Synthesis, structure and characterisation of two 2,4-diamino-6-R-1,3,5- triazine derivatives (R=3-cyanophenyl and 4-cyanophenyl)

Article abstract of DOI:10.1016/j.molstruc.2005.04.028

Two triazine derivatives, 2,4-diamino-6-(3′-cyanophenyl)-1,3,5- triazine (1) and 2,4-diamino-6-(4′-cyanophenyl)-1,3,5-triazine (2), in the crystalline form by addition of cyanoguanidine to the 1,3- and 1,4-dicyanobenzene have been obtained. In both cases

Full text of DOI:10.1016/j.molstruc.2005.04.028

Journal of Molecular Structure 751 (2005) 74–84
www.elsevier.com/locate/molstruc
Synthesis, structure and characterisation of two
2,4-diamino-6-R-1,3,5-triazine
derivatives (RZ3-cyanophenyl and 4-cyanophenyl)
*
Jan Janczak , Ryszard Kubiak
´
Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Okolna 2 str., P.O. Box 1410, 50 950 Wrocław, Poland
Received 26 February 2005; revised 11 April 2005; accepted 15 April 2005
Available online 27 June 2005
Abstract
Two triazine derivatives, 2,4-diamino-6-(30-cyanophenyl)-1,3,5-triazine (1) and 2,4-diamino-6-(40-cyanophenyl)-1,3,5-triazine (2), in the
crystalline form by addition of cyanoguanidine to the 1,3- and 1,4-dicyanobenzene have been obtained. In both cases the addition of
cyanoguanidine to the CbN group of dicyanobenzene isomers and formation the triazine ring needs migration of both hydrogens from one
amine group of cyanoguanidine to its cyano group. In the final step of the 1,3,5-triazine ring closing reaction, the CbN group of
dicyanobenzene contributes in the migration of hydrogen from one amine group to the cyano group of cyanoguanidine. The addition of
cyanoguanidine molecule, in both cases (1,3-dicyanobenzene and 1,4-dicyanobenzene), takes place only when one of two CbN groups of
dicyanobenzene is incorporated into triazine ring. Both triazine derivatives crystallise in the monoclinic system in the space group of P21/c
(1) and C2/c (2). In the crystal the molecules are not planar, but due to small rotations about the C–C bond the cyanophenyl and the 1,3,5-
triazine rings are inclined by 3.4(1) and 17.3(1)8 in 1 and 2, respectively. Meanwhile, the geometries of isolated molecules 1 and 2, both are
planar, when optimised theoretically. Thus in the crystal the rotation of one ring in relation to other results from the intermolecular
interactions like hydrogen bonds, p–p interactions between the aromatic rings and the crystal packing forces. The rotation barrier for the
rings rotation around the inter-rings C–C bond is w28.4 and w27.7 kJ/mol for (1) and (2), respectively.
q 2005 Elsevier B.V. All rights reserved.
Keywords: Triazine derivative; Transformation; Cyanoguanidine; Crystal structure; DFT
1. Introduction
non-covalent supramolecular architectures. The usually
weaker C–H/O and C–H/N hydrogen bonds also play a
significant role in the formation and/or stabilisation of
supramolecular architectures, especially in the biological
systems [13,14]. The formation of non-covalent association
of proteins and lipids, formation of a phospholipid bilayer,
interaction of a transcription factor with DNA, and folding
of tRNA into its three-dimensional conformation are
examples of the processes that in a part depend on the
weaker C–H/O and C–H/N interactions [14].
The triazine derivatives studied here form characteristic
supramolecular structures. Both triazine derivatives have
been obtained from dicyanobenzene isomers in the presence
of cyanoguanidine. Our interest in the investigations of the
cyano-compounds such as o–dicyanobenzene [15], 2,3-
dicyanonaphthalene [16] or cyanopyridine isomers [17]
arise from their ability to catalytic tetramerisation with the
formation of the phthalocyaninato(2-) or naphthalocyani-
nato(2-) macrocyclic rings [18,19], or to oligomerisation
Self-assembly of small molecules into non-covalent
supramolecular arrays is extensively used in the crystal
engineering and technology [1]. The hydrogen bonding
system is the main key for organisation of the molecules
containing complementary arrays of the hydrogen bonding
sites [2–6]. The N–H/N, N–H/O and O–H/O hydrogen
bonds have been used for designing various supramolecular
nanoarchitectures: layers, ribbons, sheets, tubes, tapes and
spheres [7–12]. Certain supramolecular motifs of hydrogen
bonding patterns of symmetric and translationally repetitive
occurrence are important for design of the crystals with
*
Corresponding author. Tel.: C48 71 343 5021; fax: C48 71 344 10 29.
E-mail address: janczak@int.pan.wroc.pl (J. Janczak).
0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2005.04.028

J. Janczak, R. Kubiak / Journal of Molecular Structure 751 (2005) 74–84
75
was mixed with m–dicyanobenzene in the molar proportion
of 1:1. Next the mixture was pressed into pellets, and they
were inserted into an evacuated glass ampoule and sealed.
The ampoule (ca 15 cm long) was annealed in the
temperature gradient, hot zone at about 250 8C in which
were the pellets and cold zone at 230 8C in which after one
day colourless crystals were present. A similar procedure
has been used for the p–isomer, but in this case the hot and
cold zone was about 30 8C higher than for m–isomer (280
and 260 8C, respectively). In both cases, by a crushing the
ampoule no enhanced pressure in it has been stated. An
elemental analysis of the crystals formed during the heating
process indicates on the composition of C10H8N6 in both
cases (found: C, 56.46; H, 3.84; N, 39.70%, calculated for
C10H8N6: C, 56.59; H, 3.80 and N, 39.61%). The single
crystal analyses give the structures-the triazine derivatives
and indicate that only one CbN group of both isomers
undergoes transformation in presence of cyanoguanidine.
