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© 2019 American Chemical Society. We report a class of perfunctionalized dodecaborate clusters that exhibit stability during galvanostatic cycling. These boron clusters afford several degrees of freedom in material design to tailor properties including solubility and redox potential. The exceptional stability of these clusters was demonstrated by using a symmetric flow cell setup for electrochemical cycling between two oxidation states for 45 days, with post-run analysis showing negligible decomposition of the active species (

This Viewpoint Article describes major advances pertaining to perfunctionalized boron clusters in synthesis and their respective applications. The first portion of this work highlights key synthetic methods allowing one to access a wide range of polyhedral boranes (B4 and B6 – B12 cluster cores) that contain exhaustively functionalized vertices. The second portion of this Viewpoint showcases the historical developments in using these molecules for applications ranging from materials science to medicine. Lastly, we suggest potential new directions for these clusters as they apply to both synthetic methods and applications.

We report the synthesis of air-stable Pd(I) dimer complexes featuring biaryl phosphine ligands. Catalytic experiments suggest that these complexes are comptent precatalysts that can mediate cross-coupling amination reactions between aryl halide electrophiles with both aliphatic and aromatic amine nucleophiles. This work represents an expansion of the air-stable precatalyst toolbox for Pd-catalyzed cross-coupling transformations.

Redox-active proanions of the type B_(12)(OCH_2Ar)_(12) [Ar = C_6F_5 (1), 4-CF_3C_6H_4 (2), 3,5-(CF_3)_2C_6H_3 (3)] are introduced in the context of an experimental and computational study of the visible-light-initiated polymerization of a family of styrenes. Neutral, air-stable proanions 1–3 were found to initiate styrene polymerization through single-electron oxidation under blue-light irradiation, resulting in polymers with number-average molecular weights (M_n) ranging from ∼6 to 100 kDa. Shorter polymer products were observed in the majority of experiments, except in the case of monomers containing 4-X (X = F, Cl, Br) substituents on the styrene monomer when polymerized in the presence of 1 in CH_2Cl_2. Only under these specific conditions are longer polymers (>100 kDa) observed, strongly supporting the formulation that reaction conditions significantly modulate the degree of ion pairing between the dodecaborate anion and cationic chain end. This also suggests that 1–3 behave as weakly coordinating anions (WCA) upon one-electron reduction because no incorporation of the cluster-based photoinitiators is observed in the polymeric products analyzed. Overall, this work is a conceptual realization of a single reagent that can serve as a strong photooxidant, subsequently forming a WCA.

The majority of biomolecules are intrinsically atomically precise, an important characteristic that enables rational engineering of their recognition and binding properties. However, imparting a similar precision to hybrid nanoparticles has been challenging because of the inherent limitations of existing chemical methods and building blocks. Here we report a new approach to form atomically precise and highly tunable hybrid nanomolecules with well-defined three-dimensionality. Perfunctionalization of atomically precise clusters with pentafluoroaryl-terminated linkers produces size-tunable rigid cluster nanomolecules. These species are amenable to facile modification with a variety of thiol-containing molecules and macromolecules. Assembly proceeds at room temperature within hours under mild conditions, and the resulting nanomolecules exhibit high stabilities because of their full covalency. We further demonstrate how these nanomolecules grafted with saccharides can exhibit dramatically improved binding affinity towards a protein. Ultimately, the developed strategy allows the rapid generation of precise molecular assemblies to investigate multivalent interactions.

