@HP-UiO-66 should be mainly attributed to the hierarchical pores in the support HP-UiO-66 promoting the diffusion of alkene molecules, the uniform distribution of highly active CsPM clusters in the octahedral cages of HP-UiO-66, the introduction of cesium cations to form the insoluble cesium phosphomolybdate and the strong metal-support interactions (SMSI) between the CsPM clusters and the HP-UiO-66 framework.

First-principles studies of the caged germanium clusters with gold doping and their adsorption on graphdiyne nanosheets

Graphdiyne (GDY) is a novel two-dimensional (2D) carbon material, and has the promising applications due to its unique structural features. A new series of GDY-based complexes was theoretically designed by adsorbing the AuGen (n = 14–16) clusters on GDY surface, namely AuGen-GDY complexes, and the geometries, electronic properties, and optical absorption spectra of these complexes were systematically studied using density functional theory calculations. Firstly, the stable structures of endohedral AuGen (n = 14–16) clusters were successfully found. The endohedral clusters possess high chemical stability, strong aromaticity, and delocalized 4c-2e and 5c-2e σ-bonds. Besides, the AuGen clusters can stably adsorb on triangular hole of conjugated GDY surface, by not only covalent bonds, but also weak interactions (e.g., van der Waals). Moreover, the addition of GDY reduced the HOMO-LUMO gaps and natural charges on Au atom, while GDY can effectively modulate the electronic structures of complexes. The optical absorption spectra of AuGen-GDY were discussed, and the type of the main electronic transitions is local excitation, which can be further confirmed by the hole-electron distributions. This study not only highlights the important of the adsorption of endohedral clusters on GDY surface, but also stimulates the further synthesis as potential candidate of novel GDY-based cluster-assembled materials.

Lanthanide-Incorporated Polyoxometalates Assembled from Mixed-Heteroatom-Oriented Three-Layered Cage Clusters.

Discovering innovative metal-oxo cluster materials with uncommon building blocks and exploiting their application potentiality are fairly challengeable. Here, we provide a novel type of lanthanide-incorporated polyoxometalates [H2N(CH3)2]10Na8H6{[Ln0.5/Na0.5(HGCA)(H2O)1.5]2[(BiO3)(SeO3)2W21O66]2}·36H2O [Ln = Eu3+ (1), Er3+ (2), H2GCA = α-glycolic acid] synthesized by a dual-heteroatom-directed synergetic strategy, which are established from two unique BiIII-SeIV heteroatom-oriented cylindrical three-layered [(BiO3)(SeO3)2W21O66]13- cage clusters integrated by lanthanide-organic groups. Compound 1 works as a fluorescence probe for high-sensitivity detection toward a neurotransmitter dopamine. This finding not only shows the enormous possibility and feasibility to create novel polyoxometalate building units by means of the self-categorization of different heteroatoms, which are subsequently employed for further assembly chemistry, but also provides a platform to exploit latent utilizations of polyoxometalate-based materials in the realm of detecting biological molecules.

Geometries and electronic structures of Pn − 1Al (n = 20–40) cages: A DFT study

Density functional theory calculations have been performed to study the geometrical structures and electronic properties of Pn − 1Al cage clusters in the range of n = 20–40 atoms. The structures of the cage Pn − 1Al are deformed at the doping position due to the doping of aluminum, but they are still cage shape in general. Most of these cage structures are composed of slightly distorted pentagons and hexagons. In the Pn − 1Al cage clusters studied in this work, P19Al has relatively excellent properties. The binding energy, ionization potential, electron affinity, electrostatic potential, hardness, aromaticity, bond length, HOMO and LUMO orbital, Mulliken charge and density of states of these clusters are discussed.

Synergetic storage of ammonia over Al quantum dots embedded graphene sheets: A first principles perspective

In view of the increasing energy demand and global warming, it is imperative to search for a renewable and environmental friendly fuel in lieu of non-renewable energy resources. Hydrogen stands out to be the best fuel as both, renewable and clean. Concerning the use of hydrogen as a fuel, its production as well as storage are current global challenges being worked on. In this article, a density functional theory based study is performed to identify the potential of supported Al cluster cages for ammonia storage. In this context, initially, stability of pristine and doped aluminum nanoclusters anchored on graphene sheet is evaluated following which thus supported stable nanoclusters are studied for the adsorption of NH3 to identify their storage capacity. For both, complexes and NH3 adsorbed complexes, Density of States (DOS), Charge Density Difference (CDD) and Bader charge analysis is done to understand their electronic properties.

