The field of organic electronics has been heavily impacted by the discovery and development of π-conjugated conducting polymers. These polymers show great potential for integration into future ...optical and electronic devices due to their capacity to transition between semiconducting and conducting states as well as the ability to alter mechanical properties by controlled doping, chemical modification, and stacking or creating composites with other materials. Among π-conjugated polymers, polythiophene and its derivatives has been one of the most extensively studied and is widely investigated computationally and experimentally for use in electronic devices such as light-emitting diodes, water purification devices, hydrogen storage, and biosensors. Various theoretical modeling studies of polythiophene ranging from an oligothiophene approach to infinite chain lengths (periodic boundary conditions) have been undertaken to study a variety of electronic and structural properties of these polymers. In this review, we discuss the recent advances in the understanding of pristine polythiophene and its derivatives from fundamental perspectives to device applications.
The title compounds, AnO2(H2O)5 n +, n = 1 or 2 and An = U, Np, and Pu, are studied using relativistic density functional theory (DFT). Three rather different relativistic methods are used, ...small-core effective core potentials (SC-ECP), a scalar four-component all-electron relativistic method, and the zeroeth-order regular approximation. The methods provide similar results for a variety of properties, giving confidence in their accuracy. Spin-orbit and multiplet corrections to the AnVI/AnV reduction potential are added in an approximate fashion but are found to be essential. Bulk solvation effects are modeled with continuum solvation models (CPCM, COSMO). These models are tested by comparing explicit (cluster), continuum, and mixed cluster/continuum solvation models as applied to various properties. The continuum solvation models are shown to accurately account for the effects of the solvent, provided that at least the first coordination sphere is included. Reoptimizing the structures in the presence of the bulk solvent is seen to be important for the equatorial bond lengths but less relevant for energetics. Explicit inclusion of waters in the second coordination sphere has a modest influence on the energetics. For the first time, free energies of solvation are calculated for all six AnO2(H2O)5 n + species. The calculated numbers are within the experimental error margins, and the experimental trend is reproduced correctly. By comparison of different relativistic methods, it is shown that an accurate relativistic description leads to marked improvements over the older large-core ECP (LC-ECP) method for bond lengths, vibrational frequencies, and, in particular, the AnVI/AnV reduction potential. Two approximate DFT methods are compared, B3LYP, a hybrid DFT method, and PBE, a generalized gradient approximation. Either method yields AnVI/AnV reduction potentials of comparable quality. Overall, the experimental reduction potentials are accurately reproduced by the calculations.
Density functional theory (DFT) calculations have been carried out on the possible degradation/demethylation mechanism of methyl mercury (CH3Hg+) complexes with free cysteine and seleonocysteine. The ...binding of CH3Hg+ ions with one (seleno)amino acid is thermodynamically favorable. However, the binding with another acid molecule is a highly unfavorable process. The CH3Hg-(seleno)cysteinate then degrades to bis(methylmercuric)sulphide (selenide for the Se-containing complex) which in turn forms dimethyl mercury and HgS/HgSe, the latter being precipitated out as nanoparticles. The dimethyl mercury interacts with water molecules and regenerates the CH3HgOH precursor. The calculated free energies of formation confirm the thermodynamic feasibility of every intermediate step of the degradation cycle and fully support earlier experimental results. In completing the cycle, one unit of mercury precipitates out from two units of sources, and thereby Se antagonizes the Hg toxicity. The degradation of CH3Hg-l-cysteinate is thermodynamically more favorable than the formation of CH3Hg-l-cysteinate. The preferred degradation of the CH3Hg-l-cysteinate suggests that another mechanism for CH3Hg to cross the blood−brain barrier should exist.
Based on density functional theory calculations, the structural and electronic properties of polythiophene in periodic and oligomer forms have been investigated. In particular, the effects of Li or ...Cl adsorption onto a monolayer and Li or Cl intercalation into bulk or bilayer polythiophene are addressed using periodic calculations. The binding energy of Li or Cl adsorbed bulk or bilayer polythiophene is significantly larger than for the monolayer. The trends in the binding energy as a function of adsorbent remain the same for both the periodic and molecular cases. The band gap or HOMO–LUMO gap and charge transfer are analyzed. In addition, for the bulk or bilayer, different kinds of stacking have been considered. It is found that the parallel bulk or bilayer structure is energetically favorable compared to flipping the second layer by 180°. This has been considered for both the periodic and oligomer forms. Moreover, for Li adsorption, polarons are found to be more stable than bipolarons, while the situation is opposite for Cl adsorption. The detailed analysis of the present study will be useful for understanding the structural properties and the tuneability of the electronic states, which is an important step to construct polythiophene-based electronic devices.
The most common motif in uranium chemistry is the d(0)f(0) uranyl ion UO(2)(2+) in which the oxo groups are rigorously linear and inert. Alternative geometries, such as the cis-uranyl, have been ...identified theoretically and implicated in oxo-atom transfer reactions that are relevant to environmental speciation and nuclear waste remediation. Single electron reduction is now known to impart greater oxo-group reactivity, but with retention of the linear OUO motif, and reactions of the oxo groups to form new covalent bonds remain rare. Here, we describe the synthesis, structure, reactivity and magnetic properties of a binuclear uranium-oxo complex. Formed through a combination of reduction and oxo-silylation and migration from a trans to a cis position, the new butterfly-shaped Si-OUO(2)UO-Si molecule shows remarkably strong U(V)-U(V) coupling and chemical inertness, suggesting that this rearranged uranium oxo motif might exist for other actinide species in the environment, and have relevance to the aggregation of actinide oxide clusters.
