Crystals of the Kemp's triacid salts - Part VI: Supramolecular architecture in the crystal of Kemp's triacid with tris(2-aminoethyl)amine

Article abstract of DOI:10.1016/j.molstruc.2011.04.005

A complex crystal [H₃KTA-TAEA-EA] is composed of triply deprotonated Kemp's triacid molecule (KTA^3-), triply protonated tris(2-aminoethyl)amine (H₃TAEA³⁺) molecule and one ethanol molecule (EA) as a solvate. The

Full text of DOI:10.1016/j.molstruc.2011.04.005

Journal of Molecular Structure 996 (2011) 48–52
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Crystals of the Kemp’s triacid salts – Part VI: Supramolecular architecture
in the crystal of Kemp’s triacid with tris(2-aminoethyl)amine
a,
b
a,
⇑
⇑
´
Adam Huczynski , Jan Janczak , Bogumil Brzezinski
a Faculty of Chemistry, A. Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland
b Institute of Low Temperature and Structure Research, Polish Academy of Sciences, PO Box 1410, 50-950 Wroław, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
A complex crystal [H3KTA–TAEA–EA] is composed of triply deprotonated Kemp’s triacid molecule
(KTA3ꢀ), triply protonated tris(2-aminoethyl)amine (H3TAEA3+) molecule and one ethanol molecule
(EA) as a solvate. The ring of the (KTA3ꢀ) trianion exhibits an uncommon twisted boat conformation with
two carboxylic groups in the axial positions and one in the equatorial position. In the crystal each KTA3ꢀ
trianion is hydrogen-bonded with four H3TAEA3+ molecules forming three-dimensional hydrogen-
bonded network within the supramolecular complex. The ethanol molecules form a uncommon dimer
bonded by very weak tandem hydrogen bonds. The IR spectrum of the crystal is consistent with the
results obtained by the X-ray study and provides spectroscopic evidence for the crystal formation.
Ó 2011 Elsevier B.V. All rights reserved.
Received 11 March 2011
Received in revised form 6 April 2011
Accepted 6 April 2011
Available online 14 April 2011
Keywords:
X-ray
FT-IR
Kemp’s triacid (KTA)
Tris(aminoethyl)amine (TAEA)
Hydrogen bond
Supramolecular complex
1. Introduction
tetramethylguanidine (TMG) [22], 7-methyl-1,5,7-triazabicy-
clo[4.4.0]dec-5-ene (MTBD) [23] and melamine (MEL) [24]. It was
Crystal engineering has provided chemists with a useful para-
digm for the rational design of solid-state structures [1–3]. In par-
ticular, self-assembly of preselected molecular building blocks can
yield designed supramolecular structure in one-pot synthesis.
Crystal engineering and the design of solid-state architectures
are of considerable contemporary interest from the point of view
of potential applications of functional materials. In this context
several research groups [4–15] have studied the crystalline molec-
ular complexes between carboxylic acid and several amines
including hydrogen bonds.
demonstrated that the chair conformation of the KTA molecule
was retained also in its salts in which monoanion or dianion of
Kemp triacid was present. In these crystals the multiple charge-
assisted OAHꢁꢁꢁOꢀ intramolecular and OAHꢁꢁꢁOꢀ, N+AHꢁꢁꢁOꢀ inter-
molecular hydrogen bonds are the main interactions stabilizing
their structures.
As a continuation of these studies we synthesized a new
hydrogen-bonded crystal formed by Kemp’s triacid (H3KTA) and
tris(2-aminoethyl)amine (TAEA) and studied its structure by
X-ray diffraction and FT-IR spectroscopy.
Nowadays, there is growing interest in supramolecular chemis-
try of tripodal ligands with C3 topology. Tris(aminoethyl)amine
(TAEA) (Scheme 1) is a well-known representative of this group
of ligand commonly used and commercially available [16–18].
The tricarboxylic acid such as Kemp’s triacid (cis,cis-l,3,5-trimeth-
ylcyclohexane-l,3,5-tricarboxylic acid, H3KTA) (Scheme 1) is consid-
ered an interesting agent in designing molecular system for crystal
engineering and for studies of three-dimensional hydrogen-bonded
networks within the supramolecular complexes [19].
