Spectroscopic, thermal and single crystal structure investigations of 2-bromotrimesic acid and its trimethyl ester analogue

Article abstract of DOI:10.1016/j.molstruc.2014.06.035

Two analogues of the well investigated trimesic acid viz. the 2-bromobenzene-1,3,5-tricarboxylic acid 1 and their ester trimethyl 2-bromobenzene-1,3,5-tricarboxylate 2, have been synthesised and their X-ray structures were solved. Acid 1 crystallises as 1

Full text of DOI:10.1016/j.molstruc.2014.06.035

Journal of Molecular Structure 1074 (2014) 542–548
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Spectroscopic, thermal and single crystal structure investigations
of 2-bromotrimesic acid and its trimethyl ester analogue
Alexander S. Münch a, Felix Katzsch b, Tobias Gruber b, Florian O.R.L. Mertens a,
⇑
a Institute of Physical Chemistry, Technical University Bergakademie Freiberg, Leipziger Straße 29, 09599 Freiberg, Germany
b Institute of Organic Chemistry, Technical University Bergakademie Freiberg, Leipziger Straße 29, 09599 Freiberg, Germany
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
ꢀ
ꢀ
ꢀ
Bromotrimesic acid (1) and
bromotrimesic trimethyl ester (2)
were synthesised.
Single crystal structures were
determined to study supramolecular
interactions.
The 1:1 inclusion compound of 1 with
water has been investigated by IR
spectroscopy and TG-DSC
measurements.
a r t i c l e i n f o
a b s t r a c t
Article history:
Two analogues of the well investigated trimesic acid viz. the 2-bromobenzene-1,3,5-tricarboxylic acid 1
and their ester trimethyl 2-bromobenzene-1,3,5-tricarboxylate 2, have been synthesised and their X-ray
structures were solved. Acid 1 crystallises as 1:1 inclusion compound with water in a layer structure. Like
in the solid state structure of trimesic acid, we found strong OAHꢁꢁꢁO hydrogen bonds between one of the
carboxyl groups and a neighbouring molecule to form a hydrogen bonding motif R22(8). Additionally, a
water molecule and a second acid function of 1 are involved in further hydrogen bonding featuring the
graph set R44(12) forming what might be called a water inserted dimer. As shown by TG-DSC measure-
ments the water molecule in the 1:1 inclusion compound of 1 is engaged in two strong OAHꢁꢁꢁO hydrogen
bonds, it escapes at a rather low temperature of 99 °C. Bromine monosubstitution at the benzene ring
forces the third carboxylic acid out of the mean plane of the molecule, which disturbs the coplanar
arrangement of the three COOH moieties. Thus, the typical ‘‘chicken-wire’’ network formation is hin-
dered. In the trimethyl 2-bromobenzene-1,3,5-tricarboxylate (2), the formation of strong OAHꢁꢁꢁO hydro-
gen bonds is disabled by esterification of the acid functions. Nevertheless, the packing of 2 features
solvent free molecular layers formed by BrꢁꢁꢁO contacts and connected van der Waals interactions. These
layers are linked to each other by inverse bifurcated hydrogen bonds in term weak CAHꢁꢁꢁO contacts. The
results of the X-ray analysis could be confirmed by infrared spectroscopy.
Received 28 April 2014
Received in revised form 7 June 2014
Accepted 9 June 2014
Available online 18 June 2014
Keywords:
Trimesic acid analogues
Hydrogen bonding
Single crystal structure analysis
Infrared spectroscopy
Thermogravimetry coupled with differential
scanning calorimetry
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
⇑
Since its first synthesis in 1867 by Fittig [1] and the single crys-
tal structure determination in 1969 by Duchamp and Marsh [2],
Corresponding author. Tel.: +49 (0)3731 39 3192; fax: +49 (0)3731 39 3588.
E-mail address: florian.mertens@chemie.tu-freiberg.de (F.O.R.L. Mertens).
http://dx.doi.org/10.1016/j.molstruc.2014.06.035
0022-2860/Ó 2014 Elsevier B.V. All rights reserved.

