Structural similarity of hydrogen-bonded networks in crystals of isomeric pyridyl-substituted diaminotriazines

Article abstract of DOI:10.1021/cg101290r

Crystals of isomeric pyridyl-substituted diaminotriazines 1a-c and elongated analogues 2a-b were grown under various conditions, and their structures were solved by X-ray crystallography. Analysis of the structures revealed three shared features: (1) The compounds favor flattened conformations; (2) they participate in approximately coplanar hydrogen bonding according to motifs characteristic of diaminotriazines; and (3) these interactions play a key role in directing molecular organization. Together, the consistent molecular topologies and the shared presence of a dominant site of association ensure that the compounds crystallize similarly to give structures that feature chains, tapes, and layers. In certain cases, in fact, the molecular organization adopted by different pyridyl-substituted diaminotriazines is virtually identical, even when the length of the molecule or the orientation of the pyridyl group has been changed. Together, these observations show how functional groups such as diaminotriazinyl, which can control association by forming multiple directional intermolecular interactions according to reliable patterns, can be incorporated within more complex molecular structures to determine how crystallization will occur.

Full text of DOI:10.1021/cg101290r

DOI: 10.1021/cg101290r
Structural Similarity of Hydrogen-Bonded Networks in Crystals of
Isomeric Pyridyl-Substituted Diaminotriazines
2011, Vol. 11
287–294
Adam Duong, Thierry Maris, and James D. Wuest*
Deꢀpartement de Chimie, Universiteꢀ de Montreꢀal, Montreꢀal, Queꢀbec H3C 3J7 Canada
Received October 1, 2010; Revised Manuscript Received October 28, 2010
ABSTRACT: Crystals of isomeric pyridyl-substituted diaminotriazines 1a-c and elongated analogues 2a-b were grown under
various conditions, and their structures were solved by X-ray crystallography. Analysis of the structures revealed three shared
features: (1) The compounds favor flattened conformations; (2) they participate in approximately coplanar hydrogen bonding
according to motifs characteristic of diaminotriazines; and (3) these interactions play a key role in directing molecular
organization. Together, the consistent molecular topologies and the shared presence of a dominant site of association ensure
that the compounds crystallize similarly to give structures that feature chains, tapes, and layers. In certain cases, in fact, the
molecular organization adopted by different pyridyl-substituted diaminotriazines is virtually identical, even when the length of
the molecule or the orientation of the pyridyl group has been changed. Together, these observations show how functional groups
such as diaminotriazinyl, which can control association by forming multiple directional intermolecular interactions according to
reliable patterns, can be incorporated within more complex molecular structures to determine how crystallization will occur.
Introduction
Isomeric pyridyl-substituted diaminotriazines 1a-cand elon-
gated analogues 2a-b define a coherent series of small mole-
cules with well-defined geometries and a marked ability to
associate by forming hydrogen bonds, aromatic interactions,
and coordinative bonds to metals. Aryltriazines normally adopt
conformations in which the triazinyl ring and aryl substituent
are approximately coplanar,1 and diaminotriazines participate
in characteristic patterns of intermolecular hydrogen bonding,
as defined by isomeric supramolecular homosynthons I-III.1-5
Together, these properties are expected to play a dominant role
in determining how isomeric pyridyl-substituted diaminotria-
zines 1a-c and 2a-b will crystallize, and they should favor a
series of related structures in which the compounds adopt
flattened conformations and form extensive networks of hydro-
gen bonds directed primarily within the molecular plane.
Results and Discussion
Syntheses of Isomeric Pyridyl-Substituted Diaminotriazines
1a-c and 2a-b. Compounds 1a,4 1b,6 1c,7 and 2a8 were pre-
pared by methods reported previously. Extended analogue 2b
was synthesized in 81% overall yield by Suzuki-Miyaura
coupling of 4-bromobenzonitrile with 3-pyridineboronic acid,
followed by heating the resulting 3-(4-cyanophenyl)pyridine9
with dicyandiamide according to standard procedures.10
Structure of Crystals of 2,4-Diamino-6-(4-pyridyl)-1,3,5-
triazine (1a). Previous work reported the structure of crystals
of compound 1a, which were grown from EtOH and shown
to belong to the monoclinic space group C2/c.3,4 We have found
that crystals grown from DMSO/MeCN have the same structure.
To facilitate comparison of this known structure with new ones,
it is presented succinctly in Figure 1, and other crystallographic
data are summarized in Table 1. Two crystallographically
*To whom correspondence should be addressed. E-mail: james.d.
wuest@umontreal.ca.
r
2010 American Chemical Society
Published on Web 11/24/2010
pubs.acs.org/crystal

288 Crystal Growth & Design, Vol. 11, No. 1, 2011
Duong et al.
