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 O₂ 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 P2₁/c (a = 8.6397(4), b = 5.8359(4), c = 14.9767(11) Å, β = 92.088(4)°) with half a molecule in the asymmetric unit; 2 crystallizes in the triclinic space group P[Formula: see text] (a = 6.5330(5), b = 8.2084(6), c = 14.7264(9) Å, α = 84.483(4)°, β = 77.112(4)°, γ = 87.879(3)°); 3 was found to crystallize in two forms: recrystallization from CH₂Cl₂ at room temperature yielded a solvent-free, triclinic phase, space group P[Formula: see text] (a = 6.5060(9), b = 7.0739(9), c = 9.1164(8) Å, α = 81.860(3)°, β = 83.406(5)°, γ = 66.589(5)°), whereas cooling a solution to –5°C yielded a solvated form, 3·CH₂Cl₂, which crystallizes in the monoclinic space group P2₁/m (a = 6.179(1), b = 10.960(2), c = 13.884(3) Å, β = 92.69(3)°). 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.Key words: dithiatetrazocine, crystal structure, crystal engineering, molecular electrostatic potential.