A.S. Münch et al. / Journal of Molecular Structure 1074 (2014) 542–548
543
the interest in trimesic acid (benzene-1,3,5-tricarboxylic acid,
TMA) increased dramatically in the last decades. A various number
of applications of trimesic acid are conceivably, e.g. as a material in
dosimeters [3], in spectrofluorimetry for analysing different metal
ions, like terbium [4], and as a linker for antibacterial acting metal–
organic frameworks [5]. Due to their supramolecular properties
and the possibility to form a wide spectrum of metal coordination
compounds, trimesic acid can be regarded as a prototype for supra-
molecular self-assemblies [6,7]. In its guest-free solid state struc-
ture TMA forms the so-called ‘‘chicken-wire’’ network induced by
a centrosymmetric dimerization of the carboxylic acid groups
forming a cyclic hydrogen bonding motif with the graph set
R22(8). As a result, voids with a diameter of approximately 14 Å
are observed [2]. These supramolecular assemblies are also found
in deposited TMA on metal surfaces [8,9]. Besides the structure
of the simple trimesic acid, a large number of inclusion complexes
are described, e.g. clathrates with dimethylamine and N,N,N0,N0-
tetramethylethylenediamine [10], with dimethyl sulfoxide [11],
with water and 1,4-dioxane [12], as well as the respective water
5
complexes TMAꢁ6 H2O [11] and TMAꢁ2 H2O [13], and the inclusion
compounds of TMA with water and picric acid [14]. In addition to
these, the benzene-1,3,5-tricarboxylate is also known to form
metal–organic frameworks [15] with the HKUST-1 [16,17] and
MIL-100 [18] as prominent examples and ordinary salts, e.g. with
rare earth elements [19].
So far, a considerable number of monosubstituted benzene-
1,3,5-tricarboxylic acids are described in the literature, such as
the 2-amino-[20], 2-methyl-[21], 2-nitro-[22], 2-hydroxy-[23], 2-
fluoro-[20], 2-chloro-[24], and 2-methoxybenzene-1,3,5-tricarbox-
ylic acid [25] and their respective esters. However, X-ray data of
such monosubstituted trimesic acids are only available for the
hydroxyl [26] and carboxy [27] derivatives. In this paper, we
describe the synthesis and first comprehensive analytic character-
ization of 2-bromobenzene-1,3,5-tricarboxylic acid 1 [28,29], and
its trimethyl ester, trimethyl 2-bromobenzene-1,3,5-tricarboxylate
2 [28], together with the X-ray structures of 1 as 1:1 inclusion
compound with water and the guest-free structure of ester 2.
Additionally, the molecular interactions between 1 and water
were investigated by infrared spectroscopy and thermogravimetry
coupled with differential scanning calorimetry. Furthermore, the
melting behaviour, the heat of fusions, and the infrared spectra
of the title compounds have been studied.
Experimental
Fig. 2. Molecular diagrams of the title compounds
1
(a) and
2
(b). Thermal
ellipsoids are drawn at the 50% probability level.
General experimental and physical measurements
calorimetry (TG-DSC) were performed with a Setaram Sensys TGA
DSC under an argon/oxygen flow (20% O2) of 20 mL/min in the
temperature range from 25 to 400 °C using a temperature ramp
of 5 K/min.
All denoted chemicals are commercially available and were
used without further purification. Methanol was subjected to stan-
dard drying procedures. 1H and 13C NMR spectra were recorded
(25 °C) with
a Bruker Avance III 500 NMR spectrometer at
500.13 MHz and 125.76 MHz, respectively, using DMSO-d6:D2O
in ratio 1:1 (1) and DMSO-d6 (2) as solvents. Chemical shifts (d)
are given in ppm referring to tetramethylsilane as internal stan-
dard. The infrared (IR) spectra were obtained from a Varian 3100
FT-IR spectrometer in the region of 4000–450 cmꢂ1 (KBr pellet).
