Two new 5,12-disubstituted 2,3-di-ethyl-naphtho-[2,3-g]quinoxaline-6,11-dione compounds were readily synthesized from the commercial dye quinizarin. For 2,3-diethyl-5,12-di-hydroxy-naphtho-[2,3-g]quinoxaline-6,11-dione, (II), C20H16N2O4, the mol-ecule displays a near planar conformation and both hy-droxy groups participate in intra-molecular O-H⋯O(carbon-yl) hydrogen bonds. In the crystal, π-π ring inter-actions [minimum ring centroid separation = 3.5493 (9) Å] form stacks of co-planar mol-ecules down the c axis, while only minor inter-molecular C-H⋯O inter-actions 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, mol-ecules 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 inter-molecular C-H⋯O hydrogen-bonding inter-actions are present. Electron density associated with additional solvent mol-ecules disordered about a fourfold axis was accounted for using the SQUEEZE procedure in PLATON [Spek (2015 ▸). Acta Cryst. C71, 9-18].
Keywords: crystal structure; hydrogen bonding; naphthoquinoxaline-6,11-dione; π–π interaction.