Оценка экологической опасности рассеивания газопылевого облака при массовых взрывах в карьерах

Heteroanion (HA) moieties have a key role in templating of heteropolyoxometalate (HPA) architectures, but clusters templated by two different templates are rarely reported. Herein, we show how a cross-shaped HPA-based architecture can self-sort the HA templates by pairing two different guests into a divacant {XYW₁₅O₅₄} building block, with four of these building block units being linked together to complete the cross-shaped architecture. We exploited this observation to incorporate HA templates into well-defined positions within the clusters, leading to the isolation of a collection of mixed-HA templated cross-shaped polyanions [(XYW₁₅O₅₄)₄(WO₂)₄]^32–/36– (X = H–P, Y = Se, Te, As). The template positions have been unambiguously determined by single crystal X-ray diffraction, NMR spectroscopy, and high-resolution electrospray ionization mass spectrometry; these studies demonstrated that the mixed template containing HPA clusters are the preferred products which crystallize from the solution. Theoretical studies using DFT calculations suggest that the selective self-sorting originates from the coordination of the template in solution. The cross-shaped polyoxometalate clusters are redox-active, and the ability of molecules to accept electrons is slightly modulated by the HA incorporated as shown by differential pulse voltammetry experiments. These results indicate that the cross-shaped HPAs can be used to select templates from solution, and themselves have interesting geometries, which will be useful in developing functional molecular architectures based upon HPAs with well-defined structures and electronic properties

Bingel–Hirsch Addition on Non-Isolated-Pentagon-Rule Gd₃N@C_2<i>n</i> (2<i>n</i> = 82 and 84) Metallofullerenes: Products under Kinetic Control

Bingel–Hirsch reactions on fullerenes take place under kinetic control. We here predict, by means of DFT methodology, the products of the Bingel–Hirsch addition on non-isolated-pentagon-rule (non-IPR) metallofullerenes Gd₃N@C_2<i>n</i> (2<i>n</i> = 82, 84), as modeled by closed-shell Y₃N@C_2<i>n</i> systems. Adducts on [6,6] B-type bonds placed near the pentalene unit are predicted for the two cages, as found for other non-IPR endohedral fullerenes such as Sc₃N@C₆₈

La₃N@C₉₂: An Endohedral Metallofullerene Governed by Kinetic Factors?

Different structures have been proposed so far for the C₉₂ isomer that encapsulates M₃N (M = La, Ce, Pr). We show here that the electrochemical properties of the predicted most abundant (thermodynamic) isomer for La₃N@C₉₂ does not agree with experiment. After a systematic search within the huge number of possible C₉₂ isomers, we propose other candidates with larger electrochemical gaps for La₃N@C₉₂ before its structure could be finally determined by X-ray crystallography. We do not discard that the thermodynamic isomer could be detected in future experiments though

Relevance of Thermal Effects in the Formation of Endohedral Metallofullerenes: The Case of Gd₃N@<i>C</i>_s(39663)‑C₈₂ and Other Related Systems

Thermal contributions to the free energy have to be taken into account to rationalize the formation of Gd₃N@<i>C</i>_s(39663)-C₈₂, a nitride endohedral metallofullerene that shows a carbon cage with two fused pentagons which is not predicted to have the lowest electronic energy among the isomers of C₈₂. The lower symmetry and the larger number of pyracylene units of <i>C</i>_s(39663)-C₈₂ with respect to the cage in the lowest-energy metallofullerene, <i>C</i>_2<i>v</i>(39705)-C₈₂, favor its formation at high temperatures, as seen for other similar cage isomers that encapsulate metal clusters within the C₈₀ and C₈₂ families. These cages, which share common motifs with the prototypical <i>I</i>_<i>h</i>(7)-C₈₀, are all related by C₂ insertions/extrusions and Stone–Wales transformations

Counterintuitive Adsorption of [PW₁₁O₃₉]^7– on Au(100)