The thermogravimetric analyses coupled with differential scanning
Synthesis
2-Bromobenzene-1,3,5-tricarboxylic acid 1
2-Bromomesitylene (25.1 mmol, 5 g) was suspended in a mix-
ture of Na2CO3 (55.5 mmol, 5.88 g) and 2 mL AliquatÒ 336 in
Fig. 1. Scheme of synthesis of compound 1 and 2.

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A.S. Münch et al. / Journal of Molecular Structure 1074 (2014) 542–548
Table 1
Crystal data and refinement details of the structure determination.
Crystal data
1
2
Empirical formula
Formula weight (g/mol)
Crystal description
Crystal system
Space group
a (Å)
C9H5BrO6ꢁH2O
307.05
Colourless needle
C12H11BrO6
331.11
Colourless needle
Triclinic
Triclinic
ꢀ
ꢀ
P 1
P 1
7.9513(4)
8.3744(5)
8.6638(5)
114.510(2)
93.060(2)
100.346(2)
511.082
2
8.2399(2)
9.0362(2)
9.7471(2)
95.9350(10)
111.3160(10)
107.6560(10)
625.31
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
2
Dc (g cmꢂ3
)
1.995
4.045
304
1.759
3.307
332
Absorption coefficient (mmꢂ1
F (000)
)
Crystal size (mm)
0.54 ꢃ 0.51 ꢃ 0.08 0.39 ꢃ 0.18 ꢃ 0.16
Data collection
Temperature (K)
Radiation, wavelength (Å)
Collected reflections
h Range (°)
100(2)
Mo K
13,180
2.61–25.00
100(2)
Mo K , 0.71073
13,363
2.83–24.99
a
, 0.71073
a
Index ranges
Unique data, Rint
R1, wR2 [l > 2 (l)]
h
k
l
ꢂ9/9, ꢂ9/9, ꢂ10/10 ꢂ9/9, ꢂ10/10, ꢂ11/11
1790, 0.0401
0.0192, 0.0521
0.0195, 0.0523
2195, 0.0198
0.0148, 0.0378
0.0151, 0.0379
r
R1, wR2 (all data)
Refinement
Nref, Npar
1790, 165
1.097
2195, 178
1.090
Goodness of fit on F2
Max. and av. shift/error
0.001, 0.000
0.001, 0.000
ꢂ0.214, 0.311
Min. and max. resid. dens. (e Å3) ꢂ0.436, 0.089
Table 2
Selected intermolecular hydrogen bonds of the studied structure 1 and 2.
Atoms involved
Symmetry
Distance (Å)
Angle (°)
DAHꢁꢁꢁA
DꢁꢁꢁA
HꢁꢁꢁA
1
O2AH2ꢁꢁꢁO1
O1GAH1GꢁꢁꢁO3
O4AH4ꢁꢁꢁO1G
O1GAH2GꢁꢁꢁO5
O6AH6ꢁꢁꢁO3
ꢂx, 1 ꢂ y, 1ꢂz
1 ꢂ x, ꢂy, ꢂz
x, y, ꢂ1 + z
x, ꢂ1 + y, z
x, 1 + y, z
2.685(2)
2.930(2)
2.566(2)
2.777(2)
2.644(2)
1.86(3)
2.19(1)
1.76(3)
1.94(1)
1.91(3)
176(3)
146(2)
163(3)
176(2)
161(3)
2
C10AH10AꢁꢁꢁO5
C11AH11AꢁꢁꢁO5
C12AH12CꢁꢁꢁO1
C12AH12BꢁꢁꢁO2
1 ꢂ x, 1 ꢂ y, ꢂz
x ꢂ 1, y ꢂ 1, z ꢂ 1
x + 1, y, z + 1
ꢂ1 + x, ꢂ1 + y, z
3.369(2)
3.539(2)
3.522(2)
3.390(2)
2.46
2.58
2.54
2.64
153.9
167.6
176.6
133.2
Fig. 3. (a) Layer structure of 1 parallel to the (201) plane with hydrogen bond
motifs R44(12) and R22(8), as well as BrꢁꢁꢁBr contacts. (b) Packing arrangement of 1
viewed down the b axis containing OAHꢁꢁꢁO hydrogen bonds between the layers.