Figure 1. Views of the structure of crystals of 2,4-diamino-6-(4-pyridyl)-1,3,5-triazine (1a) grown from EtOH3,4 or DMSO/MeCN. Hydrogen
bonds are represented by broken lines, and carbon atoms are shown in gray, hydrogen atoms in white, and nitrogen atoms in blue. (a) View
along the b axis showing alternating (AB)n chains of independent molecules A and B, which are held together by hydrogen bonding according to
motif III. The chains are paired to form tapes, primarily by hydrogen bonding of molecules A according to motif I. (b) View showing how the
association of tapes is directed in part by π-stacking and by edge-to-face N-H N interactions within a herringbone arrangement of
3 3 3
molecules B. (c) View showing further association of tapes controlled by head-to-tail π-stacking of molecules A along the b axis.
Table 1. Crystallographic Data for Isomeric Pyridyl-Substituted Diaminotriazines 1a-c
compound
1a
2 1a MeOH
3
DMSO/MeOH
1b
1b
MeCN
1c
1c DMSO
3
DMSO
crystallization medium
DMSO/CH2Cl2
DMSO/MeCN
C8H8N6
monoclinic
C2/c
27.3388(10)
7.1786(3)
19.9614(7)
90
120.433(1)
90
3377.8(2)
16
1.480
DMSO
MeCN
formula
crystal system
space group
C17H20N12
triclinic
P1
O
C8H8N6
monoclinic
P21/c
12.063(4)
19.226(5)
7.016(2)
90
95.029(2)
90
1620.9(8)
8
1.542
C8H8N6
orthorhombic
Pbca
6.8585(2)
13.2958(4)
18.5050(5)
90
C8H8N6
monoclinic
P21/c
11.9471(9)
6.9732(6)
21.0822(18)
90
101.590(4)
90
1720.5(2)
8
1.453
C10H14N6OS
monoclinic
P21/c
11.7704(1)
9.0941(1)
11.8294(1)
90
97.160(1)
90
1256.36(2)
4
1.408
˚
a (A)
8.4261(6)
10.1297(7)
˚
b (A)
˚
c (A)
12.2194(10)
75.928(4)
87.136(4)
70.451(4)
952.8(1)
2
1.424
100
0.823
R (o)
β (o)
γ (o)
90
90
3
˚
V (A )
Z
1687.46(8)
8
1.482
150
0.836
F
calc (g cm-3
T (K)
)
200
0.835
100
0.870
150
0.819
100
2.299
μ (mm-1
)
R1, I > 2σ(I)
R1, all data
wR2, I > 2σ(I)
wR2, all data
independent reflections
observed reflections [I > 2 σ(I)]
0.0408
0.0415
0.0986
0.0990
3056
2738
0.0453
0.0523
0.1339
0.1387
3252
0.0516
0.0518
0.1202
0.1203
2842
0.0307
0.0338
0.0808
0.0835
1474
0.0514
0.0538
0.1569
0.1586
2989
0.0360
0.0371
0.0963
0.0992
2215
2764
2714
1295
2785
2100
independent molecules are present (A and B), which are linked
along the ac diagonal into alternating (AB)n chains by hydrogen
bonding according to a distorted form of motif III (Figure 1a).
Individual (AB)n chains are paired to form tapes, primarily by
additional hydrogen bonding of molecules A according to motif I
(Figure 1a).

Article
Crystal Growth & Design, Vol. 11, No. 1, 2011 289
Figure 2. Views of the structure of the 2:1 solvate of 2,4-diamino-6-(4-pyridyl)-1,3,5-triazine (1a) with MeOH grown from DMSO/MeOH.
Hydrogen bonds are represented by broken lines, and carbon atoms are shown in gray, hydrogen atoms in white, nitrogen atoms in blue, and
oxygen atoms in red. (a) View showing how N-H N hydrogen bonds of type III link molecules into chains along the c axis, and how sheets
3 3 3
are formed by additional N-H N(pyridine) hydrogen bonds. (b) View along the b axis showing the packing of four sheets.
