The synthesis and structural studies of a new Kemp's triacid oxaalkyl ester and its complexes with Li+, Na+ and K+ cations

Article abstract of DOI:10.1016/j.molstruc.2008.06.014

A new derivative of Kemp's triacid (KTA) with 2-bromoethyl methyl ether (triester, KTEG1) and its complexes with monovalent cations (Li⁺, Na⁺ and K⁺) have been synthesized and studied by EI MS, multinuclear NMR, FT-IR as well as by the PM5 semiempirical methods. It has been demonstrated that KTEG1 forms stable complexes of 1:1 stoichiometry with the metal cations studied. The mass fragmentation pathways for triester and its complexes are proposed. The FT-IR spectra of the complexes show that in the coordination process no oxygen atoms of the carbonyl groups are involved. The FT-IR and NMR data taken together indicated that the coordination process is realized by the oxygen atoms from the oxaalkyl chains. The structures of the KTEG1 and its complexes with Li⁺, Na⁺ and K⁺ cations are visualized and discussed in detail.

Full text of DOI:10.1016/j.molstruc.2008.06.014

Journal of Molecular Structure 892 (2008) 470–476
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
The synthesis and structural studies of a new Kemp’s triacid oxaalkyl ester
and its complexes with Li+, Na+ and K+ cations
*
´
Piotr Przybylski, Adam Huczynski, Bogumił Brzezinski
´
Faculty of Chemistry, Adam Mickiewicz University, 60-780 Poznan, Grunwaldzka 6, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 May 2008
Received in revised form 11 June 2008
Accepted 16 June 2008
Available online 25 June 2008
A new derivative of Kemp’s triacid (KTA) with 2-bromoethyl methyl ether (triester, KTEG1) and its com-
plexes with monovalent cations (Li+, Na+ and K+) have been synthesized and studied by EI MS, multinu-
clear NMR, FT-IR as well as by the PM5 semiempirical methods. It has been demonstrated that KTEG1
forms stable complexes of 1:1 stoichiometry with the metal cations studied. The mass fragmentation
pathways for triester and its complexes are proposed. The FT-IR spectra of the complexes show that in
the coordination process no oxygen atoms of the carbonyl groups are involved. The FT-IR and NMR data
taken together indicated that the coordination process is realized by the oxygen atoms from the oxaalkyl
chains. The structures of the KTEG1 and its complexes with Li+, Na+ and K+ cations are visualized and dis-
cussed in detail.
Keywords:
Kemp’s triacid ester
Monovalent cations
Complexes
Mass spectrometry
Spectroscopy
Ó 2008 Elsevier B.V. All rights reserved.
PM5 semiempirical method
1. Introduction
COOH
CH3
COOH
COOH
cis,cis-1,3,5-Trimethylcyclohexane-1,3,5-tricarboxylic acid
(Kemp’s triacid, KTA) was first prepared by Kemp and Petrakis in
1981 year [1] (Scheme 1). Three axially positions of the three
carboxylic groups were confirmed by structural studies of some
derivatives of KTA [1–3]. Recently, the structures of KTA hydro-
gen-bonded complexes with 1,8-diazabicyclo[5.4.0]undec-7-ene
(DBU) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) bases were
also investigated by X-ray methods [4,5]. Kemp’s triacid was used
for selective recognition studies of carboxylate anions [6–9] and its
some imide derivatives (m-xylenediamine bis(Kemp’s triacid
H3C
H3C
Kemp’s triacid
Scheme 1. Structure of the Kemp’s triacid (KTA).
Our earlier papers have reported formation of complexes be-
tween various antibiotics or natural products derivatives contain-
ing oxaalkyl moieties and metal cations [26–36]. We have shown
that the length of the oxaalkyl chains influences the antibacterial
or antifungal activity of the compounds studied [37,38].
