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

From chemical gardens to chemobrionics

Chemical gardens are perhaps the best example in chemistry of a self-organizing nonequilibrium process that creates complex structures. Many different chemical systems and materials can form these self-assembling structures, which span at least 8 orders of magnitude in size, from nanometers to meters. Key to this marvel is the self-propagation under fluid advection of reaction zones forming semipermeable precipitation membranes that maintain steep concentration gradients, with osmosis and buoyancy as the driving forces for fluid flow. Chemical gardens have been studied from the alchemists onward, but now in the 21st century we are beginning to understand how they can lead us to a new domain of self-organized structures of semipermeable membranes and amorphous as well as polycrystalline solids produced at the interface of chemistry, fluid dynamics, and materials science. We propose to call this emerging field chemobrionics

Controlling the Minimal Self Assembly of “Complex” Polyoxometalate Clusters

Despite the vast number of polyoxometalate clusters now known, an ongoing and important challenge is to understand causality in the assembly of “complex” clusters at a mechanistic level, since this is the only way the rational, targeted synthesis of new compounds will ever be achieved. Often, the complexity of the reactions themselves makes such investigations near impossible, as very small changes can often make dramatic differences. Herein, we explore a very simple [A + B] binary synthetic system that gives rise to the facile assembly of two isomeric anions, [Fe^III(H₂O)₂{γ-Fe^IIISiW₉O₃₄(H₂O)}₂]^11– (<b>1</b>) and [Fe^III(H₂O)₂{γ-Fe^III₂SiW₈O₃₃(H₂O)₂}­{γ-SiW₁₀O₃₅}]^11– (<b>2</b>), which can be formed as individual and dimeric species (<b>3</b>) and (<b>4</b>). Furthermore, the simple binary nature of this synthetic system allowed its investigation by a comprehensive time-resolved ESI-MS analysis, yielding unprecedented mechanistic information regarding the initial interactions and reorganizations of the {γ-SiW₁₀} precursor in the presence of Fe²⁺

Synthesis and Characterization of a Series of [M₂(β-SiW₈O₃₁)₂]^<i>n</i>− Clusters and Mechanistic Insight into the Reorganization of {β-SiW₈O₃₁} into {α-SiW₉O₃₄}

Lacunary polyoxometalates of low nuclearity are difficult to synthesize in isolation. We report the facile synthesis of six {M₂(B-β-SiW₈O₃₁)₂} clusters (M = Co/Mn/Ni/Zn/Cu²⁺, Fe³⁺) that can be employed as building blocks for the formation of larger architectures. We show for the first time that such {B-β-SiW₈O₃₁} lacunae are capable of reorganizing into larger Keggin lacunary species even in the absence of an external source of tungstate. We hypothesize, based on electrospray ionization mass spectrometry evidence obtained, not only that such a transformation is only possible via an initial decomposition of the {SiW₈} precursor into a {SiW₆}-based intermediate but also that it is this {SiW₆} species that acts as the template for the growth of the larger fragments

Configurable Nanosized Metal Oxide Oligomers via Precise “Click” Coupling Control of Hybrid Polyoxometalates

Polyoxometalates (POMs) are discrete clusters of redox-active metal oxides, many of which can be linked to organic moieties. Here, we show how it is possible to link Mn Anderson POMs to terminal alkyne and azide groups and develop appropriate conditions for their Cu-catalyzed alkyne–azide cycloaddition (or “click” reaction). These coupling reactions are then used to link the clusters together, forming monodisperse linear Mn Anderson oligomers, here with examples ranging in size from two to five clusters. These oligomers are built up sequentially using a combination of mono- and difunctionalized clusters, giving an unprecedented level of control over the size and structure of the resulting hybrid POMs. This new synthetic methodology therefore opens the way for the synthesis of metal oxide hybrid oligomers and polymers by coupling control, minimizing side products, producing nanosized molecular hybrid organic–inorganic oxides ca. 4–9 nm in size, with molecular weights ranging 2–10 kDa

