Pyrites structure

The sulfides are fewer and less familiar than the oxides but, as is to be expected, favour lower oxidation states of the metals. Thus manganese forms MnS2 which has the pyrite structure (p. 680) with discrete Mn and 82 ions and is converted on heating to MnS and... 

Ruthenium and osmium form only disulfides. These have the pyrite structure and are diamagnetic semiconductors this implies that they contain M . RuSc2, RuTc2, OsSc2 and OsTc2 are very similar. All 6 dichalcogenides are obtained directly from the elements. 

Nickel sulfides are very similar to those of cobalt, consisting of NiS2 (pyrites structure, p. 680), Ni3S4 (spinel structure, p. 247), and the black, nickel-deficient Nii-j S (NiAs structure, p. 555), which is precipitated from aqueous... 

The mineral laurite is the mixed sulphide (Ru,Os)S2 this and RuS2 and OsS2 have the pyrite structure as does RuQ2 (Q = Se, Te). These can be made from the reaction of the chalcogen with the metals, while RuCl3 will also react with Se and Te. 

On heating with sulphur, MS2 result. PtS2 has the 6-coordinate Cdl2 structure whereas PtS2 is Pd2+(S2 ) in a distorted pyrite structure (4-coordinate PdPd—S 2.30 A) confirming the preference for the divalent state for... 

The pyrites structure is exhibited by several pnictides MAs2 and MSb2 (M = Pd, Pt) and PtP2 (Figure 3.10). 

Fig. 1.2 Crystal structures of the major sulfides (metal atoms are shown as smaller or black spheres) (A) galena (PbS) structure (rock salt) (B) sphalerite (ZnS) structure (zinc blende) (C) wurtzite (ZnS) strucmre (D) pyrite structure and the linkage of metal-sulfur octahedra along the c-axis direction in (/) pyrite (FeSa) and (//) marcasite (FeSa) (E) niccolite (NiAs) structure (F) coveUite (CuS) structure (layered). (Adapted from Vaughan DJ (2005) Sulphides. In Selley RC, Robin L, Cocks M, Plimer IR (eds.) Encyclopedia of Geology, MINERALS, Elsevier p 574 (doi 10.1016/B0-12-369396-9/00276-8))...

With respect to non-noble and non-Ru catalysts, transition metal chalcogenides with spinel and pyrite structures have been investigated and shown that these can also be active to oxygen reduction processes. The motivation in the present case is that chalcogen addition might enhance the stability and activity toward the ORR... 

Nowack, E., Schwarzenbach, D. and Hahn, T. (1991) Charge densities in CoS2 and NiS2 (pyrite structure), Acta Cryst., B47, 650-659. 

Transitional-metal sulphides and selenides with pyrite structure of the form MS2 and MSe2 Ni(Sej —xSx)2... 

The oxidation state of the metals in the bulk sulfides corresponds to what is expected for a given metal in a sulfur environment. Generally the lattice sulfur is tightly bound to several metal atoms (usually three) and is very stable. Consequently, narrow valence distributions are observed. For the early layered TMS, the oxidation state is 4+. In the later isotropic TMS, the valence is usually 2+ or 4+. For example, in RuS2 the oxidation state is 2+ because of the pyrite structure. In Rh2S3 the oxidation state is 3 +. In other TMS inthe stable catalytic state such as amorphous OsS, it is not clear what the oxidation state is although formally it would be 2+. 

From similar data for other crystals with the pyrite structure or a closely related structure (of the marcasite or arsenopyrite types), given... 

Cobalt disulfide has a cubic pyrite structure, a0 = 5.5362(5)A. It is ferromagnetic with a Tc of 124 K and shows metallic behavior from 4 K to room temperature. 

It fits into this picture that the normal marcasites easily transform under pressure to the pyrite structure whereas the loellingites FeP2 and FeAs2 as well as the arsenopyrite-type representative C0AS2 retain their structure up to at least 65 kbar/400- 1100° C (16). 

Meanwhile, the structure of Rl Ses has been determined by Hohnke and Parthe (491). The space group of this structure is R3—C31. The cations are located at positions 3(e), the empty cation site of the pyrite structure being 1 (a) 000. Thus, in a layer of cations, which in the pyrite structure are in a close-packed arrangement, every second row is only... 

Another unexpected example of non-metallic d6 phases is offered by this group of compounds. Since RhSeD(h) crystallizes in the pyrite structure... 

When the distortion of the anion octahedra in PdS2 is reduced by pressure the semiconductor transforms into a metal before a change to the pyrite structure takes place (16). 

Whereas palladium is divalent in the non-metallic PdP2, the pyrite structure of the diarsenide and diantimonide suggests a Pd valency of four, although these compounds show metallic properties. The metallic behaviour of the bismuthide is not surprising since the metallic character increases with heavier anions. PdBi2 crystallizes in two modifications... 

It will not be possible, in this paper, to deal with all of the platinum metal chalcogenides. Instead, a number of examples will be chosen and their electrical as well as magnetic properties correlated with the atomic positions in the various structures formed. The first group of compounds to be discussed crystallize with the pyrite structure, which is shown in Figure 1. This structure is similar to the NaCl structure if we replace Na by Fe and each Cl by an S2 group. However, the S-S distance within... 

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