Wave-like structure in 3-(4,6-diamino-1,3,5-triazin-2-yl)-2-naphthonitrile

Article abstract of DOI:10.1107/S0108270108003831

In the title compound, C14H10N6, which crystallizes with Z′ = 2 in the C2/c space group, the mol-ecules are linked by N - H...N hydrogen bonds into chains, which are arranged in a wave-like form stabilized by aromatic π-π stacking inter-actions. This work demonstrates the usefulness of aromatic triazine derivatives in crystal engineering.

Full text of DOI:10.1107/S0108270108003831

organic compounds
Compound (I) crystallizes with Z0 = 2 and the two inde-
pendent molecules, M1 and M2, are linked by N—Hꢀ ꢀ ꢀN
hydrogen bonds (Table 2) into a dimeric unit (Fig. 1). These
units are linked by further N—Hꢀ ꢀ ꢀN hydrogen bonds to form
Acta Crystallographica Section C
Crystal Structure
Communications
ISSN 0108-2701
Wave-like structure in 3-(4,6-diamino-
1,3,5-triazin-2-yl)-2-naphthonitrile
Jan Janczak
Institute of Low Temperature and Structure Research, Polish Academy of Sciences,
PO Box 1410, 50-950 Wrocław, Poland
a zigzag chain (Fig. 3a). Although the bond lengths and angles
in the two independent molecules are very similar, their
conformations differ in the rotation angle of the triazine ring
relative to the naphthalene system around the inter-ring bond:
the dihedral angles between the triazine and naphthalene
planes are 27.0 (2) and 10.7 (2)ꢁ in molecules M1 and M2,
respectively. The rotation is caused by an interaction of the
highly polar C N group with the triazine ring.
Correspondence e-mail: j.janczak@int.pan.wroc.pl
Received 23 January 2008
Accepted 5 February 2008
Online 16 February 2008
In the title compound, C14H10N6, which crystallizes with Z0 = 2
in the C2/c space group, the molecules are linked by N—
Hꢀ ꢀ ꢀN hydrogen bonds into chains, which are arranged in a
wave-like form stabilized by aromatic ꢀ–ꢀ stacking inter-
actions. This work demonstrates the usefulness of aromatic
triazine derivatives in crystal engineering.
The gas-phase geometry obtained by ab initio molecular-
orbital calculations (GAUSSIAN98; Frisch et al., 1998) at the
B3LYP/6-31+G* level confirms the nonplanar conformation of
(I) (Fig. 2). The calculated dihedral angle between the planes
of the triazine and naphthalene rings, viz. 14.7ꢁ, represents a
global minimum on the potential energy surface (PES).
During rotation of the triazine ring relative to naphthalene
around the inter-ring bond from 0 to 360ꢁ, four equivalent
minima and two pairs of maxima are found. The minima are
observed at rotation angles of ꢂ14.7 and 180ꢂ14.7ꢁ (i.e. 165.3
and 194.7ꢁ), while the maxima are observed at 0ꢁ (and 180ꢁ),
with a barrier energy of ꢃ5.85 kJ molꢄ1, and at 90ꢁ (and 270ꢁ),
Comment
A productive strategy in crystal engineering utilizes molecules
which can form multiple interactions with their neighbours
(Wuest, 2005). Hydrogen bonds are widely used as the prin-
cipal interactions in this strategy since they are directional and
relatively strong (Moulton & Zaworotko, 2001; Seiter, 2002).
Many different self-complementary hydrogen-bonding groups
can be used to control association in crystal engineering and to
produce different arrangements, such as chains, sheets,
ribbons, tapes, rosettes, etc., having predictable structural
features (Desiraju, 1990, 2002). Several studies have demon-
strated the usefulness of melamine and its organic and in-
organic complexes or salts in crystal engineering (Whitesides
with a barrier energy of ꢃ14.35 kJ molꢄ1
.
The difference between the barrier energies of the confor-
mations at 0 and 90ꢁ (ÁE = 8.5 kJ molꢄ1) can be attributed to
the ꢀ-delocalization energy of the ꢀ electrons along the inter-
ring bond. At a rotation angle of 90ꢁ (rings perpendicular),
delocalization of the ꢀ electrons between the rings is impos-
sible due to the symmetry of the orbitals. The lengthening of
˚
´
et al., 1995; Janczak & Perpetuo, 2001, 2002, 2003, 2004, 2008;
Perpetuo & Janczak, 2003, 2005, 2007), since their components
the inter-ring bond, from 1.488 A for the mosꢁt stable confor-
˚
mation to 1.511 A for a rotation angle of 90 , supports this
´
contain complementary arrays of hydrogen-bonding sites.
While ꢀ–ꢀ interactions are intermolecular forces whose
nature is still a matter of discussion (Hunter & Sanders, 1990;
Janiak, 2000; Cozzi et al., 2003; Kobayashi & Saigo, 2005), in
general, such an interaction can be said to consist of two
aromatic rings arranged in a face-to-face orientation with a
˚
distance of 3.2–3.8 A between the planes of the rings.
In an effort to engineer expanded versions of the structures
formed during the transformation of the cyano group in
dicyanobenzene isomers in the presence of cyanoguanidine
(Janczak & Kubiak, 2005a,b), we have replaced the phenyl
rings with naphthyl systems, using 2,3-dicyanonaphthalene,
and we have investigated the role of ꢀ–ꢀ stacking interactions
in the organization and stabilization of the resulting structures.
We present here the crystal structure of one of these expanded
systems, viz. the title compound, (I).
Figure 1
The independent components of compound (I), showing the atom-
labelling scheme and the hydrogen bonds (dashed lines) within the
selected asymmetric unit. Displacement ellipsoids are drawn at the 30%
probability level and H atoms are shown as small spheres of arbitrary
radii.
Acta Cryst. (2008). C64, o159–o161
doi:10.1107/S0108270108003831
# 2008 International Union of Crystallography o159