3 3 3
As expected,1 molecules A and B both adopt conforma-
tions in which the triazinyl ring and pyridyl substituent are
nearly coplanar, with torsional angles of approximately 7°
and 16°, respectively. In addition, molecules A that are paired
by hydrogen bonding according to motif I lie in essentially
the same plane. However, hydrogen bonding of diaminotria-
zines can accommodate substantial deviations from coplanar-
ity, as illustrated by the distorted geometry of motif III in the
(AB)n chains (Figure 1a). These deviations do not appear to
weaken the hydrogen bonds substantially, and the average
Key structural features of pyridyl-substituted diamino-
triazine 1a and its phenyl-substituted relative 3, including
their rather rigid flattened shape and ability to form multiple
coplanar hydrogen bonds of types I-III, help ensure that
their options for crystallization are limited to a narrow set of
similar possibilities. To test this hypothesis, we grew new
crystals of compound 1a from DMSO/MeOH, which proved
to belong to the triclinic space group P1 and to have the
composition 2 1a MeOH. Views of the structure appear in
3
Figure 2, and other crystallographic data are summarized in
Table 1. The structure consists of two crystallographically
independent molecules A and B, which differ primarily in the
torsional angles between the triazinyl and pyridyl rings
(approximately 47° and 39°). Both values are atypically
high for aryltriazines.1 Molecules A and B are linked by
N-H N distances in the nearly coplanar pair A2 are similar
3 3 3
˚
to those in the deformed pair AB (3.033 and 3.052 A, res-
pectively).
Cohesion between the tapes is provided in part by an
˚
N-H N(pyridine) hydrogen bond (3.107 A) involving the
3 3 3
pyridyl nitrogen atom of a molecule B and the single N-H
bond of a nearby molecule A not used in motifs I and III.
Association of the tapes is also maintained by unusual
N-H N hydrogen bonds of type III with normal average
3 3 3
˚
distances (3.098 A), thereby producing alternating (AB)n
chains that lie along the c axis (Figure 2a). The chains are
then connected to form sheets parallel to the bc plane by
N-H aromatic interactions within a stacked herringbone
3 3 3
˚
arrangement of molecules B (Figure 1b). In these inter-
˚
additional N-H N(pyridine) hydrogen bonds (2.986 A),
3 3 3
actions, the average N-H N distances (3.177 A) are
and stacking of the sheets is controlled by multiple weak
interactions (Figure 2b). As in other structures of pyridyl-
substituted diaminotriazine 1a and its phenyl-substituted
relative 3, crystals grown from DMSO/MeOH show a pre-
ference for molecular organization based on the formation of
extensively hydrogen-bonded chains.
3 3 3
significantly longer than those in normal N-H N hydro-
3 3 3
gen bonds within tapes (motifs I and III). The overall
network is further stabilized by head-to-tail π-stacking of
molecules A along the b axis (Figure 1c).
In the resulting structure, each molecule A participates in a
total of seven N-H N hydrogen bonds with four neigh-
bors, and each molecule B engages in nine related inter-
Structure of Crystals of 2,4-Diamino-6-(3-pyridyl)-1,3,5-
triazine (1b). The similar behavior of pyridyl-substituted
diaminotriazine 1a and phenyl-substituted analogue 3 estab-
lished that the pyridyl nitrogen atom does not necessarily
play a decisive role in directing crystallization, thereby
suggesting that isomeric pyridyl-substituted diaminotriazine
1b should also form a closely related structure. Crystals of
compound 1b grown from DMSO were found to belong to
the monoclinic space group P21/c. The molecular organiza-
tion proved to be essentially identical to that observed in
crystals of analogues 1a and 3 (Figure 1). A view of the
structure of compound 1b is provided in Figure 3, and other
3 3 3
actions (five N-H N hydrogen bonds and four N-
3 3 3
H
aromatic interactions) with five neighbors. Hydrogen
3 3 3
bonding of the pyridyl nitrogen atom of compound 1a plays
only a minor role in controlling crystallization, possibly
because the diaminotriazinyl groups can compete effectively
by forming doubly hydrogen-bonded pairs. This hypothesis
is supported by the nearly identical molecular organization
found in the structures of compound 1a and 2,4-diamino-
6-phenyl-1,3,5-triazine (3), in which the pyridyl group of
compound 1a has been replaced by phenyl.2

290 Crystal Growth & Design, Vol. 11, No. 1, 2011
Duong et al.
Figure 4. View along the b axis of the structure of crystals of 2,4-
diamino-6-(3-pyridyl)-1,3,5-triazine (1b) grown from MeCN. Hy-
drogen bonds are represented by broken lines, and carbon atoms are
shown in gray, hydrogen atoms in white, and nitrogen atoms in blue.
Chains aligned with the a axis are held together by paired hydrogen
Figure 3. View of the structure of crystals of 2,4-diamino-6-(3-
pyridyl)-1,3,5-triazine (1b) grown from DMSO. Hydrogen bonds
are represented by broken lines, and carbon atoms are shown in
gray, hydrogen atoms in white, and nitrogen atoms in blue. Alter-
nating (AB)n chains of independent molecules A and B are held
together by hydrogen bonding according to motif III, and the chains
are paired to form tapes, primarily by hydrogen bonding of mole-
cules A according to motif I.
bonds of type II. N-H N(pyridine) hydrogen bonds between the
chains (not shown) define layers parallel to the ab plane, which are
3 3 3
connected by additional single N-H N(triazine) hydrogen
bonds to give a three-dimensional network.
