Solution dynamics and gas-phase chemistry of Pd2@Sn18 4-

[CuSn5Sb3]24- as a dual spherical-spherical aromatic heterometallic cluster bridged via an antiaromatic Cu2Sn2 motif

The formation of [CuSn5Sb3]24- serves as a template for heterometallic species to evaluate the resulting aromatic properties. Our results indicated that the spherical aromatic characteristics of the [CuSn5Sb3]2- building unit remained in the overall aggregate, featuring an induced shielding cone from different orientations of the external field. Furthermore, the isostructural and isoelectronic [Sn18]4- cluster sustained similar characteristics, which supported the notion of a direct relationship between [CuSn5Sb3]24- and [Sn18]4- cluster dimers. This indicated the suitable application of the pseudo-element concept relating similar connectivity between isoelectronic atoms, which could lead to further heterometallic clusters.

[Ba4@Sn56]36- as a Main-Group Second-Order Superatom. Interpenetrated Dodecahedrons as a Three-Dimensional Cluster-of-Clusters Structure

Superatomic clusters are relevant species to further understanding of bonding and structural properties of atomically precise molecular nanoparticles. Here, we explore the characteristics of ligand-free [Ba4@Sn56]36- Zintl-ion, as a three-dimensional aggregate of clusters featuring four fused Ba@Sn19 building units as an extension of the understanding in linear and cyclic superatomic cluster arrays. We provide a rational picture of the electronic shell in [Ba4@Sn56]36- as a cluster-of-clusters motif through the recently introduced second-order superatom approach, as a three-dimensional aggregation of superatomic clusters where their shells are able to interact. The electronic structure features both tangential and radial shells from the four building Ba@Sn19 units, leading to a set of 1S'21P'61D'101F'14 and higher angular momentum shells and a second set of 2S'22P'62D'102F'142G'8 second-order shells. Thus, the current approach serves to encourage the rationalization of molecular materials conceived from cluster building blocks toward a rational guide for synthetic efforts.

Ligand-free supermolecules: [Pd2@Ge18]4- and [Pd2@Sn18]4- as multiple-bonded Zintl-ion clusters based on Pd@Ge9 and Pd@Sn9 assembled units

Understanding intercluster bonding interactions is important in the rational synthesis of building blocks for molecular materials. Such characteristics have been developed for coinage metal clusters resembling single-, double-, and triple-bonded species, coined as supermolecules. Herein, we extend such an approach for understanding main-group clusters, thus evaluating [Pd2@E18]4- clusters (E = Ge, Sn) involving the fusion of parent spherical aromatic [Pd@E12]2- building units. Our results indicate intercluster bonding provided by contribution from 2P and 1G shells centered at each building motif, leading to an overall bond order of 2.70 and 2.31 for [Pd2@Ge18]4- and [Pd2@Sn18]4-, respectively. In addition, 119Sn-NMR patterns were evaluated to complement the experimental characterization of a single peak owing to the insolution fluxional behavior of [Pd2@Sn18]4- as three peaks owing to the three sets of unique Sn atoms within the structure. Magnetic response properties revealed that spherical aromatic characteristics from parent [Pd@E12]2- building units are retained in the overall [Pd2@E18]4- oblate cluster as two spherical aromatic units. Hence, the notion of superatomic molecules is extended to Zintl-ion clusters, favoring further rationalization for the fabrication of cluster-assembled solids.

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.

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.

Current advances in tin cluster chemistry

This perspective summarizes highlights and most recent advances in tin cluster chemistry, thereby addressing the whole diversity of (mostly) discrete units containing tin atoms. Although being a (semi-)metallic element, tin is in the position to occur both in formally positive or negative oxidation states in these molecules, which causes a broad range of fundamentally different properties of the corresponding compounds. Tin(iv) compounds are not as oxophilic and not as prone to hydrolysis as related Si or Ge compounds, hence allowing for easier handling and potential application. Nevertheless, their reactivity is high due to an overall reduction of bond energies, which makes tin clusters interesting candidates for functional compounds. Beside aspects that point towards bioactivity or even medical applications, materials composed of naked or ligand-protected tin clusters, with or without bridging ligands, show interesting optical, and ion/molecule-trapping properties.

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-.

[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.