Gamma-Ray-Induced Formation of Uranyl Peroxide Cage Clusters.

Aqueous solutions of lithium uranyl triperoxide, Li4[UO2(O2)3] (LiUT), were irradiated with gamma rays at room temperature and found to form the uranyl peroxide cage cluster, Li24[(UO2)(O2)(OH)]24 (Li-U24). Raman spectroscopy and 18O labeling were used to identify the Raman-active vibrations of LiUT. With these assignments, the concentration of LiUT was tracked as a function of radiation dose. A discrepancy between monomer removal and cluster formation suggests that the reaction proceeds by the assembly of an intermediate. Non-negative matrix factorization was used to separate Raman spectra into components and resulted in the identification of a unique intermediate species. Much of the conversion appears to be driven by water radiolysis products, particularly the hydroxyl radical. This differs from the 18O-labeled copper-catalyzed formation of U24, which progresses at a steady rate with no observation of intermediates. Li-U24 in solution decomposes at high radiation doses resulting in a solid insoluble product similar to Na-compreignacite, Na2(UO2)6O4(OH)6·7H2O, which contains uranyl oxyhydroxy sheets.

Synthesis of a monolayer fullerene network.

Two-dimensional (2D) carbon materials, such as graphene, have attracted particular attention owing to the exceptional carrier transport characteristics that arise from the unique π-electron system in their conjugated carbon network structure1-4. To complement zero-bandgap graphene, material scientists have devoted considerable effort to identifying 2D carbon materials5-8. However, it is a challenge to prepare large-sized single-crystal 2D carbon materials with moderate bandgaps5,9. Here we prepare a single-crystal 2D carbon material, namely monolayer quasi-hexagonal-phase fullerene (C60), with a large size via an interlayer bonding cleavage strategy. In this monolayer polymeric C60, cluster cages of C60 are covalently bonded with each other in a plane, forming a regular topology that is distinct from that in conventional 2D materials. Monolayer polymeric C60 exhibits high crystallinity and good thermodynamic stability, and the electronic band structure measurement reveals a transport bandgap of about 1.6 electronvolts. Furthermore, an asymmetric lattice structure endows monolayer polymeric C60 with notable in-plane anisotropic properties, including anisotropic phonon modes and conductivity. This 2D carbon material with a moderate bandgap and unique topological structure offers an interesting platform for potential application in 2D electronic devices.

Rational Design of Endohedral Superhalogens without Using Metal Cations and Electron Counting Rules.

Superhalogens, predicted 40 years ago, have attracted considerable attention due to their potential as building blocks of novel materials with various applications. While a large number of superhalogen clusters have been theoretically predicted and experimentally synthesized, they either require the use of a metal cation or electron counting rules. In particular, very rare endohedral cage clusters in defiance of the above requirements have been found to be superhalogens. In this work, motivated by recent experimental advances in endohedral cage clusters, we present a rational design principle for creating a new class of such superhalogens. Focusing on the chemical formula of A@Si20X20 (A = F, Cl, Br, I, BH4, BF4; X = H, F, Cl, Br, I, BO, CN, SCN, CH3), we use first-principles calculations to study 54 different clusters and show that these clusters possess electron affinities as high as 8.5 eV. Some of these clusters with X = BO and CN can even be stable as dianions, with large second electron affinity ∼2 eV. Similarly, Cl@C60 is found to be a superhalogen. This class of superhalogens is different from the conventional ones with chemical formula MXk+1, where X is a halogen and M is a cation with a formal +k oxidation state. Interestingly, the electron affinities of A@Si20X20 are almost independent of the central A moiety, but are guided by the functional group X. The potential of these endohedral superhalogens as electrolytes in Li-ion batteries is discussed.

