New Molecular Cage Clusters of Pb by Encapsulation of Mg

Endohedral clusters formed from the Zintl ions Pb₁₀^2? and Pb₁₂^2? are particularly stable and therefore suitable for the assembly of larger aggregates. We therefore investigate the formation of Mg‐doped lead clusters in the gas phase, and demonstrate that a whole series of new molecular cage clusters of lead can be generated by encapsulation of magnesium. Mass spectrometry reveals that some of the cluster compounds, with one and two Mg atoms attached to the lead clusters, display large intensities compared to the pure lead clusters, which indicates that the compound clusters are particularly stable. The magnesium‐doped lead‐cluster assemblies were further analyzed within a molecular‐beam electric deflection experiment. Almost vanishing permanent dipole moments for MgPb_10–16 support the idea that a single Mg atom could be encapsulated within a highly symmetric lead cage, which results in structures with not only enhanced stability but also increased symmetry compared to the pure lead clusters Pb_N.     

Rationally functionalized deltahedral zintl ions: synthesis and characterization of [Ge9-ER3]3-, [R3E-Ge9-ER3]2-, and [R3E-Ge9-Ge9-ER3]4- (E=Ge, Sn; R=Me, Ph)

Six new derivatized deltahedral Zintl ions have been synthesized by reactions between the known Zintl ions Ge(9) (n-) with the halides R(3)EX and/or the corresponding anions R(3)E(-) for E=Ge or Sn. This rational approach is based on our previous discovery that these derivatization reactions are based on nucleophilic addition to the clusters. All species were structurally characterized as their salts with potassium countercations sequestered in 2,2,2-crypt or [18]crown-6 ether. The tin-containing anions were characterized also in solutions by (119)Sn NMR spectroscopy. The reaction types for such substitutions and the structures of the new anions are discussed.     

On the Formation of Intermetalloid Clusters: Titanocene(III)diammin as a Versatile Reactant Toward Nonastannide Zintl Clusters

The reactivity of TiCp₂Cl₂ (d⁰) towards Zintl clusters was studied in liquid ammonia (Cp=cyclopentadienyl). Reduction of Ti^IVCp₂Cl₂ and ligand exchange led to the formation of [Ti^IIICp₂(NH₃)₂]⁺, also obtainable by recrystallization of [CpTi^IIICl]₂. Upon reaction with [K₄Sn₉], ligand exchange leads to [TiCp₂(η¹‐Sn₉)(NH₃)]^3?. A small variation of the stoichiometry led to the formation of [Ti(η⁴‐Sn₈)Cp]^3?, which cocrystallizes with [TiCp₂(NH₃)₂]⁺ and [TiCp₂(η¹‐Sn₉)(NH₃)]^3?. Finally, the large intermetalloid cluster anion [Ti₄Sn₁₅Cp₅]^n? (n=4 or 5) was obtained from the reaction of K₁₂Sn₁₇ and TiCp₂Cl₂ in liquid ammonia. The isolation of three side products, [K([18]crown‐6)]Cp, [K([18]crown‐6)]Cp(NH₃), and [K([2.2]crypt)]Cp, suggests a stepwise elimination of the Cl^? and Cp^? ligands from TiCp₂Cl₂ and thus gives a hint to the mechanism of the product formation in which [Ti(η⁴⁺²‐Sn₈)Cp]^3? has a key role.     

[(Me3Si)Si]3EtGe9Pd(PPh3), a Pentafunctionalized Deltahedral Zintl Cluster: Synthesis,Structure, and Solution Dynamics

The title compound, which has a ten‐atom deltahedral cluster core of Ge₉Pd, was synthesized through insertion of Pd(PPh₃) into the tetrasubstituted nona‐germanium cluster [(Me₃Si)Si]₃EtGe₉ 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 Ge₉Pd 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. ¹H and ¹³C NMR spectroscopy show that, in contrast to the parent tetra‐substituted [(Me₃Si)Si]₃EtGe₉, the new compound does not exhibit dynamics. Relativistic DFT calculations are used to explain the differences.     