We report a class of perfunctionalized dodecaborate clusters that exhibit high stability towards high concentration electrochemical cycling. These boron clusters afford several degrees of freedom in material design to tailor properties including solubility and redox potential. The exceptional stability of these clusters was demonstrated using a symmetric flow cell setup for electrochemical cycling between two oxidation states for 45 days, with post-run analysis showing negligible decomposition of the active species (

We report a new class of redox-­‐active vertex-­‐differentiated dodecaborate clusters featuring pentafluoroaryl groups. These [B12(OR)11NO2] clusters share several unique photophysical properties with their [B12(OR)12] analogues, while exhibiting significantly higher (+0.5 V) redox potentials. This work describes the synthesis, characterization, and isolation of [B12(O-­‐CH2C6F5)11NO2] clusters in all 3 oxidation states (dianion, radical, and neutral). Reactivity to post-­‐functionalization with thiol species via SNAr on the pentafluoroaryl groups is also demonstated.

We have developed a fast and efficient route to obtain perfunctionalized ether-linked alkyl and benzyl derivatives of the closo-[B12(OH)12]2− icosahedral dodecaborate cluster via microwave-assisted synthesis. These icosahedral boron clusters exhibit three-dimensional delocalization of the cage-bonding electrons, tunable photophysical properties, and a high degree of stability in air in both solid and solution states. A series of closo-[B12(OR)12]2−, hypocloso-[B12(OR)12]1− and hypercloso-[B12(OR)12]0 clusters have been prepared with reaction times ranging from hours to several minutes. This method is superior to previously reported protocols since it dramatically decreases the reaction times required and eliminates the need for inert atmosphere conditions. The generality of the new microwave-based method has been further demonstrated through the synthesis of several new derivatives, which feature redox potentials up to 0.6 V more positive than previously known B12(OR)12 cluster compounds. We further show how this method can be applied to a one-pot synthesis of hybrid, vertex-differentiated species B12(OR)11(OR) that was formerly accessible only via multi-step reaction sequence.

Mechanochemical syntheses avoid or considerably reduce the use of reaction solvents, thus providing green chemistry synthetic alternatives that are both environmentally friendly and economically advantageous. The increased solid-state reactivity generated by mechanical energy imparted to the reactants by grinding or milling can offer alternative synthetic routes, occasionally yielding products (structures or stoichiometries) not obtainable via solution chemistry. Additionally, small volumes of solvents added during grinding can control the polymorphic form of the products. An undergraduate organic chemistry experiment is described involving liquid-assisted grinding (LAG) synthesis of the green and black polymorphs of the tetrathiafulvalene-chloranil (TTF-CA) charge transfer salt and their solid state characterization using FT-IR and melting point analysis.

Nanostructured materials such as zinc oxide (ZnO) nanorods, exhibit novel physical properties compared with their bulk [1-2]. For example, ZnO is an important material widely used in piezoelectric transducers and actuators, surface acoustic coatings, sensors and photocatalysts [1-6]. To optimize the potential applications of ZnO, it is essential to modify the ZnO with functional groups to integrate the ZnO into desired structures or attach suitable nanostructures on the nanotubes. Among them, metal-nanotube interactions are especially attractive for the development of novel catalysts. The self-assembled gold nanoparticles assembled over ZnO nanorods are particularly promising as novel catalysts.

Recent research has shown that choline chloride (vitamin B4)-based solutions can be used as a greener alternative to acid-based electrochemical polishing solutions. This study demonstrated a successful method for electrochemical deposition of niobium compounds onto the surface of copper substrates using a novel choline chloride-based ionic liquid. Niobium ions present in the ionic liquid solution were dissolved into the solution prior to deposition via electrochemical polishing of solid niobium. A black coating was clearly visible on the surface of the Cu following deposition. This coating was analyzed using scanning electron microscopy (SEM), electron dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), and X-ray fluorescence spectroscopy (XRF). This ionic liquid-based electrochemical deposition method effectively recycles previously dissolved niobium from electrochemical polishing of superconducting radio frequency (SRF) cavities.

