J. Fernández-Bertrán

Mechanochemical reactions in alkali halide pressed disks

Mechanochemical reactions that take place when milling and pressing analytes with KBr to form a disk suitable for IR spectral work are reviewed. The topic is extended to other alkali halides matrices. The literature from 1952 is surveyed from an analytical point of view. Several reactions are discussed at length with emphasis on the nature of the products. The mechanism and the factors affecting the mechanochemical changes are discussed in detail for copper sulphate, alkaline and transition metal ferricyanides, and Ag, Hg and Pb salts.

The existence of ferrous ferricyanide

Evidence in the literature on the synthesis of ferrous ferricyanide is critically discussed. Pyrolysis and pressure effects on Prussian Blue lead to ferrous ferrocyanide together with decomposition by-products, and not to ferrous ferricyanide. The latter compound could be a precursor in the formation of Turnbulls Blue or an excited state of Prussian Blue, but it is not a stable chemical species.

Proton transfer in the solid state: Reactions of organic acids and amines

Grinding of crystalline organic acids and amines leads to proton transfer with ammonium salt formation or to hydrogen bonded complexes. Formation of amides is not achieved with these reagents even under strong impact. The mechanochemical processes were monitored by IR spectroscopy. Thirteen acids and four amines covering a wide range of acidity, basicity and hardness were employed.

Mössbauer spectroscopic study of Prussian Blue from different provenances

Ferric ferrocyanides synthesized from different sources of ferric cations and ferrocyanide anions and those derived from ferrous ferricyanide, ferrous ferrocyanide and ferric ferricyanide have been studied using Mössbauer and XRD techniques. Structural information of the effect of the provenance on the properties of the final compound is obtained. Significant correlations between isomer shift and quadrupole splitting of inner and outer iron cations have been observed.

On the interactions of ozone with manganous hexacyanoferrates

The ozonization of manganous ferro- and ferricyanides has been studied in the solid state using IR, Mossbauer and XRD techniques. Ferrocyanides are oxidized to ferrycanides without disruption of the complex anions, while Mn2+ is oxidized to the Mn3+ and Mn4+ states. On aging the mn3+ and Mn4+ species are reduced to Mn2+. The ferricyanide is not reduced to ferrocyanide, except in the case of the mixed K, Mn salt. The unstable product Mn4+3[Fe111(CN6]4·xH2O has been determined as a cubic species with a0 = 10.35(1)A.

Effect of the water of crystallization on the Mössbauer spectra of hexacyanoferrates (II and III)

Mössbauer spectra were recorded on hydrated, dehydrated and rehydrated hexacyanoferrate (II and III) samples including alkaline, alkaline-earth, transition metal and rare-earth salts. The location of the water molecules around the complex hexacyanoferrate anion has a decisive role on the quadrupole splitting of the low-spin FeIII cation.

Spectroscopic study of the interactions of alkali fluorides with D-xylose.

The interactions of alkali fluorides with D-xylose have been studied by X-ray diffraction (XRD), infrared spectroscopy (IR), nuclear magnetic resonance (NMR, 1H and 13C) and atomic absorption spectrophotometry. KF and CsF form complexes with D-xylose in a 1:1 molar ratio. These complexes can be obtained by solid state milling the reactants in an agate mortar or from methanolic solutions of the sugar and the salt. LiF and NaF do not form complex with D-xylose. IR and XRD prove the identical nature of the complexes obtained by milling and from solution. IR spectra indicate strong perturbation of the OH stretching vibrations with considerable shifts to lower frequencies, which must be caused by strong hydrogen bond formation to the fluorine anion. The perturbations of C-O bond are weak, indicating that cation binding to the oxygen atoms is not the main interaction responsible for the complex formation. 1H NMR spectra of the D-xylose-KF complex dissolved in deuterium oxide is equal to that of pure D-xylose, indicating the destruction of the complex in solution. The complex is stable in DMSO, and 13C spectra of the complex in DMSO-d6 and in solid state (CPMAS) spectra are in accordance with the observed interactions in the IR spectra. As far as we know, this is the first report of a sugar-halide salt complex in which the anion instead of the cation provides the binding forces.

Behaviour of Prussian Blue during its interaction with ozone

The interaction of ozone with Prussian Blue has been studied by Mössbauer, infrared and XRD techniques. All spectral results reveal a reversible conversion of ferrocyanide to ferricyanide with preservation of the crystal skeleton. Ferric ferricyanide obtained by ozonization of ferric ferrocyanide has Mössbauer parameters different to those of an ordered Prussian Brown, which has been attributed to secondary reaction products located at the zeolite voids of the former compound.

Transformation of cadmium ferricyanide by heating, milling and sonication

Abstract On heating, milling and sonication, cadmium ferricyanide decomposes and reduces to cadmium ferrocyanide. Two compositions were studied, pure cadmium ferricyanide and mixed potassium-cadmium ferricyanide. The role of reducing agent is played by the CN− anions liberated during the decomposition process. The solid decomposition product is composed by several phases of cadmium ferrocyanide, an Fe3+ phase and also potassium ferrocyanide in the case of the mixed complex salt. The decomposition process was monitored using DTA, XRD, IR and Mossbauer techniques. No occurrence of linkage isomerization in cadmium ferricyanide was detected.

Mechanochemical synthesis of hemin±imidazole complexes

Solid state reactions of hemin and imidazole were performed by milling the crystalline materials in an agate mortar. The process was monitored by i.r., x.r.d. and Mössbauer spectroscopies. Samples with different hemin to imidazole molar ratios were studied. The interactions of imidazole with the central Fe atom and with the propionic acid groups in the periphery of the hemin molecule were detected. The latter interactions are suppressed by washing with MeOH. Complexes with 1:2 and 1:4 hemin-to-imidazole molar ratios were identified.