C. Furlani

“Copper chromite” Catalysts: XPS structure elucidation and correlation with catalytic activity

Abstract The oxidation state and composition at the surface of “copper chromite” catalysts at various stages of catalytic use and after reductive pretreatment have been studied by means of X-ray photoelectron spectroscopy (XPS). Catalytic activity for double-bond isomerization and for hydrogenation is found to be correlated with the oxidation state of copper at the surface. The XPS data support the hypothesis proposed previously that Cu(I) is the active species for the isomerization reaction, and Cu(O) for the hydrogenation of conjugated dienes.

XPS of coordination compounds: Data on the electronic structure of a series of Cu(II) N,N′-cyclic substituted dithiocarbamates

Abstract A series of copper(II) dithiocarbomates Cudtc2 with dtc− = S, NH, NCH3, O) has been investigated by XPS. The compounds proved sufficiently stable under X-irradiation; b.e. data confirm substantial identity of the electronic structure of the metal chromophores throughout the series, in which remote ligand effects find evidence in a linear correlation between relative intensity of Cu2p 3 2 satellite peaks and variations of magnetic moments of the Cu(II) species.

Electronic structure and spectra of tetrahalogenoferrates (II)

Abstract The spectrum of the tetrahedral complex [FeCl4]= consists of only one, rather intensive d-d band in the near infrared region which is assigned to the transition 5E → 5T2 (Td), and has γmax ∼ 2.47 μ with log Emol = 1,9. Suitable solvents for spectroscopic absorption measurements in this region are CD3NO2 or ClCH2CN.

Relationship between XPS core binding energies and atomic charge in adducts of SnIV derivatives with pyrazine, and comparison with mössbauer isomer shift data

Abstract Adducts Snhal·pyz (hal = Cl, Br, I; pyz = pyrazine), RnSnCl 4−n ·pyz (n = 1, R = Me, Bu n , Oct n , Ph; n = 2, R = Ph) and SnCl 4 ·(pyz) 2 have been investigated by X-ray photoelectron spectroscopy. Binding energy (b.e.) values are discussed in the light of structural characteristics of the adducts as well as of valence state electronegativities of atoms and groups bound to tin. Sn 3d 5 2 b.e.s, corrected for the Madelung potential at the metal atom, linearly correlate with both partial atomic charges on tin, accounting for relaxation upon ionization, and 119 Sn Mossbauer isomer shifts. The results are interpreted in terms of six-coordinated, octahedral type, configurations of the environment of tin throughout all terms of the homologous series.

New Fe(III) complexes with sulfur and selenium ligands

Abstract FeL3 complexes, where L = dithiobenzoate C6H5-CSS, dithiophenylacetate C6H5-CH2-CSS, or diethyldiselenocarbamate (C2H5)2N-CSe2, are deeply colored nonelectrolyte inner complexes containing pseudooctahedral [Fe(III)S6] or [Fe(III)Se6] chromophores. They all exhibit low-spin magnetic behaviour, with only a small lower-symmetry splitting of the octahedral 2T2g groundstate, contrarily to the doublet-sextet equilibria known of other [Fe(III)S6] chromophores like Fe(III) dithiocarbamates. The low-spin behaviour is produced here by the relatively high ligand-field strength of dithiocarboxylates, respectively by the pronounced nephelauxetic effect of selenium ligands, both effects favoring magnetic crossover to the spin-paired d5 groundstate. Diselenocarbomates dsc forms with iron(III) also a pentacoordinated species Fedsc2Cl, whose existence and properties stress the close similarity between dithio- and diselenocarbamato complexes. Mossbauer spectra of iron(II) dithiocarboxylates exhibit rather large quadrupole splitting of the order of 1·8 mm/ sec.

X-ray photoelectron spectroscopy characterization of hydrated palladium(II) oxide species used in catalysis

Palladium oxide systems, both pure and supported on various substrates such as alumina, zinc oxide, silica and titania, are of interest because of both their semiconducting behaviour and their catalytic activity, and they have been the subject of a number of X-ray photoelectron spectroscopy (XPS) investigations. The XPS technique is used here to investigate properties of various hydrated PdO · nH2O systems prepared both by a single impregnation method on various supports and by various impregnation treatments on the same support. XPS data for supported palladium oxide show that the intensity of interaction with the support is very weak, if indeed it exists. The processes occurring during the impregnation of the supports by the precursors are discussed; the nature of the species obtained depends on the activity of the support.

The force constants of Cr(CN)63− and Cr(CO)6

Abstract The complete vibrational analysis of an octahedral molecule Me(XY)6 is presented, together with its application to the spectra of Cr(CO)6 and of Cr(CN)63−, as a refinement of a previous treatment where each ligand group was regarded as a single point mass. With a potential function of the valence force type, the force constant of the stretching metal-carbon bond is greater for Cr(CO)6 than for Cr(CN)63−. A discussion of the assignment of the vibrational spectra of octahedral complex cyanides shows that, owing to intermixing of the symmetry co-ordinates in the normal modes and to perturbations due to lattice interactions, no simple direct relationship can be expected between the values of the fundamental frequencies and the metal-carbon bond character.

Solid state reactions of RhCl(PPh3)3: an XPS study

Rh(I) complexes frequently used as catalysts reveal from XP spectra systematically the presence of oxidized species on the surface. As a sample system the phenomenon has been studied in greater detail on the Wilkinson compound RhCl(PPh3)3. XPS data are reported and discussed along with hypotheses on the structure of the oxidized species, taking into account peculiar features showing similarities to Rh(III) species. A series of solid state reaction, whose behaviour has been followed by means of XPS, is discussed, including air oxygenation, oxygen removal by H2 under mild conditions, and displacement reactions by strong π-acceptor ligands (CO, C2H4) leading to stable Rh(I) substitution products.

Surface reactions of a plasma-sprayed CaO-P2O5-SiO2-based glass with albumin, fibroblasts and granulocytes studied by XPS, fluorescence and chemiluminescence

X-ray photoelectron spectroscopy (XPS) was used to define the chemical composition of the outermost surface layer and the surface modification of a plasma-coated phospho-silicate glass (identified as BVA) when immersed in K-phosphate buffer or in phosphate buffered human albumin solution. Its behavior was compared with that of a soda-lime-based glass (identified as BVH) treated in the same way. The surface % composition of plasma-sprayed glass was consistent with bulk composition. After incubation with buffer, a Ca-P-rich layer developed only on the surface of BVA glass. Human serum albumin was bound reversibly to both glasses maintaining its native state. However, the protein completely covered the BVA glass surface within 24 h, with the formation of a mixed albumin-Ca-P layer, while 4 days incubation was necessary for complete coverage of BVH glass surface. Murine fibroblasts seeded on plasma-coated BVA glass showed a proliferation pattern similar to that of control cells grown on Petri dish, while cells seeded on BVH had more restricted growth. A limited response was induced in polymorphonuclear granulocytes by both bulk glasses powder. In conclusion, the glass identified as BVA has the suitable characteristics of its surface layers to be considered biologically active from both a chemical and a cellular point of view.

Coordinative bond and d-shell ionisations in the UV photoelectron spectra of bis(β-diketonato) cobalt(II) and copper(II) complexes, and their thioanalogues

Abstract The analysis of UV photoelectron spectra of the title compounds, as well as of their Ni(II) analogues, is presented, with particular regard to the identification of d -ionisation bands. The spectra are assigned on the grounds both of a framework of interpretation similar to that usually applied to β-diketonato metal complexes, and of a systematic comparison between He(I) and He(II) data.