Hydrothermal recrystallization as a strategy to reveal the structural diversity in hexacyanometallates: Nickel and copper hexacyanoosmates(II)

The results herein discussed reinforce the relevance of the hydrothermalrecrystallization in transition metal hexacyanometallates as a suitable strategy to access the structural diversity of this family of coordination polymers. Copper(2+) and nickel(2+) hexacyanoosmates(II) were prepared by the precipitation method using hexacyanoosmic(II) acid as the complex anion source, obtaining powders of insufficient crystalline quality for the structural study. These powders were then recrystallized under hydrothermal conditions. For Ni, three new phases where formed, monoclinic and tetragonal, and a hexagonalmodification when the monoclinic one is dehydrated under soft heating. For copper, one new tetragonal phase was found, in addition to the previously reported cubic one, typical of Prussian blue analogues. The crystal structure for these four nickel and cooper hexacyanoosmates(II) were solved and refined ab initio from powder XRD data. The refined crystal structures are properly supported by a detailed spectroscopic study from IR and UVvisdata, Ligand Field Analysis, and thermal, magnetic and hydrogen adsorptionmeasurements. In the anhydrous phase for nickel, neighboring Ni atoms were foundcoordinated by bifurcated N end, an atypical coordination mode for the CN- ligand. The results herein discussed contribute to shed light on the vast information unrevealed on the coordination chemistry of transition metal hexacyanometallates.Fil: Reguera, Leslie. Universidad de La Habana; CubaFil: López, Noeldris L.. Universidad de La Habana; CubaFil: Rodríguez Hernández, Joelis. Centro de Investigación En Química Aplicada; MéxicoFil: Martinez Garcia, Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; ArgentinaFil: Reguera Ruíz, Edilso. Universidad de La Habana; Cub

Photocatalytic water oxidation with cobalt-containing tungstobismutates: Tuning the metal core

A new type of tungstobismutate water oxidation catalyst (WOC) with a disordered Co|W core, [{Co(H2O)3}2{CoBi2W19O66(OH)4}]10− (1) was tested for visible-light-driven performance and compared to a series of isostructural Co- and Mn-containing polyoxometalates with variable transition metal contents,([Co2.5(H2O)6{Bi2W19.5O66(OH)4}]8− (2) and [Mn1.5(H2O)6{Bi2W20.5O68(OH)2}]6− (3)). All compounds were structurally characterized, and no indications for significant decomposition under catalytic conditions for visible-light-driven water oxidation ([Ru(bpy)3]2+ as photosensitizer (PS) and {{S}2{O}8}2− as electron acceptor in different buffer systems) were found. For the first time, subtle differences in the core disorder patterns of isostructural POM-WOCs were revealed to be decisive for the catalytic activity of (1) (maximum TON of 21 with 97% oxygen yield for 115 μM (1)). Performance comparison of the POM series sheds new light on the structure–activity relationships for targeted POM-WOC construction. Indeed, the Co disorder differences between (1) and (2) exclusively affect the sterically more accessible external site of the two crystallographically independent Co core positions which has a 25% higher Co occupancy in (1). This points to a stereoselective reaction pattern for the tetranuclear POM core of WOC (1) which might open up novel construction strategies for the economic redesign of sandwich-type POM-WOCs. In parallel, we demonstrate for the POM series (1)–(3) that electrochemical measurements under catalytic conditions are a promising and convenient pre-screening strategy for WOC activity. Furthermore, POM/PS complex formation of (1) with [Ru(bpy)3]2+ is investigated in detail, and the different roles of Mn- and Co-centers in POM-WOC synthesis are compared