Supramolecular hydrogen-bonded 1D arrangement in the crystals of 2,4-diamino-6-benzyl-1,3,5-triazine and 2,4-diamino-6-(4′-methylbenzyl)-1,3,5-triazine

Article abstract of DOI:10.1016/j.molstruc.2008.10.035

Two crystals of triazine derivatives, 2,4-diamino-6-benzyl-1,3,5-triazine (1) and 2,4-diamino-6-(4′-methylbenzyl)-1,3,5-triazine (2), are synthesised by a direct reaction of cyanoguanidine with the respective cyanocompounds. The IR spectra of the compounds are very similar. In the crystals the molecules are interconnected by N{single bond}H?N hydrogen bonds forming one-dimensional hydrogen bonded polymer in 1 and three-dimensional hydrogen bonded network in 2. The arrangement of molecules in the crystal of 1 is denser than in 2 due to the π-π interactions between the π-clouds of the aromatic triazine rings that are absent in the crystal of 2. The geometries of the molecules in the crystals have been compared with those obtained by ab-initio molecular orbital calculated results that represent the geometries of molecules in the gas-phase.

Full text of DOI:10.1016/j.molstruc.2008.10.035

Journal of Molecular Structure 920 (2009) 75–81
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Supramolecular hydrogen-bonded 1D arrangement in the crystals
of 2,4-diamino-6-benzyl-1,3,5-triazine and 2,4-diamino-6-(40-methylbenzyl)-
1,3,5-triazine
*
Jan Janczak , Ryszard Kubiak
Institute of Low Temperature and Structure Research, Polish Academy of Sciences, PO Box 1410, 50950 Wrocław, Poland
a r t i c l e i n f o
a b s t r a c t
Two crystals of triazine derivatives, 2,4-diamino-6-benzyl-1,3,5-triazine (1) and 2,4-diamino-6-(40-meth-
ylbenzyl)-1,3,5-triazine (2), are synthesised by a direct reaction of cyanoguanidine with the respective
cyanocompounds. The IR spectra of the compounds are very similar. In the crystals the molecules are
interconnected by NAHꢀ ꢀ ꢀN hydrogen bonds forming one-dimensional hydrogen bonded polymer in 1
and three-dimensional hydrogen bonded network in 2. The arrangement of molecules in the crystal of
Article history:
Received 20 August 2008
Received in revised form 16 October 2008
Accepted 17 October 2008
Available online 5 November 2008
1 is denser than in 2 due to the p–p interactions between the p-clouds of the aromatic triazine rings that
Keywords:
are absent in the crystal of 2. The geometries of the molecules in the crystals have been compared with
those obtained by ab-initio molecular orbital calculated results that represent the geometries of mole-
cules in the gas-phase.
Triazine derivatives
Cyanoguanidine
Crystal structure
Hydrogen bond
DFT calculation
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
Our interest in the melamine and its derivatives arises from the
possibilities to obtain new materials for non-linear optics. The
The control of supramolecular assembly using non-covalent
interactions is a major area in supramolecular chemistry as well
as in biology [1,2]. In particular the directional interactions result-
ing from multiple hydrogen bonding with the neighbours are ex-
plored in the crystal engineering [2–4]. The NAHꢀ ꢀ ꢀN, NAHꢀ ꢀ ꢀO
and OAHꢀ ꢀ ꢀO hydrogen bonds are the main key for organisation
of molecules containing complementary arrays of the hydrogen
bonding sites [5,6]. Many different self-complementary hydrogen
bonding groups can be used to control association in supramolec-
ular chemistry to produce different and programmed arrange-
ments in solids, such as chains, sheets, ribbons, tapes, rosettes
etc. [7–10].
