Oxidative Addition of Halogens to Homoleptic Perfluoromethyl or Perfluorophenyl Derivatives of Platinum(II): A Comparative Study

Chlorocarbon solvents (solv=CH₂Cl₂, CHCl₃) are suggested to play an active role in the oxidative addition of halogens, X₂ (X=Cl, Br, I), to homoleptic d⁸ perfluoromethyl and ‐phenyl platinum(II ) species [Pt(R^F)₄]^2? (R^F=CF₃, C₆F₅). The perfluoromethyl group, CF₃, has been found to be considerably less prone to undergo reductive elimination processes, and is, therefore, more suitable for stabilizing organoplatinum(IV ) derivatives (see scheme).

     

Photoionization of highly charged ions using an ECR ion source and undulator radiation

Photoionization of Xe4+ to Xe7+ ions was studied by combining an electron cyclotron resonance ion source with synchrotron radiation. Multiconfiguration Dirac-Fock calculations were performed to interpret the data. Many autoionization lines were measured and identified, resulting from excitation of a 4d electron into nf and np orbitals followed by Auger decay of the excited states. Continuum photoionization is negligible for the higher members of the isonuclear series.     

Four-coordinated palladium(II) and platinum(II) complexes containing the Lewis-acid {M(S2CNHR)(PR3′)} group combined with a variety of other ligands

A new series of four-coordinated Pd(II) and Pt(II) complexes in which the Lewis-acid (14-electron) {M(S₂CNHR)(PR₃′)} group is combined with a variety of other ligands (such as RHNCS₂^?, I^?, SCN^?, SnCl₂I^?) has been synthesised and studied. The structures of the new compounds are discussed in relation to their specroscopic, magnetic and thermal properties. In the case of [M(S₂CNHR)₂(PR₃′)] complexes both the spectroscopic data (IR, ¹H NMR, UV-Vis) and their thermal behaviour strongly suggest the coexistence of two kinds of gem-disulphide ligands, one acting as a bidentate ligand and the other one as a unidentate. Also it was confirmed that the chemical behaviour of the bis(N-alkyldithiocarbamato) complexes of Pd(II) and Pt(II) towards tertiary phosphines is similar to that of the isoelectronic xanthate complexes rathe than to the bis(N,N-dialkyldithiocarbamato) complexes.     

High-temperature transport and electrochemical properties of YBaCo4O7+δ

The total conductivity of oxygen-hyperstoichiometric YBaCo₄O₇₊ is predominantly p-type electronic at oxygen partial pressures from 5×10⁴ Pa down to the phase decomposition limit, 10^–11–10^–4 Pa at 973–1223 K. The ion transference numbers, determined by the oxygen permeation and faradaic efficiency measurements at 1073–1223 K, vary in the range 3×10^–5–2×10^–4 and increase with temperature. The oxygen permeability of YBaCo₄O₇₊ ceramics, with overall level similar to that of K₂NiF₄-type cuprates, is mainly limited by the bulk ionic conduction. Heating above 1050–1100 K and redox processes under oxidizing conditions lead to a first-order transition accompanied with extensive oxygen losses from the lattice, resulting in decreasing total oxygen content from 8.5 down to approximately seven atoms per unit formula. Except for the variations associated with this transition, the electron–hole conductivity and Seebeck coefficient are essentially p(O₂)-independent within the phase stability limits. The use of different synthesis methods, namely the standard ceramic technique and the glycine–nitrate process, has no significant effect on the properties of YBaCo₄O₇₊ ceramics. The thermal expansion coefficients averaged at 600–1100 K in air are (7.3–7.6)×10^–6 K^–1. Porous YBaCo₄O₇-based cathodes show a very high electrochemical activity in contact with LaGaO₃-based solid electrolyte at 873–1073 K.     