In this paper, we report on a new of KTA 2-methoxy-ethyl tri-
ester (Scheme 2) synthesized and discuss in detail its structure
as well as properties concerning the complexation of Li+, Na+ and
K+ cations.
imide) as complexones of divalent metal cations such as Zn2+
,
Co2+, Mg2+ [10–18]. KTA complexes with Fe+2 were used as models
of non-heme iron enzymes [19] and as a porphyrin-linked dicar-
boxylate ligand in tri-iron complexes [20]. Condensation of Kemp’s
triacid with aromatic diamines has given new type of ionophore
selective toward Hg+2 cations [21]. It is interesting to note that
crown-ether derivatives of KTA were also investigated as trans-
porters of various metal cations [22,23]. Only a few reports have
appeared about triesters of Kemp’s triacid. A model substance for
the active site of bacteriorhodopsin has been synthesised from
Kemp’s triacid triethyl ester [24], whereas only tribenzyl ester of
KTA has been studied by the X-ray method [25].
2. Experimental
Kemp’s triacid, 2-bromoethyl methyl ether, DBU and respective
salts: LiClO4, NaClO4 and KClO4 were commercial product of
Aldrich. Because the salts were hydrates it was necessary to dehy-
drate them by the several evaporations from the mixtures of aceto-
nitrile or benzene with the respective metal salt. CH3CN and CD3CN
were stored over the 3-Å sieves.
* Corresponding author. Tel.: +48 618291330.
E-mail addresses: adhucz@amu.edu.pl (A. Huczyn´ ski), bbrzez@main.amu.edu.pl
(B. Brzezinski).
0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2008.06.014

P. Przybylski et al. / Journal of Molecular Structure 892 (2008) 470–476
471
Table 1
7''
EI MS data of KTEG1
7
6''
O
7'
Ion
m/z
Relative abundance (%)
O
M+
b
c
d
e
f
g
h
i
j
j1
k
l
m
n
o
a
432
374
357
299
267
253
241
225
224
195
2
2
17
23
9
5''
6
6'
O
O
O
O
O
5
4''
4
O
O
5'
4'
1
3
1''
3''
3
2''
10
35
7
2
H2b
1'
2'
3'
4
H2a
167
149
121
107
59
18
5
100
17
46
KTEG1
Scheme 2. Structure of a new ester of KTA synthesised.
2.1. Synthesis of KTA 2-methoxy-ethyl triester (KTEG1)
ene. The filtrate was evaporated under reduced pressure at room
temperature. The residue was purified by chromatography on silica
gel (Fluka type 60). The column was eluted with dichlorometh-
ane:acetone (7:1) solvent mixture. The combined fractions were
evaporated under reduced pressure. The yield of yellow oily prod-
uct was 48%.
The mixture of 2-bromoethyl methyl ether (962 mg;
6,97 mmol), cic,cis-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic
acid (Kemp’s triacid) (300 mg, 1,16 mmol) and 1,8-diazabicy-
clo[5.5.0]-undec-7-ene (DBU) (796 mg; 5,23 mmol) and 10 ml tol-
uene was heated at 80 °C for 15 h. After cooling the precipitate
DBU-hydrobromide (DBUꢀHBr) was filtered and washed with tolu-
CH3O(CH2)2O
CH3O(CH2)2O
O
O
O(CH2)2OCH3
CH3O(CH2)2O
CH3O(CH2)2O
O
O
OH
O
*
O
*
[M - C18H29O8]
r H
[M - CH2CHOCH3]
CH3
O
CH2 CH2
M.+
m/z = 432
a
o
b
m/z = 59
m/z = 374
*
[M - O(CH2)2OCH3]
- OH
*
O
O
O(CH2)2OCH3
- HCOOH
O
O
O(CH2)2OCH3
H
O
O
O(CH2)2OCH3
CH3O(CH2)2O
O
O
O(CH2)2OCH3
O
*
O
r H
- CO
- CH2CHOCH3
*
*
d
f
h
c
m/z = 299
m/z = 253
r H
m/z = 225
m/z = 357
- CH3OH
r H
*
*
- HCOO(CH2)2OCH3
*
- CH2CHOCH3
*
- CH2CHOCH3
O
H
O
O
O
O
CH2 CH2
O
O
OH
O
H
O
O
O
- CO
O
- HCOOH
O
*
j1
m/z = 195
HO
e
k
g
m/z = 267
m/z = 167
m/z = 241
- H2O
O
- C3H4O3
- H2O
*
*
O
O
O
O
O
O
O
O
- CO
n
m/z = 107
l
i
j
m/z = 149
m/z = 224
m/z = 195
- CO
m
m/z = 121
Scheme 3. The fragmentation routes proposed on the basis of the EI-MS data.

