1,5-Bis(piperidin-1-yl)-9,10-anthraquin­one

In the centrosymmetric title compound, C₂₄H₂₆N₂O₂, the piperidine ring adopts a chair conformation and is inclined at a dihedral angle of 37.5 (1)°to the anthracene ring system. In the crystal, adjacent mol­ecules are linked through C—H...π and π–π [centroid–centroid distances = 3.806 (1) Å] inter­actions, forming a layer parallel to the bc plane.

2,6-Dimethyl­phenyl acridine-9-carboxyl­ate

In the title compound, C₂₂H₁₇NO₂, the acridine ring system and the benzene ring are oriented at a dihedral angle of 37.7 (1)°. The carboxyl group is twisted at an angle of 67.7 (1)° relative to the acridine skeleton. In the crystal, mol­ecules are arranged in stacks along the b axis, with all of the acridine rings involved in multiple π–π inter­actions [centroid–centroid distances in the range 3.632 (2)–4.101 (2) Å]. The acridine moieties are parallel within the stacks, but inclined at an angle of 52.7 (1)° in adjacent stacks.

Phenyl acridine-9-carboxyl­ate

The acridine ring system and the benzene ring in the title compound, C₂₀H₁₃NO₂, are oriented at a dihedral angle of 6.4 (2)°. The carboxyl group is twisted at an angle of 83.6 (2)° relative to the acridine skeleton. The mol­ecules in the crystal are arranged in stacks along the b axis, with two of the acridine rings involved in multiple π–π inter­actions [centroid–centroid distances in the range 3.536 (2)–3.894 (2) Å]. Stacks arranged parallel are linked via C—H...π inter­actions, forming layers in the ac plane that are in contact with adjacent, inversely oriented layers via other C—H...π inter­actions, giving rise to double layers. The inversely oriented double layers inter­act dispersively. The acridine units are parallel within the parallel-oriented stacks, but inclined at an angle of 79.6 (2)° in the inversely oriented stacks.