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 Turnbull's Blue or an excited state of Prussian Blue, but it is not a stable chemical species.     

Complex Formation of Ferric Protoporphyrin IX From the Reaction of Hemin with Ammonia and Small Aliphatic Amines

Complexes of Fe^III protoporphyrin IX (Fe^IIIPPIX) with the amido anion were obtained from the reaction of Fe^IIIPPIX chloride (hemin) with ammonia and small aliphatic amines under solvent free conditions. The reaction of hemin with gaseous ammonia leads to a pentacoordinated complex at the iron site, PPIX–Fe–NH₂, plus NH₄Cl, while at the peripheral propionic acidic groups ammonium carboxylate is formed. The corresponding stoichiometry (1:4 molar ratio of hemin to ammonia) was confirmed by the adsorption isotherm. Analogous reactions and complex formation were observed with EtNH₂ and Et₂NH. These reactions were monitored using X-ray diffraction (XRD), and i.r. and Mössbauer spectroscopies. The isomer shift and quadrupole splitting values of the resulting complexes are in correspondence with the strong -donor character of the amido anion linked to the iron atom. For comparison, the Mössbauer parameters for hemin complexes with arginine and 2-aminoguanidine, which also have pure interaction with the porphyrin iron, were included and discussed.     

Thermo-kinetics study of orange peel in air

Thermal degradation of orange peel was studied in dynamic air atmosphere by means of simultaneous TG-DSC and TG-FTIR analysis. According to the obtained thermal profiles, the orange peel degradation occurred in at least three steps associated with its three main components (hemicellulose, cellulose and lignin). The volatiles compounds evolved out at 150–400 °C and the gas products were mainly CO₂, CO, and CH₄. A mixture of acids, aldehydes or ketones C=O, alkanes C–C, ethers C–O–C and H₂O was also detected. The E _α on α dependence reveled the existence of different and simultaneous processes suggesting that the combustion reaction is controlled by oxygen accessibility, motivated by the high evolution low-molecular-mass gases and volatile organic compounds. These results could explain the non-autocatalytic character of the reactions during the decomposition process.     

Mixed valence states in cobalt iron cyanide

Cobalt iron cyanide with both Co and Fe in mixed valence states were prepared and characterized. In this mixed valence system the cobalt atom is found both as high spin Co(2+) and low spin Co(III) while iron always appears in low spin state to form two solid solutions: Co(2+)Co(III) hexacyanoferrates (II,III), and Co(2+)Co(III) hexacyanoferrate (II). Such solid solutions have the following formula units: (Co²⁺)_x(Co^III)_1−xK[(Fe^II)_1−x(Fe^III)_x(CN)₆]·H₂O and (Co²⁺)_1.5x(Co^III)_1−xK[Fe^II(CN)₆]·yH₂O (0?x?1, 1?y?14). Compounds within these two series were characterized from Infrared, Mössbauer, X-ray diffraction and thermo-gravimetric data, and magnetic measurements at low temperature. A model for their crystal structure is proposed and the structure for a representative composition refined from XRD powder patterns using the Rietveld method. A simple and reproducible procedure to prepare these solid solutions is provided. Within hexacyanoferrates, such mixed valence states system in both metal centres shows unique features, which are discussed from the obtained data.     

129Xe NMR spectroscopy study of porous cyanometallates

Zinc and cadmium hexacyanocobaltates(III) were prepared, and their porous networks were explored using 129Xe spectroscopy. The crystal structures of these two compounds are representative of porous hexacyanometallates, cubic (Fm-3m) for cadmium and rhombohedral (R-3c) for zinc. In the cubic structure, the porosity is related to systematic vacancies created from the elemental building block (i.e., the hexacyanometallate anion), whereas the rhombohedral (R-3c) structure is free of vacant sites but has tetrahedral coordination for the zinc atom, which leads to relatively large ellipsoidal pores communicated by elliptical windows. According to the Xe adsorption isotherms, these porous frameworks were found to be accessible to the Xe atom. The structure of the higher electric field gradient at the pore surface (Fm-3m) appears and is accompanied by a stronger guest-host interaction for the Xe atoms and a higher capacity for Xe sorption. For cadmium, the 129Xe NMR signal is typical of isotropic movement for the Xe atom, indicating that it remains trapped within a spherical cavity. From spectra recorded for different amounts of adsorbed Xe, the cavity diameter was estimated. For the zinc complex, 129Xe NMR spectra are asymmetric because of the Xe atom movement within an elongated cavity. The line-shape asymmetry changes when the Xe loading within the porous framework increases, which was ascribed to Xe-Xe interactions through the cavity windows. The Xe adsorption revealed additional structural information for the studied materials.     

Thermal evolution of microporous nitroprussides on their dehydration process

Divalent transition metal nitroprussides form a family of microporous materials which lose their crystallization water (coordinated and zeolitic) below 100°C and then remain stable up to above 150°C. The dehydration process of representative samples in their stable phases was studied by thermo-gravimetry (TG) and differential scanning calorimetry (DSC). The copper complex dehydrates in a single step through a practically irreversible process. For cadmium and cobalt complexes the water evolution on heating takes place in two stages. The first one, where only zeolitic waters are removed, is dominated by a diffusion mechanism while, during the loss of the strongly bonded waters (second stage) the material framework effect is added. The involved activation energy and its dependence on the conversion degree were estimated evaluating the thermo-gravimetric data according to an isoconversion model.     

Structural Characterization of Cadmium Hexacyanometallates(II) and Related Complexes

Cadmium hexacyanometallates (II) crystallize in the same monoclinic cell (space group C⁵ _2h–P2_1/n) reported for the analogs of manganous complexes. In that monoclinic framework, two outer cations (M = Mn²⁺ or Cd²⁺) of neighboring structural units M₂[L^II(CN)₆], (L = Fe^II, Ru^II, Os^II), are linked by two common water molecules. On heating above 100°C, these water bridges are removed. In dehydrated complexes, the outer cation (M) remains linked to only three CN ligands. The loss of aquo-ligands induces a remarkable -back donation from the inner cation (L) to CN ligands, which was studied using IR, Raman, and Mössbauer spectroscopies.