C12H6Br2N2, orthorhombic, Pna21 (no. 33), a = 19.6816(9) Å, b = 4.6554(2) Å, c = 11.8795(6) Å, V = 1088.47(9) Å3, Z = 4, Rgt(F) = 0.043, wRref(F2) = 0.107, T = 293 K. A stable one-dimensional (1D) layered structure is formed by π⋅⋅⋅π stacking interactions between 2,9-dibromo-1,10-phenanthroline molecules that pack along the crystallographic b-axis. The quantum chemical calculation shows the interaction energy between 2,9-dibromo-1,10-phenanthroline molecules is −9.22 kcal/mol. The 1D layered structures are linked to form a two-dimensional (2D) sheet via C2—H2⋅⋅⋅Br2 hydrogen bonds with d(H2⋅⋅⋅Br2) = 3.028 Å and <(C2—H2⋅⋅⋅Br2) = 158.55°. The 2D sheets pack dispersive interactions to construct the three-dimensional (3D) crystal structure. Compared to the π⋅⋅⋅π stacking interaction, the aforementioned C2—H2⋅⋅⋅Br2 hydrogen bond is much weaker. At the ωB97X-D/def2-TZVPP theory level, the interaction energy of the C2—H2⋅⋅⋅Br2 hydrogen bond is −2.48 kcal/mol.
Under an argon atmosphere, 2.0 mL of phosphorus tribromide was added to 2,9-dichloro-1,10-phenanthroline (70.0 mg, 0.281 mmol), and the mixture was stirred at 165°C for seven hours. The reaction solution was cooled with ice, and the aqueous solution of sodium hydrogen carbonate was added thereto little by little until the reaction solution became weakly basic. The resulting mixture was filtrated, and the filtrated matter was washed lightly with methanol. The filtrated matter was extracted with chloroform potassium carbonate aqueous solution, and the organic phase was dried over anhydrous sodium sulfate, filtrated, and concentrated on providing 76.6 mg (81.1percent yield) of the colourless solid 2, 9-dibromo-1,10-phenanthroline.