472
P. Przybylski et al. / Journal of Molecular Structure 892 (2008) 470–476
Table 2
The main peaks in the ESI mass spectra of the complexes of KTEG1 with cations at
various cone voltages (10–90 V)
Mixture
Cone voltage (V)
Main peaks m/z
KTEG1–Li+
10
30
50
70
90
10
30
50
70
90
10
30
50
70
90
440 (A)
440 (A)
440 (A)
440 (A), 305 (B), 169 (C), 150 (D), 121 (E)
440 (A), 305 (B), 169 (C), 150 (D), 121 (E)
455 (A)
455 (A)
455 (A)
455 (A), 321 (B), 169 (C), 150 (D), 121 (E)
455 (A), 321 (B), 169 (C), 150 (D), 121 (E)
472 (A)
KTEG1–Na+
KTEG1–K+
472 (A)
472 (A), 337 (B), 169 (C), 150 (D), 121 (E)
472 (A), 337 (B), 169 (C), 150 (D), 121 (E)
337 (B), 169 (C), 150 (D), 121 (E)
Elemental analysis: C21H36O9 (KTEG1) calculated: C = 58.26%,
H = 8.32%; found: C = 58.24%, H = 8.33%.
2.2. ESI-MS and EI-MS measurements
The ESI (Electrospray Ionisation) mass spectra were recorded
on a waters/micromass (Manchester, UK) ZQ mass spectrome-
ter equipped with a Harvard apparatus syringe pump. All sam-
ples were prepared in acetonitrile. The measurements were
performed for the two types of samples being the solutions
of Kemp’s triacid ester (5 ꢁ 10ꢂ5 mol dmꢂ3) with: (a) each of
the cations Li+, Na+ and K+ (2.5 ꢁ 10ꢂ4 mol dmꢂ3) taken sepa-
rately and (b) the cations Li+, Na+ and K+ (5 ꢁ 10ꢂ5
/
3 mol dmꢂ3
) taken together. The samples were infused into
the ESI source using
a Harvard pump at a flow-rate of
20
l
l minꢂ1. The ESI source potentials were: capillary 3 kV, lens
0.5 kV, extractor 4 V. The standard ESI mass spectra were re-
corded at 30 V. The source temperature was 120 °C and the
dessolvation temperature was 300 °C. Nitrogen was used as
the nebulizing and drying gas at flow-rates of 100 and
300 dm3 hꢂ1, respectively. Mass spectra were acquired in the
positive ion detection mode with unit mass resolution at a
step of 1 m/z unit and at cone voltages cv = 10, 30, 50, 70,
90 V. The mass range for ESI experiments was from m/z = 100
to m/z = 1000. Low- and high-resolution EI-mass spectra were
recorded using on a AMD-Intectra GmbH (Harpstedt) D-27243
model 402 double-focusing sector mass spectrometer (ionizing
voltage 70 eV; accelerating voltage 8 kV; resolution 10,000;
10% valley definition). Kemp’s triacid ester sample was intro-
duced using direct insertion probe at a source temperature of
ꢃ150 °C. The elemental compositions of the ions were deter-
mined using the same instrument by peak matching relative
to perfluorokerosene. The mass range for EI experiments was
from m/z = 50 to m/z = 700. The error of mass determination
in the EI and ESI experiments was 1.
