Schiff base ligands and their transition metal complexes in the mixtures of ionic liquid + organic solvent: A thermodynamic study

Article abstract of DOI:10.1039/c4cp04432k

Schiff bases and their metal complexes in the mixtures of ionic liquid (IL) + organic solvent have shown great potential in attractive oxidation catalytic processes. The efficiency of such a process is strongly dependent on the various molecular interactions occurring between components. Thermodynamic properties of these systems can provide valuable information about structural interactions. Therefore, in this work, the interactions of the IL 1-hexyl-3-methylimidazolium chloride ([HMIm]Cl) with Schiff bases in organic solvents were studied through the measurements of density, viscosity, and electrical conductivity. The effect of solvent on the interactions was examined by the solutions of IL + BPIC Schiff base + solvent (C₂H₆O-C₃H₈O-C₄H₁₀O). Moreover, the influence of Schiff base ligand and Schiff base complex structures was probed by the solutions of IL + DMA + ligand (salcn/salpr/salen) and IL + DMA + complex (VO(3-OMe-salen)/VO(salophen)/VO(salen)), respectively. Using the experimental data, some important thermodynamic properties, such as standard partial molar volume (V_f,IL⁰), experimental slope (S_v), viscosity B-coefficient, solvation number (B/V_f,IL⁰), and limiting molar conductivity (Λ₀) were calculated and discussed in terms of solute-solvent (IL-DMF/alcohol) and solute-cosolute (IL-Schiff base) interactions.

Full text of DOI:10.1039/c4cp04432k

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Page 1 of 37
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Schiff base ligands and their transition metal complexes in the
mixtures of ionic liquid + organic solvent: thermodynamic study
Hemayat Shekaari,*† Amir Kazempour‡ and Maryam Khoshalhan§
†
Department of Physical Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz, Iran
‡
Young Researchers and Elite Club, Tabriz Branch, Islamic Azad University, Tabriz, Iran
§
Department of Chemistry, Faculty of Science, University of Guilan, Rasht, Iran
* Corresponding author, Tel: +98ꢀ41ꢀ33393139; Fax: +98ꢀ41ꢀ33340191.
Eꢀmail addresses: hemayatt@yahoo.com; hemayatt@tabrizu.ac.ir (H. Shekaari).

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Abstract
Schiff bases and their metal complexes in the mixtures of ionic liquid (IL) + organic solvent have
presented great potential in attractive oxidation catalytic processes. The efficiency of such
process is strongly dependent on the various molecular interactions existing between
components. Thermodynamic properties of these systems can provide valuable information about
structural interactions. Therefore, in this work, the interactions of the IL 1ꢀhexylꢀ3ꢀ
methylimidazolium chloride ([HMIm]Cl) with Schiff bases and organic solvents were studied
through the measurements of density, viscosity, and electrical conductivity. The effect of solvent
structure on the interactions was examined by the solutions of IL + BPIC Schiff base + solvent
(C2H6O/C3H8O/C4H10O). Moreover, the influence of structure of Schiff base ligands and Schiff
base complexes was probed by the solutions of IL + DMA + ligand (salcn/salpr/salen) and IL +
DMA + complex (VO(3ꢀOMeꢀsalen)/VO(salophen)/VO(salen)), respectively. Using the
experimental data, some important thermodynamic properties, such as standard partial molar
volume (Vφ0 ), experimental slope (Sv), viscosity Bꢀcoefficient, solvation number ( B/Vφ0,IL ), and
,IL
limiting molar conductivity ( Λ0 ) were calculated and discussed in terms of soluteꢀsolvent (ILꢀ
DMF/alcohol) and soluteꢀcosolute (ILꢀSchiff base) interactions.
Keywords: Ionic liquid, Schiff base, Density, Viscosity, Conductivity, Ionꢀsolvent interaction.
2

