Sulfur prismatic

Monochnic sulfur Prismatic sulfur 8-Sulfur Muthmami s sulfur ff Monochnic (f)) sulfur Crystalline cycloS% Space group P2 /c... 

Monoclinic sulfur Prismatic sulfur /3-Sulfur Muthmann s sulfur 11 Monoclinic (/S) sulfur Crystalline cyclo-Ss, Space group P2 c... 

Preparation of 2-Hydroxy-4,4 -Dicyanostilbene 10 grams of 2-amino-4,4 -dicyanostilbene thus prepared were dissolved in 400 cc of boiling glacial acetic acid and 200 cc of dilute sulfuric acid added the solution was suddenly chilled and diazotized over one and a half hours at 5° to 10°C with sodium nitrate (3.0 grams/15 cc H O). The diazonium salt solution was decomposed by boiling for 15 minutes with 600 cc of 55% aqueous sulfuric acid solution the solution was diluted, cooled and filtered. The residue crystallized from ethyl alcohol as lemon yellow prismatic needles, MP 296°C. 

The most important sulfides are MoSg and WSg, which possess a layered structure. The metal atoms occupy trigonal-prismatic holes in the plane between the hex-agonally arranged sulfur layers, as shown in Fig. 5.12. The layers are shifted with... 

Monoclinic, prismatic crystals, which are light-yellow in color. This allotrope is referred to as beta sulfur. Its density is 1.96 g/cm, with a melting point of 119.3°C. 

Dark-red crystals, flakes or granular powder bipyramidal prismatic system density 2.70 g/cm melts at 197°C decomposes on further heating highly soluble in water, 61.7 g and 67 g/100 mL at 0 C and lOO C, respectively soluble in sulfuric and nitric acids. 

Systematic studies of the structural properties of TaS2 by Jellinek10 revealed the presence of several polymorphic forms of the compound as a function of temperature. Within a layer, the tantalum atom sits in the holes formed between two layers of sulfur atoms in the S—Ta—S sandwich. The coordination of the tantalum is trigonal prismatic or octahedral, depending on whether the two sulfur layers lie one on top of the other or are rotated by 60°. Thus the various poly-... 

Elemental sulfur exhibits complicated allotropy, that is, it exists in many modifications.4 The stable, prismatic crystal form at room temperature, a-S or orthorhombic sulfur, is built up of stacks of Ss rings (Section 3.4). If heated quickly, it melts at 112.8 °C. If it is heated slowly, however, it changes to needlelike crystals of /3-S or monoclinic sulfur, which is the stable form above 95.5 °C and which melts at 119 °C. Both 0-S and the yellow mobile melt (below 160 °C) are composed exclusively of Ss rings. Solids containing S7, Sg, S10, S12, and other rings are known, but all slowly revert to Sg below 160 °C. 

Fig. 8. Crystal structure of M0S2. (a) Side view of a single-layer S-Mo S slab of M0S2. The molybdenum atoms (dark) are coordinated to six sulfur atoms (bright) in a trigonal prismatic coordination, (b) Within each layer, the sulfur lattice (and the molybdenum lattice) are hexagonal ly arranged with inplane interatomic distances tZs s or i/m., no equal to 3.15A. (c) Illustration of the 2II-M0S2 stacking sequence of successive layers in bulk M0S2. The distance between the molybdenum layers is 6.15 A.

In the case of three bidentate sulfur ligands, e.g. [Bi(pedt)3]2-EtOH (pedt = 1-pyrrolidinecarbondithioate), more complex structures are formed. The dimer contains two differently coordinated bismuth atoms one is trigonal prismatic with an extra position on a rectangular face and the other bismuth atom is pentagonal pyramidal. The overall molecular structure is (80).270... 

The sulfur atoms are also clustered in all-cis positions in the txtxp2p2 bicapped trigonal prismatic structure of tetrakis(A-methyl-p-thiotolylhydroxamato)hafnium(IV) [HffMeQJlr C(S)N Oj Me 4]. Averaged metal-ligand bond distances are Iff—0 = 2.150 and Hf—S =... 

Nickel, on the other hand, on alumina and on silica supports was found to have only five nearby sulfurs (square pyramidal) with Ni-Mo coordination numbers from 1 to 1.5. Ni-Mo-S supported on carbon was observed to have Ni-S coordination numbers of 6 in a trigonal-prismatic configuration. In addition, Ni (at low Ni concentrations) was found to have one nearby Ni, which could indicate that, in some catalysts, Ni is present as pairs on the MoS2 surface. The overall structure of the Ni-Mo-S was believed to be similar to that of millerite (i.e., Ni is located in the center of the MoS edge in a square-pyramidal configuration, with one sulfur extending perpendicular to the surface) (62-64). 

Layered sulfides predominate in Groups IV to VII except for MnS, which is isotropic. The main structural feature of this class is a strong chemical anisotropy that greatly affects their catalytic properties. In the molybdenite structure (MoS2), the metal is in trigonal prismatic coordination. Other layered sulfides are octahedrally coordinated or distorted octahedrally coordinated (ReS2) with the metal surrounded by six sulfur atoms. It should also be noted that some TMS sulfides have structures that fall in between isotropic and layered sulfides. Rh2S3 is an example and others are completely amorphous, such as IrSt and OsSr. 

---