Metal sulfides bonding

Some Aspects of the Nature of the Metal Sulfide Bond 523... 

Eyring and Wadsworth (50) and Little (51) present spectroscopic evidence that thiols bond to ZnO surfaces and xanthates bond to PbS surfaces by way of hydroxyl-exchange reactions in which metal-sulfide bonds are formed, and metal-hydroxyl bonds are broken during adsorption. We expect that trends exhibited in the relative stabilities of amino acid and hydroxo complexes of various dissolved cations should parallel trends in the relative reactivities and adsorption free energies, should this type of bonding control adsorption. 

Stmcture (1) explains the formation of sulfur and sulfite in the presence of acid stmcture (2) is consistent with the formation of sulfide and sulfate in the presence of heavy metals. The bonding in thiosulfate complexes and the chemistry of thiosulfates are normally explained on the basis of (2) (see also... 

D. J. Vaughan and J. R. Craig, Mineral Chemistry of Metal Sulfides, Cambridge University Press, Cambridge, 1978, 493 pp. A comprehensive account of the structure bonding and properties of mineral sulfides. 

A transargononic structure for sulfur, with six bonds formed by sp3d2 hybrid orbitals, was suggested for sulfur in the octahedral molecule SF6 long ago, and also for one of the sulfur atoms, with ligancy 6, in binnite (Pauling and Neuman, 1934). Some transargononic structures of metal sulfides have been proposed recently by Franzen (1966). 

Palladium dimethylsilanedithiolato complex is a precursor for Ti—Pd and Ti—Pd2 heterometal-lic complexes.311 The bis-silyl sulfides (R3Si)2S have been widely used to prepare a variety of metal sulfide clusters, because these reagents exploit the strength of the Si—O and Si—Cl bond to... 

Polysulfides of several metals can be prepared by reaction of the metals with excess sulfur in liquid NH3 (group IA metals) or by heating sulfur with the molten metal sulfide. The polysulfide ion binds to metals to form coordination compounds in which it is attached to the metal by both sulfur atoms (as a so-called bidentate ligand). One example is an unusual titanium complex containing the S52-ion that is produced by the following reaction (the use of h to denote the bonding mode of the cyclo-pentadienyl ion is explained in Chapter 16) ... 

Lack of reactivity in copper sulfide cluster anions has been associated with structural features such as linear S-Cu-S bonding. Reactivity of metal sulfide cluster anions is associated with exposed under-coordinated metal atoms able to bond to coordinating molecules this is the essence of this chapter. 

A catalytic example of C-S bond breakage in benzothiophene has been reported by Bianchini [47], A catalytic desulfurisation was not yet achieved at the time as this is thermodynamically not feasible at such mild temperatures because of the relative stability of metal sulfides formed. Bianchini used a water-soluble catalyst in a two-phase system of heptane-methanol/water mixtures in which the product 2-ethylthiophenol is extracted into the basic aqueous layer containing NaOH. Figure 2.43 gives the reaction scheme and the catalyst. The 16-electron species Na(sulfos)RhH is suggested to be the catalyst. Note that a hydrodesulfurisation has not yet been achieved in this reaction because a thiol is the product. Under more forcing conditions the formation of H2S has been observed for various systems. 

Density accumulation is also evident between the nitrogen atoms and the transition metal atom, quite close to the former. This accumulation represents the ligand participation in the metal-ligand tr-bonding orbitals, and is as observed in the charge density maps of the metal sulfides. 

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Other metal complexes such as 2,2 -bipyridine complexes of Rh and Ir are efficient electrocatalysts for the reduction of C02 in acetonitrile.134 In the production of formate the current efficiency is up to 80%. Electrochemical reduction catalyzed by mono- and dinuclear Rh complexes affords formic acid in aqueous acetonitrile, or oxalate in the absence of water.135 The latter reaction, that is, the reduction of C02 directed toward C-C bond formation, has attracted great interest.131 An exceptional example136 is the use of metal-sulfide clusters of Ir and Co to catalyze selectively the electrochemical reduction of C02 to oxalate without the accompanying disproportionation to CO and CO2-. 

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