Therefore, the reactions of cyanoguanidine with m– and
p–dicyanobenzene have been performed in the same
thermal conditions as previously, but the reagents were
taken in the molar proportion of 2:1 that would indicate that
both CbN groups of m– or p–isomer of dicyanobenzene
could be transformed. However, after one day in both
ampoules (with m–dicyanobenzene and p–dicyanobenzene)
two kinds of colourless crystals were present. By a crushing
the ampoules, in contrast to the first samples (the reagents
taken in 1:1) an explosion and sharp smell have been stated.
Selected single crystals were checked on a KUMA KM-4
diffractometer with area CCD detector. One kind of the
crystals is identical in both ampoules and is the known
monoclinic form of melamine [25], while the second kind of
the crystals is identical with those obtained in the reaction of
m–dicyanobenzene or p–dicyanobenzene with cyanoguani-
dine take in the molar proportion of 1:1. Always in the
reaction of m–dicyanobenzene or p–dicyanobenzene with
excess of cyanoguanidine in relation to dicayanobenzene
isomers (more than 1:1) the monoclinic melamine crystals
have been observed and have been checked several times
using different molar proportion (1.5:1, 2:1 and 3:1).
N
C
N
N
N
C
C
C
N
3
3
N
C
N
N
N
N
C
sp2
Scheme 1.
sp
with the formation of trimers [20]. The cyanopyridine
isomers as well as others cyanocompound due to their
donation features are useful in the field of coordination
chemistry and have been used to complexation of
metallophthalocyanines [21–23].
In the course of our work on metallophthalocyanines
syntheses we have stated many times that prolonged heating
of phthalonitrile with powdered metals leads not only to
metallophthalocyanines (main products), but also leads to
the formation of colourless crystals of a triazine deriva-
tive—a product of trimerisation of phthalonitrile. During the
trimerisation only one CbN group changes the orbital
hybridisation from sp to sp2 yielding the triazine derivative
(Scheme 1).
To expand the understanding of the functionality and
reactivity of the CbN groups in phthalonitrile, most recently
we investigated the transformation process of CbN in
o–dicyanobenzene at the presence of cyanoguanidine [24].
Presently we have investigated the two other isomers of
dicyanobenzene (m– and p–isomer) in presence of cyano-
guanidine. The main aims of this work have been focused at:
(1) the influence of the localisation of CbN groups in the
benzene ring on the transformation process, (2) one or two
CbN groups undergoing transformation at the presence of
cyanoguanidine with the formation of triazine derivative,
(3) correlating of the reactivity of CbN group(s) with the
electronic structure and the distribution of the charge
density of their parent dicyanobenzene isomers that form
the studied here triazine derivatives. The distribution of the
charge density, especially on the function groups enables to
inside into the nature and character of the chemical bonds
and also indicate the active side(s) in the molecules. This
will be helpful for understanding the transformation
mechanism of CbN group(s) in the m– and p–dicyanoben-
zene in presence of cyanoguanidine yielding the triazine
derivatives.
2.2. IR-spectroscopy
IR spectra (Fig. 1(a) and (b)) of solid materials as a Nujol
mulls were recorded at room temperature on a Bruker IFS
113 V FTIR spectrometer (4000–450 cmK1). Resolution
was set to 2 cmK1
.
2. Experimental
2.3. X-ray crystallography
2.1. Preparation
A colourless single crystal of 2,4-diamino-6-(30-cyano-
phenyl)-1,3,5-triazine and 2,4-diamino-6-(40-cyanophenyl)-
1,3,5-triazine with approximate dimensions of 0.32!
0.22!0.20 and 0.44!0.24!0.18 mm were used for data
collection on a four-circle KUMA KM-4 diffractometer
equipped with a two-dimensional area CCD detector. The
Cyanoguanidine (99% purity), m–dicyanobenzene (over
99% purity) and p–dicyanobenzene (98% purity) were
purchased from Sigma-Aldrich and were used for the
syntheses without further purification. The cyanoguanidine

76
J. Janczak, R. Kubiak / Journal of Molecular Structure 751 (2005) 74–84
of intensities, correction for Lorenz and polarisation effects
(a)
1.0
0.8
0.6
0.4
0.2
were performed using KUMA KM-4 CCD software [26].
The face-indexed analytical absorption was calculated using
the SHELXTL program [27].
The structure was solved by direct methods and refined
with anisotropic thermal parameters for all non-hydrogen
atoms using the SHELXL-97 program [28]. The hydrogen
atoms were located from difference Fourier maps, and their
positional parameter were refined, but temperature factors
were constrained with the UisoZ1.2Uiso of the carbon atoms
joined directly the H atom, or UisoZ1.2Uiso of the nitrogen
atoms joined directly the H atom. The final difference
Fourier maps showed no peaks of chemical significance.
The final agreement factors and details of data collection are
summarised in the Table 1.
N
N
N
4000
3500
3000
2500
2000
1500
1000
500
v [cm–1
]
1.0
0.8
0.6
0.4
0.2
(b)
N
N
2.4. Theoretical calculations
N
4000
3500
3000
2500
2000
1500
1000
500
Ab initio molecular orbital calculations full geometry
optimisation were performed with the GAUSSIAN98 program
package [29]. All calculations were performed by the
density functional three-parameters hybrid (B3LYP)
methods [30,31] with the 6-31CG(d) basis set starting
from the X-ray geometry. As convergence criterion the
threshold limits of 0.00025 and 0.0012 a.u. were applied for
the maximum force and the displacement, respectively. The
rotation barriers of the cyanophenyl and triazine rings
around the inter-rings C–C bond were calculated using the
same basis set functions and the GAUSSIAN 98 program. In
this case, the all full optimised parameters were kept frozen
v [cm–1
]
Fig. 1. IR-spectra of: (a) 2,4-diamino-6-(30-cyanophenyl)-1,3,5-triazine;
and (b) 2,4-diamino-6-(40-cyanophenyl)-1,3,5-triazine as nujol mulls. The
bands of the nujol are assigned as N.
graphite monochromatised Mo Ka radiation (lZ
˚
0.71073 A) and u-scan technique with DuZ0.758 for one
image were used for data collection. The lattice parameters
were refined by least-squares methods on the basis of all
collected reflections with F2(2s(F2)). One image was
monitored as a standard for every 60 images. Integration
Table 1
Crystallographic data for 2,4-diamino-6-(30-cyanophenyl)-1,3,5-triazine (1) and 2,4-diamino-6-(40-cyanophenyl)-1,3,5-triazine (2) and details for data
collection and refinement parameters
Formula
C10H8N6
C10H8N6
Mol. wt.
