Synthesis and structural characterization of 2,5-dihalo-3,4-dinitrothiophenes

Using new nitration protocols, we have been able to efficiently dinitrate 2,5-dihalothiophenes with yields of ～80–95%. The resulting products 2,5-dibromo-3,4-dinitrothiophene (1), 2,5-dichloro-3,4-dinitrothiophene (2), 2-bromo-5-chloro-3,4-dinitrothiophene (3), as well as the analogous 2-bromo-3,4-dinitrothiophene (4), all crystallize easily allowing their characterization via X-ray crystallography. Crystallization of 1 occurs in the monoclinic space group C2/c with a = 14.547(3) Å, b = 7.3534(15) Å, c = 10.775(2) Å, β = 128.89(3)°, and Z = 4. Crystallization of 2 occurs in the tetragonal space group I-42d with a = 9.9398(14) Å, b = 9.9398(14) Å, c = 16.866(3) Å, and Z = 8. Crystallization of 3 occurs as a pseudo-merohedral twin in the triclinic space group P-1 with a = 7.340(5) Å, b = 8.094(5) Å, c = 9.112(5) Å, α = 82.059(5)°, β = 66.232(5)°, γ = 63.021(5)°, and Z = 2. Crystallization of 4 occurs in the triclinic space group P-1 with a = 7.1787(14) Å, b = 7.4092(15) Å, c = 8.3151(17) Å, α = 101.67(3)°, β = 96.00(3)°, γ = 116.13(3)°, and Z = 2. The structures of all compounds exhibit the formation of interesting solid-state assemblies due to halogen-bonding interactions between the halogen and nitro groups.