Kinetic studies of complexation reaction of polyoxaalkyl phosphates with Fe(III) in ethanol

Article abstract of DOI:10.1016/S0022-2860(02)00164-3

Complexation reactions of the Fe(III) cation by seven oxaalkyl phosphate esters and ethyl phosphate in ethanol were studied by kinetic methods, as well as ³¹p NMR and semi-empirical methods. The ΔG^≠ values for almost all phosphates were in the range of 53-56 kJ mol^-1. The greatest differences were observed for the ΔS^≠ values of the systems studied, whereas the enthalpies of activation ΔH^≠ were compensated by the entropy of activation. The structures of the complexes formed between the Fe(III) cation and the oxaalkyl phosphate esters and the mechanisms of these reactions are discussed.

Full text of DOI:10.1016/S0022-2860(02)00164-3

Journal of Molecular Structure 643 (2002) 9–19
www.elsevier.com/locate/molstruc
Kinetic studies of complexation reaction of polyoxaalkyl
phosphates with Fe(III) in ethanol
˙
˙
Bogusława Łe˛ska, Iwona Kałuzna, Błazej Gierczyk, Grzegorz Schroeder,
*
Piotr Przybylski, Bogumił Brzezinski
Faculty of Chemistry, Adam Mickiewicz University, ul Grunwaldzka 6, 60-780 Poznan, Poland
Received 8 March 2002; accepted 2 April 2002
Abstract
Complexation reactions of the Fe(III) cation by seven oxaalkyl phosphate esters and ethyl phosphate in ethanol were studied
by kinetic methods, as well as 31P NMR and semi-empirical methods. The DG– values for almost all phosphates were in the
range of 53–56 kJ mol21. The greatest differences were observed for the DS– values of the systems studied, whereas the
enthalpies of activation DH– were compensated by the entropy of activation. The structures of the complexes formed between
the Fe(III) cation and the oxaalkyl phosphate esters and the mechanisms of these reactions are discussed. q 2002 Elsevier
Science B.V. All rights reserved.
Keywords: Kinetics; Complexation; Iron(III); Podandes; Phosphates; 31P NMR; 17O NMR; Semiempirical calculation
1. Introduction
cation potential along the O-atoms in the channels
formed by the polyoxaalkyl chains, whereas the size
of the cation and the length of the polyoxaalkyl
ligands influence the properties of these complexes.
Due to the fast fluctuations of the cations, the proton
and cation polarisabilities, the so-called Zundel’s
polarisabilities [16–19], appeared and were mani-
fested in the infrared spectra by a continuous
absorption in MIR and FIR regions. In the case of
complexes with CoCl2, NiCl2 and CuCl2 the respect-
ive cations are coordinated by oxygen atoms of three
polyoxaalkyl chains and also by one chlorine atom.
The Fe(II) and Fe(III) cations and their complexes
are interesting because of their important role in
biological systems. The recent interest in iron
complexes derives from the importance of such
compounds in controlled solubilisation, transport
and release of iron by various organism [20]. Iron(III)
The formation of complexes between the crown
ethers or cryptands (macrocyclic and macrobicyclic
ligands) and protons or the monovalent cations is
discussed in detail in Refs. [1–4]. Particularly
interesting are the open-chained, polyoxaalkyl ligands
complexating with a variety of organic and metallic
cations (mostly of I and II group) [5–9]. In our
previous papers, the behaviour of such ligands
complexed by protons and various metal cations was
studied by spectroscopic methods [10–15]. We have
demonstrated that proton and monovalent metal
cations undergo fast fluctuations in a multiminima
*
Corresponding author. Tel.: þ48-61-8291330; fax: þ48-61-
865-8008.
E-mail address: bbrzez@main.amu.edu.pl (B. Brzezinski).
0022-2860/02/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-2860(02)00164-3