The cyclo-Sb6 ring in the [Sb6(RuCp*)2]2− ion

The [Sb₆(RuCp*)₂]²⁻ anion represents the first example of a Zintl cluster with a boat-like cyclo-Sb₆ subunit and the first ruthenium polyantimonide complex. The anion is dynamic in solution and fragments in the gas phase. Structural parameters and DFT calculations suggest the possibility of SbSb double bond character.

Formation of the intermetalloid cluster [AgSn18]7− – the reactivity of coinage metal NHC compounds towards [Sn9]4−

A series of novel polyanionic coinage metal NHC Zintl clusters [NHC^DippM(η⁴-Sn₉)]³⁻ are obtained from the reaction of [Sn₉]⁴⁻ with NHC^DippMCl (M: Cu, Ag, Au; Dipp: diisopropylphenyl) in liquid ammonia. For M = Ag a larger intermetalloid Ag-bridged nonastannide dimer [(η⁴-Sn₉)Ag(η¹-Sn₉)]⁷⁻ forms.

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.

Scalar and Spin-Orbit Relativistic Corrections to the NICS and the Induced Magnetic Field: The case of the E12(2-) Spherenes (E = Ge, Sn, Pb)

Can relativistic effects modify the NICS and the B(ind) values? In this manuscript we evaluate the relativistic corrections incorporated via the zeroth-order regular approximation to the calculations of nucleus-independent chemical shifts and the induced magnetic field (B(ind)) in the E12(2-) spherenes (E = Ge, Sn, Pb). We found that both electron delocalization descriptors are strongly affected by the relativistic corrections. For instance, for plumbaspherene, the difference in values from the nonrelativistic to the relativity-included calculation is almost 40 ppm! Our results show that the changes observed in the NICS and B(ind) values in the title cages are a consequence of the treatment of the relativistic effects. If these effects are included as scalar or spin-orbit calculations, then we can establish the next trend: Ge12(2-) is a nonaromatic species, Sn12(2-) is a low aromatic species, and Pb12(2-) is strongly aromatic, according to calculated NICS and B(ind) values. Thus, any prediction of electron delocalization in molecules containing heavy elements without considering an adequate treatment for relativistic effects may lead to an erroneous chemical interpretation.

Coordination of Tri-Substituted Nona-Germanium Clusters to Cu(I) and Pd(0)

The recently developed approach for the rational functionalization of deltahedral nona-germanium clusters Ge9(4-) with three substituents to form Ge9R3(-) (R = Si(SiMe3)3) in large amounts has made the latter a convenient starting material for further reactivity studies. Reported here are the synthesis, structures, and solution studies of two compounds where Ge9R3(-) are used as ligands to transition metals, [(Ge9R3)Cu(I)(Ge9R3)Cu(I)PPh3] (1) and [(Ge9R3)Pd(0)(Ge9R3)](2-) (2). The former adds to the families of anionic [(Ge9R3)M(I)(Ge9R3)](-) (M(I) = Cu, Ag, and Au) as a neutral member and of the neutral [(Ge9R3)M(II)(Ge9R3)] (M(II) = Zn, Cd, and Hg), while the latter represents the first compound involving a metal from group 10.

[V@Ge8As4]3− and [Nb@Ge8As6]3−: encapsulation of electron-poor transition metal atoms

The first known M–As–Ge clusters, [V@Ge₈As₄]³⁻ and [Nb@Ge₈As₆]³⁻, exhibit non-deltahedral topologies, with “V⁵⁺” being the hardest cation ever embedded in endohedral Zintl anions.

Making practical use of the pseudo-element concept: an efficient way to ternary intermetalloid clusters by an isoelectronic Pb(-)-Bi combination

Syntheses of [K([2.2.2]crypt)](+) salts of binary Pb-Bi Zintl anions and their reaction with ZnPh(2) or Ni(cod)(2), yielding ternary intermetalloid Ni-Pb-Bi or Zn-Pb-Bi clusters, proved the use of binary precursors with fully isoelectronic atoms as an efficient and thus valuable synthetic approach to this class of clusters. (207)Pb NMR and ESI mass spectra provided insight into the solution behavior of the binary or ternary cages.