212.22
212.22
Crystal system, space group
Monoclinic, P21/c
Monoclinic, C2/c
˚
Unit cell dimensions a, b, c, (A)
b (8)
10.116(2), 7.351(1), 13.181(3)
25.373(5), 3.778(1), 21.480(4)
93.76(3)
111.44(3)
3
Volume, V (A )
˚
978.1(3)
1916.6(8)
Z
4
8
D
calc (g/cm3)
1.441
1.471
Dobs measured, flotation (g/cm3)
1.44
1.47
˚
Radiation, Mo Ka, l, (A)
2q range
0.71073
0.71073
3-60.52
3-60.16
Temperature, (K)
Refls. Collected
Independent refls.
Observed refls.
293
293
9214
5925
2852 (RintZ0.0411)
2246
2401, (RintZ0.0195)
1491
Absorption coefficient, m, (mmK1
)
0.097
0.099
Correction
Lorenz, polarisation, face-indexed analytical
absorption, TmaxZ0.956, Tmin.Z0.975
Lorenz, polarisation, face-indexed analytical
absorption, TmaxZ0.952, Tmin.Z0.976
Refinement on F2
R(F2(2s(F2))a
wR (F2 all reflections)b
0.0371
0.0316
0.0525
0.0861
Goodness-of-fit, S
˚
Residual electron density, e A
1.109
1.057
K3
C0.125. K0.152
C0.144, K0.125
a
RZSkFoj–kFcj/SFo.
ꢀ
ꢁ1=2
P
P
b
2
2
2
wRZ
½w½ðFo2 KFc2Þ ꢀ= wFo4
; wK1 Zs2ðFo2ÞCð0:0011PÞ for (1) and wK1 Z½s2ðFo2ÞCð0:0381PÞ C0:7470Pꢀ for (2), where PZðFo2 C2Fc2Þ=3.

J. Janczak, R. Kubiak / Journal of Molecular Structure 751 (2005) 74–84
77
while the ring of 3-cyanophenyl (or 4-cyanophenyl) was
rotated in steep of 58 around the inter-rings C–C bond (C2–
C7 bond for 3-cyanophenyl or C1–C7 for 4-cyanophenyl
see Fig. 2(a) and (b)). The high of the rotation barriers were
than derived from the variations of the total energy as
functions of the rotation angle (the torsion angle of C1–C2–
C7–N3 (Fig. 2(a)) or C2–C1–C7–N2 (Fig. 2(b)) that define
the inter-rings dihedral angle). The analysis of the
theoretical charge density r(r) and Laplacian V2r(r) at the
bond critical points were calculated using the AIMPAC
program [32]. The topological properties of the charge
density distribution are summarised in terms of their critical
points, i.e. the points where V(r(r)) is equal to zero.
(a)
(b)
3. Results and discussion
3.1. Synthesis
During the heating process of m-dicyanobenzene and
p-dicyanobenzene in presence of cyanoguanidine the
transformation of only one of two CbN groups takes
place with the formation of triazine derivatives. To under-
stand the reaction mechanism the canonical forms of
cyanoguanidine, as well as the distribution of the charge
density on the CbN groups in dicyanobenzne isomers
should be taken into account. The X-ray determination of
the charge density in cyanoguanidine [33] shows, that to
explain the structure of cyanoguanidine molecule at least
five resonance structures should be taken into account
Fig. 2. View of the X-ray molecular structure of 2,4-diamino-6-(30-
cyanophenyl)-1,3,5-triazine (a) and 2,4-diamino-6-(40-cyanophenyl)-1,3,5-
triazine (b) with the atom labelling. Thermal ellipsoids are shown at a
probability level of 50%. H atoms are shown as spheres with arbitrary radii.
_
N
N
+
H N
C
C
H N
2
2
_
C
N
C
N
H N
2
H N
2
(c)
+
(d)
N
_
N
C
H N
2
+
H N
2
C
_
C
N
C
N
H N
2
N
H N
2
+
(b)
(e)
C
H N
2
C
N
H N
2
(a)
N
NH
N
NH
C
H
C
HN
C
H
C
H N
2
H N
2
H N
2
C
C
N
C
C
N
N
N
H N
2
HN
HN
HN
(f)
(g)
(h)
(i)
Scheme 2.

78
J. Janczak, R. Kubiak / Journal of Molecular Structure 751 (2005) 74–84
(Scheme 2, resonance structures of a–e). The contribution of
the respective resonance form in the real structure is
significant, since the observed bond lengths [33] as well as
the net atomic charges on the atoms of cyanoguanidine
molecule are intermediate between the standard values [34].
