Adamantane-type clusters: compounds with a ubiquitous architecture but a wide variety of compositions and unexpected materials properties.

The research into adamantane-type compounds has gained momentum in recent years, yielding remarkable new applications for this class of materials. In particular, organic adamantane derivatives (AdR4) or inorganic adamantane-type compounds of the general formula [(RT)4E6] (R: organic substituent; T: group 14 atom C, Si, Ge, Sn; E: chalcogenide atom S, Se, Te, or CH2) were shown to exhibit strong nonlinear optical (NLO) properties, either second-harmonic generation (SHG) or an unprecedented type of highly-directed white-light generation (WLG) - depending on their respective crystalline or amorphous nature. The (missing) crystallinity, as well as the maximum wavelengths of the optical transitions, are controlled by the clusters' elemental composition and by the nature of the organic groups R. Very recently, it has been additionally shown that cluster cores with increased inhomogeneity, like the one in compounds [RSi{CH2Sn(E)R'}3], not only affect the chemical properties, such as increased robustness and reversible melting behaviour, but that such 'cluster glasses' form a conceptually new basis for their use in light conversion devices. These findings are likely only the tip of the iceberg, as beside elemental combinations including group 14 and group 16 elements, many more adamantane-type clusters (on the one hand) and related architectures representing extensions of adamantane-type clusters (on the other hand) are known, but have not yet been addressed in terms of their opto-electronic properties. In this review, we therefore present a survey of all known classes of adanmantane-type compounds and their respective synthetic access as well as their optical properties, if reported.

Insight into the formation of bismuth-tungsten carbonyl clusters.

Multimetallic clusters play a key role as models to doped metals, as candidates to new types of superatomic catalysts and as precursors to new multimetallic solids. Understanding formation pathways is an essential and necessary step forward in the development of cluster synthesis and research, yet remains considerably lacking owing to difficulty in identification of intermediates and the ill-defined nature of common starting materials. Here we show progress in this regard by investigating the reactivity of an intermetallic solid of nominal composition 'K5Ga2Bi4' with [W(cod)(CO)4] upon extraction with ethane-1,2-diamine (en) and 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (crypt-222). Several polybismuthide intermediates and by-products were identified along the reaction pathway, ultimately forming the new polybismuthide salt [K(crypt-222)]3[µ:η3-Bi3{W(CO)3}2]∙en∙tol. DFT calculations revealed plausible reaction schemes for the transformations taking place in the reaction mixture providing insight into the complex reactivity of 'K5Ga2Bi4' on the basis of in situ generation of Bi22-.

Assembly of One to Four As4 Analogues, (Ge2 As2 )2- or (Ge3 As)3- , in the Coordination Sphere of [PhM]+ , [MesM]+ , or M2+ (M=Zn, Cd, Hg).

Pseudo-tetrahedral units of p-block atoms proved to be excellent building blocks for novel molecular architectures and for introducing new elemental combinations which are not otherwise accessible. In this work, we present a series of clusters obtained by reactions of binary Ge/As anions with [MPh2 ] (M=Zn, Cd, Hg; Ph=phenyl). The study is grounded on the fact that the binary reactant gained by extracting the solid 'K2 GeAs' with ethane-1,2-diamine (en) co-exists as (Ge2 As2 )2- and (Ge3 As)3- in solution. This allows for a larger variety of products by 'selecting' the most suitable species for the final ternary complex to crystallize. The reactions afforded the unprecedented first step of the corresponding interaction, thus attachment of (MPh)+ to a pseudo-tetrahedral unit in [PhZn(Ge3 As)]2- (1) and [PhHg(Ge3 As)]2- (2), and complex anions with two, three, or four units, [(Ge3 As)Zn(Ge2 As2 )]3- (3), [Cd3 (Ge3 As)3 ]3- (4), and [Zn3 (Ge3 As)4 ]6- (5). Quantum chemistry confirmed the compositions and the positions of the Ge or As atoms, beside explaining structural peculiarities. The subtle impact of different [MR2 ] reactants was additionally studied by corresponding reactions using [ZnMes2 ] (Mes=mesityl), which showed success in selectively crystallizing [MesZn(Ge3 As)]2- (6). Based on our findings, we derive a suggestion of the underlying reaction cascade.

