Evidence for the Existence of Oxygen Clustering and Understanding of Structural Disorder in Prussian Blue Analogues Molecular Magnet M_1.5[Cr(CN)₆]·zH₂O (M = Fe and Co): Reverse Monte Carlo Simulation and Neutron Diffraction Study

Abstract

A detailed structural disorder investigation of Prussian blue analogues M 1.5 [Cr(CN) 6 ]·zH 2 O (M = Fe and Co) has been done by carrying out a reverse Monte Carlo (RMC) simulation on the powder neutron diffraction data. Xray diffraction, infrared spectroscopy, Mossbauer spectroscopy, and dc magnetization measurements have also been employed to investigate the structural and magnetic properties of the compounds. The Rietveld refinement of the X-ray and neutron diffraction patterns reveals that both compounds are in a single phase with a face-centered cubic crystal structure (space group Fm3m). The observation of characteristic absorption bands in the range 1900−2200 cm −1 of infrared (IR) spectra, which corresponds to the CN stretching frequency of M II NCCr III sequence, confirms the formation of Prussian blue analogues, M 1.5 [Cr(CN) 6 ]·zH 2 O. The IR study also infers the presence of cyanide flipping in the Fe 1.5 [Cr(CN) 6 ]·zH 2 O compound. The Mossbauer study on the Fe 1.5 [Cr(CN) 6 ]·zH 2 O compound confirms the presence of high as well as low spin Fe II ions due to isomerization of some Cr III CNFe II linkages to the Cr III NCFe II form. The magnetization data show a soft ferromagnetic nature of both compounds with a Curie temperature of ∼17 and ∼22 K for Fe 1.5 [Cr(CN) 6 ]·zH 2 O and Co 1.5 [Cr(CN) 6 ]·zH 2 O, respectively. A large amount of structural disorder is present in both compounds, which is manifested in the form of a diffuse scattering in neutron diffraction patterns. The RMC results, obtained after the modeling, simulation, and analysis of the neutron diffraction data, propose that the water molecules and the [Cr(CN) 6 ] vacancies are mainly responsible for the structural disorder. Moreover, a clustering of the noncoordinated oxygen atoms around the coordinated oxygen atoms is also ascertained by the RMC analysis. The correlation of structural disorder with the water content and [Cr(CN) 6 ] vacancies is also discussed. ■ INTRODUCTIONPeriodic arrangements of atoms in a material decide the crystalline nature, and the local deviation of atoms from their atomic sites leads to the structural disorder in the materials. Structural disorder occurs due to an uncertainty in the spatial arrangements of atoms in a material. The disordered materials display interesting physical properties that are not always seen in their crystalline counterparts. Therefore, the disordered materials have also received great attention and are equally important from the scientific as well as technological point of view when compared to crystalline materials. For example, the disordered semiconductor materials, produced by metal doping, are highly useful in microelectronics technology. 1 Further, the high temperature superconductor can be synthesized with an optimal amount of doping of defects/disorder in the materials. 2,3 The disorder can be introduced in the materials either by using external stimuli, such as temperature, pressure, heat, magnetic field, or light, or intrinsically due to doping of atomic species,...

Structure and adsorption properties of a porous cooper hexacyanoferrate polymorph

“…4b) and dehydrated ( Fig. 4d [32]. Since, Cu-PBA-I is a rather pure material, as is evidenced in the XRD pattern (Fig.…”

“…For the last years the investigation of PBAs became an expanding research field, specially, when materials with high thermal stability and porosity are produced [32][33][34][35][36]. Thereafter, the main questions investigated here were: the structural elucidation and the study of the adsorption properties and thermal stability of a porous Cu(II) hexacyanoferrate (III) polymorph (labelled Cu-PBA-I) and the synthesis and characterization of the standard Cu(II) hexacyanoferrate (III) (labelled Cu-PBA) for comparison.…”

Synthesis, structural elucidation and carbon dioxide adsorption on Zn (II) hexacyanoferrate (II) Prussian blue analogue

“…Variable Soller slits were included and a Ni filter was placed, prior to the detector. Additionally, a LynxEye™ onedimensional detector was used to produce large counting that resulted to high quality XRD profiles that can be accurately resolved by least square methods [17]. To confirm the assigned structure of the synthesized materials, the gathered XRD patterns were refined with the Pawley method.…”

“…PBAs are good adsorbents of small molecules [17][18][19][20][21][22][23]; hence, the main questions investigated here were, the synthesis and structural characterization of a Zn(II) hexacyanoferrate(II) (labeled Zn-HII); together, with the investigation of carbon dioxide adsorption in the low pressure (up to 1 Bar) and high pressure (up to 30 Bar) ranges, to investigate the structural transformations induced by adsorption in the framework of the tested Prussian blue analogue.…”

“…Lastly, carbon dioxide (Praxair, 99.99 %) adsorption was investigated at 273 K and 300 K in the low pressure (LP) range (pressure up to 1 bar) on samples degassed at 373 K for four hours in high vacuum(10 -6 Torr) in a Quantachrome AS-1 automatic sorption analyzer. To measure the carbon dioxide (Praxair, 99.99 %) adsorption at temperatures of 273 K, 300 K and 318 K on samples degassed at 373 K for four hours in high vacuum(10 -6 Torr) in the high pressure range , growth in a gel, growth on a solid alkali-metal ferrocyanide and others[17][18][19][20][21][22]. Here we applied a precipitation method to produce the Zn(II) hexacyanoferrate (II).…”