Oxidative dissolution of synthetic vivianites as a method for the crystallization of molecular structural motifs
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ORIGINAL RESEARCH
Oxidative dissolution of synthetic vivianites as a method for the crystallization of molecular structural motifs Esteban Rojas-Gatjens 1,2,3 & Christian Viales-Montero 1,3 & Roberto Urcuyo 1,2,3 & Diego González-Flores 1,2,3 & Mavis L. Montero 1,3 Received: 22 July 2020 / Accepted: 16 September 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Isolation of structural motifs from minerals can be used to improve the understanding of fundamental processes such as catalytic mechanisms and spectroscopic vibrations. In this study, we designed an oxidative dissolution reaction using 2,2′-bipyridine in combination with minerals from the vivianite family. Vivianites are structurally similar to amorphous cobalt oxide water oxidation catalysts (CoCat). Specifically, we used pakhomovskyite (Pak: Co 3 (PO 4 ) 2 •8H 2 O) and erythrite (Ery: Co3(AsO4)2•8H2O)). Through the designed synthetic route, we crystallized two mononuclear isostructural complexes containing phosphate or arsenate and a cobalt-arsenate trinuclear cluster. We observed three main binding modes from the anions: (i) both arsenates or phosphates bind to cobalt forming an O-μ2-bridge, (ii) arsenate forms a bridge between two cobalt atoms, and (iii) arsenate binds between three cobalt atoms expanding its coordination sphere to five. This structural information allows us to propose an updated structural model for amorphous cobalt oxide catalysts containing arsenate. Keywords Oxidative dissolution . Molecular motif . Cobalt oxide catalysts . Pakhomovskyite . Erythrite
Introduction Oxidative dissolution has been widely studied for mineral leaching and the processing of minerals that contain radioactive isotopes [1]. More recently, oxidative dissolution has been used in kinetic studies of nanoparticle dissolution and the modeling of specific nanoparticle morphologies [2–13]. This synthetic method usually consists of the dissolution of a mineral or solid phase accompanied by a change in the
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11224-020-01644-3) contains supplementary material, which is available to authorized users. * Mavis L. Montero [email protected] 1
Centro de Investigación en Ciencia e Ingeniería de Materiales (CICIMA), Universidad de Costa Rica San José, San Pedro, San José 11501 2060, Costa Rica
2
Centro de Electroquímica y Energía Química (CELEQ), Universidad de Costa Rica San José, San Pedro, San José 11501 2060, Costa Rica
3
Escuela de Química, Universidad de Costa Rica San José, San Pedro, San José 11501 2060, Costa Rica
oxidation state of the metal or metal ions involved. Typical oxidizing agents are oxygen or hydrogen peroxide. We implemented this synthetic strategy to crystallize new structural motifs associated with minerals, specifically minerals with catalytic behavior. Minerals offer an enormous number of structural motifs with varied geometries, sizes, coordination numbers, atomic compositions, and binding configurations [14]. U
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