Substantial π-aromaticity in the anionic heavy-metal cluster [Th@Bi12]4.

The concept of aromaticity was originally defined as a property of unsaturated, cyclic planar organic molecules like benzene, which gain stability by the inherent delocalization of 4n + 2 π-electrons over the ring atoms. Since then, π-aromaticity has been observed for a large variety of organic and inorganic non-metal compounds, yet, for molecules consisting only of metal atoms, it has remained restricted to systems with three to five atoms. Here, we present the straightforward synthesis of a metal 12-ring that exhibits 2π-aromaticity and has a ring current much stronger than that of benzene (6π) and equivalent to that of porphine (26π), despite these organic molecules having (much) larger numbers of π-electrons. Highly reducing reaction conditions allowed access to the heterometallic anion [Th@Bi12]4-, with interstitial Th4+ stabilizing a Bi128- moiety. Our results show that it is possible to design and generate substantial π-aromaticity in large metal rings, and we hope that such π-aromatic heavy-metal cycles will eventually find use in cluster-based reactions.

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.

[Am(C5 Me4 H)3 ]: An Organometallic Americium Complex.

We report the small-scale synthesis, isolated yield, single-crystal X-ray structure, 1 H NMR solution spectroscopy /solid-state UV/Vis-nIR spectroscopy, and density functional theory (DFT)/ab initio wave function theory calculations on an Am3+ organometallic complex, [Am(C5 Me4 H)3 ] (1). This constitutes the first quantitative data on Am-C bonding in a molecular species.

Intermetalloid and Heterometallic Clusters Combining p-Block (Semi)Metals with d- or f-Block Metals.

Clusters have been the subject of intense investigations since their famous definition launched by Cotton in 1963, and the area has expanded ever since. One obvious development addresses the widening of the definition of what to call a cluster: from purely (transition) metal-metal linked assemblies, as per Cotton's early denomination, to nonmetal/metal clusters or purely nonmetal cages, like fullerenes, and even noncovalent aggregates such as water clusters. The other extension concerns the broadened spectrum of compositions within the aforementioned cluster types and their corresponding structures that range from trinuclear motifs to clusters with sizes in the range of the hemoglobin unit. This review article reports on one cluster family that has its origins in traditional Zintl anion chemistry but has undergone rapid development in recent years, namely, ligand-free clusters that combine main group and transition metal atoms. Depending on the position of the transition metal atom(s), one refers to such clusters as intermetalloid (endohedral) clusters or as a special type of heterometallic clusters. The predominant synthetic access makes use of soluble Zintl anions. Other pathways for their preparation include traditional solid state reactions of according element combinations or bottom-up syntheses employing low valent organo-main group element sources. This survey will shed light on all of these approaches, with an emphasis on the syntheses that employ soluble Zintl anion compounds. The article will give a comprehensive overview of the currently known compounds, their different synthesis protocols, and analytic techniques for determination of their compositions, structures, and further properties. Additionally, this survey will report peculiarities of bonding situations found within some of the cluster molecules, which were studied by means of sophisticated quantum chemical investigations.

Polybismuthide Anions as Ligands: The Homoleptic Complex [(Bi7 )Cd(Bi7 )]4- and the Ternary Cluster [(Bi6 )Zn3 (TlBi5 )]4.

We present the results from a reactivity study of the binary anion (TlBi3 )2- towards Group 12 metal compounds MPh2 (M=Zn, Cd, Hg) to gain access to coordination compounds of polycyclic polypnictide molecules such as Bi7 3- or Bi11 3- . The coordination chemistry of these polybismuthide cages has been unprecedented to date, while it has been known for a long time for the lighter Group 15 anions Pn7 3- (Pn=P, As, Sb). The use of (TlBi3 )2- , previously shown to release Tl under certain conditions in situ, resulted in the formation of the first heterometallic polyanion in which a nortricyclane-type polybismuthide coordinates a transition-metal atom, [(Bi7 )Cd(Bi7 )]4- . Reactions with the lighter Group 12 metal precursor yielded the uncommon ternary cluster [(Bi6 )Zn3 (TlBi5 )]4- , most likely representing a reaction intermediate, and at the same time hinting at the formation of the nortricyclane-shaped cage. Quantum-chemical studies provide deeper insight into the stability trends of the [(E7 )M(E7 )]4- anion family and reveal a complex bonding situation in [(Bi6 )Zn3 (TlBi5 )]4- , which features both localized and multi-center bonding.

The Identity of "Ternary" A/Tl/Pb or K/Tl/Bi Solid Mixtures and Binary Zintl Anions Isolated From Their Solutions.

Investigations of solid mixtures of the elemental combinations A/Tl/Pb (A=Na, K) and K/Tl/Bi indicate the presence of multiple binary and ternary Zintl phases, among them new ones containing Tl and Pb or Bi, respectively. Extractions with en/crypt-222 afford single crystals of several novel binary anions, including [Tl@Tl4 Pb8 ]4- and (Tl4 Bi3 )3- . [Tl@Tl4 Pb8 ]4- adopts a closo-type cage structure despite possessing one additional electron; it is therefore isostructural, yet not isoelectronic, with homoatomic [Tl@Tl12 ]11- obtained by solid state reactions. (Tl4 Bi3 )3- is a rare case of a pentagonal bipyramidal Zintl anion, yet the first binary one, and (unlike Tl77- ) the first one with a proper closo-type electron count. Assignment of the numbers and positions of the Tl/Pb or Tl/Bi atoms within the anionic clusters, indistinguishable in classical X-ray diffraction experiments, was achieved by means of quantum chemistry. The studies shed light on the complex situation in solid heavy element mixtures and their substantial differences from the composition of the Zintl anions obtained from them by extraction.

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.

Main Group Metal-Actinide Magnetic Coupling and Structural Response Upon U(4+) Inclusion Into Bi, Tl/Bi, or Pb/Bi Cages.

The encapsulation of actinide ions in intermetalloid clusters has long been proposed but was never realized synthetically. We report the isolation and experimental, as well as quantum chemical, characterization of the uranium-centered clusters [U@Bi12](3-), [U@Tl2Bi11](3-), [U@Pb7Bi7](3-), and [U@Pb4Bi9](3-), upon reaction of (EE'Bi2)(2-) (E = Ga, Tl, E' = Bi; E = E' = Pb) and [U(C5Me4H)3] or [U(C5Me4H)3Cl] in 1,2-diaminoethane. For [U@Bi12](3-), magnetic susceptibility measurements rationalize an unprecedented antiferromagnetic coupling between a magnetic U(4+) site and a unique radical Bi12(7-) shell.