The reaction heats and PM5 semiempirical studies of complexes formed between silicon podand and monovalent cations

Article abstract of DOI:10.1016/j.molstruc.2004.08.021

Silicon podands (1-10) were synthesised and their complexation reaction of Na⁺ cations were studied by calorimetric and PM5 theoretical methods. Both methods provide evidence for formation of the respective complexes with Na⁺ cations

Full text of DOI:10.1016/j.molstruc.2004.08.021

Journal of Molecular Structure 733 (2005) 231–237
www.elsevier.com/locate/molstruc
The reaction heats and PM5 semiempirical studies of complexes
formed between silicon podand and monovalent cations
a
Bogusława Łe˛ska , Piotr Przybylski , Joanna Wyrwał , Bogumił Brzezinski ,
a
a
a,
*
Grzegorz Schroedera, Volodimir Rybachenkob, Angelamaria Maiac
a
´
Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, Poznan 60-780, Poland
bInstitute of Physical Organic and Coal Chemistry, NAS, R. Luxemburg 70, Donetsk 340114, Ukraine
`
CNR-Istituto di Scienze e Tecnologie Molecolari (ISTM) and Dipartimento di Chimica Organica e Industriale dell’Universita,
c
Via C. Golgi 19, Milano I-20133, Italy
Received 14 July 2004; accepted 16 August 2004
Abstract
Silicon podands (1–10) were synthesised and their complexation reaction of NaC cations were studied by calorimetric and PM5
theoretical methods. Both methods provide evidence for formation of the respective complexes with NaC cations of different
stoichiometry. In most cases, only formation of the complexes of 1:1 stoichiometry has been observed. For compounds with longer
oxaalkyl chains (9 and 10) the formation of 1:4 and 1:6 complexes has been found. The structures of the complexes are visualised and
discussed.
q 2004 Elsevier B.V. All rights reserved.
Keywords: Silicon podand; Alkali metal cation complexes; Calorimetric methods; PM5 calculation
1. Introduction
relatively short, i.e. if they included two to four oxygen
atoms.
As a contribution to our earlier studies, we have
synthesised four groups of Si-podands containing various
polyoxaalkyl chains with different terminal alkyl groups.
The complexation process of NaC cations by these esters
was studied using calorimetric titration and PM5 semi-
empirical method.
Various phosphorus, boron, sulphur and silicon inor-
ganic esters with different length of polyoxaethylene
glycols have been synthesised and studied by spectro-
scopic, spectrometric and theoretical methods [1–10].
These inorganic esters make a very interesting class of
compounds, because they can be used for the complexation
of monovalent, divalent and heavy metal cations. For-
mation of very stable complexes by these esters with metal
cations can also be successfully used in Phase Transfer
Catalysis (PTC) [7,11]. Furthermore, many of these esters
are liquids and they could be used as solvents in various
organic reactions [8,9].
2. Experimental
2.1. Synthesis of silicon podands
Earlier studies of silicon podands have shown that they
form mainly complexes of the 1:1 stoichiometry with
monovalent cations, if the polyoxaethylene chains are
New Si-podands were obtained according to the follow-
ing reaction [2]
ðRÞm–SiCl4Km Cð4 ÿ mÞHOðOCH2CH2ÞnR1Š
/ðRÞm–Si½ðOCH2CH2ÞnR1Š4Km Cð4 ÿ mÞHCl
* Corresponding author. Tel.: C48 61 829 1330; fax: C48 61 865 8008.
E-mail address: bbrzez@main.amu.edu.pl (B. Brzezinski).
0022-2860/$ - see front matter q 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2004.08.021