Several studies have demonstrated the usefulness of melamine
and its organic and inorganic complexes or salts in crystal engi-
neering [11–15], since their components contain complementary
arrays of hydrogen bonding sites. Protonation of its triazine ring
decreases the number of the active sites resulting in the dimen-
sionality of the arrangements. For example, single protonated mel-
aminium ring cations form one-dimensional hydrogen bonded
chains [16], while double protonated can form only the dimeric
structures [17]. In addition, supramolecular networks containing
both protonated melaminium cations and neutral melamine mole-
cules have been also reported [18–20].
crystals of melamine selenate with the non-centrosymmetric space
group are optically active and generate the SHG (SHG = second har-
monic generation) with c.a. 40% efficiency of KDP (KDP = KH2PO4)
[21]. High efficiency of SHG is observed in the crystals of double
protonated melaminium bis(trichloroacetate) dihydrate (about
3-times greater than that of KDP) [22]. Another non-centrosym-
metric crystals of melaminium phosphate may also be used for
non-linear optics [23].
Besides the hydrogen bonds as non-covalent interactions
responsible for organisation and design of the supramolecular
architectures, the p–p interactions are the molecular forces whose
the nature is still a matter of discussion [24–26]. In general, such
interaction integrates two aromatic rings arranged in a face-to-face
orientation with a distance of 3.2–3.8 Å 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 the dicya-
nobenzene isomers [27,28] or 2,3-dicyanonaphthalene [29] in
presence of cyanoguanidine, we have replaced the dicyanocom-
pounds with cyanocompounds in which the cyano group is sepa-
rated from the aromatic ring by the aliphatic methylene group
(ACH2A) as illustrates the scheme 1.
Our intention was to investigate the influence of the methylene
group on the conformation of the molecule as well as on the p–p
interactions and stabilisation of the resulting supramolecular
* Corresponding author.
networks.
E-mail address: j.janczak@int.pan.wroc.pl (J. Janczak).
0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2008.10.035

76
J. Janczak, R. Kubiak / Journal of Molecular Structure 920 (2009) 75–81
1.2 Ueq of the carbon atoms joined directly to the hydrogen atoms).
Final difference Fourier maps showed no peaks of chemically sig-
nificance. Details of the data collection parameters and final agree-
ment factors are collected in Table 1. Selected bond lengths and
angles and torsion angles are listed in Table 2.
CH3
CH2
C
CH2
C
N
N
Scheme 1.
2.4. Quantum MO calculations
Ab-initio molecular orbital calculations were carried out with
the Gaussian98 program package [33]. Full optimisations were per-
formed by the density functional three-parameters hybrid (B3LYP)
methods [34,35] with the 6-31G(d,p) basis set starting from the
2. Experimental
All materials were commercially available (Aldrich) and used
for synthesis as received. The Fourier transform infrared spectra
were recorded from nujol mulls between 400 and 4000 cmꢁ1 on
a Bruker IFS 113 V FTIR spectrometer at room temperature. Ele-
mental analyses were carried out with a Perkin-Elmer 240 elemen-
tal analyser.
Table 1
Crystallographic data and structure refinement parameters.
Compounds
1
2
Formula
C10H11N5
201.14
295(2)
C11H13N5
215.26
295(2)
2.1. Synthesis of 2,4-diamino-6-benzyl-1,3,5-triazine (compound 1)
Molecular weight
Temperature (K)
Crystal system
Cyanoguanidine (1 g) was added to 5 ml benzylcyanide. Next,
the suspension was inserted into a glass ampoule, degassed and
sealed off. After it, the ampoule with the reagents was heated by
c.a. half an hour. After as the components formed an apparently
uniform liquid, the ampoule was cooled to 180 oC and left by one
day. In the result of such thermal processing, the transparent and
colourless, tiny and elongated crystals were formed. Finally, the
crystals were separated and dried in air. Elemental analysis, found:
C, 59.82; H, 5.44 and N, 34.74%, calculated for C10H11N5: C, 59.68;
H, 5.51 and N, 34.81%.
