Here we report on the ion conductance through individual, small diameter single-walled carbon nanotubes. We find that they are mimics of ion channels found in natural systems. We explore the factors ...governing the ion selectivity and permeation through single-walled carbon nanotubes by considering an electrostatic mechanism built around a simplified version of the Gouy–Chapman theory. We find that the single-walled carbon nanotubes preferentially transported cations and that the cation permeability is size-dependent. The ionic conductance increases as the absolute hydration enthalpy decreases for monovalent cations with similar solid-state radii, hydrated radii, and bulk mobility. Charge screening experiments using either the addition of cationic or anionic polymers, divalent metal cations, or changes in pH reveal the enormous impact of the negatively charged carboxylates at the entrance of the single-walled carbon nanotubes. These observations were modeled in the low-to-medium concentration range (0.1–2.0 M) by an electrostatic mechanism that mimics the behavior observed in many biological ion channel-forming proteins. Moreover, multi-ion conduction in the high concentration range (>2.0 M) further reinforces the similarity between single-walled carbon nanotubes and protein ion channels.
Conjugated Molecular Nanotubes Mirzaei, Saber; Castro, Edison; Hernández Sánchez, Raúl
Chemistry : a European journal,
June 16, 2021, Letnik:
27, Številka:
34
Journal Article
Recenzirano
Molecular compounds with permanent tubular architectures displaying radial π‐conjugation are exceedingly rare. Their radial and axial delocalization presents them with unique optical and electronic ...properties, such as remarkable tuning of their Stokes shifts, and redox switching between global and local aromaticity. Although these tubular compounds display large internal void spaces, these attributes have not been extensively explored, thus presenting future opportunities in the development of materials. By using cutting‐edge synthetic methodologies to bend aromatic surfaces, large opportunities in synthesis, property discovery, and applications are expected in new members of this family of conjugated molecular nanotubes.
Synthetic efforts to bend aromatic surfaces have had a remarkable evolution during the last dozen years. Conjugated nanorings and nanobelts are among the most well‐known examples. However, this progress has also led to the synthesis of molecular compounds with permanent tubular shapes with radial and axial π surfaces, which are the highlight of this Minireview.
The field of single molecule magnetism remains predicated on super- and double exchange mechanisms to engender large spin ground states. An alternative approach to achieving high-spin architectures ...involves synthesizing weak-field clusters featuring close M–M interactions to produce a single valence orbital manifold. Population of this orbital manifold in accordance with Hund’s rules could potentially yield thermally persistent high-spin ground states under which the valence electrons remain coupled. We now demonstrate this effect with a reduced hexanuclear iron cluster that achieves an S = 19/2 (χMT ≈ 53 cm3 K/mol) ground state that persists to 300 K, representing the largest spin ground state persistent to room temperature reported to date. The reduced cluster displays single molecule magnet behavior manifest in both variable-temperature zero-field 57Fe Mössbauer and magnetometry with a spin reversal barrier of 42.5(8) cm–1 and a magnetic blocking temperature of 2.9 K (0.059 K/min).
Oxidation of the nucleophilic nitride, (salen)Mn≡N (1) with stoichiometric Ar3NX initiated a nitride coupling reaction to N2, a major step toward catalytic ammonia oxidation ...(salen=N,N′‐bis(salicylidene)‐ethylenediamine dianion; Ar=p‐bromophenyl; X=SbCl6− or B(C6F5)4−). N2 production was confirmed by mass spectral analysis of the isotopomer, 1‐15N, and the gas quantified. The metal products of oxidation were the reduced MnIII dimers, (salen)MnCl2 (2) or (salen)Mn(OEt2)2B(C6F5)42 (3) for X=SbCl6− or B(C6F5)4−, respectively. The mechanism of nitride coupling was probed to distinguish a nitridyl from a nucleophilic/electrophilic coupling sequence. During these studies, a rare mixed‐valent MnV/MnIII bridging nitride, (salen)MnV(μ‐N)MnIII(salen)B(C6F5)4 (4), was isolated, and its oxidation‐state assignment was confirmed by X‐ray diffraction (XRD) studies, perpendicular and parallel‐mode EPR and UV/Vis/NIR spectroscopies, as well as superconducting quantum interference device (SQUID) magnetometry. We found that 4 could subsequently be oxidized to 3. Furthermore, in view of generating a catalytic system, 2 can be re‐oxidized to 1 in the presence of NH3 and NaOCl closing a pseudo‐catalytic “synthetic” cycle. Together, the reduction of 1→2 followed by oxidation of 2→1 yield a genuine synthetic cycle for NH3 oxidation, paving the way to the development of a fully catalytic system by using abundant metal catalysis.
