N,N'-dimethylpyrazinediium bis(tetrafluoroborate) and N,N'-diethylpyrazinediium bis(tetrafluoroborate): new examples of anion-pi triads.

Crystallization of N,N'-dimethylpyrazinediium bis(tetrafluoroborate), C(6)H(10)N(2)(2+).2BF(4)(-), (I), and N,N'-diethylpyrazinediium bis(tetrafluoroborate), C(8)H(14)N(2)(2+).2BF(4)(-), (II), from dried acetonitrile under argon protection has permitted their single-crystal studies. In both crystal structures, the pyrazinediium dications are located about an inversion center (located at the ring center) and each pyrazinediium aromatic ring is pi-bonded to two centrosymmetrically related BF(4)(-) anions. Strong anion-pi interactions, as well as weak C-H...F hydrogen bonds, between BF(4)(-) and pyrazinediium ions are present in both salts.