The shortening of both C–NH2 bonds explains well the (b) to
(e) canonical forms. Besides these five resonance structures of
cyanoguanidine molecule few others canonical forms can be
proposed (Scheme 2, resonance forms of h and i).
of CbN group of cyanoguanidine. The migration of one
hydrogen atom from NH2 group to CbN group is possible in
cyanoguanidine itself, yielding the resonance structure with
imine groups, since as shown the molecular orbital
calculations the energy of this form is comparable to those
of the form (a). However, the migration of the second H
atom from amine group to cyano group requires the
presence of the highly polar CbN group of m– or
p–dicyanobenzene that contains oppositely net charged C
and N atoms. Thus the CbN group of dicyanobenzene
contributes in the migration of HC from one NH to the other
NH yielding NH2 (Scheme 3). The formation of triazine
derivative from m- and p-dicyanobenzene in presence of
cyanoguanidine takes place independent on the molar
proportion of substrates (1:1, as well as in all cases with
excess of cyanoguanidine). The transformation process of
both CbN groups of m- or p-dicyanobenzene in presence of
excess of cyanoguanidine (see experimental part) has been
not stated. The excess of cyanoguanidine used under
reaction conditions undergoes dimerisation with the for-
mation of monoclinic crystals of melamine and with partial
decomposition (2(NH2)2CNCbN/C3N3(NH2)3C1/2
NH2NH2 C1/2 (CN)2). Melamine crystals have been
identified on single crystal KUMA KM-4 CCD diffract-
ometer. The gaseous by-product of the melamine formation
from cyanoguanidine is in agreement with the observations
and the results of the experiment. The formation mechanism
of gaseous by-products has been discussed in details in our
previous work reporting investigation of o-dicyanobenzene
with cyanoguanidine [24]. It should be add that the reaction
takes place in the hot zone, but during the annealing process
the formed triazine derivatives migrate to the cooler zone
The canonical forms with the imine group, that form as a
result of HC migration from the amine group to the highly
electronegative cyano group, will be helpful for under-
standing the reaction mechanism of cyanoguanidine with m-
and p-dicyanobenzene with the formation of 2,4-diamino-6-
(30-cyanophenyl)-1,3,5-triazine (1) and 2-(30-cyanophenyl)-
4,6-diamino-1,3,5-triazine (2) as illustrates the Scheme 3.
The cyanoguanidine in its canonical form of (h) or (i)
interacts with the CbN group of m– or p–dicyanobenzene.
This interaction results the migration of the HC to the more
negative N atom (with about K0.5 net charge) and
containing the lone-pair of electrons. This process yields
to the change of the hybridisation of the orbitals from sp to
sp2 on the carbon atom of the interacting CbN group (a).
Next the terminal NH group of cyanoguaninidne accepts the
proton forming NH2 group with the positive charge on the N
atom. Simultaneously, the positively charged carbon atom
interacts with the oppositely charged nitrogen atom forming
C–N bond (b). Consequently, the NHC2 group accepts one
pair of electron from the neighbouring double CaN bond (c)
changing the hybridisation of the orbitals from sp to sp2 of
the C atom and finally the C–N bond closes the aromatic
triazine ring (d). Thus the triazine ring formation needs
migration of both H atoms of one NH2 group to the N atom
N
N
H N
2
H N
2
H N
N
C
C
2
C
C
NH
NH
C
C
_
N
NH
N
NH
2
N
NH
+
C
C
C
C
N
N
(b)
(a)
N
H N
NH
2
2
H N
2
N
C
C
N
N
NH
2
+
_
N
N
C
C
N
(c)
(d)
C
N
Scheme 3.

J. Janczak, R. Kubiak / Journal of Molecular Structure 751 (2005) 74–84
79
forming single crystals as a result of self-assembling and
non-covalent intermolecular interactions.
K714.468 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 6.188 D and 7.015 D, respectively.
3.2. Vibrational spectroscopy
Both aromatic six-membered rings, i.e. benzene and
triazine, of both compounds in the crystal are almost planar
(the displacements of the C atoms from the mean plane of
The IR spectra of 2-(30cyanophenyl)-4,6-diamino-1,3,5-
triazine (1) and 2,4-diamino-6-(40-cyanophenyl)-1,3,5-tria-
zine (2) (Fig. 1(a) and (b)) show the characteristic band at
2226 cmK1 for (1) and 2229 cmK1 for (2) assigned to the
cyano group. These bands are slightly shifted to the lower
frequency in relation to that observed in the spectrum of
parent dicyanobenzene in which the CbN band is observed
at 2233 cmK1. In (1) and (2) the nitrogen atom of the CbN
group is involved in the hydrogen bonds. This CbN/H
hydrogen bonding interaction results in the decrease of the
population for molecular orbital of CbN group, hence
decrease in the bond order and the stretching force constant
yielding shift of the absorption band. The shift correlates
with the CbN bond lengths observed in the X-ray structures
(see next capital). The bands observed in the spectral region
of 3500–3400 cmK1 can be attributed to the NH2 asym-
metric stretching vibration of the two amine groups
substituted the triazine ring, whereas the broad band at
about 3325 cmK1 is attributed to the NH2 symmetric
stretching vibration. The broad band at around 3160 cmK1
supported by the theoretical calculations [35] and by the
analysis of the IR spectrum of melamine [36] can be
assigned to a mode having a superposition of N–H/N
hydrogen bond and side-chain asymmetric C–N stretching.
In the spectral region of 1650–1500 cmK1 two strong and
two weak bands are observed. The strong band at 1639 for
(1) and 1637 cmK1 for (2) according to the literature can be
attributed to the NH2-bending, while the band at 1545 (for
1) and 1542 cmK1 (for 2) can be assigned to the ring-
quadrant stretching [36]. The bands at 1258 and 1210 cmK1
(for 1) and 1256 and 1208 cmK1 (for 2) are assigned to side-
chain in plane C–N–C and N–C–N bending [37,38]. The
band at 814 cmK1 for (1) and at 826 cmK1 for (2) can be
attributed to C–H deformation in 1,3- and 1,4-disubstituted
benzene derivatives. The other band at 776/777 cmK1 is
assigned to ring-sextant out-of-plane bending, while
the band in the range of 560–550 cmK1 as a contribution
tone of NH2-bending and NH2-rocking vibration [37,38].
The band of the C–H of the phenyl ring are overlapped with
the bands of the Nujol.
