2-[(5-Chloro-2-hydroxybenzylidene)amino]-3′,6′-bis(diethylamino)spiro[isoindoline-1,9′-xanthen]-3-one

The title compound, C35H35ClN4O3, resulted from a spirolactam ring closure of rhodamine B dye. The xanthene ring system is approximately planar [r.m.s. deviation = 0.050 (9) Å for the xanthene ring]. The dihedral angles formed by the spirolactam and 5-chloro-2-hydroxybenzene rings with the xanthene ring system are 87.9 (7) and 79.1 (7)°, respectively.

The title compound, C 35 H 35 ClN 4 O 3 , resulted from a spirolactam ring closure of rhodamine B dye. The xanthene ring system is approximately planar [r.m.s. deviation = 0.050 (9) Å for the xanthene ring]. The dihedral angles formed by the spirolactam and 5-chloro-2-hydroxybenzene rings with the xanthene ring system are 87.9 (7) and 79.1 (7) , respectively. Comment Among many fluorescent compounds, rhodamine dyes are known to have excellent photophysical properties, and they are one of the most widely used fluorophores for labeling and sensing biomolecules. There are a few single-crystal reports on rhodamine derivatives bearing a lactam moiety (Xu et al., 2009;Kwon et al., 2005;Wu et al., 2007;Zhang et al., 2008;Tian et al., 2008;Deng et al., 2009). Detailed information on their molecular and crystal structures is necessary to understand their photophysical and photochemical properties.

Related literature
In agreement with other reported models, (Xu et al., 2009;Wu et al., 2007;Zhang et al., 2008;Tian et al., 2008) the main skeleton of the molecule is formed by the xanthene ring and the spirolactam-ring. As shown in Figure 1, the atoms of the xanthene ring or the spirolactam-ring are both nearly planar and are almost perpendicular to each other. The dihedral angle between the xanthene and the spirolactam ring fragment mean planes is 87.9 (7)°. The dihedral angle between the xanthene mean plane and the 2-hydroxy-5-cholorobenzene ring is 79.1 (7)°.

Experimental
A portion of rhodamine B hydrazide (0.46 g, 1 mmol) and 2-hydroxy-5-chlorobenzaldehyde (0.17 g, 1.1 mmol) were mixed in 20 ml ethanol to which three drops acetic acid was added. The reaction solution was refluxed for 3 hours under N 2 atmosphere, the precipatate was separated and washed by ethanol to give 0.30 g of the title compound in 50% yield. Single crystals suitable for X-ray measurements were obtained from the mother liquid by slow solvent evaporation at room temperatures.

Refinement
The H atoms attached to C, N and O atoms were placed in geometrically calculated positions (C-H = 0.93-0.97 Å and O-H = 0.82 Å) and refined as riding, with U iso (H) = 1.2U eq (C, N) or 1.5U eq (methyl C, O). Fig. 1

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 > σ(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.