organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
±CH NÐN CH± bridges in benzalazines. Two polymorphs,
A and B, were found for 4-(4-chlorobenzylidenehydrazono-
methyl)benzonitrile, viz. (CN//Cl-A) and (CN//Cl-B). Poly-
morph (CN//Cl±B), 4-(4-bromobenzylidenehydrazonomethyl)-
benzonitrile, (CN//Br), and 4-(4-iodobenzylidenehydrazono-
methyl)benzonitrile, (CN//I), are isostructural. All four
structures show end-for-end disorder of the molecules.
ISSN 0108-2701
4-(4-Chlorobenzylidenehydrazono-
methyl)benzonitrile and the bromo
and iodo analogs
Charles R. Ojala,a William H. Ojalab and Doyle Brittonc*
aDepartment of Chemistry, Normandale Community College, Bloomington,
MN 55431, USA, bDepartment of Chemistry, University of St Thomas, St Paul,
MN 55105, USA, and cDepartment of Chemistry, University of Minnesota,
Minneapolis, MN 55455, USA
The atom labeling and the anisotropic displacement para-
meters for (CN//Cl-A) are shown in Fig. 1. The displacement
parameters are similar and the labeling scheme is the same for
the other three polymorphs. In every case, there is partial
disorder between the two ends; the major component of the
disorder has 59.0 (4)% occupancy in (CN//Cl-A), 67.2 (2)% in
(CN//Cl-B), 81.45 (8)% in (CN//Br) and 70.16 (4)% in (CN//I).
Judging from the changes in these percentages over the course
of the re®nements, these s.u. values are very optimistic. If the
disorder were 50/50, the average molecule, in every case,
would lie on a center of symmetry. When the disorder is other
than 50/50, there is only a pseudo-center of symmetry and the
space group becomes noncentrosymmetric. There are no
unusual bond lengths or angles in any of the structures
although, again, the s.u. values seem low. The molecules
Correspondence e-mail: britton@chem.umn.edu
Received 20 October 2007
Accepted 2 December 2007
Online 12 January 2008
4-Cyano-40-chlorobenzalazine [systematic name: 4-(4-chloro-
benzylidenehydrazonomethyl)benzonitrile], C15H10ClN3, oc-
curs in two polymorphs. Polymorph A is isostructural with the
corresponding dichloro compound. Polymorph B is isostruc-
tural with the bromo and iodo analogs, viz. C15H10BrN3 and
C15H10IN3, respectively. The latter three structures all have
approximately linear CÐNÁ Á ÁXÐC intermolecular contacts in
which the NÁ Á ÁX contact distances are longer than those in the
corresponding benzylideneanilines.
Comment
In earlier work (Ojala et al., 1999, 2001), the packings of
p-halo-N-(p-cyanobenzylidene)anilines and p-cyano-N-(p-
halobenzylidene)anilines were reported for the chloro, bromo
and iodo compounds. [Hereafter, we will use the descriptor
(X/Y) to denote XÐC6H4ÐCH NÐC6H4ÐY.] This
previous work was prompted by earlier work (Bernstein &
Schmidt, 1972; Bernstein & Izak, 1976; Bernstein et al., 1976;
Bar & Bernstein, 1977, 1982, 1983; Haller et al., 1995) in which
it was shown that in (Cl/Cl), (CH3/CH3), (CH3/Cl) and (Cl/
CH3) there was extensive disorder among the orientations of
the molecules. The disorder could be by inversion through the
pseudo-center of symmetry in the molecule, or by rotation
around the XÁ Á ÁY axis, or by both, leading in some cases to
fourfold disorder. The purpose of the earlier work (Ojala et al.,
1999, 2001) was to see whether a possible ±CNÁ Á ÁX± inter-
action could reduce the disorder. In (I/CN), (CN/I), (CN/Br)
and (CN/Cl), such interactions did occur; the disorder was
eliminated in (I/CN) and (CN/I) and reduced to only the
inversion disorder in (CN/Br) and (CN/Cl). In (Br/CN) and
(Cl/CN), no ±CNÁ Á ÁX± interactions were found, but ±XÁ Á ÁX±
interactions removed the disorder completely. We report here
the structures of the corresponding 4-(4-halobenzylidene-
hydrazonomethyl)benzonitriles, with the descriptor (CN//X).
The ±CH N± bridges in benzylideneanilines are replaced by
Figure 1
A view of the molecule of (CN//Cl-A). Displacement ellipsoids are shown
at the 50% probability level. The molecule is disordered: atoms Cl1, N3
and C8 have 59.0 (4)% occupancy, and atoms Cl2, N4 and C18 have
41.0 (4)% occupancy.
Figure 2
The packing in (CN//Cl-A), viewed along the b axis. The compound is
isostructural with (Cl//Cl).
Acta Cryst. (2008). C64, o37±o40
DOI: 10.1107/S0108270107065171
# 2008 International Union of Crystallography o37
Ojala, Charles R.
