The Arachno-Zintl Ion (Sn5 Sb3 )3- and the Effects of Element Composition on the Structures of Isoelectronic Clusters: Another Facet of the Pseudo-Element Concept

Exploration of the potential energy surface in mixed Zintl clusters applying an automatic Johnson polyhedra generator: the case of arachno E6M24- (E = Si, Ge, Sn; M = Sb, Bi)

A new algorithm called Automatic Johnson Cluster Generator (AJCG) is presented, which, as its name indicates, allows the definition of the desired Johnson polyhedron to subsequently carry out all the possible permutations between the atoms that form this polyhedron. This new algorithm allows the exhaustive study of the structures' potential energy surface (PES). In addition, the AJCG algorithm is helpful for the study of three-dimensional compounds such as boranes or Zintl clusters and their structural derivatives with two or more different atoms. The automatic filling of vertices is particularly useful in mixed compounds because of the possibility of taking into account all possible configurations in the structure. As a test system, we investigated the arachno-type E6M24- (E = Si, Ge, Sn; M = Sb, Bi) structure which has eight vertices and complies with Wade-Mingos rules. Initially, we defined a bipyramidal structure (10 vertices), and filled the vertices with the atoms in all possible configurations. Since the selected system has eight atoms, the two remaining vertices were filled with pseudo atoms to complete the structure. After re-optimizing the initial population generated with AJCG, a large number of isomers with energy below 10 kcal mol-1 are identified. These results show that the most stable isomers possess homonuclear M-M bonds, except Sn6Bi24-. Although the overall putative minima differ at the PBE0-D3 and DLPNO-CCSD(T) levels, they are always competitive minima. In addition to using high-precision methodologies to correctly study relative energies, applying solvent effects in highly charged systems becomes mandatory. The aromatic character of these studied systems was demonstrated qualitatively with two- and three-dimensional mapping and quantitatively by calculating the value of the z-component of the induced magnetic field at the cage center, including scalar and spin-orbit correction for relativistic effects. The compounds studied have a high degree of aromaticity, which allows us to establish that despite structural modifications (i.e., from closo to arachno), the aromaticity is preserved.

[M@Sn14-xSbx]q- (M = La, Ce, or U; x = 6-8; q = 3, 4): Interaction of 4f or 5f Metal Ions with 5p Metal Atoms in Intermetalloid Clusters

The impact of 4f metal ions Ln³⁺ (Ln = La or Ce) versus 5f metal ions Uⁿ⁺ (n = 3 or 4) on the compositions and distribution of 5p metal atoms in the cluster shells of endohedral species [M@Sn_14-xSb_x]^q- (M = La, Ce, or U; x = 6-8; q = 3, 4) was studied by means of combined experimental and quantum chemical investigations. While all known f-block metal ion-centered endohedral clusters possessed combinations of larger main group metal atoms so far (Sn/Bi or Pb/Bi), resulting in mixtures of 13- and 14-atom cages, the 14-atom cages reported herein comprise exclusively Sn and Sb atoms and therefore are challenged in accommodating the large 4f and 5f ions. We show that the clusters form in reactions of (Sn₂Sb₂)^2- anions with [Ln(C₅Me₄H)₃] or [U(C₅Me₄H)₃Cl], and that salts of [La@Sn₆Sb₈]^3-, [La@Sn₇Sb₇]^4-, [U@Sn₈Sb₆]^4-, and [U@Sn₇Sb₇]^3- can be isolated from them. The assignment of Sn versus Sb in the encapsulating cage follows a simple rule. Different central atoms cause only slight differences in this regard and with respect to distortions of the cluster shells. The reactions also yielded the salt of the new binary anion (Sn₄Sb₄)^2- that was recently predicted by quantum chemical studies.

