There is emerging evidence that growth of synthetic and natural phases occurs by the aggregation of prenucleation clusters, rather than classical atom-by-atom growth. Ferrihydrite, an iron ...oxyhydroxide mineral, is the common form of Fe3+ in soils and is also in the ferritin protein. We isolated a 10 angstrom discrete iron-oxo cluster (known as the Keggin ion, Fe13) that has the same structural features as ferrihydrite. The stabilization and manipulation of this highly reactive polyanion in water is controlled exclusively by its counterions. Upon dissolution of Fe13 in water with precipitation of its protecting Bi3+-counterions, it rapidly aggregates to ∼22 angstrom spherical ferrihydrite nanoparticles. Fe13 may therefore also be a prenucleation cluster for ferrihydrite formation in natural systems, including by microbial and cellular processes.
Understanding and controlling the electronic structure of molecules is crucial when designing and optimizing new organic semiconductor materials. We report the regioselective synthesis of eight ...π-expanded diarenoindacene analogues based on the indeno1,2-bfluorene framework along with the computational investigation of an array of diareno-fused antiaromatic compounds possessing s-indacene, pentalene, or cyclobutadiene cores. Analysis of the experimental and computationally derived optoelectronic properties uncovered a linear correlation between the bond order of the fused arene bond and the paratropicity strength of the antiaromatic unit. The E red 1 for the pentalene and indacene core molecules correlates well with their calculated NICSπZZ values. The findings of this study can be used to predict the properties of, and thus rationally design, new diareno-fused antiaromatic molecules for use as organic semiconductors.
Cycloparaphenylenes, or "carbon nanohoops," are unique conjugated macrocycles with radially oriented π-systems similar to those in carbon nanotubes. The centrosymmetric nature and conformational ...rigidity of these molecules lead to unusual size-dependent photophysical characteristics. To investigate these effects further and expand the family of possible structures, a new class of related carbon nanohoops with broken symmetry is disclosed. In these structures, referred to as
cycloparaphenylenes, a single carbon-carbon bond is shifted by one position in order to break the centrosymmetric nature of the parent
cycloparaphenylenes. Advantageously, the symmetry breaking leads to bright emission in the smaller nanohoops, which are typically non-fluorescent due to optical selection rules. Moreover, this simple structural manipulation retains one of the most unique features of the nanohoop structures-size dependent emissive properties with relatively large extinction coefficients and quantum yields. Inspired by earlier theoretical work by Tretiak and co-workers, this joint synthetic, photophysical, and theoretical study provides further design principles to manipulate the optical properties of this growing class of molecules with radially oriented π-systems.
Molecules and materials that demonstrate large amplitude responses to minor changes in their local environment play an important role in the development of new forms of nanotechnology. Molecular ...daisy chains are a type of a mechanically interlocked molecule that are particularly sensitive to such changes in which, in the presence of certain stimuli, the molecular linkage enables muscle‐like movement between a reduced‐length contracted form and an increased‐length expanded form. To date, all reported syntheses of molecular daisy chains are accomplished via passive‐template methods, resulting in a majority of structures being switchable only through the addition of an exogenous stimuli such as metal ions or changes in pH. Here, we describe a new approach to these structural motifs that exploits a multi‐component active‐metal template synthesis to mechanically interlock two pi‐rich nanohoop macrocycles into a molecular daisy chain that undergoes large conformational changes using thermal energy.
Molecular muscle: The synthesis and characterization of a fluorescent, small, pi‐rich c2daisy chain is described. The synthesis is accomplished using a multi‐component CuI‐catalysed active‐template Cadiot–Chodkiewicz reaction, ultimately assembling four molecular components into a single mechanically interlocked architecture. Through variable temperature NMR, the motion of this structure is then described.
Understanding the aqueous state of discrete metal-oxo clusters, prenucleation clusters, and even simple ions is valuable for controlling the growth of metal-oxide materials from water. Niobium ...polyoxometalates (Nb-POMs) are unique in the aqueous metal-oxo cluster landscape in their unusual solubility behavior: specifically, their solubility in water increases with increasing ion-pairing contact with their counterions, and thus provides a rare opportunity to observe these and related solution phenomena. Here, we isolate in the solid state the monomeric and dimeric building blocks, capped Keggin ions, of the extended Keggin chain materials that are now well-known: not only in Nb-POM chemistry, but Mo and V POM chemistry as well. Rb13GeNb13O41·23H2O (Rb1), Cs10.6H2.4GeNb13O41·27H2O (Cs1) and Cs18H6(NbOH)SiNb12O402·38H2O (Cs2) were characterized by single-crystal X-ray diffraction. Small angle X-ray scattering (SAXS) of solutions of Rb1 and Cs1 in varying conditions revealed oligomerization of the monomers into chain structures: the extent of oligomerization is controlled by pH, concentration, and the counterion. We distinctly observe chains of up to six Keggin ions in solution, with the large alkali cations for charge-balance. This combined solid state and solution study reveals in great detail the growth of a complex material from discrete monomeric building blocks. The fundamentals of the processes we are able to directly observe in this study, ion-association and hydrolysis leading to condensation, universally control the self-assembly and precipitation of materials from water.
