Solution behaviour of (N,N'-ethylenebis(salicylideneiminato))- iron(III) chloride in aqueous methanol at 298.15, 303.15 and 313.15 K

Article abstract of DOI:10.2298/JSC170413082B

In this study partial molar volumes (φ⁰_v ) and viscosity B-coefficients of (N,N'-ethylene-bis(salicylideneiminato))iron(III) chloride, abbreviated as Fe^III(salen)Cl, in different aqueous methanolic solutions were determine

Full text of DOI:10.2298/JSC170413082B

J. Serb. Chem. Soc. 79 (2) 225–239 (2014)
JSCS–4578
UDC 546.723+547.313.2’131+
547.261–145.2:532.13
Original scientific paper
Solution behaviour of (N,N′-ethylenebis(salicylideneiminato))-
iron(III) chloride in aqueous methanol
at 298.15, 303.15 and 313.15 K
DHIRAJ BRAHMAN and BISWAJIT SINHA*
Department of Chemistry, University of North Bengal, Darjeeling-734013, India
(
Received 14 April, revised 19 July 2013)
0
Abstract: In this study partial molar volumes (ϕ ) and viscosity B-coefficients
V
of (N,N′-ethylene-bis(salicylideneiminato))iron(III) chloride, abbreviated as
III
Fe (salen)Cl, in different aqueous methanolic solutions were determined
from solution density and viscosity measurements at the temperatures
298.15, 303.15, and 313.15 K under ambient pressure. The apparent molar
volumes (φ ) and densities (ρ) were used to calculate the apparent molar
V
0
expansibilities (φ ), the partial molar expansibilities (ϕ ) and the tempe-
E
E
0
rature dependence of the partial molar expansibilities (ϕ ) at constant pres-
E
0
III
sure, (∂ϕ / ∂T) of Fe (salen)Cl solutions to reveal the nature of different
E
p
interactions in the ternary solutions. The transition state theory was applied to
analyze the viscosity B-coefficients based on the activation parameters of
viscous flow. The overall results indicated strong solute–solvent interactions
III
between Fe (salen)Cl and the solvent molecules, preferentially with water
III
molecules and that Fe (salen)Cl acts as a net structure promoter in the
ternary solutions. The UV–Vis absorption spectra of the ternary solutions
stand in support of the obtained results.
Keywords: partial molar volumes; viscosity B-coefficients; (N,N′-ethylene-
bis(salicylideneiminato))iron(III) chloride; aqueous methanol.
INTRODUCTION
Many natural products contain structural units similar to those of metal
heterocyclic compounds that could be used as targets for synthetic, methodolo-
1
gical, and biological applications. Schiff base metal complexes belong to class
of the many potential materials that deserve extensive studies and, amongst the
traditional metal complexes, salen-type Schiff base ligands or their derivatives
2
are of great importance in coordination chemistry and homogeneous catalysis.
3
They can also be regarded as models of reaction centres for metalloenzymes and
*
Corresponding author. E-mail: biswachem@gmail.com
doi: 10.2298/JSC170413082B
2
25
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26
BRAHMAN and SINHA
4
5–7
nonlinear optical materials. According to Groves et al.,
simple iron(III) por-
phyrins can be used as models for the reaction site of cytochrome P-450. In this
regard, metal complexes of the salen ligand are also of great interest to synthetic
chemists, since they share features in common with metalloporphyrins as far as
their electronic structure and catalytic activities are concerned. Interestingly,
III
III
Fe (salen)Cl and Fe porphyrins have some structural and chemical simil-
8
,9
III
III
arities. Like Fe porphyrins, the iron atom of Fe (salen)Cl has a penta-coor-
dinated pyramidal geometry wherein the tetradentate salen ligand is in a square
planar coordination and the chloride ligand is attached at an apical position. The
complex has an open sixth coordination site and salen forms some complexes
that mimic porphyrin chemistry. Moreover, Fe (salen)Cl has an affinity for
oxygen molecules and is capable of forming oxo-species as do Fe porphyrin
derivatives. Amongst the conventional solvents, methanol is used in numerous
chemical processes and it is has a structure analogous to water but with a –CH3
group in place of a proton. This substitution affects the liquid structure and
causes significant differences between methanol and water. Hence it is important
1
0
III
III
8
,9
III
to understand how solutes such as Fe (salen)Cl behave in these mixed metha-
nol–water solvents, because an understanding of such behaviour could throw
light on the effects of solute concentration on the hydrogen-bonded network,
1
1
solvation structure and solute dynamics, etc.
III
However, such studies on Fe (salen)Cl in various pure and mixed
solvents are still rare in the literature. To the best of our
knowledge, only one report on the solvent effects on the electrochemical
behaviour of Fe (salen)Cl is available in the literature. Hence in this work,
the solution behaviour of Fe (salen)Cl in different aqueous methanol solutions
III
12
III
were studied at 298.15, 303.15 and 313.15 K under ambient pressure and the
results are discussed in terms of solute–solute and solute–solvent interactions.
EXPERIMENTAL
Materials
Analytical reagent (AR) grade ferric chloride, FeCl ·6H O (s), 1,2-ethylenediamine (l),
3
2
and salicylaldehyde (l), each of purity > 99 %, were purchased from Merck, India. These
chemicals were used as received. Spectroscopic grade methanol (minimum assay, GC, purity
>
99.8 %) with 0.05 % of water was purchased from Merck, India and used as received.
-6
-1
Doubly distilled de-ionized water with a specific conductance of 1×10 S cm at 298.15 K
was used for preparing the mixed solvents. Various binary solvents were prepared by mass,
with necessary adjustments by volume, to achieve the exact mass fraction of methanol (w =
1
=
0.60, 0.70, 0.80 and 0.90) at 298.15 K. The relative error in solvent composition was
estimated to be about 1 %. The physical properties of different solvent/solvent mixtures at the
experimental temperatures are reported in Table S-I of the Supplementary material to this
1
3-16
paper and compared against available literature values.
III
17
Fe (salen)Cl was prepared by a known method taking FeCl ·6H O(s) and the Schiff
3
2
base, salenH (s) in ethanol (in a 1:1 molar ratio). SalenH (N,N′-ethylenebis(salicylidene-
2
2