Store that H2! Oxidation of a simple (salen)Mn≡N resulted in the 6e− nitride coupling reaction, central to NH3 oxidation to N2. A complete synthetic cycle was established with implications for catalytic NH3 oxidation for H2‐storage applications. An unusual mixed‐valent MnV/MnIII species was also isolated and characterized (see scheme).
A Helicene Nanoribbon with Greatly Amplified Chirality Schuster, Nathaniel J; Hernández Sánchez, Raúl; Bukharina, Daria ...
Journal of the American Chemical Society,
05/2018, Letnik:
140, Številka:
20
Journal Article
Recenzirano
We report the synthesis and characterization of a chiral, shape-persistent, perylene-diimide-based nanoribbon. Specifically, the fusion of three perylene-diimide monomers with intervening naphthalene ...subunits resulted in a helical superstructure with two 6helicene subcomponents. This π-helix-of-helicenes exhibits very intense electronic circular dichroism, including one of the largest Cotton effects ever observed in the visible range. It also displays more than an order of magnitude increase in circular dichroism for select wavelengths relative to its smaller homologue. These impressive chiroptical properties underscore the potential of this new nanoribbon architecture in the context of chiral electronic materials.
Chemical oxidation and reduction of the all-ferrous (HL)2Fe6 in THF affords isostructural, coordinatively unsaturated clusters of the type (HL)2Fe6 n : (HL)2Fe6BArF24 (1, n = +1; where BArF24− = ...tetrakis(3,5-trifluoromethyl)phenylborate), Bu4N(HL)2Fe6 (2a, n = −1), P(HL)2Fe6 (2b, n = −1; where P+ = tributyl(1,3-dioxolan-2-ylmethyl)phosphonium), and Bu4N2(HL)2Fe6 (3, n = −2). Each member of the redox-transfer series was characterized by zero-field 57Fe Mössbauer spectroscopy, near-infrared spectroscopy, single-crystal X-ray crystallography, and magnetometry. Redox-directed trends are observed when comparing the structural metrics within the Fe6 core. The metal octahedron Fe6 decreases marginally in volume as the molecular reduction state increases as gauged by the Fe–Feavg distance varying from 2.608(11) Å (n = +1) to 2.573(3) (n = −2). In contrast, the mean Fe–N distances and ∠Fe–N–Fe angles correlate linearly with the Fe6 oxidation level, or alternatively, the changes observed within the local Fe–N4 coordination planes vary linearly with the aggregate spin ground state. In general, as the spin ground state (S) increases, the Fe–N(H)avg distances also increase. The structural metric perturbations within the Fe6 core and measured spin ground states were rationalized extending the previously proposed molecular orbital diagram derived for (HL)2Fe6. Chemical reduction of the (HL)2Fe6 cluster results in an abrupt increase in spin ground state from S = 6 for the all-ferrous cluster, to S = 19/2 in the monoanionic 2b and S = 11 for the dianionic 3. The observation of asymmetric intervalence charge transfer bands in 3 provides further evidence of the fully delocalized ground state observed by 57Fe Mössbauer spectroscopy for all species examined (1–3). For each of the clusters examined within the electron-transfer series, the observed spin ground states thermally persist to 300 K. In particular, the S = 11 in dianionic 3 and S = 19/2 in the monoanionic 2b represent the highest spin ground states isolated up to room temperature known to date. The increase in spin ground state results from population of the antibonding orbital band comprised of the Fe–N σ* interactions. As such, the thermally persistent ground states arise from population of the resultant single spin manifolds in accordance with Hund’s rules. The large spin ground states, indicative of strong ferromagnetic electronic alignment of the valence electrons, result from strong direct exchange electronic coupling mediated by Fe–Fe orbital overlap within the Fe6 cores, equivalent to a strong double exchange magnetic coupling B for 3 that was calculated to be 309 cm–1.