232
B. Łe˛ska et al. / Journal of Molecular Structure 733 (2005) 231–237
where RZ–CH3, –C2H5, –Ph; R1Z–OCH3, –OC12H25,
–OC16H33; and m is the number of alkyl or phenyl groups;
and n is the number of oxaethylene groups.
3. Results and discussion
The formulas of the compounds studied are shown in
Tables 1 and 2. These Si-podands can be formally classified
into four groups. The first group includes two polyoxaethy-
lene chains and it belongs to the so-called dipodand
compounds. The other groups are the so-called tripodands
with not only various polyoxaalkyl chain length but also
with different alkyl terminal groups. The terminal groups in
the studied Si-podands studied are: methyl-CH3 (II group),
dodecyl-C12H25 (III group) and hexadecyl-C16H33 (IV
group).
All glycols and substituted chlorosilanes (Aldrich) were
purified by distillation directly before use.
A stoichiometric amount of anhydrous polychlorosilanes
with methyl, ethyl or phenyl chlorosilane (R)m–SiCl4Km
was dropwise added into respective polyoxaethylene glycol.
This solution was intensely stirred and heated for 4-8 h
under reflux until total hydrogen chloride elimination from
the reaction mixture. The purity of the obtained compounds
was analyzed by elementary analysis, whose results are
given in Table 1.
The heats of complexation reaction between Si-podands
and NaC were determined by calorimetric titrations. The
two types of the relationships observed between the
measured enthalpy (Q) and CNaClO4/CL (where CNaClO4 is
the concentration of NaClO4 and CL is the concentration of
the Si-podand) are shown in Fig. 1a and b.
2.2. Calorimetric measurements
The reaction heats were determined by the titration of Si-
podands with NaClO4 in acetonitrile following the pro-
cedure given in Refs. [12,13].
The relationship shown in Fig. 1a is always observed
for the formation of the complexes of 1:1 stoichiometry.
This type of the titration curve was observed for 1, 2, 4
and 5 compounds and can be explained by the limited
number of oxygen atoms in the oxaalkyl chains.
Fig. 1b shows the other type of the calorimetric titration
curve observed for the complexation reaction of NaC
cations by the others compounds, i.e. for 3 and 6–10
ones. The stoichiometry of these complexes depends on
2.3. Theoretical calculations
PM5 semiempirical calculations were performed using
the WinMopac 2003 program [14]. In all cases full
geometry optimisation of podand and its complexes was
carried out without any symmetry constraints [15,16].
Table 1
Elementary analysis of compounds 1–10
Number of compound
Compound (Si-ligand)
Elementary analysis
%C (calculated)
%H (calculated)
%C (determined)
%H (determined)
1
2
Me2Si(OCH2CH2OCH3)2
46.31
50.00
52.41
46.79
50.54
52.61
65.26
66.67
62.85
58.42
9.61
9.37
46.32
49.99
52.33
46.80
50.59
52.43
65.30
66.70
62.88
58.41
9.61
9.39
Me2Si[(OCH2CH2)3OCH3)]2
Me2Si[(OCH2CH2)8OCH3)]2
EtSi(OCH2CH2OCH3)3
3
9.28
9.17
4
9.22
9.23
5
EtSi[(OCH2CH2)3OCH3)]3
EtSi[(OCH2CH2)8OCH3)]3
EtSi[(OCH2CH2)4OC12H25)]3
PhSi[(OCH2CH2)4OC12H25)]3
EtSi[(OCH2CH2)10OC16H33)]3
EtSi[(OCH2CH2)20OC16H33)]3
9.16
9.14
6
9.71
9.67
7
11.23
10.77
10.67
9.85
11.27
10.82
10.86
9.88
8
9
10
Table 2
The experimental heat of the complexation reaction between Si-podands and NaC cations in acetonitrile and the number (x) of complexed cations
Number of compound
Compound (Si-ligand)
Number (x) of complexed
NaC cations
KDH (kJ molK1) of the complexation reaction
1:1 complex
1:x complex
1
2
Me2Si(OCH2CH2OCH3)2
1
8G1
9G1
Me2Si[(OCH2CH2)3OCH3)]2
Me2Si[(OCH2CH2)8OCH3)]2
EtSi(OCH2CH2OCH3)3
1
3
2–3
1
8G2
9G2
19G1
4
5
EtSi[(OCH2CH2)3OCH3)]3
EtSi[(OCH2CH2)8OCH3)]3
EtSi[(OCH2CH2)4OC12H25)]3
PhSi[(OCH2CH2)4OC12H25)]3
EtSi[(OCH2CH2)10OC16H33)]3
EtSi[(OCH2CH2)20OC16H33)]3
1
10G2
11G2
15G1
16G2
20G2
20G2
6
2–3
2
26G2
32G2
35G2
84G2
125G2
7
8
2
9
10
4
6

