Dimethyl and diethyl esters of 5,6-bis(pyridin-2-yl)- pyrazine-2,3-dicarboxylic acid: a comparison

In dimethyl 5,6-bis­(pyridin-2-yl)pyrazine-2,3-di­carboxyl­ate, C18H14N4O4, (I), and diethyl 5,6-bis­(pyridin-2-yl)pyrazine-2,3-di­carboxyl­ate, C20H18N4O4, (II), the dimethyl and diethyl esters of 5,6-bis­(pyridin-2-yl)pyrazine-2,3-di­carb­oxy­lic acid, the orientation of the two pyridine rings differ. In (I), pyridine ring B is inclined to pyrazine ring A by 44.8 (2)° and the pyridine and pyrazine N atoms are trans to one another, while pyridine ring C is inclined to the pyrazine ring by 50.3 (2)°, with the pyridine and pyrazine N atoms cis to one another. In compound (II), the diethyl ester, which possesses twofold rotation symmetry, the pyridine ring is inclined to the pyrazine ring by 40.7 (1)°, with the pyridine and pyrazine N atoms trans to one another. In the crystal of (I), mol­ecules are linked by C—H⋯N hydrogen bonds, forming chains along [001]. The chains are linked by C—H⋯π inter­actions, forming a three-dimensional structure. In the crystal of (II), mol­ecules are linked via C—H⋯O hydrogen bonds, forming a three-dimensional framework. There are C—H⋯π inter­actions present within the framework.