10
B.ł. Łe˛ska et al. / Journal of Molecular Structure 643 (2002) 9–19
chloride and other simple salts react with a range of
organic ligands, such as alcohols, ethers, aldehydes,
ketones, amides, sulphoxides, phosphine oxides, etc.
The structures of many of these complexes are
unknown, some appear to be simple addition com-
pounds, while they have salt structures [21]. The
complexes of FeCl3 with alcohols ROH (R ¼ Me, Et,
etc.) have been isolated from solutions of FeCl3 in
benzene containing the appropriate alcohol [22]. The
anhydrous binary FeCl3 has nearly regular octahedral
coordination, but the hexahydrate of FeCl3 has a trans
octahedral arrangement [Fe(H2O)4Cl2)Cl·2H2O and
exhibits pronounced quadrupole splitting [23,24].
With Ph3PO, Ph3AsO and analogous ligands, the
complexes of the stoichiometry as in FeL4(ClO4)3 and
FeL2Cl3 are common [25,26].
were synthesised by mixing respective anhydrous
glycolmonomethyl ether (0.1 mol) and phosphorus
trichloride (0.33 mol) in 250 cm3 benzene at tem-
perature 0 8C during 3 h. After this time, the mixture
was heated under reflux for 2 h. The solvent was
evaporated under reduced pressure. The obtained
product OPH2.2 ðyield ¼ 85%Þ was distilled under
reduced pressure bp ¼ 130–132 8C=0:1 mmHg:
OPH2.3 was purified by the chromatographic method
(SiO2–ethyl acetate). Yield ¼ 80%:
Tetrakis(oxaalkyl) pyrophosphates [(R3O)2PO–
O–PO(OR3)2 and (R7O)2OP–O–PO(OR7)2] were
obtained by dropping to the mixture of pyrophos-
phoric tetrachloride (0.1 mol) in xylene the corre-
sponding glycolmonomethyl ether (0.4 mol) in
50 cm3 xylene. The mixture was stirred all time.
Afterwards the mixture was heated to temperature
80 8C for 3 h. Xylene was evaporated under reduced
pressure and the residue was purified by the
chromatographic method (SiO2 –ethyl acetate).
Yield ¼ 82%:
In this paper, we present kinetic results of the
complexation reaction of some bis- and tris-(oxaalkyl)
phosphates, as well as tetrakis(oxaalkyl) phosphates
with Fe(III) cation in the ethanol solvent. These new
compounds are characterised by different number of
oxygen atoms in the oxaalkyl chains. The obtained
results are compared with those of simple triethyl
phosphate with non-podand-like character.
2.2. NMR measurements
The 31P NMR spectra were recorded in CD3CN
using a Varian Gemini 300 MHz spectrometer using
the following parameters: sfrq ¼ 121:472; pw ¼ 608;
sw ¼ 50; 000 Hz; at ¼ 2 s; T ¼ 293 K and 85%
H3PO4 as external standard. All spectra were locked
to deuterium resonance of CD3CN. The error in ppm
values is 0.1.
2. Experimental
Ethanol and anhydrous FeCl3 were used as a
commercial product (Fluka). Triethyl phosphate
(PO3Et) was used as a commercial product (BDH
Chemicals Ltd.).
31P chemical shifts for the synthesised compounds
are: 22.2 ppm (septet, JH3P ¼ 8:1 Hz) for PO3Et,
2.1. Syntheses of polyoxaalkyl phosphates
20.1 ppm
(septet,
septet,
JH3P ¼ 7:5 Hz;
JH4P ¼ 1:6 Hz) for OP3.2, 1.72 ppm (septet, septet,
JH3P ¼ 7:5 Hz; JH4P ¼ 1:6 Hz) for OP3.7, 1.93 ppm
(septet, septet, JH3P ¼ 7:5 Hz; JH4P ¼ 1:6 Hz) for
OP3.12, 9.3 ppm (dq, JH1P ¼ 7:2 Hz; JH3P ¼ 9:2 Hz)
for OPH2.2, 9.0 ppm (dq, JH1P ¼ 7:5 Hz;
JH3P ¼ 9:0 Hz) for OPH2.3, 20.3 ppm for
(R3O)2OP–O–PO(OR3)2 and (R7O)2OP–O–
PO(OR7)2.
Tris(oxaalkyl) phosphates (OP3.2, OP3.7 and
OP3.12) were obtained by the dropping of phosphorus
oxychloride (0.33 mol) under reduced pressure
(200 mmHg) to the respective mixtures of anhydrous
glycolmonomethyl ethers (1.3 mol) in 250 cm3
xylene) at temperature 210 8C. Afterwards, the
mixture was heated to temperature 50 8C for 1 h and
the solvent was evaporated. The OP3.2 product
ðyield ¼ 80%Þ was distilled under reduced pressure.
bp ¼ 160–163 8C=0:04 mmHg: OP3.7 and OP3.12
compounds were purified by the chromatographic
method (SiO2–ethyl acetate). Yield ¼ 80%:
2.3. Kinetic study
The complexation of the iron cation (Fe3þ), by a
ligand (L) in ethanol (Sol) can be represented by the
Bis(oxaalkyl) phosphates (OPH2.2 and OPH2.3)