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1. Introduction
Schiff bases are extensively used as analytical reactants since they allow simple and inexpensive
determination of several organic and inorganic substances.1 They also form stable complexes
with metals that perform important role in biological systems. Due to their interest in analytical
and bioinorganic chemistry, complexes of tetraꢀcoordinated Schiff bases and transition metals are
widely studied. Such complexes present many applications in catalysis and oxygen storage
devices2 and also present antitumoral, antiviral, and antibacterial activity3 and are used as
mimetic systems for enzyme models.4 Several Schiff bases have recently been investigated as
corrosion inhibitors for various metals and alloys in acid media.5–9 The existing data show that
these inhibitors act by adsorption on the metal/solution interface.10
One of the major drawbacks of the homogeneous catalysts is the difficulty in separating
catalysts from the reaction mixture at the end of the process. The possible contamination of
catalyst in the product also restricts their use in industry. Recently, ionic liquids have shown
unique class of reaction media for catalytic processes. The number of catalytic reactions
involving ionic liquids is rapidly increasing. These liquids offer promising solutions to the
problems associated with conventional organic solvents, and the potential advantages may
include enhanced reaction rates and facile separation of products and catalyst recovery.11–14
Because most transition metal complexes are soluble in ionic liquids, the ionic liquids are
particularly suitable for the isolation of catalysts from products. It will be desirable to have a
high solubility of the reactants combined with a low solubility of the main products in the ionic
liquid phase. In such a system, the removal of the reaction products from the ionic liquid phase
can totally lead to high yields. Also ionic liquids referred to designer solvents because their
properties can be tailored by the variation of the structure and the composition of the cations and
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anions. This advantage permits to design ionic liquids with the possibility to alter the solubility of
organic reactants in the ionic liquids.
Moreover, the addition of coꢀsolvents has been found to strongly affect various physicoꢀ
chemical properties of ionic liquids. The mixed organic solvents and ionic liquids can be used
advantageously to achieve homogeneous systems in which the reactants and catalysts have the
best solubility. Therefore, various thermophysical properties of the systems composed of Schiff
base, ionic liquid, and molecular solvents can provide useful information about ionꢀion and ionꢀ
solvent interactions that probably characterize their solution thermodynamics and structure in
solution phase and such information would permit developing a suitable experimental procedure
for a convenient biphasic reusable catalytic system.
In this article, we synthesized several Schiff base ligands and their oxovanadium
complexes and reported some of their thermodynamic properties in the mixtures of ionic liquid
([HMIm]Cl) with different organic solvents (C2H6O, C3H8O, C4H10O, and DMF). The results
were discussed in terms of ILꢀsolvent and ILꢀSchiff base interactions. In addition, the influence
of the solvent structure, temperature, and the structure of Schiff base ligands and their complexes
were examined on the interactions.
2. Experimental section
2.1 Materials
The solvents used in this work are C2H6O (>99.5%, Merck), C3H8O (>99%, Merck), C4H10O
(>99%, Merck), and DMF (99.9%, Merck), and the chemicals used to synthesize and purify the
ionic liquid ([HMIm]Cl) are Nꢀmethylimidazole (>99%, Merck), 1ꢀchlorohexane (>99%, Merck),
and ethyl acetate (99.8%, Merck). The materials for synthesis of Schiff bases and their complexes
are pyridineꢀ2ꢀaldehyde (>99%, Merck) and 1,2ꢀcyclohexanediamine (>99%, Merck) for BPIC,
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salicylaldehyde (2ꢀhydroxybenzaldehyde) (99%, Fluka) and ethylenediamine (99.9%, Merck) for
salen, 1,3ꢀdiaminopropane (>99%, Merck) and salicylaldehyde for salpr, 1,2ꢀ