Monoclinic
P21/c (No. 14)
10.087(2)
12.213(2)
8.027(2)
103.10(2)
963.1(3)
4
1.388
1.38
0.091
0.26 ꢂ 0.24 ꢂ 0.16
11421/2518/1802
0.0381
0.0509
0.0691
Monoclinic
C2/c (No.15)
23.096(5)
8.0416(16)
13.826(3)
117.51(2)
2277.4(10)
8
1.256
1.25
0.082
0.38 ꢂ 0.22 ꢂ 0.12
12956/2944/1806
0.0294
0.0444
0.1074
Space group
0
a (ÅA)
0
b (AÅ)
0
c (AÅ)
b (°)
0
V (AÅ3)
Z
Dcalc (g cmꢁ3
)
)
Dobs. (g cmꢁ3
l
(mmꢁ1
)
Crystal size (mm3)
Total/unique/observed reflections (Rint
)
2.2. Synthesis of 2,4-diamino-6-(40-methylbenzyl)-1,3,5-triazine
(compound 2)
R (F2 > 2
r
(F2))a
wR (F2 all refls)
S
D
1.003
+0.196, ꢁ0.220
1.006
+0.109, ꢁ0.146
0
The suspension of 1 g cyanoguanidine in 5 ml 4-meth-
ylbenzylcyanide was thermally processed as for compound 1. Fi-
nally, the colourless, well developed in the prismatic form
crystals of compound 2 were obtained. Elemental analysis, found:
C, 61.55; H, 6.18 and N, 32.27%. Calculated for C11H13N5: C, 61.38;
H, 6.09 and N, 32.53%.
qmax
,
D
qmin (e ÅAꢁ3
)
a
w = 1/[
r
2(F2o ) + (0.0082P)2] for 2(F2o) + (0.041P)2] for
1 and w = 1/[r 2 where
P = (F2o + 2F2o )/3.
Table 2
Geometric parameters (bond lengths in Å, bond angles in °).
2.3. X-ray single crystal analysis
Compounds
1
2
X-ray
ab-initio
X-ray
ab-initio
X-ray intensity data for both crystals were collected, using
graphite monochromatised Mo K
geometry KUMA KM-4 diffractometer with a two-dimensional area
CCD detector. The -scan technique with
= 1.0o for each image
a radiation, on a four-circle j-
C1AC2
C2AC3
C3AC4
C4AC5
C5AC6
C1AC6
C1AC7
C7AC8
C8AN1
N1AC9
C9AN2
N2AC10
C10AN3
N3AC8
C9AN4
C10AN5
C4AC11
C8AN1AC9
C9AN2AC10
C8AN3AC10
N1AC8AN3
N1AC9AN2
N2AC10AN3
C1AC7AC8
C1AC7AC8AN1
C6AC1AC7AC8
1.397(3)
1.376(3)
1.378(3)
1.366(4)
1.393(4)
1.379(3)
1.519(3)
1.501(3)
1.323(3)
1.357(3)
1.337(3)
1.328(3)
1.367(3)
1.335(3)
1.348(3)
1.345(3)
1.402
1.397
1.398
1.398
1.398
1.402
1.522
1.515
1.337
1.350
1.341
1.341
1.351
1.337
1.358
1.358
1.370(2)
1.383(2)
1.355(3)
1.374(3)
1.396(2)
1.374(2)
1.514(2)
1.503(2)
1.333(2)
1.349(2)
1.343(2)
1.336(2)
1.347(2)
1.332(2)
1.331(2)
1.333(2)
1.520(2)
114.83(12)
114.44(13)
114.83(11)
125.69(13)
124.89(12)
125.65(12)
118.87(12)
ꢁ172.71(2)
60.3(2)
1.400
1.398
1.401
1.403
1.396
1.402
1.522
1.514
1.337
1.350
1.341
1.341
1.350
1.337
1.358
1.359
1.512
114.4
114.0
114.4
125.6
125.8
125.8
112.0
-91.0
83.6
x
Dx
was used for data collection. The 960 images for six different runs
covering over 99% of the Ewald sphere were performed. Initially
the lattice parameters were refined on 650 (for I) and 835 (for II)
reflections obtained from 40 images for eight runs with different
orientation in the reciprocal space. Finally the lattice parameters
were refined by least-squares methods based on all the reflections
with I > 2r
(F2). One image was used as a standard after every 40
images for monitoring the crystal’s stability as well as for monitor-
ing the data collection, and no correction on the relative intensity
variation was necessary. Integration of the intensities, correction
for Lorenz and polarization effects were performed using a CrysAlis
CCD program [30]. The face-indexed analytical absorption was cal-
culated using the SHELXTL program [31]. The max. and min. trans-
mission factors are 0.952 and 0.975 for 1 and 0.997 and 0.966 for 2.
