Revealing the Intercalation Mechanism of Aluminum Fluoride in Graphite

The electrolyte intercalation mechanism facilitates the insertion/extraction of charge into the electrode material in rechargeable batteries. Aluminum fluoride (AlF$_{3}$) has been used as an electrolyte in rechargeable aluminum batteries with graphite electrodes, demonstrating improved reversibility of battery charging and discharging processes; however, the intercalation mechanism of this neutral molecule in graphite is so far unknown. In this work, we combine scanning tunneling microscopy (STM) in ultra-high vacuum conditions, calculations based on density functional theory, and large-scale molecular dynamics simulations to reveal the mechanism of AlF$_{3}$ intercalation in highly oriented pyrolytic graphite (HOPG). We report the formation of AlF$_{3}$ molecules clusters between graphite layers, their self-assembly by graphene buckling-mediated interactions, and explain the origin and distribution of superficial {\it blisters} in the material.Comment: 8 pages, 3 figures, SI on deman

Incorporation of either molybdenum or tungsten into formate dehydrogenase from Desulfovibrio alaskensis NCIMB 13491; EPR assignment of the proximal iron-sulfur cluster to the pterin cofactor in formate dehydrogenases from sulfate-reducing bacteria

J Biol Inorg Chem (2004) 9: 145–151 DOI 10.1007/s00775-003-0506-zWe report the characterization of the molecular properties and EPR studies of a new formate dehydrogenase (FDH) from the sulfate-reducing organism Desulfovibrio alaskensis NCIMB 13491. FDHs are enzymes that catalyze the two-electron oxidation of formate to carbon dioxide in several aerobic and anaerobic organisms. D. alaskensis FDH is a heterodimeric protein with a molecular weight of 126+/-2 kDa composed of two subunits, alpha=93+/-3 kDa and beta=32+/-2 kDa, which contains 6+/-1 Fe/molecule, 0.4+/-0.1 Mo/molecule, 0.3+/-0.1 W/molecule, and 1.3+/-0.1 guanine monophosphate nucleotides. The UV-vis absorption spectrum of D. alaskensis FDH is typical of an iron-sulfur protein with a broad band around 400 nm. Variable-temperature EPR studies performed on reduced samples of D. alaskensis FDH showed the presence of signals associated with the different paramagnetic centers of D. alaskensis FDH. Three rhombic signals having g-values and relaxation behavior characteristic of [4Fe-4S] clusters were observed in the 5-40 K temperature range. Two EPR signals with all the g-values less than two, which accounted for less than 0.1 spin/protein, typical of mononuclear Mo(V) and W(V), respectively, were observed. The signal associated with the W(V) ion has a larger deviation from the free electron g-value, as expected for tungsten in a d(1) configuration, albeit with an unusual relaxation behavior. The EPR parameters of the Mo(V) signal are within the range of values typically found for the slow-type signal observed in several Mo-containing proteins belonging to the xanthine oxidase family of enzymes. Mo(V) resonances are split at temperatures below 50 K by magnetic coupling with one of the Fe/S clusters. The analysis of the inter-center magnetic interaction allowed us to assign the EPR-distinguishable iron-sulfur clusters with those seen in the crystal structure of a homologous enzyme

KPFM and DFT as tools to correlate the charge distribution and molecular orientation of dendritic adsorbates on different surfaces

The interaction between metals and organic layers is currently a hot topic due to its relevance in future applications based on hybrid organic/inorganic systems at the nanoscale. This work studies the surface modification of HOPG and gold substrates by spontaneous adsorption of aryl-dendrons based on either 3,5-bis(3,5-dinitrobenzoylamino) or 3,5-bis(3,5-diaminobenzoylamino) benzoic acids at fully controlled conditions. KPFM is used to assess the local work function variations upon assembly. A correlation between changes in work function values and spatial ordering of the adsorbates is observed. The aryl-dendrons interact with graphite surfaces through π-π stacking, allowing the formation of ordered layers. Due to depolarization effects, these films cause changes in the local work function values that are smaller on graphite surfaces than on gold substrates. Furthermore, the presence of molecular aggregates driven by intermolecular hydrogen bonding for the case of amino functionalized surfaces has a direct impact on the local work function, which varies depending on whether the areas are partially covered or densely packed. DFT calculations were performed in order to gain a deeper understanding of the correlation between the work function variations and the orientation of the effective molecular dipole moment due to the underlying molecular structures of the adsorbed layer.Fil: Farias, Eliana Desiree. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica; ArgentinaFil: Zoloff Michoff, Martin Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Química Teórica y Computacional; ArgentinaFil: Sueldo Occello, Valeria Noemi. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Brunetti, Veronica. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Passeggi, Mario Cesar Genaro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Glatzel, Thilo. Universitat Basel; Suiz

