Density functional theory study of single-molecule ferroelectricity in Preyssler-type polyoxometalates

A detailed study on the single-molecule ferroelectric property of Preyssler-type polyoxometalates (POMs), [M3+P5W30O110]12− (M = La, Gd, and Lu), is performed by density functional theory calculations. Linked to one H2O molecule, the cation (M3+) encapsulated in the cavity of the Preyssler framework is off-centered, and it generates a permanent dipole, which is essential for a ferroelectric ground state. Accompanied with a 180° rotation of H2O, the switching of M3+ between two isoenergetic sites on both sides of the cavity results in a calculated barrier of 1.15 eV for Gd3+, leading to the inversion of electric polarization. The height of the barrier is in good agreement with the experimentally measured barrier for the Tb3+ ion, whose ionic radius is similar to Gd3+. The total polarization value of the crystal is estimated to be 4.7 µC/cm2 as calculated by the modern theory of polarization, which is quite close to the experimental value. Considering that the order of contributions to the polarization is M3+–H2O > counter-cations (K+) > [P5W30O110]15−, the interconversion of M3+–H2O between the two isoenergetic sites is predicted to be the main origin of ferroelectricity with a polarization contribution of 3.4 µC/cm2; the K+ counter-cations contribute by 1.2 µC/cm2 and it cannot be disregarded, while the framework appears to contribute negligibly to the total polarization. Our study suggests that a suitable choice of M3+–H2O could be used to tune the single-molecule ferroelectricity in Preyssler-type polyoxometalates

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

DFT Studies on Polyoxopalladates and Polyoxometalate-surface Composites: From Structure to Catalysis