Cluster Fusion: Face‐Fused Nine‐Atom Deltahedral Clusters in [Sn14Ni(CO)]4−

The title anion was synthesized by heating dimethylformamide (DMF) solution of the known Ni‐centered and Ni(CO)‐capped tin clusters [Ni@Sn₉Ni(CO)]^3?. The new anion represents the first example of face‐fused nine‐atom molecular clusters. The two clusters are identical elongated tricapped trigonal prisms of nido‐[Sn₈Ni(CO)]^6? with nickel at one of the capping positions. They are fused along a triangular face adjacent to a trigonal prismatic base and made of two Sn and one Ni atoms. The new anion is structurally characterized by single‐crystal X‐ray diffraction in the compound (K[222‐crypt])₄[Sn₁₄Ni(CO)]?DMF. Its presence in solution is corroborated by electrospray mass spectrometry.     

Synthesis and Reactivity Studies of Amido-Substituted Germanium(I)/Tin(I) Dimers and Clusters

Three amide ligands of varying steric bulk and electronic properties were utilized to prepare a series of amido-germanium(II)/tin(II) halide compounds, (LEX)_n, (L= -N{B(DipNCH)₂}(SiMe₃), ^TBoL; -N{B(DipNCH)₂}(SiPh₃), ^PhBoL; -N(Dip)(tBu), ^DBuL; Dip=C₆H₃iPr₂-2,6; E=Ge or Sn; X=Cl or Br; n=1 or 2). Reductions of these with a magnesium(I) dimer, {(^MesNacnac)Mg}₂ (^MesNacnac=[(MesNCMe)₂CH]⁻, Mes=mesityl), afforded singly bonded amido-digermynes (^TBoLGe−Ge^TBoL and ^PhBoLGe−Ge^PhBoL), and an amido-distannyne (^PhBoLSn−Sn^PhBoL), in addition to several low-valent, amido stabilized tetrel–tetrel bonded cluster compounds, (^DBuLGe)₄, (^DBuLSn)₆ and Sn₅(^TBoL)₄. The nature of the products resulting from these reactions was largely dependent on the steric bulk of the amide ligand employed. Cluster (^DBuLGe)₄ possessed an unusual folded butterfly structure, the bonding and electronic of which were examined using DFT calculations. Reactions of the amido-germanium(I) compounds with H₂ were explored, and gave rise to the amido-digermene, ^TBoL(H)Ge=Ge(H)^TBoL and the cyclotetragermane, {^DBuL(H)Ge}₄. Reactions of (^DBuLGe)₄ with a series of unsaturated small molecule substrates yielded ^DBuLGeOGe^DBuL, ^DBuLGe(μ-C₂H₄)₂Ge^DBuL and ^DBuLGe(μ-1,4-C₆H₈)(μ-1,2-C₆H₈)Ge^DBuL. The latter results imply that (^DBuLGe)₄ can act as a masked source of the digermyne ^DBuLGeGe^DBuL in these reactions. All further reactivity studies indicated that the germanium(I) compounds exhibit a “transition-metal-like” behavior, which is closely related to that previously described for bulky digermynes and related compounds.     

Two‐, One‐, and Zero‐Dimensional Elemental Nanostructures Based on Ge9‐Clusters

We investigated the structural principles of novel germanium modifications derived by oxidative coupling of Zintl‐type [Ge₉]^4?clusters in various ways. The structures, stabilities, and electronic properties of the predicted {²_∞[Ge₉]_n} sheet, {¹_∞[Ge₉]_n} nanotubes, and fullerene‐like {Ge₉}_n cages were studied by using quantum chemical methods. The polyhedral {Ge₉}_n cages are energetically comparable with bulk‐like nanostructures of the same size, in good agreement with previous experimental findings. Three‐dimensional structures derived from the structures of lower dimensionality are expected to shed light on the structural characteristics of the existing mesoporous Ge materials that possess promising optoelectronic properties. Furthermore, 3D networks derived from the polyhedral {Ge₉}_n cages lead to structures that are closely related to the well‐known LTA zeolite framework, suggesting further possibilities for deriving novel mesoporous modifications of germanium. Raman and IR spectra and simulated X‐ray diffraction patterns of the predicted materials are given to facilitate comparisons with experimental results. The studied novel germanium modifications are semiconducting, and several structure types possess noticeably larger band gaps than bulk α‐Ge.     

