Crystal structure, Hirshfeld surface and frontier molecular orbital analysis of 10-benzyl-9-(3-ethoxy-4-hydroxyphenyl)-3,3,6,6-tetramethyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione

In the acridinedione moiety of the title compound, the central ring adopts a flattened-boat conformation, whereas the cyclohexenone rings adopt envelope conformations.

In the fused ring system of the title compound, C 32 H 37 NO 4 , the central dihydropyridine ring adopts a flattened boat conformation, the mean and maximum deviations of the dihydropyridine ring being 0.1429 (2) and 0.2621 (2) Å , respectively. The two cyclohexenone rings adopt envelope conformations with the tetrasubstituted C atoms as flap atoms. The benzene and phenyl rings form dihedral angles of 85.81 (2) and 88.90 (2) , respectively, with the mean plane of the dihydropyridine ring. In the crystal, molecules are linked via an O-HÁ Á ÁO hydrogen bond, forming a helical chain along the b-axis direction. A Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from HÁ Á ÁH (65.2%), OÁ Á ÁH/HÁ Á ÁO (18.8%) and CÁ Á ÁH/HÁ Á ÁC (13.9%) contacts. Quantum chemical calculations for the frontier molecular orbitals were undertake to determine the chemical reactivity of the title compound.

Chemical context
The crystal structures of acridinedione derivatives are expected to provide useful information on the molecular conformation, which has a direct relationship to biological activity. Acridine derivatives (Nasim & Brychcy, 1979;Thull & Testa, 1994;Má ndi et al., 1994), well known as therapeutic agents, are important because of their range of applications in the dye and pharmaceutical industries. Certain acridinedione derivatives exhibit good inhibition against the pathogen vibro isolate-I (Josephrajan et al., 2005), display anti-cancer (Sondhi et al., 2004;Sugaya et al., 1994;Kimura et al., 1993) and antitumour (Talacki et al., 1974) activity and act as K-channel openers (Li et al., 1996). ISSN 2056-9890

Frontier molecular orbital analysis
The chemical reactivity of the title compound was studied by frontier molecular orbital analysis. For the calculation, the starting structural geometry was taken from the refined experimental structure obtained from X-ray diffraction data. The energy levels for the compound were computed using the DFT-B3LYP/6-311G++(d,p) level of theory as implemented in Gaussian09W (Frisch et al., 2010). The calculated frontier molecular orbitals, HOMO-1, HOMO, LUMO and LUMO+1, are shown in Fig. 2. The energies of HOMO-1, HOMO, LUMO and LUMO+1 were calculated to be À5.8632, À5.5078, À1.8307 and À1.0100 eV, respectively, and the energy required to excite one electron from HOMO to LUMO and from HOMO-1 to LUMO+1 are 3.6671 and 4.8532 eV, respectively. The chemical potential, chemical hardness, chemical softness and electrophilicity index of the title molecule are listed in Table 1. Parr et al. (1999) have proposed the electrophilicity index as a quantitative measure of the energy lowering due to the maximal electron flow between donor and acceptor orbitals. The molecular structure of the title compound, showing the atomnumbering scheme. Displacement ellipsoids are drawn at the 50% probability level. Only one component of the disordered ethyl group is shown.

Figure 2
The frontier molecular orbitals of the title compound, showing positive (red) and negative (green) regions.
shows the global electrophilic nature of the molecule. Based on the wide band gap and its chemical hardness value of 1.8335 eV, the title molecule seems to be hard.

Supramolecular features and Hirshfeld surface analysis
In the crystal, the molecules are linked via O1-H1Á Á ÁO3 i hydrogen bonds, forming helical chains along the b-axis direction ( Table 2). The chains are further connected by weak C26-H26BÁ Á ÁO3 ii hydrogen bonds, forming a sheet structure parallel to (101) (Fig. 3).

Database survey
The bond lengths in the title compound, are close to those reported for similar compounds, for example, 10-benzyl-9- Hirshfeld surfaces of the title compound mapped over d norm . Table 2 Hydrogen-bond geometry (Å , ).

Figure 3
A packing diagram of the title compound, showing the O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds (dashed lines).

Figure 5
Two-dimensional fingerprint plots for the title compound.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. C-bound H atoms were fixed in calculated positions (C-H = 0.93-0.98 Å ) and allowed to ride with respect to the parent atoms with U iso (H) = 1.2 or 1.5U eq (C). The O-bound H atom was refined freely. For the disordered ethyl group, bond distance and displacement restraints (DFIX, SADI and SIMU) were applied.

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