1-[(Anthracen-9-yl)carbonyl]-2,7-dimethoxynaphthalene: a chain-like structure composed of face-to-face type dimeric molecular aggregates

The asymmetric unit of the title compound contains two independent molecules (A and B). In the crystal, molecules of each conformer make a face-to-face type dimeric molecular aggregate with two pairs of C—H⋯π hydrogen bonds (A) or a pair of (sp 2)C—H⋯O hydrogen bonds (B). The dimeric molecular aggregates composed of same conformers are linked to each other into a chain through π–π stacking interactions (A) or a pair of C—H⋯π hydrogen bonds (B) along the b axis. The chains are aligned along the c axis by weak van der Waals interactions or (sp 2)C—H⋯O=O hydrogen bonds, and they are alternately stacked along the a axis.


Chemical context
Compounds of coplanar aggregation of -conjugated aromatic rings have received attention from a wide range of material chemists and organic ones because of their excellent conductivity properties (Lu et al., 2010). Recently, uniquely shapedconjugated aromatic aggregation compounds have moved into the limelight as promising molecular frameworks in nanoelectronics, e.g. bucky bowls (Schmidt et al., 2013), coannulene (Yoshimoto et al., 2010) and cycloparaphenylene (Bunz et al., 2012). These compounds can be regarded as molecules of partial structure and motif of fullerene and carbon nanotubes. On the other hand, aromatic aggregate compounds bearing a non-consecutive -conjugated structure have also started to garner attention. For example, the molecular geometry of 9-arylanthracene compounds is of photochemical and photophysical interest because a coplanar spatial arrangement of the anthracene and the aryl substituent -systems is precluded due to intramolecular hindrance involving the hydrogen atoms (Becker et al., 1992). In such molecules, the -conjugation is weakened and deviations from molecular planarity are borne out in electronic absorption and emission spectra. In particular, the fluorescence spectra of non-coplanarly situated bichromophoric compounds, characterized by large Stokes shifts, are indicative of differences between the geometry of the ground state and that of the more planar emitting excited state (Becker et al., 1990). ISSN 2056-9890 The present authors have studied the synthesis and structure analysis of peri(1,8)-aroylated naphthalene compounds in which aromatic rings accumulate non-coplanarly, giving highly congested intramolecular circumstances (Okamoto & Yonezawa, 2015;Okamoto et al., 2016). As one of the categories of the accumulated -conjugated aromatic ring compounds, periaroylnaphthalene compounds have some distinguishable structural characteristics. peri-Aroylnaphthalene compounds belong to the class of poly(aromatic ring) molecules where aromatic rings are linked by ketonic carbonyl groups. Furthermore, the two aroyl groups at peri-positions of the naphthalene ring core are situated in positions very close to each other. Accordingly, a coplanar alignment of the aromatic rings in a molecule is not possible in peri-aroylnaphthalene compounds because of their highly congested molecular arrangement. On the other hand, the spatial organization around the ketonic carbonyl groups of a diaryl ketone structure is supposed to be rather loose compared to that of directly combined aromatic ring systems, as shown in the rotation barrier for an analogous compound in solution . In this regard, the expected flexibility of the aromatic ketone compound probably shows great variation in the molecular and packing structures in the crystal. Such a situation offers a good opportunity to reveal the hitherto unknown interactions that determine the structure of aromatic rings of accumulated molecules in the crystalline state. This article reports the synthesis and crystal structure of the title 1-anthroylated naphthalene compound.

Structural commentary
There are two independent molecules in the asymmetric unit of the title compound. The conformers, labeled A and B, are shown in Fig. 1. Each conformer has essentially the same noncoplanar structure, with the methoxy group adjacent to the anthroyl group being oriented to the endo side against the naphthalene ring core. The main difference between the conformers is in the orientation of the anthracene ring with respect to the naphthalene ring core. Conformer A shows a dihedral angle of 86.38 (5)  The structure of the independent molecules A and B, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level for non-H atoms. Table 1 Hydrogen-bond geometry (Å , ).

Supramolecular features
Observed non-covalent bonding interactions are summarized in Table 1. In the crystal structure, each conformer forms an inversion dimer with a face-to-face type molecular aggregate by complementary hydrogen bonds. In the dimer of conformer A, a pair of (naphthalene)C-HÁ Á Á (anthracene) interactions and another pair of (methoxy)C-HÁ Á Á (naphthalene) ones are observed (C3-H3Á Á ÁCg1 iv and C26-H26AÁ Á ÁCg2 iv ; symmetry code in Table 1; Fig. 2). The dimeric aggregates of conformers A are connected into a chain along the b axis through astacking interaction between the anthracene rings [centroid-centroid distance of 3.8198 (10) Å between the C12-C13/C18-C20/C25 and C13-C18 rings]. The chains of conformer A are aligned along the c axis by weak van der Waals interactions, forming a sheet structure parallel to the bc plane. In the dimer of conformer B, a pair of (anthracene)C-HÁ Á ÁO(methoxy) hydrogen bonds are observed (C50-H50Á Á ÁO6 iii ; Table 1 and Fig. 3). Furthermore, a pair of (naphthalene)C-HÁ Á Á(anthracene) interactions connect the dimeric aggregates into a chain along the b axis (C30-H30Á Á ÁCg3 v ; Table 1 and Fig. 3). The chains of conformer B are linked by intermolecular (anthracene)C-HÁ Á ÁO C hydrogen bonds (C49-H49Á Á ÁO4 ii ; Table 1) along the c axis, forming a sheet parallel to the bc plane. The two sheets of conformers A and B are stacked alternately along the a axis by (naphthalene)C-HÁ Á ÁO C and (anthracene)C-HÁ Á ÁO C hydrogen bonds (C46-H46Á Á ÁO1 and C7-H7Á Á ÁO4 i ; Table 1 and Figs. 4 and 5).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2 Two kinds of (sp 2 )C-HÁ Á ÁO C hydrogen bonds between conformers A and B are shown as red broken lines. [Symmetry code: (i) x, y À 1, z.]

Figure 5
The arrangement of the molecules in the crystal structure, viewed down the b axis.  Data collection: PROCESS-AUTO (Rigaku, 1998); cell refinement: PROCESS-AUTO (Rigaku, 1998); data reduction: CrystalStructure (Rigaku, 2010); program(s) used to solve structure: Il Milione (Burla et al., 2007); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPIII (Burnett & Johnson, 1996); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.31 e Å −3 Δρ min = −0.22 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.00184 (13) 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 > 2sigma(F 2 ) is used only for calculating R-factors(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.