The structures were solved by direct methods using SHELXS97 and
refined using SHELXL97 programs [32]. All non-hydrogen atoms
were refined with the anisotropic thermal parameters. The hydro-
gen atoms were positionated geometrically (HFIX 43 for all H
atoms of the phenyl rings with isotropic thermal parameters of
112.9(2)
113.0(2)
113.5(2)
126.9(2)
127.3(3)
126.2(3)
111.09(18)
84.9(2)
114.4
114.0
114.4
125.7
125.7
125.7
112.0
87.7
ꢁ103.9(2)
85.4

J. Janczak, R. Kubiak / Journal of Molecular Structure 920 (2009) 75–81
77
X-ray geometry. As convergence criterions the threshold limits of
0.00025 and 0.0012 a.u. were applied for the maximum force and
the displacement, respectively.
a
(1)
1.00
0.75
0.50
0.25
0.00
3. Results and discussion
3.1. Synthesis
We proved that initialisation of the reaction between the cyano-
guanidine and benzylcyanide or 4-methylbenzylcyanide (Scheme
2) requires a relatively high temperature, but the processing at
high temperature (230 °C) should not be too long.
N
N
N
This is because the dicyandiamide in its active form is in the real
balance with cyanamide and therefore prolonged heating at this
temperature (ꢃ230 °C) will lead to increasing quantity of mela-
mine in the reaction products, formed due to competitive cyclisa-
tion of dicyandiamide with cyanamide. The details of the formation
of melamine from dicyandiamide have been discussed earlier in
[27]. On the other hand some excess of the liquidic component,
i.e. benzylcyanide or 4-methylbenzylcyanide, unambiguously pro-
vides the adequate conditions for the growth and developing of the
1 and 2 crystals. The yields of the compounds 1 and 2 in relation to
the cyanoguanidine used in the reactions are higher than 90%.
4000
3000
2000
1000
Wavenumber [cm-1]
b
0.8
0.6
0.4
0.2
(2)
3.2. Vibrational spectroscopy
N
The IR spectra of compounds 1 and 2 are very similar (Fig. 1).
N
They show characteristic bands of
m
(NH2) at 3471 and 3447 cmꢁ1
in 1 and at 3469 and 3449 cmꢁ1 in 2. Both
m
(NH2) are assigned
N
to ms and ma mode of NH2 group. For the NH2 group, besides the
stretching vibration, the bending vibration d(NH2) are also ob-
served at 1656 and 1633 cmꢁ1 for 1 and at 1660 and 1639 cmꢁ1
for 2. This assignment is supported by the theoretical calculations
[36] and by the analysis of the IR spectrum of melamine [37]. The
band at 1547 cmꢁ1 in 1 and 1543 cmꢁ1 in 2 can be assigned to the
ring-quadrant stretching [37]. The bands in the spectral region of
1250–1100 cmꢁ1 are assigned to the side-chain in plane CANAC
and NACAN bending of triazine ring [38,39]. The band at
806 cmꢁ1 in 1 and at 808 cmꢁ1 in 2 is assigned to CAH deformation
in benzene ring and the another band at ꢃ770 cmꢁ1 is assigned to
ring-sextant out-of-plane bending. The bands in the range of 588–
540 cmꢁ1 are a contribution tone of NH2-bending and NH2-rocking
vibrations [38,39]. The molecules of 1 and 2 in the crystal are inter-
connected via NAHꢀ ꢀ ꢀN hydrogen bonds (Table 3), which are also
evidenced by the IR-spectroscopy as broad bands at 3304 and
3111 cmꢁ1 for 1 and at 3311 and 3127 cmꢁ1 for 2.
