N,N′-Dimethyl-pyrazinediium bis-(tetra-fluoro-borate) and N,N′-diethyl-pyrazinediium bis-(tetra-fluoro-borate): New examples of anion-π triads

Crystallization of N,N′-dimethyl-pyrazinediium bis-(tetra-fluoro- borate), C6H10N2 ²⁺·2BF4 ^-, (I), and N,N′-diethyl-pyrazinediium bis-(tetra-fluoro-borate), C8H14N2 ²⁺·2BF4 ^-, (II), from dried acetonitrile under argon protection has permitted their single-crystal studies. In both crystal structures, the pyra-zine-diium dications are located about an inversion center (located at the ring center) and each pyrazinediium aromatic ring is π-bonded to two centrosymmetrically related BF4 ^- anions. Strong anion-π inter-actions, as well as weak C - H⋯F hydrogen bonds, between BF4 ^- and pyrazinediium ions are present in both salts.