˚
benzene are smaller than 0.012(2) A, the displacements of C
or N from the mean plane of triazine are smaller than
0.017(2)), but show significant distortions from the ideal
hexagonal form. The internal C–N–C angles in the triazine
ring are significantly smaller than 1208 while the internal N–
C–N angles are significantly greater than 1208 (see Fig. 2
and Tables 2 and 3). This is a result of the steric effect of a
lone-pair of electrons at the N atoms of triazine rings,
predicted by the valence-shell electron-pair repulsion theory
(VSEPR) [39,40]. The ab initio optimised geometry of the
triazine ring in (1) and in (2) shows a similar correlation
between the internal C–N–C and N–C–N angles within the
ring as observed in the crystal. Thus, the triazine ring
distortion in both compounds mainly results from the steric
effect on lone-pair of electrons. However, the slightly
differences in the equivalent internal C–N–C and N–C–N
angles within the triazine ring in both compounds should be
attributed to the intermolecular interactions (hydrogen
bonding system and p–p between the rings) and crystal
packing forces. The small differences between the C–C
bond lengths and C–C–C angles in benzene rings arise
mainly from the 1,3- or 1,4-substitution effect of CbN
group and diaminotriazine ring. The slightly shorter C–C
bonds observed in the crystals in relation to the gas-phase
(ab initio) results from the p–p stacking interactions, since
in both crystals the rings are separated by a distance of
˚
w3.4 A, the distance for the interacting p-aromatic ring
system [41]. The p–p interaction contributes to the
shortening of the C–C bonds within the aromatic ring in
both crystals in relation to the gas-phase structure obtained
by the molecular orbital calculations. The X-ray C–CN
˚
˚
distances of 1.442(2) A in (1) and 1.438(2) A in (2) are
compared with those obtained by molecular orbital
calculations, while the triple CbN bonds with distances of
˚
˚
1.145(2) A in (1) and 1.142(2) A in (2) are slightly shorter
than those obtained by molecular orbital calculations. The
C–CbN angle in both crystals is slightly distorted from 1808
as obtained by the ab initio calculations. These distortions
should be attributed to the hydrogen-bonding interaction in
which the N atom of CbN group acts as acceptor H. The
most interesting feature between the ab initio gas-phase and
X-ray crystal structure of (1) and (2) is the conformation of
the molecules, especially the relative orientation of the
triazine and benzene rings around the inter-rings C–C bond.
In the crystal of (1) and (2) the rings are not coplanar in
contrast to the gas-phase structures in which the molecules
are whole planar. In the crystal the rotation of the rings to
each other in (1) equals to 3.4(1)8 and 17.3(1)8 in (2). The
slightly rotation of the rings around inter-rings C–C bond in
3.3. X-ray and gas-phase structures
The molecular geometry of (1) and (2) obtained by single
crystal X-ray analysis with the labelling of the atoms are
shown in Fig. 2(a) and (b). The X-ray experimental
geometrical parameters are collected in Tables 2 and 3
together with ab initio fully optimised parameters that
correspond to gas-phase structures. The absolute energies
calculated using B3LYP methods and 6-31CG(d) basis set
functions were found to be K714.437 a.u. for (1) and

80
J. Janczak, R. Kubiak / Journal of Molecular Structure 751 (2005) 74–84
Table 2
Bond distances and angles 2,4-diamino-6-(30-cyanophenyl)-1,3,5-triazine
Table 3
Bond distances and angles 2,4-diamino-6-(40-cyanophenyl)-1,3,5-triazine
˚
(A, 8)
˚
(A, 8)
X-ray
Ab initio
X-ray
Ab initio
C1–C2
1.389(3)
1.393(3)
1.388(3)
1.368(3)
1.377(3)
1.390(3)
1.444(3)
1.145(4)
1.488(3)
1.334(3)
1.362(3)
1.338(3)
1.321(3)
1.333(3)
1.336(3)
1.335(3)
1.333(3)
118.5(3)
120.5(3)
120.5(3)
119.9(3)
120.3(3)
120.4(3)
118.8(3)
178.9(3)
119.8(2)
117.3(2)
113.6(2)
117.1(2)
125.1(2)
114.7(2)
117.1(2)
126.5(2)
112.9(2)
127.1(2)
1.400
1.404
1.396
1.394
1.407
1.403
1.436
1.164
1.490
1.338
1.350
1.341
1.342
1.350
1.338
1.354
1.353
119.3
120.5
120.4
119.4
120.3
120.1
119.8
179.9
120.1
117.3
114.5
116.9
125.8
114.0
117.4
125.7
114.6
125.4
C1–C2
1.3913(14)
1.3822(16)
1.3935(17)
1.3902(15)
1.3802(15)
1.3862(16)
1.4378(15)
1.1421(15)
1.4917(15)
1.3346(15)
1.3568(14)
1.3347(14)
1.3373(16)
1.3400(15)
1.3544(14)
1.3304(14)
1.3256(14)
120.2(1)
1.404
1.391
1.406
1.406
1.391
1.404
1.435
1.164
1.490
1.338
1.350
1.342
1.354
1.342
1.350
1.354
1.338
120.6
119.9
119.8
119.9
120.6
119.2
120.1
180.0
120.4
117.3
114.6
125.7
114.0
125.7
114.6
125.4
116.9
125.7
C2–C3
C2–C3
C3–C4
C3–C4
C4–C5
C4–C5
C5–C6
C5–C6
C6–C1
C6–C1
C6–C10
C4–C10
C10–N10
C2–C7
C10–N10
C1–C7
C7–N1
C7–N2
N1–C8
N2–C9
C8–N2
C9–N1
N2–C9
C9–N9
C9–N3
N1–C8
N3–C7
C8–N3
C8–N8
C8–N8
C9–N9
N3–C7
C1–C2–C3
C2–C3–C4
C3–C4–C5
C4–C5–C6
C5–C6–C1
C6–C1–C2
C1–C6–C10
C6–C10–N10
C1–C2–C7
C2–C7–N1
C7–N1–C8
N1–C8–N8
N1–C8–N2
C8–N2–C9
N2–C9–N9
N2–C9–N3
C9–N3–C7
N3–C7–N1
C1–C2–C3
C2–C3–C4
C3–C4–C5
C4–C5–C6
C5–C6–C1
C6–C1–C2
C3–C4–C10
C4–C10–N10
C2–C1–C7
C1–C7–N2
C7–N2–C9
N2–C9–N1
C9–N1–C8
N1–C8–N3
C8–N3–C7
N3–C7–N2
N2–C9–N9
N1–C8–N8
119.7(1)
120.6(1)
118.9(1)
121.3(1)
119.3(1)
120.8(1)
178.4(2)
121.6(1)
117.1(1)
113.4(1)
125.6(1)
114.8(1)
124.9(1)
114.2(1)
127.0(1)
116.5(1)
118.4(1)
(1) could be understand if take into account the highly polar
CbN group and the diaminotriazine ring substituted in 1,3-
positions of benzene ring. This location of the substituents
makes the slight rotation of the rings around inter-rings C–C
bond. For a comparison in the studied by us the crystal of 2-
(20-cyanophenyl)-4,6-diamino-1,3,5-triazine the steric
effect and the interaction of the polar CbN group and
diaminotriazine ring around the inter-rings C–C bond is
much more greater (37.2(1)8) [24], due to the closest
location of substituents. However, the steric effect in the (2)
in which the substituents, i.e. polar CbN group and the
diaminotriazine ring, are located in 1,3-positions of benzene
ring, is not present, thus the rotation of the rings around the
inter-rings C–C bond results from the intermolecular
interactions and crystal packing forces.
