A competition between O⋯N and O⋯C through space interactions in the crystal structures of 3,3′-dinitro-2,2′-bipyridine N-oxides and N,N′-dioxides

Abstract

The crystal structures of a series of 3,3′-dinitro-2,2′-bipyridine N-oxides and N,N′-dioxides consistently show 1,5 interactions between nitro oxygen atoms and aromatic carbon atoms ((ON)O⋯C: 2.623(2)–2.839(2) Å) while there are also 1,6 interactions between N-oxide oxygen atoms and nitro nitrogen atoms in most cases (O⋯N(O₂): 2.737(2)–2.874(3) Å). The O⋯C interactions appears to be a common feature in ortho-nitro-biphenyl systems, and there is some evidence that the effect is cooperative when there are ortho nitro groups on both rings. The O⋯N interactions are considerably longer than the corresponding 1,5 O⋯N interaction measured here in 8-nitroquinoline-1-oxide [O⋯N(O₂): 2.5418(17) Å], which in turn is longer than the corresponding O⋯N interaction in the corresponding 8-diazonium-1-oxide.