3 3 3
engages in a total of eight N-H N hydrogen bonds with six
3 3 3
crystallographic data are presented in Table 1. The structure
incorporates two crystallographically independent mole-
cules A and B with slightly different torsional angles between
the triazinyl and pyridyl rings (approximately 2° and 12°,
respectively). As in the structures of analogues 1a and 3,
molecules A and B are linked into (AB)n chains by character-
neighbors. These data provide additional evidence that iso-
meric pyridyl-substituted diaminotriazines 1a-b and phenyl-
substituted analogue 3 are predisposed to adopt similar flat-
tened conformations and to engage reliably in approximately
coplanar hydrogen bonds of type I-III, therebyleadingtoself-
association that predictably favors the formation of related
chains, tapes, and layers.
istic hydrogen bonding of type III, with an average N-
˚
N distance of 3.052 A (Figure 3). The chains are further
H
connected to form tapes aligned with the a axis by additional
Structure of Crystals of 2,4-Diamino-6-(2-pyridyl)-1,3,
5-triazine (1c). The closely related behavior of pyridyl-sub-
stituted diaminotriazines 1a-b and phenyl-substituted ana-
logue 3 suggested that isomeric pyridyl-substituted diamino-
triazine 1c would also crystallize in a similar way. Crystals
grown from MeCN were found to belong to the monoclinic
space group P21/c, and Table 1 provides additional crystal-
lographic data. As confirmed by Figure 5, the molecular
organization is virtually identical to that observed in crystals
of isomer 1a grown from EtOH or DMSO/MeCN (Figure 1),
isomer 1b grown from DMSO (Figure 3), and phenyl-sub-
stituted analogue 3.2 In the structure of compound 1c,
crystallographically independent molecules A and B have
flattened conformations with slightly different torsional
angles between the triazinyl and pyridyl rings (approxi-
mately 15° and 32°, respectively). (AB)n chains are linked
along the a axis by characteristic hydrogen bonding of type
3 3 3
˚
N-H N hydrogen bonding (3.096 A) of molecules A
3 3 3
according to motif I (Figure 3). Cohesion of the tapes is
ensured by multiple interactions, including (1) N-H N-
3 3 3
˚
(pyridine) hydrogen bonds (3.085 A) involving the pyridyl
nitrogen atom of a molecule B and the single N-H bond of a
nearby molecule A not used in motifs I and III; (2) π-stacking
˚
and edge-to-face N-H N interactions (3.174 A) within a
3 3 3
herringbone arrangement of molecules B (as in Figure 1b); and
(3) head-to-tail π-stacking of molecules A (as in Figure 1c).
The closely related behavior of isomeric pyridyl-substi-
tuted diaminotriazines 1a-b and phenyl-substituted ana-
logue 3 under various conditions is consistent with the hypo-
thesis that crystallization is controlled primarily by the
flattened molecular topology and by the ability of diamino-
triazinyl groups to direct the formation of hydrogen-bonded
chains. To test this notion further, we grew additional
crystals of compound 1b from MeCN, which proved to belong
to the orthorhombic space group Pbca. A view of the structure
is shown in Figure 4, and other crystallographic data are pre-
sented in Table 1. Molecules of compound 1b adopt a flattened
conformation with an interaryl angle of approximately 21°,
and they associate to form chains along the a axis held together
˚
III, with an average N-H N distance of 3.068 A
3 3 3
(Figure 5), and the chains are further connected to form
˚
tapes by additional N-H N hydrogen bonding (3.050 A)
3 3 3
of molecules A according to motif I (Figure 5). Association
of the tapes involves multiple interactions, including (1)
N-H N(pyridine) hydrogen bonds of normal average
3 3 3
˚
distance (3.115 A) involving the pyridyl nitrogen atom of a
by characteristic paired hydrogen bonds of type II, with an
˚
molecule B and the single N-H bond of a nearby molecule A
average N-H N distance of 3.008 A (Figure 4). Each
not used in motifs I and III; (2) π-stacking and edge-to-face
3 3 3
˚
molecule in a chain participates in a total of four additional
˚
N-H N interactions (3.326 A) within a herringbone
3 3 3
N-H N(pyridine) hydrogen bonds (3.020 A), which con-
arrangement of molecules B (as in Figure 1b); and (3)
head-to-tail π-stacking of molecules A (as in Figure 1c).