Hydrogen sulfide (H2S) is an important biological signaling agent that exerts action on numerous (patho)physiological processes. Once generated, H2S can be oxidized to generate reductant-labile ...sulfane sulfur pools, which include hydrodisulfides/persulfides. Despite the importance of hydrodisulfides in H2S storage and signaling, little is known about the physical properties or chemical reactivity of these compounds. We report here the synthesis, isolation, and characterization (NMR, IR, Raman, HRMS, X-ray) of a small-molecule hydrodisulfide and highlight its reactivity with reductants, nucleophiles, electrophiles, acids, and bases. Our experimental results establish that hydrodisulfides release H2S upon reduction and that deprotonation results in disproportionation to the parent thiol and S0, thus providing a mechanism for transsulfuration in the sulfane sulfur pool.
Nanoscale carbon‐rich molecular architectures are not only aesthetically appealing but also of practical importance for energy and biomedical technologies. Herein, we report the synthesis of ...cyclic‐oligophenylene‐based nanopropeller 1 by using an efficient synthon strategy involving sequential intramolecular bisboronate homocoupling and reductive aromatization by H2SnCl4. The nanopropeller molecules pack into a layered hexagonal lattice featuring long‐ranged nano‐sized channels and a total guest‐accessible volume of 48 %, as revealed by X‐ray diffraction studies. We suggest that such a solid‐state arrangement is determined by the interplay between the propeller architecture and the intermolecular van der Waals interactions.
Nanohoops propel ahead: A triptycene‐based molecular propeller with three nanohoop blades was synthesized by a three‐fold intramolecular bisboronate homocoupling and subsequent reductive aromatization. Such nanopropeller molecules pack into a lamellar hexagonal structure with 11 Å‐diameter channels that run perpendicularly to the layers.
The consequence of unpaired electrons in organic molecules has fascinated and confounded chemists for over a century. The study of open-shell molecules has been rekindled in recent years as new ...synthetic methods, improved spectroscopic techniques and powerful computational tools have been brought to bear on this field. Nonetheless, it is the intrinsic instability of the biradical species that limits the practicality of this research. Here we report the synthesis and characterization of a molecule based on the diindenob,ianthracene framework that exhibits pronounced open-shell character yet possesses remarkable stability. The synthetic route is rapid, efficient and possible on the gram scale. The molecular structure was confirmed through single-crystal X-ray diffraction. From variable-temperature Raman spectroscopy and magnetic susceptibility measurements a thermally accessible triplet excited state was found. Organic field-effect transistor device data show an ambipolar performance with balanced electron and hole mobilities. Our results demonstrate the rational design and synthesis of an air- and temperature-stable biradical compound.
Reactive sulfur species (RSS) and reactive selenium species (RSeS) play integral roles in hydrogen sulfide (H2S) and hydrogen selenide (H2Se) biological signaling pathways, and dichalcogenide anions ...are proposed transient intermediates that facilitate a variety of biochemical transformations. Herein we report the selective synthesis, isolation, spectroscopic and structural characterization, and fundamental reactivity of persulfide (RSS–), perselenide (RSeSe–), thioselenide (RSSe–), and selenosulfide (RSeS–) anions. The isolated chalcogenides do not rely on steric protection for stability and have steric profiles analogous to cysteine (Cys). Simple reduction of S8 or Se by potassium benzyl thiolate (KSBn) or selenolate (KSeBn) in the presence of 18-crown-6 afforded K(18-crown-6)BnSS (1), K(18-crown-6)BnSeSe (2), K(18-crown-6BnSSe (3), and K(18-crown-6BnSeS (4). The chemical structure of each dichalcogenide was confirmed by X-ray crystallography and solution-state 1H, 13C, and 77Se NMR spectroscopy. To advance our understanding of the reactivity of these species, we demonstrated that reduction of 1–4 by PPh3 readily generates EPPh3 (E: S, Se), and reduction of 1, 3, and 4 by DTT readily produces HE–/H2E. Furthermore, 1–4 react with CN– to produce ECN–, which is consistent with the detoxifying effects of dichalcogenide intermediates in the Rhodanese enzyme. Taken together, this work provides new insights into the inherent structural and reactivity characteristics of dichalcogenides relevant to biology and advances our understanding of the fundamental properties of these reactive anions.
Porous molecular materials combine benefits such as convenient processability and the possibility for atom-precise structural fine-tuning which makes them remarkable candidates for specialty ...applications in the areas of gas separation, catalysis, and sensing. In order to realize the full potential of these materials and guide future molecular design, knowledge of the transition from molecular properties into materials behavior is essential. In this work, the class of compounds termed cycloparaphenylenes (CPPs)shape-persistent macrocycles with built-in cavities and radially oriented π-systemswas selected as a conceptually simple class of intrinsically porous nanocarbons to serve as a platform for studying the transition from analyte sorption properties of small aggregates to those of bulk materials. In our detailed investigation, two series of CPPs were probed: previously reported hoop-shaped nCPPs and a novel family of all-phenylene figure-8 shaped (lemniscal) bismacrocycles, termed spiron,nCPPs. A series of nanocarbons with different macrocycle sizes and heteroatom content have been prepared by atom-precise organic synthetic methods, and their structural, photophysical, and electronic attributes were disclosed. Detailed experimental studies (X-ray crystallography, gas sorption, and quartz-crystal microbalance measurements) and quantum chemical calculations provided ample evidence for the importance of the solid-state arrangement on the porosity and analyte uptake ability of intrinsically porous molecular nanocarbons. We demonstrate that this molecular design principle, i.e., incorporation of sterically demanding spiro junctions into the backbone of nanohoops, enables the manipulation of solid-state morphology without significantly changing the nature and size of the macrocyclic cavities. As a result, the novel spiron,nCPPs showed a remarkable performance as high affinity material for vapor analyte sensing.
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