Crystal structure of 7-hydroxy-8-[(4-methylpiperazin-1-yl)methyl]-2H-chromen-2-one

There is an intramolecular O—H⋯N hydrogen bond forming an S(6) ring motif in the title compound. In the crystal, molecules are linked by C—H⋯O hydrogen bonds with a C(4) chain motif, and also by C—H⋯π interactions. The chains are linked by π–π interactions, forming a sheet parallel to the bc plane.


Chemical context
Coumarin (2H-chromen-2-one) derivatives have wide applications in diverse areas such as pharmaceuticals (Neyts et al., 2009), dyes (Hara et al., 2003) and liquid crystal (Schadt et al., 1996). Since piperazine is a heterocyclic and aliphatic diamine, having a flexible structure and a high solubility not only in organic solvents but also in water, its derivatives form complexes with various metal ions in chair and boat conformations. For example, the piperazine ring in a dinuclear zinc(II) complex with a piperazine-based Schiff base adopts a chair form, whereas that in a mononuclear cobalt(III) complex with the same ligand is in a boat form (Cretu et al., 2015). Moreover, the piperazine ring has recently been utilized as a proton-recognition site in pH-sensitive fluorescent probes (Lee et al., 2014) and a linker bridging two chromophores in fluorescent ion-sensors (Srivastava et al., 2014;Jiang et al., 2011). We are attempting to develop water-soluble chemosensors based on coumarin, and report here the molecular and crystal structure of the title compound.

Synthesis and crystallization
The title compound was prepared by modification of the reported procedure (Mazzei et al., 2008). 1-Methylpiperazine (0.64 g, 6.4 mmol) and formaldehyde (37% aqueous solution 0.64 mL, 0.64 mmol) in 50 ml of acetonitrile was stirred for 30 min at 333 K. To the product obtained was added 7-hydroxycoumarin (1.04 g, 0.64 mmol), and the mixture was heated for 3 h at 338 K. After the completion of the reaction, as indicated by TLC, the solvent was removed under vacuum. The residue was suspended in water and extracted with chloroform, and the extract was washed with a saturated sodium chloride aqueous solution. The organic phase was separated, dried with anhydrous sodium sulfate, and the solvent was removed under vacuum to yield a yellow product. The product was recrystallized from acetonitrile solution to obtained colorless crystals of the title compound (yield: 76% The molecular structure of the title compound, showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. The intramolecular O-HÁ Á ÁN hydrogen bond is shown as a dashed line. Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A view along the a axis of the crystal packing of the title compound. The hydrogen bonds and C-HÁ Á Á interactions are shown as dashed lines. H atoms not involved in these interactions have been omitted for clarity.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The hydroxy H atom was located in a difference Fourier map and freely refined. The C-bound H atoms were positioned geometrically and refined using a riding model: C-H = 0.93-0.97 Å with U iso (H) = 1.2U eq (C).

7-Hydroxy-8-[(4-methylpiperazin-1-yl)methyl]-2H-chromen-2-one
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. Refinement. Refinement was performed using all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F 2 . R-factor (gt) are based on F. The threshold expression of F 2 > 2.0 sigma(F 2 ) is used only for calculating Rfactor (gt).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq O1 0.30930 (10