diaminocyclohexane (>99%, Merck) and salicylaldehyde for salcn, vanadyl acetylacetonate,
which was added to salen, for VO(salen), 3ꢀOMeꢀsalen and vanadyl acetylacetonate for VO(3ꢀ
OMeꢀsalen), and salophen and vanadyl acetylacetonate for the synthesis of VO(salophen).
2.2 General method for preparation of the Schiff base ligands
The bisꢀsalicyldimine Schiff base ligands: salen [N,N′ꢀbis(salicylidene)ꢀethylenediamine], salpr
[N,N′ꢀbis(salicylaldehyde)ꢀ1,3ꢀdiaminopropane],
and
salcn
[N,N′ꢀ1,2ꢀcyclohexylꢀ
bis(salicyldiamine)] were prepared as follows:15,16
A solution of salicyladehyde was added drop wise onto a solution of the amine in 50ml ethanol in
molar ratio of 1:1 or 1:2 for a period of 1h. The reaction mixture was refluxed for 1h with
continuous stirring. The reaction was left to cool where coloured compounds were filtrated off
and washed several times with water and ethanol and dried in vacuum desiccator.
The Schiff base BPIC [N,N′ꢀbis(2ꢀpyridylmethylidene)ꢀtransꢀ1,2ꢀdiiminocyclohexane]
was also prepared as follows:
The pyridineꢀ2ꢀaldehyde was added slowly to 1,2ꢀcyclohexanediamine in ethanol solution. After
stirring the mixture gently for 1 h and the removal of the ethanol by rotary evaporation, an
orangeꢀyellow residual liquid product was obtained. The product was extracted with hot hexane
several times. After cooling, an orange product was obtained and recrystallized from diethyl
ether. The schematic reactions of the ligands preparation are given as follows:
BPIC: elemental analysis. Calc. for C18N4H20: C, 73.93; H, 6.91; N, 19.16. Found: C, 73.95; H,
6.92; N, 19.32.
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N
N
N
O
EtOH
N
N
H
H2N
NH2
Reflux
Salen: elemental analysis. Calc. for C16N2O2H16: C, 71.61; H, 6.02; N, 10.44. Found: C, 71.40; H,
6.20; N, 10.30.
OH HO
NH2
H2N
OH
EtOH
N
N
H
O
Reflux
Salpr: elemental analysis. Calc. for C17N2O2H18: C, 72.32; H, 6.43; N, 9.92. Found: C, 72.11; H,
6.24; N, 9.78.
OH
HO
OH
EtOH
H2N
NH2
H
N
N
Reflux
O
Salcn: elemental analysis. Calc. for C20N2O2H22: C, 74.51; H, 6.88; N, 8.69. Found: C, 74.34; H,
6.57; N, 8.85.
OH
HO
NH2
NH2
N
N
OH
EtOH
H
Reflux
O
2.3 General method for the preparation of VO complexes
The vanadium complexes of Schiff base were prepared as follows:
The required weights of the inorganic salts were dissolved in methanol (20 ml) for Schiff base
and refluxed with the desired weight of the ligand in methanol (20 ml) for Schiff base. The
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reaction mixture was refluxed with stirring. The corresponding solid complexes were filtered,
washed several times with methanol and dried in vacuum desiccator. The schematic reactions of
the VO complexes preparation are given as follows:
VO(salen): elemental analysis. Calc.for C20N2O2H22: C, 57.67; H, 4.23; N, 8.41. Found: C, 57.50;
H, 4.10; N, 8.50. IR (KBr, cmꢀ1): υ 989 (V=O), υ 1623 (C=N).
O
O
N
O
N
OH HO
VO(acac)2
V
Reflux , MeOH
N
N
VO(salophen): elemental analysis. Calc. for C20N2O3VH14: C, 58.13; H, 3.41; N, 6.78; V, 12.33.
Found: C, 58.00; H, 3.32; N, 6.89; V, 12.28. IR (KBr, cm−1): υ 980 (V=O), υ 1630 (C=N).
O
O
N
O
N
OH HO
VO(acac)2
V
Reflux , MeOH
N
N
VO(3ꢀOMeꢀsalen): elemental analysis. Calc. for C18N2O5VH18: C, 54.96; H, 4.62; N, 7.12; V,
12.95. Found: C, 54.85; H, 4.70; N, 7.00; V, 12.89.
OMe
O
MeO
O
OMe
MeO
O
V
OH HO
VO(acac)2
Reflux , MeOH
N
N
N
N
2.4 Synthesis of the ionic liquid
1ꢀHexylꢀ3ꢀmethylimidazolium chloride was prepared by the reaction of Nꢀmethylimidazole with
an excess amount of 1ꢀchlorohexane in a round bottom flask mixed by a magnetic stirrer under a
nitrogen atmosphere. The reaction mixture was stirred for one week, and finally, the crude
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product was separated from reagents and then washed three times with fresh ethylacetate. The
0
removal of residual volatile compounds from the ionic liquid was done in high vacuum at 60 C
using a rotary evaporator for at least 4 h at reduced pressure. The obtained ionic liquid had purity
1
greater than 98% verified by H NMR spectroscopy
.
The ionic liquid was used after vacuum
desiccated for at least 48 h to remove trace amount of moisture. Water content found by Karl
Fischer method in the ionic liquid was less than 0.2%. The schematic reaction of the ionic liquid