Surface characterizationofself-assembled NCu nanostructures

We report on the process of low energy nitrogen implantation and annealing of a copper surface. Through auger electron spectroscopy we study the nitrogen diffusion features as a function of the substrate temperature. With STM and LEIS we characterize the surface mofphology and the electronic sturcturi es analyzed with ARUPS.Fil: Cristina, Lucila Josefina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Moreno López, Juan Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Sferco, Silvano Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas; ArgentinaFil: Passeggi, Mario Cesar Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Vidal, Ricardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Ferron, Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química; Argentin

Synthesis, crystal structure and magnetic properties of a new dinuclear copper(II) amino acid complex [Cu-2(L-arg)(2)(mu-HPO4-O)(mu-HPO4-O,O ')(mu-OH)]-.(H3O)+.(H2O)6

A novel dinuclear copper(II) complex with the amino acid L-arginine (L-arg), with mono and bidentate HPO42- oxoanions and an OH- anion. [Cu2(L-arg)2(mu-HPO4-O)(mu-HPO4-O,O´)(mu-OH)]-.(H3O)+.6H2O (1) was prepared and its structure was determined by X-ray diffraction methods. The two independent copper ions are in a distorted square pyramidal coordination, each bonded to one L-arginine molecule. These two Cu(L-arg) units are bridged by two monoatomic equatorial-apical oxygen ligands belonging to a monodentate hydrogenphosphate group, and to the hydroxyl group. The copper ions in the dinuclear unit at d = 3.1948(8) angstrom are also connected by two equatorial oxygen belonging to a bidentate hydrogenphosphate. This dinuclear character and bridging scheme, not common for metal-amino acid compounds, is a consequence of the properties of the phosphate anions. The magnetic susceptibility at temperatures between 2 and 300 K and the isothermal magnetization curves at T = 2.29(1) K with applied fields up to 9 T were measured. The magnetic data indicate an antiferromagnetic intradinuclear exchange coupling J/kB = -3.7(1) K and using a molecular field approximation we estimated a weaker ferromagnetic, interaction J´/kB ~ 0.3 K between neighbour dinuclear units. Fil: Santana, R. C.. Universidade Federal de Goiás; BrasilFil: Carvalho, J. F.. Universidade Federal de Goiás; BrasilFil: Vencato, I.. Universidade Federal de Goiás; BrasilFil: Napolitano, H. B.. Universidade Estadual de Goiás; BrasilFil: Bortoluzzi, A. J.. Universidade Federal de Santa Catarina; BrasilFil: Barberis, G. E.. Universidade Estadual de Campinas; BrasilFil: Rapp, R. E.. Universidade Federal do Rio de Janeiro; BrasilFil: Passeggi, Mario Cesar Genaro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Calvo, Rafael. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin

Single Crystal EPR of the Mixed-Ligand Complex of Copper(II) with l‑Glutamic Acid and 1,10-Phenanthroline: A Study on the Narrowing of the Hyperfine Structure by Exchange

