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

Crystal structure of (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane-κ 8 N 2, O 6) potassium cyclopentadienide, [K([2.2.2]crypt)]Cp, C23H41KN2O6

C23H41KN2O6, monoclinic, P21/c (no. 14), a = 10.9817(6) Å, b = 23.8330(15) Å, c = 9.7379(7) Å, β = 94.705(5)°, V = 2540.1(3) Å3, Z = 4, R gt (F) = 0.0327, wR ref(F 2) = 0.0682, T = 120 K.

Contrasting Bonding Extremes in Two [Ge6]n- Complexes: A Wadian Polyhedron (n = 2) versus a Hydrocarbon-like 2c-2e Polygermanide (n = 12)

[Nb(η⁶-C₆H₃Me₃)₂] reacts with ethylenediamine (en) solutions of K₄Ge₉ in the presence of 18-crown-6 to give [(η⁶-C₆H₃Me₃)NbHGe₆]^2- (1) and [(η⁶-C₆H₃Me₃)NbGe₆Nb(η⁶-C₆H₃Me₃)]^2- (2) as their corresponding [K(18-crown-6)]⁺ salts. The crystalline solids are dark brown, air-sensitive, and sparingly soluble or insoluble in most solvents. The [K(18-crown-6)]⁺ salts of cluster ions 1 and 2 have been characterized by energy-dispersive X-ray (EDX) analysis, NMR studies, single-crystal X-ray diffraction, and electrospray ionization time-of-flight (ESI-TOF) mass spectrometry studies. Cluster ions 1 and 2 have markedly different [Ge₆] moieties: an electron-deficient carborane-like subunit in 1 and a two-center, two-electron cyclohexane-like subunit in 2.

[Sn8 ]6- -Bridged Mixed-Valence ZnI /ZnII in {[K2 ZnSn8 (ZnMes)]2 }4- Inverse Sandwich-Type Cluster Supported by a ZnI -ZnI Bond

Since [Sn₈ ]^6- was discovered from the solid-state phase in 2000, its solution chemistry has been elusive due to the high charges and chemical activity. Herein, we report the synthesis and characterization of an inverse sandwich-type cluster dimer {[K₂ ZnSn₈ (ZnMes)]₂ }^4- (1 a), in which the highly charged [Sn₈ ]^6- is captured by mixed-valence Zn^I /Zn^II to form the dimer {closo-[Zn₂ Sn₈ ]}₂ moieties bridged by a Zn-Zn bond. Such Zn-Sn cluster not only exhibits a novel example of mixed-valence Zn^I /Zn^II for stabilizing highly active anion species, but also indicates the [Sn₈ ]^6- cluster can act as a novel bridging ligand, like arene, with a η⁴ :η⁴ -fashion. Theoretical calculations indicate that a significant delocalization of electrons over Zn atoms plays a vital role in the stabilization of the [Sn₈ ]^6- species. The AdNDP and magnetic response analyses clearly showed the presence of local σ-aromaticity in three cluster fragments: two ZnSn₄ caps and Sn₈ square antiprism.

Cluster Expansion versus Complex Formation: Coinage Metal Coordination to Silylated [Ge9] Cages

Deltahedral nine-atom tetrel element Zintl clusters are promising building blocks for the straightforward solution-based synthesis of intermetalloid clusters through the reaction with organometallic compounds. Herein we report on novel coordination sites of metal-N-heterocyclic carbene (NHC) complexes to [Ge₉] clusters and unexpected cluster isomerization. We present the synthesis of a series of coinage metal-NHC complexes of silylated [Ge₉] clusters [NHC^iPrCu(η⁴-Ge₉{Si(TMS)₃}₃)] (1; TMS = trimethylsilyl) and [NHC^RM(η⁴-Ge₉{Si(TMS)₃}₂)]^- (2a, M = Cu, R = iPr; 3a, M = Cu, R = Mes; 4a, M = Cu, R = Dipp; 5a, M = Ag, R = Dipp; 6a, M = Au, R = Dipp), in which the coinage metals coordinate to open rectangular cluster faces and act as additional cluster vertex atoms. Besides representing promising intermediates on the way to larger intermetalloid clusters, the formation of compound 1 shows that Cu-NHC fragments also coordinate to the open-square Ge faces of the tris-silylated [Ge₉] clusters, contrasting the typical interactions with triangular faces of tris-silylated [Ge₉] clusters. In compounds 3a and 4a bearing bulky NHC moieties, an unusual silyl group substitution pattern is observed in contrast to 2a, which corresponds to the silyl group arrangement of other metal complexes of bis-silylated [Ge₉] clusters. In this context, potential silyl group migration mechanisms are discussed.

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.