These observations reinforce the notion that crystalliza-
tion of isomeric pyridyl-substituted diaminotriazines 1a-c
and phenyl-substituted analogue 3 is directed primarily by
3 3 3
nect the chains to form layers parallel to the ab plane.11 The
layers are joined by single N-H N(triazine) hydrogen
3 3 3
˚
bonds (3.127 A) as shown in Figure 4, leading to a three-
dimensional network in which each molecule of compound 1b

Article
Crystal Growth & Design, Vol. 11, No. 1, 2011 291
their similar flattened topologies and their shared ability to
form approximately coplanar hydrogen bonds directed by
diaminotriazinyl groups. As a further test of structural
homology, we grew additional crystals of compound 1c from
DMSO, which proved to belong to the monoclinic space
hydrogen bonds of type III (average N-H N distance=
3 3 3
˚
3.086 A), reinforced by additional N-H N(pyridine)
hydrogen bonds (3.070 A). Packing of the chains, controlled
3 3 3
˚
in part by π-stacking of pyridyl groups, produces a structure
with alternating layers consisting of compound 1c and
hydrogen-bonded molecules of DMSO (Figure 6b).
group P21/c and to have the composition 1c 1DMSO.
3
Figure 6 shows views of the structure, and Table 1 provides
additional crystallographic data. Molecules of compound 1c
have a flattened conformation with an angle of approxi-
mately 26° between the average planes of the pyridyl and
triazinyl rings. As shown in Figure 6a, chains aligned
with the c axis result from the formation of typical paired
Structure of Crystals of 2,4-Diamino-6-[4-(4-pyridyl)-
phenyl]-1,3,5-triazine (2a). Together, our observations con-
firm that isomeric pyridyl-substituted diaminotriazines 1a-c
and phenyl-substituted analogue 3 all inherently favor flat-
tened conformations and participate in approximately co-
planar hydrogen bonding according to motifs I-III. As a
result, the compounds crystallize similarly under various
conditions to give structures that feature chains, tapes, and
layers. In certain cases, in fact, the overall molecular orga-
nization is virtually identical.
To see if these consistent patterns are maintained when
molecular topology is altered, we examined the behavior of
elongated pyridyl-substituted diaminotriazine 2a. Crystal-
lization from wet DMSO under various conditions yielded
two polymorphs, as well as a monohydrate and a dihydrate.
One of the polymorphs proved to belong to the triclinic space
group P1. A view of its structure is shown in Figure 7, and
other crystallographic data are summarized in Table 2. The
molecules have flattened conformations and are linked into
chains along the ab diagonal by hydrogen bonds of type II
˚
(average N-H N distance = 3.151 A). Adjacent chains
3 3 3
are further connected by N-H N(pyridine) hydrogen
3 3 3
˚
bonds (average N-H N distance = 2.950 A) to give a
three-dimensional network.
3 3 3
The second polymorph of elongated pyridyl-substituted
diaminotriazine 2a was found to belong to the monoclinic
space group P21/n. Figure 8 provides a view of its structure,
and Table 2 summarizes other crystallographic data. The
structure consists of crystallographically independent mole-
cules A and B that adopt flattened conformations and are
Figure 5. View of the structure of crystals of 2,4-diamino-6-(2-
pyridyl)-1,3,5-triazine (1c) grown from MeCN. Hydrogen bonds
are represented by broken lines, and carbon atoms are shown in
gray, hydrogen atoms in white, and nitrogen atoms in blue. Alter-
nating (AB)n chains of independent molecules A and B are held
together by hydrogen bonding according to motif III, and the chains
are paired to form tapes, primarily by hydrogen bonding of
molecules A according to motif I.
paired by hydrogen bonding according to motif I (average
˚
N-H N distance = 3.056 A). Pairs are further connected
3 3 3
Figure 6. Views of the structure of the 1:1 solvate of 2,4-diamino-6-(2-pyridyl)-1,3,5-triazine (1c) with DMSO. Hydrogen bonds are
represented by broken lines, and carbon atoms are shown in gray, hydrogen atoms in white, nitrogen atoms in blue, oxygen atoms in red,
and sulfur atoms in yellow. (a) View showing how N-H N hydrogen bonds of type III and additional N-H N(pyridine) hydrogen bonds
link molecules into chains along the c axis. (b) View along the b axis showing alternating layers composed of compound 1c and DMSO.
3
3
3
3
3
3

292 Crystal Growth & Design, Vol. 11, No. 1, 2011
Duong et al.
by single N-H N(pyridine) hydrogen bonds of normal
the ac diagonal by hydrogen bonding of type III (average
˚
3 3 3
˚
average distance (3.029 A) to nearly orthogonal adjacent
N-H N distance = 3.083 A). The chains are connected to
3 3 3
molecules, thereby creating corrugated sheets with extensive
edge-to-face aromatic interactions.11 Packing of the sheets
introduces additional aromatic interactions.
form sheets by further coplanar hydrogen bonding between
pyridyl and triazinyl groups, mediated by intervening mole-
cules of H2O (Figure 10).