Atomistic insights into the performance of thermodynamic inhibitors in the nucleation of methane hydrate

Figure TOC Comparison of methane hydrate nucleation process (a) without or (b) with EG molecules. Critical nucleus size increase under the influence of Thermodynamic hydrate inhibitors. • Hydrophobic groups from the alcohols could approach the initial hydrate cages and destroy initial clusters. • The –OH groups were observed to form hydrogen bonds with the cage clusters and even initiate a new hydrate cage. • Alcohols can increase the critical nucleus size of gas hydrate. Thermodynamic inhibitors are intensively used in oil and gas pipelines to modify the formation conditions of gas hydrate, preventing the blockage of pipelines. However, their kinetic performance in hydrate nucleation is largely unclear. Herein, the molecular interactions of the small molecules of ethylene glycol and methanol with hydrate clusters were investigated. It was found that the hydrophobic groups from the glycols could approach the initial hydrate cages, thereby constricting the regional distribution of adjacent water molecules; thus, they functioned in the same way as the guest molecules that transiently helped to stabilize the water framework. However, these glycols would eventually dissolve into the solution to stay at the water/nanobubble interface; this would consequently destroy the initial cages upon losing the constraint from the surrounding hydrophobic molecules. In addition, the –OH groups were observed to form hydrogen bonds with the cage clusters and even initiate a new hydrate cage; however, they cannot stably reside there due to different atom coordination. Notably, these glycols can increase the critical nucleus size, which is considered the intrinsic mechanism of thermodynamic inhibition. Our results provide atomistic insights into the performance of glycols in the kinetic nucleation of gas hydrates and can help understand the interactions between guest and host molecules in the presence of hydrophobic and hydrophilic functional groups.

First-principles study of luminescence of fullerene-like clusters

Thermally activated delayed fluorescence (TADF), a unique molecular fluorescence mechanism, plays a key role in designing emitters of high efficiency. Carbon fullerenes such as C<sub>60</sub> and C<sub>70</sub> exhibit strong TADF with intensity even higher than that of the prompt fluorescence, owing to their long lifetimes of triplet state and modest singlet-triplet energy gaps. Thus, there arises the intriguing question whether other fullerene-like clusters can also have fluorescence and host the TADF effect. In this work, by time-dependent density functional theory (TD-DFT) calculations, we explore the excited-states of the experimentally reported boron nitride cage clusters B<sub>12</sub>N<sub>12</sub>, B<sub>24</sub>N<sub>24</sub> and B<sub>36</sub>N<sub>36</sub>, as well as compound clusters B<sub>12</sub>P<sub>12</sub>, Al<sub>12</sub>N<sub>12</sub> and Ga<sub>12</sub>N<sub>12</sub> with the same geometry as B<sub>12</sub>N<sub>12</sub>. Using the HSE06 hybrid functional, the predicted energy gaps of these fullerene-like clusters are obtained to range from 2.83 eV to 6.54 eV. They mainly absorb ultraviolet light, and their fluorescence spectra are all in the visible range from 405.36 nm to 706.93 nm, including red, orange, blue, and violet emission colors. For the boron nitride cages, the energy gap of excited states increases with the cluster size increasing, accompanied by a blue shift of emission wavelength. For the clusters with B<sub>12</sub>N<sub>12</sub> geometry and different elemental compositions, the excited energy gap decreases as the atomic radius increases, resulting in a red shift of emission wavelength. In addition, the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) of these compound cage clusters are distributed separately on different elements, resulting in small overlap between HOMO and LUMO wavefunctions. Consequently, these fullerene-like clusters exhibit small singlet-triplet energy differences below 0.29 eV, which is beneficial for the intersystem crossing between the excited singlet state and triplet state, and hence promoting the TADF process. Our theoretical results unveil the fluorescence characteristics of cage clusters other than carbon fullerenes, and provide important guidance for precisely modulating their emission colors by controlling the cluster sizes and elemental compositions. These experimentally feasible fullerene-like compound clusters possess many merits as fluorophors such as outstanding stabilities, non-toxicity, large energy gap, visible-light fluorescence, and small singlet-triplet energy gap. Therefore, they are promising luminescent materials for applications in display, sensors, biological detection and labelling, therapy, and medicine.

Steering Lu3N clusters in C76-78 cages: cluster configuration dominated by cage transformation.

