Computational Prediction of Speciation Diagrams and Nucleation Mechanisms: Molecular Vanadium, Niobium and Tantalum Oxide Nanoclusters in Solution

Abstract

Understanding the aqueous speciation of molecular metal-oxo clusters plays a key role in different fields such as catalysis, electrochemistry, nuclear waste recycling, and biochemistry. To accurately describe the speciation, it is essential to elucidate the underlying self-assembly processes. Herein, we apply a computational method to predict the speciation and formation mechanisms of polyoxovanadates, -niobates and -tantalates. While polyoxovanadates have been widely studied, polyoxoniobates and -tantalates lack the same level of understanding. In the first place, we proposed a pentavanadate cluster ([V5O14]3-) as a key intermediate for the formation of the decavanadate. Our computed phase speciation diagram is in particularly good agreement with the experiments. Secondly, we report the formation constants of the heptaniobate, [Nb7O22]9-, decaniobate, [Nb10O28]6-, and tetracosaniobate [H9Nb24O72]9-. Additionally, we have computed the speciation and phase diagram of niobium, which so far was restricted to Lindqvist derivates. Finally, we have predicted the formation constant of the decatantalate ([Ta10O26]6-) in water, even though it had only been synthetized in toluene. Furthermore, the corresponding speciation and phase diagrams for polyoxotantalates have been also calculated. Overall, we show that our method can be successfully applied to different families of molecular metal oxides without any need for readjustments; therefore, it can be regarded as a trustworthy tool for exploring polyoxometalates’ chemistry.

Computational Prediction of Speciation Diagrams and Nucleation Mechanisms: Molecular Vanadium, Niobium, and Tantalum Oxide Nanoclusters in Solution

“…The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.inorgchem.2c00925. Molecular sets; computational details; overview of the Python code developed; full list of chemical reactions; and speciation models and formation constants plus additional data (PDF) …”

“…Molecular sets; computational details; overview of the Python code developed; full list of chemical reactions; and speciation models and formation constants plus additional data (PDF)…”

Carbon Dioxide Capture by Niobium Polyoxometalate Fragments

“…Instead, Nb24 forms, in response to the pH decrease, as indicated by computational and experimental speciation studies. 24,27 Nb24 does not have available metal sites to bind carbonate in a bidentate fashion, as is observed in the isolated POMs. Alternatively, the carbonate observed in the bulk could be either Nb-carbonate monomers that are not observable by SAXS, or free bicarbonate.…”

“…23 In this study, we hypothesized that Nb-POM speciation change and concomitant gaseous CO2 capture via Nb-carbonate binding could be achieved, using aqueous solutions of Nb6. Up-to-date computed speciation diagrams 24 predict that decreasing the pH of an Nb6 solution (i.e. from 14 to ~9) would drive topology and nuclearity from Nb6 to Nb7 ([Nb7O20(OH, H2O)2] (5-7)-).…”