Understanding the interaction between charged species and surfaces is one of the most challenging topics in chemistry, given its wide involvement in several fields such as electrocatalysis, stabilization of metal nanoparticles, preparation of devices, etc. In general, these systems are particularly complex to model because of the elevated number of factors that must be taken into account. Here, we report a robust strategy based on density functional theory for studying these interactions, which has been applied to the highly charged lacunary [PW₁₁O₃₉]^7– (PW₁₁) adsorbed on gold and silver surfaces. In this context, we find that, unlike the modeling of polyoxoanions in solution, the incorporation of counterions in the computational models is crucial for accurately reproducing the properties of the system, even if an implicit solvent is used. Most interestingly, we find that the PW₁₁ cluster does not preferentially adsorb to the gold surface via its more nucleophilic monodefect face but, rather, through less negatively charged terminal oxygen ligands, with an orientation similar to that found for the nondefective Keggin anion [SiW₁₂O₄₀]^4–, induced by the strong anion–cation interactions from the same and neighboring units. This counterintuitive result is important for ongoing efforts to understand and utilize the properties of polyoxometalate monolayers on gold and other reactive metal surfaces

Endohedral Metallofullerenes Containing Lanthanides: A Robust Yet Simple Computational Approach

Endohedral metallofullerenes (EMFs) containing lanthanides are thoroughly analyzed using density functional theory. Our methodology, which uses planes waves as basis functions and pseudopotentials and takes into account the on-site Coulomb repulsion via the Hubbard-like U parameter, is able to reproduce the electronic structure and the main geometrical parameters for this family of compounds that presents unpaired f electrons. In addition, the relative abundances of lanthanide EMFs observed in chromatograms as well as the preference of a nitride cluster for a given fullerene are properly predicted. Cluster–cage interactions are optimal when the cluster fits perfectly within the available hollow space of the carbon cage. Except for cerium nitride fullerenes, f electrons do not play a significant role in the electrochemical properties of lanthanide EMFs. If one is only interested in a qualitative prediction of the structure, reactivity, and electronic properties, then calculations that do not explicitly consider the unpaired f electrons can be acceptable

Photoreduction Mechanism of CO₂ to CO Catalyzed by a Rhenium(I)–Polyoxometalate Hybrid Compound

The photoreduction mechanism of carbon dioxide to carbon monoxide by the Re–organic hybrid polyoxometalates (POMs) {NaH­[PW₁₂O₄₀]^3–Re^IL­(CO)₃DMA}^<i>n</i>− (L = 15-crown-5 phenanthroline, DMA = <i>N</i>,<i>N</i>-dimethylacetamide) has been investigated by means of DFT and TD-DFT calculations. The reaction mechanism can be divided into several steps, including (i) photoexcitation and charge transfer, (ii) DMA release, (iii) CO₂ addition, (iv) protonation, and (v) CO release and regeneration of the catalyst. The charge transfer (CT) states, POM to Re complex, are efficiently induced by metal-centered (MC) excitations occurring on the <i>reduced</i> POM. Once one electron is transferred to the organometallic unit from the excited POM, the Re is able to bind and activate the CO₂ substrate. Subsequent steps that involve protonation of CO₂ and CO release are favorable thermodynamically and are induced by a second electron transfer from the POM to the Re complex. In this reaction, the POM acts as photosensitizer, electron reservoir, and electron donor

Aerobic Carbon–Carbon Bond Cleavage of Alkenes to Aldehydes Catalyzed by First-Row Transition-Metal-Substituted Polyoxometalates in the Presence of Nitrogen Dioxide

