CENTRIC ORGANIC DISULFIDE (C-S-S-C = 180-DEGREES) - CRYSTAL AND MOLECULAR-STRUCTURES OF CHLORO[BIS(2-PYRIMIDYL) DISULFIDE]COPPER(I) MONOHYDRATE AND OF BIS-(2-PYRIMIDYL) DISULFIDE

The crystal and molecular structures of chloro[bis(2-pyrimidyl) disulfide]copper(1) monohydrate, Cu(C8H6N4S2)Cl-H2O, and of bis(2-pyrimidyl) disulfide, C8H6N4S2, have been determined by single-crystal X-ray diffraction techniques using 2401 and 1873 unique reflections, respectively. These structures were refined by full-matrix least-squares procedures to final conventional R indices of 0.039 and 0.036, respectively. Counter methods and monochromatized Mo Kα radiation were employed. The complex crystallizes in the monoclinic space group [formula ommited]and with 4 formula units per unit cell. The ligand crystallizes in the triclinic space group [formula ommited] and with 4 molecules per unit cell. In the complex, ligand molecules bridge between Cu(I) ions to form polymeric sheets. Each Cu(I) ion is coordinated by two chloride ions and by two nitrogen atoms from two bis(2-pyrimidyl) disulfide ligand molecules, forming a distorted tetrahedron with coordination angles ranging from 95.7 to 142.2°. The chloride ions bridge between pairs of Cu(I) ions to form rhombic CuClCuCl rings. The relatively short Cu1-N bond distance, 1.966 (3) Å, indicates strong d →π π* back-bonding from the Cu(I) d orbitals into the lowest lying π* molecular oribtal of each pyrimidine ring. The most unusual structural feature of the complex is the C-S-S-C torsion angle of 180° (by symmetry), a value not heretofore reported for an organic disulfide. This unusual torsion angle is stabilized by a π system which extends over the entire planar ligand, although the π component of the S-S bond is small. In this conformation, the repulsive forces between the sulfur 3pπ lone-pair electrons and those of the nitrogens on adjacent rings are largely eliminated. Repulsions between the sulfur atoms are at a maximum, however, accounting for the long S-S bond distance of 2.113 (1) Å. The two independent molecules in the structure of the free ligand have normal C-S-S-C torsion angles (83.9 and 85.4°) and normal S-S bond lengths (2.017 (2) and 2.020 (2) Å) for aromatic disulfides in the equatorial conformation (N-C-S-S torsion angle near 0°). © 1979, American Chemical Society. All rights reserved.