De la tesi doctoral es poden extreure les següents conclusions: • La captura d'un ió Mq+ per una capa PdII-oxo perifèrica implica la competència entre el receptor mare PdII i l’ió metàl·lic convidat. Els principals factors que governen la formació d'un particular MPd12 són la interacció electrostàtica entre el catió i els lligands oxo circumdants i la capacitat de deshidratació del catió en solució, on la càrrega i la mida del catió hoste són crítiques. • Per als nous compostos Ag4Pd13 i Ag5Pd15, s’ha caracteritzat amb el mètode QTAIM la naturalesa de la interacció Pd-Ag i Ag-Ag-Ag. • Per a la reducció completa Au (III) → Au (0), s’ha demostrat que el POM tipus Kabanos constitueix una font suficient d’electrons. Aquest procés és altament favorable des d’un punt de vista termodinàmic. • S’ha establert una estratègia sòlida per a la modelització de l’adsorció d’espècies carregades sobre superfícies. La incorporació dels contraions en els models computacionals és crucial per reproduir acuradament les propietats electròniques. La inclusió del dissolvent redueix la sobreestabilització de les interaccions anió-catió o anió-superfície, la qual cosa permet descriure molt millor el sistema adsorbit. • El POM lacunar PW11 no s’adsorbeix preferentment sobre la superfície d'or per la banda de la llacuna, sinó que més aviat ho fa a través dels oxígens terminals menys negativament carregats degut a les fortes interaccions anió-catió de la mateixa unitat i de les unitats veïnes. • En el mecanisme corresponent a la WSGR a partir de H2O i CO adsorbits sobre la interfície PMo12-Au(111) s’ha proposat el grup carboxil adsorbit (*COOH) com a principal intermedi de la reacció. El paper dels POMs adsorbits és servir tant de acceptor d’electrons com de protons. • La interacció de la superfície de TiO2(101) tant amb la forma totalment oxidada com amb la forma reduïda del PW11Ti exhibeix una naturalesa covalent. La presència de l’anió reduït millora eficientment la feble absorció del TiO2 en la regió del visible. La simulació de l’espectre UV-Vis suggereix que el PW11Ti reduït pot transferir electrons al TiO2 sota irradiació amb llum visible.De la tesis doctoral se pueden extraer las siguientes conclusiones: • La captura de un ión Mq+ por una capa PdII-oxo periférica implica la competencia entre el receptor madre PdII y el ión metálico invitado. Los principales factores que gobiernan la formación de un particular MPd12 son la interacción electrostática entre el catión y los ligandos oxo circundantes y la capacidad de deshidratación del catión en solución, donde la cargar y el tamaño del catión huésped son críticos. • Para los nuevos compuestos Ag4Pd13 i Ag5Pd15, se ha caracterizado mediante el método QTAIM la naturaleza de la interacción Pd-Ag i Ag-Ag-Ag. • Para la reducción completa Au (III) → Au (0), se ha demostrado que el POM tipo Kabanos constituye una fuente suficiente de electrones. Este proceso es altamente favorable desde un punto de vista termodinámico. • Se ha establecido una estrategia sólida para la modelización de la adsorción de especies cargadas sobre superficies. La incorporación de los contraiones en los modelos computacionales es crucial para reproducir cuidadosamente las propiedades electrónicas. La inclusión del disolvente reduce la sobreestabilización de las interacciones anión-catión o anión-superficie, lo que permite describir mucho mejor el sistema adsorbido. • El POM lacunar PW11 no se adsorbe preferentemente sobre la superficie de oro por el lado de la laguna, sino que más bien lo hace a través de los oxígenos terminales menos negativamente cargados debido a las fuertes interacciones anión-catión de la misma unidad y de les unidades vecinas. • En el mecanismo correspondiente a la WSGR a partir de H2O i CO adsorbidos sobre la interface Au(111)-PMo12 se ha propuesto el grupo carboxilo adsorbido (*COOH) como el principal intermedio de la reacción. El papel de los POMs adsorbidos es servir tanto de aceptor de electrones como de protones. • La interacción de la superficie de TiO2(101) tanto con la forma totalmente oxidada como con la forma reducida del PW11Ti exhibe una naturaleza covalente. La presencia del anión reducido mejora eficientemente la débil absorción del TiO2 en la región del visible. La simulación del espectro UV-Vis sugiere que el PW11Ti reducido puede transferir electrones al TiO2 bajo irradiación con luz visible.The following general conclusions can be drawn from this thesis • The capture of a Mq+ ion by a peripheral PdII-oxo shell involves the competition between the mother PdII and the guest metal ions, the main factors governing the formation of a particular MPd12 being the electrostatic-interaction between the cation and the surrounding oxo ligands and the dehydration ability of the cation in solution, in which the charge and size of the guest cation are critical. The following general conclusions can be drawn from this thesis: • The capture of a Mq+ ion by a peripheral PdII-oxo shell involves the competition between the mother PdII and the guest metal ion. The main factors governing the formation of a particular MPd12 are the electrostatic interaction between the cation and the surrounding oxo ligands and the dehydration ability of the cation in solution, in which the charge and size of the guest cation are critical. • The nature of the interaction for Pd-Ag and Ag-Ag-Ag in novel Ag4Pd13 and Ag5Pd15 compounds have been characterized with QTAIM method. • The Kabanos-type POM is proved to electron sufficient resources for completely Au(III)→Au(0) reduction. This process is highly favourable from thermodynamic perspectives. • We have established a robust strategy for the modelling of charged species adsorbed on surfaces. The incorporation of counterions in the computational models is crucial for accurately reproducing the electronic properties. The inclusion of solvent reduces the over stabilization of the anion-cation or anion-surface interactions, describing much better the adsorbed system. • The lacunary PW11 cluster does not preferentially adsorb on the gold surface via its more nucleophilic mono defect face but, rather, through less negatively charged terminal oxygen ligands, induced by the strong anion−cation interactions from the same and neighbouring units. • The WGSR mechanism is proposed to mainly involves the adsorbed carboxyl (COOH*) intermediate induced from CO and H2O adsorbed on the PMo12-Au(111) interface. The role of POMs is to serve as both electron and proton acceptors. • The interaction of the TiO2 surface with both the fully oxidized PW11Ti and its reduced partner exhibits a covalent nature. The presence of the reduced anion efficiently improves the weak absorption of TiO2 in the visibl

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

Constructing Transition Metal Single-Atom-Modified MoB₂: Extraordinary Electrocatalytic Hydrogen Evolution and Mechanism Investigation