A new aerobic carbon–​carbon bond cleavage reaction of linear di-substituted alkenes, to yield the corresponding aldehydes/ketones in high selectivity under mild reaction conditions, is described using copper­(II)-substituted poly­oxo­metalates, such as {α₂-Cu­(L)­P₂W₁₇O₆₁}^8– or {[(Cu­(L)]₂WZn­(ZnW₉O₃₄)₂}^12–, as catalysts, where L = NO₂. A bio­renewable-based substrate, methyl oleate, gave methyl 8-formyl­octanoate and nonanal in >90% yield. Interestingly, cylco­alkenes yield the corresponding epoxides as products. These catalysts either can be prepared by pre­treatment of the aqua-coordinated poly­oxo­metalates (L = H₂O) with NO₂ or are formed in situ when the reactions are carried with nitro­alkanes (for example, nitro­ethane) as solvents or cosolvents. Nitroethane was shown to release NO₂ under reaction conditions. ³¹P NMR shows that the Cu-NO₂-substituted poly­oxo­metalates act as oxygen donors to the C–C double bond, yielding a Cu-NO product that is reoxidized to Cu-NO₂ under reaction conditions to complete a catalytic cycle. Stoichiometric reactions and kinetic measurements using {α₂-Co­(NO₂)­P₂W₁₇O₆₁}^8– as oxidant and <i>trans</i>-stilbene derivatives as substrates point toward a reaction mechanism for C–C bond cleavage involving two molecules of {α₂-Co­(NO₂)­P₂W₁₇O₆₁}^8– and one molecule of <i>trans</i>-stilbene that is sufficiently stable at room temperature to be observed by ³¹P NMR

Electrochemical Behavior of α₁/α₂-[Fe(H₂O)P₂W₁₇O₆₁]^7– Isomers in Solution: Experimental and DFT Studies

The unusual redox behavior displayed by the two isomers of the Wells–Dawson phosphotungstate anion [Fe­(H₂O)­P₂W₁₇O₆₁]^7– is presented. The electrochemical measurements have been performed in aqueous media at different pH values from 0.5 up to 8.0. The cyclic voltammetry has also been carried out in organic media to get additional experimental data to establish the effect of the protonation on the redox properties of both isomers. At high pH values (pH ≥ 6) or in an organic medium, the reduction of the Fe center is easier in the case of the alpha-1 isomer, whereas for the alpha-2 isomer such reduction takes place at more negative potentials, as expected. In contrast, at lower pH values (pH ≤ 5), an inversion of this trend is observed, and the reduction of the Fe center becomes easier for the alpha-2 isomer compared to the alpha-1. We were able to highlight the influence of the pH and the p<i>K</i>_a of the electrolyte on POM-based redox potentials given the p<i>K</i>_a of the latter. A complementary theoretical study has also been performed to explain the experimental data obtained. In this sense, the results obtained from the DFT study are in good agreement with the experimental data mentioned above and have provided additional information for the electrochemical behavior of both isomers according to their different molecular orbital energies. We have also shown the influence of protonation state of the iron derivative on the relative reduction potentials of both isomers

Assembly Mechanism of Zr-Containing and Other TM-Containing Polyoxometalates

The mechanism by which Zr-substituted and other transition metal-substituted polyoxometalates (POMs) form covalently linked dimers has been analyzed by means of static density functional theory (DFT) calculations with a continuous solvent model as well as Car–Parrinello molecular dynamics (CPMD) simulations with explicit solvent molecules. The study includes different stages of the process: the formation of the active species by alkalination of the solution and formation of intercluster linkages. CPMD simulations show that the Zr-triaqua precursor, [W₅O₁₈Zr­(H₂O)₃]^2–, under basic conditions, reacts with hydroxide anions to form Zr-aqua-hydroxo active species, [W₅O₁₈Zr­(OH)­(H₂O)]^3–. We computed the DFT potential energy profile for dimerization of [W₅O₁₈TM­(OH)]^<i>n</i>− [TM = Zr^IV(H₂O), Zr^IV, Ti^IV, and W^VI] anions. The resulting overall energy barrier is low for Zr^IV, moderate for Ti^IV, and high for W^VI. The computed thermodynamic balance favors the dibridged (μOH)₂ linkages for Zr^IV, the monobridged (μOH) linkage for Ti^IV, and the monomeric forms for W^VI, in agreement with experimentally observed trends. The lowest energy barrier and largest coordination number of Zr-substituted POMs are both a consequence of the flexible coordination environment and larger radius of Zr