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

Abstract

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.