preparation is given as follows:
1HNMR (300 MHZ, CDCl3) (ppm): 10.21 (s, 3H), 7.52 (d, 1H, J= 1.5 HZ), 7.28 (d, 1H, J= 1.5
HZ), 4.02 (t, 2H, J= 12.9 HZ), 3.83 (s, 1H), 1.59 (m, 2H), 0.99 (t, 3H, J= 6.6).
CH3
Cl
N
n-C6H13Cl
N
N
N
H3C
2.5 Instruments and methods
Densities were measured with a vibratingꢀtube densimeter (Anton Paar, DMA 4500 M),
calibrated at the experimental temperatures with doubly distilled water at atmospheric pressure.
The temperature was automatically kept constant with an accuracy of ±1×10ꢀ2 K using the builtꢀ
in Peltier technique. The stated repeatability and uncertainty of the densities were ±1×10ꢀ5 g cmꢀ3
and ±5×10ꢀ5 g cmꢀ3, respectively. However, the estimated uncertainty of the measured densities
tested by the solutions with known densities was found to be less than ±3×10ꢀ5 g cmꢀ3 for most of
the solutions.
Viscosities were measured using an Ubbelohdeꢀtype viscometer, calibrated at the
experimental temperatures with doubly distilled water. The clean, dried viscometer was filled
with experimental liquid and placed vertically in a glass sided thermostat maintained constant to
±0.01 K. After attainment of thermal equilibrium, the efflux times of flow of liquids were
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recorded with a digital stopwatch correct to ±0.01 s. The maximum uncertainty of the solutions
viscosities was estimated to be ±0.006 mPa s.
Specific conductivities were measured using a conductivity meter (Metrohm model 712,
Switzerland) with accuracy of ±0.5%. The cell constant was calculated by repeated
measurements of KCl solution in 0.01 mol kg−1. About 50 ml of solvent (Schiff base
ligand/complex + organic solvent) was filled into the conductivity cell and the cell was closed.
Weighting was performed by an analytical balance (Sartrious, AG TE214S) with precision
±1×10−4 g. After the measurement of the solvent conductivity, a weighed amount of pure ionic
liquid ([HMIm]Cl) was added with a syringe to the cell containing solvent and the measurement
was repeated. To minimize the risk of the presence of concentration gradients in the cell, the
solution was continuously stirred with a magnetic stirrer. The water from a thermostatically
regulated bath was circled around the cell with double wall to maintain the temperature with an
uncertainty ±0.02 K.
3. Data processing
3.1 Density
The measured densities of the solutions (Table 1) were used to calculate the apparent molar
volumes (Vφ,IL ) of the ionic liquid ([HMIm]Cl) at
T = 298.15, 303.15, 308.15, and 313.15 K
using the following equation:
MIL 1000(d − d0 )
Vφ
=
−
,
(1)
,IL
d
mILdd0
where MIL and mIL are the molar mass and the molality of the IL, and d and d0 are the densities of
ternary solutions (IL + Schiff base + solvent) and binary mixtures (Schiff base + solvent),
respectively. The obtained values for apparent molar volume are shown in Table 1. The standard
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partial molar volumes (Vφ0,IL ) of the IL were calculated by the extrapolation of Vφ against mIL to
,IL
zero concentration using the following equation:
Vφ = Vφ0,IL + SvmIL
,
(2)
,IL
where Sv is experimental slope and represents soluteꢀcosolute and ionꢀion interactions. We know
that the use of purely empirical Masson equation to extrapolate the apparent molar volume at
infinite dilution is at best a crude approximation. The proper method is to use the RedlichꢀMayer
and Pitzer equations. However, these equations make use of the theoretical slope, and this
approach requires accurate data of the pressure derivative of the dielectric constant of the solvent.
These data for organic solvents are not available or available at 298.15 K only. Since the value of
the pressure derivative of the relative permittivity of the solvent seems to be very sensitive to
temperature and our data cover the temperature range from 298.15 to 313.15 K, we decided to fit
our data to the simplest equation.
The temperature variation of Vφ,IL values is expressed as follows:
Vφ0,IL = a0 + a1T + a2T 2
,
(3)
where a0, a1, and a2 are regression coefficients. Differentiation of Eq. (3) with respect to
temperature at constant pressure gives the partial molar expansivities of the IL ( Eφ0,IL ) by the
following relation:
0





