Importance of O•••N interaction between nitro groups in crystals

Perpendicular arrangement of two nitro groups of adjacent molecules was found in 104 structural fragments deposited in the Cambridge Structural Database. In the most cases, this non-hydrogen bonding O-NO2 center dot center dot center dot pi(N)NO2 interaction is shorter than 3 angstrom. Ab initio calculations of the interaction energy indicates the attractive nature of this interaction, comparable to the E-int of C-H center dot center dot center dot O.