Crystal structure of (E)-9-({[4-(diethylamino)phenyl]imino}methyl)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol

In the title compound, the hydroxy group forms a intramolecular hydrogen bond to the imine N atom and generates an S(6) ring motif. The conformation about the C=N bond is E, and the aromatic ring of the julolidine moiety is inclined to the benzene ring by 3.74 (14)°.

The title compound, C 23 H 29 N 3 O, was synthesized from the condensation reaction of 8-hydroxyjulolidine-9-carbaldehyde and N,N-diethyl-p-phenylenediamine. The hydroxy group forms a intramolecular hydrogen bond to the imine N atom and generates an S(6) ring motif. The conformation about the C N bond is E, and the aromatic ring of the julolidine moiety is inclined to the benzene ring by 3.74 (14) . One of the fused non-aromatic rings of the julolidine moiety adopts an envelope conformation and the other has a screw-boat conformation. In the crystal, molecules are linked by C-HÁ Á Á interactions involving the aromatic julolidine ring, forming slabs parallel to the bc plane. The tricyclic fragment of the julolidine ring and the azomethine C N bond are disordered over two sets of sites with a refined occupancy ratio of 0.773 (3):0.227 (3).

Chemical context
8-Hydroxyjulolidine-9-carboxaldehyde is a well-known chromophore used in fluorescence chemosensors, and chemosensors with the julolidine moiety are usually soluble in aqueous solutions (Narayanaswamy & Govindaraju, 2012;Maity et al., 2011;Na et al., 2013;Noh et al., 2013). Compounds containing a julolidine group exhibit chromogenic naked-eye detection of copper, zinc, iron and aluminium ions as well as fluoride ions (Choi et al., 2015;Wang et al., 2013a,b;Kim et al., 2015;Jo et al., 2015). There are many reports in the literature on 8-hydroxyjulolidine-9-carboxaldehyde-based Schiff bases and their application as metal sensors (Park et al., 2014;Lee et al., 2014;Kim et al., 2016). Julolidine dyes exhibit excited state intramolecular proton transfer (Nano et al., 2015), and julolidine ring-containing compounds are also used as fluorescent probes for the measurement of cell membrane viscosity. ISSN 2056-9890 The present work is a part of an ongoing structural study of Schiff bases and their utilization in the synthesis of new organic and polynuclear coordination compounds (Faizi & Sen, 2014;Faizi et al., 2015Faizi et al., , 2016a. We report herein on the synthesis and crystal structure of a new julolidine derivative.

Supramolecular features
In the crystal, molecules are linked by C-HÁ Á Á interactions (Table 1), involving the aromatic julolidine ring, forming layers lying parallel to the bc plane, as illustrated in Fig. 2.

Database survey
There are very few examples of similar compounds in the literature and, to the best of our knowledge, the new fluorescent chemosensor for the selective detection of Zn 2+ in aqueous solution, mentioned in the Chemical context section (Choi et al., 2015), has not been characterized crystallographically. A search of the Cambridge Structural Database (CSD, Version 5.37, update May 2016; Groom et al., 2016) gave 121 hits for the julolidine moiety. Of these, six have an OH group in position 8, and four also have a C N group in position 1. Of the latter, one compound, viz. 9-{[(4-chlorophenyl)imino]methyl}-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol (CSD refcode: IGALUZ; The molecular structure of the title compound, showing the atom labelling. Displacement ellipsoids are drawn at the 40% probability level. The intramolecular O-HÁ Á ÁN hydrogen bond is shown as a dashed line (see Table 1). The minor component of the disordered fragment has been omitted for clarity. Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A view along the b axis of the crystal packing of the title compound. The C-HÁ Á Á interactions are shown as dashed lines (see Table 1) and the minor component of the disordered fragment has been omitted for clarity. Kantar et al., 2013), resembles the title compound and also exists in the phenol-imine form with an intramolecular O-HÁ Á ÁN hydrogen bond.

Synthesis and crystallization
An ethanolic solution of 8-hydroxyjulolidine-9-carboxaldehyde (100 mg, 0.46 mmol) was added to N,N-diethyl-pphenylenediamine (75 mg, 0.46 mmol) in absolute ethanol (3 ml). Two drops of HCl were added to the reaction solution and it was stirred for 30 min at room temperature. The resulting yellow precipitate was recovered by filtration, washed several times with a small portions of ice EtOH and then with diethyl ether to give 130 mg (78%) of the title compound. Colourless block-like crystals, suitable for X-ray diffraction analysis, were obtained within three days by slow evaporation of a solution in methanol.

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.

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