B.ł. Łe˛ska et al. / Journal of Molecular Structure 643 (2002) 9–19
11
following equilibrium:
ꢀ
ꢁ
k
nðLÞSol þ ðFe3þÞSol O ðL; Fe3þÞSol O LnFe3þ
Sol
k2
where k and k2 are the rate constants for complexation
and decomplexation process, respectively. The for-
mation of 1:1 complexes is the rate-determining step.
The kinetic runs were carried out using a stopped-flow
spectrophotometer (Applied Photophysics) with the
cellblock thermostated to ^0.1 8C. The kinetic runs
were completed under pseudo-first-order conditions
with the ligands concentration in large excess. The
observed rate constants were calculated from the
traces of absorbance versus time. The observed rate
constant kobs depends on the initial ligands concen-
tration [L] and is given by the equation: kobs
k½Lꢀ þ k2:
¼
Rate constants for forward (k ) reaction were
calculated by linear least-squares fit of the variation
of kobs versus the base concentration. The activation
parameters were calculated by the linear least-square
fit of ln k versus 1=T:
2.4. AM1d calculations
AM1d semi-empirical calculations were per-
formed using the Win Mopac 2002 program [27]. In
all cases, full geometry optimisation was carried out
without any symmetry constraints [28,29].
3. Results and discussion
The structures of ethyl phosphate (OP3Et) and
oxaalkyl phosphate esters are shown in Scheme 1.
These compounds belong to three groups distin-
guished on the basis of the number of oxaalkyl chains.
The first group, of the so-called tripodands (OP3Et,
OP3.2, OP3.7, OP3.12) forms complexes with the
metal cation preferably via the oxygen atoms of the
oxaalkyl chains. The compounds of the second group
(OPH2.2 and OPH2.3) are dipodands. The complexa-
tion of the cation by these compounds can occur via
oxygen atoms of the oxaalkyl chains or oxygen atoms
of the (OyP) groups. The coordination by the oxygen
atoms of (OyP) groups is more favourable if the
concentration of ligands is high enough. The third
group is represented by two pyrophosphates
Scheme 1.