137.1, 130.9, 130.2, 121.5 (ArAC). FTIR (dried sample, KBr, cmꢂ1):
ꢀ
m
= 3087, 2978, 2882, 2662, 2546, 1698, 1596, 1412, 1392, 1360,
1290, 1270, 1207, 1178, 1138, 1036, 962, 922, 895, 764, 703,
666, 624, 580, 547, 482.
100 mL water and heated to reflux. Potassium permanganate
(0.316 mol, 50 g) was added portionwise during a period of 6 h.
After an additional reaction time of 6 h (reflux conditions), the
excess KMnO4 was destroyed by 25 mL methanol. The formed
MnO2 was separated from the solution and washed three times
with water. The combined filtrates were concentrated to half of
the original volume and acidified to pH 1 with concentrated hydro-
chloric acid and extracted thoroughly with diethyl ether
(3 ꢃ 25 mL). The combined organic phases were washed with
water (25 mL), dried over Na2SO4, and evaporated to obtain a pale
yellow powder. This was purified by recrystallisation using a sol-
vent mixture of tetrahydrofuran and ethanol (5:1) to yield 1 as a
white powder (2.07 g, 29%). Mp = 279–282 °C (Lit.: 260–275 °C
[28], 276–279 °C [29]). 1H NMR (500.13 MHz, DMSO-d6/D2O,
ppm): dH = 8.15 (s, ArAH), 13.79 (s, ArACOOH). 13C NMR
(125.76 MHz, DMSO-d6/D2O, ppm): dC = 166.9, 165.3 (ACOOH),
Trimethyl 2-bromobenzene-1,3,5-tricarboxylate 2
Carboxylic acid 1 (3 mmol, 866.7 mg) was dissolved in a mix-
ture of 35 mL dry methanol and 1 mL concentrated sulphuric acid
and heated under reflux conditions for 18 h. Subsequently, the
methanol was removed by distillation, the residue was diluted in
20 mL water, and extracted with diethyl ether (3 ꢃ 25 mL). The
combined organic phases were washed with water (25 mL) and
dried over Na2SO4. Evaporation of the solvent yielded a yellow
oil, which was diluted in 10 mL ethanol and cooled in a refrigerator
at 7 °C for 12 h, which delivered 2 as colourless needles (0.22 g,
22%). Mp = 96 °C (Lit.: 93–95 °C [28]). 1H NMR (500.13 MHz,
DMSO-d6, ppm): dH = 8.28 (s, ArAH), 3.90, 3.89 (s, ACH3). 13C NMR
(125.76 MHz, DMSO-d6, ppm): dC = 165.4, 164.1 (ACOOCH3), 135.7,

A.S. Münch et al. / Journal of Molecular Structure 1074 (2014) 542–548
545
131.9, 129.3, 122.7 (ArAC), 53.0, 52.7 (ACOOCH3). FTIR (KBr,
Results and discussion
cmꢂ1):
m = 3461, 3429, 3103, 3074, 3049, 3022, 2954, 2899, 2841,
ꢀ
1741, 1726, 1594, 1582, 1438, 1420, 1404, 1338, 1290, 1243,
1199, 1174, 1138, 1123, 1036, 947, 916, 890, 867, 800, 790, 773,
758, 735, 722, 708, 607, 559, 509, 469.
Synthesis of compounds
The title compounds 1 and 2 were synthesised applying a mod-
ified synthesis protocol of Holy´ et al. [28]. Starting from 2-bromo-
mesitylene compound 1 was synthesised by an oxidation reaction
of the methyl groups using potassium permanganate and AliquatÒ
336 as a phase transfer catalyst because of the low solubility of the
liquid adduct in water. In contrast to the literature the raw product
was purified by recrystallisation from a mixture of tetrahydrofuran
and ethanol. This procedure leads to the desired tricarboxylic acid
(1). Trimethyl ester 2 was synthesised using dried methanol and
concentrated sulphuric acid similar to a Fischer esterification
(Fig. 1). All synthesised compounds were characterised by 1H and
13C NMR spectroscopy, X-ray diffraction, TG-DSC measurements
and infrared spectroscopy.