∂Vφ
∂T
,IL 
Eφ0
=
= a1 + 2a2T .
(4)
,IL

P
The sign of second derivatives of Vφ0 with respect to temperature at constant pressure is
,IL
used to discuss the structureꢀbreaking or ꢀmaking tendency of the ionic liquid in the solutions.
This equation is given as:
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2
0





,IL 

∂ Vφ

0 
∂C


P 

= −T
,
(5)
∂P
∂T 2

T
P
where CP0 is the heat capacity of the ionic liquid at infinite dilution.
The isobaric thermal expansion coefficients of the IL at infinite dilution (
determined as follows:
α
IL ) were also
∂Vφ0
,IL )P =
∂T
Eφ0
,IL
1
αIL
=
(
.
(6)
Vφ0
Vφ0
,IL
,IL
3.2 Viscosity
Viscosity of the solutions (η ) is given by the following equation:
η
d
K
t
= Lt −
,
(7)
where
d
is density,
t is the efflux time of solutions, and L and K are viscometer constants. The
values of
L
and K
were obtained, respectively, as 3.9648×10ꢀ6 mPa cm3 gꢀ1 and 2.1995×10ꢀ3 mPa
s2 cm3 gꢀ1 using the known viscosity values of double distilled water.17 The viscosity data (Table
3) were analysed using the Jones–Dole viscosity equation:
η
/
η0 =1+ Ac1/ 2
0 are the viscosities of ternary solutions (IL + Schiff base + solvent) and binary
mixtures (Schiff base + solvent), respectively. is the molarity of the IL, and , and are
empirical constants known as the viscosity ꢀ, ꢀ, and ꢀcoefficients. According to conventional
technique of the viscosity coefficient determination, the ꢀ and ꢀcoefficients can be estimated
from the experimental viscosity data by extrapolating the following function:
+
Bc
+
Dc2
,
(8)
where
η and η
c
A
,
B
D
A
B
D
B
D
η
/
η
0 −1− Ac1/ 2
B
+
Dc
=
(9)
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to zero concentration using the value of
A, which can be obtained theoretically or as the intercept
of the dependence [(η /η0 ) −1]/c
1/ 2 on c1/ 2 as follows:
η
/
η0
−1
=
A
+
Bc1/ 2
.
(10)
c1/ 2
The
A
value can be calculated theoretically as follows:18
1
−1/ 2
A
=
A∗η0−
Fe2 N1A/ 2 (1
(ε
0T
)
f
(11)
(12)
1
−1/ 2
A∗
=
+
2)(12
π εk)
)− (
2
z+ z−
(
λ∞+
+
λ∞−
)
4(λ∞+
− )
λ∞−
f
=
[1
−
2 ],
(13)
4(2
+
2)(λ∞+ λ∞−
)
(1
+
2)2 (λ∞+ λ∞−
+ )
where
infinite dilution of the ions and the ion charges (z±),
constant, and is vacuum permittivity.
In this article, the ꢀcoefficients were obtained by the intercept of Eq (10) and used to
calculate the ꢀ and ꢀcoefficients by Eq (9).
3.3 Conductivity
A
∗=1.113×10ꢀ5 C2 m1/2 K1/2 molꢀ3/2
,
f
is the function of the equivalent conductivities (
λ
∞± ) at
ε
0 is dielectric constant, is Boltzmann
k
ε
A
B
D
The molar conductivities of [HMIm]Cl in the mixtures of Schiff base + solvent were calculated
by the following equation:
1000
κ
Λ =
is the specific conductivity of the ionic liquid solutions. The obtained
included in Table 5. Limiting molar conductivities (
,
(14)
c
where
κ
Λ
values are
Λ
0 ) and ion association constants (KA) of the
IL were obtained by leastꢀsquares fitting the experimental molar conductivities to a wellꢀknown
conductivity equation, named as low concentration Chemical Model (lcCM).19 Three adjustable
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parameters: limiting molar conductivity (
parameter ( ) are defined from the analysis of conductivity data based on this model as the
following set of equations:
Λ0 ), ion association constant (KA), and distance
R
1/ 2
Λ
=
α
[
Λ0
−
S
(c
α
)
+
Ec
α
ln(
c
α
)
+
J1c
α
+
J2
(c
α
)3/ 2 ]
(15)
(16)
1−α
α
KA
=
2cγ ±2
κ
q
lnγ± = −
(17)
(18)
1
+
κ
R
16
×
103 N A z 2e2
ε0εk BT
αc
κ2
=
z 2e2
q
=
,
(19)
8
πε0εk BT
and Λ0 are the molar conductivities at molarity
fraction of oppositely charged ions acting as ion pairs, KA
constant of ionic liquid, distance parameter, and the corresponding mean activity coefficient of
the free ions, respectively. In Eq (15), is the coefficient of the DebyeꢀHückelꢀOnsager, and
depends only on the properties of the solvent and the charge of the ions. J1 and J2 depend on the
same parameters as does as well as the distance parameter. The J1, and J2 values required for
where
Λ
c
and at infinite dilution, 1ꢀ
α
is the
,
R, and γ± are the ion association
S
E
E
E,
calculations were taken from literature.19 The rest quantities have the usual meaning. Threeꢀ
parameter fits of molar conductivity data yield the ionꢀassociation constant (KA), the limiting
molar conductivity (Λ0), and the distance parameter (R) by nonꢀlinear leastꢀsquares iteration
procedure. The starting Λ0 value were obtained from DebyeꢀHückelꢀOnsager extrapolation of the
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data. The calculation was made by finding the Λ0
deviation ) as follows:
,
KA, and
R
values that minimized the standard
σ(Λ