Differential Solvation Schreckenbach, Georg
Chemistry : a European journal,
March 17, 2017, Letnik:
23, Številka:
16
Journal Article
Recenzirano
Solvation effects influence reaction equilibria by preferentially stabilizing reactants or products (differential solvation). We propose using simple electrostatic concepts to qualitatively interpret ...and understand these effects, applying the Born and Kirkwood–Onsager equations. Scenarios include, for charged species, redox potentials, different total absolute charges between reactants and products, and size differences between reactants and products. In addition, for neutral species, they are differences in total dipole moment and size differences. These scenarios are illustrated with several examples from different areas of chemistry.
Size and charge matter: Simple electrostatic concepts can qualitatively explain solvation effects.
To understand interfacial behavior of actinides adsorbed onto mineral surfaces and unravel their structure–property relationship, the structures, electronic properties, and energetics of various ...ligated uranyl species adsorbed onto TiO2 surface nanoparticle clusters (SNCs) were examined using relativistic density functional theory. Rutile (110) and anatase (101) titania surfaces, experimentally known to be stable, were fully optimized. For the former, models studied include clean and water-free Ti27O64H20 (dry), partially hydrated (Ti27O64H20)(H2O)8 (sol) and proton-saturated (Ti27O64H20)(H2O)8(H)22+ (sat), while defect-free and defected anatase SNCs involving more than 38 TiO2 units were considered. The aquouranyl sorption onto rutile SNCs is energetically preferred, with interaction energies of −8.54, −10.36, and −2.39 eV, respectively. Energy decomposition demonstrates that the sorption is dominated by orbital attractive interactions and modified by steric effects. Greater hydrogen-bonding involvement leads to increased orbital interactions (i.e., more negative energy) from dry to sol/sat complexes, while much larger steric interaction in the sat complex significantly reduces the sorption interaction (i.e., more positive energy). For dry SNC, adsorbates were varied from aquo to aquo-carbonato, to carbonato, to hydroxo uranyl species. Longer U–Osurf/U–Ti distances and more positive sorption energies were calculated upon introducing carbonato and hydroxo ligands, indicative of weaker uranyl sorption onto the substrate. This is consistent with experimental observations that the uranyl sorption rate decreases upon raising solution pH value or adding carbon dioxide. Anatase SNCs adsorbing aquouranyl are even more exothermic, because more bonds are formed than in the case of rutile. Moreover, the anatase sorption can be tuned by surface defects as well as its Ti and O stoichiometry. All the aquouranyl–SNC complexes show similar character of molecular orbitals and energetic order although differing in highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gaps and orbital energy levels, but changes can be accomplished by adding carbonato and hydroxo ligands.
Ascidians are marine animals that adopt unusual techniques to deter predation. The three main methods are sequestration of unusual metals, high concentrations of sulfuric acid/sulfate ions in ...tunicate cells, and the presence of eudistomins. In this study, we hypothesize that ascidians sequester metals in their sulfate form, and the complexation of eudistomins with the metals could liberate the sulfate ion. Three representative metal aqua ions were chosen, viz., vanadyl, uranyl, and thorium ions, as well as four simple eudistomins which act as bidentate ligands, viz., eudistomin-W, debromoeudistomin-K, eudistomidin-C, and eudistomidin-B. By designing 7 model reactions, we tested our hypothesis using density functional theory (DFT) methods PBE-D3, BLYP, and B3LYP. The ΔG values of the model reactions provide strong support for our hypothesis. To verify the hypothesis further, we calculated the metal-eudistomin interactions with Be, Zn, and Pb. Based on our results, we suggest that ascidians may not prefer any particular metal. In addition, despite using different DFT functionals, we have observed similar ΔG values for each case. With our work, we have successfully used computational tools in our attempt to understand the unique behavior of ascidians.
The recently reported tris(bis(2,4,6-triisopropylbenzoyl)-phosphide)uranium (UIII(trippBAP)3, 2) complex (Inorg. Chem. 2022, 61 (32), 12508–12517) demonstrated a silent 31P NMR spectrum. This ...complex was described as a U(III) complex with an organic radical ligand fragment. Moreover, the EPR spectrum of 2 was indicative of an organic radical in the ligand framework complexed to uranium, in contrast to that of UIV(mesBAP)4, 1. Herein, with the help of relativistic density functional theory (DFT) calculations, the electronic structures of 1, 2, and U(mesBAP)3 (4) are examined in an effort to understand the unusual 31P NMR spectrum of 2. Results indicate the reduction of the carbonyl bonds and delocalization of the electrons over the ligands, indicative of U → L backbonding. Additionally, the reduced acyl carbons are found to exist as ketyl radicals OC• – that are responsible for the silent 31P NMR spectra of 2. These findings demonstrate the redox noninnocent nature of BAP– in 2 and 4, causing uranium to exist in a formal oxidation state of +4.
Frontispiece: Differential Solvation Schreckenbach, Georg
Chemistry : a European journal,
March 17, 2017, Letnik:
23, Številka:
16
Journal Article
Recenzirano
Solvent Effects In the Concept article on page 3797 ff., G. Schreckenbach proposes the use of simple electrostatic concepts based on the Born and Kirkwood–Onsager equations to qualitatively (and ...sometimes semi‐quantitatively) interpret the influence of solvation effects on reaction equilibria. While most of the examples reflect his interest in inorganic and especially heavy‐element chemistry, these ideas are much more general and are equally well applicable to other areas including organic and biochemistry.
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