Pyrite type structure

Cupric sulfide, CuS, occurring as the mineral covellite (also known as covelline), exhibits a very unusual structure, in which the Cu is again partly 3-coordinate and partly 4-coordinate, with two-thirds of the sulfur atoms existing as S2 groups like those in pyrites. The low-temperature form of CuSe has also a covellite structure, the high-temperature modification (P-CuSe) being orthorhombic. All CuX2 compounds assume pyrite-type structures. 

Pyrite-type structure FeSj (pyrite) CoS, (cattierite) NiS, (vaesite) MnS, (hauerite) CoSe, (trogtalite) CoAsS (cobaltite) NiAsS (gersdorffite) NiSbS (ullmannite) NiSe, (penroseite) CoSbS, CuS ZnS,... 

One form of SiP has a cubic zinc blende-type structure with 4 4 tetrahedral coordination of both Si and P atoms (Figure 4.23a). Both cubic and orthorhombic forms of SiPj are known. The former has a pyrite-type structure consisting of octahedral [SiP ] and tetrahedral [PSiJ units (Figure 4.23b). 

Finally, many disulfides have a quite different structure motif, being composed of infinite three-dimensional networks of M and discrete Sj units. The predominate structural types are pyrites, FeSa (also for M = Mn, Co, Ni, Ru, Os), and marcasite (known only for FeS2 among the disulfides). Pyrites can be described as a distorted NaCl-type structure in which the rodshaped S2 units (S-S 217 pm) are centred on the Cl positions but are oriented so that they are inclined away from the cubic axes. The marcasite structure is a variant of the rutile structure (Ti02,... 

The telluride TcTe2 has been found to crystallize in a monoclinic layer structure. The disulfides of Re and Tc, unlike the pyrite-type Mn S2, contain monoatomic units. 

Ru and Os alloys. A specimen of structure types observed in the alloys of these metals (very often as solid solution ranges) is shown in Table 5.48a. The formation of Laves-type phases, a phases and several CsCl-type phases can be underlined. Notice the formation of marcasite and pyrite type compounds with the semimetals and non-metals of the 15th and 16th groups. 

Sulphides. The partially ionic alkali metal sulphides Me2S have the anti-fluorite-type structure (each Me surrounded by a tetrahedron of S, and each S atom surrounded by a cube of Me). The NaCl-structure type (6/6 coordination) is adopted by several mono-sulphides (alkaline earth, rare earth metals), whereas for instance the cubic ZnS-type structure (coordination 4/4) is observed in BeS, ZnS, CdS, HgS, etc. The hexagonal NiAs-type structure, the characteristics of which are described in 7.4.2.4.2, is observed in several mono-sulphides (and mono-selenides and tellurides) of the first-row transition metals the related Cdl2 (NiAs defect-derivative) type is formed by various di-chalcogenides. Pyrite (cP 12-FeS2 type see in 7.4.3.13 its description, and a comparison with the NaCl type) and marcasite oP6-FeS2 are structural types frequently observed in several sulphides containing the S2 unit. 

The chemical bonding in the two forms is quite different. The low-pressure form has the GeAs2 type of structure, in which the coordination of the atoms is normal, i.e., fourfold for Ge and threefold for As. In the pyrite type silicon is octahedrally coordinated, and phosphorus is tetrahedrally coordinated. The difference is reflected in the density and properties. The density of the GeAs2 type is 2.47 g./cc., whereas for the pyrite type it is 3.22 g./cc. The pyrite type is a metallic conductor, whereas the GeAs2 type is a semiconductor. 

This is, even to a greater extent, true of oxide glasses with the coordination number Z > 6. It is obvious that with another increase in pressure to P 1 Mbar (the stability region of an a-PbC>2 structure type), the coordination number in glassy silica should slightly rise [98] and approach eight at P 2-3 Mbar (the stability region of a pyrite-like structure of crystalline silica). This state of the... 

TOPOLOGICAL PROPERTIES AND ELECTRONIC STRUCTURES OF COMPOUNDS WITH PYRITE-TYPE CRYSTAL STRUCTURES... 

AX2 compounds with crystal structures belonging to the pyrite type (C2) are well documented in the literature. Due to the constant interest in the electronic, optical, and magnetic properties of these materials, there exists extended experimental and theoretical work. Among the title compounds, synthetic or natural pyrites, FeS2, turn out to be very well studied, like other transition metal disulphides, in both respects [1-5], while the electronic structures of pyrite-type SiP2 [6,7] and AuSb2 [8] are only partially known, and no theoretical study exists for the latter. 

Chattopadhyay T. K. and von Schnering, H. G., Pyrite-type silicon diphosphide p-SiP2 Structural parameters and valence electron density distribution, Z f. Kristallographie 167 (1984) pp. 1-12. 

Disulfide group (all containing dianion units in the structure) Pyrite-type (cubic) Pyrite (FeS,), cattierite (CoS,), vaesite (NiS,), etc. 

Fig. 6.15. The electronic structures of pyrite-type disulfides based on MS-SCF-Xa calculations on clusters (after Harris, 1982 Vaughan and Tossell,...

As Fe + ions oxidise HgS, HS and the precipitation of FcgSg free from sulphur is impossible, Monohydrated iron(III) oxide reacts with dry H2S to give primarily FcgSg some of which disproportionates into FeSg and FeS (Pearson and Robinson, 1928). A cobalt(III) sulphide cannot be precipitated from aqueous solution and there is no unequivocal evidence for its formation or that of NigSg in dry reactions. However, disulphides are known, of which the most important is FeS.2. In its commonest form, pyrites, Fe atoms and Sg pairs are arranged in a sodium chloride-type structure with the axes of the sulphur pairs parallel to the four trigonal axes (Fig. 261). 

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