Bismuth-Based Metal Clusters─From Molecular Aesthetics to Contemporary Materials Science.

ConspectusBismuth-based research has become a highly topical field in recent years, yielding remarkable prospects for new fundamental insights and new materials applications, ranging from innovative catalysts to novel pharmaceuticals, due to this heavy metal's virtually nonradioactive and nontoxic properties. Given that the 6s2 electron pair can be stereochemically active under certain circumstances, bismuth atoms adopt a variety of coordination modes and bonding environments with oxidation states ranging from (formally) +V to -III. As a consequence, bismuth-based compounds cover the entire spectrum from simple coordination compounds to much more unusual cluster cations and cluster anions exhibiting metal-metal bonding in a homoatomic manner, or in concert with other s-, d-, p-, or f-block metal atoms. Such bismuth clusters show high potential for the development of new bismuth-based materials, but they are also interesting objects by themselves. Given the relatively recent development of bismuth-rich cluster molecules, a deep understanding of their properties─including unprecedented structural features, complex electronic structures, substantial heavy metal aromaticity, as well as their formation pathways─is still in its infancy. The topic thus spans a broad range from highly sophisticated synthetic chemistry through interdisciplinary experimental and theoretical analyses to materials science.Based on our recent work and several notable reports from other groups, this article will highlight the successful access to a number of novel bismuth-rich cluster ions emerging from both solution-based approaches and solid-state chemistry. It will shed light on the unique structural and electronic properties that cause chemical and physical peculiarities of such compounds. Selected examples include, but are not limited to, (1) the first encapsulation of actinide ions in intermetalloid clusters which additionally served to manifest substantial all-metal π-aromaticity with a (calculated) record ring current per electron; (2) a large metalloid {Zn12} unit stabilized in a porphine-related {Zn8Bi16} moiety in [K2Zn20Bi16]6-; (3) the largest assembly of bismuth atoms within one molecule, observed in [{Ru(cod)}4Bi18]4- that consists of two Bi-Bi-linked "[{Ru(cod)}2Bi9]2-" subunits.Notably, cluster growth has remained largely a black box, which is starting to be revealed, however. We discuss possible formation pathways of such (multi)metallic nanoarchitectures on the basis of smaller subunits that were detected by mass spectrometric analyses and could also be captured upon reaction with organometallic complexes. In addition to the intrinsic structural and electronic properties of the cluster anions and cluster cations reviewed herein, we will briefly introduce the emerging usage of bismuth-based compounds in material science and give an outlook to future developments.

Charge Makes a Difference: Molecular Ionic Bismuth Compounds.

Key challenges in modern synthetic chemistry include the design of reliable, selective, and more sustainable synthetic methods, as well as the development of promising candidates for new materials. Molecular bismuth compounds offer valuable opportunities as they show an intriguing spectrum of properties that is yet to be fully exploited: a soft character, a rich coordination chemistry, the availability of a broad variety of oxidation states (at least +V to -I) and formal charges (at least +3 to -3) at the Bi atoms, and reversible switching between multiple oxidation states. All this is paired with the status of a non-precious (semi-)metal of good availability and a tendency towards low toxicity. Recent findings show that some of these properties only come into reach, or can be substantially optimized, when charged compounds are specifically addressed. In this review, essential contributions to the synthesis, analyses, and utilization of ionic bismuth compounds are highlighted.

φ-Aromaticity in prismatic {Bi6}-based clusters.

The occurrence of aromaticity in organic molecules is widely accepted, but its occurrence in purely metallic systems is less widespread. Molecules comprising only metal atoms (M) are known to be able to exhibit aromatic behaviour, sustaining ring currents inside an external magnetic field along M-M connection axes (σ-aromaticity) or above and below the plane (π-aromaticity) for cyclic or cage-type compounds. However, all-metal compounds provide an extension of the electrons' mobility also in other directions. Here, we show that regular {Bi6} prisms exhibit a non-localizable molecular orbital of f-type symmetry and generate a strong ring current that leads to a behaviour referred to as φ-aromaticity. The experimentally observed heterometallic cluster [{CpRu}3Bi6]-, based on a regular prismatic {Bi6} unit, displays aromatic behaviour; according to quantum chemical calculations, the corresponding hypothetical Bi62- prism shows a similar behaviour. By contrast, [{(cod)Ir}3Bi6] features a distorted Bi6 moiety that inhibits φ-aromaticity.