Minimal surface roughness is a critical feature for high-field superconducting radio frequency (SRF) cavities used to engineer particle accelerators. Current methods for polishing Niobium cavities typically utilize solutions containing a mixture of concentrated sulfuric and hydrofluoric acid. Polishing processes such as these are effective, yet there are many hazards and costs associated with the use (and safe disposal) of the concentrated acid solutions. An alternative method for electrochemical polishing of the cavities was explored using a novel ionic liquid solution containing choline chloride. Potentiostatic electrochemical impedance spectroscopy (EIS) was used to analyze the ionic polishing solution. Final surface roughness of the Nb was found to be comparable to that of the acid-polishing method, as assessed by atomic force microscopy (AFM). This indicates that ionic liquid-based electrochemical polishing of Nb is a viable replacement for acid-based methods for preparation of SRF cavities.

Recent research has shown that choline chloride-based solutions can be used to replace acid-based electrochemical polishing solutions. In this study niobium metal was successfully deposited on the surface of copper substrate via electrochemical deposition using a novel choline chloride-based ionic liquid. The niobium metal used for deposition on the Cu had been dissolved in the solution from electrochemical polishing of a solid niobium piece prior to the deposition. The visible coating on the surface of the Cu was analyzed using scanning electron microscopy (SEM) and electron dispersive x-ray spectroscopy (EDX). This deposition method effectively recycles previously dissolved niobium from electrochemical polishing.

There is significant interest in the development of methods to create hybrid materials that transform capabilities, in particular for Earth-abundant metal oxides, such as TiO2, to give improved or new properties relevant to a broad spectrum of applications. Here we introduce an approach we refer to as ‘molecular cross-linking’, whereby a hybrid molecular boron oxide material is formed from polyhedral boron-cluster precursors of the type [B12(OH)12]2–. This new approach is enabled by the inherent robustness of the boron-cluster molecular building block, which is compatible with the harsh thermal and oxidizing conditions that are necessary for the synthesis of many metal oxides. In this work, using a battery of experimental techniques and materials simulation, we show how this material can be interfaced successfully with TiO2 and other metal oxides to give boron-rich hybrid materials with intriguing photophysical and electrochemical properties.

Modern particle accelerators require minimal interior surface roughness for Niobium superconducting radio frequency (SRF) cavities. Polishing of the Nb is currently achieved via electrochemical polishing with concentrated mixtures of sulfuric and hydrofluoric acids. This acid-based approach is effective at reducing the surface roughness to acceptable levels for SRF use, but due to acid-related hazards and extra costs (including safe disposal of used polishing solutions), an acid-free method would be preferable. This study focuses on an alternative electrochemical polishing method for Nb, using a novel ionic liquid solution containing choline chloride, also known as Vitamin B{sub 4} (VB{sub 4}). Potentiostatic electrochemical impedance spectroscopy (EIS) was also performed on the VB4-based system. Nb polished using the VB4-based method was found to have a final surface roughness comparable to that achieved via the acid-based method, as assessed by atomic force microscopy (AFM). These findings indicate that acid-free VB{sub 4}-based electrochemical polishing of Nb represents a promising replacement for acid-based methods of SRF cavity preparation.

The majority of biomolecules are intrinsically atomically precise, an important characteristic that enables rational engineering of their recognition and binding properties. However, imparting similar precision to hybrid nanoparticles has been challenging due to inherent limitations of the existing chemical methods and availability of properly designed functional building blocks. Here we report a new approach to form atomically precise and highly tunable hybrid nanomolecules with well-defined three-dimensionality. Perfunctionalization of atomically precise clusters with pentafluoroaryl-terminated linkers produces size-tunable rigid cluster nanomolecules. These species are amenable to facile modification with a variety of thiol-containing molecules and macromolecules. Assembly proceeds at room temperature within hours under mild conditions, and the resulting nanomolecules exhibit high stabilities due to their full covalency. We further demonstrate how these nanomolecules grafted with saccharides can exhibit dramatically improved binding affinity toward a protein. Ultimately, the developed strategy allows the rapid generation of precise molecular assemblies for investigating multivalent interactions.