Low pH Electrolytic Water Splitting Using Earth-Abundant Metastable Catalysts That Self-Assemble in Situ

Typical catalysts for the electrolysis of water at low pH are based on precious metals (Pt for the cathode and IrO₂ or RuO₂ for the anode). However, these metals are rare and expensive, and hence lower cost and more abundant catalysts are needed if electrolytically produced hydrogen is to become more widely available. Herein, we show that electrode-film formation from aqueous solutions of first row transition metal ions at pH 1.6 can be induced under the action of an appropriate cell bias and that in the case of cobalt voltages across the cell in excess of 2 V lead to the formation of a pair of catalysts that show functional stability for oxygen evolution and proton reduction for over 24 h. We show that these films are metastable and that if the circuit is opened, they redissolve into the electrolyte bath with concomitant O₂ and H₂ evolution, such that the overall Faradaic efficiency for charge into the system versus amounts of gases obtained approaches unity for both O₂ and H₂. This work highlights the ability of first row transition metals to mediate heterogeneous electrolytic water splitting in acidic media by exploiting, rather than trying to avoid, the natural propensity of the catalysts to dissolve at the low pHs used. This in turn we hope will encourage others to examine the promise of metastable electrocatalysts based on abundant elements for a range of reactions for which they have traditionally been overlooked on account of their perceived instability under the prevailing conditions

Solution-Phase Monitoring of the Structural Evolution of a Molybdenum Blue Nanoring

The inorganic host–guest complex Na₂₂{[Mo^VI₃₆O₁₁₂(H₂O)₁₆]⊂[Mo^VI₁₃₀Mo^V₂₀O₄₄₂(OH)₁₀(H₂O)₆₁]}·180H₂O ≡ {Mo₃₆}⊂{Mo₁₅₀}, compound <b>1</b>, has been isolated in its solid crystalline state via unconventional synthesis in a custom flow reactor. Carrying out the reaction under controlled flow conditions selected for the generation of {Mo₃₆}⊂{Mo₁₅₀} as the major product, allowing it to be reproducibly isolated in a moderate yield, as opposed to traditional “one-pot” batch syntheses that typically lead to crystallization of the {Mo₃₆} and {Mo₁₅₀} species separately. Structural and spectroscopic studies of compound <b>1</b> and the archetypal Molybdenum Blue (MB) wheel, {Mo₁₅₀}, identified compound <b>1</b> as a likely intermediate in the {Mo₃₆} templated synthesis of MB wheels. Further evidence illustrating the template effect of {Mo₃₆} to MB wheel synthesis was indicated by an increase in the yield and rate of production of {Mo₁₅₀} as a direct result of the addition of preformed {Mo₃₆} to the reaction mixture. Dynamic light scattering (DLS) techniques were also used to corroborate the mechanism of formation of the MB wheels through observation of the individual cluster species in solution. DLS measurement of the reaction solutions from which {Mo₃₆} and {Mo₁₅₀} crystallized gave particle size distribution curves averaging 1.9 and 3.9 nm, consistent with the dimensions of the discrete clusters, which allowed the use of size as a possible distinguishing feature of these key species in the reduced acidified molybdate solutions and to observe the templation of the MB wheel by {Mo₃₆} directly

Exploring the Assembly of Supramolecular Polyoxometalate Triangular Morphologies with Johnson Solid Cores: [(Mn^II(H₂O)₃)₂(K⊂{α-GeW₁₀Mn^II₂O₃₈}₃)]^19–

A new polyoxometalate (POM) cluster compound is presented which incorporates a trimeric assembly of Keggin-type germanotungstate fragments trapping a Johnson-type solid {Mn₈} core. The mixed K–Li salt of the polyanion [(Mn^II(H₂O)₃)₂(K⊂{α-GeW₁₀Mn^II₂O₃₈}₃)]^19– was characterized in the solid state and solution. The correlation of the assembly processes and the observed architecture of the “trinity” family of POMs is discussed

