[Ag(Sn9-Sn9)]5- and [(η4-Sn9)Ag(η1-Sn9)]7-, as aggregates of spherical aromatic building blocks. Persistence of aromaticity upon cluster gathering

Formation of cluster-based materials requires a fundamental understanding of the resulting cluster aggregation processes. The Sn94- Zintl-ion structure can be viewed as a building block featuring a spherical aromatic species, leading to a cluster gathering upon oxidative coupling and/or mediated by transition metals. Here, we evaluate the spherical aromatic properties of [Sn9-Sn9]6-, [Ag(Sn9-Sn9)]5- and [(η4-Sn9)Ag(η1-Sn9)]7-, as aggregates of two Sn9 building units held together via oxidative coupling and mediated by a Ag(I) transition metal center. Our results from magnetic criteria of aromaticity show that the inherent spherical aromatic characteristics of the parent Sn94- cluster are persistent in the overall aggregate where the enabled shielding cones ascribed to each Sn9 unit are able to interplay between them, leading to an overlap of the shielding regions. Hence, the two approaches for bringing cluster units together are able to retain the inherent spherical aromatic features for each Sn9 unit, leading to a cluster-based dimer where the parent properties remain. Thus, further cluster-based materials can be envisaged from aggregation upon oxidative coupling and/or mediated by transition metals, where the constituent building blocks retain their initial features, useful to guide the formation of more complex cluster-based aggregates.

Snap-shots of cluster growth: structure and properties of a Zintl ion with an Fe3 core, [Fe3Sn18]4

The endohedral Zintl-ion cluster [Fe3Sn18]4- contains a linear Fe3 core with short Fe-Fe bond lengths of 2.4300(9) Å. The ground state is a septet, with significant σ and π contributions to the Fe-Fe bonds. The Sn18 cage is made up of two partially fused Sn9 fragments, and is structurally intermediate between [Ni2CdSn18]6-, where the fragments are clearly separated and [Pd2Sn18]4-, where they are completely fused. It therefore represents an intermediate stage in cluster growth. Analysis of the electronic structure suggests that the presence of the linear Fe-Fe-Fe unit is an important factor in directing reactions towards fusion of the two Sn9 units rather than the alternative of oligomerization via exo bond formation.

Reactive Solubilization of Heterometallic Clusters by Treatment of (TrBi3 )2- Anions (Tr=Ga, In, Tl) with [Mn{N(SiMe3 )2 }2 ]

Lowering the charge of Zintl anions by (element-)organic substituents allows their use as sources of (semi)metal nanostructures in common organic solvents, as realized for group 15 anions or Ge9 4- and Sn9 4- . We developed a new strategy for other anions, using low-coordinate 3d metal complexes as electrophiles. [K(crypt-222)]+ salts of (TrBi3 )2- anions dissolved in situ in Et2 O and/or THF when reacted with [Mn(hmds)2 ]. Work-up afforded soluble [K(crypt-222)]+ salts of [{(hmds)2 Mn}2 (TlBi3 )]2- (in 1), [{(hmds)2 Mn}2 (Bi2 )]2- (in 2), and [{(hmds)Mn}4 (Bi2 )2 ]2- (in 3) (crypt-222=4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane; Tr=Ga, In, Tl; hmds=N(SiMe3 )2 ), representing rare cases of Zintl clusters with open-shell metal atoms. 1 comprises the first coordination compound of the (TlBi3 )2- anion, 2 features a diamond-shaped {Pn2 M2 } unit, and 3 is a mixed-valent MnI /MnII compound. The uncommon electronic structures in 1-3 and magnetic coupling were studied by comprehensive DFT calculations.

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.

[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.

Atom Exchange Versus Reconstruction: (Gex As4-x )x- (x=2, 3) as Building Blocks for the Supertetrahedral Zintl Cluster [Au6 (Ge3 As)(Ge2 As2 )3 ]3

The Zintl anion (Ge2 As2 )2- represents an isostructural and isoelectronic binary counterpart of yellow arsenic, yet without being studied with the same intensity so far. Upon introducing [(PPh3 )AuMe] into the 1,2-diaminoethane (en) solution of (Ge2 As2 )2- , the heterometallic cluster anion [Au6 (Ge3 As)(Ge2 As2 )3 ]3- is obtained as its salt [K(crypt-222)]3 [Au6 (Ge3 As)(Ge2 As2 )3 ]⋅en⋅2 tol (1). The anion represents a rare example of a superpolyhedral Zintl cluster, and it comprises the largest number of Au atoms relative to main group (semi)metal atoms in such clusters. The overall supertetrahedral structure is based on a (non-bonding) octahedron of six Au atoms that is face-capped by four (Gex As4-x )x- (x=2, 3) units. The Au atoms bind to four main group atoms in a rectangular manner, and this way hold the four units together to form this unprecedented architecture. The presence of one (Ge3 As)3- unit besides three (Ge2 As2 )2- units as a consequence of an exchange reaction in solution was verified by detailed quantum chemical (DFT) calculations, which ruled out all other compositions besides [Au6 (Ge3 As)(Ge2 As2 )3 ]3- . Reactions of the heavier homologues (Tt2 Pn2 )2- (Tt=Sn, Pb; Pn=Sb, Bi) did not yield clusters corresponding to that in 1, but dimers of ternary nine-vertex clusters, {[AuTt5 Pn3 ]2 }4- (in 2-4; Tt/Pn=Sn/Sb, Sn/Bi, Pb/Sb), since the underlying pseudo-tetrahedral units comprising heavier atoms do not tend to undergo the said exchange reactions as readily as (Ge2 As2 )2- , according to the DFT calculations.

Intermediates and products of the reaction of Zn(ii) organyls with tetrel element Zintl ions: cluster extension versus complexation

Upon reactions of Zintl ions with Zn(ii) organyls various Zn-Zintl clusters as well as Zn-amide intermediates were isolated.

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-.

[Hyp-Au-Sn9(Hyp)3-Au-Sn9(Hyp)3-Au-Hyp]-: the longest intermetalloid chain compound of tin

The reaction of the metalloid tin cluster [Sn₁₀(Hyp)₄]^2- with (Ph₃P)Au-SHyp (Hyp = Si(SiMe₃)₃) gave an intermetalloid cluster [Au₃Sn₁₈(Hyp)₈]^-1, which is the longest intermetalloid chain compound of tin to date. 1 shows a structural resemblance to binary AuSn phases, which is expected for intermetalloid clusters.

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.

Low oxidation state silicon clusters – synthesis and structure of [NHCDippCu(η4-Si9)]3−

The reaction of NHC^DippCuCl with the silicide phases A₁₂Si₁₇ (A: K, K/Rb, Rb) in NH₃(l) yields [NHC^DippCu(η⁴-Si₉)]³⁻ as a rare example of a metal complex of a [Si₉] cluster.

[Ge5Ni2(CO)3]2−: the first functionalized cluster of closo-[Ge5]2−

A functionalized cluster derivative of closo-[Ge₅]²⁻ has been prepared and structurally characterized for the first time.