3′,6′-Bis(ethylamino)-2-[(2-hydroxyethyl)amino]-2′,7′-dimethylspiro[isoindoline-1,9′-xanthen]-3-one

In the title compound, C28H32N4O3, the dihedral angle between the planes of the xanthene ring system and the spirolactam ring is 85.99 (3)°. Molecules are linked by intermolecular O—H⋯O and N—H⋯O hydrogen-bonding interactions.


Related literature
Data collection: APEX2 (Bruker 2005); cell refinement: APEX2; data reduction: APEX2; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL. Comment Among many fluorescent compounds, rhodamine dyes are known to have excellent photophysical properties, (Lakowicz, 2006) and they are one of the most widely used fluorophores for labeling and sensing biomolecules (Ko et al., 2006;Wu et al., 2007). There are a few single-crystal reports about rhodamine derivatives bearing a lactam moiety (Wu et al., 2007;Zhang et al., 2008). Detailed information on their molecular and crystal structures is necessary to understand their photophysical and photochemical properties.
In agreement with other reported models, (Wu et al., 2007) the main skeleton of the title molecule is formed by the xanthene ring and the spirolactam-ring. As shown in Figure 1, the atoms of the xanthene ring and spirolactam-rings are both nearly planar and are almost perpendicular to each other. R.m.s. deviations from planarity are 0.028 (1) Å for the xanthene ring and 0.033 (0) Å for the spirolactam-ring, respectively. The dihedral angle between the planes of the xanthene ring and the spirolactam ring is 85.99 (3)°.
Analysis of the crystal packing of the title molecule (Figure 2), shows that the molecules of the title compound are connected via intermolecular N3-H3A···O3 and O3-H3C···O1 hydrogen bonds (Table 1). The oxygen atom on the spirolactam-ring acts as acceptor for an O-H···O hydrogen bond from a neighboring molecule. The oxygen atom of the hydroxyl group in turn acts as acceptor for a N-H···O hydrogen bond from again another molecule, thus forming a chain with two consecutive hydrogen bonds of the type N-H···O-H···O═C. Via these hydrogen bonds molecules are connected into double stranded chains as shown in Figure 2.

Experimental
Sodium borohydride (15.2 mg, 0.4 mmol) was slowly added to a solution of 3',6'-bis(ethylamino)-2',7'-dimethyl-2-(2oxoethylideneamino)spiro [isoindoline-1,9'-xanthen]-3-one (132 mg, 0.3 mmol) in ethanol (20 ml). The reaction mixture was stirred for 2 h at room temperature and the solvent was totally removed under reduced pressure. The crude product was dissolved in CH 2 Cl 2 (20 ml) and 3 ml of an aqueous solution of K 2 CO 3 was added. The organic layer was separated and dried over MgSO 4 . After filtration, the solvent was removed under reduced pressure. The residue was placed on a silica gel column (200-300 mesh). The column was eluted with a mixture (2:1, v/v) of petroleum ether /ethyl acetate, to give 131.5 mg of the title compound (93%). Crystals were grown by dissolving the compound in CH 2 Cl 2 and slowly diffusing n-hexane into the solution.

Refinement
Geometrically constrained hydrogen atoms were placed in calculated positions and refined using the riding model (C-H = 0.93-0.96 Å, and O-H = 0.82 Å), with U iso (H) = 1.2U eq (C) or 1.5U eq (methyl C, O). All amine hydrogen atoms were supplementary materials sup-2 located in difference density Fourier maps, were introduced with a distance restraint (N-H = 0.89 (2) Å) and refined freely.
The isotropic displacement parameter was set to U iso (H) = 1.2U eq (N). Fig. 1. The structure of the title compound, showing the atom-numbering scheme and displacement ellipsoids at the 30% probability level. H atoms are represented as small spheres of arbitrary radius.

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 > 2σ(F 2 ) is used only for calculating Rfactors(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.