2. Experimental
All materials were obtained from Sigma–Aldrich or Fluka and
used without any further purification.
2.1. Synthesis of H3KTA–TAEA–EA complex
A 1:1 mixture of H3KTA and TAEA was dissolved in hot ethanol
(EA) and left at room temperature. After a few days transparent
colourless crystals were formed.
In our previous papers we reported on the molecular structures
of several crystals of H3KTA with 1,5,7-triazabicyclo-[4.4.0]dec-
5-ene (TBD) [20], 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) [21],
2.2. X-ray measurements
⇑
Corresponding authors. Tel.: +48 618291330 (B. Brzezinski).
E-mail addresses: adhucz@amu.edu.pl (A. Huczyn´ ski), bbrzez@amu.edu.pl (B.
A colourless single crystal of [(C12H15O6)3ꢀ ꢁ (C6H21N4)3+
ꢁ
Brzezinski).
(C2H5OH)] of the size of 0.27 ꢂ 0.24 ꢂ 0.21 mm was measured on a
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.04.005

´
49
A. Huczynski et al. / Journal of Molecular Structure 996 (2011) 48–52
NH2
3. Results and discussion
COOH
COOH
COOH
CH3
3.1. Description of the structure
H3C
The Kemp triacid (C6H3(CH3)3(COOH)3) has three ionisable car-
boxyl groups and it can form mono-, di- and tri-deprotonated salts.
The molecular structure of the neutral Kemp triacid molecule in
the crystal exhibits chair conformation of the skeletal cyclohexane
ring with cis,cis triaxial arrangement of the carboxyl groups [28–
31]. In several crystals of single H2KTAꢀ and double deprotonated
HKTA2ꢀ salts that have been structurally characterised [20–
24,32–34] the chair conformation of the cyclohexane ring and tri-
N
H3C
H2N
NH2
TAEA
H3KTA
Scheme 1. The formula of H3KTA and TAEA.
KUMA KM-4 diffractometer equipped with two-dimensional area
CCD detector. The graphite monochromatized Mo (k =
K
a
0.71073 Å) radiation was used for data collection. The lattice param-
eters were refined by the least-squares methods on the basis of 1262
reflections. 157709 reflections (5558 independent, Rint = 0.0385)
were measured up to 56° in 2h covering over 99% of the Ewald
sphere. Data collection was made using the CrysAlis CCD program
[25], integration, scaling of the reflections and absorption correc-
tions were performed with the CrysAlis Red program [25]. The struc-
ture was solved by direct methods using SHELXS-97 and refined
using the SHELXL-97 program [26]. The hydrogen atoms joined to
the carbon atoms were constrained. The H atoms involved in the
hydrogen bonds were refined. The final differences Fourier maps
showed no peaks of chemical significance. The largest peaks on the
final
D
q
map were +0.359 and ꢀ0.306 e Åꢀ3. Details of the data col-
lection parameters, crystallographic data and final agreement
parameters are collected in Table 1. Visualisation of the structure
was made with the Diamond 3.0 program [27].
Fig. 1. View of the asymmetric unit of the H3KTA–TAEA–EA crystal with the
labelling of the atoms. Displacement ellipsoids are shown at the 50% probability
level and H atoms are drawn as small spheres of arbitrary size.
2.3. FT-IR measurements
Table 2
Selected geometric parameters (Å, °).
The FT-IR spectra of H3KTA–TAEA–EA crystals, TAEA and H3KTA
were recorded in the mid infrared region in nujol/fluorolube mulls
at 300 K. The spectra were taken with an IFS 113v FT-IR spectro-
photometer (Bruker, Karlsruhe) equipped with a DTGS detector;
resolution 2 cmꢀ1, NSS = 64. The Happ–Genzel apodization func-
tion was used.