Low pH Electrolytic Water Splitting Using Earth-Abundant Metastable Catalysts That Self-Assemble in Situ

Typical catalysts for the electrolysis of water at low pH are based on precious metals (Pt for the cathode and IrO₂ or RuO₂ for the anode). However, these metals are rare and expensive, and hence lower cost and more abundant catalysts are needed if electrolytically produced hydrogen is to become more widely available. Herein, we show that electrode-film formation from aqueous solutions of first row transition metal ions at pH 1.6 can be induced under the action of an appropriate cell bias and that in the case of cobalt voltages across the cell in excess of 2 V lead to the formation of a pair of catalysts that show functional stability for oxygen evolution and proton reduction for over 24 h. We show that these films are metastable and that if the circuit is opened, they redissolve into the electrolyte bath with concomitant O₂ and H₂ evolution, such that the overall Faradaic efficiency for charge into the system versus amounts of gases obtained approaches unity for both O₂ and H₂. This work highlights the ability of first row transition metals to mediate heterogeneous electrolytic water splitting in acidic media by exploiting, rather than trying to avoid, the natural propensity of the catalysts to dissolve at the low pHs used. This in turn we hope will encourage others to examine the promise of metastable electrocatalysts based on abundant elements for a range of reactions for which they have traditionally been overlooked on account of their perceived instability under the prevailing conditions

One-Pot versus Sequential Reactions in the Self-Assembly of Gigantic Nanoscale Polyoxotungstates

By using a new type of lacunary tungstoselenite {Se₂W₂₉O₁₀₃} (<b>1</b>), which contains a “defect” pentagonal {W­(W)₄} unit, we explored the assembly of clusters using this building block and demonstrate how this unit can give rise to gigantic nanomolecular species, using both a “one-pot” and “stepwise” synthetic assembly approach. Specifically, exploration of the one-pot synthetic parameter space lead to the discovery of {Co_2.5(W_3.5O₁₄)­(SeW₉O₃₃)­(Se₂W₃₀O₁₀₇)} (<b>2</b>), {CoWO­(H₂O)₃(Se₂W₂₆O₈₅)­(Se₃W₃₀O₁₀₇)₂} (<b>3</b>), and {Ni₂W₂O₂Cl­(H₂O)₃(Se₂W₂₉O₁₀₃) (Se₃W₃₀O₁₀₇)₂} (<b>4</b>), effectively demonstrating the potential of the {Se₂W₂₉} based building blocks, which was further extended by the isolation of a range of 3d transition metal doped tetramer family derivatives: {M₂W_<i>n</i>O_<i>m</i>(H₂O)_<i>m</i>(Se₂W₂₉O₁₀₂)₄} (M = Mn, Co, Ni or Zn, <i>n</i> = 2, <i>m</i> = 4; M = Cu, <i>n</i> = 3, <i>m</i> = 5) (<b>5</b> - <b>9</b>). To contrast the ‘one-pot’ approach, an optimized stepwise self-assembly investigation utilizing <b>1</b> as a precursor was performed showing that the high nuclearity clusters can condense in a more controllable way allowing the tetrameric clusters (<b>5</b> - <b>8</b>) to be synthesized with higher yield, but it was also shown that <b>1</b> can be used to construct a gigantic {W₁₇₄} hexameric-cluster {Cu₉Cl₃(H₂O)₁₈(Se₂W₂₉O₁₀₂)₆} (<b>10</b>). Further, <b>1</b> can also dimerize to {(Se₂W₃₀O₁₀₅)₂} (<b>11</b>) by addition of extra tungstate under similar conditions. All the clusters were characterized by single-crystal X-ray crystallography, chemical analysis, infrared spectroscopy, thermogravimetric analysis, and electrospray ionization mass spectrometry, which remarkably showed that all the clusters, even the largest cluster, <b>10</b> (∼50 kD), could be observed as the intact cluster demonstrating the extraordinary potential of this approach to construct robust gigantic nanoscale polyoxotungstates