12
B.ł. Łe˛ska et al. / Journal of Molecular Structure 643 (2002) 9–19
Table 1
Kinetics parameters (^standard deviation) for the reaction of OP3Et with FeCl3 in ethanol
Temperature kobs (s21) for ligands concentration
(8C)
k
k2
(s21
DH –
(kJ mol21
DS –
(J mol21 deg21
DG –
(kJ mol21
)
(M21 s21
)
)
)
)
0.062
(M)
0.085
(M)
0.100
(M)
0.125
(M)
25
30
40
50
42.1 ^ 3.8 284 ^ 12
67.0 ^ 3.8
0.3 ^ 0.1 0.6 ^ 0.2 1.0 ^ 0.1 1.3 ^ 0.2 16 ^ 2
0.8 ^ 0.1 1.3 ^ 0.1 1.8 ^ 0.1 2.4 ^ 0.1 26 ^ 1
1.5 ^ 0.1 2.4 ^ 0.1 3.5 ^ 0.1 4.4 ^ 0.1 47 ^ 4
20.7 ^ 0.2
20.8 ^ 0.1
21.5 ^ 0.4
(R3O)2OP–O–PO(OR3)2 and (R7O)2OP–O–
PO(OR7)2 the so-called two-core ligands, which can
form complexes through O–P–O–P–O bonds or
oxygen atoms of oxaalkyl chains. Thus, these
compounds differ not only in the number of oxaalkyl
chains, but also in the chain length.
structures are shown in Figs. 1–4. The kinetic studies
were performed in ethanol and for this reason the
complexes with this solvent are also calculated and
discussed. From literature data, it is well known that
the PyO phosphate group is a strong proton acceptor
[30–32]. A comparison of the total energy values
given in Table 9 for hydrogen-bonded complexes with
one ethanol molecule and without this hydrogen bond,
The obtained DH–; DS– and DG– values for the
reactions studied are shown in Tables 1–8.
It is well known that the activation entropy
ðDS–Þ is a measure of the difference in the
solvation degree of the substrates and the tran-
sition product. Low ðDS–Þ values are observed
when in the transition state the complex motions
are restricted as a result of the solvation process.
The lowest values of ðDS–Þ are found for
complexes of Fe(III) cation with OP3.2 and
OPH2.3 esters (2156 and 2138 J mol21 deg21
,
respectively), which become stereochemically
ordered. This situation is a result of a substantial
restriction of the complex motions in transition
state, while in the complexes obtained with a
small steric hindrance, DS– values are, relatively,
large (the highest values are for OP3.7, where
DS– ¼ 25 J mol21 deg21 and (R3O)2OP–O–
OP(OR3)2, where DS– ¼ 24 J mol21 deg21). The
enthalpies of activation DH– are compensated by
the entropy of activation, DS–: The values of DG–
in Tables 1–8 are comparable and they are in the
range of 53–56 kJ mol21 except for the complex
formation by the simple ethyl phosphate and
OP3.12 ester, i.e. with the longest oxaalkyl chains.
For them, the DG– values are slightly higher (67
and 64 kJ mol21).
The data calculated for some exemplary complexes
formed between phosphate esters and Fe(III) cation
are shown in Tables 9–11 and the respective
Fig. 1. Structures of 1:1:1 complexes of phosphate esters with
Fe(III) cation and one ethanol molecule calculated by AM1d
method. (a) OP2.3 and (b) OP3.2.

Table 2
Kinetics parameters (^standard deviation) for the reaction of OP3.2 with FeCl3 in ethanol
Temperature (8C)
kobs (s21) for ligands concentration
k (M21 s21
)
k2 (s21
)
DH – (kJ mol21
)
DS – (J mol21 deg21
)
DG – (kJ mol21
)
0.005 (M)
0.010 (M)
0.015 (M)
0.020 (M)
15
25
35
45
18.2 ^ 1.0
23.9 ^ 1.2
30.2 ^ 2.4
38.7 ^ 3.3
32.5 ^ 1.7
42.8 ^ 2.1
52.6 ^ 2.7
61.8 ^ 0.9
48.4 ^ 3.0
57.8 ^ 2.3
68.1 ^ 1.0
80.7 ^ 2.3
62.2 ^ 1.5
74.9 ^ 2.1
87.4 ^ 1.2
103.1 ^ 2.0
2958 ^ 55
3.4 ^ 0.8
7.9 ^ 1.4
2.5 ^ 2.0
18.1 ^ 1.5
3360 ^ 102
3742 ^ 180
4242 ^ 111
6.6 ^ 0.2
2156 ^ 1
52.9 ^ 0.3
Table 3
Kinetics parameters (^standard deviation) for the reaction of OP3.7 with FeCl3 in ethanol
Temperature
kobs (s21) for ligands concentration
k
k2
(s21
DH –
(kJ mol21
DS –
(J mol21 deg21
DG –
(kJ mol21
)
(8C)
(M21 s21
)
)
)
)
0.0031
(M)
0.0063
(M)
0.0125
(M)
0.0250
(M)
0.0375
(M)
15
25
35
45
0.5 ^ 0.1
2.7 ^ 0.1
5.6 ^ 0.2
14.9 ^ 0.5
1.4 ^ 0.1
4.3 ^ 0.2
10.2 ^ 0.3
22.9 ^ 0.7
3.1 ^ 0.1
8.4 ^ 0.4
14.5 ^ 0.6
43.8 ^ 1.3
8.2 ^ 0.1
17.3 ^ 0.6
40.9 ^ 1.3
85.7 ^ 2.4
12.9 ^ 0.3
27.2 ^ 0.7
61.1 ^ 2.0
132.3 ^ 4.3
366 ^ 13
716 ^ 20
21.0 ^ 0.3
20.1 ^ 0.4
21.5 ^ 2.3
2.0 ^ 1.6
55.0 ^ 2.4
25 ^ 8
56.6 ^ 2.4
1654 ^ 109
3429 ^ 75