B. Łe˛ska et al. / Journal of Molecular Structure 733 (2005) 231–237
233
Fig. 1. The curves of heats of complexation reaction between Si-podands and NaC determined by calorimetric titrations. Q, enthalpy (kJ molK1); CNaClO4/CL
(where CNaClO4 is the concentration of NaClO4 and CL is the concentration of the Si-podand).
Table 3
The heat of formation (HOF) values (kcal/mol) of various Si-podands complexes with sodium cations
Compound
Mixture
HOF (PM5) (kcal/mol)
DHOF (kcal/mol)
The favourable complex
Me2Si(OCH2CH2OCH3)2 (1)
1
K236.33
K94.36
K263.95
C65.08
C94.89
–
1CNaC
1CNaC
(uncomplexed)
(complexed)
K169.59
1:1
1C2NaC
1C2NaC
(uncomplexed)
(complexed)
C29.81
–
Me2Si[(OCH2CH2)3OCH3]2 (2)
Me2Si[(OCH2CH2)8OCH3]2 (3)
2
K381.61
K239.54
K431.41
K84.19
K52.17
2CNaC
(uncomplexed)
(complexed)
K191.87
2CNaC
1:1
1:2
1:1
1:1
2C2NaC
(uncomplexed)
(complexed)
C32.02
–
2C2NaC
3
K758.48
K616.49
K776.57
K449.32
K608.18
K284.59
K241.19
3CNaC
(uncomplexed)
(complexed)
K160.08
3CNaC
3C2NaC
3C2NaC
3C3NaC
3C3NaC
(uncomplexed)
(complexed)
(uncomplexed)
(complexed)
K158.86
C43.40
–
EtSi(OCH2CH2OCH3)3 (4)
EtSi[(OCH2CH2)3OCH3]3 (5)
4
K336.63
K194.47
K397.82
K13.98
K10.03
4CNaC
(uncomplexed)
(complexed)
K203.33
4CNaC
4C2NaC
4C2NaC
(uncomplexed)
(complexed)
C3.95
–
5
K581.33
K539.32
K597.73
K371.43
K363.25
K203.36
K199.63
5CNaC
(uncomplexed)
(complexed)
K58.41
5CNaC
5C2NaC
5C2NaC
5C3NaC
5C3NaC
(uncomplexed)
(complexed)
(uncomplexed)
(complexed)
K8.18
C3.73
–
EtSi[(OCH2CH2)8OCH3]3 (6)
6
K1012.36
K870.23
K1046.14
K712.75
K1130.19
K548.24
K622.65
K379.73
K312.49
6CNaC
(uncomplexed)
(complexed)
K175.91
6CNaC
6C2NaC
6C2NaC
6C3NaC
6C3NaC
6C4NaC
6C4NaC
(uncomplexed)
(complexed)
(uncomplexed)
(complexed)
(uncomplexed)
(complexed)
K417.44
K74.41
1:2
C62.24
–
EtSi53Brij12 (7)
7
K908.73
K801.04
K945.23
K549.58
K967.29
K382.47
K373.21
7: NaC
(uncomplexed)
(complexed)
K144.19
7: NaC
7: 2NaC
7: 2NaC
7: 3NaC
7: 3NaC
(uncomplexed)
(complexed)
(uncomplexed)
(complexed)
1:2
K417.71
C9.26
(continued on next page)