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(N,N′-ETHYLENEBIS(SALICYLIDENEIMINATO))IRON(III) CHLORIDE IN AQUEOUS METHANOL
227
amine)) was obtained from an ethanolic solution of 1,2-ethylenediamine and salicylaldehyde
in a 1:2 molar ratio) for 1 h. The bright yellow crystalline solid (m.p. 128 °C) was filtered
(
and washed with ethanol several times and dried under vacuum. Metallation was realized by
refluxing an ethanolic solution containing FeCl ·6H O (s) (1.08 g, 4 mmol) and salenH (1.07
3
2
2
III
g, 4 mmol) with little triethylamine (NEt ) for 30 min at 60 °C. Fe (salen)Cl was obtained
3
as adeep brown microcrystalline solid from the mixture and was dried under vacuum at 50–
60 °C and then recrystallized from ethanol. It was kept in a vacuum desiccator over anhydrous
CaCl . The purity of the complex was checked by elemental analysis (Calcd.: C, 53.74; H,
2
3
.95; N, 7.84; Cl, 9.91; Fe, 15.63 %. Found: C, 53.64; H, 4.01; N, 7.94; Cl, 9.85; Fe, 15.60 %)
and IR spectroscopy. Elemental micro-analyses were realised with the aid of a Perkin–Elmer
Model 240C) instrument. The IR spectra ware recorded on a Perkin–Elmer FT-IR
(
-1
spectrophotometer. Characteristic IR bands for the prepared complex (KBr, cm ) are 585.76,
17.44, 757.92, 795.02, 904.87, 1445.82, 1544.35, 1629.76, 3448.17. The magnetic moment
6
1
8
(
measured with a Sherwood Scientific magnetic balance) was found to be 5.31 μ (5.29 μ
)
B
B
at room temperature. The molecular structures of the ligand SalenH , the complex
2
III
III
Fe (salen)Cl and its dimer [Fe (salen)Cl] are illustrated in Fig. S-1 of the Supplementary
material. The IR spectra of the ligand SalenH and Fe (salen)Cl are shown in Fig. S-2 of the
2
III
2
Supplementary material.
Stock solutions of the complex in different aqueous methanol solutions were prepared by
mass and the working solutions were prepared by mass dilution. Solute molalities (m) were
converted into molarities (c) using experimental density values. All solutions were prepared
fresh and degassed with dry nitrogen before use. The uncertainty in the molarity of
III
-3
Fe (salen)Cl solutions was evaluated to be ±0.0001 mol dm .
Methods
The mass measurements were performed on a digital electronic analytical balance
(Mettler, AG 285, Switzerland) with a precision of ±0.01 mg. The densities were measured
with a vibrating-tube density meter (Anton Paar, DMA 4500M), which was calibrated at the
experimental temperatures with doubly distilled, degassed water and dry air at atmospheric
-3
pressure. The temperature was automatically kept constant with an accuracy of ±1×10
K
using a built-in Peltier device. The stated repeatability and accuracy of the densities were
-5
-5
-3
±
1×10 and ±5×10 g cm , respectively. However, when the accuracy of the measured
densities was checked with the density of an aqueous NaCl solution of known molality based
19
on the data given by Pitzer, the uncertainty of the measured densities for most of the
-5
-3
solutions was estimated to be ±1×10 g cm . The viscosity was measured by means of a
suspended Ubbelohde (Canon-type) viscometer thoroughly cleaned, dried and calibrated at the
experimental temperatures with triply distilled, degassed water and purified methanol.2
0-22
It
was filled with experimental solution and placed vertically in a glass sided thermostat
maintained constant to ± 0.01 K) with the aid of wooden clumps. Sufficient time was allowed
(
for the attainment of thermal equilibrium and the flow times of the solutions were recorded
with a digital stopwatch (correct to ± 0.01 s). In all determinations, adequate precautions were
taken to minimize evaporation losses and at least three repetitions of each data (reproducible
to ±0.02 s) were taken as the average of the flow times. The uncertainty in viscosity measu-
-
4
III
rements was estimated to be within ±4×10 mPa s. The absorption spectra of Fe (salen)Cl
(
-5
-3
5×10 mol dm ) in different aqueous methanol solutions at 298.15 K were recorded on
Jasco V-530 double beam UV–Vis spectrophotometer (coupled with a thermostatic arrange-
ment). A quartz cell with a path length of 1 cm was used and the reference solvent was
spectroscopic grade methanol for all the spectroscopic measurements.
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28
BRAHMAN and SINHA
RESULTS AND DISCUSSION
Molalities (m), densities (ρ) viscosities (η) and the apparent molar volumes
III
(
φ ) for the experimental solutions of Fe (salen)Cl in different aqueous metha-
V
nol solutions at various temperatures are given in Table S-II of the Supplement-
III
ary material. The apparent molar volumes (φ ) of Fe (salen)Cl in different
V
aqueous methanol solutions were determined from the solution densities by using
the following equation:
ϕ = (M / ρ ) −1000(ρ − ρ ) / (mρρ )
(1)
V
1
1
1
III
where M is the molar mass of Fe (salen)Cl, m is the molality of the solution, ρ1
and ρ are the densities of the solvent and solution, respectively. When the φV
values were plotted against the square root of molal concentrations (√m), a linear
0
dependence was observed. Hence the partial molar volumes (ϕ )at infinite dilu-
V
tion and the experimental slopes (S ) were determined using the least squares
V
23
fitting of φ values to the Masson Equation:
V
0
*
φ = φ + S
m
(2)
V
V
V
The φ0 and S* values are reported in Table I, which shows that the φ0
V
V
V
values are positive and increase as the amount of water in the mixtures increases
0
*
TABLE I. Partial molar volumes (ϕ ) and the slopes (S ) of Eq. (2) with the corresponding
V
V
III
standard deviations (σ) for Fe (Salen)Cl in different aqueous methanol solutions at different
temperatures (standard errors are given in parenthesis); w – mass fraction of methanol
1
0
6
3
-1
S ×10 / m kg mol-3/2
*
6
3
1/2
6
3
-1
T / K
ϕ
× 10 / m mol
σ×10 / m mol
V
V
w = 1.00
1
2
3
3
98.15
03.15
13.15
247.37 (±4.65)
228.45 (±4.26)
216.30 (±5.18)
–1537.95 (±56.44)
–1400.29 (±51.76)
–1335.03 (±62.88)
3.10
2.84
3.45
w = 0.90
1
2
3
3
98.15
03.15
13.15
257.09 (±5.83)
243.14 (±3.17)
232.10 (±4.65)
–1659.90 (±72.09)
–1554.86 (±39.15)
–1524.93 (±57.44)
3.86
2.10
3.08
w = 0.80
1
2
3
3
98.15
03.15
13.15
260.72 (±4.47)
253.03 (±0.02)
244.78 (±3.02)
–1779.20 (±56.26)
–1734.17 (±50.46)
