Crystal structures of two 2,3-diethylnaphtho[2,3-g]quinoxaline-6,11-dione derivatives
Two new 5,12-disubstituted 2,3-diethylnaphtho[2,3-g]quinoxaline-6,11-dione compounds were readily synthesized from the commercial dye quinizarin. For 2,3-diethyl-5,12-dihydroxynaphtho[2,3-g]quinoxaline-6,11-dione, (II), C20H16N2O4, the molecule displays a near planar conformation and both hydroxy groups participate in intramolecular O—H...O(carbonyl) hydrogen bonds. In the crystal, π–π ring interactions [minimum ring centroid separation = 3.5493 (9) Å] form stacks of co-planar molecules down the c axis, while only minor intermolecular C—H...O interactions are present. In contrast, in 2,3-diethyl-5,12-bis(piperidin-1-yl)naphtho[2,3-g]quinoxaline-6,11-dione, (IV), C30H34N4O2, which contains two independent, but similar, molecules in the asymmetric unit, the polycyclic cores have a significant twist, with dihedral angles of 29.79 (6) and 29.31 (7)° between the terminal rings and only minor intermolecular C—H...O hydrogen-bonding interactions are present. Electron density associated with additional solvent molecules disordered about a fourfold axis was accounted for using the SQUEEZE procedure in PLATON [Spek (2015). Acta Cryst. C71, 9–18].