H. Yee-Madeira

Petroleum solid adherence on tubing surface

Blocking of the crude oil flow is induced occasionally by the presence of a black layer of material adhered along the internal walls of petroleum wells. A piece of tubing with a significant amount of organic material, collected from a Mexican oil well, was analyzed by Mossbauer Spectroscopy (MS), X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIRS). At room temperature, a fraction of the adherence detaches easily off from the tubing surface, but part of it remains firmly adhered. Non-stoichiometric iron oxides (oxidized magnetite or maghemite) and iron sulfides (pyrrhotite) and also small amounts of iron hydroxides and organic material were found on the tubing surface with adhered-material. This suggests a competitive adsorption of sulfur atoms and hydroxyl groups from petroleum, on the surface iron sites. Finally, the organic material, which contains alkyl chains and aromatic rings, is adsorbed non-dissociatively on the modified surface but only in the presence of non-stoichiometric iron sulfide.

Behavior of Prussian blue-based materials in presence of ammonia

Prussian blue and related materials, usually considered that behave as a zeolite for ammonia adsorption, when hydrated are unstable in the presence of this gaseous species. They remain stable only in the anhydrous form. In the decomposition products ammonium hexacyanometallates and an XRD amorphous iron(III) oxyhydroxide are detected. The crystallization and adsorbed water present in these solid materials participates in a decomposition reaction to give NH4 and OH 2 . The very basic OH 2 anion removes the iron(III) cations from the complex to form Fe(OH)3 and finally FeOOH, while the formed NH4 appears as the salt of the complex anion. As reference reactions, the interaction of ammonia with ferrocyanic acid and ferric chloride, both in solid state, were studied where crystalline ammonium ferrocyanide and ammonium chloride, respectively, are formed. q 2003 Published by Elsevier Science Ltd.

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.

On the crystal structures of some nickel hexacyanoferrates (II,III)

The crystal structures of some nickel hexacyanoferrates ~II, III!, including mixed compositions containing Na1, K1 and Cs1, were resolved and refined from XRD powder patterns. Data from infrared, Mo¨ssbauer and adsorption techniques provided complementary structural information. The crystal structures of Ni3@Fe(CN)6#2 16H2O and NiCs2@Fe(CN)6# were refined in space group Fm3m. NiNa2@Fe(CN)6# 2H2O and NiK2@Fe(CN)6# 2H2O were found to be orthorhombic ~space group Pmn21). This structure (Pmn21) results from a distortion around the alkali ion, which appears as a monohydrated interstitial species. On ionic exchange in an aqueous solution containing Cs1, the orthorhombic distortion disappears and the cubic cell is obtained. Cs1 is a large cation and space is not available for interstitial water molecules. This orthorhombic model is also supported by the Mo¨ssbauer spectra of the ferrous analogs, FeK2@Fe(CN)6# xH2O and Fe@Pt(CN)6#.

Mössbauer spectra of ferrous salts of transition metal cyano complexes. A survey

Ferrous salts of ten hexacyanometallates and three tetracyanometallates were obtained and their Mössbauer spectra interpreted according to recent structural models for these families of compounds. Ferrous ferrocyanide (Williamson White) and its ruthenium and osmium analogs prepared mechanochemically are stable for hours, allowing their study by Mössbauer spectroscopy and other related techniques. For ferrous salts of trivalent hexacyanometallate anions, the random distribution of anion vacancies is discarded and a model of two well defined relative positions of CN and H2O ligands around the Fe2+ is suggested. Iron was found octahedrally coordinated in tetracyanometallates.

MECHANOCHEMICAL REACTIONS OF FLUORIDES WITH HEMIN

Abstract Hemin has two potential sites to react with fluorides, the peripheral acid groups and the central FeIII cation. The mechanochemical reactions of hemin with fluorides (LiF, NaF, KF, CsF, NH4F and AgF) were monitored using X-ray diffraction (XRD), and IR and Mossbauer spectroscopies. LiF and NaF were found inert when milled with hemin, however KF, CsF, NH4F and AgF react at both hemin sites. At the iron site Cl− is replaced by F− with formation of KCl, CsCl, NH4Cl, and AgCl, as detected by XRD, while with the peripheral acid groups, fluorides collect the acidic protons to form KHF2, CsHF2, NH4HF and AgHF2. The reactions of hemin with the reactive fluorides take place first at the iron site and then at the propionic acid groups.