From organotin hydrides to heteronuclear main group metal compounds: isolation of the first neutral bismuth/tin clusters

From conversions of Ar₂SnH₂ (Ar = Tripp, Dipp; Tripp = 2,4,6-Triisopropylphenyl, Dipp = 2,6-Diisopropylphenyl), and a bismuth(III) amide, Bi[N(SiMe₃)₂]₃, we isolated the first representatives of mixed, uncharged Bi/Sn clusters, Bi₈Sn₃Ar₆. Along with unprecedented bicyclo[2.2.0]hexanes, (HAr₂Sn)₂Sn₂Bi₄, these have been characterized by single crystal X-Ray diffraction, heteronuclear NMR, vibrational and UV-Vis spectroscopy. Quantum-chemical calculations were carried out in order to understand bonding within the isolated polyhedral compounds.

Ternary aromatic and anti-aromatic clusters derived from the hypho species [Sn2Sb5]3

Heterometallic clusters have attracted broad interests in the synthetic chemistry due to their various coordination modes and potential applications in heterogeneous catalysis. Here we report the synthesis, experimental, and theoretical characterizations of four ternary clusters ([M₂(CO)₆Sn₂Sb₅]^3- (M = Cr, Mo), and [(MSn₂Sb₅)₂]^4-, (M = Cu, Ag)) in the process of capturing the hypho- [Sn₂Sb₅]^3- in ethylenediamine (en) solution. We show that the coordination of the binary anion to transition-metal ions or fragments provides additional stabilization due to the formation of locally σ-aromatic units, producing a spherical aromatic shielding region in the cages. While in the case of [Mo₂(CO)₆Sn₂Sb₅]^3- stabilization arises from locally σ-aromatic three-centre and five-centre two-electron bonds, aromatic islands in [(AgSn₂Sb₅)₂]^4- and [(CuSn₂Sb₅)₂]^4- render them globally antiaromatic. This work describes the coordination chemistry of the versatile building block [Sn₂Sb₅]^3-, thus providing conceptual advances in the field of metal-metal bonding in clusters.

Insights into Formation and Relationship of Multimetallic Clusters: On the Way toward Bi-Rich Nanostructures

Bismuth-rich polyanions show a unique potential in constructing nanostructured bismuth-based materials, but they are still poorly investigated. We use a ternary precursor of the nominal composition "K₅Ga₂Bi₄" for the formation of [K(crypt-222)]⁺ salts of novel Bi-rich polyanions [Bi@Ga₈(Bi₂)₆]^q- (q = 3, 5; in 1), (Ga₂Bi₁₆)^4- (in 2), and [{Ru(cod)}₄Bi₁₈]^4- (in 3). Their bismuth contents exceed that of the largest homoatomic polyanion, Bi₁₁^3-. The numbers of bismuth atoms in the anions in 2 and 3 furthermore surmount that of the Bi-richest binary main-group anion, (Ge₄Bi₁₄)^4-, and they equal (2) or surmount (3) that reported for the anion and the cations with the largest number of Bi atoms so far, [K₂Zn₂₀Bi₁₆]^6-, [(Bi₈)Ru(Bi₈)]⁶⁺, and [(Bi₈)Au(Bi₈)]⁵⁺. Compounds 1 and 2 were obtained from reaction mixtures that contain [La(C₅Me₄H)₃], apparently assisting in the network formation without being included in the products. In the presence of [Ru(cod)(H₂CC(Me)CH₂)₂], yet another reaction pathway leads to the formation of the anions in 3 (conformers 3a and 3b), which are Bi-Bi linked dimers of two "[{Ru(cod)}₂Bi₉]^2-" subunits. They comprise the largest connected assemblies of Bi atoms within one molecule and may be viewed as snapshots on the way toward even larger polybismuthide units and, ultimately, new bismuth modifications. Mass spectrometry allowed insight into the processes in solution that precede the cluster formation. In-depth quantum chemical studies were applied to explain structural peculiarities, stabilities of the observed isomers, and bonding characteristics of these bismuth-rich nanoarchitectures. The work demonstrates the high potential of the method for the access of new Bi-based materials.

[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.

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.