Fig. 1. ESI MS spectra of (a) 1:1 mixture of KTEG1 with NaClO4 at various cone
voltages (cv) and (b) 1:1:1:3 mixture of cation perchlorates (LiClO4, NaClO4 and
KClO4) with KTEG1 (cv = 30).
2.3. FT-IR measurements
All manipulations with the substances were performed in a
carefully dried and CO2-free glove box.
The FT-IR spectra of Kemp’s tracid ester and its 1:1 complexes
(0.05 mol dmꢂ3) with LiClO4, NaClO4, and KClO4 were recorded in
the mid infrared region in acetonitrile solutions.
2.4. NMR measurements
A cell with Si windows and wedge-shaped layers was used
The NMR spectra of KTEG1 and its 1:1 complexes (0.05 mol lꢂ1
)
to avoid interferences (mean layer thickness 170
l
m). The
with monovalent metal cations salts were recorded in CD3CN solu-
tions using a Varian Gemini 300 MHz spectrometer. All spectra
were locked to deuterium resonance of CD3CN.
spectra were taken with an IFS 113 V FT-IR spectrophotometer
(Bruker, Karlsruhe) equipped with a DTGS detector; resolution
2 cmꢂ1, NSS = 125. The Happ–Genzel apodization function was
used.
The 1H NMR measurements in CD3CN were carried out at the
operating frequency 300.075 MHz; flip angle, pw = 45°; spectral

P. Przybylski et al. / Journal of Molecular Structure 892 (2008) 470–476
473
M
CH3O(CH2)2O
CH3O(CH2)2O
O
O
O(CH2)2OCH3
O
M+
A
- C6H14O3
M
OH
O
O
O(CH2)2OCH3
- C5H8O5M
O
HO
O
O
- C5H5O4M
- CO
B
E
C
D
O
,where M = Li+, Na+, K+
Scheme 4. The fragmentation pathways proposed on the basis of ESI-MS spectra at various cone voltages.
width, sw = 4500 Hz; acquisition time, at = 2.0 s; relaxation delay,
d1 = 1.0 s; T = 293.0 K and using TMS as the internal standard. No
window function or zero filling was used. Digital resolution was
0.2 Hz per point. The error of chemical shift value was 0.01 ppm.
13C NMR spectra were recorded at the operating frequency
75.454 MHz; pw = 60°; sw = 19,000 Hz; at = 1.8 s; d1 = 1.0 s;
T = 293.0 K and TMS as the internal standard. The line broadening
parameters were 0.5 or 1 Hz. The error of the chemical shift value
was 0.1 ppm.
tra, the principal mass spectral fragmentation pathways of KTEG1
were determined and shown in Scheme 3. The low abundance sig-
nal of the molecular ion of KTEG1 arises at m/z = 432. The molecu-
lar ion a can decompose in three ways with the formation of b, c
and o ions. Ion c can be form alternatively from ion b by the
abstraction of one hydroxyl radical. Further decompositions are
concerned only with ion c and have a complex character. During
these mass decompositions always only small neutral molecules
are released.
The 1H and 13C NMR signals were assigned for each species
using one or two-dimensional (COSY, HETCOR, HMBC) spectra.
The ESI-MS spectra of KTEG1 with Li+, Na+ and K+ cations at
cv = 10 V show m/z signals at 440, 455 and 472, respectively,
proving the formation of the respective 1:1 (KTEG1 + M)+ com-
plexes (Table 2, ion A type). The exemplary spectra of KTEG1
2.5. PM5 calculations
Calculations were performed using the WinMopac 2007 pro-
gram [31,32]. In all cases full geometry optimisation of Kemp’s tri-
acid ester as well as its complexes with monovalent cations was
carried out without any symmetry constraints using PM5 semiem-
pirical method.