–1672.77 (±38.05)
2.96
2.66
2.00
w = 0.70
1
2
3
3
98.15
03.15
13.15
262.39(±3.59)
257.29 (±3.95)
256.91 (±3.95)
–1830.54 (±45.76)
–1799.56 (±50.35)
–1826.92 (±50.39)
2.39
2.63
2.63
w = 0.60
1
2
3
3
98.15
03.15
13.15
264.36 (±5.07)
261.07 (±6.86)
261.20 (±4.89)
–1912.71 (±65.74)
–1917.72 (±88.93)
–1931.27 (±63.41)
3.40
4.60
3.28
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(N,N′-ETHYLENEBIS(SALICYLIDENEIMINATO))IRON(III) CHLORIDE IN AQUEOUS METHANOL
229
but decrease with increasing temperature. This indicates the presence of strong
solute–solvent interactions2
2,24
and these interactions were further strengthened
at higher contents of water but weakened at higher temperatures. The depend-
0
ences of the φ values on the solvent composition and temperature are shown in
V
III
Fig. 1. Fe (salen)Cl can exist either as dimer or monomer in the solid state. Its
behaviour in the solid state depends on the nature of the solvent used in its
recrystallization. However, the two forms can be distinguished by their magnetic
moments and IR spectra (shown in Fig. S-2 of the Supplementary material). For
monomeric complexes, the range of the magnetic moment is 5.29–6.06 μ . A
B
III
value of 5.31 μ was obtained for the complex Fe (salen)Cl and the IR spectra
are devoid of any band near 850 cm . Thus, the complex was in monomeric
form rather than in the dimeric form and hence, it contains a d high spin
B
–1
25
5
electronic configuration2
6,27
with a square planar geometry around Fe at the
3+
centre and an apical chlorine atom as coordinated to the fifth coordination site.
Thus, solvent molecules can coordinate to the unoccupied sixth position of the
coordination site. In this regard, the donor power of individual solvents plays a
crucial role. Aqueous methanol solutions are characterized by hydrophobic and
hydrophilic interactions. Both computer simulation28 and experimental studies29–34
revealed that water strongly interacts with methanol to form complexes. Recent
spectroscopic and high performance liquid chromatographic studies revealed that
methanol forms a number of complexes with a number of water molecules at low
2
9–34
methanol but at high methanol content, it forms a 1:1 complex.
According
to Zhang and Wu,35 the two critical solvent compositions are H O:CH OH ≈ 5:1
2
3
and ≈ 1:1. Thus, as the methanol concentration decreases, more water molecules
become free in the bulk solvent mixtures. Hence methanol and water molecules
III
…
may coordinate for the sixth vacant coordination site of Fe (salen)Cl via O Fe
III
interactions. Moreover, methanol/water may also interact with Fe (salen)Cl via
hydrogen bond interactions with ONNO sites of the complex and thereby
affecting its spin-equilibrium in solution. No doubt, H O will have comparatively
2
more such hydrogen bond interactions than CH OH and because of the fact that
3
36
methanol (with an effective hard sphere diameter 0.364 nm ) is more bulky than
water (with effective hard sphere diameter 0.284 nm ), the increase in the φ
values as well as the concomitant increase in the φ0 values with increasing
water content in the mixtures may be attributed to preferential coordination of the
unoccupied sixth position of Fe (salen)Cl by water molecules or preferential
solvation of Fe (salen)Cl by water molecules due to stronger electrostatic inter-
action and comparatively more donor strength of water than methanol. Again,
as the φ0 values for the ternary systems increase with more water or polarity of
the solvent mixture (the order of relative permittivity of the solvent mixtures:
3
6
V
V
III
III
37
V
2
4
3
1.5, 35.7, 40.1, 45.0 and 50.1 for w = 1.00, 0.90, 0.80, 0.70 and 0.60, res-
1
pectively), the complex most probably remains in its monomeric form in the
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30
BRAHMAN and SINHA
solution phase, because the Fe-atom is comparatively more available to the
…
18
solvent molecules for O Fe interactions in the monomeric form than in the
dimeric form. However, the decrease in the φ0 values with rising temperature
indicates disruption of hydrogen bonds and O Fe interactions at elevated
temperatures. The slight increase in the φ0 values at 303.15 and 313.15 K for
V
…
V
solvent mixtures with w = 0.60 may probably arise from a delicate balance
1
between the loosely bound dimer and the monomer in this solvent compo-
sitions.2
5,27
The parameter SV is a volumetric viral coefficient and characterizes
*
3
8,39
the pair-wise interactions between solvated species
in solution. Its sign is
determined by the interactions between solute species (solute–solute inter-
actions). The negative values of S* and their trend opposite to that of the φ
0
V
V
III
values indicate weak solute–solute interactions for Fe (salen)Cl in the studied
experimental aqueous methanol solutions.
Fig. 1. Dependence of partial molar
0
volume (ϕ ) on the mass fraction of
V
methanol (w ) in the aqueous methanol
1
solutions at different temperatures. Sym-
bols: T = 298.15 K, □; T = 303.15 K,
○; T = 313.15 K, ∆.
These results are reflected in the UV–Vis absorption spectra of the studied
solutions. The absorption spectra of the Schiff base, salenH in methanol and
2
various aqueous methanol solutions at 298.15 K are shown in Fig. 2. The spec-
trum of salenH in methanol is characterized by the presence of two strong peaks
2
at 254 and 316 nm and a weak peak at 404 nm, which were discussed pre-
viously.22 Interestingly, when water was introduced, the peak at 404 nm of
salenH gradually disappeared and a valley was formed as the concentration of
2
water increased in the ternary solutions and thus, the position of the weak peak at
404 nm varies with the polarity of the aqueous methanol solutions. In addition,
the 316 nm peak underwent hypochromic shifts on addition of water. The absorp-
III
tion spectra of Fe (salen)Cl in methanol and various aqueous methanol solutions
at 298.15 K are shown in Fig. 3, which shows that the 404 nm peak of the Schiff
base disappeared in methanol as well as in all the aqueous methanol solutions
due to coordination of solvent molecules to Fe(III). Simultaneously, an additional
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(N,N′-ETHYLENEBIS(SALICYLIDENEIMINATO))IRON(III) CHLORIDE IN AQUEOUS METHANOL