Single crystal X-ray analysis
The single crystal X-ray diffraction data of compound 1 and 2
were collected at 100 K on a Bruker Kappa diffractometer equipped
with an APEX II CCD area detector and graphite-monochromatised
Mo Ka radiation (k = 0.71073 Å) employing u and x scan modes.
The data were corrected for Lorentz and polarization effects. Semi-
empirical absorption correction was applied using the SADABS pro-
gramme [30]. The SAINT programme [30] was used for the
integration of the diffraction profiles. The crystal structures were
solved by direct methods using SHELXS-97 [31] and refined by
full-matrix least-squares refinement against F2 using SHELXL-97
[31]. All non-hydrogen atoms were refined anisotropically. The
hydrogen atoms were included in the models in calculated posi-
tions and were refined as constrained to bonding atoms. Geomet-
rical calculations were performed using PLATON [32] and
molecular graphics were generated using SHELXTL [31].
X-ray single crystal analysis
Transparent colourless needles suitable for single crystal X-ray
investigations were yielded by slow evaporation of the solvent
from a solution of 1 in water/ethanol (5:1) and by refrigerating a
solution of 2 in ethanol at 7 °C for 18 h, respectively. The molecular
Fig. 4. (a) BrꢁꢁꢁO contacts in the layer structure of 2. (b) Packing structure containing CAHꢁꢁꢁO hydrogen bonds between the molecular layers.

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A.S. Münch et al. / Journal of Molecular Structure 1074 (2014) 542–548
structures of the title compounds are displayed in Fig. 2. Crystal
data and details of the structure determination are given in Table 1.
The parameter details of the intermolecular interactions are spec-
ified in Table 2.
p p interactions among the benzene rings [35] (d = 3.795 Å) as
well as between the aromatic units and a C@O group (C8@O3)
(d = 3.321 Å) [36] can be discussed.
ꢁꢁꢁ
X-ray single crystal analysis of 2
Trimethyl 2-bromobenzene-1,3,5-tricarboxylate (2) crystallises
in the same space group as 1 (P 1), though the polar protic solvent
X-ray single crystal analysis of 1
ꢀ
2-Bromobenzene-1,3,5-tricarboxylic acid crystallises in the tri-
ꢀ
ethanol is not included. The molecular structure is presented in
Fig. 2b showing the three carboxyl groups turned out of the aro-
matic ring plane as indicated by the interplanary angles of 4.20°
(O3AC8AO4), 39.06 (O1AC7AO2), and 66.76° (O6AC9AO5). In
comparison to compound 1 the twisting of the acid functions is
higher, induced probably by the arrangement of the molecules in
absence of solvent molecules in the overall packing. The molecules
are assembled in chains along the [110] direction by BrꢁꢁꢁO
[d(Br1ꢁꢁꢁO3) = 3.3387(12) Å]. These chains are oriented oppositely
to each other and interconnected only by van der Waals interac-
tions (Fig. 4a). The resulting layers are inclined to the (ꢂ110) plane
(20.88°), and held together by aromatic stacking [33] (d = 3.620 Å)
and interactions between the benzene rings and the C@O
group C8AO3 (d = 3.527 Å) [34]. In addition, we found weak
CAHꢁꢁꢁO hydrogen bonds [37] between methyl groups and a meth-
oxy oxygen [d(C12ꢁꢁꢁO2) = 3.390(2) Å] as well as carbonyl oxygens
[d(C10ꢁꢁꢁO5) = 3.369(2) Å, d(C11ꢁꢁꢁO5) = 3.539(19) Å, d(C12ꢁꢁꢁO1) =
3.522(2) Å]. As in 1, one of the carbonyl oxygens (O5) is engaged
in an inverse bifurcated hydrogen bond linked to the methyl
hydrogens H10A and H11A (Fig. 4b).