one-dimensional chains. These chains in the crystal are
ꢀ
alternatively located parallel to the (020) and (020) planes
forming a p–p interacting stacking structure along the [010]
direction (Fig. 3). The inter-planar angle between the planes
of neighbouring chains equals to 33.1(2)8 (Fig. 3(b)). Within
Table 4
Hydrogen-bonding geometry for 2,4-diamino-6-(30-cyanophenyl)-1,3,5-
˚
triazine (A, 8)
D-H/A
D–H
H/ A
D/ A
D–H/ A
N9–H91/ N10a 0.86
2.428
2.305
2.258
2.728
2.735
2.486
3.106(3)
3.021(3)
3.110(3)
3.332(3)
3.321(3)
3.375(3)
136.3
140.8
170.8
127.5
126.6
160.1
N9–H92/ N1a
N8–H81/ N2a
N8–H82/ N9a
0.86
0.86
0.86
N8–H82/ N10a 0.86
C5–H5/ N10a
0.93
a
Symmetry code: KxC1, yC1/2, KzC1/2.
x,KyC1/2, zK1/2.
3.4. Intermolecular interaction and crystal packing
b
c
d
e
f
KxC2, KyC1, KzC1.
Kx, KyC1/2, zC1/2.
xC1, KyC1/2, zC1/2.
In the crystal the molecules of (1) related by the inversion
centre and the translation interact via two pairs of N–H/N
and weaker C–H/N hydrogen bonds (Table 4) forming
xC1, KyC1/2, zC1/2.

J. Janczak, R. Kubiak / Journal of Molecular Structure 751 (2005) 74–84
81
and in remaining as acceptor. One N atom of the three N
atoms of triazine ring (N3) does not form any hydrogen
bond due to the steric effect of relatively close location of
the cyano group.
(a)
The molecules of (2) related by an inversion centre form
by pair of almost linear hydrogen bonds (N8–H81/N1i
(iZKxC1, Ky, KzC1), Table 5) dimeric structure that in
the crystal form a stacking structure along the [010]
direction, but the rings are not parallel to the (101) plane,
but the normal to the weighted mean plane of molecule is
inclined by w79.9, 19.6 and 73.48 to the x, y and z-axis,
respectively. In contrast to the crystal of (1), in which the
p–p interaction within the stack takes place between the
triazine and benzene rings that are overlapped (Fig. 3(a)), in
the crystal of (2) the p–p interaction takes place only
between the triazine-triazine and benzene–benzene rings
and does not between the triazine–benzene rings, since
within one stack the molecules are related only by a
translation (Fig. 4). Within the stack the aromatic rings are
˚
separated by w3.4 A indicating p–p interaction [41]. Each
molecule of (2) is involved into six hydrogen bonds, in three
as a donor and in three as an acceptor. One of the N atoms of
triazine ring (N3) does not form any hydrogen bond.
(b)
3.5. Molecular conformation and the rotational barriers
The rotation of one ring relative to the other around the
inter-rings C–C bond (C2–C7 in (1) and C1–C7 in (2), see
Fig. 2) in the crystal is hindered due to the intermolecular
interactions, mainly the N–H/N hydrogen bonds (Figs. 3
and 4). However, in the gas-phase the rotation of the rings
around the inter-rings C–C bond is possible. Molecular
orbital calculations with fully optimisation performed on
isolated molecules of (1) and (2) show their planar
structures, in contrast to those in the crystals. The
calculations exposed two equivalent global maxima and
two equivalent minima on the potential energy surface
(PES) for both compounds. The value of rotation barriers
were derived from the variations of the total energy as
a function of rotation angles of one ring to the other
Table 5
Hydrogen-bonding geometry for 2,4-diamino-6-(40-cyanophenyl)-1,3,5-
˚
triazine (A, 8)
Fig. 3. View of the crystal packing of 1 showing the p–p interactions
between the overlapped rings: view along the b-axis (a) and c-axis (b).
Dashed lines show complementary arrays of hydrogen bonds.
