B-podand complexes with sodium ions: the reaction heats and PM5 semiempirical calculation

Article abstract of DOI:10.1016/j.molstruc.2006.10.050

The complexation reactions of two types of tris(oxaalkyl) borates (B-podands with CH₃ or C₁₆H₃₃ terminal groups) with Na⁺ cations have been studied by calorimetric and PM5 theoretical methods. Both methods provi

Full text of DOI:10.1016/j.molstruc.2006.10.050

Journal of Molecular Structure 840 (2007) 1–5
www.elsevier.com/locate/molstruc
B-podand complexes with sodium ions: the reaction heats
and PM5 semiempirical calculation
a
a
b
Bogusława Łe˛ska , Radosław Pankiewicz , Oksana Nevecheriya ,
b
a
a,
*
Volodimir I. Rybachenko , Grzegorz Schroeder , Bogumił Brzezinski
a
Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, PL-60 780 Poznan´, Poland
Institute of Physical Organic and Coal Chemistry, National Academy of Science, R. Luxemburg 70, Donetsk, Ukraine
b
Received 2 October 2006; accepted 23 October 2006
Available online 20 December 2006
Abstract
The complexation reactions of two types of tris(oxaalkyl) borates (B-podands with CH3 or C16H33 terminal groups) with Na+ cations
have been studied by calorimetric and PM5 theoretical methods. Both methods provide evidence for formation of the respective com-
plexes with Na+ cations of different stoichiometry. For compounds with short oxaalkyl chains the formation of 1:1 complexes and for
compounds with longer oxaalkyl chains the formation of 1:x (x > 1) complexes has been found. The stoichiometry of the complexes esti-
mated from the HOF values of the complexes is in well agreement with the calorimetric results. The structures of the complexes are vis-
ualised using semiempirical PM5 method.
Ó 2007 Published by Elsevier B.V.
Keywords: Tris(oxaalkyl) borates; Calorimetric titration; Reaction heat; Alkali metal cation complexes; Calorimetric methods; PM5 calculation
1. Introduction
of the structure of them with different stoichiometry. The
influence of alkyl terminal groups in B-podands on the
complexation process is also discussed.
The complexation of cations by tris(oxaalkyl) borates
has been studied by FTIR and NMR methods [1–4]. In
the case of the B-podands complexes with respective H+,
Li+, Na+ and K+ cations, the cation polarizability is
observed due to fast fluctuations of these cations. The pro-
ton and cation polarizabilities are indicated in the infrared
spectra by a continuous absorption in the MIR and FAR
regions, respectively [1]. Recently, we studied boron pod-
ands as strong complexing agents of alkali metal cations
and catalysts in typical anion promoted reactions under
solid–liquid conditions [5].
2. Experimental
Tris(oxaalkyl) borates of two types, i.e., that terminated
with a methyl group (1–7) and the other one terminated
with a hexadecane group (8–14), were obtained in the
reactions of boric(III) acid with the anhydrous HO–
[CH2–CH2–O]n–R alcohols (where n = 1, 2, 3, 10, 12 or
16, and R = CH3 or C16H33) by the general method
described previously [5].
In this paper, the formation of tris(oxaalkyl) borate
complexes with Na+ cations is studied by calorimetric
titration and using semiempirical method for visualisation
2.1. Calorimetric measurements
The reaction heats were determined following the
description in Refs. [6,7] by the titration of the borates
(0.02 mol dmꢀ3) using NaClO4 (0.003 mol dmꢀ3) both
dissolved in acetonitrile.
*
Corresponding author. Tel.: +4861 829 1330; fax: +4861 8658008.
E-mail address: bbrzez@main.amu.edu.pl (B. Brzezinski).
0022-2860/$ - see front matter Ó 2007 Published by Elsevier B.V.
doi:10.1016/j.molstruc.2006.10.050