While the strong interaction between the internal unit and the fullerene cage inside metallofullerenes is widely acknowledged, how the cage transformation interacts with the cluster configuration remains elusive. For this purpose, we herein synthesized three metallofullerene molecules with an easy-to-compare cluster configuration and cage arrangement, namely Lu3N@Cs(17 490)-C76, Lu3N@C2(22 010)-C78, and Lu3N@D3h(5)-C78. The three lutetium-based nitride clusterfullerenes (NCFs) with small C76-78 carbon cages were synthesized by a modified arc-discharge method and their structures were unambiguously confirmed by X-ray crystallography. Notably, the cage transformation from Cs(17 490)-C76 to C2(22 010)-C78via a simple C2-unit insertion leads to a remarkable configuration change of the encapsulated Lu3N cluster from an unusual asymmetric plane to a common symmetric one. This close correlation between the cluster configuration and cage transformation is further confirmed by the pyramidal Lu3N cluster in Lu3N@D3h(5)-C78 other than the symmetric planar Lu3N unit in Lu3N@C2(22 010)-C78, as a result of an even larger difference in the cage arrangement. Astonishingly, such a cluster shrinkage, accompanied by an increase in the cage size from Cs(17 490)-C76 to D3h(5)-C78, is dramatically opposite to the cluster expansion with cage elongation found in La2C2- or Y2C2-based metallofullerenes.

Stimuli-Responsive and Structure-Adaptive Three-Dimensional Gold(I) Cluster Cages Constructed via "De-aurophilic" Interaction Strategy.

Self-assembly of three-dimensional (3D) metallosupramolecular cages has drawn increasing attention for their potential to interconvert between different architectures due to the dynamic and reversible features of the coordination bond. These supramolecular transformations can provide unique approaches for the construction of stimuli-responsive supramolecular model systems to mimic biological transformation processes. While gold(I) clusters have attracted much interest due to their propensity to exhibit aurophilic interactions, the construction of 3D gold(I) cluster cages has remained a challenging and daunting task. Here, we proposed a "de-aurophilic" interaction strategy, which involves the prevention of aurophilic interaction formation between the basic [(μ3-S)Au3]+ units, to construct 3D gold(I) cluster cages. Through the judicious design of diphosphine ligands, an unprecedented class of gold(I) cluster cages with adaptive structures has been constructed. These gold(I) cluster cages are found to show intriguing stimuli-responsive structure transformation and interconversion. This work not only provides a strategy for the design and construction of novel 3D supramolecular cages based on cluster nodes but also offers a paradigm to study the stimuli-responsive structural interconversion between the unique structures of these gold(I) cluster cages.

Nanoblackberries of {W72Fe33} and {Mo72Fe30}: Electrocatalytic Water Reduction.

The reversible self-assembly of a {Mo72Fe30} cluster into nanoblackberries in a dilute solution of the relevant crystalline compound [Mo72Fe30O252(CH3COO)12{Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O)91]·150H2O ({Mo72Fe30}cryst) was demonstrated by Liu, Müller, and their co-workers as a landmark discovery in the area of polyoxometalate chemistry. We have described, in the present work, how these ∼2.5 nm nano-objects, {M72Fe30} (M = W, Mo) can be self-assembled into nanoblackberries irreversibly, leading to their solid-state isolation as the nanomaterials Fe3[W72Fe30O252(CH3COO)2(OH)25(H2O)103]·180H2O ({W72Fe33}NM) and Na2[Mo72Fe30O252(CH3COO)4(OH)16(H2O)108]·180H2O ({Mo72Fe30}NM), respectively (NM stands for nanomaterial). The formulations of these one-pot-synthesized nanoblackberries of {W72Fe33}NM and {Mo72Fe30}NM have been established by spectral analysis including Raman spectroscopy, elemental analysis including ICP metal analysis, volumetric analysis (for iron), microscopy techniques, and DLS studies. The thermal stability of the tungsten nanoblackberries {W72Fe33}NM is much higher than that of its molybdenum analogue {Mo72Fe30}NM. This might due to the extra three ferric (Fe3+) ions per {W72Fe30} cluster in {W72Fe33}NM, which are not part of the {W72Fe30} cluster cage but are placed between two adjacent clusters (i.e., each cluster has six surrounding 0.5Fe3+) to form this self-assembly. The isolated blackberries behave like an inorganic acid, a water suspension of which shows pH values of 3.9 for {W72Fe33}NM and 3.7 for {Mo72Fe30}NM because of the deprotonation of the hydroxyl groups in them. We have demonstrated, for the first time, a meaningful application of these inexpensive and easily synthesized nanoblackberries by showing that they can act as electrocatalysts for the hydrogen evolution reaction (HER) by reducing water. We have performed detailed kinetic studies for the electrocatalytic water reduction catalyzed by {W72Fe33}NM and {Mo72Fe30}NM in a comparative study. The relevant turnover frequencies (TOFs) of {W72Fe33}NM and {Mo72Fe30}NM (∼0.72 and ∼0.45 s-1, respectively), the overpotential values of {W72Fe33}NM and {Mo72Fe30}NM (527 and 767 mV, respectively at 1 mA cm-2), and the relative stability issues of the catalysts indicate that {W72Fe33}NM is reasonably superior to {Mo72Fe30}NM. We have described a rationale of why {W72Fe33}NM performs better than {Mo72Fe30}NM in terms of catalytic activity and stability.

