organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
In sharp contrast, the NÐOÁ Á ÁN interaction of atom O2
with the neighbouring nitro group is surprisingly strong. Thus,
the intermolecular distance between atoms O2 and N2i is
1
1
Ê
ISSN 0108-2701
2.869 (2) A [symmetry code: (i) x + 2, 2 y, z]. Such a short
intermolecular NÁ Á ÁO distance is very rare for aromatic nitro
compounds and only the extremely electron-poor superacid
N,N-dipicrylamine, DPA, and some of its derivatives exhibit
p-Nitrophenyl isocyanide
Â
similarly short intermolecular NÁ Á ÁO contacts (Wozniak et al.,
1994, 1997; Szumma et al., 2000). Indeed, only the NÁ Á ÁO
Matthias Zeller and Allen D. Hunter*
Ê
distance of 2.826 A observed for DPA itself is shorter than
Department of Chemistry, Youngstown State University, One University Plaza,
Youngstown, OH 44555-3663, USA
Â
that observed for (I) (Wozniak et al., 1994).
DPA has been analyzed in detail, both by a charge-density
Correspondence e-mail: adhunter@ysu.edu
study (Platts et al., 1995) and by computational methods using
Â
HNO2 and FNO2 as model compounds (Wozniak et al., 2002).
Received 6 February 2004
Accepted 25 March 2004
Online 11 May 2004
Both studies indicate that these types of bonds are mainly
dispersive van der Waals-type interactions. Electrostatic
stabilization seems to play only a minor role. The calculated
NÁ Á ÁO distance found by Platts et al. (1995). For HNO2 lies
Achiral p-nitrophenyl isocyanide, C7H4N2O2, crystallizes in
the orthorhombic chiral space group P212121. Attractive
intermolecular interactions between the nitro O atoms and
both aromatic H and nitro N atoms of neighbouring molecules
are observed. The OÁ Á ÁN interaction is surprisingly strong
Ê
between 2.8 and 2.9 A, and both (I) and DPA fall well within
this range. The strength of this interaction was estimated to be
at least 10±13 kJ mol 1, and is thus comparable with weak
hydrogen-bond interactions.
Ê
[NÁ Á ÁO = 2.869 (2) A] compared with other aromatic nitro
compounds.
Comment
The title compound, p-nitroisocyanobenzene, (I), is achiral in
solution but crystallizes in the orthorhombic chiral space
group P212121, with four symmetry-equivalent molecules in
the unit cell. The bond lengths and angles of (I) are in the
expected ranges for an aromatic isonitrile. The arene moiety is
basically planar and the isocyano group, as well as the N atom
Ê
of the nitro substituent, are located within 0.053 (3) A of the
mean plane of the benzene ring. The nitro group is rotated by
5.9 (2)ꢀ out of the benzene plane.
While the cyano isomer of (I), p-nitrobenzonitrile, is
essentially isosteric with (I), it is not isostructural, and crys-
tallizes in the space group P21 (Higashi & Osaki, 1977). In the
Cambridge Structural Database (CSD, Version 5.25,
November 2003 update; Allen, 2002), we found ten aromatic
nitrile/isonitrile pairs. As with (I), the majority of these were
not isostructural and, indeed, only four had at least one
isomorphous nitrile/isonitrile pair.
In the case presented here, the formation of isomorphous
crystals is prevented by surprisingly strong interactions of the
nitro group with neighbouring molecules. Thus, each of the
nitro O atoms is in close contact with either a neighbouring
aromatic H atom or with the nitro N atom of a neighbouring
Based on these ®ndings, short NÁ Á ÁO contacts between nitro
groups should be common among nitrobenzene derivatives,
but the opposite is the case. For the bulk of organic nitro
compounds, the average non-bonding distance between two
Ê
nitro groups is around 3.3 A and only a small fraction are
Ê
shorter than the van der Waals radius of 3.07 A (Szczesna &
Â
Urbanczyk-Lipkowska, 2002). Of all 5921 aromatic nitro
compounds in the CSD, only m-chloronitrobenzene has an
ii
Ê
Ê
molecule (Fig. 1). The O1Á Á ÁH7 distance is 2.46 (2) A and the
NÁ Á ÁO distance shorter than 3.2 A (Sharma et al., 1985) (DPA
corresponding O1Á Á ÁC7ii distance is 3.246 (2) A [symmetry
and some of its derivatives are not listed in the CSD). This
makes both (I) and DPAunusual cases, and a closer look at the
geometry of the NÁ Á ÁO interaction found in (I) seems
appropriate.
Ê
code: (ii) x 1, y + 1, z]. While this OÁ Á ÁHÐC interaction is
de®nitely attractive and stabilizing, it is in the usual range
found for aromatic nitro compounds.
Acta Cryst. (2004). C60, o415±o417
DOI: 10.1107/S0108270104007115
# 2004 International Union of Crystallography o415