1/ 2
σ
(
Λ
) =
[
Λexp ꢀ
Λ
calc ]2 /(n ꢀ p)
,
(20)
∑




where
n and p show the number of experimental data and the obtained parameters, respectively.
4. Results and discussion
4.1 Volumetric properties
Volumetric properties of ternary solutions give important information about structural changes
and different kinds of interactions happening in the solution. These interactions can be affected
by many elements, such as the solvent, the solute, the solution concentration, and the
temperature.
4.1.1 Effect of solvent on the volumetric properties
To examine the effect of solvent structure on the interactions of the studied ternary systems, we
obtained the values of experimental slopes (Sv) and standard partial molar volumes (Vφ0IL ) of the
,
ionic liquid ([HMIm]Cl) in the mixtures of BPIC Schiff base ligand (0.05 mol kgꢀ1) +
C2H6O/C3H8O/C4H10O at temperatures ranging from 298.15 K to 313.15 K. The obtained values
have been reported in Table 2, and the solvent effect on the Vφ0IL values is graphically presented
,
by Fig. 1. In the studied systems, the Sv values show the soluteꢀcosolute interactions between the
IL and the ligand and also the soluteꢀsolute or the ionꢀion interactions between the ions of the IL.
Moreover, the Vφ0IL values display the soluteꢀsolvent interactions mainly between the IL and the
,
alcohol. These interactions can be classified into three major kinds including (i) nonpolarꢀ
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nonpolar interactions between the alkyl chain of the IL cation and the alkyl chain of alcohol, (ii)
hydrogen bond between the H atom of alcohol and the Clꢀ anion of the IL, and (iii)20 interactions
between the O atom of alcohol and the cationic ring πꢀelectrons. Table 2 shows that the
Vφ0IL values increase with the elongation of the alcohol chain and also increase with the increase
,
of temperature. This observation indicates that the soluteꢀsolvent interactions are favoured at
higher temperatures and when the alcohol has longer alkyl chain. According to the classified ILꢀ
alcohol interactions, it seems that the elongation of alcohol alkyl chain has two opposite effects
on the soluteꢀsolvent interactions. On the one hand, the alcohols under investigation exhibit
dipole moments in the sequence C2H6O > C3H8O > C4H10O reflecting their individual abilities to
form hydrogen bonds. Therefore, the (ii)ꢀtype interactions are weakened when the alcohol chain
is lengthened, which results in the lower Vφ0 values. On the other hand, butanol with a long
,
IL
alkyl chain feels less electron deficit on its OꢀH bond and as a sequence shows stronger O ̶ πꢀ
electrons interactions. Moreover, the nonpolarꢀnonpolar interactions between the alkyl chains of
the IL and the alcohol are intensified by the increase of alcohol chain length resulting in the
higher Vφ0IL values. The increasing trend found in the Vφ0IL values implies that the (i)ꢀ and (iii)ꢀ
,
,
type interactions predominate over (ii)ꢀtype interactions in the studied systems. It is also clear
from Table 2 that the Vφ0IL values increase with temperature. It seems that the anionꢀalcohol
,
interaction has a significant portion in the increasing Vφ0IL values with temperature due to the
,
smaller molecular weight of the anion. At high temperatures, the hydrogenꢀbonding formation
between the alcohol and the Clꢀ anion may be favoured due to the faster molecular movement of
the anion and the alcohol that would lead to a higher number of molecules with energy to
overcome the energy barrier for hydrogenꢀbonding formation. The increase of temperature makes
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the small anions get into the interstices within hydrogen bonded clusters of alcohol molecules and
interact with them.
Table 2 also indicates that the Sv values are positive and decrease with the elongation of
alcohol alkyl chain but increase as temperature increases. The positive Sv values show that there