231
peak at around 500 nm appeared and suffered hypsochromic shifts, indicating
coordination or solvation by solvent molecules.40 The peak at 258 nm did not
change appreciably but a new peak at around 320 nm appeared as the amount of
water in the ternary systems increased.27
Fig. 2. Changes in the UV–Vis absorption spectra of salenH solutions in different aqueous
2
methanol solutions at 298.15 K for w : 1, 0.70; 2, 0.60; 3, 0.90; 4, 0.80. w is the mass fraction
1
1
of methanol in the aqueous methanol solutions. Inset: 1, salenH in methanol; 2, average
2
absorption spectra in aqueous methanol mixtures at 298.15 K.
III
Fig. 3. Changes in the UV–Vis absorption spectra of Fe (salen)Cl solutions in different
aqueous methanol solutions at 298.15 K for w : 1, 1.00; 2, 0.90; 3, 0.70; 4, 0.80. w is the
1
1
III
mass fraction of methanol in the aqueous methanol solutions. Inset: 1, Fe (salen)Cl in
methanol; 2, average absorption spectra in aqueous methanol mixtures at 298.15 K.
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32
BRAHMAN and SINHA
The apparent molar volumes (φ ) and densities (ρ) were used to derive the
V
III
apparent molar expansibilities (φ ) of Fe (salen)Cl solutions by using the rela-
E
24
tion:
ϕ =αϕ +1000(α −α ) / (mρ )
(3)
E
V
0
0
where α and α are the coefficients of isobaric thermal expansion of the solvent
0
and solution, respectively, and the other symbols have their usual significances; α
–
1
–1
and α are defined as: α = –ρ0 (δρ /δT) and α = –ρ (δρ/δT) , respectively. The
0
0
p
p
–6
–1
uncertainty of the α and α values was ±6×10
values was within ±(0.006–0.061)×10 m mol K . The partial molar expan-
sibilities (φ ) were determined from the relation:
K
and the uncertainty in the φE
–1 –1
0
–6
3
0
24
V
0
ϕ =ϕ + S
m
E
(4)
E
E
0
The φ values for the different experimental solutions at different tempera-
E
tures are listed in Table S-III of the Supplementary material. The Table reveals
0
that the φ values are negative and decrease further as the temperature increases
E
but increase with increasing content of H O for all the solutions. These facts may
2
be attributed to structural perturbation influenced by the gradual appearance or
disappearance of the caging/packing effect41 as the water content increases in the
ternary solutions or as the temperature of the solutions increases, respectively.
According to Hepler,42 the sign of (δ φ /δT) is a better criterion in charac-
0
P
E
terizing the long-range structure making or breaking ability of a solute in the
0
solution phase. If the (δ φ /δT) values are small negative or positive, the solute
P
E
acts as a structure maker, otherwise it acts as a structure breaker. The
δ φ /δT) values were obtained from the slope of a linear fit of the φ values
P
E E
against the experimental temperature (T). The correlation coefficients (R ) values
were within the range (0.97210–0.99552). The (δ φ /δT) values for different
ternary solutions are given in Table S-III of the Supplementary material and
Fe (salen)Cl was found to act as a net structure promoter in the aqueous meth-
0
0
(
2
0
P
E
III
anol solutions.
It is reported43 that Fe (salen)Cl can produce a stable [Fe (salen)] cation
III
III
+
–
but the experimental solutions did not respond to the AgNO test for free Cl .
3
Hence, the solution viscosities (η) were analysed with a modified Jones–Dole
equation:44
η η =η =1+ Bc
(5)
1
r
where η = η/η is the relative viscosity; η and η are the viscosities of solvent
r
1
1
and solution, respectively. The adjustable parameter B, referred to as the visco-
sity B-coefficient, was obtained by least squares analysis and the obtained values
0
45,46
are reported in Table II. Similar to φ , the viscosity B-coefficient
provides
V
another avenue to the effects of solute–solvent interactions based on the solution
viscosity. Table II shows that the viscosity B-coefficients for Fe (salen)Cl in the
III
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(N,N′-ETHYLENEBIS(SALICYLIDENEIMINATO))IRON(III) CHLORIDE IN AQUEOUS METHANOL
233
studied solvent systems were positive but their temperature dependence was
negative. A solute that has positive viscosity B-coefficients with a negative
dependence on temperature is generally considered as a structure maker. Accord-
III
ingly Fe (salen)Cl can be considered as a structure maker for the present solvent
systems studied. However, the viscosity B-coefficients decreased on the intro-
duction of water (w from 1.00 to 0.90), but after that the viscosity B-coefficients
1
increased monotonically with further addition of water to the ternary solutions.
This is probably due to a sudden perturbation of the arrangement of methanol
molecules in the bulk methanol structure arising from strong solvent–solvent
interactions in the solvent mixture with w = 0.90. However, for the remaining
1
solvent compositions, solute–solvent interaction seems to dominate in the charac-
terisation of the solution viscosities and the viscosity B-coefficients.
III
TABLE II. Viscosity B-coefficients with standard deviations (σ) for Fe (salen)Cl in different
aqueous methanol solutions for linear regression of Eq. (5) at different temperatures (standard
errors are given in parenthesis); w – mass fraction of methanol
1
T / K
303.15
Parameter
2
98.15
313.15
w = 1.00
8.424 (±0.254)
0.99459
1
3
3
-1
-1
-1
-1
-1
B×10 / m mol
R
σ×10
8.255 (±0.161)
0.99772
8.124 (±0.143)
0.99815
2
3
0.002
0.001
0.001
w = 0.90
1
7.295 (±0.156)
0.99725
3
3
B×10 / m mol
6.941 (±0.265)
0.99131
6.706 (±0.124)
0.99794
2
R
3
σ×10
0.001
0.002
0.001
w = 0.80
1
7.649(±0.180)
0.99667
3
3
B×10 / m mol
7.123 (±0.244)
0.99302
6.887 (±0.199)
0.99502
2
R
3
σ×10
0.001
0.002
0.001
w = 0.70
1
7.883 (±0.364)
0.98738
3
3
B×10 / m mol
7.193 (±0.004)
0.99999
6.991 (±0.079)
0.99922
2
R
3
σ×10
0.002
0.001
0.001
w = 0.60
1
7.891 (±0.231)
0.99490
3
3
B×10 / m mol
7.439 (±0.261)
0.99265
7.133 (±0.298)
0.98962
2
R
3
σ×10
0.002
0.002
0.002
According to Eyring and co-workers,46 the application of statistical thermo-
dynamics to the hole model of viscous flow based on the absolute reaction rate
theory yielded the following relation for the free energy of activation for viscous

