Empirical relations between disulfide bond lengths, (nitrogen or carbon)-carbon-sulfur-sulfur torsion angles, and substituents in aromatic disulfides. Crystal and molecular structure of 3,3'-dihydroxydi-2-pyridyl disulfide

Abstract

In the 21 reported crystal structures of symmetric disulfides whose sulfur atoms are bound to sp2 carbon atoms, an empirical relationship is found between the S-S bond length and the X-C-S-S, X = C or N, torsion angle. When X-C-S-S is within about 20°of 90°, the average S-S bond length is 2.08 Á (2.059-2.108 Á) in six structures; when X-C-S-S is within about 20°of 0°, S-S averages to 2.03 Á (1.999-2.050 Á) in 15 structures. The C-S-S-C torsion angles are generally within about 20°of 90°in those molecules. In addition, it is noted that the less frequently encountered X-C-S-S angles near 90°o ccur only when one strongly electron-donating substituent is present in a position ß to the disulfide group in each of the R groups of the RSSR molecule, or when both ß positions on each R group are substituted, independent of electronegativity. (If an aromatic ring of an R group is bonded to the disulfide group, the nomenclature ortho instead of ß is usually used.) A relatively neutral or electron-withdrawing group in only one ß position of each R group (or any substituents at any more distant positions) allows the X-C-S-S torsion angles to be near 0°, and the S-S bond, therefore, to be short. This result is supported by the crystal and molecular structure of 3,3'-dihydroxydi-2-pyridyl disulfide, C10H8N2S2O2, which has been determined by single-crystal X-ray diffraction techniques using counter methods, and has been refined by full-matrix least-squares procedures to a final conventional R index of 0.035. The yellow monoclinic crystals form in the space group P2\jc with a = 7.165 (1) Á, b = 7.656 (1) Á, c = 19.517 (3) Á, /3 = 96.77 (1)°, and four molecules per unit cell. The average N-C-S-S torsion angle (9°) indicates that the S-S bond (2.0180 (7) Á) is nearly in the plane of each pyridine ring. The C-S-S-C torsion angle is 93.2°, and the average S-C bond length is 1.782 Á. The empirical rules presented also successfully describe the 11 transition metal ion complexes involving these disulfides whose structures are known. The C-S-S-C torsion angle has a role in governing the S-S bond length, but is important only when X-C-S-S is within about 20°of 90°or when C-S-S-C deviates by about 40°o r more from 90°.

Conformational consequences of intramolecular hydrogen bonding by OH to the directional lone-pair of sulfur in derivatives of methyl phenyl sulfide, diphenyl sulfide, and diphenyl disulfide

“…From our viewpoint, this conformation is expected. Again, the corresponding dinitro compound has an equatorial form (48), as anticipated because of the absence of a stereospecific hydrogen bond and probably also because the nitro groups enhance the 3p ,n conjugation (37,49).…”

“…3p ,z conjugation is largely lost and there is a CZ axis perpendicular to the S-S bond. The anisotropy model for the benzene ring and reasonable geometry about sulfur (37) predicts that for 8,-H, H-3, and H-4 should shift (downfield) by 0.09,0.04, and 0.02 ppm, respectively; whereas H-5 and H-6 should shift (upfield) by -0.03 and -0.36 ppm, respectively. In the above order, the observed shifts relative to 1 are 0.10, 0.04, 0.10, -0.03, and -0.22 ppm.…”

Metal‐Catalysed Oxidation Processes in Thiosemicarbazones: New Complexes with the Ligand N‐{2‐([4‐N‐Ethylthiosemicarbazone]methyl)phenyl}‐p‐toluenesulfonamide

“…This means that both www.chemeurj.org sulfur atoms lie approximately in the plane of the N-N-C-N thiosemicarbazone skeleton to which they are bound (0.0267 and 0.0319 ). In addition, according to the criteria of Higashi et al, [24] the equatorial conformation is also confirmed by the S2ÀS3 distance, which is shorter than the typical axial range (2.060-2.108 ), and the C-S-S angles [C15-S2-S3 103.3(8) and C20-S3-S2 104.5(8)8], which are larger than those in other organic disulfides showing an axial conformation (100-1038).…”

4,4′-Di-3-pyridyl-2,2′-dithiodipyrimidine

“…For general background to heterocyclic disulfides, see Horikoshi & Mochida (2006). For related crystal structures, see: Higashi et al (1978); Tabellion et al (2001).…”