Sulfur structural parameters

NMR Assignments, Structural Constraints, and Structural Parameters for the Available NMR Solution Structures of Iron-Sulfur Proteins"- ... 

The normal vibrations and structural parameters of Sg S, S, and Sjj have been used to calculate several thermodynamic functions of these molecules in the gaseous state. Both the entropy (S°) and the heat capacity (C°) are linear functions of the number of atoms in the ring in this way the corresponding values for Sj, Sg, Sjo and can be estimated by inter- and extrapolation For a recent review of the thermodynamic properties of elemental sulfur see Ref. 

The structural parameters of the sulfur tetrafluoride molecule correspond well with its observed chemical properties only two fluorine atoms are active in reactions carried out at temperatures not exceeding 300 C. 

Selected Structural Parameters of the Sulfur-Rich 1,1-Dithio Complexes. 

Detailed structural parameters are given in Table 13. On the other hand, the bidentate sulfur donor ligands in [Te (SPPh2)2N 2] form six-membered chelate rings with large normalized bites, b - 1.37, and the complex has an undistorted planar rectangular structure, 4>a = 47.0°, [Pg.60]

A theoretical study on 5V-methylselenabenzene 192 and its oxygen and sulfur analogues has been carried out using ab initio calculations with the DFT method <2006M1791> (cf. Section 7.11.2, structure 3). The X-H compounds were also evaluated. These structures have 6ji electrons and are homoaromatic with ylide character. Structural parameters were also determined for these structures. The substituent on the chalcogen atom is calculated to be more stable in a pyramidal rather than a planar conformation. 

A wealth of x-ray diffraction data is available on this group of heterocycles and selected structural parameters are summarized in Table 2. In all the systems having generalized structures (25) or (26), the six-membered ring has an envelope conformation with the sulfur atom out of the plane (ca 0.2-0.5 A) defined by the other five atoms. The five-membered rings are planar and quasiplanar with the nonsulfur atoms of the six-membered ring. The study of compound (25 R1 = NH2, R2 = H,... 

Some effort has gone into prediction and verification of structural parameters of complexes from interaction of HX with thiirane <2004SAA1883>. By means of ab initio MO and B3LYP DFT at the 6-311++(d,p) level, Araujo and co-workers obtained structural and electronic parameters for HF and HCl complexes with thiirane. The complexes have CS symmetry with the HX unit lying in a plane perpendicular to the plane of the thiirane ring. The MP2 distance between H of HF and the thiirane sulfur was 2.164 A, in good agreement with the experimental distance, 2.193 A. 

Dorofeeva and Gurvich evaluated the available structural parameters, fundamental frequencies, and enthalpies of formation of thiirane, thiirene, and other sulfur compounds as well as some other quantities <1995JPCRD1351>. For thiirane, ideal gas values at lb and 300K recommended in 1995 are Gp = 53.603, A = 255.569J K mol , AfAA = 81.917 kjmol , and AfG = 96.897. Analogous values for thiirene are 54.929, 255.678, 299.973, and 275.665. The latter were all calculated because experimental numbers were not available. The situation does not appear to have changed since that time. 

The crystalline structure parameters of y-Sy and 5-87 are summarized in Table 3. While the asymmetric unit of y-87 is built by one molecule, in -87 we have to deal with two independent molecules due to intermolecular forces. Figure 2 represents a view of the unit cells of the two allotropes of 87 which have been studied so far. A detailed analysis and modeling of the intermolecular forces in 12 sulfur allotropes using a non-spherical sulfur atom potential yielded a slightly higher lattice energy for y-Sy than for S-Sy [73]. 

Table 19 Crystal and molecular structure parameters of fibrous sulfur, [8, 54, 128-130]. The pseudo-orthorhombic unit cell proposed by Tuinstra has been overcome in favor of a monoclinic structure. The unit cell contains eight segments of ten atoms of the helices ...

Table 20 Crystal structure parameters of 2nd fibrous suUur (S -=Sa,i) and of laminar sulfur (S j=Sa,2) [54, 115]. The molecular parameters were claimed to be very similar to those of fibrous sulfur, ...

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