clinic space group P 1, with the unit cell containing one molecule
of 1 and one water molecule. The molecular structure is presented
in Fig. 2a showing the three carboxyl groups twisted out of the aro-
matic ring plane, i.e. 5.56° (O3AC8AO4), 24.58° (O1AC7AO2), and
56.82° (O6AC9AO5), respectively. In contrast to the typical
‘‘chicken wire’’ network of the trimesic acid [2], the molecules of
1 form a rather different structure. On the one hand two water
molecules act as hydrogen donors and acceptors and connect two
carboxyl groups of two neighbouring molecules of 1 by strong
OAHꢁꢁꢁO hydrogen bonds [33] [d(O4ꢁꢁꢁO1G) = 2.566(2) and
d(O1GꢁꢁꢁO3) = 2.930(2) Å] to yield a ring motif with the graph set
R44(12). One the other hand two further molecules are directly con-
nected by strong hydrogen bonds between the carboxyl groups
[d(O2ꢁꢁꢁO1) = 2.6851(19) Å] to form the ring motif R22(8), displayed
in Fig. 3a. In the crystal structure the molecules are linked together
in direction of the b axis by these two different hydrogen bonding
schemes leading to a zig-zag pattern. The respective chains are
interconnected by strong OAHꢁꢁꢁO bonds [d(O6ꢁꢁꢁO3) = 2.644(2) Å]
and BrꢁꢁꢁBr contacts [d = 3.3168(3) Å] [34], resulting in layers paral-
lel to the (201) plane. Interestingly, by close examination of the
hydrogen bonding pattern, we found, that the oxygen O3 forms
an inverse bifurcated hydrogen bond to the carboxyl hydrogen
H6 and the water hydrogen H1G of the included water molecule.
The molecular (201) layers are linked via strong OAHꢁꢁꢁO hydrogen
bonds [d(O1GꢁꢁꢁO5)] between the heavily twisted carboxyl group
(O6AC9AO5) and the water hydrogen H2G (Fig. 3b). Furthermore,
FTIR spectroscopic study of 1
Beside the single crystal analyses of the title compounds, their
FTIR spectra were recorded. The spectrum of 1 (Fig. 5a) contains the
typical bands of the synthesised 2-bromobenzene-1,3,5-tricarboxylic
Fig. 5. FTIR spectra of compounds 1 (a) and 2 (b).

A.S. Münch et al. / Journal of Molecular Structure 1074 (2014) 542–548
547
modes of the methyl groups binding on the oxygen atom of the
ester group [38].
The single crystal analysis of compound 1 reveals hydrogen
bonds between a water molecule and the carboxyl groups of two
different molecules of 2-bromobenzene-1,3,5-tricarboxylic acid.
In order to determine the influence of the included solvent on
the molecular arrangement of the carboxylic acid functionalities,
an IR spectrum of a dried sample of 1 (70 °C, 2 h, vacuum) was
recorded in the region from 850 to 1750 cmꢂ1. Hence, we were
able to compare its vibrational modes with the corresponding ones
of the crystals investigated by the XRD measurements, which can
indicate an interaction between the guest molecule and the acid
groups. A relative small shift of the C@O and CAO stretching vibra-
tions in the spectrum of the water complex (Fig. 6 grey line) in
comparison to the corresponding bands of the dried sample
(Fig. 6 black line) underline this fact.
TG-DSC measurements
Fig. 6. IR-spectrum of a dried sample of 1 (black line) in comparison to a sample of
the single crystal structure analysis of 1 including water in the crystal lattice (grey
The thermal stabilities of the synthesised compounds 1 and 2
were investigated by TG-DSC analyses. For the experiment we used
6.88 mg of a dried sample of the 2-bromotrimesic acid (Fig. 7a,
black line), 7.20 mg of the complex between water and 1 (Fig. 7a,
grey line), and 6.00 mg of the ester 2 (Fig. 7b). The single crystal
structure analysis and the infrared spectrum of 1 indicate that acid
and water form a 1:1 inclusion compound. Analysing the corre-
line) in the range of 1750–850 cmꢂ1
.