4000
3000
2000
1000
Wavenumber [cm-1]
Fig. 1. IR-spectra of (a) 2,4-Diamino-6-benzyl-1,3,5-triazine (1) and (b) 2,4-
diamino-6(-40-methylbenzyl)-1,3,5-triazine as nujol mulls. The bands of the nujol
are assigned as N.
Table 3
Geometric parameters of the hydrogen bonds in the structure of 1 and 2.
Compound 1
DAHꢀ ꢀ ꢀA
DAH (Å)
0.86
Hꢀ ꢀ ꢀA (Å)
2.14
2.19
Dꢀ ꢀ ꢀA (Å)
2.996(3)
3.045(3)
<DHA (o)
170
178
N4AH42ꢀ ꢀ ꢀN3i
N5AH52ꢀ ꢀ ꢀN1ii
0.86
Symmetry code: i = 1 ꢁ x, ꢁ0.5 + y, 0.5 ꢁ z; ii = 1 ꢁ x, 0.5 + y, 0.5 ꢁ x
Compound 2
3.3. X-ray and gas-phase structures
N4AH41ꢀ ꢀ ꢀN1i
N4AH42ꢀ ꢀ ꢀN2ii
N5AH52ꢀ ꢀ ꢀN3iii
0.86
0.86
0.86
2.24
2.17
2.18
3.0345(19)
3.0274(16)
2.9936(18)
153
174
159
The molecular geometry of 1 and 2 obtained by single crystal X-
ray analysis with the labelling scheme of the atoms are shown in
Fig. 2a and Fig. 3a, whereas the gas-phase conformation of the mol-
Symmetry code: i = ꢁx, y, 0.5 ꢁ z; ii = ꢁx, 1 ꢁ y, 1 ꢁ x; iii = 0.5 ꢁ x, 0.5 ꢁ y, 1 ꢁ z
H
NH2
N
N
N
C
N
N
NH2
C
NH2
+
N
NH
CH2
R
R
CH2
R = H (1) and R = CH3 (2)
Scheme 2.

78
J. Janczak, R. Kubiak / Journal of Molecular Structure 920 (2009) 75–81
ecules are shown in Fig. 2b and Fig. 3b, respectively. The X-ray
experimental geometrical parameters together with ab-initio fully
optimised parameters that correspond to the gas-phase structures
are collected in the Table 2.
70.5° in gas-phase of 1, whereas in 2 the angle is 62.9(1)° and
109.2° in the crystal and gas-phase molecule, respectively. Thus
in 1 the C7AC1 bond is almost perpendicular to the triazine ring
in the crystal and gas-phase conformations (see Fig. 2). In 2 the
C7AC1 bond linking the phenyl ring is almost coplanar with the
triazine ring in the crystal, while in the gas-phase conformation
of molecule, similarly as in 1, it is almost perpendicular to the tri-
azine ring (see Fig. 3). In triazine ring the internal CANAC angles
are significantly smaller than 120° while the internal NACAN an-
gles are significantly greater than 120° in both X-ray and ab-initio
data (see Table 2). This is a result of the steric effect of the lone-pair
of electrons at the N atoms of triazine ring and is in agreement
with the valence-shell electron pair repulsion model, VSEPR [40],
according to which the lone-pair of electrons afford a wider space
than the covalent, bonding pair. The respective bond distances and
angles in 1 and 2 are very similar and are in agreement with the
expected values observed in the related compounds [41].
