Abstract: : The mapping of the energy levels in metallophthalocyanines is accomplished by a combination of electrochemistry, electronic spectroscopy, and photochemistry. This chapter reviews the electrochemical properties of metallopthalocyanines and includes a large amount of previously unpublished data. The results are rationalized in terms of the nature of the electron transfer, that is, redox at metal or ligand. Well-defined correlations are shown to exist between the ease of oxidation or reduction of the phthalocyanine ligand and the oxidation state, and/or polarizing power, of the metal ion. Solvent and ring substitution effects also are presented and explained. Charge transfer transition energies can be calculated directly from these data, and agreement between experiment and theory is excellent. Finally, the data are used to calculate both the photo-generated excited state redox energies and the thermodynamics of quenching by donors and acceptors. (Author)

Abstract: We discuss the structural aspects of crystals that contain molecular stacks and are comprised of two components, at least one of which is a planar transition-metal chelate complex. One of the components may be viewed as an electron donor, D, or its cation, D+p, the other an acceptor, A, or its anion, A−q. In these crystals either one or both components tend to form stacks, and we employ a classification scheme whose first major division is structural: crystals either contain stacks that integrate the D and A units, or the D and A units can be segregated with D or A stacking, or both. The second major division is physical. In an integrated stack crystal the metal-ligand complex is either neutral or ionic; in a segregated stack crystal it either has an integral oxidation state or a non-integral oxidation state. The non-integral oxidation state is sometimes referred to as “partial oxidation”, “mixed valence”, or “incomplete charge transfer”.

Abstract: Core and valence X-ray photoelectron spectra of 18 uranium halides (U/sup 3 +/ to U/sup 5 +/) and oxyhalides (U/sup 3 +/ to U/sup 6 +/) (fluorides, chlorides, and bromides) are described. The results are discussed, as a function of halogen nature and compounds stoichiometry, in terms of ionicity of the bonds, of U 5f participation in bonding, and effect of oxygen. Evidence is produced that UF/sub 3/ has an unexpectedly strong covalent character. The experimental study of uranium halides (F, Cl, Br) and oxyhalides has brought to light some important information about the nature of chemical bonding in these compounds: (a) The combined examination of valence photoelectron peaks (particularly U 5f), core levels, and U 4f shake-up satellites is a powerful tool in the determination of the ionicity of the solid. Only core level chemical shifts are not sufficient by themselves. (b) There is evidence for U 5f participation in chemical bonding; this contribution increases when the compound becomes more covalent. (c) Ionicity is largest for the higher halides (higher uranium oxidation state) and with the more electronegative halogens; and exception to this rule is UF/sub 3/, which is more covalent than UCl/sub 3/. (d) The oxygen in oxyhalidesmore » shows a growing tendency to form uranyl groups, as the uranium oxidation state goes up. These uranyl groups have covalent bonding and behave as a single species vs. the halogen.« less

Abstract: A wide range of modern physical and chemical techniques can be used to evaluate the properties of gold compounds. These allow the identification of the design features which control their pharmacological activity: the oxidation state (formal charge) on the gold atom, number and types of atoms bonded to gold (coordinated ligands), the stereochemical arrangement of ligands around gold (coordination geometry), and specific targeting groups in the ligands. The polymeric, hydrophilic, gold thiolate compounds are contrasted with the monomeric, lipophilic triethylphosphine gold compound auranofin (AF). The dynamic ligand exchange reactions of the 2 classes of drugs differ markedly; however other reactions are possible, and may lead to some common intermediates in vivo. This conclusion is based on preliminary results using nuclear magnetic resonance spectroscopy, a technique which allows us to monitor reactions in intact cells.

Abstract: EXAFS fluorescence spectra were recorded for high-potential c-type cytochromes which range in oxidation-reduction potential from +145 to +365 mV. No average Fe-ligand bond length differences greater than 0.03 A were observed, for any cytochrome source of oxidation state. Least-squares analysis in combination with model calculations allowed limits to be set on the average Fe-N bond length (1.97-1.99 A) and the Fe-S bond length (2.29-2.32 A). A change of 0.05 A in either the average Fe-N or the Fe-S bond length is readily detectable with the range and quality of the data presented here. Two major conclusions are drawn from this study: In octahedrally coordinated iron porphyrin systems, Fe-N and Fe-S bond lengths are independent of oxidation-reduction potential, and they are also independent of oxidation state. A model for the regulation of oxidation-reduction potential in cytochrome c is proposed.

Abstract: The oxidation state of a glass melt is governed by the interdependence of the oxygen partial pressure of the furnace atmosphere, the basicity of the melt, and the concentration and type of polyvalent species present in the melt. The overall result of this interdependence is reflected in the oxygen activity of the glass melt. However, in the past the oxidation states of glass melts were not characterized by the activity, but instead by exploiting the ratio of valence states of a redox pair as an indicator. Such an indirect method is based on the assumption that the ratio of valence states at glass melt temperatures is preserved in quenched samples. Moreover, the relationship between the oxidation state and valence state ratio seems to fail completely when more than one redox pair is present, leading to ratios of valence states which become independent of oxygen partial pressure in non-equilibrated melts and thus are no longer indicative of the oxygen activity of the glass melt. Therefore, the possibility of directly determining the oxygen activity in glass melts is highly desirable. Such an in situ measurement has become feasible by utilizing a newly developed oxygen sensor based on a zirconia solid electrolyte. Data on the behavior of soda-lime-silica glass melts will be given, demonstrating the usefulness of the sensor in characterizing glass melts with respect to their oxidation state. In particular the action of additions of arsenic, sodium sulfate and carbon on the oxygen activity will be discussed.

Abstract: The previously reported inhibition of the oligomerization of HCN by montmorillonite clays was investigated. The inhibition is due to the oxidation of diaminomaleonitrile (DAMN) by the Fe3+ in the clay lattice. Fe2+ and oxalic acid were shown to be the reaction products. From these reaction products and the previous report that two equivalents of HCN are formed per equivalent ofDAMN, it was established that diiminosuccinonitrile (DISN) is the initial reaction product, which is rapidly hydrolyzed to oxalic acid and HCN. The same oxidative transformations are effected by Fe3+ bound to Dowex 50, Fe3+ in solution and Ni(NH3)62+. The rate of reaction of DAMN decreased in the order Fe3+ > Fe3+-Dowex > montmorillonite, indicating no catalytic role for the clay in the oxidation of DAMN. Little reaction of DAMN was observed with montmorillonite in which the bulk of the iron was in the Fe2+ oxidation state. The possible significance of these redox reactions to chemical evolution is discussed.

Abstract: Hydrogen peroxide is produced by oxidation of a coordination complex of a metal ion capable of existing in at least two oxidation states and a ligand, the coordination complex being sufficiently stable for the metal ion to be oxidized and reduced without decomposition of the complex and the metal ion being in its lower oxidation state. In a cyclic process, the step of reduction of the complex with the metal ion in its higher oxidation state precedes the oxidation step, and the reduction and oxidation steps are repeated sequentially. Novel coordination complexes which may be used in the process have the formula: ##STR1## in which n represents an integer; M represents a cobalt ion or other metal ion having at least two oxidation states; x and y, which may be the same or different, each represent .tbd.N, .tbd.P or .tbd.C--R', in which R' represents a hydrogen or halogen atom, or a hydroxyl, nitro, nitroso, amino, alkyl, or cyano group, or a group of the formula --COOR", --COCOOR" or --NH--COCH--CHCOOR" in which R" is a hydrogen atom or alkyl group; provided that when M represents a cobalt ion and n is 2, x and y do not both represent .tbd.N.

