Dimorphism of 2,3,5,6‐tetraphenylpyrazine

Two forms of 2,3,5, 6-tetraphenylpyrazine (TPP), C 28 H 20 N 2 , have been crystallized. The first variety (α) is primitive monoclinic (P2 1 /c), in which the TPP molecule is centrosymmetric. The second variety (β) is C-face-centred monoclinic (C2/c) with two symmetry-independent molecules having binary axis symmetry, where in one of the molecules, the binary axis passes through the two N atoms of the pyrazine ring, while in the second molecule, the binary axis passes through the midpoints of the two C-C bonds of the pyrazine ring. In these two compounds, the phenyl rings are differently disposed, showing a wing-like conformation in the α form and a propeller-like conformation for the two molecules in the β form. The rotations of the phenyl rings, given by the dihedral angles between the pyrazine rings and the phenyl rings, are in the range 37.56 (8)-49.72 (8)°.