1-[4-(Diaminomethyleneaminosulfonyl)phenyliminiomethyl]-2-naphtholate N,N-dimethylformamide disolvate

The asymmetric unit the title compound, C18H16N4O3S·2C3H7NO, contains a molecule in a zwitterionic form with a deprotonated hydroxyl group and an iminium group, and two dimethylformamide solvent molecules. The dihedral angles of the guanidine group and the naphthyl ring system with respect to the central benzene ring are 76.04 (7) and 3.45 (9)°, respectively. The conformation of the molecule may be influenced, in part, by two intramolecular hydrogen bonds, while in the crystal structure, intermolecular hydrogen bonds form one-dimensional chains along [010].

The asymmetric unit of (I) consists of one independent molecule of a zwitterion and two molecules of dimethylformamide. The oxygen atom attached to the naphthyl group (O3) is found to be a deprotonated form of hydroxyl group. The imine unit connecting the naphthyl and phenyl groups is in a protonated form, giving an iminium unit. Two intramolecular hydrogen bonds (N4-H4A···O3 and N2-H2B···O2; Table 2) are formed to stabilize the conformation of the molecule.
Three intermolecular hydrogen bonds also take part in stabilizing the conformation together with the crystal packing of the compound [N1-H1B···O2(i), N1-H1A···O5(ii), N2-H2A···O5(ii); symmetry operation (i): -x, y-0.5, 1-z, (ii): -x+1, 0.5+y, 1-z]. The guanidine unit, consisting of C1 and N1-N3 atoms, forms a planar geometry and is canted with respect to the central phenyl ring at an angle of 76.04 (7) °. The C=N double bond character of the guanidine moiety is fully delocalized over the unit as shown by the similar C-N distances within the unit. On the other hand, the naphthyl plane is declined only by 3.45 (9) ° with regard to the phenyl ring. The iminium unit, consisting of atoms C8 and N4 [C8-N4 = 1.322 (2) Å], is nearly coplanar to the naphthyl plane, as can be seen by the torsion angles about the C8-C9 axis, i.e., N4-C8-C9-C10 = -1.0 (3) and N4-C8-C9-C18 = 178.27 (17) °. Good planarity is exhibited by the guanidine and phenyl moieties, while the naphthyl moiety shows a deviation from the planar geometry, where the ten atom r.m.s deviation estimated in the best plane calculation is 0.024 Å. No obvious stacking interaction is found in the crystal (see Fig. 2).

Experimental
Compound (I) was prepared as follows. A hot methanolic solution of 2-hydroxy-1-naphthaldehyde (0.9 mmol, 0.154 g) was added to a methanolic solution of sulfaguanidine (0.9 mmol, 0.192 g). The resulting solution was then refluxed with stirring for 2 h during which a yellow precipitate deposited. The precipitate was then filtered off from hot solution and then air-dried A good quality single-crystal of (I) was prepared by vapour diffusion method as follow. Compound (I) was dissolved in a minimum amount of N,N-dimethylformamide and the solution was left in refrigerator in the presence of ether pool. Upon leaving the solution for 3 days, it gradually raised its volume to give crystals suitable for X-ray diffraction analysis.

Refinement
All H atoms were placed in idealized positions (methyl C-H = 0.98 Å, aromatic C-H = 0.95 Å, and N-H = 0.88 Å), and included in the refinement in a riding-model approximation, with U iso (H) = 1.5U eq (methyl C) and U iso (H) = 1.2U eq (aromatic C and N). In the final difference Fourier map, the highest peak was located 0.86 Å from atom C2. The deepest hole was located 0.51 Å from atom S1. Fig. 1. The molecular structure of (I) showing the atom-labeling scheme. Displacement ellipsoids are drawn at the 50% probability level. The solvent molecules are not shown.

Special details
Experimental. The first 50 frames were rescanned at the end of data collection to evaluate any possible decay phenomenon. Since it was judged to be negligible, no decay correction was applied to the data. as those based on F, and R-factors based on ALL data will be even larger.