A careful choice of the surface coverage of iron phthalocyanine (FePc) on Ag (110) around the single monolayer allows us to drive with high precision both the long-range supramolecular arrangement ...and the local adsorption geometry of FePc molecules on the given surface. We show that this opens up the possibility of sharply switching the catalytic activity of FePc in the oxygen reduction reaction and contextual surface oxidation in a reproducible way. A comprehensive and detailed picture built on diverse experimental evidence from scanning tunnelling microscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, coupled with density functional theory calculations, sheds new light on the nature of the catalytically active molecule-surface coordination and on the boundary conditions for its occurrence. The results are of relevance for the improvement of the catalytic efficiency of metallo-macrocycles as viable substitutes for platinum in the cathodic compartment of low-temperature fuel cells.
Surface alloying of Cu(001) by Sn deposition is a finely controllable method of tuning the degree of copper reactivity in order to drive the on-surface assembly and synthesis of metal–organic ...coordination networks. In this work we show that the ( 3 2 × 2 ) R 45 ° reconstruction of the Sn/Cu(001) surface alloy acts as a weakly interacting substrate ideal for the assembly of rectangular metal–organic networks based on transition metals. As a demonstration, we have grown a two-dimensional coordination network formed by manganese and TCNQ (7,7,8,8-tetracyanoquinodimethane) with 1:1 stoichiometry. In contrast with the same structure grown on Au(111), the use of the Sn/Cu(001) substrate enables a commensurate structure with larger and more regular ordered domains. We show that the formation of a Cu–TCNQ coordination network and subsequent Mn–Cu transmetalation reactions are the key steps of the growth mechanism. Moreover, ab initio density-functional calculations indicate that the system studied in the present work is a unique example of a metal–organic coordination network weakly interacting with the substrate.
Iron(II) phthalocyanine (FePc) self-assembly on Ag(110) has been studied in ultrahigh-vacuum conditions at room temperature by means of scanning tunneling microscopy (STM) and density functional ...theory (DFT) calculations. For submonolayer to monolayer coverage, FePc molecules lie parallel to the Ag(110) surface, arranged in rows running along the 001 direction. Two similar yet distinct ordered phases are formed, the c(10 × 4) and p(10 × 4) superstructures. The latter is characterized by two equivalent equilibrium configurations of the constituent FePc units, that interconvert by means of a concerted transformation wherein molecules belonging to adjacent rows collectively rotate in opposite directions around the molecular axis perpendicular to the surface. The FePc adsorption site for both superstructures and the transition mechanism between the two configurations in the p(10 × 4) phase have been inferred from high resolution STM images and rationalized by means of DFT calculations. In the case of multilayer films a (1 ± 4, 4 ∓3) phase is observed, whose stacking geometry has been revealed by STM analysis. The p(10 × 4)/c(10 × 4) → (1 ± 4, 4 ∓3) coverage-dependent transformation is analyzed by DFT calculations, and shown to be driven by the overlayer−substrate interaction. The inclusion of the dispersion contribution to this interaction is found to be essential to correctly reproduce the observed phenomenon.
A combined experimental and theoretical study provides a rationale of the chemical and physical behavior for Pt(II)-acetonitrile and -benzonitrile complexes. The increased reactivity of the nitrile ...ligands, after coordination to Pt(II), can be explained by the energy decreasing of the ligands’ LUMOs. The theoretical models are able to reproduce the spectroscopic observations and show an excellent agreement between crystallographic data and optimized structures, nicely supporting the proposed models. Display omitted
•A combined experimental and theoretical study on Platinum(II) nitrile complexes.•Spectroscopic characterization including CP/MAS NMR data.•Redetermination of X-ray structures of cis-and trans-PtCl2(NCPh)2 and cis-PtCl2(NCCH3)2.•Theoretical study for a rationale of spectroscopic data.•Theoretical study for a rationale of the reactivity towards nucleophiles.
The spectroscopic characterization of cis- and trans-PtCl2(NCR)2 (R=CH3, Ph, CH2Ph) was reported in solid state and solution phase. Moreover, the X-ray structures of cis-PtCl2(NCCH3)2, cis- and trans-PtCl2(NCPh)2 were redetermined at low temperature. FT-IR and NMR showed a blue-shift and a slight shielding of the νCN and δ(13CCN) values, respectively, in a counterintuitive way with respect to the well known improved reactivity towards nucleophiles of nitriles ligands coordinated to platinum(II), when compared to their free forms. These spectroscopic behaviors were also confirmed by theoretical experiments at DFT level. Moreover, DFT approach showed that the increased reactivity of the nitrile ligands, after coordination to Pt(II), can be explained by the energy decreasing of the ligands’ LUMOs, instead of an increased polarization of the CN bond, accordingly with the orbital control model previously proposed for trans-PtCl2(MeCN)2. Finally, bond analysis also discarded the occurrence of Pt→N back-donation.