100
50
2.6. Elemental analysis
a
The elemental analysis of Kemp’s triacid ester was carried out
on Vario ELIII (Elementar, Germany).
0
4000
3500
3000
2500
2000
1500
1000
500
100
3. Results and discussions
3.1. EI-MS and ESI-MS studies
50
0
The new triester of KTA (KTEG1, Scheme 2) was characterized
by spectroscopic methods and EI-mass spectrometry. The spectro-
scopic properties of KTEG1 are compared below with those of its
complexes with metal cations. For KTEG1 the EI-mass spectrome-
try studies were performed to determine its fragmentations path-
ways. The low-resolution EI-MS data of KTEG1 spectrum are
collected in Table 1. On the basis of these signals as well as the ex-
act mass measurements and also the B/E and B2/E linked scan spec-
1732
b
1800
1775
1750
1725
1700
1675
1650
Wavenumber [cm-1
]
Fig. 2. FT-IR spectra of: (—) KTEG1, (– –) KTEG1–Li+, (ꢀꢀꢀ) KTEG1–Na+, and (–ꢀꢀ–)
KTEG1–K+ in the ranges of (a) 4000–400 cmꢂ1; (b)
m(C@O) stretching vibrations.

474
P. Przybylski et al. / Journal of Molecular Structure 892 (2008) 470–476
Table 3
13C NMR chemical shift (ppm) of KTEG1 and its complexes in CD3CN
No. atom
Chemical shift (ppm)
Differences (
D
) between chemical shift (ppm)
KTEG1
KTEG1:Li+
KTEG1:Na+
KTEG1:K+
D
1
D
2
D
3
1, 10, 100
2, 20, 200
3, 30, 300
4, 40, 400
5, 50, 500
6, 60, 600
7, 70, 700
41.93
43.18
31.06
176.78
64.05
71.00
58.80
42.02
43.02
30.97
177.28
64.24
70.89
58.92
42.01
43.20
31.11
177.50
64.41
70.85
58.98
41.99
43.26
31.11
177.12
64.17
70.94
58.89
0.09
0.08
0.02
0.05
0.72
0.36
0.06
0.08
0.05
0.34
0.12
ꢂ0.16
ꢂ0.09
0.50
0.19
ꢂ0.12
ꢂ0.15
ꢂ0.06
0.12
0.18
0.09
D
1, d KTEG1+LiClO4–dKTEG1; D2, d KTEG1+NaClO4–dKTEG1; D3, dKTEG1+KClO4–dKTEG1.
Table 4
1H NMR chemical shift (ppm) of KTEG1 and its complexes in CD3CN
No. atom
1H NMR chemical shift (ppm) and coupling constants (Hz)
KTEG1
KTEG1:Li+
KTEG1:Na+
KTEG1:K+
00
2eq, 2eq0, 2eq
d 2.62
2J = 14.8
d 1.09
2J = 14.8
s 1.19
m 4.06
m 3.54
s 3.31
d 2.62
2J = 14.9
d 1.09
2J = 14.9
s 1.19
m 4.10
m 3.55
s 3.36
d 2.62
2J = 14.7
d 1.09
2J = 14.7
s 1.19
m 4.11
m 3.58
s 3.39
d 2.62
2J = 14.7
d 1.09
2J = 14.7
s 1.19
m 4.08
m 3.56
s 3.35
00
2ax, 2ax0, 2ax
3, 30, 300
5, 50, 500
6, 60, 600
7, 70, 700
Eq, equatorial; ax, axial.
Table 5
3.2. Spectroscopic studies
Heat of formation HOF (kcal/mol) of KTEG1 and its 1:1 complexes with monovalent
metal cations calculated by PM5 method at semiempirical level (WinMopac 2007)
The FT-IR spectra of the KTEG1 triester and its complexes with
Li+, Na+ and K+ cations (used as perchlorate salts) in acetonitrile
solutions are compared in Fig. 2. These spectra are very similar.
