Bis(dimethylammonium) 3,3′-dicarboxy-5,5′-(5,7,12,14-tetraoxo-6,13-diazatetracyclo[6.6.2.04,16.011,15]hexadeca-1,3,8,10,15-pentaene-6,13-diyl)dibenzoate dihydrate

The title compound, 2C2H8N+·C30H12N2O12 2−·2H2O, comprises dimethylammonium cations, 3,3′-dicarboxy-5,5′-(5,7,12,14-tetraoxo-6,13-diazatetracyclo[6.6.2.04,16.011,15]hexadeca-1,3,8,10,15-pentaene-6,13-diyl)dibenzoate dianions and water molecules. The dianion is situated on a crystallographic inversion centre. Two very strong symmetry-restricted O⋯H⋯O hydrogen bonds are present which are situated about the crystallographic inversion centres. In one of these hydrogen bonds, the H atom is situated at its centre, while in the other one the H atom is disordered about its centre. Both H atoms are involved in the chain-like C 2 2(16) motif, and not in a more common motif R 2 2(8) that is composed of a pair of hydrogen carboxylates with the H atoms situated about the centre between the pair of O atoms. In the crystal, interaction of these hydrogen bonds results in formation of anionic layers of dianions parallel to (-111). The water molecules donate their H atoms to one of two of the carboxylate O atoms, forming strong hydrogen bonds. The dimethylammonium donates a bifurcated hydrogen bond to an oxo group of the dianion, forming weak hydrogen bonds. All the hydrogen bonds form a three-dimensional hydrogen-bonded network.

The title compound, 2C 2 H 8 N + ÁC 30 H 12 N 2 O 12 2À Á2H 2 O, comprises dimethylammonium cations, 3,3 0 -dicarboxy-5,5 0 -(5,7,12,14-tetraoxo-6,13-diazatetracyclo[6.6.2.0 4,16 .0 11,15 ]hexadeca-1,3,8,10,15-pentaene-6,13-diyl)dibenzoate dianions and water molecules. The dianion is situated on a crystallographic inversion centre. Two very strong symmetry-restricted OÁ Á ÁHÁ Á ÁO hydrogen bonds are present which are situated about the crystallographic inversion centres. In one of these hydrogen bonds, the H atom is situated at its centre, while in the other one the H atom is disordered about its centre. Both H atoms are involved in the chain-like C 2 2 (16) motif, and not in a more common motif R 2 2 (8) that is composed of a pair of hydrogen carboxylates with the H atoms situated about the centre between the pair of O atoms. In the crystal, interaction of these hydrogen bonds results in formation of anionic layers of dianions parallel to (111). The water molecules donate their H atoms to one of two of the carboxylate O atoms, forming strong hydrogen bonds. The dimethylammonium donates a bifurcated hydrogen bond to an oxo group of the dianion, forming weak hydrogen bonds. All the hydrogen bonds form a three-dimensional hydrogen-bonded network.

sup-1
Acta Cryst.  (Pantos et al., 2007). Recently, much attention has been paid to formation of multi-component molecular crystals or organic co-crystals as a means of modification of properties of organic molecules in the solid state (Bond, 2007;MacGillivray, 2008;Yan et al., 2011). However, an effective strategy for tuning functionality of co-crystal solids still remains challenging (Pigge, 2011).
In the title structure, these short hydrogen bonds form 2D-layers (Fig. 2). The 2D-framework is extended to a 3D network by involvement of water which donates strong O-H···O hydrogen bonds to the oxo-groups of the hydrogen carboxylates. Dimethylammonium donates a weak bifurcated hydrogen bond to the oxo-group O5.

Refinement
All the hydrogens were discernible in the difference electron density maps. Notably in the final stages of the refinement it turned out that the hydrogens H1 and H2 involved in the symmetry restricted strong hydrogen bonds were situated just at the centre or disorded about it, respectively. The positional as well as the displacement parameters of these hydrogens have been refined. The positional parameters of the water hydrogens H3 and H4 were refined using the following restraints: The O7-H3 and O7-H4 distances equal to 0.965 (20) Å while for the angle was used restraint DANG 1.5555 (400) (SHELXL97; Sheldrick, 2008) which corresponds to the average angle H-Ow-H (107.407°) retrieved from the Cambridge Structural Database (CSD) (Allen, 2002) from the structures determined by neutron diffraction. The isotropic displacement parameters of these hydrogens (H3 and H4) were constrained as U iso (H) = 1.5U eq (O). Other H atoms were allowed to ride on their respective parent atoms at distances of C-H(phenyl) = 0.93 Å with U iso (H) = 1.2 U eq (C), C-H(methyl) = 0.96 Å with U iso (H) = 1.5U eq (C), N-H(ammonium) = 0.90 Å with U iso (H) = 1.2U eq (N).

Figure 1
The title molecule with the displacement ellipsoids drawn at the 30% probability level and with the labelling scheme. The  View of the anionic layer with very strong symmetry-restricted hydrogen bonds. Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. 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 > 2sigma(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.