Abstract: Metal (Cr3+, Fe3+, Cu2+, Ni2+, Co2+, Vo2+, Mn2+, Zn2+, Hg2+, Tl+ complexes of 4-aminophenazone dithiocarbamate (4-Apdtc) have been prepared in aqueous alcoholic medium from stoichiometric amounts of the metal salt and 4-aminophenazone dithiocarbamic acid generated in situ. The complexes have been characterised on the basis of elemental analyses, molecular weights, magnetic moments, electronic and infrared spectra and thermogravimetric studies. Infrared studies suggest that 4-Apdtc acts as a bidentate ligand. The general composition of the complexes can be given as M(4-Apdtc)n (where n=oxidation state of metal).

Abstract: Reaction of MnO(OH) and a concentrated solution of AHF2 (A = NH4 +, Na+, K+ or Cs+) in 40% hydrofluoric acid gives instantaneously rose-pink coloured alkali metal pentafluoromanganate(III), A2MnF5 (A = NH4 + or Na+), and alkali metal pentafluoromanganate(III) monohydrate, A2MnF5.H2O (A = K+ or Cs+). Li2MnF5 has been synthesised by reacting lithium carbonate with a solution of MnO (OH) in 40% hydrofluoric acid followed by addition of a small amount of alcohol. Characterisation of the compounds and assignment of molecular structure were made from the elemental analyses, chemical determination of oxidation state of manganese in the compounds, magnetic susceptibility measurements and infra red spectral studies.

Abstract: Titanium dioxide samples containing a few per cent of rhodium oxide, heated in air at 1273 K, have been investigated in order to study the formation of solid solutions. The results, monitored by X-ray diffraction, thermogravimetry in a hydrogen stream and ESR spectroscopy, show that rhodium is present both as separate phase (Rh2O3) and in solid solution in the rutile structure. The incorporated rhodium is mainly present in the 3 + oxidation state, only a small fraction being present as Rh(II). Rh2O3 and the rhodium species in solid solution are reduced by hydrogen to metal in different temperature ranges. By combining thermogravimetric and analytical data, the average oxidation state of rhodium,n, has been evaluated. The variation ofn with the rhodium content has been accounted for on the basis of a strong metal-support interaction developing with the reduction. This interaction affects the metal dispersion.

Abstract: examples of this behavior have been reported in transitionmetal chemistry in which s u b s t i t ~ t i o n ~ ~ or isomerizationm at a transition-metal center occurs with no net current flow in an electrochemical experiment. In the present case, reduction requires two electrons and reoxidation provides one; thus, a net one-electron reduction from Mo(V) to Mo(1V) is observed. This combination of redox and coordination chemistry provides a link between the redox chemistries of higher oxidation state oxomolybdenum species and lower oxidation state nonoxo species. The structural change associated with this reaction

Abstract: The effect of the oxidation state of iron in sodium borosilicate glasses on the immiscibility temperature and magnetic characteristics was investigated. The oxidation state was varied by changing the melting conditions and the raw materials and was determined by chemical analysis. The immiscibility temperatures of these glasses, determined by an opalescence method, showed a minimum at an intermediate oxidation state. A similar tendency has already been observed in glasses containing molybdenum oxide. Magnetic susceptibility measured at 4.2 K and the electron spin resonance signal of Fe 3+ ( g ≅4.28) observed at room temperature displayed maximum intensities for the composition where the minimum in the immiscibility temperature was observed. These results are explained in terms of the aniferromagnetic pairing of iron ions.

Abstract: The extended x-ray absorption fine structure (EXAFS) technique is discussed with relevance to the determination of details of the local structural environment of the copper active sites of beef heart mitochondrial cytochrome c oxidase. By studying the copper x-ray absorption edges and EXAFS of the resting state, fully reduced, and mixed valence-formate derivatives of the enzyme, most if not all of the oxidation state-sensitive sulfur ligands can be assigned to CuA, the epr-detectable copper. No evidence can be found for radiation induced oxidation state changes in these samples at -60 C under the flux conditions of these experiments.