Stabilizing a metalloid {Zn12} unit within a polymetallide environment in [K2Zn20Bi16]6

The access to molecules comprising direct Zn–Zn bonds has become very topical in recent years for various reasons. Low-valent organozinc compounds show remarkable reactivities, and larger Zn–Zn-bonded gas-phase species exhibit a very unusual coexistence of insulating and metallic properties. However, as Zn atoms do not show a high tendency to form clusters in condensed phases, synthetic approaches for generating purely inorganic metalloid Zn_x units under ambient conditions have been lacking so far. Here we show that the reaction of a highly reductive solid with the nominal composition K₅Ga₂Bi₄ with ZnPh₂ at room temperature yields the heterometallic cluster anion [K₂Zn₂₀Bi₁₆]^6–. A 24-atom polymetallide ring embeds a metalloid {Zn₁₂} unit. Density functional theory calculations reveal multicenter bonding, an essentially zero-valent situation in the cluster center, and weak aromaticity. The heterometallic character, the notable electron-delocalization, and the uncommon nano-architecture points at a high potential for nano-heterocatalysis.

Low-valent zinc clusters, though exceedingly rare, are appealing synthetic targets because there is evidence that they may show unconventional chemical and physical behavior. Here, the authors obtain a large heterometallic zinc-bismuth cluster anion and discover that it bears a metalloid {Zn₁₂} core with four-center bonding and essentially zero-valent character.

Analytical Model of CVD Growth of Graphene on Cu(111) Surface

Although the CVD synthesis of graphene on Cu(111) is an industrial process of outstanding importance, its theoretical description and modeling are hampered by its multiscale nature and the large number of elementary reactions involved. In this work, we propose an analytical model of graphene nucleation and growth on Cu(111) surfaces based on the combination of kinetic nucleation theory and the DFT simulations of elementary steps. In the framework of the proposed model, the mechanism of graphene nucleation is analyzed with particular emphasis on the roles played by the two main feeding species, C and C2. Our analysis reveals unexpected patterns of graphene growth, not typical for classical nucleation theories. In addition, we show that the proposed theory allows for the reproduction of the experimentally observed characteristics of polycrystalline graphene samples in the most computationally efficient way.

The Many Meanings of Placebo

Physicians throughout medical history knew three possible ways to explain the association between treatment and cure: 1. the beneficial effect of the treatment itself, 2. the healing power of nature, and 3. the placebo effect. In the modern definition by Grünbaum, a treatment is a placebo when the effect cannot be explained by the theory that describes its activity. In clinical practice the placebo phenomenon is commonly misunderstood. Placebos are given to prove the patient wrong or to punish him. Nevertheless, most clinical pain can be reduced to at least half of its intensity by placebos. Also cough, headaches, asthma and other ailments can thus be relieved. Explanatory theories are often much narrower in focus than the phenomenon they seek to explain. A Meaning Model could offer new possibilities, as it includes the doctor-patient relationship, belief systems, social support, and feelings of mastery over the symptoms. One way to make such a model visible is the exploration of the deep-seated cultural assumptions about illness in different countries.

Multiscale Model of CVD Growth of Graphene on Cu(111) Surface

Due to its outstanding properties, graphene has emerged as one of the most promising 2D materials in a large variety of research fields. Among the available fabrication protocols, chemical vapor deposition (CVD) enables the production of high quality single-layered large area graphene. To better understand the kinetics of CVD graphene growth, multiscale modeling approaches are sought after. Although a variety of models have been developed to study the growth mechanism, prior studies are either limited to very small systems, are forced to simplify the model to eliminate the fast process, or they simplify reactions. While it is possible to rationalize these approximations, it is important to note that they have non-trivial consequences on the overall growth of graphene. Therefore, a comprehensive understanding of the kinetics of graphene growth in CVD remains a challenge. Here, we introduce a kinetic Monte Carlo protocol that permits, for the first time, the representation of relevant reactions on the atomic scale, without additional approximations, while still reaching very long time and length scales of the simulation of graphene growth. The quantum-mechanics-based multiscale model, which links kinetic Monte Carlo growth processes with the rates of occurring chemical reactions, calculated from first principles makes it possible to investigate the contributions of the most important species in graphene growth. It permits the proper investigation of the role of carbon and its dimer in the growth process, thus indicating the carbon dimer to be the dominant species. The consideration of hydrogenation and dehydrogenation reactions enables us to correlate the quality of the material grown within the CVD control parameters and to demonstrate an important role of these reactions in the quality of the grown graphene in terms of its surface roughness, hydrogenation sites, and vacancy defects. The model developed is capable of providing additional insights to control the graphene growth mechanism on Cu(111), which may guide further experimental and theoretical developments.

Planar Iron Hydride Nanoclusters: Combined Spectroscopic and Theoretical Insights into Structures and Building Principles

The controlled assembly of well-defined planar nanoclusters from molecular precursors is synthetically challenging and often plagued by the predominant formation of 3D-structures and nanoparticles. Herein, we report planar iron hydride nanoclusters from reactions of main group element hydrides with iron(II) bis(hexamethyldisilazide). The structures and properties of isolated Fe4 , Fe6 , and Fe7 nanoplatelets and calculated intermediates enable an unprecedented insight into the underlying building principle and growth mechanism of iron clusters, metal monolayers, and nanoparticles.

Molecular Self-Assembly of DBBA on Au(111) at Room Temperature

We have investigated the self-assembly of the graphene nanoribbon molecular precursor 10,10'-dibromo-9,9'-bianthryl (DBBA) on Au(111) with frequency modulation scanning force microscopy (FM-SFM) at room temperature combined with ab initio calculations....

Experimental and theoretical evidence for low-lying excited states in [Cr6E8(PEt3)6] (E = S, Se, Te) cluster molecules

Three [Cr₆E₈(PEt₃)₆] cluster molecules with E = S, Se, and Te have been synthesized by reaction of stoichiometric mixtures of Cr(II) and Cr(III) metal salts with silylated chalcogen reagents E(SiMe₃)₂ (E = S, Se, Te) in the presence of L = PEt₃ = triethylphosphine. For the sulfide- and selenide-bridged clusters two crystallographic forms (trigonal R3̄ and triclinic P1̄), which differ in the presence of lattice solvent molecules, have been isolated. Structural data, optical spectra and quantum chemical calculations reveal the presence of low-lying excited states in [Cr₆E₈(PEt₃)₆] (E = S, Se), which would help in rationalizing the non-vanishing magnetic moments at 2 K revealed by DC magnetic measurements and EPR spectroscopy. These findings are partially in contrast to a previous report by Saito and co-workers (S. Kamiguchi, H. Imoto, T. Saito, Inorg. Chem., 1998, 37, 6852-6857.), who postulated an incorporated hydrogen atom as the source of paramagnetism at low temperatures for the trigonal forms of [Cr₆E₈(PEt₃)₆] (E = S, Se).