2
B. Łe˛ska et al. / Journal of Molecular Structure 840 (2007) 1–5
2.2. Theoretical calculations
types of relationships. One type of the dependence was
always observed for the formation of the complexes of
1:1 stoichiometry and can be explained by the limited num-
ber of oxygen atoms in the oxaalkyl chains (compounds
B2.3, B3.3, B2.3H and B3.3H). The calorimetric titration
curve of the second type was observed for the complexation
reaction of Na+ cations by the other compounds having
more than two or three oxygen atoms in the oxaalkyl
chains. The stoichiometry of these complexes depended
on the number of oxygen atoms in these chains. This
behaviour of the titration curve of the second type indicates
the existence of a complex equilibrium, which can be
described by the following reactions:
PM5 semiempirical calculations were performed using
the WinMopac 2002 program [8]. In all cases, full geometry
optimization of podand and its complexes was carried out
without any symmetry constraints [9,10].
3. Results and discussion
The structures of the B-podands studied are shown in
Table 1.
The heats of complexation reaction between B-podands
and Na+ cations were determined by calorimetric titra-
tions. The resulting dependencies between the measured
enthalpy (Q) and CNaClO /CL (where CNaClO is the concen-
4
4
tration of NaClO4 and CL is the concentration of the
B-podand) always represented one of the two possible
Table 3
The heat of formation (HOF) of B-podands (ꢀOCH3 ended) and their
energetically favourable complexes with Na+ cations
Table 1
The compounds studied
No. of
Compound Mixture
HOF
[kJ molꢀ1
DHOF
compound
]
[kJ molꢀ1
]
No. of compound
Short name
Compound (B-ligand)
1
2
3
B2.3
B3.3
B4.3
B2.3
ꢀ1402.16
ꢀ807.77
B2:3 : NaþðuncomplexedÞ
ꢀ281.51
ꢀ326.81
1
2
B2.3
B3.3
B(OCH2CH2OCH3)3
B[(OCH2CH2)2OCH3)]3
B[(OCH2CH2)3OCH3)]3
B[(OCH2CH2)8OCH3)]3
B[(OCH2CH2)10OCH3)]3
B[(OCH2CH2)12OCH3)]3
B[(OCH2CH2)16OCH3)]3
B2:3 : NaþðcomplexedÞ
ꢀ1089.28
3
B4.3
B9.3
4
B3.3
ꢀ1928.37
5
B11.3
B13.3
B17.3
B2.3H
B3.3H
B4.3H
B9.3H
B11.3H
B13.3H
B17.3H
B3:3 : NaþðuncomplexedÞ
ꢀ1333.98
B3:3 : NaþðcomplexedÞ
ꢀ1660.79
6
7
B4.3
ꢀ2463.15
8
B(OCH2CH2OC16H33)3
B4:3 : NaþðuncomplexedÞ
ꢀ1868.76
ꢀ314.85
ꢀ87.41
9
B[(OCH2CH2)2OC16H33)]3
B[(OCH2CH2)3OC16H33)]3
B[(OCH2CH2)8OC16H33)]3
B[(OCH2CH2)10OC16H33)]3
B[(OCH2CH2)12OC16H33)]3
B[(OCH2CH2)16OC16H33)]3
B4:3 : NaþðcomplexedÞ
B4:3 : 2NaþðuncomplexedÞ
B4:3 : 2NaþðcomplexedÞ
ꢀ2183.61
ꢀ1274.37
ꢀ1361.78
10
11
12
13
14
4
B9.3
B9.3
ꢀ4987.33
B9:3 : NaþðuncomplexedÞ
ꢀ4392.94
ꢀ323.57
ꢀ585.69
ꢀ943.35
ꢀ472.27
B9:3 : NaþðcomplexedÞ
B9:3 : 2NaþðuncomplexedÞ
B9:3 : 2NaþðcomplexedÞ
B9:3 : 3NaþðuncomplexedÞ
B9:3 : 3NaþðcomplexedÞ
B9:3 : 4NaþðuncomplexedÞ
B9:3 : 4NaþðcomplexedÞ
ꢀ4716.51
ꢀ3798.55
ꢀ4384.24
ꢀ3204.16
ꢀ4147.51
ꢀ2609.77
ꢀ3082.04
Table 2
The experimental heat of the complexation reaction between B-podands
and Na+ cations in acetonitrile and the number (x) of complexed cations
No. of
Compound
Number (x) of
complexed Na+
cations
-DH (kJ molꢀ1) of
the complexation
reaction
compound (B-podand)
7
B17.3
B17.3
ꢀ9097.34
B17:3 : NaþðuncomplexedÞ
ꢀ8502.94
ꢀ327.05
ꢀ582.90
ꢀ853.44
1:1
1:x
complex complex
B17:3 : NaþðcomplexedÞ
ꢀ8829.99
1
2
B2.3
B3.3
1
1
1–2
3
3–4
4
5
1
1
1–2
3
25
26
27
29
30
32
39
18
19
20
26
26
29
33
1
1
1
1
1
1
1
1
1
2
4
4
4
3
–
–
B17:3 : 2NaþðuncomplexedÞ ꢀ7908.54
B17:3 : 2NaþðcomplexedÞ
ꢀ8491.44
3
B4.3
B9.3
42
85
4
5
6
8
4
B17:3 : 3NaþðuncomplexedÞ ꢀ7314.14
B17:3 : 3NaþðcomplexedÞ
ꢀ8167.58
5
B11.3
B13.3
B17.3
B2.3H
B3.3H
B4.3H
B9.3H
B11.3H
B13.3H
B17.3H
109
135
196 10
–
–
6
B17:3 : 4NaþðuncomplexedÞ ꢀ6719.74 ꢀ1087.62
7
B17:3 : 4NaþðcomplexedÞ
ꢀ7807.36
8
B17:3 : 5NaþðuncomplexedÞ ꢀ6125.34 ꢀ1308.12
9
10
11
12
13
14
31
75
80
1
7
7
8
7
B17:3 : 5NaþðcomplexedÞ
B17:3 : 6Naþðuncomplexed
ꢀ7433.46
ꢀ5530.94
ꢀ6493.43
Þ
ꢀ962.49
3–4
4
5
B17:3 : 6Naþðcomplexed
Þ
119
163
DHOF = HOF(complexed) ꢀ HOF(uncomplexed)
.