D–H/ A
D–H
0.86
H/ A
D/ A
D–H/ A
N8–H81/
N1a
2.228
3.077(2)
168.8
one stack that is aligned to [010] direction the p-aromatic
˚
rings are separated by a distance of 3.33(1) A. This distance
N8–H82/
N10b
0.86
0.86
0.86
2.547
2.650
2.339
3.283(2)
3.359(2)
3.196(2)
144.1
140.5
173.8
N9–H91/
N10c
indicates on the strong p–p interactions between the
triazine and benzene rings along the stacks. These
interactions contribute to the shortening of the C–C and
C–N bonds within the aromatic rings in relation to those in
the gas-phase structure as obtained by the molecular orbital
calculations. Each molecule of (1) in the crystal is involved
into ten hydrogen bonds, in five of them it acts as a donor
N9–H92/
N2d
a
Symmetry code: KxC1, Ky, KzC1.
KxC1/2, KyC3/2, KzC1.
xC1/2, yK1/2, z.
b
c
d
KxC1, y, KzC3/2.

82
J. Janczak, R. Kubiak / Journal of Molecular Structure 751 (2005) 74–84
(a)
30
(a)
25
20
15
10
~28.4
5
0
0
45
90
135
180
225
270
315
360
Torsion Angle [deg.]
(b)
30
25
20
15
10
5
(b)
~27.7
0
0
45
90
135
180
225
270
315
360
Torsion Angle [deg.]
Fig. 5. Potential energy of molecules 1 (a) and 2 (b) in the function of the
rings rotation around the inter-ring C–C bond computed by molecular
orbital calculations at the B3LYP/6-31CG(d) level.
Fig. 4. View of the crystal packing of 2 showing the p–p interactions
between the overlapped rings: view along the b-axis (a) and a-axis (b).
Dashed lines show complementary arrays of hydrogen bonds.
˚
˚
1.488 to 1.505 A in (1) and from 1.490 to 1.506 A in (2)
supports this hypothesis. These values of inter-rings C–C
bond lengths have been obtained by DFT molecular orbital
calculations in which the torsion angles were kept to 908
(the rings are perpendicular to each other). In the
conformations of the molecules with the lower energies
(the planar conformation) the delocalisation of the p
electrons between the inter-rings C–C bond play important
role. Thus the inter-rings C–C bond possesses a slightly
double-bond character as a result of the delocalisation of p
electrons between the rings. This observation is quite
similar to that found in 2-(30-pyridyl)-1,3,5-triazanaphtha-
lene as well as in 2-(20-cyanophenyl)-2,4-diamino-1,3,5-
triazine, both compound studied by us [24,42]. The
contribution of the p electrons in the delocalisation along
the inter-rings C–C bond clearly evidenced the ellipticity of
the bond, 3 [43] that equals to 0.0913 and 0.0911 in 1 and in
2, respectively in optimised molecules (i.e. at the rotation
angle of the rings equals to 08). The decreasing of the 3 of
this bond for the molecules with the rings perpendicular to
each other to the values of 0.0172 (in 1) and 0.0169 (in 2)
shows that the p electrons several times smaller delocalised
over this inter-rings bond. The ellipticities have been
calculated at the bond critical points, i.e. at the ‘staddle’
points in the electron density along the bond between
(the respective torsion angle for 1 and 2 is C1–C2–C7–N3
and C2–C1–C7–N2, see Fig. 2) and the results are illustrated
in Fig. 5. As can be seen from the Fig. 5 during rotation of
one ring relative to other from 0 to 3608 in both compounds
two equivalent minima of energy at 0 and 1808 and two
equivalent maxima at 90 and 2708 are observed. The
rotation barrier between these conformations equals to
w28.4 and w27.7 kJ/mol for (1) and (2), respectively. The
difference between the energies of rotation barriers is not
great (w0.7 kJ/mol) results from the interaction of the polar
CbN group that is located more close in (1) than in (2) in
relation to the diaminotriazine ring. The rotation barrier at
908 between the equivalent minima (at 08 and 1808) is about
ten times greater than the energy RT (w2.5 kJ/mol), thus in
the absence of any specific interactions (as present in the
crystal) the rotation of the rings between the minima is
hindered. The difference between the energy of the
conformations of the molecules at 08 and 908 can be
attributed to the p-delocalisation energy of the p electrons
along the inter-rings C–C bond. At the rotation angle of 908
the delocalisation of the p electrons between the rings along
the inter-rings C–C bond is impossible since of the
symmetry of the orbitals. The lengthening of the along
the inter-rings C–C bond (C2–C7 of 1 and C1–C7 of 2) from

J. Janczak, R. Kubiak / Journal of Molecular Structure 751 (2005) 74–84
83
Table 6
Charge density topological parameters calculated for 2,4-diamino-6-(30-cyanophenyl)-1,3,5-triazine
K3
2
V r (e A
K5
˚
Length [A]
˚
r (e A
˚
Bond
)
)
l1
l2
l3
6.62
3
AT1-CP
CP-AT2
C1–C2
C2–C3
C3–C4
C4–C5
C5–C6
C6–C1
C6–C10
C10–N10
C2–C7
C7–N1
N1–C8
C8–N2
N2–C9
C9–N3
N3–C7
C8–N8
C9–N9
1.400
1.404
1.396
1.394
1.407
1.403
1.436
1.164
1.490
1.338
1.350
1.341
1.342
1.350
1.338
1.354
1.353
2.202
2.185
2.209
2.222
2.186
2.198
1.908
3.301
1.904
2.492
2.480
2.512
2.510
2.495
2.480
2.341
2.345
K24.350
K24.230
K24.631
K24.904
K24.093
K24.312
K21.975
16.694
K16.98
K16.89
K17.04
K17.21
K16.92
K17.03
K13.71
K25.58
K14.42
