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), C(20)H(16)N(2)O(4), 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), C(30)H(34)N(4)O(2), 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].