234
B. Łe˛ska et al. / Journal of Molecular Structure 733 (2005) 231–237
Table 3 (continued)
Compound
Mixture
HOF (PM5) (kcal/mol)
DHOF (kcal/mol)
The favourable complex
PhSi53Brij12 (8)
8
K896.21
K795.32
K931.74
K536.13
K942.86
K350.11
K341.29
–
8: NaC
8: NaC
(uncomplexed)
K136.42
(complexed)
8: 2NaC
8: 2NaC
8: 3NaC
8: 3NaC
(uncomplexed)
(complexed)
(uncomplexed)
(complexed)
1:2
K406.73
C8.82
EtSi113Brij16 (9)
9
K1594.49
K1522.09
K1684.61
K1454.08
K1771.03
K1493.47
K1889.12
K1347.93
K2078.45
K1182.47
K998.31
–
9: NaC
(uncomplexed)
K162.52
9: NaC
(complexed)
9: 2NaC
9: 2NaC
9: 3NaC
9: 3NaC
9: 4NaC
9: 4NaC
9: 5NaC
9: 5NaC
(uncomplexed)
(complexed)
(uncomplexed)
(complexed)
(uncomplexed)
(complexed)
(uncomplexed)
(complexed)
K316.95
K395.65
K730.52
1:4
C184.16
–
EtSi213Brij16 (10)
10
10: NaC
10: NaC
K3221.12
K3131.72
K3314.19
K3073.09
K3375.21
K2930.11
K3419.43
K2861.39
K3563.28
K2761.78
K3898.36
K2607.66
K4074.03
K2447.82
K3912.63
K2281.87
K1938.92
(uncomplexed)
K182.47
(complexed)
10: 2NaC
10: 2NaC
10: 3NaC
10: 3NaC
10: 4NaC
10: 4NaC
10: 5NaC
10: 5NaC
10: 6NaC
10: 6NaC
10: 7NaC
10: 7NaC
10: 8NaC
10: 8NaC
(uncomplexed)
(complexed)
(uncomplexed)
(complexed)
(uncomplexed)
(complexed)
(uncomplexed)
(complexed)
(uncomplexed)
(complexed)
(uncomplexed)
(complexed)
(uncomplexed)
(complexed)
K302.12
K489.32
K701.89
K1136.58
K1666.37
K1464.81
C342.95
1:6
DHOFZHOFcomplexedKHOFuncomplexed
.
the number of oxygen atoms in the oxaalkyl chains. This
behaviour of this titration curve indicates existence of a
complex equilibrium, which can be described by the
following reactions
NaC CL%NaLC CQ1
NaLC CNaC%Na2L2C CQ2
Na2L2C CNaC%Na3L3C CQ3
etc.
NaðxK1Þ
L
ðxK1ÞC CNaC%NaxLxC CQx
where L, Si-podand and x, number of complexed NaC
cations (given in Table 2).
The DH values of the complexation reaction between
compounds 1–10 and NaC cations are summarized in
Table 2. The DH values of the 1:1 complexes are in
the range of 8–20 kJ molK1 and they are slightly dependent
on the number of the oxygen atoms in the oxaalkyl chains.
Scheme 1. Complex structure of Me2Si[(OCH2CH2)3OCH3]2 with NaC
cation calculated by PM5 method.

B. Łe˛ska et al. / Journal of Molecular Structure 733 (2005) 231–237
235
Scheme 2. Complex structure of PhSi53Brij12 with 2NaC cations calculated by PM5 method.
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
NaC cations. Due to these interactions the NaC cations can
perform fast fluctuations and show very large cation
polarizability. Such fast fluctuations of various monovalent
cations between oxygen atoms in oxaalkyl chains were
reported in our earlier papers [17]. Furthermore, the
Scheme 3. Complex structure of EtSi113Brij16 with 4NaC cations calculated by PM5 method.