B. Łe˛ska et al. / Journal of Molecular Structure 840 (2007) 1–5
3
The DH values of the complexation reaction between
compounds 1–14 and Na+ cations are summarized in
Table 2. The DH values of the 1:1 complexes are in
the range of 18–39 [kJ molꢀ1] and they are clearly depen-
dent on the number of the oxygen atoms in the oxaalkyl
chains. This effect could be explained by the energetic
profit produced by the involvement of increasing
numbers of oxygen atoms in the polyoxaalkyl chains
interacting with Na+ cations. Due to these interactions
the Na+ cations can perform fast fluctuations and show
very large cation polarizability. Such fast fluctuations of
various monovalent cations between the oxygen atoms
in oxaalkyl chains were reported in our earlier papers
[11–16]. Furthermore, the reorganisation of the micelle
Na+ + L
NaL+ + Na+
Na2L2++ Na+
NaL+ + Q1
Na2L2+ + Q2
Na3L3++ Q3
etc.
_______________________________________
Na(x-1)L(x-1)++ Na+ NaxLx++ Qx
where, L – B-podand and x – number of complexed Na+
cations (given in Table 2).
Table 4
The heat of formation (HOF) of B-podands (OC16H33 ended) and their energetically favourable complexes with Na+ cations
No. of compound
Compound
B2.3H
Mixture
HOF [kJ molꢀ1
]
DHOF [kJ molꢀ1
]
8
B2.3H
ꢀ2459.28
ꢀ1864.89
ꢀ2108.70
B2:3H : NaþðuncomplexedÞ
ꢀ243.81
B2:3H : NaþðcomplexedÞ
9
B3.3H
B4.3H
B3.3H
ꢀ2969.91
ꢀ2375.52
B3:3H : NaþðuncomplexedÞ
ꢀ332.38
B3:3H : NaþðcomplexedÞ
ꢀ2707.90
10
B4.3H
ꢀ3486.08
ꢀ2891.69
ꢀ3165.16
ꢀ2891.69
ꢀ2961.65
B4:3H : NaþðuncomplexedÞ
ꢀ273.47
ꢀ69.96
B4:3H : NaþðcomplexedÞ
B4:3H : 2NaþðuncomplexedÞ
B4:3H : 2NaþðcomplexedÞ
11
B9.3H
B9.3H
B9:3H : NaþðuncomplexedÞ
ꢀ6076.84
ꢀ5482.45
ꢀ326.40
ꢀ574.09
ꢀ901.41
ꢀ434.51
B9:3H : NaþðcomplexedÞ
B9:3H : 2NaþðuncomplexedÞ
B9:3H : 2NaþðcomplexedÞ
B9:3H : 3NaþðuncomplexedÞ
B9:3H : 3NaþðcomplexedÞ
B9:3H : 4NaþðuncomplexedÞ
B9:3H : 4NaþðcomplexedÞ
ꢀ5808.85
ꢀ4888.06
ꢀ5462.15
ꢀ4293.67
ꢀ5195.08
ꢀ3699.28
ꢀ4133.79
14
B17.3H
B17.3H
B17:3H : NaþðuncomplexedÞ
ꢀ10211.71
ꢀ9617.31
ꢀ334.10
ꢀ611.65
ꢀ869.47
ꢀ997.44
ꢀ1295.80
ꢀ949.42
B17:3H : NaþðcomplexedÞ
B17:3H : 2NaþðuncomplexedÞ
B17:3H : 2NaþðcomplexedÞ
B17:3H : 3NaþðuncomplexedÞ
B17:3H : 3NaþðcomplexedÞ
B17:3H : 4NaþðuncomplexedÞ
B17:3H : 4NaþðcomplexedÞ
B17:3H : 5NaþðuncomplexedÞ
B17:3H : 5NaþðcomplexedÞ
B17:3H : 6NaþðuncomplexedÞ
B17:3H : 6NaþðcomplexedÞ
ꢀ9951.41
ꢀ9022.91
ꢀ9634.56
ꢀ8428.51
ꢀ9297.98
ꢀ7834.11
ꢀ8831.55
ꢀ7239.71
ꢀ8535.51
ꢀ6645.31
ꢀ7594.73
DHOF = HOF(complexed) ꢀ HOF(uncomplexed)
.