Molecular compounds with zigzag carbon nanotube geometries are exceedingly rare. Here we report the synthesis and characterization of carbon-based nanotubes with zigzag geometry, best described as ...radially oriented ncyclo-meta-phenylenes, extending the tubularene family of compounds. By the incorporation of edge-sharing benzene rings into the tubularene’s radial π-surface, we have uncovered the first step to give rise to the emergence of radial orbital distribution in zigzag nanorings.
This manuscript presents a working redox battery in organic media that possesses remarkable cycling stability. The redox molecules have a solubility over 1 mol electrons/liter, and a cell with 0.4 M ...electron concentration is demonstrated with steady performance >450 cycles (>74 days). Such a concentration is among the highest values reported in redox flow batteries with organic electrolytes. The average Coulombic efficiency of this cell during cycling is 99.868%. The stability of the cell approaches the level necessary for a long lifetime nonaqueous redox flow battery. For the membrane, we employ a low cost size exclusion cellulose membrane. With this membrane, we couple the preparation of nanoscale macromolecular electrolytes to successfully avoid active material crossover. We show that this cellulose-based membrane can support high voltages in excess of 3 V and extreme temperatures (−20 to 110 °C). These extremes in temperature and voltage are not possible with aqueous systems. Most importantly, the nanoscale macromolecular platforms we present here for our electrolytes can be readily tuned through derivatization to realize the promise of organic redox flow batteries.
Macrocyclic arenes laid the foundations of supramolecular chemistry and their study established the fundamentals of noncovalent interactions. Advancing their frontier, here we designed rigidified ...resorcin4arenes that serve as hosts for large nonspherical anions. In one synthetic step, we vary the host's anion affinity properties by more than seven orders of magnitude. This is possible by engineering electropositive aromatic C-H bond donors in an idealized square planar geometry embedded within the host's inner cavity. The hydrogen atom's electropositivity is tuned by introducing fluorine atoms as electron withdrawing groups. These novel macrocycles, termed fluorocages, are engineered to sequester large anions. Indeed, experimental data shows an increase in the anion association constant (
K
a
) as the number of F atoms increase. The observed trend is rationalized by DFT calculations of Hirshfeld Charges (HCs). Most importantly, fluorocages in solution showed weak-to-medium binding affinity for large anions like PF
6
−
(10
2
<
K
a
<10
4
M
−1
), and high affinity for MeSO
3
−
(
K
a
>10
6
).
Fluorocages: new class of rigidified host utilizing nontraditional C-H hydrogen bonds to capture the nonspherical anions.
Electron Cartography in Clusters Hernández Sánchez, Raúl; Champsaur, Anouck M.; Choi, Bonnie ...
Angewandte Chemie (International ed.),
October 15, 2018, Letnik:
57, Številka:
42
Journal Article
Recenzirano
Odprti dostop
Deconvoluting the atom‐specific electron density within polynuclear systems remains a challenge. A multiple‐wavelength anomalous diffraction study on four clusters that share the same Co6Se8 core was ...performed. Two cluster types were designed, one having a symmetric ligand sphere and the other having an asymmetric ligand sphere. It was found that in the neutral, asymmetric, CO‐bound cluster, the Co−CO site is more highly oxidized than the other five Co atoms; when an electron is removed, the hole is distributed among the Se atoms. In the neutral, symmetric cluster, the Co atoms divide by electron population into two sets of three, each set being meridional; upon removal of an electron, the hole is distributed among all the Co atoms. This ligand‐dependent tuning of the electron/hole distribution relates directly to the performance of clusters in biological and synthetic systems.
Here be electrons: Deconvoluting the atom‐individual valence information in delocalized mixed‐valent polynuclear systems remains a challenge. The electron density across Co6Se8 clusters is mapped and its reconfiguration upon single‐electron oxidation is elucidated.
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