Crystals of the monohydrate of pyridyl-substituted dia-
minotriazine 2a (2a 1H2O) proved to belong to the triclinic
space group P1. A view of its structure is shown in Figure 9,
and other crystallographic data are presented in Table 2.
The polymorphs and hydrates of elongated pyridyl-
substituted diaminotriazine 2a show certain expected features,
including a preference for a flattened molecular structure that
forms coplanar hydrogen bonds according to standard motifs.
However, the behavior of compound 2a is not always com-
pletely analogous to that of relatives 1a-c and 3; in particular,
the P21/n polymorph of compound 2a clearly shows the effects
of its increased aromatic surface, which favors a structure with
more significant π-stacking and edge-to-face interactions.
Structure of Crystals of 2,4-Diamino-6-[4-(3-pyridyl)-
phenyl]-1,3,5-triazine (2b). To complete our analysis of the
effect of altered molecular topology, we studied the behavior
of a second isomer, elongated pyridyl-substituted diamino-
triazine 2b. Crystals grown from DMSO/MeCN proved to
3
Molecules of compound 2a are paired by hydrogen bonding
˚
of type I (average N-H N distance = 3.044 A) to give a
3 3 3
layered structure closely similar to that shown in Figure 8,
except that hydrogen bonding to pyridyl groups is mediated
by intervening molecules of H2O (Figure 9). This allows the
molecular components of each layer to lie approximately in
the same plane, giving sheets that pack to create the overall
three-dimensional structure.11
Crystals of the dihydrate of elongated pyridyl-substituted
diaminotriazine 2a (2a 2H2O) were found to belong to the
3
monoclinic space group P21/n. Figure 10 provides a view of
its structure, and Table 2 summarizes other crystallographic
data. Molecules of compound 2a are linked into chains along
Figure 7. View of the structure of crystals of the triclinic P1 poly-
morph of 2,4-diamino-6-[4-(4-pyridyl)phenyl-1,3,5-triazine (2a)
grown from wet DMSO. Hydrogen bonds are represented by
broken lines, and carbon atoms are shown in gray, hydrogen atoms
in white, and nitrogen atoms in blue. Chains aligned with the ab
diagonal are formed by hydrogen bonding of type II and are further
Figure 8. View of the structure of crystals of the monoclinic P21/n
polymorph of 2,4-diamino-6-[4-(4-pyridyl)phenyl-1,3,5-triazine
(2a) grown from wet DMSO. Hydrogen bonds are represented by
broken lines, and carbon atoms are shown in gray, hydrogen atoms
in white, and nitrogen atoms in blue. Pairs of independent molecules
A and B are held together by hydrogen bonding according to motif I
connected to adjacent chains by N-H N(pyridine) hydrogen
bonds to give a three-dimensional network.
and are further connected by single N-H N(pyridine) hydrogen
bonds to nearly orthogonal adjacent molecules.
3 3 3
3 3 3
Table 2. Crystallographic Data for Elongated Isomeric Pyridyl-Substituted Diaminotriazines 2a-b
compound
2a
2a
2a 1H2O
3
2a 2H2O
3
2b
crystallization medium
formula
DMSO/H2O
C14H12N6
triclinic
P1
9.5053(5)
14.2146(7)
19.4909(9)
98.832(2)
94.263(2)
104.765(2)
2498.5(2)
8
1.405
150
0.738
0.0721
0.1026
0.1876
0.2050
42622
30414
DMSO/H2O
C14H12N6
monoclinic
P21/n
16.9150(7)
8.6926(4)
17.8433(7)
90
109.956(2)
90
2466.06(18)
8
1.424
DMSO/H2O
C14H14N6O
triclinic
P1
9.310(1)
9.719(1)
15.859(2)
96.589(2)
99.854(2)
111.024(3)
1295.3(3)
4
1.448
100
0.806
0.0371
0.0372
0.0880
0.0881
4604
DMSO/H2O
C14H16N6O2
monoclinic
P21/n
7.2112(2)
49.9305(13)
11.9101(3)
90
103.679(1)
90
4166.70(19)
12
1.436
100
0.840
0.0547
0.0747
0.1346
0.1466
7516
5785
DMSO/MeCN
C14H12N6
orthorhombic
Pbca
7.0142(2)
18.5089(4)
18.5309(4)
90
crystal system
space group
˚
a (A)
˚
b (A)
˚
c (A)
R (o)
β (o)
γ (o)
90
90
3
˚
V (A )
Z
2405.78(10)
8
1.459
100
0.766
0.0314
0.0322
0.0845
0.0855
2190
F
calc (g cm-3
T (K)
)
150
0.748
μ (mm-1
)
R1, I > 2σ(I)