We report an EPR study at X- and Q-bands of polycrystalline and single crystal samples of the mixed copper­(II) complex with l-glutamic acid (glu) and 1,10-phenantroline (phen), [Cu­(glu)­(phen)­(H₂O)]⁺ NO₃^–·2­(H₂O). The polycrystalline sample spectrum at Q-band showed well resolved <i>g</i>_∥and <i>g</i>_⊥ features and partially solved hyperfine structure at <i>g</i>_∥, typical for weakly exchange coupled systems. This is confirmed from the angular variation of the EPR spectra which shows for certain magnetic field orientations a partially solved hyperfine structure characteristic of weak exchange, whereas a single Lorentzian line corresponding to strong exchange is observed for others. Analysis and simulation of the single crystal EPR spectra were performed using the random frequency modulation model of Anderson. Numerical simulations of the angular variation of the EPR spectra showed that the narrowing of the hyperfine structure is due to an exchange-mediated mechanism in which transitions between any pair of lines are equally likely. The exchange interaction responsible for this process is mediated by hydrophobic interactions between two phen molecules and a mixed chemical path of the type CuA–O_apH···O–C–O_eq–CuB, for which we evaluated an average isotropic exchange parameter |<i>J</i>| ≈ 25 × 10^–4 cm^–1

Thermally Annealed Sub‐Monolayers of AlF3 on Cu(100): An STM and XPS Study

A steady and durable transition from rough and randomly oriented 2D aluminum fluoride clusters to ultra‐thin films with defined arrangement is here reported. Scanning tunneling microscopy images show that the material deposited on top of Cu(100) reveals a smooth surface with a preferential arrangement and a transition in the morphology of the islands after performing a post‐deposition annealing treatment at 575 K. X‐ray photoelectron spectroscopy shows that the chemical environment of fluoride atoms remains unaltered after performing annealing treatments at this temperature. However, the tunneling voltage used to acquire STM images of the films changes from typical insulator values to metallic‐like ones after annealing. These results suggest an important change in the local density of states of the aluminum fluoride islands after the post‐deposition annealing treatment.© 2018 The Author

Magnetic Properties of Weakly Exchange-Coupled High Spin Co(II) Ions in Pseudooctahedral Coordination Evaluated by Single Crystal X‑Band EPR Spectroscopy and Magnetic Measurements

We report single-crystal X-band EPR and magnetic measurements of the coordination polymer catena-(trans-(μ2-fumarato)tetraaquacobalt(II)), 1, and the Co(II)-doped Zn(II) analogue, 2, in different Zn:Co ratios. 1 presents two magnetically inequivalent high spin S = 3/2 Co(II) ions per unit cell, named A and B, in a distorted octahedral environment coordinated to four water oxygen atoms and trans coordinated to two carboxylic oxygen atoms from the fumarate anions, in which the Co(II) ions are linked by hydrogen bonds and fumarate molecules. Magnetic susceptibility and magnetization measurements of 1 indicate weak antiferromagnetic exchange interactions between the S = 3/2 spins of the Co(II) ions in the crystal lattice. Oriented single crystal EPR experiments of 1 and 2 were used to evaluate the molecular g-tensor and the different exchange coupling constants between the Co(II) ions, assuming an effective spin S′= 1/2. Unexpectedly, the eigenvectors of the molecular g-tensor were not lying along any preferential bond direction, indicating that, in high spin Co(II) ions in roughly octahedral geometry with approximately axial EPR signals, the presence of molecular pseudo axes in the metal site does not determine preferential directions for the molecular g-tensor. The EPR experiment and magnetic measurements, together with a theoretical analysis relating the coupling constants obtained from both techniques, allowed us to evaluate selectively the exchange coupling constant associated with hydrogen bonds that connect magnetically inequivalent Co(II) ions (|JAB1/2| = 0.055(2) cm?1) and the exchange coupling constant associated with a fumarate bridge connecting equivalent Co(II) ions (|JAA1/2| ≈ 0.25 (1) cm?1), in good agreement with the average J3/2 value determined from magnetic measurements.Fil: Neuman, Nicolás Ignacio. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Winkler, Elin Lilian. Comision Nacional de Energia Atomica. Fundación Jose A. Balseiro; Argentina. Universidad Nacional de Cuyo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Peña, Octavio. Universite de Rennes I. Institut Des Sciences Chimiques de Rennes.; FranciaFil: Passeggi, Mario Cesar Guillermo. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Rizzi, Alberto Claudio. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Brondino, Carlos Dante. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentin