Crystal structure and thermal expansion of N,N,N′,N′-tetrakis-[(1H,2,4-triazol-1-yl)methyl]-ethane-1,2-diamine

Article abstract of DOI:10.1007/s11224-015-0611-y

The crystal structure of N,N,N′,N′-tetrakis-[(1H,2,4-triazol-1-yl)methyl]-ethane-1,2-diamine has been fully determined at six different temperatures by X-ray single-crystal diffraction, and the thermal expansion has been determined from 100 K to ambient temperature. The expansion is anisotropic, and it is negative in one direction of the unit cell. The supramolecular structure formed by weak hydrogen bonds of the type C-H···N resembles a trellis analogous to that observed in other organic systems with strong hydrogen bonds.

Full text of DOI:10.1007/s11224-015-0611-y

Struct Chem
DOI 10.1007/s11224-015-0611-y
ORIGINAL RESEARCH
Crystal structure and thermal expansion of N,N,N0,N0-tetrakis-
[(1H,2,4-triazol-1-yl)methyl]-ethane-1,2-diamine
A. Zerrouki1 H. Allouchi2 B. Nicola¨ı3 S. El Kadiri1 Z. Bahari4
•
•
•
•
•
R. Ceolin I. B. Rietveld3
3
•
´
Received: 16 December 2014 / Accepted: 5 June 2015
Ó Springer Science+Business Media New York 2015
Abstract The crystal structure of N,N,N0,N0-tetrakis-
[(1H,2,4-triazol-1-yl)methyl]-ethane-1,2-diamine has been
fully determined at six different temperatures by X-ray
single-crystal diffraction, and the thermal expansion has
been determined from 100 K to ambient temperature. The
expansion is anisotropic, and it is negative in one direction
of the unit cell. The supramolecular structure formed by
weak hydrogen bonds of the type C–HÁÁÁN resembles a
trellis analogous to that observed in other organic systems
with strong hydrogen bonds.
Introduction
Identification of recurring patterns in crystal structures is
important for crystal engineering in order to design new
solids with specific physical and chemical properties [1].
Crystal structures are governed by a combination of a
large number of intermolecular interactions. A specific
combination of molecular functionalities may lead to a
particular supramolecular synthon, which in turn may lead
to a large number of similar crystal structures. In neutral
molecular solids, hydrogen bonds (traditionally O–HÁÁÁO
and N–HÁÁÁO) are generally considered as important
building blocks for supramolecular synthons and
networks.
Keywords Crystal Á Negative thermal expansion Á
Triazole derivative Á C–HÁÁÁN hydrogen bonds
The ability of the C–H group to act as a proton donor in
hydrogen bonds has been the subject of controversy for many
years. The possibility was first described in 1935 [2], and it
was for the first time systematically studied in purines and
pyrimidines in the 1960’s [3]. In 1999, the weak C–HÁÁÁO
hydrogen bond has been treated in a book [4], but the inter-
action is broadly applicable to other hydrogen bond accep-
tors. Neutron diffraction data have provided conclusive
evidence for the existence of C–HÁÁÁA hydrogen bonds [4].
They are known to be rather long and weak. In spite of their
weakness, they can be important as secondary interactions
and in certain cases even as primary ones defining the crystal
structure. They also play an important role in biological
systems [5]. Typically, criteria to establish the presence of
this type of hydrogen bonds are based on geometrical or
spectral observations [4]. Theoretical calculations show that
the proton-donor property of the C–H groups varies with C
hybridization (Csp [ Csp2 [ Csp3) [6]. The energy of the
C–HÁÁÁA interactions (A being O, N or F) can vary from 0.6 to
3.6 kcal/mol, the strongest being C–HÁÁÁN. However, the
energies are often difficult to evaluate experimentally.
Electronic supplementary material The online version of this
article (doi:10.1007/s11224-015-0611-y) contains supplementary
material, which is available to authorized users.
¨
& B. Nicolaı
beatrice.nicolai@parisdescartes.fr
1
2
3
´
Laboratoire de Chimie Appliquee et Environnement LCAE-
URAC18, Faculte des Sciences, Universite Mohamed 1er,
boulevard Mohammed VI, B.P. 717, 60000 Oujda, Maroc
´
´
Laboratoire de Chimie Physique, RICM UMR-ISP 1282,
´
Faculte de Pharmacie, Universite de Tours, 31 avenue
Monge, 37200 Tours, France
´
´
Laboratoire de Chimie Physique, CAMMAT (Caracterisation
des Materiaux Moleculaires a Activite Therapeutique),
´
´
`
´
´
´
Faculte de Pharmacie, Universite Paris Descartes, 4 avenue
de l’observatoire, 75006 Paris, France
´
4
´
Laboratoire de Chimie du Solide, Minerale et Analytique,
Faculte des sciences, Universite Mohamed 1er, boulevard
´
´
Mohammed VI, B.P. 717, 60000 Oujda, Maroc
123

Struct Chem
N,N,N0,N0-tetrakis-[(1H,2,4-triazol-1-yl)methyl]-ethane-
1,2-diamine (TTYED) has been prepared in the framework
of a study on triazole derivatives with novel modes of
action in their antifungal properties [7, 8]. Considering the
molecular structure of this neutral molecular compound
(Fig. 1), only weak intermolecular interaction was expec-
ted. The molecular structure was confirmed by single-
crystal X-ray diffraction using crystals found in the powder
obtained after synthesis. The crystal structure clearly
demonstrated the presence of C(sp2)–HÁÁÁN hydrogen
bonds.
more prevalent than overall NTE, i.e., the decrease in the
entire unit-cell volume, but reports on this subject are rare,
whereas it will certainly contribute to our understanding of
strong and weak interactions in crystal structures.
In the present paper, the NTE mechanism involving C–
HÁÁÁN hydrogen bonds is discussed. To our knowledge, this
is the first time that an NTE mechanism is reported
involving such weak hydrogen bonds.
Materials and methods
In addition to the structure determination, lattice
expansion was studied by collecting X-ray diffraction data
and solving the crystal structure at different temperatures
from 100 to 297 K. Intermolecular interactions can be
studied with the isobaric expansion tensor derived from
these results [9–11]. The thermal expansion of the com-
pound is presented in this paper, and it will be demon-
strated that it exhibits uniaxial shrinking with increasing
temperature. Most materials tend to expand in all directions
when heated. Unusual and nonuniform thermal expansion
in crystals has recently attracted attention as it is of interest
for technological applications and from the fundamental
point of view.
Materials
Synthesis of (1H-1, 2, 4-triazol-1-yl) methanol
The compound was synthesized with some modifications
compared
to
Ref.
[14]:
(1,2,4)-triazole
[98 %
(Aldrich),1,73 g, 25 mmol] in 20 ml of ethanol (absolute
ethanol, C99.8 %, Sigma-Aldrich) and 3.5 ml of formalde-
hyde solution (C36,5 %, Sigma-Aldrich) were stirred,
refluxed for 1 h, and mixing was continued atroom temperature
for 12 h. After the elimination of the solvent under reduced
pressure, the obtained residue was treated with cold water. A
white solid appeared, which was collected by filtration, washed
with diethyl ether (99 %, Sigma-Aldrich) and dried under
vacuum to yield the pure product (79 %).
Materials with negative thermal expansion (NTE) have
the counterintuitive property to expand on cooling. NTE is
generally considered rare and even more rare in organic
materials. Mechanisms that give rise to this phenomenon
are still poorly documented, but several mechanisms have
been reported: torsional vibrations in polymers, ordering of
water molecules in organic crystals or cooperative move-
ments involving strong hydrogen bonds in, for example,
hydrated methanol [12], (S,S0)-octa-3,5-duyin-2,7-diol [13]
and tienoxolol [10].
Synthesis of N,N,N0,N0-tetrakis-[(1H,2,4-triazol-1-
yl)methyl]-ethane-1,2-diamine
This compound was prepared from the condensation of
four equivalents of 1H-(1, 2, 4)-triazol-1-yl methanol
(10 mmol, 1 g) with one equivalent of ethane-1,2-diamine
(C99,0 %, Fluka, 2,5 mmol, 0,15 g) in anhydrous ace-
tonitrile (C99,8 %, Sigma-Aldrich) as the solvent. The
mixture was stirred under reflux for 4 h. Then, the solution
was dried over anhydrous MgSO4. After filtration, the
solvent was removed under reduced pressure and the
obtained residue was washed with a mixture of dichlor-
omethane (99.8 %, Sigma-Aldrich) and diethyl ether (3/1
ratio) to give an oily product, which was recrystallized with
ethanol to yield white crystals.
Uniaxial NTE (contraction in one direction whereas the
total volume increases with temperature) is expected to be
Single-crystal X-ray diffraction
A single crystal (Fig. 2) was mounted on a glass rod.
Single-crystal X-ray diffraction data were collected on an
X-CALIBUR-2 CCD four-circle diffractometer (Oxford
Diffraction) at 100, 150, 170, 200, 250 and 297 K. Data
collections, unit-cell determinations and data reductions
˚
Fig. 1 Chemical structure of N,N,N0,N0-tetrakis-[(1H,2,4-triazol-1-
yl)methyl]-ethane-1,2-diamine, C14H20N14, M = 384.44 g mol-1
were carried out with Mo Ka radiation (k = 0.710 73 A)
and performed with the CRYSTALIS program suite [15]
123

Struct Chem
atoms were refined with anisotropic thermal parameters.
The hydrogen atoms were positioned geometrically. Both
programs were used within the WINGX package [12].
Empirical absorption correction using spherical harmonics
was carried out using the SCALE3 ABSPACK program
[18]. The cooling device was a CryoJetÒ from Oxford
Instruments (UK). The crystal was allowed to equilibrate in
the nitrogen flux for 30 min before starting each isothermal
data collection. Crystallographic data at different temper-
atures are given in Table 1.
Isobaric thermal expansion tensor
Fig. 2 Optical microscopy photograph of single crystals of
N,N,N0,N0-tetrakis-[(1H,2,4-triazol-1-yl)methyl]-ethane-1,2-diamine
(TTYED)
Intermolecular interactions can be studied with the isobaric
thermal expansion tensor, which is a measure for how
intermolecular distances change with temperature. A small
value for a tensor eigenvalue is commonly referred to as a
‘hard’ direction and a large value as a ‘soft’ direction [19].
The tensor has been calculated by the PASCAL software
[20].
on the full data set. The structures were solved by direct
methods and successive Fourier difference calculations
with the ShelxS97 program [16] and refined on F2 by
weighted anisotropic full-matrix least-squares methods
using the SHELXL-2014 program [17]. Nonhydrogen
Table 1 Crystal data and structure refinement
Common details
˚
Wavelength/A
Formula
C14 H20 N14
384.44
Monoclinic
C 2/c
0.71073
Formula weight/g mol-1
Crystal system
Space group
Z
Crystal size/mm
Limiting indices
F (000)
0.40 9 0.30 9 0.08
-24 \ h \ 24; -11 \ k \ 11; -15 \ l \ 13
808
Full-matrix least squares on F2
4
Refinement method
Temperature/K
100
150
170
200
250
297
Cell parameters as a function of temperature
˚
Unit-cell dimensions/A, °
a = 18.6498 (9) a = 18.6598 (6) a = 18.6696 (8) a = 18.654 (1)
a = 18.673 (1)
b = 8.6470 (6)
a = 18.667 (1)
b = 8.6944 (7)
b = 8.5225 (5)
b = 8.5656 (3)
b = 8.5776 (5)
b = 8.5988 (5)
c = 11.3310 (6) c = 11.3354 (4) c = 11.3343 (6) c = 11.3266 (6) c = 11.3388 (7) c = 11.3376 (8)
b = 100.680 (5) b = 100.595 (4) b = 100.532 (5) b = 100.511 (6) b = 100.441 (7) b = 100.365 (7)
3
˚
Volume/A
1769.8 (2)
1.443
1780.9 (1)
1.434
1784.5 (2)
1.431
1786.3 (2)
1.429
1800.5 (2)
1.418
1810.1 (2)
1.411
dc/g cm-3
l/mm-1
0.101
0.101
0.100
0.100
0.100
0.099
h
max/°
Reflections collected/unique 7633/2197
28.280
28.280
28.277
28.282
28.272
28.277
7683/2208
7707/2211
7660/2215
7680/2236
7688/2246
[Rint = 0.0603] [Rint = 0.0260] [Rint = 0.0294] [Rint = 0.0656] [Rint = 0.0729] [Rint = 0.0821]
Completeness (%)
99.9
99.9
99.9
99.9
99.9
99.9
Data/restraints/parameters
Goodness of fit on F2
R indices [I [ 2r (I)]
2197/0/128
1.038
2208/0/127
1.030
2211/0/128
1.046
2215/0/128
1.014
2236/0/128
1.032
2246/0/128
0.991
R1 = 0.0490
wR2 = 0.0854
R1 = 0.0931
wR2 = 0.1031
0.0004 (4)
0.256/-0.283
R1 = 0.0367
wR2 = 0.0860
R1 = 0.0513
wR2 = 0.0940
0.0000 (4)
0.231/-0.172
R1 = 0.0365
wR2 = 0.0839
R1 = 0.0565
wR2 = 0.0905
0.0000 (5)
0.248/-0.181
R1 = 0.0511
wR2 = 0.0780
R1 = 0.1173
wR2 = 0.1017
0.0007 (3)
0.194/-0.212
R1 = 0.0534
wR2 = 0.0703
R1 = 0.1432
wR2 = 0.1071
0.0010 (2)
0.198/-0.188
R1 = 0.0548
wR2 = 0.0778
R1 = 0.1612
wR2 = 0.1209
0.0017 (3)
0.196/-0.177
R indices (all data)
Extinction coefficient
-3
˚
Dqmax/Dqmin, e A
123

Struct Chem
Table 2 Isobaric thermal tensor coefficients (in MK-1) and the ori-
entation of the tensor in the unit cell
Eigenvalues
Eigenvectors
a
b
c
a11
a22
a33
-7.6 (9)
e1
e2
e3
0.4258
0
0
-0.9048
0.8100
0
20 (1)
0.5864
0
101 (3)
-1
Results
Crystal structure
TTYED crystallizes in the monoclinic system, space group
C 2/c, and the molecule is located on the twofold rotational
axis; thus, only half of the molecule is found in the
asymmetric unit. Crystal and structure-refinement data at
different temperatures are compiled in Table 1. Supple-
mentary crystallographic data can be found in the CCDC
deposit (CCDC 1036547–1036552) and obtained free of
charge from the Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif/. The molecular
structure and atomic numbering are shown in Fig. 3.
Influence of the temperature on the crystal structure
Expansivity
The unit-cell parameters determined from 100 to 297 K are
compiled in Table 2. The specific volume v (in cm3 g-1) of
TTYED as a function of temperature T (in K) can be fitted
to a straight line, with r2 = 0.986:
v ¼ 0:68489 þ 7:9588 Â 10À5 Â T
ð1Þ
It demonstrates that the volume increases linearly with
temperature in the range from 100 K up to 297 K. It cor-
responds to an expansivity av of 1.16 9 10-4 K-1
.
Thermal expansion tensor
The eigenvalues of the thermal expansion tensor, calcu-
lated with the PASCAL program [20], are compiled in
Table 2. Because the cell is monoclinic, the principal axis
e3 is parallel to the b axis of the unit cell and the axes e1
and e2 can be found in the ac plane (Table 2). The tensor
parameters are constant, because the volume and the cell
parameters depend linearly on the temperature between
100 and 297 K. The maximum expansion can be found
along e3 [101 (3) MK-1], the minimum expansion along e2
[20 (1) MK-1] and a negative expansion along e1 [-7.6 (9)
MK-1].
