Crystal structure of 1,3-bis(1,3-dioxoisoindolin-1-yl)urea dihydrate: a urea-based anion receptor

The title compound possesses twofold rotation symmetry, with the planes of the phthalimide moieties inclined to one another by 73.53 (7)° and by 78.62 (9)° to that of the urea unit. In the crystal, molecules are linked via N—H⋯O and O—H⋯O hydrogen bonds, forming a three-dimensional framework structure.


Chemical context
Hydrogen bonding andinteractions are two of the principal forces which determine structure, self-assembly and recognition in some chemical and biological systems (Lehn, 1990). A variety of urea-based anion receptors of varying complexity and sophistication have been synthesised (Amendola et al., 2010). It has been shown that the efficiency of urea as a receptor subunit depends on the presence of two proximate polarised N-H fragments, capable of (i) chelating a spherical anion or (ii) donating two parallel hydrogen bonds to the O atoms of a carboxylate or of an inorganic oxoanion. A review of the biological activity of phthalimides has been published by Sharma et al. (2010) and a review of its the supramolecular chemistry by Barooah & Baruah (2007). Phthalimides and isoindolines have been shown to possess photophysical properties and have applications as colourimetric and other types of anion sensors (Griesbeck & Schieffer, 2003;Griesbeck et al., 2007Griesbeck et al., , 2010Devaraj & Kandaswamy, 2013). In our ongoing research on 1,3-dioxoisoindolines as anion receptors (Lujano, 2012), we report herein on the synthesis and crystal structure of the title ureabased anion receptor.

Figure 1
The molecular structure of the title molecule, showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. Atoms with the suffix A are generated by the symmetry operator (Àx, y, Àz + 1 2 ) and the symmetry-related water molecule is not shown.

Figure 2
A view along the b axis of the crystal packing of the title compound. Hydrogen bonds are shown as dashed lines (see Table 1 for details. Cbound H atoms have been omitted for clarity.

Figure 3
A view of the crystal packing of the title compound. The hydrogen bonds (dashed lines; see Table 1 for details) enclose R 4 4 (24) and R 3 3 (15) ring motifs.

Figure 4
Two molecules of the title compound showing the offsetinteractions involving the benzene rings of neighbouring phthalimide moieties (dashed line).

Synthesis and crystallization
Carbohydrazide (0.5 g, 5.5 mmol) and phthalic anhydride (1.64 g, 11 mmol) were dissolved in dimethyl sulfoxide (15 ml) and refluxed for 6 h at 323 K. The solvent was removed under reduced pressure in a rotatory evaporator and the pale-yellow solid residue was washed with water and dried under vacuum. The product was recrystallized from water/ethanol (30:70 v/v) to give colourless prismatic crystals suitable for X-ray diffraction analysis (m.p. 491-493 K). 1

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. 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.