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

Abstract The material under study belongs to the Prussian blue analogues family, which are coordination compounds with a porous framework appropriate for the storage of small molecules, among them hydrogen. The porous framework results from systematic vacancies for the octahedral building block, [M(CN)6], in a 3D structure. Mössbauer spectroscopy is a powerful tool to obtain structural information on the local environment for the iron nucleus in these materials. Mössbauer spectra of iron (2+) hexacyanometallates (III) show two slightly asymmetric quadrupole splitting doublets. These two doublets correspond to two non-equivalent structural sites for the iron atom in the framework related with a non-random vacancy distribution. The observed asymmetry was ascribed to a vibrational anisotropy for these iron sites. The asymmetry decreases on the sample cooling and for 7 K it practically disappears. The iron atom is found at the cavities surface with a mixed coordination sphere, Fe(NC)6–x(H2O)x. Such anisotropic coordination environment could explain the presence of certain vibrational anisotropy detected as asymmetric quadrupole splitting doublets.

Solid State Reactions of Hemin with Basic Substances: Formation of bis and Mixed Complexes

The solid state reactions of hemin with KCN, Na2S⋅xH2O, arginine, imidazole, 1-methylimidazole, 2-methylimidazole, benzimidazole, and mixtures of these basic reagents were monitored using IR, Mössbauer, and XRD techniques. All these basic substances react at the peripheral propionic acid group of hemin-forming salts. Binary mixtures of KCN, arginine, imidazole, 1-methylimidazole, 2-methylimidazole, and benzimidazole were found to form complexes with mixed ligands at the iron site of hemin. According to the structural information obtained for these mixed complexes, mechanisms for their formation are proposed. The solid state synthesis and the properties of the obtained products reveal the specifities of the involved ligands.

Mechanochemical Reaction Between the Probe and the Matrix: A Possible Source of Errors When IR Spectra of Alkali Acid Bifluorides Are Recorded in Alkali Halide Pressed Disks

Abstract The mechano‐chemical reactions of alkali acid bifluorides (MHF2), with alkali halides (MX), were studied by x‐ray diffraction (XRD) and IR spectroscopy. The reactions were carried out by milling the solid reagents in equimolar ratio by hand in an agate mortar. LiHF2 is unstable on milling and decomposes to LiF and HF. Rb, Cs, and NH4 acid bifluorides react with KBr leading to the corresponding bromides and stable KHF2. Similar reactions are observed with Na halides, leading to NaHF2. NaHF2 reacts with KF to form KHF2 and NaF. The mechano‐chemical reactions with alkali halides are considered in connection with the use of alkali halides as matrices for IR spectroscopy.

Mechano‐chemical Synthesis and Spectroscopic Characterization of Hemin Complexes with Some Amino Acids

The mechano‐chemical reactions of hemin with arginine (Arg), histidine (His), lysine (Lys), methionine (Met) and tryptophan (Trp) were monitored using IR and Mössbauer spectroscopies. According to IR spectra, with exception of Arg, these basic amino acids don´t react at the peripheral propionic acid groups of hemin which is related with their relatively low basicity. Arg also forms a penta‐coordinated complex with hemin at the iron site, as revealed by the Mössbauer spectra of the hemin–Arg milled mixtures. The hemin–Arg solid state reaction is completed in 1:3 molar ratio suggesting that this is the stoichiometry of the formed complex. The binding of Arg to the carboxylic groups of hemin and to the central Fe(III) cation inhibits any interaction between vicinal hemin molecules, which explains the solubility and stability of the Arg–hemin complex in water. His binds iron only in basic media but, in addition, hematin is also formed. It seems that the inter‐ and intramolecular hydrogen bonding interactions within crystalline His limit its ability to form a complex with hemin in a solid state reaction. No complex formation at the iron site was observed with Lys, Met and Trp.