Fig. 3 a Ortep of N,N,N0,N0-tetrakis-[(1H,2,4-triazol-1-yl)methyl]-
ethane-1,2-diamine (TTYED) with thermal ellipsoids at 297 K (20 %
probability level). Only the atoms of the asymmetric unit are labelled.
b Crystal structure of TTYED projected on plane ac (H atoms omitted
for clarity)
123

Struct Chem
Table 3 Selected torsion
angles (°) as a function of the
temperature
100 K
150 K
170 K
200 K
250 K
297 K
C3–N2–C2–N3
N2–C2–N3–C7
C6–N1–C7–N3
N1–C7–N3–C2
N3–C1–C1–N3
C2–N3–C1–C1a
a
133.7 (2)
151.4 (2)
107.9 (2)
67.7 (2)
133.6 (1)
150.9 (1)
107.7 (1)
67.8 (1)
133.4 (1)
150.9 (1)
107.7 (1)
67.8 (1)
133.2 (2)
150.7 (2)
107.7 (2)
67.8 (2)
133.2 (3)
150.3 (2)
107.2 (3)
68.1 (3)
133.3 (3)
149.7 (2)
107.9 (3)
67.6 (3)
49.5 (2)
50.2 (1)
50.4 (1)
50.4 (2)
50.4 (3)
51.2 (3)
119.1 (2)
118.8 (1)
118.6 (1)
118.4 (2)
118.4 (3)
117.8 (3)
Equivalent atom by symmetry transformation -x ? 1, y, -z ? 1/2
Table 4 Evolution of the intramolecular hydrogen bond as a function
of temperature
˚
D–H, A
˚
˚
D–HÁÁÁA
HÁÁÁA, A
DÁÁÁA, A
DHA,°
100 K
C7–H7BÁÁÁN4
150 K
0.99
0.99
0.98
0.99
0.98
0.97
2.71
2.72
2.73
2.72
2.74
2.74
3.573 (2)
3.593 (2)
3.587 (2)
3.594 (3)
3.592 (3)
3.596 (3)
146
146
146
146
146
147
C7–H7BÁÁÁN4
170 K
C7–H7BÁÁÁN4
200 K
C7–H7BÁÁÁN4
250 K
C7–H7BÁÁÁN4
297 K
C7–H7BÁÁÁN4
The molecule is rather flexible with 11 torsion angles of
which 6 are independent due to the twofold axis (Table 3).
The torsion angles C3–N2–C2–N3 and N2–C2–N3–C7
define the orientation of the second crystallographically
independent triazole group (see Fig. 3), whereas the torsion
angles C6–N1–C7–N3 and N1–C7–N3–C2 define the ori-
entation of the first triazole group. The torsion angles N3–
C1–C1–N3 and C2–N3–C1–C1 define the orientation of
half of the molecule relative to the other half.
The mean plane of the molecule is approximately par-
allel to the (0 1 0) plane. The first triazole group is parallel
to the mean plane, and the second triazole forms an angle
of 59.634 (49)° to the mean plane.
The two torsions, N1–C7–N3–C2 and C6–N1–C7–N3
(Table 3; Fig. 3), defining the orientation of the first tria-
zole group remain virtually constant with the temperature.
All the other torsion angles vary linearly with the tem-
perature (Fig. 4). However, the variation is relatively small
(Fig. 4) and the conformation remains virtually the same
from 100 K up to ambient temperature.
Fig. 4 Changes in selected torsion angles as
temperature
a function of
Discussion
Molecular conformation
Because a twofold axis parallel to the b axis intersects the
central C–C bond of the molecule, the asymmetric unit
consists of half a molecule.
Considering geometrical criteria [4], two intramolecular
hydrogen bonds can be identified in the molecule. Due to
123

Struct Chem
Table 5 Evolution of the
intermolecular close contacts as
a function of the temperature
˚
D–H, A
˚
˚
D–HÁÁÁA
HÁÁÁA, A
DÁÁÁA, A
DHA, °
Symmetry
100 K
C2–H2AÁÁÁN5
C3–H3ÁÁÁN7
C4–H4ÁÁÁN6
C7–H7BÁÁÁN3
150 K
0.99
0.95
0.95
0.99
2.69
2.44
2.37
2.62
3.387 (2)
3.242 (2)
3.317 (2)
3.193 (2)
128
141
177
117
-x ? 3/2, -y ? 1/2,-z ? 1
-x ? 3/2, y-1/2, -z ? ‘
x, y, z ? 1
-x ? 1, y, -z ? ‘
C3–H3ÁÁÁN7
C4–H4ÁÁÁN6
C7–H7BÁÁÁN3
170 K
0.95
0.95
0.99
2.46
2.38
2.62
3.256 (2)
3.328 (2)
3.197 (2)
141
177
117
-x ? 3/2, y-1/2, -z ? 1/2
x, y, z ? 1
-x ? 1, y, -z ? 1/2
C3–H3ÁÁÁN7
C4–H4ÁÁÁN6
C7–H7BÁÁÁN3
200 K
0.94
0.94
0.98
2.48
2.39
2.62
3.263 (2)
3.330 (2)
3.198 (2)
141
177
118
-x ? 3/2, y-1/2, -z ? 1/2
x, y, z ? 1
-x ? 1, y, -z ? 1/2
C3–H3ÁÁÁN7
C4–H4ÁÁÁN6
C7–H7BÁÁÁN3
250 K
0.95
0.95
0.99
2.47
2.38
2.61
3.270 (3)
3.330 (3)
3.196 (2)
141
177
118
-x ? 3/2, y-1/2, -z ? 1/2
x, y, z ? 1
-x ? 1, y, -z ? ‘
C3–H3ÁÁÁN7
C4–H4ÁÁÁN6
C7–H7BÁÁÁN3
297 K
0.94
0.94
0.98
2.50
2.40
2.63
3.292 (3)
3.337 (4)
3.201 (3)
142
177
118
-x ? 3/2, y-1/2, -z ? 1/2
x, y, z ? 1
-x ? 1, y, -z ? ‘
C3–H3ÁÁÁN7
C4–H4ÁÁÁN6
C7–H7BÁÁÁN3
0.93
0.93
0.97
2.52
2.41
2.63
3.298 (4)
3.343 (4)
3.206 (3)
142
178
118
-x ? 3/2, y-1/2, -z ? 1/2
x, y, z ? 1
-x ? 1, y, -z ? 1/2
conformation of the first triazole group does not change
with temperature in relation to the second triazole group.
Crystal packing and intermolecular interactions
at 297 K
Each molecule of TTYED is involved in eight inter-
molecular hydrogen bonds C(sp2)–HÁÁÁN with 6 different
molecules. Due to the symmetry of the molecule and the
fact that the molecule can be donor and acceptor, only two
hydrogen bonds are independent (see Table 5). A weak
intermolecular close contact can also be identified at each
temperature (C7–H7BÁÁÁN3 in Table 5).
Fig. 5 View perpendicular to the infinite chain of hydrogen bonds
C(10) interconnected with infinite chain of C(11) weak hydrogen
bonds. The trellis-like structure made up by hydrogen bonds can be
recognized
The hydrogen bonds C4–H4ÁÁÁN6 form cyclic dimers
[graph set notation [21] R22(12)] and an infinite chain
[graph set notation C(10), figure S1 in supplementary
materials]. All the C(10) chains present in the crystal are
parallel to each other and parallel to the crystallographic
c axis and connected to each other via the C3–H3ÁÁÁN7
hydrogen bonds (see Fig. 5; Table 5).
its symmetry, only one hydrogen bond needs to be defined:
C7–H7BÁÁÁN4 between the C(sp3)H2 group attached to the
first triazole group and one of the N atoms of the second
triazole group (see Table 4). This may explain why the
The C3–H3ÁÁÁN7 hydrogen bonds form also infinite
chains of hydrogen bonds interlocked [graph set notation
123

Struct Chem
Influence of the temperature on the crystal structure
From Table 5 and Fig. 6, it can be seen that the C4–
H4ÁÁÁN6 hydrogen bond giving rise to the C(10) chains is
the strongest hydrogen bond in the system: Its angle is
closest to 180°, and the donor–acceptor distance is the
smallest [4]. Moreover, the D–H–A angle and the donor–
acceptor distance do not change significantly with tem-
perature. It corresponds also to the hydrogen bond making
up the infinite hydrogen bond parallel to the c axis, made of
cyclic dimers R22(12) (figure S1 in supplementary
materials).