In the crystal of 1 the molecules related by twofold screw axis
interact by two pairs of almost linear NAHꢀ ꢀ ꢀN hydrogen bonds
with a graph of R22(8) [42] forming 1D-polymer (Fig. 4a). The
R22(8) graph of hydrogen bonds is one of the 24 most frequently ob-
served bimolecular cyclic hydrogen-bonded synthons in organic
crystal structures [41,42]. The 1D-polymer related by the c-glide
plane and translation are arranged in a zig-zag shape forming lay-
ers parallel to the (001) crystallographic plane (Fig. 4b). The layers
are separated by a distance of 3.245(1) Å between the parallel tri-
azine rings that form stack along the [100] direction. The distance
of 3.245(1) Å between the triazine rings within the stack indicates
The absolute energies calculated using B3LYP methods and 6-
31+G(d) basis set functions were found to be ꢁ661.521 for 1 and
ꢁ700.839 a.u. for 2. In both cases there are the global minima on
the potential energy surface (PES). The calculated dipole moment
of 1 and 2 molecules is equal to 1.75 and 2.13 D, respectively.
For a comparison the calculated energies for molecules with the
geometries as in crystals are equal ꢁ661.275 and ꢁ700.564 a.u.,
respectively for 1 and 2. The differences in energies are compen-
sated by the hydrogen bonds and by the crystal packing forces.
As can be seen from the Figs. 2 and 3, the X-ray and ab-initio geom-
etries of 1 are very similar, while for 2 are different, especially the
orientation of the phenyl ring in relation to the triazine ring. The
conformation of 1 and 2 molecules can be described by the torsion
angles of C1AC7AC8AN3 and C6AC1AC7AC8 and by the inter-pla-
nar angles between the planes of the phenyl and triazine rings. The
respective torsion angles in 1 are ꢁ93.5(1)° and ꢁ103.9(1)° in the
crystal and ꢁ91.4° and ꢁ93.7o in the gas-phase molecule, and in 2
are 8.3(1)° and 60.3(1)o in the crystal and ꢁ91.0 and 83.6 in the
gas-phase molecule. The inter-planar angle between the planes
of triazine and phenyl rings is equal to 72.4(1)° in the crystal and
the
since the value is nearly intermediate between the sum of the C
and N atoms van der Waals radii of the
aromatic rings (ꢃ3.4 Å)
and the distance at which the interaction between the aromatic
ring system becomes predominantly repulsive (ꢃ3.08 Å) [43]. No
interactions have been observed between the phenyl rings
p–p interactions between the p-clouds of the triazine rings,
p
p
p–p
due to their mutual orientation.
Fig. 2. View of the X-ray (a) and gas-phase structure of 1 (b). Thermal ellipsoids are
Fig. 3. View of the X-ray (a) and gas-phase conformation of 2 (b). Thermal ellipsoids
shown at the 50% probability level.
are shown at the 50% probability level.

J. Janczak, R. Kubiak / Journal of Molecular Structure 920 (2009) 75–81
79
Fig. 4. View of the NAHꢀ ꢀ ꢀN hydrogen bonded 1D-polymer of 1 (a) and the molecular arrangement in the crystal showing the zig-zag layers and the stacks of melamine rings
(b).
In the crystal of 2, the molecules related by an inversion cen-
ter interact via two pairs of almost linear NAHꢀ ꢀ ꢀN hydrogen
bonds (see Table 3) forming 1D-polymer (Fig. 5a). In addition,
the 1D-polymer of hydrogen bonded molecules interact with an-
other molecules, which are also arranged in the 1D-polymer, re-
lated by a screw twofold symmetry via bent NAHꢀ ꢀ ꢀN hydrogen
bonds forming together three-dimensional hydrogen bonded
supramolecular network. As can be seen from the Fig. 5b the
1D-polymer of hydrogen-bonded molecules are running in the
crystal along the a-axis and with the neighbours they form a
wave-like layers parallel to the (010) plane. Between these lay-
[27,28] is built of two six-membered aromatic rings (C6 and
C3N3) which illustrate Scheme 3.