Stability and oxygen ionic conductivity of zircon-type Ce1−xAxVO4+δ (A=Ca, Sr)

Zircon-type Ce_1−xA_xVO_4+δ (A=Ca, Sr; x=0-0.2) are stable in air up to approximately 1300 K, whilst further heating or reducing oxygen partial pressure leads to formation of A-site deficient zircon and CeO_2−δ phases. The stability boundaries of Ce_1−xA_xVO_4+δ are comparable to those of vanadium dioxide and calcium orthovanadate. At oxygen pressures lower than 10⁻¹⁵ atm, perovskite-type CeVO_3−δ is formed. The oxygen ion transference numbers of Ce_1−xA_xVO_4+δ, determined by faradaic efficiency measurements in air, vary in the range from 2×10⁻⁴ to 6×10⁻³ at 973-1223 K, increasing with temperature. The oxygen ionic conductivity has activation energy of 87-112 kJ/mol and is essentially independent of A-site dopant content. Contrary to the ionic transport, p-type electronic conductivity and Seebeck coefficient of Ce_1−xA_xVO_4+δ are influenced by the divalent cation concentration. The average thermal expansion coefficients of Ce_1−xA_xVO_4+δ, calculated from high-temperature XRD and dilatometric data in air, are (4.7-6.1)×10⁻⁶ K⁻¹.     

Characterisation of zeolitic materials with a HEU-type structure modified by transition metal elements: definition of acid sites in nickel-loaded crystals in the light of experimental and quantum-chemical results

Nickel-loaded HEU-type zeolite crystals have been obtained by well-known synthetic procedures and characterised by X-ray fluorescence (XRF), scanning-electron microscopy/ energy-dispersive spectroscopy (SEM-EDS), FT-IR, diffuse reflectance UV/ Vis spectroscopy (DR(UV/Vis)S) and X-ray photoelectron spectroscopy (XPS) measurements as non-homoionic and non-stoichiometric substances containing exchangeable hydrated Ni2+ ions in the micropores and nickel hydroxide phases supported on the surface. Thermogravimetric analysis/differential gravimetry (TGA/DTG) and differential thermal analysis (DTA) demonstrated that full dehydration below approximately 400 degrees C follows a clearly endothermic process, whereas at higher temperatures the zeolite is amorphised and finally partially recrystallised to Ni(Al,Si) oxides, detected by powder X-ray powder diffraction (XRD). The solid acidity of NiHEU, initially determined by temperature-programmed desorption (TPD) of ammonia to be 8.93 mgg(-1) NH3, is attributed to the weak acid sites (fundamentally Lewis sites) resolved at approximately 183 degrees C, and to the strong acid sites (essentially Br?nsted sites) resolved at approximately 461 degrees C in the TPD pattern. A more sophisticated study based on in situ/ex situ FT-IR with in situ/ex situ 27Al MAS NMR and pyridine (Py) as a probe molecule, revealed that the Lewis acid sites can be attributed primarily to Ni2+ ions, whereas the Br?nsted ones can probably be associated with the surface-supported nickel hydroxide phases. The spectroscopic measurements in conjunction with powder XRD and 29Si MAS NMR data strongly suggest that distorted Al tetrahedra are formed during the dehydration process and Py chemisorption/complexation (NiHEU-Py), whereas the crystal structure is remarkably well preserved in the rehydrated material (NiHEU-Py/R). The structural, electronic, energetic and spectroscopic properties of all possible nickel(II) aqua and dihydroxy complexes absorbed in the zeolite micropores or supported on the zeolite surface were studied theoretically by density functional theory (DFT). The computed proton affinity, found to be in the range 182.0-210.0 kcalmol(-1), increases with increasing coordination number of the aqua and dihydroxy nickel(II) complexes.     

Transport and Electrochemical Properties of SrFe(Al,Mo)O<Subscript>3–δ</Subscript>

In this work, effects of molybdenum doping on the crystal structure, stability, electrical conductivity, oxygen permeability and thermomechanical properties of Sr(Fe,Al)O_3–δ-based perovskites, were studied. The electrochemical performance of model anodes of solid oxide fuel cells (SOFCs), made of SrFe_0.7Mo_0.3O_3–δ, was assessed. Whilst the introduction of Mo cations improves structural stability with respect to the oxygen vacancy ordering processes, excessive molybdenum content leads to a worse phase and mechanical stability under oxidizing conditions. Mo-doping was shown to decrease the thermal and chemical expansivity, to reduce p-type electronic conductivity and to increase n-type electronic conduction. The oxygen permeation fluxes through gas-tight Sr_0.97Fe_0.75Al_0.2Mo_0.05O_3–δ membranes are determined by both the bulk oxygen diffusion and surface exchange kinetics. The role of the latter factor increases on decreasing temperature and reducing oxygen partial pressure. Due to a relatively high electrical conductivity and moderate thermal expansion coefficients in reducing conditions, SrFe_0.7Mo_0.3O_3–δ-based anodes show a substantially high electrochemical activity.