Clusters sulfide

Hydrodesulfurization of Benzothiophene Catalyzed by Molybdenum Sulfide Cluster Encapsulated into Zeolites... 

A cationic molybdenum sulfide cluster [Mo3S4(H20)9] " with incomplete cubane-type structure and a cationic nickel-molybdenum mixed sulfide cluster [Mo3NiS4Cl(H20)9p " with complete cubane-type structure were introduced into zeolites NaY, HUSY and KL by ion exchange. Stoichiometry of the ion exchange was well established by elemental analyses. The UV-visible spectra and EXAFS analysis data exhibited that the structure of the molybdenum cluster remained virtually intact after ion exchange. MoNi/NaY catalyst prepared using the molybdenum-nickel sulfide cluster was found to be active and selective for benzothiophene hydrodesulfurization. 

In the present study, we synthesized in zeolite cavities Co-Mo binary sulfide clusters by using Co and Mo carbonyls and characterized the clusters by extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and high resolution electron microscopy (HREM). The mechanism of catalytic synergy generation in HDS is discussed. 

It was shown by EXAFS that the structure and dispersion of the Mo sulfide species in MoSx/NaY were unaltered by a prolonged sulfidation of 20-h at 673 Kina stream of H,S/Hj. This fact indicates that highly dispersed Mo sulfide species are thermally stable. On the other hand, with MoSx/AljOj prepared by using Mo(CO) [12], a considerable agglomeration of highly dispersed Mo sulfide species was observed at a shorter treatment time. It is considered that highly dispersed Mo sulfide clusters are thermally stabilized in zeolite cavities. 

Taking into consideration the preparation procedures, the Mo content of 2.1Mo/SC, and the Co/Mo atomic ratio of ca. unity at the maximum HDS activity, highly dispersed Co-Mo binary sulfide clusters, possibly COjMOjSx, in the supercage of the NaY zeolite are suggested for catalytically active species. The HDS activity of the CoSx-MoSx/NaY was not changed even after a 20-h treatment at 673 K in a stream of HjS/H (Fig.3), demonstrating a high thermal stability of the active species. 

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... 

Swayambunathan V, Hayes D, Schmidt KH, Liao YX, Meisel D (1990) Thiol surface complexation on growing cadmium sulfide clusters. J Am Chem Soc 112 3831-3837... 

Metal oxide and sulfide clusters form the bulk of the reactivity studies of binary cluster anions. 

In a series of papers, metal sulfide cluster anions of first-row transition metals, principally copper, have been reacted with a variety of reagents including thiols, sulfur, phosphorus, and phosphines (99, 145, 256, 257). 

The P4 molecule also reacts with the copper sulfide cluster anions generally giving products involving addition of P2 and in some cases the addition of a further P2 unit (257). Only Cu6S4 was unreactive toward P4 and even [Cu3S3p reacted, albeit slowly, to produce the P2 adduct. The CID studies of Cu2S2P2 (XIV) yielded P2S, and [Cu2S3P2p XV yielded P2S and PS2, consistent with calculated structures that showed insertion of P2 into the Cu-S bonds as shown in XIV and XV. 

The reactions of P4 with the metal sulfide cluster anions has been extended to Ni, Co, and Fe (99). The copper sulfide cluster anions were generally the least reactive anions toward P4 with similar anions having reactivities [NinSJ > [Co SA ... 

Photoelectron spectroscopy has been used to determine the threshold of electron detachment in small cluster anions and in some cases electronic transitions may be observed. The group of Nakajima and co-workers (261-264) studied several metal sulfide cluster anions. Many other systems have been studied by photoelectron spectroscopy including the [LaCJ (265), [AuC6F6] (266), and mixed-metal cluster anions (267). 

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. 

K), Fe-S cluster assembly (nIfM) and the biosynthesis of the iron molybdenum cofactor, FeMo-co (nifN, B, E, Q, V, H)(5a). It is the last two functions, involving the placement of unusual transition metal sulfide clusters into the nitrogenase proteins, that cause nitrogenase and its components to be appropriately included in this symposium. 

This caveat notwithstanding, the Dominant Hypothesls( ) designates [FeMo] as the protein responsible for substrate reduction. The FeMo protein contains an 02fi2 subunit structure due to expression of the nifD and nlfK genes(24,25). Its overall M.W. of about 230,000 reflects the 50-60,000 M.W. of each of its four subunits. The nonprotein composition of 30 Fe, 2 Mo, and 30 s2- betokens the presence of transition metal sulfide clusters, which are presumed to be the active centers of the protein. 

In the presence of an excess of sulfide ions, [Cd2+]/[S2 ] = 5, a strong change in the absorption spectra at low water content is observed compared to that obtained for a ratio of [Cd2+]/[S2-] equal to 2. By increasing the water content, the sharp peak disappears and a similar behavior as in the case of excess of cadmium is observed, i.e., a red shift in the absorption spectrum. The sharp peak observed at low water content increases with the relative amount of sulfide ions (45). This peak is attributed to sulfide clusters (55) formed on the CdS particles because of the high local concentration of sulfide ions. The disappearance of this peak when increasing the water content could be explained by the fact that sulfide clusters, with negative charges, are repelled to the center of the droplets and redissolve themselves inside the water pool. 

Semiconductor clusters were prepared via multifunctional 116 inorganic-organic sol-gel processing. The reaction of hexamethyldisilylthiane with metal alkoxide (in THF + alcohol) produced silane functionalized metal sulfide clusters and inorganic/organic network formers. 

W-W distances (2.634(3) A) are significantly shorter than those in the rhombus cluster and consistent with 12 CVE. The W4S6 framework may be regarded as an adamantanoid core, but the coordination geometry around the tungsten atoms is distorted from a regular tetrahedron. This reductive core rearrangement of sulfide clusters is unique and will open a preparative pathway to similar clusters. 

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-. 

The biological significance of these reactions is considered further in Chapters 18 and 24. The 132-kDa dimeric N20 reductase from Pseudomonas stiltzeri contains four copper atoms per subunit.546 One of its copper centers resembles the CuA centers of cytochrome c oxidase. A second copper center consists of four copper ions, held by seven histidine side chains in a roughly tetrahedral array around one sulfide (S2 ) ion. Rasmussen et al. speculate that this copper-sulfide cluster may be an acceptor of the oxygen atoms of N20 in the formation of N2.546a There is also a cytochrome cdj type of nitrite reductase.1433... 

Copper-sulfide cluster 884s Coproporphyrin III 843,845s Comified cell envelope 439 Corrin in transmethylation 592 Corrin ring 867, 868 Corrinoid-dependent synthesis of acetyl-CoA 876, 877 Cosmarium 22 COSY-NOESY diagram 143 Cotransport (symport) process 411,416,417 Coulomb 283... 

Figure 24-3 Structures of the metal-sulfide clusters of the MoFe-protein.

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