Complex
HOF (kcal/mol)
D
HOF (kcal/mol)
KTEG1
ꢂ424.13
ꢂ298.96
ꢂ446.38
ꢂ279.32
ꢂ454.55
ꢂ274.33
ꢂ402.67
—
KTEG1+Li+uncomplexed
KTEG1+Li+complexed
KTEG1+Na+uncomplexed
KTEG1+Na+complexed
KTEG1+K+uncomplexed
KTEG1+K+complexed
ꢂ147.52
ꢂ175.23
ꢂ128.34
The bands assigned to the
m(C@O) stretching vibrations arise in
all spectra at 1732 cmꢂ1 clearly indicating the lack of participation
of the carbonyl groups in the complexation process of metal cat-
ions. This result should be taken into account when interpreting
the NMR data which are summarized in Tables 3 and 4. The 1H
and 13C resonances were assigned on the basis of two-dimensional
NMR experiments. The 13C NMR signals of the KTEG1 carbonyl C
atoms are shifted towards higher ppm values with the complexation
D
HOF = HOFcomplexed–HOFuncomplexed
.
complex with Na+ at various cone voltages are shown in
Fig. 1a. In the ESI-MS spectra of complexes with Li+ and Na+
cations at cv = 70 V as well as at cv = 50 V in the spectrum
of K+ complex additional signals appear due to a beginning
fragmentation of the respective complexes. The signals as-
signed to the B type ions arise at m/z = 305, 321 and 337 indi-
cating the formation of other types of complexes after the
abstraction of two oxaalkyl moieties, as shown in Scheme 4.
At the same cv values besides the signals of ion B other sig-
nals assigned to ions C–E are present in all spectra. The m/z
values of these signals are independent of the kind of the cat-
ion used indicating the common fragmentation pathways of
ion B. The proposed fragmentation pathways of the complexes
are shown in Scheme 4.
Table 6
The interatomic distances (Å) and partial charges for O atoms of KTEG1 coordinating
metal cations in complexes structures calculated by PM5 method (WinMopac 2007)
Complex
with
monovalent
cation
Monovalent
cation partial atom
charge
Coordinating Coordinating
Distance (Å)
coordinating
atom ? cation
atom partial
charge
KTEG1+Li+
+0.483
+0.379
O4–5
O6–7
ꢂ0.401
ꢂ0.384
ꢂ0.376
ꢂ0.390
ꢂ0.405
ꢂ0.419
ꢂ0.420
ꢂ0.405
ꢂ0.412
ꢂ0.402
ꢂ0.475
ꢂ0.428
ꢂ0.469
ꢂ0.427
ꢂ0.415
ꢂ0.421
2.23
1.99
2.04
2.06
2.27
2.36
2.37
2.28
2.31
2.24
2.98
2.84
2.88
2.82
2.72
2.76
0
0
O6 –7
0 0–70 0
O6
KTEG1+Na+
O4–5
0
0
O4 –5
O4
The ESI spectrum of the mixture of Li+, Na+ and K+ cations with
33% of the equivalent concentration of KTEG1 shows three charac-
teristic signals at m/z = 440, 455 and 472 assigned to the 1:1 + spe-
cies (Fig. 1b). The intensity of the KTEG1–Na+ complex signal is
dominant, clearly indicating that KTEG1 preferentially forms com-
plexes with Na+ cations. The intensity of the signal of KTEG1–Li+
complex is slightly lower and that of KTEG1–K+ complex is signif-
icantly lower, demonstrating that KTEG1 shows only low affinity to
K+ cation.
0 0–50 0
O6–7
0
0
O6 –7
O6
0 0–70 0
KTEG1+K+
+0.772
O4–5
0
0
O4 –5
O4
0 0–50 0
O6–7
0
0
O6 –7
O6
0 0–70 0

P. Przybylski et al. / Journal of Molecular Structure 892 (2008) 470–476
475
Scheme 5. Structures of KTEG1 (a) and KTEG1–Li+ (b) complex calculated by the
PM5 semiempirical method.