R1, all data
wR2, I > 2σ(I)
wR2, all data
independent reflections
observed reflections [I > 2 σ(I)]
0.0383
0.0391
0.1104
0.1113
4269
4124
4508
2126

Article
Crystal Growth & Design, Vol. 11, No. 1, 2011 293
belong to the orthorhombic space group Pbca. A view of its
structure is shown in Figure 11, and other crystallographic
data are provided in Table 2. The molecular organization is
essentially identical to that of the P1 polymorph of isomer 2a
(Figure 7). Again, the molecules adopt flattened conforma-
and related phenyl-substituted diaminotriazine 3 have three
shared features: (1) The compounds favor flattened confor-
mations; (2) they participate in approximately coplanar hy-
drogen bonding according to motifs characteristic of dia-
minotriazines (I-III); and (3) these interactions play a key
role in directing molecular organization. Together, the con-
sistent molecular topologies and the shared presence of a
dominant site of association ensure that the compounds
crystallize similarly under various conditions to give struc-
tures that feature chains, tapes, and layers. In certain cases, in
fact, the molecular organization adopted by different pyridyl-
substituted diaminotriazines is virtually identical, even when
the length of the molecule or the orientation of the pyridyl
tions and form chains linked by hydrogen bonds of type II
˚
(average N-H N distance = 3.002 A). Adjacent chains
3 3 3
are further connected by N-H N(pyridine) hydrogen
3 3 3
˚
bonds (3.019 A) to give a three-dimensional network.
Conclusions
We have found that crystals of isomeric pyridyl-substituted
diaminotriazines 1a-c, isomeric elongated analogues 2a-b,
Figure 11. View of the structure of crystals of 2,4-diamino-6-[4-(3-
pyridyl)phenyl-1,3,5-triazine (2b) grown from DMSO/MeCN. Hy-
drogen bonds are represented by broken lines, and carbon atoms are
shown in gray, hydrogen atoms in white, and nitrogen atoms in blue.
Chains aligned with the a axis are formed by hydrogen bonding
according to motif II, and adjacent chains are connected by
Figure 9. View of the structure of crystals of the monohydrate of
2,4-diamino-6-[4-(4-pyridyl)phenyl-1,3,5-triazine (2a) grown from
wet DMSO. Hydrogen bonds are represented by broken lines, and
carbon atoms are shown in gray, hydrogen atoms in white, nitrogen
atoms in blue, and oxygen atoms in red. Molecules of compound 2a
are paired by hydrogen bonds of type I, and sheets result from
additional hydrogen bonds involving molecules of H2O.
N-H N(pyridine) hydrogen bonds to give a three-dimensional
3 3 3
network.
Figure 10. View of the structure of crystals of the dihydrate of 2,4-diamino-6-[4-(4-pyridyl)phenyl-1,3,5-triazine (2a) grown from wet DMSO.
Hydrogen bonds are represented by broken lines, and carbon atoms are shown in gray, hydrogen atoms in white, nitrogen atoms in blue, and
oxygen atoms in red. Molecules of compound 2a are linked into chains by hydrogen bonds of type III, and the chains are connected to form
sheets by additional hydrogen bonds involving molecules of H2O.

294 Crystal Growth & Design, Vol. 11, No. 1, 2011
Duong et al.
group has been changed. Together, these observations show
how substituents such as the diaminotriazinyl group, which
can control association by forming multiple directional inter-
molecular interactions according to motifs that have a useful
degree of reliability, can be incorporated within more complex
molecular structures to control how crystallization will occur.
vapors of MeCN or MeOH in closed vessels. Compounds 1b-c
were crystallized by the slow evaporation of solutions in DMSO
(5 mg/mL) or in MeCN (saturated). Crystals of compound 2a were
obtained in various forms by exposing solutions inDMSO (5 mg/mL)
to vapors of H2O. Crystals of compound 2b were grown by exposing
solutions in DMSO (5 mg/mL) to vapors of MeCN.
