organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
attempt a consistent characterization of the differences and
similarities of the solid-state structures of the studied
compounds, we have used the Etter (1990, 1991) graph-set
descriptors.
ISSN 0108-2701
The molecule of (I) consists of a six-membered central
tetrazine ring and two chlorophenyl rings. As a twofold axis
passes through the centre of the tetrazine ring, the molecule
exhibits crystallographic C2 point-group symmetry, so the
chlorophenyl rings are symmetry equivalent. The central ring
is folded along the N1Á Á ÁN1i vector [symmetry code: (i) x, y,
Hydrogen-bonding patterns in two
structural isomers of 3,6-bis(2-chloro-
phenyl)-1,4-dihydro-1,2,4,5-tetrazine
1
2
z] and exhibits a boat conformation [puckering para-
meters Q = 0.513 (2)ꢀ, ꢀ = 90.0 (2)ꢀ and ' = 175.7 (2)ꢀ; Cremer
& Pople, 1975]. An analysis of structures deposited in the
Cambridge Structural Database (Version 5.24 of April 2003;
Allen, 2002) showed that a boat conformation is observed for
all structurally characterized tetrazine derivatives. The
chlorophenyl rings are twisted towards one another with a
dihedral angle of 77.94 (7)ꢀ. The Cl atoms lie on the same side
of the C10/N2/C10i/N2i plane. Atoms N1 and N1i lie above this
plane, and atoms H1 and H1i are located in equatorial posi-
tions. Such an arrangement enables the formation of a pair of
strong intermolecular NÐHÁ Á ÁN hydrogen bonds between
centrosymmetrically related neighbouring molecules [Table 2;
hydrogen-bond motif R22(6) (Bernstein et al., 1995), shown as
motif a in Fig. 3], leading to the formation of an in®nite
C(4)[R22(6)] chain of rings along the c axis.
The molecule of (II) consists of a ®ve-membered (hetero-
cyclic) aromatic triazole ring and two chlorophenyl rings (Ph1
and Ph2). The main difference from the molecule of (I) is the
asymmetry of the molecule of (II), in which the H atoms of the
±NH2 amine group lie on the same side of the quasi-mirror
plane that is perpendicular to the ring plane and passes
through the amine N atom and the ring NÐN bond. Excluding
these H atoms, the molecule displays almost Cm point-group
Janusz Zachara,* Izabela Madura and Marek Wøostowski
Warsaw University of Technology, Department of Chemistry, Noakowskiego 3,
00-664 Warszawa, Poland
Correspondence e-mail: janzac@ch.pw.edu.pl
Received 9 October 2003
Accepted 24 November 2003
Online 6 December 2003
Two structural isomers, 3,6-bis(2-chlorophenyl)-1,4-dihydro-
1,2,4,5-tetrazine, (I), and 3,5-bis(2-chlorophenyl)-4-amino-1H-
1,2,4-triazole, (II), both C14H10Cl2N4, form chain-like struc-
tures in the solid state, stabilized by NÐHÁ Á ÁN and NÐHÁ Á ÁCl
hydrogen bonds. A contribution from weak interactions to the
strong hydrogen-bond network is observed in both structures.
The secondary graph sets for intermolecular hydrogen bonds
[R22(11) for (I) and R22(12) for (II)] indicate the similarity
between the networks.
Comment
The compound of general formula C2H2N4(C6H4Cl)2 crystal-
lizes as 3,6-bis(2-chlorophenyl)-1,4-dihydro-1,2,4,5-tetrazine,
(I), in the form of yellow±orange needles. It undergoes irre-
versible isomerization above 353 K in acidic water solution,
forming the structural isomer 3,5-bis(2-chlorophenyl)-4-
amino-1H-1,2,4-triazole, (II).
Figure 1
The molecule of (I), with the atom-numbering scheme. Displacement
X-ray structure determination revealed that isomer (I)
crystallizes in the monoclinic space group C2/c, while isomer
(II) crystallizes in the orthorhombic space group Pbca. The
molecular structures of (I) and (II), with the atom-numbering
schemes, are shown in Figs. 1 and 2, respectively, and selected
geometric parameters are given in Tables 1 and 3.
ellipsoids are drawn at the 50% probability level. [Symmetry code: (i) x,
1
y,
z.]
2
Since both molecules retain potential strong proton-donor
groups [±NH in (I) and ±NH2 in (II)] and proton acceptors (N
and Cl atoms), we undertook a detailed analysis of the
hydrogen-bonded networks. Analysis of intra- and inter-
molecular contacts occurring in crystalline isomers indicated
that, in both cases, the weaker CÐH donor groups are also
important in the formation of the hydrogen-bonded network
(Taylor & Kennard, 1982; Desiraju & Steiner, 1999). To
Figure 2
The molecule of (II), with the atom-numbering scheme. Displacement
ellipsoids are drawn at the 50% probability level.
Acta Cryst. (2004). C60, o57±o59
DOI: 10.1107/S0108270103026945
# 2004 International Union of Crystallography o57