Structural studies of dithiatetrazocines:: X-ray crystal structures of the symmetric dithiatetrazocines p-XC6H4CN4S2CC6H4X [X=NO2, Br] and the first unsymmetric dithiatetrazocine, p-BrC6H4CN4S2CC6H4NO2

Oxidation of equimolar amounts of [p-BrC6H4CNSSN]Cl and [p-O2NC6H4CNSSN]Cl with elemental O-2 in the presence of Ph3Sb in MeCN yields a mixture of the symmetric dithiatetrazocines, O2NC6H4CN4S2CC6H4NO2 (1) and BrC6H4CN4S2CC6H4Br (2) as well as the unsymmetrically substituted derivative BrC6H4CN4S2CC6H4NO2 (3). The structures of compounds 1-3 are determined by X-ray diffraction: 1 crystallizes in the monoclinic space group P2(1)/c (a = 8.6397(4), b = 5.8359(4), c = 14.9767(11) Angstrom, beta = 92.088(4)degrees) with half a molecule in the asymmetric unit; 2 crystallizes in the triclinic space group P (1) over bar (a = 6.5330(5), b = 8.2084(6), c = 14.7264(9) Angstrom, alpha = 84.483(4)degrees, beta = 77.112(4)degrees gammaa = 87.879(3)degrees); 3 was found to crystallize in two forms: recrystallization from CH2Cl2 at room temperature yielded a solvent-free, triclinic phase, space group P (1) over bar (a = 6.5060(9), b = 7.0739(9), c = 9.1164(8) Angstrom, alpha = 81.860(3)degrees, beta = 83.406(5)degrees, gamma = 66.589(5)degrees), whereas cooling a solution to -5degreesC yielded a solvated form, 3.CH2Cl2, which crystallizes in the monoclinic space group P2(1)/m (a = 6.179(1), b = 10.960(2), c = 13.884(3) Angstrom, beta = 92.69(3)degrees). The NO2...Br intermolecular interactions observed in the unsolvated structure of 3 are disrupted in the solvate structure; the CH2Cl2 molecule in the latter is aligned such that its molecular dipole interacts with both nitro and bromo groups, retaining a molecular chain motif. The structures are discussed in relation to their semi-empirically calculated molecular electrostatic potentials and calculations of intermolecular interactions using van der Waals forces combined with an electrostatic point charge model.