(NHC)Si═C═N-R: A Two-Coordinated Si0-Isocyanide Compound as Si(NHC) Transfer Reagent.

Experimental and theoretical studies are reported of the first two-coordinated Si0-isocyanide compound (SIDipp)Si═C═N-ArMes (1: SIDipp (NHC) = C[N(Dipp)CH2]2, ArMes = 2,6-dimesitylphenyl), supported by an N-heterocyclic carbene (NHC). A Si atom economic two-step synthesis of 1 involves a 2e reduction of the isocyanide-stabilized silyliumylidene salt [SiBr(CNArMes)(SIDipp)][B(ArF)4] (2[B(ArF)4], ArF = B(C6H3-3,5-(CF3)2)4) with KC8. 2[B(ArF)4] was obtained from SiBr2(SIDipp) after bromide abstraction with an equimolar mixture of Na[B(ArF)4] and ArMesNC. Exact adherence to the stoichiometry is crucial in the latter reaction, since 2[B(ArF)4] reacts with SiBr2(SIDipp) via isocyanide exchange to afford the disilicon(II) salt [Si2Br3(SIDipp)2)][B(ArF)4] (3[B(ArF)4]), the reaction leading to an equilibrium that favors 3[B(ArF)4] (Keq(298 K) = 10.6, ΔH° = -10.6 kJ mol-1; ΔS° = -16.0 J mol-1 K-1). 3[B(ArF)4] was obtained selectively from the 2:1 reaction of SiBr2(SIDipp) with Na[B(ArF)4] and fully characterized. Detailed studies of 1 reveal an intriguing structure featuring a planar CNHC-Si-C-N skeleton with a V-shaped geometry at the dicoordinated Si0 center, a slightly bent Si═C═N core, a CNHC-Si-CCNR 3c-2e out of plane π-bond (HOMO), and an anticlinal conformation of the SIDipp and ArMes substituents leading to axial chirality and the presence of two enantiomers, (Ra)-1 and (Sa)-1. Compound 1 displays structural dynamics in solution, rapidly interconverting the enantiomers. The silacumulene 1 is a potent Si(SIDipp) transfer agent as demonstrated by the synthesis and full characterization of the NHC-supported germasilyne (Z)-(SIDipp)(Cl)Si═GeArMes (4) from 1 and Ge(ArMes)Cl.

Homoleptic Poly(nitrato) Complexes of Group 14 Stable at Ambient Conditions.

Using a novel approach in homoleptic nitrate chemistry, Sn(NO3)6(2-) (3c) as well as the previously unknown hexanitrato complexes Si(NO3)6(2-) (1c), Ge(NO3)6(2-) (2c) were synthesized from the element tetranitrates as salt-like compounds which were isolated and characterized using (1)H, (14)N, and (29)Si NMR and IR spectroscopies, elemental and thermal analyses, and single-crystal XRD. All hexanitrates are moderately air-sensitive at 298 K and possess greater thermal stability toward NO2 elimination than their charge-neutral tetranitrato congeners as solids and in solution. The complexes possess distorted octahedral coordination skeletons and adopt geometries that are highly symmetric (3c) or deformed (1c, 2c) depending on the degree of steric congestion of the ligand sphere. As opposed to the κ(2)O,O' coordination mode reported for Sn(NO3)4 previously,1 all nitrato ligands of 3c coordinate in κ(1)O mode. Six geometric isomers of E(NO3)6(2-) were identified as minima on the PES using DFT calculations at the B3LYP/6-311+G(d,p) level of which two were observed experimentally.

Homoleptic low-valent polyazides of group 14 elements.

First examples of coordinatively unsaturated, homoleptic azido complexes of low-valent group 14 elements are reported. A simple strategy uses low-valent precursors, ionic azide transfer reagents and bulky cations to obtain salt-like compounds containing E(N3)3(-) of Ge(II)/Sn(II) which are fully characterised, including XRD. Remarkably, these compounds are kinetically stable at r.t. and isolable in sub-gram quantities.