acid, such as overtone and combination bands between 2662 and
2546 cmꢂ1, aryl-C@O stretch mode at 1698 cmꢂ1, in plane OAH
band at 1392 cmꢂ1, CAO vibration at 1270 cmꢂ1, and an out-of-
plane OAH band at 922 cmꢂ1 indicating the carboxylic acid func-
tion. Besides this, typical vibrational modes of the aromatic ring
can be found in the spectra of the acid and the ester, including
CAH stretches between 3100 and 3000 cmꢂ1, aromatic C@C ring
modes at 1596 cmꢂ1 in the case of 1 and 1594 cmꢂ1ꢂi1n the case
of 2, as well as the out-of-plane CAH band at 764 cm for 1 and
758 cmꢂ1 for 2. The vibration modes at 895 cmꢂ1 (1) and
890 cmꢂ1 (2), respectively, indicate the 1,2,3,5-tetra substitution
pattern of the synthesised compounds. Furthermore, the bands at
1036 cmꢂ1 in the IR spectra of 1 and 2 are aryl-Br stretches and
demonstrate the halogen substitution of the aromatic ring, beside
the vibrational CABr band at 666 cmꢂ1 in Fig. 5a. In the infrared
spectrum Fig. 5b the typical bands of the ester functionalities can
be found, such as the intensive C@O stretching mode at
1726 cmꢂ1, the CACAO band at 1290 cmꢂ1, the OACAC band at
1123 cmꢂ1, and an asymmetric stretching vibration of the CAOAC
bond at 1199 cmꢂ1. The bands between 2954 and 2841 cmꢂ1 rep-
resent the corresponding asymmetric and symmetric vibrational
sponding TG-DSC measurement a heat effect (a) at 99 °C with an
enthalpy of 81.1 kJ/mol has been found as shown in Fig. 7a (grey
line). This temperature is close to the boiling temperature of water
and pointing to low relative stability [39] of the water inclusion
compound of 1. The corresponding mass loss (b) of 0.437 mg gives
an acid to water ratio of 1:1.03 being in a good agreement to the
analysis of the single crystal structure (1:1). The grey line of graph
(a) shows a further heat effect (c). Indicated by the low value of
37.9 kJ/mol it presumably belongs to the melting process and not
to decomposition. A very broad signal after this well-defined peak
indicates the beginning degradation process. For the dried sample
(black line, Fig. 7) integration of peak d delivers an enthalpy of
38.0 kJ/mol, which is in good agreement with the value of the com-
plex between water and 1 (
c
). Evaluating both heat effects, melting
temperatures of 279 °C (calculated for
c) and 282 °C (calculated for
d) have been determined showing a good conformity between dry
1 and its inclusion compound with water. The literature reports
values between 260–275 °C [28] and 276–279 °C [29].
Fig. 7. Thermogravimetric measurements coupled with differential scanning calorimetry of compound 1 (a, black line), 1ꢁH2O (1:1) (a, grey line), and ester 2 (b).
the heat effects of the water release with the corresponding mass loss b and the melting process. The heat effect of the melting of dried 1 is labeled with d, of the clathrate
with , and of 2 with
a Indicates
c
e.

548
A.S. Münch et al. / Journal of Molecular Structure 1074 (2014) 542–548
Fig. 7b displays the TG-DSC measurement of the synthesised
ester compound 2. A melting effect of 29.9 kJ/mol at a temperature
of 96 °C labelled with ( ) is observed in comparison to a melting
994929). These data can be obtained free of charge via
www.ccdc.cam.ac.uk/datarequest/cif, by e-mailing data-reques-
t@ccdc.com.ac.uk or by contacting the Cambridge CB21 EZ, U.K.;
Fax, +44 1223 336033. Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/
10.1016/j.molstruc.2014.06.035.
e
´
point of 93–95 °C presented by Holy et al. [28]. In addition, a
decomposition accompanied by an intensive mass loss starting at
170 °C is detected.
References
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Financial support by the European Union (European regional
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