Molecular behavior of CO2 hydrate growth in the presence of dissolvable ionic organics

Hydration-based techniques involve hydrate formation in complicated systems containing ions and organics. Consequently, it is necessary to understand the molecular behavior of hydrate nucleation and growth in such solutions. This work shows that the hydrate-growth rate in a system containing methylene blue molecules does not necessarily accelerate on increasing the subcooling. Unexpected amorphous cage clusters were observed at a lower temperature of 240 K. To the best of our knowledge, this is the first study to propose that these amorphous clusters act as mass transfer barriers disturbing the agglomeration of solutes. Herein, hydrate growth was accompanied with the exclusion of methylene blue molecules. Although methylene blue can instantaneously reside in the cavity a half-cage structure, they were subsequently replaced by CO2 molecules. Notably, chloride ions were observed to participate in cage building (42510, 512, and 51262 cages) by bonding with the oxygen atoms of the surrounding water molecules. This phenomenon shows an interaction between the methylene blue molecules and hydrate cages during the exclusion process. These results support the current understanding on hydrate formation in the presence of ion-containing organics and could help improve kinetics-dependent applications in separation process.

Small Amount Makes a Big Difference: Critical (n - 1)d Valence Orbitals of Heavy Alkaline Earth Metals inside Cage Clusters.

Heavy alkaline earth metals (Aes) are usually considered to engage in chemical bonding by donating the two electrons on ns atomic orbitals (AOs). In this work, a series of typical endohedrally doped cage clusters Ae@cage (Ae = Ca, Sr, Ba; cage = C32, C74, C94, B40, Si20, Sn12, Au16) were thoroughly investigated by means of density functional theory calculations. We found that their occupied molecular orbitals have ∼1 to 14% contributions from Ae-(n - 1)d AOs due to electron back-donation from the cage. Though the amount is small, it is hard to ignore: with the d orbitals, all these endohedral clusters exhibit obviously shortened Ae-cage distances, greatly enhanced encapsulation stabilities, changed highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps, and much lowered Ae valences far from ideal +2. Evidently, the valence orbitals of Ca/Sr/Ba in these systems should include both ns and (n - 1)d. By disclosing the critical role of unnoticed metal orbitals, our work provides completely new insights into the cluster field.

Searching for cluster Lego blocks for three-dimensional and two-dimensional assemblies

Assemblies of clusters have been sought for a long time to synthesize new materials with unprecedented physical phenomena or to integrate desired functionalities for technological applications. However, except for some carbon fullerenes and ligated clusters, little progress has been made in achieving assemblies of other clusters due to their tendency for agglomeration. Here we study interaction in dimers of 34 well-studied endohedrally doped clusters (i.e., superatoms) and propose the criteria for such superatoms to be potential building blocks in terms of surface coordination, charge state, distribution of the highest occupied molecular orbital, and electronic as well as atomic shell (double-shell) closure. From these results, the endohedrally doped $\mathrm{Ti}@{\mathrm{Ge}}_{16}$ cage cluster stands out as a suitable building block to assemble solids and nanostructures with outstanding stabilities and diverse physical properties. We report here the finding of antiferromagnetic Mott insulator in metal intercalated two-dimensional crystal of such cluster. Our study provides essential knowledge for achieving stable cluster assemblies of different dimensionalities with precisely tailorable electronic structure for device applications.

