Sulfur covalent radius

Strain energies of 23.5, 24.8 and 8.3 kJ mol 1 were estimated for tetrahydrofuran, pyrrolidine and tetrahydrothiophene, respectively (74Pmh(6)199). The larger sulfur covalent radius of 1.04 A lowers angular strain. 

The strain energies of these five-membered heterocycles are relatively small with values of 23.5, 24.8 and S.SkJmoF estimated for tetrahydrofuran, pyrrolidine and tetrahy-drothiophene respectively (74PMH(6)199). The closeness of the values for the two former compounds reflects the almost identical covalent radii of oxygen (0.66 A) and nitrogen (0.70 A) atoms. The sulfur atom with a much larger covalent radius of 1.04 A causes a... 

The covalent radii for most of the elements were obtained by taking one-half of the length of a single bond between two identical atoms. For example, the covalent radius of sulfur is obtained from the length of the S—S bond in the S8 molecule ... 

A larger covalent radius such as of sulfur, selenium, or tellurium reduces the ring strain d-orbital participation in thiophene is not significant in the ground state, and thiophene exhibits a pronounced aromatic character that is substantiated by its physical and chemical properties.103... 

Octahedral Radii.—In pyrite (Fig. 7-8) each iron atom is surrounded by six sulfur atoms, which are at the corners of a nearly regular octahedron, corresponding to the formation by iron of 3d 24 4p bonds. The iron-sulfur distance is 2.27 A. from which, by subtraction of the tetrahedral radius of sulfur, 1.04 A, the value 1.23 A for the cPsp9 octahedral covalent radius of bivalent iron is obtained (Table 7-15). 

The more lipophilic thioamide unit is also characterized by the poor H-bond acceptor nature of the sulfur and by its larger covalent radius (1.04 vs 0.74 A for O). The thioamide unit mainly adopts a Z-planar conformation, with a rotation energy barrier averaging about 23 vs 18 kcal-mol-1 for amides. 11 A recent ab initio computational study 12 suggests that conformational perturbation in linear thioamides is more likely effected in the C-terminal side. 

Crystallography of two cationic complexes which result from substitution of chloride in (30) with triphenylphosphine were found to have dissimilar structures. The structure of the hexa-fluorophosphinate is similar to the neutral complexes (C—S bond = 177 pm) while the perchlorate is unusual (C—S bond =168 pm). This shortening of the C—S bond in the perchlorate is accompanied by a lengthening of the M—C bond (15 pm) and is probably due to the influence of the perchlorate ion on crystal packing. The M—S bonds of both types of sulfur compounds are significantly longer than the M—C bonds (9-33 pm) which is consistent with sulfur s longer covalent radius. 

The sums of the respective covalent and van der Waals radii for Hg(II) and relevant donor atoms are given in Table II. An additional 0.2 A is added to the bridging sulfur covalent radii compared to terminal sulfur radii, as suggested by Bowmaker et al. (23). Although several values for the van der Waals radius of Hg(II) (29, 52, 12, 147) have been reported, the most recent work by Canty and Deacon proposed a value of 1.73 A with an acceptable range from 1.70 to 2.00 A, which is used in this chapter... 

Conclusion. There is no need to multiply examples of the type considered, especially since our knowledge of the principles determining the structures of covalent crystals is still so incomplete that we can offer no explanation for the anomalous manganese radius indeed, even the observed arrangement1) of the bonds formed by sulfur in sulvanite, Om3FS4, was entirely unexpected and has been given only an ad hoc explanation. 

Identical Ni-S and Cu-S bond distances are observed in these two structures, and the expected reduction of the ionic radius of copper is not reflected in a shorter Cu-S bond. Two possible reasons for this result are (1) a concomitant increase of the ionic radii of the sulfur donors offsets the effect of a shorter Cu(III) radius, and (2) there exists significant covalency in the Cu—S bonds. 

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