Crystal structure of (E)-1(anthracen-9-ylmethylidene)[2-(morpholin-4-yl)ethyl]amine

The title compound, C21H22N2O, crystallizes with two independent molecules in the asymmetric unit. In both molecules, the anthracene ring systems are almost planar, with maximum deviations of 0.071 (8) and 0.028 (7) Å, and make dihedral angles of 73.4 (2) and 73.3 (2)° with the least-squares planes formed by the four C atoms of the morpholine rings, which adopt a chair conformation. An intramolecular C—H⋯π interaction occurs. In the crystal, the packing is stabilized by weak C—H⋯O hydrogen bonds, which connect pairs of molecules into parallel to the c axis, and C—H⋯π interactions.


S1. Comment
Schiff bases are usually formed by the condensation of a primary amine with an active carbonyl. They are used as pigments and dyes, catalysts, intermediates in organic synthesis, and as polymer stabilisers (Dhar & Taploo, 1982). Schiff bases form an important class of organic compounds with a wide variety of biological properties (Witkop & Ramachandran, 1964). Many studies have been reported regarding the biological activities of Schiff bases, including their anticancer (Solomon & Lowery, 1993), antibacterial (Gerdemann et al., 2002, antifungal, and herbicidal activities. Therefore, Schiff base (I) was synthesized and its X-ray structure is reported here.
The (C5-C6-N2-C7 and C26-C27-N4-C28) torsion angles of the bridge -C-C-N-C-groups is -103.0 (7) ° for molecule A and 101.1 (6)° for molecule B. The bond lengths and angles in both molecules (A, B) may be regarded as normal, and they are similar with each other.
In the crystal structure, weak C-H···O hydrogen bonds (Table 1, Fig. 2) which connect pairs of molecules into parallel to the c axis, further stabilize the packing supported by C-H···π interactions (Table 1).

S3. Refinement
H atoms were located geometrically with C-H = 0.93 and 0.97 Å, and refined using a riding model with U iso (H) = 1.2U eq (C) for the aromatic and methylene H atoms. The crystal quality and data was not good enough so a sufficient fraction of the unique data is above the 2 sigma level. A total of 749 estimated Friedel pairs were merged before refinement and not used as independent data. The Flack parameter was found to be meaningless and was omitted.

Figure 1
View of the two molecules (A, B) of the title compound in the asymmetric unit with the atom-labelling scheme and 30% probability displacement ellipsoids.

Figure 2
Packing diagram of the title compound viewed down the a axis. Hydrogen bonds are indicated by broken lines. H atoms not participating in hydrogen bonding have been omitted for clarity. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.12 e Å −3 Δρ min = −0.10 e Å −3 Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses 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 observed criterion of F 2 > σ(F 2 ) is used only for calculating -R-factor-obs 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.