Table 4
Kinetics parameters (^standard deviation) for the reaction of OP3.12 with FeCl3 in ethanol
Temperature (8C) kobs (s21) for ligands concentration
0.0025 (M) 0.0070 (M) 0.0150 (M)
k (M21 s21
)
k2 (s21
)
DH – (kJ mol21
)
DS – (J mol21 deg21
)
DG – (kJ mol21
)
0.0250 (M)
15
25
35
45
0.08 ^ 0.02 0.14 ^ 0.02 0.26 ^ 0.05 0.41 ^ 0.02
0.29 ^ 0.01 0.46 ^ 0.02 0.72 ^ 0.03 1.17 ^ 0.02
14.7 ^ 0.2
38.7 ^ 2.0
0.1 ^ 0.1
0.2 ^ 0.1 62.8 ^ 4.7
0.3 ^ 0.1
24 ^ 16
64.1 ^ 4.7
0.56 ^ 0.20 0.96 ^ 0.29 1.72 ^ 0.21 2.84 ^ 0.08 101.5 ^ 3.7
1.01 ^ 0.05 2.83 ^ 0.06 3.64 ^ 1.30 5.29 ^ 0.09 174.8 ^ 30.7 1.1 ^ 0.5
Table 5
Kinetics parameters (^standard deviation) for the reaction of OPH2.2 with FeCl3 in ethanol
Temperature (8C)
kobs (s21) for ligands concentration
k (M21 s21
)
k2 (s21
)
DH – (kJ mol21
)
DS – (J mol21 deg21
)
DG – (kJ mol21
)
0.005 (M)
0.010 (M)
0.015 (M)
0.020 (M)
15
25
35
45
3.8 ^ 1.5
9.1 ^ 2.0
15.1 ^ 2.5
23.0 ^ 2.0
6.7 ^ 1.0
13.4 ^ 2.0
24.8 ^ 3.0
37.4 ^ 2.5
8.4 ^ 2.0
17.5 ^ 2.0
32.4 ^ 1.5
50.1 ^ 1.0
12.4 ^ 2.5
22.6 ^ 1.5
40.5 ^ 1.5
62.8 ^ 1.0
550 ^ 60
892 ^ 31
1676 ^ 63
2642 ^ 59
1.0 ^ 0.8
4.5 ^ 0.4
7.3 ^ 0.9
10.3 ^ 0.8
38.2 ^ 1.8
260 ^ 6
56.1 ^ 1.8

Table 6
Kinetics parameters (^standard deviation) for the reaction of OPH2.3 with FeCl3 in ethanol
Temperature (8C)
kobs (s21) for ligands concentration
k (M21 s21
)
k2 (s21
)
DH – (kJ mol21
)
DS – (J mol21 deg21
)
DG – (kJ mol21
)
0.005 (M)
0.010 (M)
0.015 (M)
0.020 (M)
15
25
35
45
12.0 ^ 0.3
18.3 ^ 0.4
26.1 ^ 0.3
29.6 ^ 0.9
25.4 ^ 0.5
33.9 ^ 0.7
43.5 ^ 0.7
54.8 ^ 0.7
37.7 ^ 0.4
49.6 ^ 1.0
64.3 ^ 0.9
77.3 ^ 1.2
51.4 ^ 0.8
66.1 ^ 1.0
83.5 ^ 1.5
99.1 ^ 1.0
2610 ^ 37
3182 ^ 30
3860 ^ 91
21.0 ^ 0.5
2.2 ^ 0.4
6.1 ^ 1.2
7.5 ^ 1.5
12.0 ^ 0.1
2138 ^ 1
53.1 ^ 0.1
4620 ^ 111
Table 7
Kinetics parameters (^standard deviation) for the reaction of (R3O)2OP–O–PO(OR3)2 with FeCl3 in ethanol
Temperature
kobs (s21) for ligands concentration
k
k2
(s21
DH –
(kJ mol21
DS –
(J mol21 deg21
DG –
(kJ mol21
)
(8C)
(M21 s21
)
)
)
)
0.0031
(M)
0.0063
(M)
0.0125
(M)
0.0250
(M)
0.0375
(M)
15
25
35
45
1.1 ^ 0.1
3.0 ^ 0.1
8.2 ^ 0.2
28.6 ^ 0.8
1.5 ^ 0.1
8.6 ^ 0.2
20.6 ^ 0.6
50.2 ^ 1.3
6.1 ^ 0.2
17.6 ^ 0.4
40.1 ^ 0.8
89.7 ^ 2.1
13.3 ^ 0.3
34.0 ^ 0.8
76.9 ^ 1.8
155.4 ^ 2.9
20.6 ^ 0.4
49.2 ^ 0.8
106.4 ^ 1.8
214.6 ^ 2.1
585 ^ 22
1331 ^ 37
2847 ^ 115
5379 ^ 190
21.4 ^ 0.5
0.0 ^ 0.8
2.4 ^ 2.4
16.9 ^ 4.0
54.1 ^ 1.2
24 ^ 4
55.3 ^ 1.2