C11AO12
C31AO31
C51AO51
O12AC11AO11
O51AC51AO52
C1AC2AC3AC4
C3AC4AC5AC6
C5AC6AC1AC2
N1AC25
N1AC23
C24AN3
C25AN1AC21
C21AN1AC23
N1AC21AC22AN2
N1AC25AC26AN4
1.241(2)
1.251(2)
1.252(2)
122.27(17)
120.95(18)
ꢀ33.3(2)
57.6(2)
ꢀ16.5(2)
1.456(2)
1.474(2)
1.495(2)
112.33(14)
112.49(15)
68.7(2)
C11AO11
C31AO32
C51AO52
O31AC31AO32
1.264(2)
1.259(2)
1.260(2)
123.44(17)
C2AC3AC4AC5
C4AC5AC6AC1
C6AC1AC2AC3
N1AC21
C22AN2
C26AN4
ꢀ23.1(2)
ꢀ35.4(2)
53.7(2)
1.464(2)
1.481(2)
1.480(3)
111.31(14)
Table 1
Crystallographic data and structure refinement parameters.
C25AN1AC23
Empirical formula
(C12H15O6)(C6H21N4)(C2H6O)
450.58
N1AC23AC24AN3
ꢀ172.5(2)
Formula weight (g molꢀ1
)
67.5(2)
Crystal system, space group
a, b, c (Å)
Triclinic, P ꢀ 1
8.811(2), 11.348(2), 12.288(3)
a
, b,
c
(°)
102.04(1), 103.64(1), 93.75(1)
1159.2(4)
V (Å3)
Table 3
Geometric parameters of the hydrogen bonds (Å, °).
Z
2
Dcalc/Dobs (g cmꢀ3
)
1.291/1.29
0.097
492
l
(mmꢀ1
F(0 0 0)
)
DAHꢁ ꢁ ꢁA
DAH
HꢁꢁꢁA
DꢁꢁꢁA
DAHꢁꢁꢁA
Crystal size (mm)
Radiation type, wavelength, k (Å)
Temperature (K)
0.27 ꢂ 0.24 ꢂ 0.21
N2AH23ꢁꢁꢁO11i
N2AH23ꢁꢁꢁO12i
N2AH24ꢁꢁꢁO32ii
N2AH25ꢁꢁꢁO12iii
N3AH31ꢁꢁꢁO51
N3AH31ꢁꢁꢁO52
N3AH32ꢁꢁꢁO32iv
N3AH33ꢁꢁꢁO31iii
N4AH43ꢁꢁꢁO11i
N4AH44ꢁꢁꢁO51i
N4AH45ꢁꢁꢁO52v
O81AH81ꢁꢁꢁO81vi
0.92(2)
0.92(2)
0.92(2)
0.85(2)
0.84(2)
0.84(2)
0.87(2)
0.95(2)
0.77(2)
0.96(2)
0.99(2)
0.82(1)
1.87(2)
2.51(2)
1.88(2)
1.92(2)
2.20(2)
2.51(2)
1.87(2)
1.83(2)
1.99(2)
1.76(2)
1.77(2)
2.44(1)
2.792(2)
3.134(2)
2.768(2)
2.762(2)
2.972(2)
3.258(2)
2.728(2)
2.761(2)
2.724(2)
2.719(2)
2.745(2)
2.969(8)
177(2)
125(2)
163(2)
172(2)
153(2)
150(2)
167(2)
166(2)
162(3)
175(2)
167(2)
123(2)
Mo Ka, 0.71073
295(2)
h range (°)
2.84–28.0
Absorption correction
Numerical, CrysAlis Red [25]
Tmin/Tmax
0.9755/0.9806
15709/5558/2780
0.0385
Reflections collected/unique/observed
Rint
Refinement on
F2
R[F2 > 2
r
(F2)]
0.0529
0.1192
1.001
+0.359, ꢀ0.306
wR(F2 all reflections)
Goodness-of-fit, S
D
qmax
,
D
qmin (e Åꢀ3
)
Symmetry codes: (i) ꢀx + 1, ꢀy + 1, ꢀz + 1; (ii) x ꢀ 1, y + 1, z; (iii) x, y + 1, z; (iv)
ꢀx + 2, ꢀy + 1, ꢀz + 1; (v) x ꢀ 1, y, z; (vi) ꢀx, ꢀy + 1, ꢀz.
