Bis(4-methoxy-3,4-dihydroquinazolin-1-ium) chloranilate

In the title compound [systematic name: bis(4-methoxy-3,4-dihydroquinazolin-1-ium) 2,5-dichloro-3,6-dioxocyclohexa-1,4-diene-1,4-diolate], 2C9H11N2O+·C6Cl2O4 2−, the chloranilate anion lies about an inversion center. The 4-methoxy-3,4-dihydroquinazolin-1-ium cations are linked on both sides of the anion via bifurcated N—H⋯(O,O) and weak C—H⋯O hydrogen bonds, giving a centrosymmetric 2:1 aggregate. The 2:1 aggregates are linked by another N—H⋯O hydrogen bond into a tape running along [1-10]. The tapes are further linked by a C—H⋯O hydrogen bond into a layer parallel to the ab plane.

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HG5342).

Comment
The title compound was accidentally obtained in the preparation process of bis(quinazolinium) chloranilate, which is an interesting candidate for the study on proton-transfer in short hydrogen-bonded systems (Nihei et al., 2000, Seliger et al., 2009  In the crystal structure of the title compound, an acid-base interaction involving proton transfer is observed between chloranilic acid and 4-methoxy-3,4-dihydroquinazoline. The chloranilate ion shows a characteristic structure having four short C-C bonds and two extremely long C-C bonds, and C-O with similar bond lengths, which is explainable in terms of the double π system of the anion (Andersen, 1967;Benchekroun & Savariault, 1995). One chloranilate anion and two 4-methoxy-3,4-dihydroquinazolin-1-ium cations are linked by bifurcated N-H···(O,O) and weak C-H···O hydrogen bonds (N1-H1···O1, N1-H1···O2 i and C10-H10···O1; symmetry code as in Table 1) to afford a centrosymmetric 2:1 aggregate (Fig. 1). The 2:1 aggregates are linked by another N-H···O hydrogen bond (N2-H2···O2 ii ; symmetry code as in Table 1), forming a tape along the [110] direction (Fig. 2). The tapes are further linked by a C-H···O hydrogen bond (C4-H4···O1 iii ; symmetry code as in Table 1) into a layer parallel to the ab plane.

Experimental
To a solution of chloranilic acid (183 mg) in acetonitrile (40 ml), a solution of quinazoline (228 mg) in acetonitrile (40 ml) was added at room temperature. A brown precipitate, which was immediately formed after mixing the solutions, was collected by filtration and then dissolved in methanol (40 ml). Single crystals of the title compound were obtained by slow evaporation from the methanol solution for ca three months at room temperature. During the slow evaporation process, quinazoline reacted with methanol under an acidic condition of chloranilic acid, yielding 4-methoxy-3,4-dihydroquinazoline.

Refinement
C-bound H atoms were positioned geometrically (C-H = 0.95 or 0.98 Å) and refined as riding, allowing for free rotation of the methyl group. U iso (H) values were set at 1.2U eq (C) or 1.5U eq (methyl C). The N-bound H atom was found in a difference Fourier map and refined isotropically. The refined N-H distances are 0.90 (3) and 0.95 (3) Å. The quality of the crystals studied were low as indicated by R int = 0.199. This is possibly due to a small amount of quinazoline which remained without reacting with methanol and incorporated in the crystallization of the title compound as an impurity.

Figure 1
The Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.