Table 8
Kinetics parameters (^standard deviation) for the reaction of (R7O)2OP–O–PO(OR7)2 with FeCl3 in ethanol
Temperature
kobs (s21) for ligands concentration
k
k2
(s21
DH –
(kJ mol21
DS –
(J mol21 deg21
DG –
(kJ mol21
)
(8C)
(M21 s21
)
)
)
)
0.0031
(M)
0.0063
(M)
0.0125
(M)
0.0250
(M)
0.0375
(M)
15
25
35
45
8.9 ^ 0.2
15.3 ^ 0.4
22.7 ^ 0.6
36.3 ^ 0.7
15.8 ^ 0.3
29.4 ^ 0.7
44.5 ^ 0.6
61.9 ^ 0.8
22.4 ^ 0.5
55.2 ^ 1.4
85.2 ^ 1.6
124.3 ^ 1.8
38.5 ^ 0.9
92.4 ^ 2.4
152.5 ^ 3.0
237.1 ^ 3.1
58.7 ^ 1.4
130.7 ^ 3.7
223.8 ^ 4.1
348.9 ^ 4.8
1398 ^ 56
3302 ^ 136
5783 ^ 121
9137 ^ 90
5.3 ^ 1.2
8.9 ^ 2.9
8.1 ^ 2.6
7.5 ^ 1.9
44.9 ^ 4.0
228 ^ 13
53.3 ^ 4.0

B.ł. Łe˛ska et al. / Journal of Molecular Structure 643 (2002) 9–19
17
Fig. 2. Structure of 1:1 complex of OP3.7 with Fe(III) cation
calculated by AM1d method.
indicates that this bond influences the coordination
strength of the cation. The same is indicated by the
partial charge (Table 10) and the distances (Table 11)
between the cation and the oxygen atoms of the
oxaalkyl chains. The OP2.3 and OP3.2 esters formed
the simplest octahedral 1:1 complexes with Fe(III)
Fig. 4. Structure of 6:1 complex of OP2.3 with Fe(III) cation
calculated by AM1d method.
cation, whose structures are shown in Fig. 1(a) and
(b), respectively. In these complexes, all oxygen
atoms of the oxaalkyl chains are involved in the
coordination process of Fe(III) cation. With increas-
ing number of the oxygen atoms in the oxaalkyl
chains, different octahedral structures, in which
various oxygen atoms are involved in the coordination
of cation, are possible. One such structure for the 1:1
complex of OP3.7 with Fe(III) cation is shown in Fig.
2.
Table 9
Values of HOF (heat of formation) and total energy of the
complexes formed between phosphate esters and Fe3þ calculated
by AM1d method
Compound
HOF
(kcal mol21
Total energy
(eV)
)
OP3.2
394.75
408.37
447.23
127.45
371.34
394.78
2243.27
111.20
132.24
203.12
255.39
24120.22
24208.34
24264.98
23956.84
24365.48
24393.27
25794.32
26154.46
26326.54
210,073.85
210,781.01
212,496.23
OP3.2/Fe3þ (1:1)
OP3.2/Fe3þ/EtOH (1:1:1)
OP2.3
OP2.3/Fe3þ (1:1)
OP2.3/Fe3þ/EtOH (1:1:1)
OP2.3/Fe3þ (6:1)
OP3.7
OP3.7/Fe3þ (1:1)
(R3O)2OP–O–PO(OR3)2
(R3O)2OP–O–PO(OR3)2/Fe3þ (1:1)
Fig. 3. Possible structures of complexes formed between
(R3O)2OP–O–PO(OR3)2 with Fe(III) cation (a) stoichiometry 2:1
and (b) stoichiometry 1:1 calculated by AM1d method.
(R3O)2OP–O–PO(OR3)2/Fe3þ (2:1) 2302.27

