Hydrothermal Recrystallization as a Strategy to Reveal the Structural Diversity in Hexacyanometallates: Nickel and Copper Hexacyanoosmates(II)

Abstract

The results discussed herein reinforce the relevance of the hydrothermal recrystallization 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 hexagonal modification when the monoclinic one is dehydrated under soft heating. For copper, one new tetragonal phase was [a] Prof. 1763found, 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 UV/Vis data, Ligand Field Analysis, and thermal, magnetic and hydrogen adsorption measurements. In the anhydrous phase for nickel, neighboring Ni atoms were found coordinated by bifurcated N end, an atypical coordination mode for the CNligand. The results herein discussed contribute to shed light on the vast information unrevealed on the coordination chemistry of transition metal hexacyanometallates. catalysis, [6] gas storage and separation, [7] batteries, [8] and environmental remediation, [9] etc. However, it is not possible to divorce both topics since functionality directly depends on the material's electronic and crystalline structure.The most studied polymeric hexacyanometallates are those where the internal metal center (M, linked to the C end of the CNgroup) belongs to the first transition series. This obeys to the greater availability of the building blocks, to historical reasons, but also to the fact that they are obtained with good crystallinity by the very easy precipitation method. The hexacyanide anions containing metals with relatively diffuse d orbitals -corresponding to the second and third transition series -have proved to improve the robustness of the polymeric frameworks. [10] However, when these compounds are prepared by the traditional precipitation method, they frequently exhibit relatively low crystallinity. [11] This is a critical issue for the structures containing a great number of vacancies of the hexacyanide building block around the outer metal (T, linked to the N end of the CNgroup), which requires recrystallization procedures after precipitation of the crude compound. [10] In this work, we explore the potentialities of solvothermal recrystallization, beyond improving the crystallinity of materials, with the aim of generating structural diversity.In general, structural diversity for each combination of inner and outer metals, is not frequently observed in polymeric hexacyanometallates. A unique behavior in this sense appears for Co 2+ a...

Thermally induced spin-crossover in the Fe(3-ethynylpyridine)2[M(CN)4] series with M = Ni, Pd, and Pt. The role of the electron density found at the CN 5σ orbital

“…This post-synthesis treatment has proved to be appropriate for obtaining the thermodynamic product for the case of transition metal hexacyanometallates and nitroprussides. [39][40][41][42] No structural modifications were found in the materials after the solvothermal treatment. The obtained materials were analyzed in terms of their nature and purity, from chemical analysis (ICP and CHONS), XRD, TG, IR, and Raman data.…”