Physchem, Volume 3, Issue 2 (June 2023) – 6 articles

We obtained thorough insight into the capabilities of various computational methods to account for the ligand field (LF) regime in lanthanide compounds, namely, a weakly perturbed ionic body and quasidegenerate orbital multiplets. The LF version of the angular overlap model (AOM) was considered. We intentionally took very simple idealized systems, the hypothetical [TbF]²⁺, [TbF₂]⁺ and [Tb(O₂NO)]²⁺, in order to explore the details overlooked in applications on complex realistic systems. We examined the 4f and 5d orbital functions in connection to f–f and f–d transitions in the frame of the two large classes of quantum chemical methods: wave function theory (WFT) and density functional theory (DFT). WFT methods are better suited to the LF paradigm. In lanthanide compounds, DFT faces intrinsic limitations because of the frequent occurrence of quasidegenerate ground states. Such difficulties can be partly encompassed by the nonstandard control of orbital occupation schemes. Surprisingly, we found that the simplest crystal field electrostatic approximation, reconsidered with modern basis sets, works well for LF parameters in ionic lanthanide systems. We debated the largely overlooked holohedrization effect that inserts artificial inversion symmetry into standard LF Hamiltonians. Full article

The crystallization and distribution the features of Pt, Pd and Pt/Pd nanoparticles in spin-on glass SiO₂ films were studied within a wide range of the dopant concentrations in silica sol (from 10 to 80 mol.% Pt, Pd or Pt/Pd per 100 mol.% Si). The grazing incidence X-ray diffraction (GIXRD) characterization revealed that the formation of 4–8 nm sized crystalline Pt, Pd and Pt/Pd nanoparticles in SiO₂ films began at the dopant concentrations of at least 10 mol.% Pt and/or Pd per 100 mol.% Si. The nanoparticles obtained from sols with the lower Pt, Pd or Pt/Pd concentrations were characterized by an amorphous structure. The dopants distribution over the film thickness (~21–47 nm) was studied using X-ray reflectometry. The effect of the dopant concentration, spin-coating modes and heat treatment temperature on the film thickness was characterized. When only one of the dopants (Pt or Pd) was introduced into the silica sol, the resulting nanoparticles were preferentially localized close to the film surface. When dopants were used together, the Pt/Pd nanoparticles were distributed more evenly. Full article

The flexible models of Novichok agents (A230, A232, and A234) from previous molecular dynamics simulations (MDSs) have been employed to create a parameter set for the Antoine equation of each of the three liquids. Furthermore, for the needs of this paper, new models of Novichok agents were created and studied via MDS due to the fact that the exact molecular structure of these compounds has been a matter of discussion in the last few years; however, recently, the literature favors a particular set of structures. Therefore, to cover our study holistically, both of the proposed molecular formulas were employed in the simulations and discussion. A range of ambient conditions was selected, and the data from the molecular dynamics simulations were employed to give the best possible fit in the selected vapor pressure range. When looking at the results for the two structures of A230, A232, and A234, we can see that, despite their differences, the A and B coefficients have the same magnitude in both cases (structures proposed by Ellison and Hoenig and structures proposed by Mirzayanov). Moving from the Ellison and Hoenig to Mirzayanov structures for substances A230 and A234 revealed a decrease (slight to major) in factors A and B of the Antoine equation. However, in the case of A232, where the Mirzayanov structure produces higher coefficients, this does not hold true. Overall, the Antoine equation of the studied agents will be an essential tool for understanding the behavior of these substances under different conditions. Full article

Electrochemical properties of transition metal complexes are important parameters that should be considered for the successful application of these compounds in catalytic reactions. The proper choice of ligands and the type of its coordination allow the construction of a catalyst with high performance. The reversibility of complex oxidation is a prerequisite for successful participation in redox catalysis, while the potential values correlate with the rate of the process and necessary catalyst loading. This work summarizes the results of the exploration of a series of ruthenium carborane complexes based on the nido-C₂B₉ ligand obtained in our group by cyclic voltammetry and describes the found correlations. The knowledge of the electrochemical properties of the studied ruthenacarboranes is required for the optimization of its structure for successful catalysis of Atom Transfer Radical Polymerization or other applications. It was found that the value of the potential of reversible Ru(II)-Ru(III) transition may vary from −0.501 to 0.389 V versus Fc|Fc⁺ couple, depending on the nature of auxiliary phosphine, halogen or nitrile ligand, natural bite angle of κ²-diphosphine ligand and the presence of alkyl substituents in the carborane cage. The further oxidation towards formal Ru(IV) may be reversible or not depending on the complex structure. The found trends are in good agreement with the earlier performed findings in the field of coordination chemistry and should be considered as a tool for obtaining of complexes suitable for catalytic applications. Full article

The in situ characterization of catalysts provides important information on the catalyst and the understanding of its catalytic performance and selectivity for a specific reaction. Temperature programmed analyses (TPX) techniques for catalyst characterization reveal the role of the support on the stabilization and dispersion of the active sites. However, these can be altered at high temperatures since sintering of active species can occur as well as possible carbon deposition which hinders the active species and deactivates the catalyst. The in situ characterization of the spent catalyst, however, may expose the causes of catalyst deactivation. For example, a simple temperature programmed oxidation (TPO) analysis on the spent catalyst may produce CO and CO₂ via a reaction with O₂ at high temperatures and this is a strong indication that deactivation may be due to the deposition of carbon. Other TPX techniques such as temperature programmed reduction (TPR) and pulse chemisorption are also valuable techniques when they are applied in situ to the fresh catalyst and then to the catalyst upon deactivation. In this work, two Ni supported catalysts were considered as examples to elucidate the importance of these techniques in the characterization study of catalysts applied to the reaction of hydrogenation of CO₂. Full article

We have measured the Raman spectra of some oligothiophenes (bithiophene, terthiophene, quarterthiophene, sexithiophene and octithiophene) and polythiophene with wavelengths from 325–1064 nm (3.815–1.165 eV). All of the materials give good quality spectra with 1064 nm excitation, although there is weak background fluorescence for some of them. The UV lines of 405 and 324 nm generally provide good-quality spectra, albeit with significant fluorescence for bithiophene and quarterthiophene. Surprisingly, there is little difference between the relative intensities (i.e., the ratio of a band’s intensity as compared to the strongest band) of the spectra with the different excitation wavelengths. However, close inspection of the 2000–3200 cm⁻¹ region of octithiophene and polythiophene with 325 and 405 nm excitation shows several modes in this region that can be assigned to combinations and overtones involving the ~1440 cm⁻¹ C–C ring stretch that do not appear with 1064 nm excitation. The presence of overtones and combinations with anomalously large intensities is a hallmark of resonance Raman spectroscopy. Full article