Richard Kellerman

Spectra of synthetic zeolites containing transition metal ions. V.* Π complexes of olefins and acetylene with Co(II)A molecular sieve

The electronic spectra of the cobalt(II) ion in anhydrous cobalt(II) zeolite A in the presence of adsorbed unsaturated hydrocarbons demonstrate that olefins and acetylene are π bonded to cobalt in well defined surface complexes. Gravimetric adsorption data show that one ethylene molecule is bound by each cobalt ion with an energy of about −68 kJ mol−1. Theoretical analysis treating the unsaturated hydrocarbon as a low symmetry electrostatic perturbation to a tetrahedral Co(II) ion gives a quantitative interpretation of the band splitting in the electronic spectra. This splitting is distinguished from that occurring through the dynamic Jahn‐Teller effect in purely tetrahedral Co(II) complexes. The low symmetry field contributions to the ligand field stabilization energies have been determined from the fine structure in the experimental spectra and have been found to decrease from ethylene to trans‐2‐butene in accord with increasing steric hindrance from substitutional methyl groups. These contributions are...

Esr studies on the role of ammonia in promoting radical species in precipitated titanium dioxide

Abstract A reinvestigation of the esr spectra of ammonia precipitated, oxygen dried, TiO2 powders has revealed that at least two of the triplets observed and previously assigned to some form of adsorbed oxygen (O2+), are caused by species resulting from the photochemical or thermal oxidation of traces of ammonia firmly held by the material. Confirmation for this view is provided in esr studies on relatively pure TiO2 following (1) contamination with 14NH3 and 15NH3 prior to drying in oxygen and (2) adsorption of oxides of nitrogen (14NO, 15NO2, 14NO2, and 15NO2). The nature of the species responsible for the triplets is discussed. TiO2 powders have been examined in the esr following γ-irradiation at liquid N2 temperature. Unlike silica, the powders showed no hyperfine structure due to H atoms produced from surface OH groups.

Water sorption in a dextran gel

The state of adsorbed water in a dextran gel has been investigated by near-infrared gravimetric-adsoprtion techniques. Water-vapor adsorption (desorption) isotherms at three temperatures are reported. The calculated sorption heats are found to be markedly temperature-dependent as well as dependent on the coverage. The near-infrared spectrum (4650-9000 cm-minus 1) is reported, together with tentative assignments. The H2O combination (v+delta) band at 5184 cm-minus 1 has been examined as a function of relative humidity. The line-shapes of this band have been analyzed by a recently established, Fourier-inversion technique, and information on the microdynamics of the absorbed water molecules has been resolved on the picosecond time-scale. At low and intermediate degrees of hydration, reorientational jumps take place with periods from four to six times longer than those for free water. The onset of saturation is then accompanied by the sudden removal of the reorientational jumps. A comparison of microdynamical and thermodynamic data indicates the hydration mechanism to be highly cooperative at all relative humidities.

The initial stages of oxidation of thin iron films as studied by ferromagnetic resonance

A series of polycrystalline iron films (1 < t < 100 nm) was prepared and examined under ultrahigh vacuum conditions. The effect of oxygen on the ferromagnetic resonance response was investigated, and a thickness-dependent, transient increase in the perpendicular mode resonance field was attributed to the formation of Fem+ cations in a reconstructed surface layer. A subsequent decrease in the resonance field was consistent with the loss of ∼1.5 nm of ferromagnetic iron at large oxygen exposures. Information on the structure of the films was obtained from transmission electron microscopy of ultrahigh vacuum deposited films coated in situ with silicon monoxide.

Dynamic effects associated with transition metal ions in zeolites

Abstract Interpretation of the temperature dependence of the magnetic moment of bare surface Cr(II) ions in Type A zeolite is given based on a model of thermally activated jumps between sites in which the orbital contribution to the magnetic moment is quenched and the trigonally coordinated sites has large orbital contributions within the Cr(II) ground state 5 E′. This behavior contrasts with the temperature independent spin-only magnetic moment of the Cr(IV)-monooxygen complex which indicates a non-degenerate ground state 3 A 2 of the Cr(IV) ion tetrahedrally coordinated by its monooxygen ligand and three framework oxygens. The fine structure of optical transitions of tetrahedrally coordinated Co (II) ions is shown to be accounted for by a semiclassical analysis of the dynamic Jahn-Teller effect associated with the 4 A 2 → 4 T 1 transitions. This interpretation is applicable to Co(II)-H 2 O-framework complexes and Co(II)-OH-framework complexes in Type A, X and Y zeolites.