Thermal-Induced Changes in Molecular Magnets Based on Prussian Blue Analogues

Abstract

The thermal-induced changes in molecular magnets based on Prussian blue analogues, M(3)[Fe(CN)(6)](2).xH(2)O (M = Mn, Co, Ni, Cu, Zn, and Cd), were studied from infrared, X-ray diffraction, thermo-gravimetric, Mössbauer, and magnetic data. Upon being heated, these materials loose the crystalline water that enhances the interaction between the metal centers, as has been detected from Mössbauer spectroscopy data. At higher temperatures, a progressive decomposition process takes place, liberating CN(-) groups, which reduces the iron atom from Fe(III) to Fe(II) to form hexacyanoferrates(II). The exception corresponds to the cobalt compound that undergoes an inner charge transfer to form Co(III) hexacyanoferrate(II). In the case of zinc ferricyanide, the thermal decomposition is preceded by a structural transformation, from cubic to hexagonal. For M = Co, Ni, Cu, and Zn the intermediate reaction product corresponds to a solid solution of M(II) ferricyanide and ferrocyanide. For M = Mn and Cd the formation of a solid solution on heating was not detected. The crystal frameworks of the initial M(II) ferricyanide and of the formed M(II) ferrocyanide are quite different. In annealed Mn(II) ferricyanide samples, an increasing anti-ferromagnetic contribution on heating, which dominates on the initial ferrimagnetic order, was observed. Such a contribution was attributed to neighboring Mn(II) ions linked by aquo bridges. In the anhydrous annealed sample such interaction disappears. This effect was also studied in pure Mn(II) ferrocyanide. The occurrence of linkage isomerism and also the formation of Ni(III), Cu(III), and Zn(III) hexacyanoferrates(II) were discarded from the obtained experimental evidence.

Enhanced precipitation of cyanide from electroplating wastewater via self-assembly of bimetal cyanide complex

“…1B). Characteristic peaks could be observed at 20.4°, 30.7°, 35.6°, 41.7°, 51.4°and 56.1°(2h), which were quite similar to the reported Prussian blue analogue and double metal cyanide complex [11,12]. It was interesting that three curves in Fig.…”

Nature of the Observed Asymmetry in Mössbauer Spectra of Iron (2+) Hexacyanometallates (III)

“…This is a typical behavior of PB analogues on heating [19]. This family of compounds decomposes liberating CN ligands [14]. On heating, both coordinated and hydrogen bonded water molecules evolve through a practically continuous process.…”

“…The experimental evidence does not support this hypothesis. For copper, for instance, the X-ray powder pattern corresponds to also a cubic unit cell but in the Pm3m space group [14]. This primitive group supposes a non-random vacancy distribution, with two available structural sites for the metal T [15].…”

Variation of magnetic properties with different annealed temperatures in the Ni3[Fe(CN)6]2·XH2O

“…Comparing these results to those of the FTIR, it is clear that the singlet can be assigned to the structure of Fe II eCNeNi III , the doublet assigned to the structure of Fe III eCNeNi II . Meanwhile, the amount of Fe III eCNeNi II decreases relatively to that of Fe II eCNeNi III as the annealing temperatures get higher [19].…”