The first group (motif 1) represents the phenyl derivative and is
characterised by the directly joined rigid aromatic rings. The an-
other group represented by benzyl derivatives (motif 2) in which
the aromatic rings are joined together by the aliphatic methylene
group. The molecules of compounds containing motif 1 [27,28] re-
main essentially planar or close to planar due to the partial delocal-
isation of the p-electrons of the aromatic rings along the inter-ring
CAC bond that is impossible in molecules containing motif 2. Thus
the conformation of the molecules containing motif 1 allows for
denser arrangement of molecules in crystal than containing motif
2, since they contain the relative flexible link (Table 4). The
arrangement of molecules containing motif 1 is mainly determined
ers there are not observed any
p–p interactions, since the rings
in the stacks (in the b-direction) are mutually shifted, but in-
stead there are present the bent NAHꢀ ꢀ ꢀN hydrogen bonds that
link the layers (Fig. 5b). The absence of
p
–p
interactions be-
by the p–p interactions between the p-clouds of the aromatic rings
tween the
formation of the molecule, and not by the methylene group
that join the triazine and phenyl rings in 2, since the inter-
p
-clouds of the aromatic rings is caused by the con-
whereas the arrangement of molecules containing motif 2 is
mainly determined by the directional NAHꢀ ꢀ ꢀN hydrogen bonds.
In consequence, the density of the crystal 1 is greater than the crys-
p–p
actions in the crystal of 1 are observed. Similarly as for molecule
1, the conformation of molecule 2 allows the formation of the
hydrogen-bonded 1D-polymer and in addition on the formation
of bent NAHꢀ ꢀ ꢀN hydrogen bonds that are absent in the crystal
of 1.
tal 2, since in 1 the crystal packing stabilises the p–p interactions
between the triazine rings which are absent in the crystal of 2. In
addition the lesser density of crystal 2 in relation to crystal 1 re-
sults also from the presence of the methyl group substituted to
the phenyl ring.
Comparing the present results obtained for 1 and 2 with our
previous data obtained for 2,4-diamino-6-(20-cyanophenyl)-1,3,5-
triazine [27] and 2,4-diamino-6-(30cyanophenyl)-1,3,5-triazine
and 2,4-diamino-6-(40-cyanophenyl)-1,3,5-triazine [28] it can be
concluded that each of the molecules discussed here and in Ref.
4. Conclusion
Two crystals of triazine derivative, 2,4-diamino-6-benzyl-1,3,5-
triazine (1) and 2,4-diamino-6-(40-methylbenzyl)-1,3,5-triazine (2)

80
J. Janczak, R. Kubiak / Journal of Molecular Structure 920 (2009) 75–81
Fig. 5. View of the NAHꢀ ꢀ ꢀN hydrogen bonded 1D-polymer of 2 (a) and view the crystal structure of 2 along the a-axis showing the vave-like layers (b).
tively high temperature for initialisation, but in a short time, since
prolonged heating leads to increasing quantity of melamine as a
by-product. The molecular arrangement depends on conformation
H
H
N
N
N
N
of the molecules. The directional NAHꢀ ꢀ ꢀN hydrogen bonds and
stacking interactions lead to denser arrangement in 1 than in 2,
since in the structure of 2 the interactions are absent. The
molecular orbital calculations show quite similar conformation of
1 as present in the crystal while the gas-phase and X-ray confor-
mation of 2 is different.
p–
N
N
p
p–p
motif 1
motif 2
Scheme 3.
Table 4
5. Supplementary material
Comparison of the crystal density of the triazine derivatives.
Compound
Crystal density
(g/cm3)
Ref.
The X-ray crystallographic data for the structures reported in
this paper have been deposited at the CCDC as supplementary
2,4-diamino-6-(20-cyanophenyl)-1,3,5-triazine
2,4-diamino-6-(3-cyanophenyl)-1,3,5-triazine
2,4-diamino-6-(4-cyanophenyl)-1,3,5-triazine
2,4-diamino-6-benzyl-1,3,5-triazine (1)
1.409
1.441
1.471
1.388
1.256
[27]
[28]
[28]
This work
This work
data, CCDC 699095
Copies of the data can be obtained on application to CCDC,
12 Union Road, Cambridge CB2 1EZ, UK. E-mail:
& 699094 for (1) and (2), respectively.
2,4-diamino-6-(40-methylbenzyl)-1,3,5-triazine (2)
deposit@ccdc.cam.ac.uk.
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