organic compounds
Figure 2
Results of the optimized ꢁmolecular-orbital calculations (at the B3LYP/6-
˚
31+G* level) for (I) (A, ).
fact. The estimated energy of molecule M1 in the conforma-
tion as present in the crystal structure is greater by
ꢃ6.75 kJ molꢄ1, while for the second molecule it is greater
only by ꢃ1.85 kJ molꢄ1. The differences between the energies
of the molecules in the crystal structure and in the gas phase
(obtained by molecular-orbital calculations) are compensated
for by ꢀ–ꢀ interactions between the aromatic rings in the
crystal structure.
Considering both conformations of independent molecules
M1 and M2 in the crystal structure of (I) (Fig. 1 and Table 1)
and in the gas-phase conformation (Fig. 2) in more detail,
besides the main difference mentioned above in the rotation
angle of the rings, several other differences can also be found.
For example, the C—C N angle in molecule M1 [173.9 (2)ꢁ]
is closer to 180ꢁ than that in molecule M2 [167.7 (2)ꢁ]. These
values correlate well with the rotation angles of the triazine
ring in relation to the naphthalene system. The greater rota-
tion angle around the inter-ring C—C bond lengthens the
distance between the polar C N group and the triazine ring
and results in a decrease in the repulsion between the
substituents at positions 2 and 3 in the naphthalene system.
In the dimer unit formed by independent molecules M1 and
M2 (Fig. 1), the two triazine rings are not coplanar; the
dihedral angle between their planes is 22.6 (1)ꢁ. Dimers
related by a c-glide plane interact via two pairs of N—Hꢀ ꢀ ꢀN
hydrogen bonds, forming infinite chains along the c axis
(Fig. 3a). There is no hydrogen bonding between the chains,
and the chains interact only via van der Waals forces and ꢀ–ꢀ
stacking interactions. Although the triazine rings each contain
one potential hydrogen-bonding site (atoms N1 and N21),
these sites are inactive due to steric hindrance from the cyano
groups.
Figure 3
(a) Aview of the N—Hꢀ ꢀ ꢀN hydrogen-bonded chains of (I), which exhibit
R22(8) topology. (b) Stereoview of the wave-like structure in the crystal
structure of (I). For the sake of clarity, H atoms bonded to C atoms have
been omitted.
Our observations underscore the potential utility of (I) in
crystal engineering. The amine groups can donate hydrogen
bonds to the N atoms of neighbouring triazine rings, which act
as acceptors, thus forming a characteristic dimeric motif. This
dimeric motif, containing hydrogen-bonding active sites, can
interact with neighbouring molecules via two pairs of N—
Hꢀ ꢀ ꢀN hydrogen bonds, favouring the formation of one-
dimensional polymers. In the absence of hydrogen bonds
between these one-dimensional polymers, ꢀ–ꢀ interactions
between offset aromatic rings stabilize the overall structure.
The various chains along [001] form a wave-like archi-
˚
tecture (Fig. 3b), with a distance of ca 3.45 A between adjacent
aromatic ring systems, consistent with the occurrence of ꢀ–ꢀ
stacking interactions, since this distance is comparable with
the sum of the van der Waals radii of two C atoms in an
aromatic ring system (Pauling, 1967). The sheets of the wave-
like structure lie parallel to the (010) plane (Fig. 3b).
ꢅ
o160 Jan Janczak C14H10N6
Acta Cryst. (2008). C64, o159–o161