K21.36
K21.39
K21.97
K21.94
K21.40
K21.39
K20.78
K20.83
K13.99
K14.01
K14.12
K14.10
K13.78
K13.82
K12.90
K24.95
K13.22
K20.35
K20.18
K20.47
K20.06
K20.20
K20.37
K19.60
K19.63
0.214
0.206
0.207
0.221
0.228
0.232
0.063
0.025
0.091
0.060
0.071
0.074
0.073
0.064
0.060
0.063
0.062
0.720
0.702
0.702
0.681
0.692
0.719
0.694
0.443
0.693
0.444
0.906
0.466
0.897
0.456
0.873
0.443
0.444
0.682
0.703
0.697
0.714
0.721
0.687
0.749
0.722
0.798
0.895
0.445
0.875
0.455
0.894
0.465
0.911
0.909
6.67
6.54
6.41
6.61
6.54
4.64
67.23
7.50
K20.135
K26.599
K33.740
K31.886
K31.867
K33.684
K26.579
K23.306
K23.358
15.11
7.83
10.56
10.13
7.92
15.18
17.07
17.10
the joined atoms and have been summarised in the Tables 6
and 7 for the 1 and 2, respectively. At these staddle points
(where VrZ0), the three principal curvatures have one
positive value (l3, along the bond path) and two and the
negative (l1 and l2) perpendicular to the bond path defines
the (3K1) bond critical points (CP’s). These principal
curvatures (l1, l2 and l3,) define the interatomic surface
between the bonded atoms. The value of the charge density
(r) at the bond critical point indicates the bond order
while the two negative curvatures define the bond ellipticity,
3Zl1/l2K1 [43]. Thus the ellipticity is a measure of the p-
character of the bond, while the location of the bond critical
points correlate to the polar character of the bonds [44]. The
value of the charge density (r) at the bond critical points
correlate with the bond order as well as with the strength of
the bonds [45]. As was mentioned the calculated bond
ellipticity of the inter-rings C–C bond in both compounds
(1 and 2) at the rotation angle of 08 indicates on the partially
delocalisation of the p electrons of the aromatic triazine and
benzene rings along the inter-rings C–C bond. The
molecules in the conformation with rotation angle of 908
the value of 3 indicates the decreasing of the delocalisaton of
the p electrons between the rings along this inter-rings C–C
bond. Thus the values of the rotation energy barriers can be
assigned to the energy of the p delocalisation energy
between the rings. The calculated values of 3 for the
aromatic C–C bond in the six-membered cyanophenyl rings
ranges from 0.205 to 0.232. These values are about 2.5 times
greater than the value of 3 of the inter-rings C–C bond and
indicate that delocalisation of p electrons take place mainly
in the ring. The slightly differences of the 3 between the C–C
bonds within the cyanophenyl ring in 1 and 2 clearly
evidenced the substitution effect of the polar CN group and
the diaminotriazine ring substituted in 1,3- and 1,4-positions
that slightly perturb the symmetric delocalisation of the p
electrons present in the non-substituted benzene molecule.
Table 7
Charge density topological parameters calculated for 2,4-diamino-6-(40-cyanophenyl)-1,3,5-triazine
K3
2
V r (e A
K5
˚
Length [A]
˚
r (e A
˚
Bond
)
)
l1
l2
l3
6.65
3
AT1-CP
CP-AT2
C1–C2
C2–C3
C3–C4
C4–C5
C5–C6
C6–C1
C4–C10
C10–N10
C1–C7
C7–N2
N2–C9
C9–N1
C9–N9
N1–C8
C8–N3
C8–N8
N3–C7
1.404
1.391
1.406
1.406
1.391
1.404
1.435
1.164
1.490
1.338
1.350
1.342
1.354
1.342
1.350
1.354
1.338
2.194
2.221
2.216
2.216
2.221
2.194
1.910
3.303
1.900
2.494
2.480
2.511
2.343
2.511
2.480
2.343
2.494
K24.223
K24.836
K24.267
K24.267
K24.836
K24.223
K22.067
16.913
K16.87
K17.18
K16.96
K16.96
K17.18
K16.87
K13.70
K25.55
K14.37
K21.39
K21.40
K21.97
K20.80
K21.97
K21.40
K20.80
K21.39
K14.00
K14.12
K13.77
K13.77
K14.12
K14.00
K13.08
K24.99
K13.26
K20.35
K20.19
K20.48
K19.61
K20.48
K20.19
K19.61
K20.36
0.205
0.217
0.232
0.232
0.217
0.205
0.048
0.019
0.091
0.061
0.060
0.073
0.061
0.073
0.060
0.061
0.061
0.710
0.690
0.673
0.734
0.702
0.696
0.618
0.409
0.725
0.443
0.886
0.455
0.443
0.888
0.465
0.443
0.895
0.696
0.702
0.734
0.673
0.690
0.710
0.818
0.756
0.767
0.895
0.465
0.888
0.911
0.455
0.886
0.911
0.443
6.47
6.46
6.46
6.47
6.65
4.72
67.46
7.52
K20.109
K26.433
K33.725
K31.799
K23.325
K31.799
K33.725
K23.325
K26.433
15.30
7.86
10.64
17.08
10.64
7.86
17.08
15.30

84
J. Janczak, R. Kubiak / Journal of Molecular Structure 751 (2005) 74–84
´
´
[17] R. Kubiak, J. Janczak, M. Sledz, J. Mol. Struct. 610 (2002) 59.
[18] R. Kubiak, J. Janczak, J. Alloys Comp. 200 (1992) L7.
[19] K. Morishige, K. Araki, J. Chem. Soc., Dalton Trans. (1996) 4303.
[20] J. Janczak, R. Kubiak, Acta Chem. Scand. 53 (1999) 602.
[21] J. Janczak, R. Kubiak, Polyhedron 21 (2002) 265.
The location of the bond critical points on the bond paths
(Table 5) well correlate with their polar character.
The synthesis procedure described here and in our
previous paper [24] may be convenient and promising
procedure to obtain from various organic R–CN compounds
and cyanoguanidine a whole class of a new specific triazine
derivatives.
[22] J. Janczak, R. Kubiak, Inorg. Chim. Acta 342 (2003) 64.
´
´
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Additional material comprising full details of the X-ray
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