4
B. Łe˛ska et al. / Journal of Molecular Structure 840 (2007) 1–5
Fig. 1. Calculated structure of 1:1 complex of B3.3 and B3.3H with Na+ cations.
Fig. 2. Calculated structure of 1:2 complex of B7.3 and B7.3H with Na+ cations.
structures during the complexation process can play an
important role. These effects cannot be taken into
account in the semiempirical calculations, therefore, the
calculated heats of formation (HOF) of the 1:1 complex-
es (Tables 3 and 4) show no dependence on the oxaalkyl
chain length.

B. Łe˛ska et al. / Journal of Molecular Structure 840 (2007) 1–5
5
Fig. 3. Calculated structure of 1:5 complex of B17.3 and B17.3H with Na+ cations.
The experimental DH values of formation of complexes
of other than 1:1 stoichiometry show an energetic additive
effect with increasing number of the Na+ cations involved
in the respective complexes.
years 2006–2007. R. Pankiewicz thank the Foundation
for Polish Science for the fellowship.
References
The HOF values calculated by the PM5 semiempirical
method for uncomplexed and complexed species and the
differences between them are presented in Tables 3 and 4.
The calculated DHOF values are consistent with the exper-
imental DH data as well as the number of complexed Na+
cations. The representative structures of the 1:1, 1:2 and 1:5
complexes are visualised in Figs. 1–3. These structures indi-
cate that the first Na+ cation is always complexed by the
oxygen atoms neighbouring the B atom and every other
cation is localised with the maximal distance between them.
If the complexes of the highest stoichiometry are formed,
the packing of the Na+ cation in the oxaalkyl chains is also
maximal.
´ _
[1] B. Gierczyk, G. Schroeder, G. Wojciechowski, B. Rozalski, B.
Brzezinski, G. Zundel, PCCP 1 (1999) 4897.
[2] B. Gierczyk, G. Schroeder, B. Nowak-Wydra, G. Wojciechowski, B.
Brzezinski, J. Mol. Struct. 513 (1999) 149.
[3] B. Gierczyk, G. Schroeder, G. Wojciechowski, B. Łe˛ska, V.I.
Rybachenko, B. Brzezinski, J. Mol. Struct. 516 (2000) 153.
[4] B. Brzezinski, B. Gierczyk, B. Ro´z_alski, G. Wojciechowski, G.
Schroeder, G. Zundel, J. Mol. Struct. 519 (2000) 119.
[5] B. Łe˛ska, R. Pankiewicz, G. Schroeder, A. Maia, Tetrahedron Lett.
47 (2006) 5673.
[6] V.I. Rybachenko, G. Schroeder, E.B. Titow, Zhurnal Ob. Chem. 66
(1996) 1007.
[7] V.I. Rybachenko, E.B. Titow, Zhurnal Fiz. Chem. 77 (1997) 248.
[8] J.J.P. Stewart, J. Comp. Chem. 10 (1989) 209.
[9] J.J.P. Stewart, J. Comp. Chem. 12 (1991) 320.
[10] CAChe 5.04 UserGuide, Fujitsu 2003.
A comparison of the experimental DH data and the
respective calculated HOF values has demonstrated that
with increasing length of the alkyl chain (–C16H33), the
complexation ability of the corresponding boron podands
slightly decreases.
[11] B. Brzezinski, G. Schroeder, A. Rabold, G. Zundel, J. Phys. Chem. 99
(1995) 8519.
[12] M. Bełtowska-Brzezinska, T. Łuczak, B. Gierczyk, K. Eitner, B.
Brzezinski, R. Pankiewicz, G. Schroeder, J. Mol. Struct. 607 (2002)
77.
Acknowledgements
[13] B. Łe˛ska, P. Przybylski, J. Wyrwał, B. Brzezinski, G. Schroeder, V.
Rybachenko, A. Maia, J. Mol. Struct. 733 (2005) 231.
[14] J. Kira, B. Łe˛ska, G. Schroeder, P. Przybylski, B. Brzezinski, J. Mol.
Struct. 738 (2005) 227.
[15] B. Łe˛ska, P. Przybylski, J. Wyrwał, B. Brzezinski, G. Schroeder, V.
Rybachenko, J. Mol. Struct. 741 (2005) 11.
The authors thank the Polish Ministry of Science and
Higher Education for financial support under Grant No.
R015 016 01 in the years 2006–2008. B. Łe˛ska thanks the
Polish Ministry of Science and Higher Education for finan-
cial support under Grant No. N204 109 31/2553 in the
[16] J. Kira, B. Łe˛ska, O. Nevecheriya, G. Schroeder, P. Przybylski, B.
Brzezinski, J. Mol. Struct. 749 (2005) 122.