Reza Behjatmanesh-Ardakani

To probe the properties of single atoms is a challenging task, especially from the experimental standpoint, due to sensitivity limits. Nevertheless, it is sometimes possible to achieve this by making corresponding choices and adjustments to the experimental technique and sample under investigation. In the present case, the absolute value of the electronic charge the Fe atoms acquire when they are adsorbed on the surface of aluminum oxide α-Al₂O₃(0001) was measured by a set of surface-sensitive techniques: low-energy ion scattering (LEIS), Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and work function (WF) measurements, in combination with density functional theory (DFT) calculations. The main focus was the submonolayer coverage of Fe atoms in situ deposited on the well-ordered stoichiometric α-Al₂O₃(0001) 7 nm thick film formed on a Mo(110) crystal face. An analysis of the evolution of the Fe LVV Auger triplet upon variation of the Fe coverage shows that there is electronic charge transfer from Fe to alumina and that its value gradually decreases as the Fe coverage grows. The same trend is also predicted by the DFT results. Extrapolation of the experimental Fe charge value versus coverage plot yields an estimated value of a single Fe atom adsorbed on α-Al₂O₃(0001) of 0.98e (electron charge units), which is in reasonable agreement with the calculated value (+1.15e). The knowledge of this value and the possibility of its adjustment may be important points for the development and tuning of modern sub-nanometer-scale technologies of diverse applied relevance and can contribute to a more complete justification and selection of the corresponding theoretical models.

The adsorption and reaction of nitric oxide (NO) molecules on the surface of the model-supported metal/oxide system, consisting of Ni nanoparticles deposited on α-Al₂O₃ (0001) in ultra-high vacuum, have been studied using in situ surface-sensitive techniques and density functional theory (DFT) calculations. As a combination of X-ray and Auger electron spectroscopy (XPS, AES), Fourier-transform infrared (FTIR) spectroscopy, and temperature-programmed desorption (TPD) techniques reveals, there is a threshold of Ni particle mean size () of c.a. 2 nm, differentiating the electron state of adsorbed NO molecules and their reaction. The main feature of Ni particles normally not exceeding 2 nm is that the NO adsorbs in the form of (NO)₂ dimers, whereas, for larger particles, the NO molecules adsorb in the form of monomers, usually characteristic for the bulk Ni substrate. This difference is demonstrated to be the main reason for the different reaction of NO molecules on the surface of Ni/alumina. The striking feature is that, in the case of ultra-small Ni particles ( ≤ 2 nm), the nitrous oxide (N₂O) molecules are formed upon heating as a result of the NO self-reduction mechanism, which are otherwise not formed in the case of larger Ni particles. According to DFT results, this is due to the significant synergistic impact of NO co-adsorption on the neighboring NO dissociation reaction over ultra-small Ni particles, mediated by the metal/oxide perimeter interface. The observed molecular conversion effects offer an opportunity to tune the catalytic selectivity of this and related metal/oxide systems via varying the supported metal particle size.

In-situ formation of boron thin films on the Mo(110) surface, as well as the formation of the molybdenum boride and its oxide and the trends of carbon monoxide catalytic oxidation on the substrates formed, have been studied in an ultra-high vacuum (UHV) by a set of surface-sensitive characterization techniques: Auger and X-ray photoelectron spectroscopy (AES, XPS), low-energy ion scattering (LEIS), reflection-absorption infrared spectroscopy (RAIRS), temperature-programmed desorption (TPD), electron energy loss spectroscopy (EELS) and work function measurements using the Anderson method. The boron deposited at Mo(110) via electron-beam deposition at a substrate temperature of 300 K grows as a 2D layer, at least in submonolayer coverage. Such a film is bound to the Mo(110) via polarized chemisorption bonds, dramatically changing the charge density at the substrate surface manifested by the Mo(110) surface plasmon damping. Upon annealing of the B-Mo(110) system, the boron diffuses into the Mo(110) bulk following a two-mode regime: (1) quite easy dissolution, starting at a temperature of about 450 K with an activation energy of 0.4 eV; and (2) formation of molybdenum boride at a temperature higher than 700 K with M-B interatomic bonding energy of 3.8 eV. The feature of the formed molybdenum boride is that there is quite notable carbon monoxide oxidation activity on its surface. A further dramatic increase of such an activity is achieved when the molybdenum boride is oxidized. The latter is attributed to more activated states of molecular orbitals of coadsorbed carbon monoxide and oxygen due to their enhanced interaction with both boron and oxygen species for Mo_xB_yO_z ternary compound, compared to only boron for the Mo_x’B_y’ double alloy.

In the current work, a symmetrical tetradentate Schiff base ligand (H₂L) derived by the condensation of methoxy-salicylaldehyde with substituted phenylenediamine is used to prepare nickel (II) and palladium (II) complexes. The chemical structures of the synthesized compounds were investigated with the help of combustion analysis and spectrophotometrically using FT-IR and ¹H NMR. H₂L and its nickel (II) complex were obtained in pure crystalline form, and hence, these compounds were characterized by diffraction analysis. It was evident from single-crystal X-ray diffraction analysis (SC-XRD) that the ligand was doubly deprotonated (L⁻²) and coordinated with the Ni(II) ion via ONNO-donor sites, and a distorted square planar geometry was achieved. Interestingly, the complex also attaches a solvent molecule (DMF) through its electronegative O atom with the H atom of DMF through hydrogen bonding. The molecular structure of the synthesized compounds was further validated with the help of density functional theory (DFT) using the B3LYP/Def2-TZVP level of theory. Furthermore, the Pd(II) complex was tested for Suzuki–Miyaura cross-coupling reactions and the results showed better catalytic activity in mild conditions concerning the traditionally available catalysts. Graphical Abstract

New zinc(II) Schiff base complexes (Z1 and Z2) were prepared through the treatment of ONNO tetradentate Schiff base ligands (H₂L¹ and H₂L²) with zinc acetylacetonate. Elemental analysis (C, H and N) and other spectroscopic techniques such as FT-IR and ¹H NMR were used to characterize the produced ligands and their associated Zn(II) complexes. The structure of Z1 was explored by single crystal X-ray diffraction analysis. The structural investigations of Z1 demonstrate that it exists in the form of a centrosymmetric dimer in which penta coordinated Zn(II) ions are inter connected via µ-phenoxo bridges from one of the phenolic oxygen atoms of each tetradentate Schiff base ligand to the opposite zinc(II) ions. The theoretical calculations, performed by DFT using the B3LYP/Def2-TZVP level of theory, directed that the intended outcomes are in compliance with the actual consequences. The nature and types of non-covalent interactions present among the sample molecules were also investigated by using QTAIM and NCI calculations. Furthermore, antimicrobial activities of the synthesized Schiff base ligands and their respective zinc(II) complexes were also examined against two Gram-positive (Staphylococcus aureus and Bacillus cereus) and two Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria, and two fungal species (Aspergillus brasiliensis and Candida albicans). The agar well diffusion method and poisoned media technique were used for the study of biological properties of bacterial and fungi species, respectively. According to assessments of inhibitory zones, metal chelates are found to be somewhat more efficient than free ligands. Graphical Abstract