(Multi-)Metallic Cluster Growth

This review article provides a survey of contemporary investigations on main group metal cluster formation, addressing homo- and heterometallic clusters (including small numbers of transition metal atoms), with or without an external ligand shell, thereby excluding clusters with non-metal atoms as bridging ligands. Most of the studies reflected herein represent insights into the formation of intermediates from the starting material, or the final cluster formation from established intermediates. In rare cases, the entire process was suggested as a result of comprehensive, multi-method elucidations. The article is to be understood as a state-of-the-art report, as the subject matter is currently a rising field of research, which is still in its infancy, despite some early activities that date back to the 1980s. At the same time, the article intends to point toward both the importance and the feasibility of according studies, in order to encourage researchers to gain even more knowledge in this field. Only deep understanding of cluster formation will allow for design, and ultimately control, of their syntheses, with the long-term goal of their optimization and purposeful application in catalysis or novel material synthesis.

[SnBi3 ]5- -A Carbonate Analogue Comprising Exclusively Metal Atoms

The new [SnBi₃ ]^5- polyanion is obtained by the reaction of K₃ Bi₂ with K₄ Sn₉ or K₁₂ Sn₁₇ in liquid ammonia. The anion is iso(valence)electronic with and structurally analogous to the carbonate ion. Despite the high negative charge of the anion, the Sn-Bi bond lengths range between single and double bonds. Quantum-chemical calculations at a DFT-PBE0/def2-TZVPP/COSMO level of theory reveal that the partial double bond character between the heavy main-group atoms Bi and Sn originates from a delocalized π-electronic system. The structure of the anion is determined by single-crystal X-ray diffraction analyses of the compounds K₅ [SnBi₃ ] 9 NH₃ (1) and K₉ [K(18-crown-6)][SnBi₃ ]₂ ⋅15 NH₃ (2). The [SnBi₃ ]^5- unit is the first example of a carbonate-like anion obtained from solution, and it consists exclusively of metal atoms and completes the series of metal analogues of CO and CO₂ .

Between Localization and Delocalization: Ru(cod)2+ Units in the Zintl Clusters [Bi9 {Ru(cod)}2 ]3- and [Tl2 Bi6 {Ru(cod)}]2

Reactions of [K(crypt-222)]₂ (TlBi₃ )⋅0.5 en (1 b) with [Ru(cod)(H₂ CC(Me)CH₂ )₂ ] (A) in 1,2-diaminoethane (en) led to the formation of two compounds with new bismuth-rich cluster anions, [K(crypt-222)]₃ [Bi₉ {Ru(cod)}₂ ]⋅1.5 en (2) and [K(crypt-222)]₂ [Tl₂ Bi₆ {Ru(cod)}]⋅2 tol (3), alongside the salt of a binary nido cluster, [K(crypt-222)]₃ (Tl₄ Bi₅ )⋅2 en (4). The anions in 2 and 3 are two further examples of rare heterometallic clusters containing Ru atoms. As one cod ligand is retained on each Ru atom in both clusters, the anions may be viewed as intermediates on the way towards larger, ligand-free intermetalloid clusters. Quantum-chemical studies provided insight into the bonding situation in these clusters. According to these studies, the anion of 2 features both electron-precise and electron-deficient parts. Electrospray ionization mass spectrometry analysis indicated that the clusters undergo stepwise fragmentation.

N-Heterocyclic Carbene Coinage Metal Complexes of the Germanium-Rich Metalloid Clusters [Ge₉R₃]- and [Ge₉RI₂]²- with R = Si(iPr)₃ and RI = Si(TMS)₃

We report on the synthesis of novel coinage metal NHC (N-heterocyclic carbene) compounds of the germanium-rich metalloid clusters [Ge₉R₃]^- and [Ge₉R^I₂]²^- with R = Si(ⁱPr)₃ and R^I = Si(TMS)₃. NHC^DippCu{η³Ge₉R₃} with R = Si(ⁱPr)₃ (1) represents a less bulky silyl group-substituted derivative of the known analogous compounds with R = Si(ⁱBu)₃ or Si(TMS)₃. The coordination of the [NHC^DippCu]⁺ moiety to the cluster unit occurs via one triangular face of the tri-capped trigonal prismatic [Ge₉] cluster. Furthermore, a series of novel Zintl cluster coinage metal NHC compounds of the type (NHCM)₂{η³Ge₉R^I₂} (R^I = Si(TMS)₃ M = Cu, Ag and Au; NHC = NHC^Dipp or NHC^Mes) is presented. These novel compounds represent a new class of neutral dinuclear Zintl cluster coinage metal NHC compounds, which are obtained either by the stepwise reaction of a suspension of K₁₂Ge₁₇ with Si(TMS)₃Cl and the coinage metal carbene complexes NHCMCl (M = Cu, Ag, Au), or via a homogenous reaction using the preformed bis-silylated cluster K₂[Ge₉(Si(TMS)₃)₂] and the corresponding NHCMCl (M = Cu, Ag, Au) complex. The molecular structures of NHC^DippCu{η³Ge₉(Si(ⁱPr)₃)₃} (1) and (NHC^DippCu)₂{η³-Ge₉(Si(TMS)₃)₂} (2) were determined by single crystal X-ray diffraction methods. In 2, the coordination of the [NHC^DippCu]⁺ moieties to the cluster unit takes place via both open triangular faces of the [Ge₉] entity. Furthermore, all compounds were characterized by means of NMR spectroscopy (¹H, ¹³C, ²⁹Si) and ESI-MS.