The combined experimental and theoretical study herein reported, provides a rationale of the chemical and physical behavior for Pt(II)-acetonitrile and -benzonitrile complexes, proving to be a potential tool to set suitable based-nitrile intermediates for the synthesis of new organometallic derivatives.
Objective
To compare counts of Aggregatibacter actinomycetemcomitans, Prevotella intermedia, Porphyromonas gingivalis and Fusobacterium nucleatum between crack users and non‐users.
Materials and ...methods
A cross‐sectional study was conducted involving seventy‐four crack cocaine users and eighty‐one non‐users matched for age, gender and tobacco use. Demographic and clinical variables were analysed. Subgingival bacterial samples were collected from four sites with the greatest probing depths and were analysed using real‐time polymerase chain reaction.
Results
No significant difference was found in the prevalence of total counts for each bacterial species analysed between groups. However, crack users had a 1.85 (95% CI: 1.03–3.31), 2.19 (95% CI 1.24–3.88), 2.53 (95% CI 1.27–5.04) and 2.40 (95% CI 1.22–4.75) greater probability of having the higher counts (≥75th percentile) for Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum, respectively.
Conclusion
Although some crack users had higher (>75th percentile) bacterial counts for Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum, total counts did not differ between crack users and non‐users, leading to the hypothesis that the higher occurrence of periodontitis on crack users may be related to other non‐bacterial factors.
A new synthetic route for the deposition of CoAl2O4 thin films at low temperature via MOCVD using the single-source precursor {CoAl(O i C3H7)42} is presented. Molecular properties of {CoAl(O i ...C3H7)42} have been investigated by means of NMR spectroscopy, mass spectrometry, and thermal analysis. Deposits have been characterized by XRD, AFM, UV−vis, and SIMS measurements.
Multicomponent supramolecular self-assemblies of exceptional long-range order and low defectivity are obtained if C60 and 5-(4-aminophenyl)-10,15,20-triphenylporphyrin (TPP-NH2) are assembled on ...Ag(110) by sequential evaporation in the submonolayer range of TPP-NH2 and fullerene on the substrate surface and subsequent annealing. A (±2 −3, 6 ± 3) array consisting of supramolecular stripes of a 1:1 C60/TPP-NH2 2D adduct develops at 410 K (the low temperature, LT, phase). If the LT phase is annealed at 470 K, then a 3:1 fullerene/TPP-NH2 (±3 −5, 5 ± 5) nanoporous array (the HT phase) forms, with each pore containing a single porphyrin molecule. Phase separation occurs by annealing the HT phase at 520 K. Structural models are proposed and discussed on the basis of the experimental scanning tunneling microscopy results.
Thermal self-assembly of C60 on (1 × 2)-Pt(110) following room-temperature deposition has been studied by means of scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and ...density functional theory (DFT) calculations. Two distinct C60 chemisorption phases have been identified and characterized as a function of the annealing temperature. After a thermal treatment at 700 K, islands of a C60 quasi-hexagonal lattice form. These islands are characterized by the highest surface density so far reported for a two-dimensional surface-supported fullerene phase (the surface area per molecule is 87.0 Å2), with intermolecular nearest-neighbor distances equal to 9.6 ± 0.1 Å. Embedded nanowires of fullerene dumbbell dimers (with an intermolecular distance equal to 9.2 ± 0.1 Å) occasionally nucleate within this high-density phase following a “molecular zip” mechanism. Highly site selective chemisorption driven by the particularly strong overlayer−substrate bonding is proposed to be responsible for the first reported example of surface-templated chemical bond formation between fullerene molecules. After annealing at 850 K, an oblique C60 chemisorption phase forms. This is characterized by a tetramolecular basis associated to each lattice point of the two-dimensional superstructure and by a peculiar bright−dim contrast in STM images acquired at positive sample bias values. The combination of high-resolution STM images with LEED data and DFT calculations leads to the conclusion that the (1 × 2) substrate reconstruction is lifted at the fullerene−platinum interface and also provides a detailed description of the molecular bonding sites and orientations found within the phase. It is proposed that the main factor ruling the interconversion of chemisorption phases is the variation of substrate atom mobility as a function of temperature.
The interaction of single C60 molecules with the (1 × 2)-Pt(110) surface has been studied by scanning tunneling microscopy and density functional theory (DFT) calculations on slab models. Molecules ...are observed to be frozen at room temperature and are found to be almost exclusively in the same configuration. Extensive DFT calculations show that this configuration is the global energy minimum, suggesting that adsorbed molecules have enough rototranslational freedom to escape from the numerous local minima. The adsorption energy (3.81 eV) is the strongest ever found for C60, and it is roughly proportional to the number of the Pt and C atoms at contact distance. Analysis of DFT results shows that the surface−adsorbate interaction is covalent in nature. A minority fraction of C60 molecules appear to be adsorbed on surface defects. A careful investigation of their registry and height with respect to the regularly adsorbed units leads to an indirect structural characterization of the nanopits which act as their adsorption sites.
PDF