The second hydrogen bond (defined by its geometry) is
C3–H3ÁÁÁN7 [giving rise to the C(11) chains], but its dis-
tance donor–acceptor exhibits the greatest variation
(Table 5; Fig. 6).
The anisotropy of the thermal expansion is shown in
Fig. 7 (see also Table 2). The thermal expansion along e1 is
negative, but small in comparison with the expansion along
e2 and e3. Therefore, the specific volume of the title com-
pound increases with temperature. However, its expansivity
(1.15 9 10-4 K-1) is found to be twice as small as the mean
value for expansivity mentioned by Gavezzotti for organic
molecular crystals (aV = 2 9 10-4 K-1) [15]. It is even
smaller than the one observed in another uncharged organic
molecule: 1.54 9 10-4 K-1 in tienoxol [10], which con-
tained strong O–HÁÁÁN hydrogen bonds.
Fig. 6 Changes in the values of the 2 independent intermolecular
hydrogen bonds and the close contact as a function of temperature
(see Table 5)
C(11), Fig. 5]. Consequently, one C(10) chain is then
connected to 4 different C(10) chains by these C3–H3ÁÁÁN7
hydrogen bonds. One can recognize the scissor- or trellis-
like structure, which is similar to the one observed in
tienoxolol [10] or methanol hydrate [12].
The major part of the expansion in TTYED is along e3
(Fig. 7); indeed, the coefficient is about 101 9 10-6 K-1
.
It is smaller than in tienoxolol (123 9 10-6 K-1 [10]), but
greater than in the zwitterionic form of L-citrulline
Fig. 7 The three major components of the thermal expansion tensor and the respective projections of the crystal structure. Negative thermal
expansion is marked in red. Hydrogen atoms omitted for clarity (Color figure online)
123

Struct Chem
(73 9 10-6 K-1 in forms a and d [11]). The high value
along the e3 axis indicates the soft direction in the crystal
with the weakest intermolecular interactions. It corre-
sponds to a direction perpendicular to the infinite chain of
the strongest hydrogen bonds in the crystal (Fig. 5).
Along e1, the expansion is negative in TTYED. The
contraction (-7.5 9 10-6 K-1) is smaller than in citrulline
(-10 9 10-6 K-1 in the d form and -18 9 10-6 K-1 in the
a form) and larger than in tienoxolol (-5 9 10-6 K-1). In
tienoxolol, the contraction was related to the decrease in the
cell parameter b with temperature. In TTYED, the observed
contraction is due to the decrease in the cell parameter b with
temperature, whereas all the other cell parameters increase
(Table 1). The infinite chains of the strongest hydrogen
bonds in the crystal remain parallel to the c axis at each
temperature, but the angle between c and a decreases with
increasing temperature; thus, along one direction, a con-
traction can be observed.
or trellis effect has previously only been observed for
stronger hydrogen bonds such as O–HÁÁÁO and N–HÁÁÁO. To
our knowledge, this is the first time such a mechanism is
reported for weak C–HÁÁÁN hydrogen bonds.
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Conclusion
The crystal structure of N,N,N0,N0-tetrakis-[(1H,2,4-tria-
zol-1-yl)methyl]-ethane-1,2-diamine (TTYED) has been
solved to unambiguously characterize the compound.
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single-crystal X-ray diffraction.
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Uniaxial contraction is observed, or uniaxial NTE,
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methanol monohydrate: The two types of hydrogen bond
chains in the crystal form a trellis. The weak hydrogen
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contraction in one direction with increasing temperature.
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¨
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123