Crystal structure of 2-(morpholino)ethylammonium picrate monohydrate

The title compound was synthesized via slow evaporation of an aqueous solution of picric acid with the substituted morpholine base and crystallized with one cation (C6H15N2O)+, one anion (C6H2N3O7)− and a water molecule in the asymmetric unit. The morpholine ring in the cation adopts a chair conformation. The structure is stabilized by C–H⋯O, O—H⋯O, O—H⋯N and N—H⋯O hydrogen-bonding interactions and π–π stacking. The intermolecular interactions of the synthesized compound were quantified by Hirshfeld surface analysis.


Chemical context
Morpholine complex materials are widely used in biomedical applications as this moiety serves as an important lysosometargeting group. Its applications include use in the synthesis of lysosome-targetable fluorescent probes for hydrogen sulfide imaging in living cells. Morpholine can be used as a ligand in metal complexes. It is also a component of protective coatings on fresh fruits and is used as an emulsifier in the preparation of pharmaceuticals and cosmetic products (Kuchowicz & Rydzyń ski, 1998). Picric acid forms stable picrates with various organic molecules through bonding or ionic bonding. It is also a well-established material for non-linear optical (NLO) substances, which crystallize in the non-centrosymmetric space group Pca2 1 (Yamaguchi et al., 1988). Compounds of the morpholine family such as 4-(2-chloroethyl)morpholinium picrate (Kant et al., 2009), 4-(4-nitrophenyl)morpholine (Wang et al., 2012), morpholinium picrate (Vembu & Fronczek, 2009) can be used in drug design. The phenolic group of the picrate anion might favour the formation of hydrogen-bonding interactions to increase the molecular hyperpolarizability and NLO effects (Takayanagi et al., 1996). Organic molecules have attracted great attention because of their ability to combine low cost and ease of processing in the assembly of optical devices. In this context, the present investigation reports the synthesis, crystal structure, Hirshfeld surface, IR and NMR analyses of 2-(morpholinyl)ethylammonium picrate monohydrate.

Figure 1
Molecular diagram of the title compound viewed down along a* axis in the unit cell. and two picrate anions and involves the phenolic oxygen anion and the para nitro group (Fig. 5). Furthermore, the picrate anions are coplanar, and are involved in two differentstacking interactions with perpendicular distances between the C1-C6 rings of 3.3532 (6) and 3.5533 (6) Å , slippage of 1.393 and 1.902 Å , and CgÁ Á ÁCg distances of 3.6311 (18) and 4.0303 (19) Å , respectively, for the rings related by symmetry operations 1 À x, 1 À y, 2 À z and 2 À x, 1 À y, 2 À z. Finally, a centrosymmetric twelve-membered ring [(picrate)O À Á Á ÁH-N-HÁ Á ÁO-H] 2 with a third order graph set R 4 6 (12) involves two of each of the three different species present in the crystal (Fig. 6).
Analysis of the Hirshfeld surface and the associated twodimensional fingerprint plot for 2-(morpholinyl)ethylammonium picrate monohydrate was performed with Crys-talExplorer 21.5 (Spackman et al., 2021). The normalized contact distance (d norm ) Hirshfeld surface of the title compound mapped over the limits À0.6471 to 1.3714 a.u. with close contacts to neighboring molecules is shown in Fig. 7. The contacts with distances equal to the sum of the van der Waals radii are indicated in white and the contacts with distances shorter than and longer than van der Waals radii are represented as red and blue, respectively (Venkatesan et al., 2016).   Three-dimensional supramolecular architecture of the title compound viewed down the a axis.

Synthesis and crystallization
2-(Morpholinyl)ethylammonium picrate monohydrate was synthesized by mixing one mole of 4-(2-ammonioethyl)morpholine and one mole of picric acid in double-distilled water at about 303 K. The solution was then allowed to evaporate at room temperature, which yielded yellow platelike crystals of 2-(morpholinyl)ethylammonium picrate monohydrate. The reaction scheme is shown in Fig. 9 The Hirshfeld surface of the title compound mapped over d norm , showing the closest molecules.  (t, 2H, -CH 2 -NH 3 + ). A suitable single crystal of 2-(morpholinyl)ethylammonium picrate monohydrate was selected for X-ray diffraction studies.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The C-bound H atoms were positioned geometrically (C-H = 0.93 for anion and 0.97 Å for cation) and refined using an isotropic approximation, with U iso (H) = 1.2 U eq (C). The acidic protons were localized from the residual electron-density map and refined with distance restraints (0.82 Å for O-H and 0.86 Å for N-H) and U iso (H) = 1.2U eq (N) and 1.5U eq (O). Reaction scheme for the title compound.  (Farrugia, 2012) and Mercury (Macrae et al., 2020); software used to prepare material for publication: SHELXL2018/2 (Sheldrick, 2015b).

2-(Morpholin-4-yl)ethan-1-aminium 2,4,6-trinitrobenzen-1-olate monohydrate
Crystal data 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.