18
B.ł. Łe˛ska et al. / Journal of Molecular Structure 643 (2002) 9–19
Table 10
Values of partial charge for O-atoms, which coordinate with Fe3þ cation in the complexes formed between phosphate esters and Fe3þ calculated
by AM1d method
Compound
Fe
O
O
O
O
O
O
OyP
OyP
OP3.2
OP3.2/Fe3þ (1:1)
–
20.728
20.677
20.703
20.755
20.664
20.676
20.717
20.676
20.704
20.724
20.666
20.681
–
20.714
20.683
20.687
20.284
20.279
20.251
–
20.295
20.270
20.262
20.286
20.269
20.247
–
20.285
20.272
20.269
20.301
20.287
20.254
–
20.292
20.274
20.269
20.302
20.288
20.253
–
21.086
20.807
20.772
21.064
20.881
20.789
20.596
21.092
21.091
21.111
21.111
20.438
–
–
–
–
–
–
–
–
0.701
0.763
–
OP3.2/Fe3þ/EtOH (1:1:1)
OP2.3
OP2.3/Fe3þ (1:1)
OP2.3/Fe3þ/EtOH (1:1:1)
OP2.3/Fe3þ (6:1)
0.693
0.706
0.402
–
OP3.7
OP3.7/Fe3þ (1:1)
(R3O)2OP–O–PO(OR3)2
(R3O)2OP–O–PO(OR3)2/Fe3þ (1:1)
(R3O)2OP–O–PO(OR3)2/Fe3þ (2:1)
20.727
20.674
20.722
20.544
20.535
20.715
20.675
20.709
20.545
20.539
20.714
20.691
20.712
20.444
20.437
20.293
20.269
20.372
20.332
20.329
20.284
20.270
20.338
20.325
–
20.292
20.281
20.394
20.336
–
0.601
–
21.132
21.329
20.434
0.391
0.372
Table 11
˚
Distances (A) between O-atoms and Fe3þ cation in the complexes formed between phosphate esters and Fe3þ calculated by AM1d method
Compound
FeO
FeO
FeO
FeO
FeO
FeO
FeOyP
FeOyP
OP3.2/Fe3þ (1:1)
2.01
2.09
1.98
2.12
–
2.02
2.11
1.97
2.10
–
2.05
2.09
1.95
1.92
–
1.91
1.95
2.01
1.97
–
1.93
1.93
1.98
1.95
–
1.94
1.92
1.98
1.93
–
–
–
OP3.2/Fe3þ/EtOH (1:1:1)
OP2.3/Fe3þ (1:1)
–
–
–
–
OP2.3/Fe3þ/EtOH (1:1:1)
OP2.3/Fe3þ (6:1)
OP3.7/Fe3þ (1:1)
(R3O)2OP–O–PO(OR3)2/Fe3þ (1:1)
(R3O)2OP–O–PO(OR3)2/Fe3þ (2:1)
–
–
1.90
–
–
1.91
1.92
–
1.93
1.94
–
1.95
1.92
1.92
1.95
1.90
1.92
1.92
1.92
1.90
1.93
1.92
1.90
–
–
–
1.89
1.86
In the case of pyrophosphate esters with four
oxaalkyl chains, two types of structures, i.e. structures
including the coordination with PyO oxygen atoms
and structures in which the cation is coordinated only
by oxygen atoms of oxaalkyl chains, are probable
(Fig. 3).
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