We report a discovery that perfunctionalized icosahedral dodecaborate clusters of the type B_(12)(OCH_2Ar)_(12) (Ar = Ph or C_6F_5) can undergo photo-excitation with visible light, leading to a new class of metal-free photooxidants. Excitation in these species occurs as a result of the charge transfer between low-lying orbitals located on the benzyl substituents and an unoccupied orbital delocalized throughout the boron cluster core. Here we show how these species, photo-excited with a benchtop blue LED source, can exhibit excited-state reduction potentials as high as 3 V and can participate in electron-transfer processes with a broad range of styrene monomers, initiating their polymerization. Initiation is observed in cases of both electron-rich and electron-deficient styrene monomers at cluster loadings as low as 0.005 mol%. Furthermore, photo-excitation of B_(12)(OCH_2C_6F_5)_(12) in the presence of a less activated olefin such as isobutylene results in the production of highly branched poly(isobutylene). This work introduces a new class of air-stable, metal-free photo-redox reagents capable of mediating chemical transformations.

In the version of this Article originally published, Liban M. A. Saleh was incorrectly listed as Liban A. M. Saleh due to a technical error. This has now been amended in all online versions of the Article.

Nanomaterials between 1 and 100 nm in size typically exhibit uniqueelectrical,optical,andcatalyticproperties.Metalnanoparticles of various sizes show a significant reduction in potential compared to bulk metals as the Fermi potential of nanoparticles becomes more negative. This specific property allows for metal nanoparticles to act as catalysts in various electron transfer processes, even if the bulk form of the same metal is typically considered to be inert. Bulk gold is often considered chemically inert due to the inability of bulk gold to oxidize in air, along with the lack of reaction with a majority of chemical reagents. This low catalytic activity is directly related to the particle sizes present in bulk gold. However, small gold nanoparticles (AuNPs) supported over certain nanomaterials exhibit unprecedented catalytic activities. Carbon nanotubes (CNTs) are a novel carbon allotrope that possesses structural and electronic properties that are unique from other carbon allotropes, such as graphite

Tetrathiafulvalene-chloranil (TTF-CA) was synthesized by two methods, liquid assisted grinding (LAG) and vapor digestion (VD), which largely reduce the use of reaction solvents. The effects of the small quantities of LAG solvent and solvent vapors in VD toward the formation of a particular TTF-CA product polymorph were studied from both tetrathiafulvalene forms (orange and brown) as reactants. It was concluded that a high solvent polarity index favors the formation of the ionic black polymorph of TTF-CA vs the quasineutral green form, whereas the crystal structure and crystal habit of the orange tetrathiafulvalene polymorph also favors the formation of the black TTF-CA. The crystal structure of the black TTF-CA was determined from synchrotron X-ray powder diffraction (XRPD), and it consists of dimerized TTF+• and CA−• radical ions, in agreement with room temperature magnetic susceptibility measurements indicating the material is diamagnetic. FT-IR showed that the compound is a semiconductor with a small band gap of ∼0.198 eV and it remains ionic at low temperatures. The latter was confirmed by XRPD showing the black TTF-CA does not undergo a phase transition in the range 298−20 K. Band structure calculations are in good agreement with the measured band gap. Fil: Lapidus, Saul H.. Stony Brook University; Estados Unidos Fil: Naik, Amit. Thomas Nelson Community College; Estados Unidos Fil: Wixtrom, Alex. Christopher Newport University; Estados Unidos Fil: Massa, Nestor Emilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; Argentina Fil: Ta Phuoc, Vinh. UniversitéFrancois Rabelais Tours; Francia Fil: del Campo, Leire. Université d’Orleans; Francia Fil: Lebegue, Sebestien. Université de Lorraine; Francia Fil: Aygyayn, Jaynos G.. Université de Lorraine; Francia Fil: Abdel Fattah, Tarek. Christopher Newport University; Estados Unidos Fil: Pagola, Silvina. College of William and Mary; Estados Unidos

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