[w(F2o ꢀ F2c )2]/
R
wF4o } ; wꢀ1 = ( 2(F2o ) + (0.0530P)2) where P = (Fo2 þ 2F2c )/3.
r
½
wR = {
R

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A. Huczynski et al. / Journal of Molecular Structure 996 (2011) 48–52
Fig. 2. Hydrogen-bonding environment of the H3TAEA3+ cation. Symmetry code as in Table 3.
Fig. 3. Hydrogen-bonding environment of the KTA3ꢀ trianion.

´
51
A. Huczynski et al. / Journal of Molecular Structure 996 (2011) 48–52
axial orientation of the COOH/COOꢀ groups are retained after
100
50
0
(a)
(b)
(c)
deprotonation (mono- or di). In all these structures, this conforma-
tion of H2KTAꢀ and HKTA2ꢀ molecules is stabilised by the intramo-
lecular charge-assisted OAHꢁ ꢁ ꢁO hydrogen bond [35,36]. In the
present structure of H3KTA–TAEA–EA the protons of the carboxyl
groups of Kemps triacid are transferred to the nitrogen atoms of
the amine groups of TAEA forming an H3TAEA3+ cation (Fig. 1).
After deprotonation the KTA3ꢀ trianion with three carboxyalate
groups (COOꢀ) change the conformation of the skeletal cyclohex-
ane ring from chair to boat or twisted boat one as a result of mu-
tual electrostatic repulsion between the COOꢀ groups (Fig. S1,
Suppl. mat.). The deprotonation of three carboxylic groups of
Kemps triacid in the present structure is evidenced by the CAO
bond lengths (Table 2), while the change in the conformation of
the skeletal cyclohexane ring from chair to twisted boat is evi-
denced by the changes in the CACACAC torsion angles from 60°
as expected for the chair conformation (Table 2). The all six CAO
bonds in the COOꢀ groups are intermediate between the single
C(sp2)AO (1.308–1.320 Å) and double C(sp2)@O (1.214–1.224 Å)
[37] indicating delocalization of the charge onto both O atoms of
the COOꢀ groups. The H3TAEA3+ cation exhibits distorted C3 sym-
metry as expected for the isolated non-interacted cation. The
CAN bonds linking the protonated amine groups are slightly longer
than that involving the central N1 atom (Table 2). The values of the
CAN bonds are in agreement with the expected values of
C(sp3)ANHþ3 (1.482–1.495 Å) and the C(sp3)AN (1.450–1.478 Å)
[37] for the tertiary amines.
4000
3500
3000
2500
2000
1500
2630
1000
500
100
50
0
3390
3356
2143
3278
3800 3600 3400 3200 3000 2800 2600 2400 2200 2000
100
1596
1559
50
0
In the crystal, the arrangement of the oppositely charged units,
KTA3ꢀ and H3TAEA3+, is mainly determined by a combination of
ionic and hydrogen bonding interactions and to a lesser degree
by the van der Waals forces (Fig. S2, Suppl. mat.). Each KTA3ꢀ tri-
anion is surrounded by six triprotonated H3TAEA3+ trications, so
the KTA3ꢀ trianion is an acceptor of eleven [COOꢀꢁ ꢁ ꢁH3N+] hydro-
gen bonds (Table 3, Fig. 2). Each triprotonated H3TAEA3+ cation is
involved as a donor in the NAHꢁ ꢁ ꢁO hydrogen bonds with six
neighbouring KTA3ꢀ trianion (Fig. 3). The interacted and hydro-
1632
1580
1700
1720
1394
1400
1800
1700
1600
1500
1300
Wavenumber [cm-1 ]
Fig. 4. FT-IR spectra in nujol/fluorolube mulls of: (- - -) H3KTA, (– ꢁ –) TAEA and (—)
H3KTA–TAEA–EA complex in the ranges: (a) 4000–400 cmꢀ1; (b) 3800–2000 cmꢀ1
and (c) 1800–1300 cmꢀ1
.
gen-bonded {KTA3ꢀꢁ ꢁ ꢁH3TAEA3+
}
aggregates related by an
inversion and translation along the a and b axes are arranged into
layers parallel to the (0 0 1) crystallographic plane (Fig. S2, Suppl.
mat.). The voids between the layers are occupied by the ethanol
molecules, which interact with each other via OAHꢁ ꢁ ꢁO hydrogen
bond forming a dimeric structure (Fig. S3, Suppl. mat.).
trum of TAEA (dash-dotted line) are no longer observed in the
spectrum of 1:1:1 H3KTA–TAEA–EA complex (solid line), which
means that the three NH2 amine groups of TAEA are protonated
and hydrogen-bonded within the complex structure.