Local Distortions and Metal–Semiconductor–Metal Transition in Quasi-One-Dimensional Nanowire Compounds AV3Q3Oδ (A = K, Rb, Cs and Q = Se, Te)

Metal cluster compounds have garnered renewed interest in the search for novel superconductors and topological semimetals owing to structural instabilities of metal-cluster geometries and broken symmetries. Here we synthesized needle-like crystals of the V-cluster-based quasi-one-dimensional (Q1D) materials AV3Q3Oδ (A = K, Rb, Cs, Q = Se, Te) which can also be viewed as being composed of parallel nanowires. We examine how changes in their average and local structure control their electronic properties. All compounds crystallize in the TlFe3Te3-type structure (P63/m space group) with infinite (V3Q3)− double-walled columnar chains separated by A+ cations. Our single-crystal and synchrotron powder diffraction studies indicate oxygen atoms partially occupy the center site of the V6 octahedral metal cluster cages in KV3Te3O0.33, RbV3Te3O0.32, and CsV3Te3O0.35, whereas KV3Se3 is structurally oxygen-free. Our synchrotron X-ray pair distribution function (PDF) analyses indicate that the oxygen-free V6 cluster octahedra in KV3Se3 are highly distorted perpendicular to the chain direction even at room temperature, reducing the symmetry of the average structure from hexagonal P63/m to monoclinic P21/m. Our theoretical calculation supports this P21/m distortion and suggests the structure further distorts to P21 or P21/c at lower temperatures. In contrast, the oxygen-centered V-cluster in KV3Te3O0.33 exhibits a V3-triangle-trimerization along the chain direction. This feature is discernible from the local PDF and is consistent with lattice dynamical calculations based on density functional theory. Resistivity measurements indicate that KV3Se3 exhibits metallic behavior, whereas a dramatic metal–semiconductor–metal transition emerges in KV3Te3O0.33, RbV3Te3O0.32, and CsV3Te3O0.35 because of oxygen disorder and changes in local structure captured from our electronic structure analyses of the Fermi surface. Our investigation of the AV3Q3Oδ family demonstrates the importance of understanding local changes in structure driven by electronic instabilities, which can guide the search for new quantum materials in other low-dimensional cluster-compound materials.

A Peanut‐Like Sb‐Embedded Polyoxoniobate Cage for Hydrolytic Decomposition of Chemical Warfare Agent

AbstractA Sb‐embedded polyoxoniobate has been originally synthesized under hydrothermal conditions. Particularly, the peanut‐like [Sb2Nb24O72]18− cluster cage in 1 with C2h symmetry is composed of two 9‐nuclear {SbNb9O33} motifs and one {Nb6O24} crown‐shaped ring. The compound 1 present the novel structure of Sb‐substituted sandwich‐type polyoxoniobate with antimoniobate cluster cage. Decomposition catalytic studies indicate that compound 1 exhibits good hydrolytic activity and stability on the degradation of nerve agent simulant dimethylphosphonate (DMMP).

Atomically Precise Insights into Metal–Metal Bonds Using Comparable Endo-Units of Sc 2 and Sc 2 C 2

The precise identification of metal–metal bonds is critical to fully understanding the nature of metal–metal bonding but remains a fundamental challenge. Herein, we show the essence of Sc–Sc bonds ...

Cluster expansion and vertex substitution pathways in nickel germanide Zintl clusters.

We describe the reactivity of the hypersilyl-functionalized Zintl cluster salt K[Ge9(Hyp)3] towards the nickel reagents Ni(COD)2 and Ni(Cp)2, which gives rise to markedly different complexes. In the case of Ni(COD)2 (COD = 1,5-cyclooctadiene), a dianionic sandwich-like cluster [Ni{Ge9(Hyp)3}2]2- (1) was obtained, in line with a simple ligand substitution reaction of COD by [Ge9(Hyp)3]-. By contrast, when an analogous reaction with Ni(Cp)2 (Cp = cyclopentadienyl) was performed, vertex substitution of the [Ge9(Hyp)3]- precursor was observed, giving rise to the nine-vertex nido-cluster (Cp)Ni[Ge8(Hyp)3] (2). This is the first instance of vertex substitution at a hypersilyl-functionalized Zintl cluster cage. The electrochemical behavior of these compounds was explored and showed reversible redox behaviour for both clusters.