*
flow per mole of the solvent/solvent mixture (Δμ1 ):
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34
BRAHMAN and SINHA
0

η ϕ
1
V ,1





*
*
Δμ1 = ΔG1 = RT ln
(6)

hNA


where N and ϕ0 are the Avogadro number and the partial molar volumes of
A
V ,1
4
5
the solvent, respectively. Other symbols have their usual meanings. The above
relation was also used for liquid mixtures4
can be expressed as:
5,46
and when rearranged this relation
0

* 
ΔH1

η ϕ
1


*  
ΔS1
1
V ,1



RT ln
 = −
 + 
 
 

(7)




hNA


R
R
 T






*
*
Hence, the values of ΔH1
and ΔS1
were obtained from a linear
2
regression treatment of Eq. (7) with correlation coefficient (R ) values within the
range 0.99866–0.99961. Plots of ln (η1ϕ0 /hN ) against (10 /T) are shown in
3
A,
V ,1
Fig. S-3 of the Supplementary material. A correlation between viscosity B-
coefficients and the deviation between the contribution per mole of a solute to the

*
free energy of activation for viscous flow of the solution (Δμ2 ) and the free
energy of activation of viscous flow per mole of the pure solvent or solvent

*
47
mixture (Δμ1 ) was suggested by Feakins et al., in the form of the following
relation:


Δμ2 −νΔμ1 *
*
(
)
B = νϕ0 −ϕ
0
+ϕ
V,1
0
(8)
(
)
V,1
V,2
RT
0
where the coefficient ν is 1 for an undissociated uncharged solute and ϕ
is the
V,2

2

*
*
partial molar volume of the solute. Thus, the (Δμ − Δμ ) values were cal-
1
culated using relation (8) and the B-coefficient values were obtained from Eq.


*
*
(
5). Again, the (Δμ2 − Δμ1 ) values can also be expressed as:


ΔS2 − ΔS 



*
*
*




*
* 
Δμ2 − Δμ1
ΔH2 − ΔH1
(
)
(
)
(
)
 1 

=
−
+
(9)


RT
R
R
 T



where ΔS  and ΔHi * are the standard partial molar entropy and enthalpy, res-
pectively, of activation for viscous flow per mole of i component in the solu-

*
i
th
tion. Hence, a linear regression treatment of Eq. (9), with the correlation
2
coefficient (R ) values within the range 0.81698–0.96863, provided the values of




1

*
*
*
*
(
ΔS2 − ΔS1 ) and (ΔH2 − ΔH1 ) from the corresponding slopes and inter-

*
*
θ*
and (Δμ − Δμ ) are reported in Table III.
1
cept. The parameters Δμ
2







*
*
*
*
*
*
ΔH1 , (ΔH2 − ΔH1 ), ΔS1 and (ΔS2 − ΔS1 ) are reported in Table IV.

*
*
3
Plots of (Δμ2 − Δμ1 ) / RT against (10 /T) are shown in Fig. S-4 of the Sup-
plementary material.
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(N,N′-ETHYLENEBIS(SALICYLIDENEIMINATO))IRON(III) CHLORIDE IN AQUEOUS METHANOL
235
TABLE III. The free energy of activation for viscous flow per mole of the solvent–solvent

*
mixture, Δμ1 , its deviation from the free energy of activation for viscous flow per mole of



*
*
*
III
the solute, Δμ , and (Δμ2 − Δμ ) for Fe (salen)Cl in different aqueous methanol solu-
tions at different temperatures (standard errors are given in parenthesis); w – mass fraction of
2
1
1
methanol


*

T / K
Δμ1 * / kJ mol-1
(Δμ2 − Δμ1 *) / kJ mol-1
w = 1.00
1
298.15
303.15
313.15
9.97 (±0.01)
9.97 (±0.01)
10.00 (±0.01)
525.22 (±0.26)
519.26 (±0.17)
521.15 (±0.15)
w = 0.90
1
298.15
303.15
313.15
10.52 (±0.01)
10.53 (±0.01)
10.61 (±0.01)
511.29 (±0.16)
491.39 (±0.27)
484.95 (±0.13)
w = 0.80
1
298.15
303.15
313.15
10.95 (±0.01)
11.04 (±0.01)
11.22 (±0.01)
593.23 (±0.18)
559.14 (±0.25)
553.04 (±0.20)
w = 0.70
1
298.15
303.15
313.15
11.12 (±0.01)
11.23 (±0.01)
11.43 (±0.01)
671.90 (±0.37)
621.36 (±0.01)
618.75 (±0.08)
w = 0.60
1
298.15
303.15
313.15
11.33 (±0.01)
11.47 (±0.01)
11.73 (±0.01)
734.73 (±0.24)
701.61 (±0.27)
689.83 (±0.30)
TABLE IV. The standard partial molar enthalpy of activation for viscous flow of a solvent–

*
solvent mixtures, ΔH
, and its deviation from the standard partial molar enthalpy of
1
*
*
*
activation for viscous flow of the solute, ΔH , (ΔH − ΔH ) , along with the standard
2
2
1

*
partial molar entropy of activation for viscous flow of a solvent–solvent mixture, ΔS , and
1
its deviation from the standard partial molar entropy of activation for viscous flow of the
*
*
*
III
solute, ΔS2
1
, (ΔS − ΔS ) , for Fe (salen)Cl in different aqueous methanol solutions;
2 1
w – mass fraction of methanol

*
*
*
*
*
*
)
1
ΔH
(ΔH2 − ΔH1
)
ΔS
(ΔS − ΔS
1
1
2
w1
-1
-1
-1 -1
-1 -1
kJ mol
kJ mol
J mol K
J mol K
1
0
0
0
0
.00
9.28 (±0.01)
8.56 (±0.02)
5.62 (±0.01)
4.95 (±0.01)
3.37 (±0.01)
587.17 (±7.34)
988.83 (±7.72)
1307.11 (±4.45)
1592.97 (±3.39)
1552.35 (±4.52)
–2.31 (±0.04)
–6.54 (±0.07)
–17.89 (±0.03)
–20.72 (±0.03)
–26.70 (±0.02)
214.20 (±4.09)
1617.19 (±6.17)
2423.24 (±8.32)
3135.12 (±6.59)
2767.67 (±7.28)
.90
.80
.70
.60
Table III shows that the Δμ1 * values are almost invariant of the solvent

*
composition and temperature, implying that Δμ
is dependent mainly on the
2
viscosity B-coefficients and the (ϕ0 −ϕ ) terms. The values Δμ2 contain
0
*
V,2
V,1
the change in the free energy of activation of solute molecules in presence of
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36
BRAHMAN and SINHA
solvent as well as the contribution from the movement of solute molecules. The

*
Δμ values were positive at all the experimental temperatures and decreased as
2
the temperature increased and increased as the content of water in the ternary

*
solutions (except for those with w = 0.90) increased. Such a trend of the Δμ
1
2
values suggest that the viscous flow becomes easier at higher temperatures but
becomes more difficult with increased amount of water in the ternary solutions,
i.e., the formation of the transition state becomes less favourable with increased
45
amounts of water but higher temperature favour its formation.
According to Feakins et al.,47 a solute molecule interacts with every solvent
molecule and the sum of these interactions for all solute and solvent molecules is
collectively defined as the solute–solvent interaction. A solute molecule interacts
with all the solvent molecules in solution including any solvent molecule in its
transition state. Thus the effect of the solute on the activation free energy of the
solvent molecule is the difference between the solvation energies of the solute in
the ground state solvent and the transition state solvent or free energy of transfer,

*
*
ΔG (1 →1′) between them. The second contribution to Δμ2 comes from the
2
*
movement of the solute through its own viscous transition state, ΔG (2 → 2′).
Hence, the term Δμ2 can also expressed as:
2
*

*
*
*
Δμ = ΔG (1→1′) + ΔG2 (2 → 2′)
(10)
The values of ΔG (2 → 2′) can be approximated with the Δμ1 values and the
2
2

*
*
*
2
*
*
values of ΔG2 (1 →1′) simply become equal to the (Δμ − Δμ1 ) values.
2
*
*
Thus, the quantity (Δμ2 − Δμ1 ) is the change in the activation energy per
mole of solute on replacing one mole of solvent by one mole of solute at infinite
*
*
dilution. The obtained values of (Δμ2 − Δμ1 ) are positive for all the solvent
mixtures and the values decrease almost linearly as the temperature increases for
all the solvent mixtures, but they increase with further addition of water in the
ternary solutions (except for those with w = 0.90). The positive (Δμ2 − Δμ1
values and their negative temperature dependence with a similar trend in the

*
*
)
1
III
viscosity B-coefficients for Fe (salen)Cl indicated the structure making ability
of the solute and transfer of solute molecules from the ground state solvent to the
transition state solvent is thermodynamically hindered.
*
Table IV shows that the ΔH2 values are positive for all the solvent sys-
tems and thus indicate rupture and distortion of the solvation bonds or intermole-
cular forces in the activated state of viscous flow and that the viscous process is
endothermic. Thus, the viscous flow will be accompanied by a decrease in order

*
and thus positive ΔS2 values were obtained for all the studied solutions. How-
*
ever, the negative ΔS1 values for all the solvent mixtures may be attributed to
the negative entropy of mixing of the solutions over the entire range of concen-
tration for aqueous methanol; such a negative entropy of mixing originates from
3
5
the strong association between the solvent molecules at low methanol contents
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(N,N′-ETHYLENEBIS(SALICYLIDENEIMINATO))IRON(III) CHLORIDE IN AQUEOUS METHANOL
237
and the tendency of the solvent molecules to segregate and form clusters48–50 in
aqueous methanol solutions, which dominate the thermodynamics of aqueous
methanol solutions.5
1,52
CONCLUSIONS
In the present study, derived parameters such as partial molar volumes
0
0
(
ϕ ), partial molar expansibilities (ϕ ), viscosity B-coefficients and various
V E
III
activation parameters for viscous flow for the under investigation Fe (salen)Cl
indicate the presence of strong solute–solvent interactions and these interactions
are further strengthened at higher content of water in the ternaries but decrease at
III
higher temperatures. The results further show that Fe (salen)Cl is preferentially
more solvated by water than methanol and it acts as a net structure promoter in
the studied ternary solutions. The UV–Vis absorption spectra of the ternary
solutions support of the obtained results. A transition state theory treatment of
viscosity B-coefficients revealed that the transfer of the solute molecules from
ground state solvent to transition state solvent is thermodynamically hindered and
the viscous process is endothermic.
SUPPLEMENTARY MATERIAL
The physical properties of different aqueous methanol solutions and experimental
III
densities, viscosities of Fe (salen)Cl solutions along with derived parameters at the expe-
rimental temperatures and their dependence on solvent composition and temperatures, etc.
(
listed in Tables S-I–S-III and Figs. S-1–S-4) are available electronically from http://
//www.shd.org.rs/JSCS/ or from the authors on request.
Acknowledgements. The authors are grateful to the Departmental Special Assistance
Scheme under the University Grants Commission, New Delhi (SAP-DRS-III, No.
F540/12/DRS/2013) for financial support. One of the authors (D. B) is also thankful to UGC,
India for granting him a UGC BSR Research Fellowship in Science [Ref. No. 4-1/2008
(
BSR)].
И З В О Д
ПОНАШАЊЕ РАСТВОРА КОЈИ САДРЖИ (N,N′-БИС(САЛИЦИЛИДЕН)-
ЕТИЛЕНДИАМИНАТО)ГВОЖЂЕ(III)-ХЛОРИД У СМЕШИ ВОДЕ И МЕТАНОЛА
НА 298,15; 303,15 И 313,15 K
DHIRAJ BRAHMAN и BISWAJIT SINHA
Department of Chemistry, University of North Bengal, Darjeeling-734013, India
0
У овом раду су одређене парцијалне моларне запремине (ϕ ) и B-коефицијенти
V
Jones–Dole једначине (N,N′-бис(салицилиден)етилендиаминато)гвожђе(III)-хлорида,
III
скраћено Fe (salen)Cl, у растворима смеше растварача воде и метанола мерењем
густине и вискозности раствора на температурама 298,15; 303,15 и 313,15 K под атмо-
сферским притиском. Привидне моларне запремине (φ ) и густине (ρ) су коришћене за
V
прорачун промена привидних моларних запремина од температуре (φ )и парцијалних
E
0
моларних запремина од температуре (ϕ ) као и одређивање облика температурне завис-
ности при константном притиску (∂ϕ / ∂T ) у растворима Fe (salen)Cl са циљем да се
E
0
III
E
p
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38
BRAHMAN and SINHA
открије природа различитих интеракција у тернарним растворима . Теорија прелазног
стања је примењена у анализи B коефицијената на основу активационих параметара
вискозног тока. Свеукупни резултати указују на јаке интеракције растворак–растварач
III
између Fe (salen)Cl и молекула растварача, превасходно молекула воде као и да се
III
Fe (salen)Cl понаша као компонента која стабилизује структуру тернарних раствора.
UV-Vis апсорпциони спектри тернарних раствора потврђују добијене резултате.
(
Примљено 14. априла, ревидирано 19. јула 2013)
REFERENCES
. M. J. Garson, Chem. Rev. 93 (1993) 1699
. T. Katsuki, Coord. Chem. Rev. 140 (1995) 189
1
2
3
. M. F. Summers, L. G. Marzilli, N. B. Pahor, L. Randaccio, J. Am. Chem. Soc. 106 (1984)
4478
4
5
6
7
8
. P. G. Lacroix, Eur. J. Inorg. Chem. (2001) 339
. J. T. Groves, T. E. Nemo, R. S. Myers, J. Am. Chem. Soc. 101 (1979) 1032
. J. T. Groves, T. E. Nemo, J. Am. Chem. Soc. 105 (1983) 5786
. J. T. Groves, Y. Watanabe, J. Am. Chem. Soc. 110 (1988) 8443
. A. Böttcher, M. W. Grinstaff, J. A. Labinger, H. B. Gray, J. Mol. Catal., A 113 (1996)
191
9. Y. W. Liou, C. M. Wang, J. Electroanal. Chem. 481 (2000) 102
10. F. L. Lindoy, The Chemistry of Macrocyclic Ligand Complexes, Cambridge University
Press, Cambridge, 1989
1
1
1
1
1
1. Y. Zhong, G. L. Warren, S. Patel, J. Comput. Chem. 29 (2008) 1142
2. D. Ranchet, J. B. Tommasino, O. Vittori, P. L. Fabre, J. Solution Chem. 27 (1988) 979
3. G. E. Papanastasiou, I. L. Zlogas, J. Chem. Eng. Data 37 (1992) 167
4. C. Carr, J. A. Riddick, Ind. Eng. Chem. 43 (1951) 692
5. J. Timmermans, Physico-Chemical Constants of Pure organic Compounds, Elsevier, New
York, 1950
1
1
6. S. Ismadji, H. Djojoputro, J. Chem. Eng. Data 50 (2005) 1343
7. M. R. Ganjali, P. Norouzi, M. Golmohammadi, M. Rezapour, M Salavati-Niasari,
Electroanalysis 16 (2004) 910
1
1
2
8. T. Matsushita, H. Kono, M. Nishino, T. Shono, Bull. Chem. Soc. Jpn. 55 (1982) 2581
9. K. S. Pitzer, J. C. Peiper, R. H. Busey, J. Phys. Chem. Ref. Data 13 (1984) 1
0. K. N. Marsh, Recommended reference materials for the realization of physicochemical
properties, Blackwell Scientific Publications, Oxford, 1987
th
2
2
2
1. J. A. Dean, Lange’s handbook of chemistry, 11 ed., McGraw-Hill, New York, 1973
2. D. Brahman, B. Sinha, J. Chem. Eng. Data 56 (2011) 3073
3. A. K. Covington, T. Dickinson, Physical chemistry of organic solvent systems, Plenum,
New York, 1973
rd
24. H. S. Harned, B. B. Owen, The Physical Chemistry of Electrolytic Solutions, 3 ed.,
Reinhold Publishing Corporation, New York, 1964
25. G. M. Bancroft, A. G. Maddock, R. P. Randl, J. Chem. Soc., A (1968) 2939
26. M. Gerloch, J. Lewis, F. E. Mabbs, A. Richards, J. Chem. Soc., A (1968) 112
27. M. Gullotti, L. Casella, A. Pasini, R. Ugo, J. Chem. Soc., Dalton Trans. (1977) 339
28. W. L. Jorgensen, J. Cao, C. Ravimohan, J. Phys. Chem. 89 (1985) 3470
29. E. D. Katz, C. H. Lochmuller, R. P. Scott, Anal. Chem. 61 (1989) 349
30. Z. Zhao, E. R. Malinowski, Anal. Chem. 71 (1999) 602
Available online at shd.org.rs/JSCS/
_______________________________________________________________________________________________________________________
_
2
014 Copyright (CC) SCS

(N,N′-ETHYLENEBIS(SALICYLIDENEIMINATO))IRON(III) CHLORIDE IN AQUEOUS METHANOL
239
31. A. Wakisaka, H. A. Carime, Y. Yamamoto, Y. Kiyozumi, J. Chem. Soc., Faraday. Trans.
9
4 (1998) 369
3
3
3
3
3
3
3
3
4
2. T. Sato, A. Chiba, R. Nazaki, J. Chem. Phys. 112 (2000) 2924
3. G. Onori, J. Chem. Phys. 87 (1987) 1251
4. A. K. Soper, J. L. Finney. Phys. Rev. Lett. 71 (1993) 4346
5. G. Zhang, C. Wu, J. Am. Chem. Soc. 123 (2001) 1376
6. L. A. Woolf, Pure Appl. Chem. 57 (1985) 1083
7. I. Persson, Pure Appl. Chem. 58 (1986) 1153
8. R. K. Wadi, P. Ramasami, J. Chem. Soc., Faraday Trans. 93 (1997) 243
9. K. Belibagli, E. Agranci, J. Solution Chem. 19 (1990) 867
0. W. R. Cordoba, J. S. Zugazagoitia, E. C. Fregoso, J. Peon, J. Phys. Chem., A 111 (2007)
6241
4
1. F. J. Millero, The partial molal volumes of electrolytes in aqueous solutions, in Water and
Aqueous Solutions: Structure, Thermodynamics, and Transport Processes, R. A. Horne,
Ed., Wiley-Interscience, New York, 1972, p. 519
4
4
4
4
4
2. L. G. Hepler, Can. J. Chem. 47 (1969) 4617
3. F. Lloret, J. Moratal, J. Faus, J. Chem. Soc. Dalton Trans. (1983) 1743
4. W. Devine, B. M. Lowe, J. Chem. Soc., A (1971) 2113
5. D. Feakins, D. J. Freemantle, J. Chem. Soc., Faraday Trans. I 70 (1974) 795
6. S. Glasstone, K. Laidler, H. Eyring, The Theory of Rate Processes, McGraw-Hill, New
York, 1941
47. D. Feakins, F. M. Bates, W. E. Waghorne, K. G. Lawrence, J. Chem. Soc., Faraday
Trans. 89 (1993) 3381
48. T. D. Pascal, W. A. Goddard, J. Phys. Chem., B 116 (2012) 13905
49. S. Dixit, J. Crain, W. C. K. Poon, J. L. Finney, A. K. Soper, Nature 416 (2002) 829
50. A. K. Soper, L. Dougan, J. Crain, J. L. Finney, J. Phys. Chem., B 110 (2005) 3472
51. J. A. V. Butler, D. W. Thomson, W. H. MacLennan, J. Chem. Soc. (1933) 674
52. R. F. Lama, B. C. Y. Lu, J. Chem. Eng. Data 10 (1965) 216.
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