Electronic Consequences of Ligand Substitution at Heterometal Centers in Polyoxovanadium Clusters: Controlling the Redox Properties through Heterometal Coordination Number

The rational control of the electrochemical properties of polyoxovanadate‐alkoxide clusters is dependent on understanding the influence of various synthetic modifications on the overall redox processes of these systems. In this work, the electronic consequences of ligand substitution at the heteroion in a heterometal‐functionalized cluster was examined. The redox properties of [V$_{5}$O$_{6}$(OCH$_{3}$)$_{12}$FeCl] (1‐[V$_{5}$FeCl] ) and [V$_{5}$O$_{6}$(OCH$_{3}$)$_{12}$Fe]X (2‐[V5Fe]X ; X=ClO$_{4}$, OTf) were compared in order to assess the effects of changing the coordination environment around the iron center on the electrochemical properties of the cluster. Coordination of a chloride anion to iron leads to an anodic shift in redox events. Theoretical modelling of the electronic structure of these heterometal‐functionalized clusters reveals that differences in the redox profiles of 1‐[V$_{5}$FeCl] and 2‐[V$_{5}$Fe]X arise from changes in the number of ligands surrounding the iron center (e.g., 6‐coordinate vs. 5‐coordinate). Specifically, binding of the chloride to the sixth coordination site appears to change the orbital interaction between the iron and the delocalized electronic structure of the mixed‐valent polyoxovanadate core. Tuning the heterometal coordination environment can therefore be used to modulate the redox properties of the whole cluster

Nanolithographic Top‐Down Patterning of Polyoxovanadate‐based Nanostructures with Switchable Electrical Resistivity

The top-down fabrication of ∼10 nm vanadium oxide nanostructures by electron beam lithography based on a molecular vanadium oxide resist material is reported. The new material enables the large-scale deposition of electrically switchable nanostructures which can be directly incorporated in established e-beam lithography. The findings could in future enable the top-down fabrication of functional metal oxide nanostructures in the < 10 nm domain. The top-down lithographic fabrication of functional metal oxide nanostructures enables technologically important applications such as catalysis and electronics. Here, we report the use of molecular vanadium oxides, polyoxovanadates, as molecular precursors for electron beam lithography to obtain functional vanadium oxide nanostructures. The new resist class described gives access to nanostructures with minimum dimensions close to 10 nm. The lithographically prepared structures exhibit temperature-dependent switching behaviour of their electrical resistivity. The work could lay the foundation for accessing functional vanadium oxide nanostructures in the sub-10-nm domain using industrially established nanolithographic methods

O IVA nas prestações de serviços de construção civil: inversão do sujeito passivo e taxas reduzidas

O setor da Construção Civil apresenta um fator importante na economia nacional. Porém, é considerado pela Autoridade Tributária e pela Comissão Europeia como um setor de risco na fraude e evasão fiscal. Assim, no seguimento de medidas implementadas pela Comissão Europeia, Portugal aprovou o Decreto-Lei 21/2007 de 29 janeiro, com o intuito de combater a fraude e evasão fiscal em sede Imposto sobre o Valor Acrescentado. Apesar disso, têm sido implementados incentivos aos serviços de construção civil, dos quais destacamos a taxa reduzida de Imposto sobre Valor Acrescentado, nomeadamente para a reabilitação urbana e para os serviços com alta intensidade de fator de trabalho. Pretendemos analisar pormenorizadamente esta legislação com a finalidade de esclarecer dúvidas omissas, adotando-se uma metodologia assente na análise de jurisprudência, Informações Vinculativas e doutrina. Da análise efetuada ficou evidente que o conceito de serviços de construção civil é muito amplo e de difícil definição introduzindo dificuldades na aplicação da taxa reduzida de IVA prevista nas verbas 2.23 e 2.27. No mesmo sentido verificou-se não serem aplicados pela AT os mesmo critérios na definição de serviços de construção civil para a regra de inversão do sujeito passivo e para a aplicação da taxa reduzida de IVA

Electronic Consequences of Ligand Substitution at Heterometal Centers in Polyoxovanadium Clusters: Controlling the Redox Properties through Heterometal Coordination Number

The rational control of the electrochemical properties of polyoxovanadate‐alkoxide clusters is dependent on understanding the influence of various synthetic modifications on the overall redox processes of these systems. In this work, the electronic consequences of ligand substitution at the heteroion in a heterometal‐functionalized cluster was examined. The redox properties of [V$_{5}$O$_{6}$(OCH$_{3}$)$_{12}$FeCl] (1‐[V$_{5}$FeCl] ) and [V$_{5}$O$_{6}$(OCH$_{3}$)$_{12}$Fe]X (2‐[V5Fe]X ; X=ClO$_{4}$, OTf) were compared in order to assess the effects of changing the coordination environment around the iron center on the electrochemical properties of the cluster. Coordination of a chloride anion to iron leads to an anodic shift in redox events. Theoretical modelling of the electronic structure of these heterometal‐functionalized clusters reveals that differences in the redox profiles of 1‐[V$_{5}$FeCl] and 2‐[V$_{5}$Fe]X arise from changes in the number of ligands surrounding the iron center (e.g., 6‐coordinate vs. 5‐coordinate). Specifically, binding of the chloride to the sixth coordination site appears to change the orbital interaction between the iron and the delocalized electronic structure of the mixed‐valent polyoxovanadate core. Tuning the heterometal coordination environment can therefore be used to modulate the redox properties of the whole cluster

Nanolithographic Top‐Down Patterning of Polyoxovanadate‐Based Nanostructures with Switchable Electrical Resistivity

The top-down fabrication of ∼10 nm vanadium oxide nanostructures by electron beam lithography based on a molecular vanadium oxide resist material is reported. The new material enables the large-scale deposition of electrically switchable nanostructures which can be directly incorporated in established e-beam lithography. The findings could in future enable the top-down fabrication of functional metal oxide nanostructures in the < 10 nm domain. The top-down lithographic fabrication of functional metal oxide nanostructures enables technologically important applications such as catalysis and electronics. Here, we report the use of molecular vanadium oxides, polyoxovanadates, as molecular precursors for electron beam lithography to obtain functional vanadium oxide nanostructures. The new resist class described gives access to nanostructures with minimum dimensions close to 10 nm. The lithographically prepared structures exhibit temperature-dependent switching behaviour of their electrical resistivity. The work could lay the foundation for accessing functional vanadium oxide nanostructures in the sub-10-nm domain using industrially established nanolithographic methods

Top-down synthesis of polyoxometalate-like sub-nanometer molybdenum-oxo clusters as high-performance electrocatalysts

The top-down fabrication of catalytically active molecular metal oxide anions, or polyoxometalates, is virtually unexplored, although these materials offer unique possibilities, for catalysis, energy conversion and storage. Here, we report a novel top-down route, which enables the scalable synthesis and deposition of sub-nanometer molybdenum-oxo clusters on electrically conductive mesoporous carbon. The new approach uses a unique redox-cycling process to convert crystalline (MoO2)-O-IV particles into sub-nanometer molecular molybdenum-oxo clusters with a nuclearity of similar to 1-20. The resulting molybdenum-oxo cluster/carbon composite shows outstanding, stable electrocatalytic performance for the oxygen reduction reaction with catalyst characteristics comparable to those of commercial Pt/C. This new material design could give access to a new class of highly reactive polyoxometalate-like metal oxo clusters as high-performance, earth abundant (electro-)catalysts