Scheme 6. Structures of KTEG1–Na+ (a) and KTEG1–K+ (b) complexes calculated by
the PM5 semiempirical method.
of metal cations. According to the FT-IR data, these changes in the
chemical shift should be explained by the involvement of the O4–5
atoms in the coordination process of the metal cation. This result
illustrates that the interpretation of the NMR data only would lead
to the wrong conclusion that the carbonyl oxygen atoms are in-
volved in the complexation. The greatest chemical shift changes
are observed in the spectra of the 1:1 complex of KTEG1 with
Na+ cation and further in the spectrum of KTEG1–Li+ complex. Rel-
atively low chemical shift changes of the carbonyl carbon atoms
are observed in the spectrum of KTEG1–K+ complex. This result is
in very good agreement with the affinity of KTEG1 towards the cat-
ions studied, determined by the ESI-MS method. The lowest differ-
ences in 1H and 13C chemical shifts are observed for the
cyclohexane moiety of KTEG1. This is understandable because no
conformational changes in the cyclohexane ring take place after
the complexation of the cations.
data showing the preferentially complexation of Na+ cations by
the KTEG1. These results are also in agreement with the calculated
partial charge values for the metal cations within the complexes
(Table 6).
According to the FT-IR measurements the most stable struc-
tures of the triester and its complexes involve no interactions be-
tween the oxygen atoms of the ester carbonyl groups and the
metal cations. Thus, the coordinating oxygen atoms are those of
the oxaalkyl chains. The energetically favorable calculated struc-
tures are shown in Schemes 5 and 6. In the structure of the triester
a tendency to dipole–dipole interactions between the polar car-
bonyl groups is very limited because they are directed to the out-
side of the cyclohexane ring. Almost the same situation was
detected earlier in the crystal structure of benzyl triester of KTA
[25].
The interatomic distances between the oxygen atoms and the
cations and partial charges of the cations and O-atoms are given
in Table 6. These data show that only four oxygen atoms are always
involved in coordination, irrespective of the kind of the cation. The
coordinating distances and the number of coordinating oxygen
atoms suggest that the Li+ cation can undergo fast fluctuations
within the structure of the complex as it was demonstrated for
the complexes of crown-ethers or derivatives of gossypol containing
3.3. PM5 semiempirical calculations of KTEG1 and its complexes
The heats of formation (HOF) of KTEG1 and its complexes with
Li+, Na+ and K+ cations are collected in Table 5. The
DHOF values of
the complexes of KTEG1 with the cations studied, reflecting the
energetic profit of the complexation process, demonstrate that
the formation of complexes is energetically favorable. These values
also correspond very well to the spectrometric and spectroscopic

476
P. Przybylski et al. / Journal of Molecular Structure 892 (2008) 470–476
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oxaalkyl chains with the monovalent cations [35]. The interatomic
distances between oxygen atoms and Na+ cation are in close range
suggesting the relatively strong localization of this cation within
the structure (Scheme 6a). Furthermore, the coordination sphere
of the Na+ cation is the most regular of all calculated ones forming
the slightly distorted octahedron. This structure of the complex can
be the reason for the hight affinity of KTEG1 towards Na+ cations.
The calculated structure of KTEG1–K+ complex is comparable
with that of KTEG1–Na+ complex, however, the interatomic dis-
tances between oxygen atoms and K+ cation are much longer and
show greater differences.
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Acknowledgement
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688 (2004) 171.
Financial assistance of the Polish Ministry of Science and Higher
Education-Grant No. N204 056 32/1432 is gratefully acknowledged
´
by P. Przybylski. Adam Huczynski wishes to thank the Foundation
[27] R. Pankiewicz, A. Pawlowska, G. Schroeder, P. Przybylski, B. Brzezinski, F. Bartl,
for Polish Science for fellowship.
J. Mol. Struct. 694 (2004) 55.
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