Sulfur valence states

Metal oxides, sulfides, and hydrides form a transition between acid/base and metal catalysts. They catalyze hydrogenation/dehydro-genation as well as many of the reactions catalyzed by acids, such as cracking and isomerization. Their oxidation activity is related to the possibility of two valence states which allow oxygen to be released and reabsorbed alternately. Common examples are oxides of cobalt, iron, zinc, and chromium and hydrides of precious metals that can release hydrogen readily. Sulfide catalysts are more resistant than metals to the formation of coke deposits and to poisoning by sulfur compounds their main application is in hydrodesulfurization. 

The interatomic distances found are V—S = 2.186 0.040 A and Cu—S — 2.285 i 0.014 A. The Cu—S distance is somewhat smaller than the sum of the tetrahedral radii2) for sulfur and univalent copper, 2.39 A. As in the case of chalcopyrite, this probably indicates that the valence states are not well defined as CuIiVvSi, but fluctuate, the copper resonating between cuprous and cupric states and the vanadium between quinquivalent and lower states. 

The induced co-deposition concept has been successfully exemplified in the formation of metal selenides and tellurides (sulfur has a different behavior) by a chalcogen ion diffusion-limited process, carried out typically in acidic aqueous solutions of oxochalcogenide species containing quadrivalent selenium or tellurium and metal salts with the metal normally in its highest valence state. This is rather the earliest and most studied method for electrodeposition of compound semiconductors [1]. For MX deposition, a simple (4H-2)e reduction process may be considered to describe the overall reaction at the cathode, as for example in... 

The above relationships between the thiiranes (20) and their dioxides (17) are reminiscent of those between cyclopropane and cyclopropanone. The entire phenomena of the C—C bond lengthening and the concomitant C—S bond shortening in the three-membered ring sulfones and sulfoxides can be accounted for in terms of the sulfur 3d-orbital participation and the variation in the donor-acceptor capacities of the S, SO and S02 . The variations of the calculated valence-state orbital energies, together with the corresponding variations of the C—C overlap populations, can be used to understand the discontinuous variations of the C—C and the C—S bond lengths in the series thiiranes -... 

Ni3Sn2S2 Valence states of nickel, tin, and sulfur in the ternary chalcogenide, and " Sn Mossbauer investigations, XPS and band structure calculations... 

There are many sulfur components in meteorites which may occur in all possible valence states (—2 to +6). TroUite is the most abundant sulfur compound of iron meteorites and has a relatively constant S-isotope composition (recall... 

The monazite sand is heated with sulfuric acid at about 120 to 170°C. An exothermic reaction ensues raising the temperature to above 200°C. Samarium and other rare earths are converted to their water-soluble sulfates. The residue is extracted with water and the solution is treated with sodium pyrophosphate to precipitate thorium. After removing thorium, the solution is treated with sodium sulfate to precipitate rare earths as their double sulfates, that is, rare earth sulfates-sodium sulfate. The double sulfates are heated with sodium hydroxide to convert them into rare earth hydroxides. The hydroxides are treated with hydrochloric or nitric acid to solubihze all rare earths except cerium. The insoluble cerium(IV) hydroxide is filtered. Lanthanum and other rare earths are then separated by fractional crystallization after converting them to double salts with ammonium or magnesium nitrate. The samarium—europium fraction is converted to acetates and reduced with sodium amalgam to low valence states. The reduced metals are extracted with dilute acid. As mentioned above, this fractional crystallization process is very tedious, time-consuming, and currently rare earths are separated by relatively easier methods based on ion exchange and solvent extraction. 

Tellurium burns in air with a greenish-blue flame. The combustion product is dioxide, Te02, the most stable oxide of the metal. Tellurium also forms other oxides the monoxide, TeO, the trioxide, TeOs, and the pentoxide, Te205. Monoxide has not yet been obtained in solid form. Like sulfur and selenium, tellurium forms oxyacids. Such oxyacids include orthotelluric acid, HeTeOe and tellurous acid, H2Te03, in which the metal is in +6 and +4 valence states respectively. 