organic compounds
Table 2
Hydrogen-bond geometry (A, ).
Experimental
ꢁ
˚
2,3-Dicyanonaphthalene (99% purity) and cyanoguanidine (99%
purity) were purchased from Sigma–Aldrich. They were mixed
together in a 1:1 molar ratio and the mixture was pressed into pellets.
The pellets were inserted into an evacuated glass ampoule and
annealed in the temperature gradient 523–503 K for 6 h. Crystals of
3-(4,6-diamino-1,3,5-triazin-2-yl)-2-naphthonitrile, (I), were formed
in the low-temperature zone during migration from the high-
temperature zone at which the compound was formed (Janczak &
Kubiak, 2005a,b). Elemental analysis found: C 64.21, N 32.00, H
3.79%; calculated for C14H10N6: C 64.11, N 32.05, H 3.84%.
D—Hꢀ ꢀ ꢀA
D—H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
N4—H4Aꢀ ꢀ ꢀN22
N5—H5Bꢀ ꢀ ꢀN23i
N24—H24Aꢀ ꢀ ꢀN2
N24—H24Bꢀ ꢀ ꢀN26ii
N25—H25Bꢀ ꢀ ꢀN3iii
0.86
0.86
0.86
0.86
0.86
2.32
2.30
2.16
2.30
2.28
3.171 (2)
3.132 (2)
2.984 (2)
3.078 (3)
3.096 (2)
172
163
161
150
158
1
2
1
2
1
2
Symmetry codes: (i) x; ꢄy; z ꢄ ; (ii) ꢄx; y; ꢄz þ ; (iii) x; ꢄy; z þ .
Diffraction, 2006); program(s) used to solve structure: SHELXS97
(Sheldrick, 2008); program(s) used to refine structure: SHELXL97
(Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg &
Putz, 2006); software used to prepare material for publication:
SHELXL97.
Crystal data
3
˚
C14H10N6
Mr = 262.28
V = 4919 (2) A
Z = 16
Monoclinic, C2=c
Mo Kꢂ radiation
ꢃ = 0.09 mmꢄ1
T = 295 (2) K
0.32 ꢆ 0.26 ꢆ 0.18 mm
˚
a = 35.798 (7) A
This work was supported financially by the Ministry of
Science and Information Society Technologies (project No.
3T09A12128).
˚
b = 7.3190 (10) A
˚
c = 21.459 (4) A
ꢁ = 118.96 (3)ꢁ
Data collection
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: GD3192). Services for accessing these data are
described at the back of the journal.
Kuma KM-4 diffractometer with a
CCD area-detector
Absorption correction: analytical,
face-indexed (SHELXTL;
Sheldrick, 2008)
27666 measured reflections
5875 independent reflections
3357 reflections with I > 2ꢄ(I)
Rint = 0.034
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˚
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˚
N6—C11
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1.136 (3)
1.425 (3)
1.443 (3)
1.488 (2)
N26—C211
C22—C211
C23—C212
1.141 (2)
1.444 (2)
1.488 (2)
C2—C11
C3—C12
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´
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N1—C12—N3
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114.13 (15)
114.67 (15)
113.74 (15)
173.9 (2)
126.72 (16)
125.04 (16)
125.60 (16)
C212—N21—C213
C214—N22—C213
C212—N23—C214
N26—C211—C22
N21—C212—N23
N22—C213—N21
N22—C214—N23
115.00 (15)
114.09 (15)
113.13 (14)
167.7 (2)
126.70 (16)
124.95 (15)
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´
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ꢅ
Acta Cryst. (2008). C64, o159–o161
Jan Janczak C14H10N6 o161