Analysis of the Structures of Pyridyl-Substituted Diaminotriazines
1a-c and 2a-b by X-ray Crystallography. Crystallographic data
were collected at 150 K using a Bruker Microstar diffractometer
with Cu KR radiation. The structures were solved by direct methods
using SHELXS-97, and non-hydrogen atoms were refined aniso-
tropically with SHELXL-97.12 Hydrogen atoms were treated by
first locating them from difference Fourier maps, recalculating their
positions using standard values for distances and angles, and then
refining them as riding atoms. In selected structural studies, calcu-
lated powder X-ray diffraction patterns were found to closely match
those obtained experimentally by analysis of bulk crystalline sam-
ples, thereby establishing that the samples consisted primarily of a
single phase.11
Experimental Section
General Notes. Pyridyl-substituted diaminotriazines 1a,4 1b,6 1c,7
and 2a8 were prepared by methods reported previously. Elongated
compound 2b was made by the procedure summarized below. Other
chemicals were purchased from commercial sources and used with-
out further purification.
3-(4-Cyanophenyl)pyridine.9 A dried pressure tube was charged
with Pd(OAc)2 (0.031 g, 0.14 mmol), 4-bromobenzonitrile (0.50 g,
2.7 mmol), 3-pyridineboronic acid (0.37 g, 3.0 mmol), and SPhos
(0.11 g, 0.27 mmol). Toluene (15 mL), water (5 mL), and methanol
(5 mL) were added, and the tube was capped with a septum. The
mixture was stirred under N2 for 10 min at 25 °C, and then K3PO4
(5.8 g, 27 mmol) was added. The septum was replaced with a screw
cap, and the mixture was heated at 110 °C until 4-bromobenzonitrile
was consumed, as judged by thin-layer chromatography. The
mixture was cooled to 25 °C and extracted with dichloromethane.
Solvent was removed from the extracts by evaporation under
reduced pressure, and the residue was purified by flash chromato-
graphy (silica gel, ethyl acetate/hexane 1:4) to give 3-(4-cyanophe-
nyl)pyridine (0.42 g, 2.3 mmol, 85%) as a colorless solid: mp 96 °C;
IR (ATR) 3058, 3039, 2224 cm-1; 1H NMR (400 MHz, CDCl3) δ
8.89 (1H, d, 4J = 2.1 Hz), 8.70 (1H, dd, 3J = 4.8 Hz, 4J = 1.6 Hz),
7.91 (1H, ddd, 3J = 7.8 Hz, 4J = 2.1 Hz, 4J = 1.6 Hz), 7.80
(2H, d, 3J = 8.6 Hz), 7.72 (2H, d, 3J = 8.6 Hz), 7.45 (1H, dd, 3J =
7.8 Hz, 3J=4.8 Hz); 13C NMR (100 MHz, CDCl3) δ 150.12, 148.60,
142.69, 135.16, 134.91, 133.27, 128.19, 124.22, 118.96, 112.30; HRMS
(ESI) calcd for C12H8N2 þ H m/e 181.0760, found 181.0763.
2,4-Diamino-6-[3-(pyridinyl)phenyl]-1,3,5-triazine (2b). A mix-
ture of 3-(4-cyanophenyl)pyridine (0.594 g, 3.30 mmol), dicyan-
diamide (0.555 g, 6.60 mmol), and KOH (0.203 g, 3.62 mmol) in
2-methoxyethanol (30 mL) was heated at reflux for 12 h. The
resulting mixture was cooled to 25 °C, the precipitated solid was
separated by filtration, and the solid was washed with hot water to
give pure 2,4-diamino-6-[3-(pyridinyl)phenyl]-1,3,5-triazine (2b;
0.829 g, 3.14 mmol, 95%) as a colorless solid: mp 320 °C; IR (ATR)
Acknowledgment. We are grateful to the Natural Sciences
ꢁ
and Engineering Research Council of Canada, the Ministere
de l’Education du Quebec, the Canada Foundation for Inno-
ꢀ
ꢀ
ꢀ
vation, the Canada Research Chairs Program, and Universite
de Montreal for financial support. In addition, we thank Dr.
ꢀ
ꢀ
Valerie Metivaud for analyzing bulk crystalline samples by
powder X-ray diffraction.
ꢀ
Supporting Information Available: Additional crystallographic
details (including thermal atomic displacement ellipsoid plots,
powder X-ray diffraction patterns, tables of structural data in
CIF format, and supplementary figures). This material is available
free of charge via the Internet at http://pubs.acs.org.
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(400 MHz, DMSO-d6) δ 8.97 (1H, dd, 4J = 2.3 Hz, 5J = 0.8 Hz),
8.61 (1H, dd, 3J = 4.7 Hz, 4J = 1.6 Hz), 8.37 (2H, d, 3J = 8.5 Hz),
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(11) See the Supporting Information for details.
Crystallization of Pyridyl-Substituted Diaminotriazines 1a-c and
2a-b. All crystallizations were carried out at 25 °C. Crystals of com-
pound 1a were grown by exposing solutions in DMSO (5 mg/mL) to
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