Bis(2-carboxy-N-{[1-(2-hydroxyethyl)-3,3-dimethylindolin-2-ylidene]methylimino}anilinium) sulfate monohydrate

The asymmetric unit of the title compound, 2C20H22N3O3 +·SO4 2−·H2O, contains four cations, two sulfate anions and two lattice water molecules. One of the four cations shows a different conformation of the hydroxyethyl group; the remaining three are all essentially superimposable. Two cations exhibit two-site orientational disorder [ratios = 0.524 (5):0.476 (5) and 0.616 (6):0.384 (6)] of the last two atoms of their hydroxyethyl groups, and one water molecule is disordered over two positions in a 0.634 (13):0.366 (13) ratio. Each imine H atom is intramolecularly in contact with the adjacent carboxyl O atom, forming an S(6) motif, while all the carboxylic acid H atoms are hydrogen bonded to O atoms of the sulfate anions. Other notable hydrogen-bond interactions involve (methylene, phenyl and imine chain) C—H⋯O (sulfate and carboxyl) and O—H⋯O(water) contacts, making up a comprehensive three-dimensional network involving D 2 2(n), with n = 4–6 and 15–16, and C 2 2(17) classical hydrogen-bond motifs. The crystal investigated was twinned by pseudomerohedry with a twin component ratio of 0.4745 (12):0.5255 (12).

The asymmetric unit of the title compound, 2C 20 H 22 N 3 O 3 + Á-SO 4 2À ÁH 2 O, contains four cations, two sulfate anions and two lattice water molecules. One of the four cations shows a different conformation of the hydroxyethyl group; the remaining three are all essentially superimposable. Two cations exhibit two-site orientational disorder [ratios = 0.524 (5):0.476 (5) and 0.616 (6):0.384 (6)] of the last two atoms of their hydroxyethyl groups, and one water molecule is disordered over two positions in a 0.634 (13):0.366 (13) ratio. Each imine H atom is intramolecularly in contact with the adjacent carboxyl O atom, forming an S(6) motif, while all the carboxylic acid H atoms are hydrogen bonded to O atoms of the sulfate anions. Other notable hydrogen-bond interactions involve (methylene, phenyl and imine chain) C-HÁ Á ÁO (sulfate and carboxyl) and O-HÁ Á ÁO(water) contacts, making up a comprehensive three-dimensional network involving D 2 2 (n), with n = 4-6 and 15-16, and C 2 2 (17) classical hydrogenbond motifs. The crystal investigated was twinned by pseudomerohedry with a twin component ratio of 0.4745 (12):0.5255 (12).
A solution of sodium nitrite (206 mg, 3 mmol) in 2 ml of water was then slowly added and the reaction stirred at 273-278 K for 30 min. To this was added a solution of 1-hydroxyethyl-3,3-trimethyl-2-methyleneindoline (2 mmol) in 10 ml of glacial acetic acid and the solution stirred for 2 h and allowed to gradually warm to room temperature ( Fig. 1) All hydroxyl H atoms were constrained to an ideal geometry (0.84 Å) at the difference Fourier map positions (AFIX 147) with U iso (H) = 1.2U eq (O). The methyl H atoms were constrained to an ideal geometry (C-H = 0.98 Å) with U iso (H) = 1.5U eq (C), but were allowed to rotate freely about the adjacent C-C bond. Imine (N-H) protons were refined using their difference Fourier map assigned positions with U iso (H) = 1.2U eq (N). All other H atoms were placed in geometrically idealized positions and constrained o ride on their parent atoms with C-H distances of 1.00 (primary), 0.99 (methylene) or 0.95 (phenyl) Å with U iso (H) = 1.2U eq (C) except for H atoms on disordered atoms for which U iso (H) = 1.5U eq (C,O).

Figure 1
Synthesis method for the title compound.

Figure 2
The atoms in the asymmetric unit with 35% probability ellipsoids. Some labels and all hydrogen atoms are omitted for clarity. Only the major conformers of the two site ethyl alcohol atoms are shown (see text).

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refined as a 2-component twin. Reflections were merged by SHELXL according to the crystal class for the calculation of statistics and refinement. _reflns_Friedel_fraction is defined as the number of unique Friedel pairs measured divided by the number that would be possible theoretically, ignoring centric projections and systematic absences. These statistics refer to single and composite reflections containing twin component 1 only. 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (