Crystal structure of N-[2-(cyclohexylsulfanyl)ethyl]quinolinic acid imide

In the crystal of the title compound, C—H⋯O hydrogen bonds and C—O⋯π interactions form a two-dimensional network lying parallel to the ab plane.


Chemical context
Quinolinic anhydrides have been used extensively as versatile intermediates in the synthesis of various heterocyclic systems, such as aphthyridines, nicotinamides and isotonic derivatives. Recently, they have been exploited in antiviral, dementia, anti-allergy and antitumor targets (Metobo et al., 2013). In addition, it is expected that various metal complexes may be formed because they are composed of N/S-donor atoms. In particular, our group reported copper(I) coordination polymers with N/S-donor-atom ligands, which showed their various luminescence and reversible/irreversible structural transformations (Jeon et al., 2014;Cho et al., 2015). As part of our ongoing studies in this area, we designed and synthesized a new N/S-donor ligand, namely N-[2-(cyclohexylsulfanyl)ethyl]quinolinic acid imide, which was prepared from the reaction of quinolinic anhydride with 2-(cyclohexylsulfanyl)ethylamine. Herein, we report its crystal structure.

Structural commentary
The crystal structure of the title compound is shown in Fig. 1. The cyclohexyl ring adopts a chair conformation, with the exocyclic C-S bond in an equatorial orientation; the dihedral angle between the mean plane (r.m.s. deviation = 0.2317 Å ) of ISSN 2056-9890 the cyclohexyl ring and the quinolinic acid imide ring is 25.43 (11) . All bond lengths and angles are normal and comparable to those observed in similar crystal structures (Garduñ o-Beltrá n et al., 2009;Inoue et al., 2009).

Theoretical calculations
To support the experimental data based on the diffraction study, computational calculations on the N-[2-(cyclohexylsulfanyl)ethyl]quinolinic acid imide molecule were performed using the GAUSSIAN09 software package (Frisch et al., 2009). Full geometry optimizations were calculated at the DFT level of theory using a basis set of 6-311++G(d,p). The optimized parameters, such as bond lengths and angles, are in generally good agreement (the largest bond-length deviation is less than 0.03 Å ) with the experimental crystallographic data ( Table 2). The calculated and experimental torsion angles for N2-C8-C9-S1 (C8-C9-S1-C10) are 53.64 (65.80) and 64.2 (3) [97.4 (2) ], respectively. The calculated and experimental dihedral angle between the ring systems were 25.34 and 25.43 (11) , respectively. However, several relatively large differences between the experimental and theoretical data (see Table 2) may be due to the packing effects induced by the intermolecular interactions in the crystal.

Synthesis and crystallization
A mixture of quinolinic anhydride (0.67 g, 5.0 mmol) and 2-(cyclohexylsulfanyl)ethylamine (0.83 g, 5.3 mmol) in toluene (15 ml) was heated at 433 K with stirring for 8 h. The crude product was extracted with dichloromethane. The dichloromethane layer was dried with anhydrous Na 2 SO 4 and  Table 1 Hydrogen-bond geometry (Å , ).

Figure 1
The molecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level.

6-[2-(Cyclohexylsulfanyl)ethyl]-5H-pyrrolo[3,4-b]pyridine-5,7(6H)-dione
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.