5,6-Dihydroxy-1,10-phenanthrolinium-1,10-ium dichloride

Abstract

5,6-Dihydroxy-1,10-phenanthroline, obtained from recrystallization of a side-product of a condensation reaction between 1,10-phenanthroline-5,6-dione and 5,6-diamino-1,3-dimethyluracil, has been isolated as a dihydrochloride (C₁₂H₈N₂O₂·2HCl·0.5CH₃CN) by vapor diffusion of acetonitrile into an ethanol/HCl solution. The compound crystallizes in the triclinic space group $P\overline{1}$ with a = 5.8334(1) Å, b = 9.8041(2) Å, c = 11.9895(2) Å, α = 81.511(1)°, β = 76.395(1)°, γ = 81.429(1)°, and V = 654.48(2) Å³, Z = 2, R[F ² > 2σ(F ²)] = 0.028, and wR(F ²) = 0.078. The crystal packing is stabilized by two N–H⁺···Cl⁻ interactions (2.18(3) Å, 2.13(2) Å) and two O–H···Cl⁻ interactions (2.11(3) Å, 2.20(3) Å). Pi-stacking of the phenanthrolinium rings results in an interplanar distance of 3.431(5) Å with the phenanthrolinium ring centroids displaced from each other by ~6 Å. The results for this diprotonated species are compared to those reported by Lin et al. (Acta Cryst E65:o2367, 2009) for the monoprotonated form and this reveals the possibility of using the relative –OH/phenanthroline ring orientations as a qualitative diagnostic of metal–ligand interactions in metal complexes of this ligand (Larsson and Ohrstrom in Inorg Chim Acta 357:657, 2004; Guan et al. in Acta Cryst C64:m311, 2008).

Index Abstract

The crystal structure of the diprotonated form of 5,6-dihdroxy-1,10-phenanthroline (5,6-dihydroxy-1,10-phenanthrolinium-1,10-ium dichloride) is discussed and compared to both the monoprotonated form and those complexed with Mn(II) and Co(III) reported in the literature.