236
B. Łe˛ska et al. / Journal of Molecular Structure 733 (2005) 231–237
Scheme 4. Complex structure of EtSi213Brij16 with 6NaC cations calculated by PM5 method.
reorganisation of the micelle structures during the com-
plexation 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 complexes (Table 3) show no dependence
on the oxaalkyl chain length.
The experimental DH values of the complex formation of
another stoichiometries than 1:1 show an energetic additive
effect with increasing number of the NaC cations involved
in complexation.
The PM5 semiempirical calculated HOF values for
uncomplexed and complexed species and the differences
Scheme 5. Complex structure of EtSi213Brij16 with 7NaC cations calculated by PM5 method.

B. Łe˛ska et al. / Journal of Molecular Structure 733 (2005) 231–237
237
´
[3] B. Brzezinski, B. Roz˙alski, G. Schroeder, F. Bartl, G. Zundel,
between them are presented in Table 3. These values are
very well comparable with the experimental DH data as well
as the number of complexed NaC cations. The visualisation
of the representative structures of the 1:1, 1:2, 1:4 and 1:6
complexes are shown in Schemes 1–4. These structures
indicate that the first NaC cation is always complexed by the
oxygen atoms neighbouring to the silicon atom and every
other cation is localised with the maximal distance between
them.
J. Chem. Soc., Faraday Trans. 94 (1998) 2093.
[4] B. Gierczyk, G. Schroeder, G. Wojciechowski, B. Rozalski,
B. Brzezinski, G. Zundel, PCCP 1 (1999) 4897.
´
[5] B. Brzezinski, B. Gierczyk, B. Roz˙alski, G. Wojciechowski,
G. Schroeder, G. Zundel, J. Mol. Struct. 519 (2000) 119.
[6] B. Gierczyk, G. Schroeder, B. Nowak-Wydra, G. Wojciechowski,
B. Brzezinski, J. Phys. Chem. B 102 (1998) 5234.
[7] A. Maia, D. Landini, B. Łe˛ska, G. Schroeder, Tettrahedron Lett. 44
(2003) 4149.
[8] B. Gierczyk, B. Łe˛ska, B. Brzezinski, G. Schoreder, Supramol. Chem.
14 (2002) 497.
In the case of compound 10 preferential stoichiometry of
the complex with NaC cations is 1:6. The DHOF value for
[9] B. Łe˛ska, I. Kałuz˙na, B. Gierczyk, G. Schroeder, P. Przybylski,
B. Brzezinski, J. Mol. Struct. 643 (2002) 9.
the formation of this complex is about K1666 kcal molK1
.
[10] G. Schroeder, B. Gierczyk, B. Łe˛ska, G. Wojciechowski,
R. Pankiewicz, B. Brzezinski, F. Bartl, J. Mol. Struct. 607 (2002) 8.
[11] A. Maia, D. Landini, B. Łe˛ska, G. Schroeder, Tetrahedron 44 (2004)
10111.
The calculated DHOF value for the complex of 1:7
stoichiometry indicates the possibility of a formation of
such type of complex. The structure of this complex is
shown in Scheme 5.
˙
[12] V.I. Rybachenko, G. Schroeder, E.B. Titow, Z. Fiz. Chem. 66 (1996)
1007.
˙
[13] V.I. Rybachenko, E.B. Titow, Z. Fiz. Chem. 77 (1997) 248.
References
[14] J.J.P. Stewart, Method J. Comp. Chem. 10 (1989) 209.
[15] J.J.P. Stewart, J. Comp. Chem. 12 (1991) 320.
[16] CAChe 5.04 UserGuide, Fujitsu, 2003.
[17] B. Brzezinski, G. Schroeder, A. Rabold, G. Zundel, J. Phys. Chem. 99
(1995) 8519.
[1] G. Schroeder, B. Gierczyk, B. Łe˛ska, J. Incl. Phenom. 35 (1999) 327.
[2] B. Łe˛ska, B. Gierczyk, K. Eitner, V.I. Rybachenko, G. Schroeder,
Supramol. Chem. 2004; (in press).