A competition between O...N and O...C through space interactions in the crystal structures of 3,39-dinitro-2,29-bipyridine N-oxides and N,N9-dioxides{

The crystal structures of a series of 3,39-dinitro-2,29-bipyridine N-oxides and N,N9-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.