The metal is attacked by mineral acids. Reactions with sulfuric and hydrochloric acids produce hydrogen. With nitric acid, no hydrogen is evolved but the pentavalent nitrogen is reduced to nitrogen at lower valence states. 

Since most base irons have sulfur levels higher than 0.01% sulfur, a desulfurization step that drives the sulfur level to about 0.01% is desirable. The rare earth elements could be used to desulfurize the iron. However, because of the valence state of the rare earths and their high mass weights, a considerable... 

Sulfur is oxidatively fluorinated up to its highest valence state, six. For instance, alkyl thiols give perfluoroalkyl-sulfurpentafluorides (Fig. 40) [104] and sulfides give perfluorodialkyl-sulfurtetrafluorides (Fig. 41) [105,106]. Similarly, phosphorous is oxidatively fluorinated up to the pentavalent state (Fig. 42) [107]. 

Polar structures must be used for compounds containing an atom in a higher valence state, such as sulfur or phosphorus. Thus, if we treat sulfur in dimethyl sulfoxide (DMSO) formally as a divalent atom, the... 

The most common valence states of arsenic are —3, 0, +3, and +5 (Shih, 2005), 86. The —3 valence state forms through the addition of three more electrons to fill the 4p orbital. In the most common form of elemental arsenic (As(0)), which is the rhombohedral or gray form, each arsenic atom equally shares its 4p valence electrons with three neighboring arsenic atoms in a trigonal pyramid structure ((Klein, 2002), 336-337 Figure 2.1). The rhombohedral structure produces two sets of distances between closest arsenic atoms, which are 2.51 and 3.15 A (Baur and Onishi, 1978), 33-A-2. The +3 valence state results when the three electrons in the 4p orbital become more attracted to bonded nonmetals, which under natural conditions are usually sulfur or oxygen. When the electrons in both the 4s and 4p orbitals tend to be associated more with bonded nonmetals (such as oxygen or sulfur), the arsenic atom has a +5 valence state. 

Like sulfide in pyrite, arsenic in arsenic-rich (arsenian) pyrite (FeS2) and many arsenide and arseno-sulflde minerals has a valence state of — 1 or 0. These valence states result from arsenic forming covalent bonds with other arsenic atoms or sulfur (Klein, 2002), 340, 369 (Foster, 2003), 35 (O Day, 2006), 80. In the arsenide niccolite (also called nickeline, NiAs), every nickel atom is surrounded by six arsenic atoms, where arsenic has a valence state of —1 and nickel is +1 (Klein, 2002), 360 (Foster, 2003), 35. The... 

Biomass may also sorb As(III) from water. Teixeira and Ciminelli (2005) removed considerable As(III) with ground chicken feathers treated with ammonium thioglycolate. X-ray absorption near edge structure (XANES) spectra indicate that the adsorbed arsenic is still in the +3 valence state and that each atom is bound to three sulfur atoms associated with reduced cysteine amino acids (HC>2CCH(NH2)CH2SH) in the feathers. At pH 5 and biomass dosages of 2.0gL 1, the sorption capacity of the material was as high as 0.265 mmol As(III) g-1 biomass (19.9 mg As(III) g-1 biomass Table 7.2). The presence of 0.01 mol L-1 of phosphate had only minor effects on the sorption capacity, which was 0.260 mmol As(III) g 1 biomass (19.5 mg As(III) g-1 biomass) (Teixeira and Ciminelli, 2005, 898). 

The cyano- complex of univalent gold, Au(CN), has been mentioned in connection with recovery of the metal. Other stable derivatives of this valence state are complexes with gold-to-sulfur, gold-to-arsenic, and gold-to-phosphorus bonds. The structures pictured below may be regarded as representative ... 

It should be noted that the common form of telluric acid, HcTeO , is not analogous to sulfuric and selenic acids but is more fully hydrated. The series of oxy-acids derived from the maximum valence state of the members of group VIb is thus formally similar to that derived from group Vb (H3PO4, H3ASO4, Sb(OH) ). 

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