Developing single-atom catalysts (SACs) and exploring the interaction between a single atom and support are crucial for identifying the active centers, clarifying the catalytic mechanisms, and deepening understanding of SACs. Herein, by employing Anderson-type POMs as molecular precursor, a series of transition metal (TM = Ni, Co, Fe) single atoms anchored on MoB2 (TM-MoB2) with high TM loading (∼6.91 wt %) are prepared. The decoration of TM promotes the electrocatalytic hydrogen evolution activity of MoB2, of which Ni-MoB2 delivers the best performance in both alkaline and acidic solutions, outperforming most TM boride-based catalysts. Density functional theory simulation reveals that the introduction of Ni single atoms endows the top Mo on the Ni-MoB2 surface with low water dissociation barrier (∼0.62 eV) and optimal H adsorption Gibbs free energy (∼0.02 eV), thus exhibiting remarkable hydrogen evolution activity. This work offers a versatile strategy for preparing TM-MoB2 SACs and paves the way to recognize SACs with a new support platform

Polyoxometalate‐Derived Hexagonal Molybdenum Nitrides (MXenes) Supported by Boron, Nitrogen Codoped Carbon Nanotubes for Efficient Electrochemical Hydrogen Evolution from Seawater

MXenes and doped carbon nanotubes (CNTs) have entered into research arenas for high-rate energy storage and conversion. Herein, a method of postsynthesis of MXenes in boron, nitrogen codoped CNTs (BNCNTs) is reported with their electrocatalytical hydrogen evolution performance. The encapsulation of hexagonal molybdenum nitrate nanoparticles (h-MoN NPs) into BNCNTs protects h-MoN NPs from agglomeration and poisoning in the complex environment. In principle, the synergism of B and N dopants on the doped CNTs and confined h-MoN NPs produces extremely active sites for electrochemical hydrogen evolution. Density functional theory calculations reveal that the active sites for hydrogen evolution originate from the synergistic effect of h-MoN(001)/CN (graphitic N doping) and h-MoN(001)/BNC. The h-MoN@BNCNT electrocatalyst exhibits a small overpotential of 78 mV at 10 mA cm −2 and Tafel slope of 46 mV per decade, which are dramatically improved over all reported MoN-based materials and doped CNTs. Additionally, it also exhibits outstanding electrochemical stability in environments with various pH values and seawater media from South China Sea

Polyoxometalate-derived hexagonal molybdenum nitrides (MXenes) supported by boron, nitrogen codoped carbon nanotubes for efficient electrochemical hydrogen evolution from seawater

MXenes and doped carbon nanotubes (CNTs) have entered into research arenas for high-rate energy storage and conversion. Herein, a method of postsynthesis of MXenes in boron, nitrogen codoped CNTs (BNCNTs) is reported with their electrocatalytical hydrogen evolution performance. The encapsulation of hexagonal molybdenum nitrate nanoparticles (h-MoN NPs) into BNCNTs protects h-MoN NPs from agglomeration and poisoning in the complex environment. In principle, the synergism of B and N dopants on the doped CNTs and confined h-MoN NPs produces extremely active sites for electrochemical hydrogen evolution. Density functional theory calculations reveal that the active sites for hydrogen evolution originate from the synergistic effect of h-MoN(001)/CN (graphitic N doping) and h-MoN(001)/BNC. The h-MoN@BNCNT electrocatalyst exhibits a small overpotential of 78 mV at 10 mA cm −2 and Tafel slope of 46 mV per decade, which are dramatically improved over all reported MoN-based materials and doped CNTs. Additionally, it also exhibits outstanding electrochemical stability in environments with various pH values and seawater media from South China Sea

Tetravalent Metal Ion Guests in Polyoxopalladate Chemistry: Synthesis and Anticancer Activity of [MO 8 Pd 12 (PO 4 ) 8 ] 12– (M = Sn IV , Pb IV )

The first two examples of polyoxopalladates(II) (POPs) containing tetravalent metal ion guests, [MO8Pd12(PO4)8]12- (M = SnIV, PbIV), have been prepared and structurally characterized in the solid state, solution, and gas phase. The interactions of the metal ion guests and the palladium-oxo shell were studied by theoretical calculations. The POPs were shown to possess anticancer activity by causing oxidative stress inducing caspase activation and consecutive apoptosis of leukemic cells

Tetravalent Metal Ion Guests in Polyoxopalladate Chemistry: Synthesis and Anticancer Activity of [MO8Pd12(PO4)8]12- (M=SnIV, PbIV)

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Self-Sorting of Heteroanions in the Assembly of Cross-Shaped Polyoxometalate Clusters

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