Endohedral zintl ions: intermetalloid clusters

Tetrels can be regarded as most promising candidates for the construction of larger clusters. Recent examples have shown that larger clusters are particularly stable if they contain interstitial atoms (e.g. [Pt@Pb12]2-). Many salts of the polyhedral anions are soluble, but a number of examples-usually those with higher charges-occur only as quasi-discrete units in saltlike crystals (Zintl phases) or as building blocks in intermetallic phases. In this Minireview, the chemistry of intermetalloid clusters is reviewed with reference to the endohedral Zintl ions, Zintl phases, and polyhedral building blocks of intermetallic compounds, including heteroatomic species in the gas phase. We focus on selected examples and discuss the new findings in the context of recent advances in the field of metalloid clusters and (endohedral) fullerenes and fullerides.     

Atomically Precise Expansion of Unsaturated Silicon Clusters

Small‐ to medium‐sized clusters occur in various areas of chemistry, for example, as active species of heterogeneous catalysis or as transient intermediates during chemical vapor deposition. The manipulation of stable representatives is mostly limited to the stabilizing ligand periphery, virtually excluding the systematic variation of the property‐determining cluster scaffold. We now report the deliberate expansion of a stable unsaturated silicon cluster from six to seven and finally eight vertices. The consecutive application of lithium/naphthalene as the reducing agent and decamethylsilicocene as the electrophilic source of silicon results in the expansion of the core by precisely one atom with the potential of infinite repetition.     

Reactivity of Liquid Ammonia Solutions of the Zintl Phase K12Sn17 towards Mesitylcopper(I) and Phosphinegold(I) Chloride

To gain more insight into the reactivity of intermetalloid clusters, the reactivity of the Zintl phase K₁₂Sn₁₇, which contains [Sn₄]^4? and [Sn₉]^4? cluster anions, was investigated. The reaction of K₁₂Sn₁₇ with gold(I) phosphine chloride yielded K₇[(η²‐Sn₄)Au(η²‐Sn₄)](NH₃)₁₆ ( 1 ) and K₁₇[(η²‐Sn₄)Au(η²‐Sn₄)]₂(NH₂)₃(NH₃)₅₂ ( 2 ), which both contain the anion [(Sn₄)Au(Sn₄)]^7? ( 1 a ) that consists of two [Sn₄]^4? tetrahedra linked through a central gold atom. Anion 1 a represents the first binary Au?Sn polyanion. From this reaction, the solvate structure [K([2.2.2]crypt)]₃K[Sn₉](NH₃)₁₈ ( 3 ; [2.2.2]crypt=4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane) was also obtained. In the analogous reaction of mesitylcopper with K₁₂Sn₁₇ in the presence of [18]crown‐6 in liquid ammonia, crystals of the composition [K([18]crown‐6)]₂[K([18]crown‐6)(MesH)(NH₃)][Cu@Sn₉](thf) ( 4 ) were isolated ([18]crown‐6=1,4,7,10,13,16‐hexaoxacyclooctadiene, MesH=mesitylene, thf=tetrahydrofuran) and featured a [Cu@Sn₉]^3? cluster. A similar reaction with [2.2.2]crypt as a sequestering agent led to the formation of crystals of [K[2.2.2]crypt][MesCuMes] ( 5 ). The cocrystallization of mesitylene in 4 and the presence of [MesCuMes]^? ( 5 a ) in 5 provides strong evidence that the migration of a bare Cu atom into an Sn₉ anion takes place through the release of a Mes^? anion from mesitylcopper, which either migrates to another mesitylcopper to form 5 a or is subsequently protonated to give MesH.