3.2. FT-IR studies
The structure of Kemp’s triacid (H3KTA) is well known. The car-
boxylic groups of H3KTA are hydrogen-bonded forming a dimeric
carboxylic–carboxylic network in the crystal structure [29–31].
The vibrations of the protons within these hydrogen bonds are
manifested as a broad structured band in the region 3400–
2400 cmꢀ1 (Fig. 4, dashed line). In contrast, the formation of
[COOꢀꢁ ꢁ ꢁH3N+] bonds is reflected in the spectrum of the complex
The FT-IR spectrum of the H3KTA–TAEA–EA complex (solid line)
is compared with the spectra of KTA (dashed line) and TAEA
(dashed-dotted line) in Fig. 4a and the same spectra with extended
scale in the regions of m(OH) and m(NH) as well as m(C@O) vibra-
tions in Fig. 4b and c, respectively. In the unit cell of the 1:1:1
H3KTA–TAEA–EA crystal, each Kemp triacid molecule is completely
deprotonated forming a trianion KTA3ꢀ, which is hydrogen-bonded
to the triprotonated H3TAEA3+ trication via 11 intermolecular
[COOꢀꢁ ꢁ ꢁH3N+] hydrogen bonds (Figs. 2 and 3). The parameters of
these hydrogen bonds are given in Table 3. These hydrogen bonds
are rather weak or of intermediate strength and from the spectro-
scopic point of view, interpretation of the FT-IR spectrum of the
hydrogen-bonded network in the crystal is difficult due to the
as a broad absorption in the region from 3200 cmꢀ1 to 2400 cmꢀ1
.
In the spectrum of crystalline H3KTA the appearance of two
bands with the maxima at 1720 cmꢀ1 and 1700 cmꢀ1 (Fig. 4c,
dashed line), connected with the m(C@O) vibrations of the carbox-
ylic groups, indicates that these groups are clearly different hydro-
gen-bonded within the structure of the hydrogen-bonded network.
In the spectrum of the complex (solid line), these bands are no
more observed and instead, a new band arises with a maximum
overlapping of the respective
m
(NHþ3 ) stretching vibrations.
at about 1559 cmꢀ1 assigned to the
respective band assigned to the
m
as(COOꢀ) vibrations. The
m
s(COOꢀ) vibrations is observed
According to the crystal structure, two ethanol molecules are
hydrogen-bonded, forming a dimer (Fig. S3, Suppl. mat.). However,
these hydrogen bonds are very weak and therefore the band with a
maximum at 3390 cmꢀ1 should be assigned to the protonic vibra-
tion of a very weakly hydrogen-bonded OH group.
at 1394 cmꢀ1. Furthermore, the broad band at 1662 cmꢀ1 is
assigned to the d(NHþ3 ) vibrations of the protonated and hydrogen
bonded TAEA molecule. The presence of these two bands con-
nected with the respective
the spectroscopic evidence of the complete proton transfer from
m
as(COOꢀ) and d(NHþ3 ) vibrations is
The bands assigned to the
mas(NAH) and ms(NAH) vibrations at
3356 cmꢀ1 and 3270 cmꢀ1, respectively and observed in the spec-

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A. Huczynski et al. / Journal of Molecular Structure 996 (2011) 48–52
52
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the complex structure.
Appendix A. Supplementary material
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The X-ray crystallographic data for the structure reported in
this paper have been deposited at the CCDC as supplementary data,
CCDC 816769. Copies of the data can be obtained on application to
CCDC, 12 Union Road, Vambridge CB2 1EZ, UK. E-mail: depos-
it@ccdc.cam.ac.uk. Supplementary data associated with this article
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