[Ge9{Si(SiMe3)3}3{SnPh3}]: a tetrasubstituted and neutral deltahedral nine-atom cluster

Reaching neutral territory: The title compound, the first tetrasubstituted deltahedral Zintl cluster, is no longer an ion (see picture; Ge green, Si purple, Sn blue). It is a neutral molecule formed by a reaction of the trisilylated anion with Ph(3) SnCl.

Synthesis of nine-atom deltahedral Zintl ions of germanium and their functionalization with organic groups

Although the first studies of Zintl ions date between the late 1890's and early 1930's they were not structurally characterized until many years later. Their redox chemistry is even younger, just about ten years old, but despite this short history these deltahedral clusters ions E9(n-) (E = Si, Ge, Sn, Pb; n = 2, 3, 4) have already shown interesting and diverse reactivity and have been at the forefront of rapidly developing and exciting new chemistry. Notable milestones are the oxidative coupling of Ge9(4-) clusters to oligomers and infinite chains, their metallation, capping by transition-metal organometallic fragments, insertion of a transition-metal atom at the center of the cluster which is sometimes combined with capping and oligomerization, addition of main-group organometallic fragments as exo-bonded substituents, and functionalization with various organic residues by reactions with organic halides and alkynes. This latter development of attaching organic fragments directly to the clusters has opened up a new field, namely organo-Zintl chemistry, that is potentially fertile for further synthetic explorations, and it is the step-by-step procedure for the synthesis of germanium-divinyl clusters described herein. The initial steps outline the synthesis of an intermetallic precursor of K4Ge9 from which the Ge9(4-) clusters are extracted later in solution. This involves fused-silica glass blowing, arc-welding of niobium containers, and handling of highly air-sensitive materials in a glove box. The air-sensitive K4Ge9 is then dissolved in ethylenediamine in the box and then alkenylated by a reaction with Me3SiC≡CSiMe3. The reaction is followed by electrospray mass spectrometry while the resulting solution is used for obtaining single crystals containing the functionalized clusters [H2C=CH-Ge9-CH=CH2](2-). For this purpose the solution is centrifuged, filtered, and carefully layered with a toluene solution of 18-crown-6. Left undisturbed for a few days, the so-layered solutions produced orange crystalline blocks of [K(18-crown-6)]2[Ge9(HCCH2))2]•en which were characterized by single-crystal X-ray diffraction. The process highlights standard reaction techniques, work-up, and analysis towards functionalized deltahedral Zintl clusters. It is hoped that it will help towards further development and understanding of these compounds in the community at large.

Photoelectron spectroscopic and computational studies of the Pt@Pb₁₀⁻¹ and Pt@Pb₁₂¹⁻/²⁻ anions

A combination of anion photoelectron spectroscopy and density functional theory calculations has elucidated the geometric and electronic structure of gas-phase endohedral Pt/Pb cage cluster anions. The anions, Pt@Pb₁₀⁻¹ and Pt@Pb₁₂¹⁻ were prepared from "preassembled" clusters generated from crystalline samples of [K(2,2,2-crypt)]₂[Pt@Pb₁₂] that were brought into the gas phase using a unique infrared desorption/photoemission anion source. The use of crystalline [K(2,2,2-crypt)]₂[Pt@Pb₁₂] also provided access to K[Pt@Pb(n)](-) anions in the gas phase (i.e., the K⁺ salts of the Pt@Pb(n)²⁻ anions). Anion photoelectron spectra of Pt@Pb₁₀⁻¹, Pt@Pb₁₂¹⁻, and K[Pt@Pb₁₂]¹⁻ are presented. Extensive density functional theory calculations on Pt@Pb₁₀³⁻/²⁻/¹⁻/⁰ and Pt@Pb₁₂²⁻/¹⁻ provided candidate structures and anion photoelectron spectra for Pt@Pb₁₀⁻¹ and Pt@Pb₁₂¹⁻. Together, the calculated and measured photoelectron spectra show that Pt@Pb₁₀⁻¹ and Pt@Pb₁₂²⁻/¹⁻ endohedral complexes maintain their respective D(4d) and slightly distorted I(h) symmetries in the gas phase even for the charge states with open shell character. Aside from the fullerenes, the Pt@Pb₁₂²⁻ endohedral complex is the only bare cluster that has been structurally characterized in the solid state, solution, and the gas phase.