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)degrees 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)degrees, 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) degrees, with the pyridine and pyrazine N atoms trans to one another. In the crystal of (I), molecules are linked by C-H center dot center dot center dot N hydrogen bonds, forming chains along [ 001]. The chains are linked by C-H center dot center dot center dot pi interactions, forming a three-dimensional structure. In the crystal of (II), molecules are linked via C-H center dot center dot center dot O hydrogen bonds, forming a threedimensional framework. There are C-H center dot center dot center dot pi interactions present within the framework.