exist interactions between the ligand and the IL, but these interactions are weakened as the
alcohol chain is lengthened. We previously discussed21 that the interactions between the Schiff
base and ionic liquid can be categorized as follows: (i) the polar–ionic interactions between the
polar
polar groups of the Schiff base and the imidazolium ring of IL, (iii) polar–nonpolar interactions
between the ꢀgroup of the Schiff base and the nonpolar alkyl chain of IL, and (iv) nonpolar–
Nꢀgroups of the Schiff base and the ions of IL, (ii) polar–polar interactions between the
N
nonpolar interactions between the nonpolar groups of the Schiff base and the alkyl chain of IL.
Of these interactions, those of types (i) and (ii) make a reduction in the electrostriction effect and,
as a sequence, lead to positive transfer volumes, while the interactions of types (iii) and (iv) lead
to negative transfer volumes. The negative values of transfer volumes obtained in our earlier
paper21 indicate that the polar–nonpolar group and nonpolar–nonpolar group interactions
predominate over the polar–ionic group and polar–polar group interactions between the Schiff
base and ionic liquid. The fact that the experimental slopes increase with the decrease of alcohol
chain length could be related to the reduced nonpolar–nonpolar interactions of the cation and the
shortꢀchain alcohol that results in an enhancement in the ILꢀSchiff base interactions.
The partial molar expansibilities ( Eφ0 IL ) measure the variation of the volume of the ionic
,
liquid with temperature. These values are included in Table 2. Clearly, the Eφ0 IL values for each
,
alcohol are positive and decrease with temperature rising from 298.15 K to 313.15 K. The
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positive Eφ0 values suggest that at high temperatures, alcohol molecules are loosely held around
,
IL
the IL and thus there is an increase in the standard partial molar volumes.
The sign of second derivatives of Vφ0IL with respect to temperature at constant pressure is a
,
better parameter to discuss the structureꢀbreaking or ꢀmaking tendency of the IL in the solutions.
For a structureꢀbreaking solute, the left side of Eq (5) should be positive and (∂2Vφ0IL /∂T 2 )P
,
consequently should be negative for structureꢀbreaking and positive for structureꢀmaking solutes.
The values of (∂2Vφ0IL /∂T 2 )P for the IL (Table 2) were found to be negative, which means that the
,
IL acts as a structureꢀbreaker in the alcohol mixtures.
Cabani et al.22 have shown that the coefficient of thermal expansion (
understanding the soluteꢀsolvent interactions. From Table 2, it is observed that the αIL values of
the ionic liquid in C3H8O mixtures at all temperatures except for = 313.15 K are greater than
α ) can be used for
T
those in C2H6O and C4H10O mixtures. This is consistent with the results of the temperature
variation of the Vφ0IL values.
,
4.1.2 Effect of Schiff base ligand structure on the volumetric properties
To study the effect of ligand structure on the volumetric properties, we measured densities of the
solutions composed of [HMIm]Cl + salcn/salpr/salen (0.05 mol kgꢀ1) + DMF at
T = 298.15 to
313.15 K. Using Eqs (2) and (3), the values of experimental slopes and standard partial molar
volumes of the ionic liquid were obtained and reported in Table 2. It is obvious that the
Vφ0IL values in pure DMF are greater than those in the mixed solvent and decrease in the order
,
salcn > salpr > salen (see Fig. 2). The most likely reason for the observed trend may be attributed
to molecular volume of the studied ligands. This volume follows the above order. It seems that
the large volume does not allow the ligand to approach the ions, especially the cation, and
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interact with them. This steric strain increases in the case of salcn due to the presence of a hexyl
cycle on its structure. As a result, the weaker interaction of the IL with salcn leads to an
enhancement in the ionꢀsolvent interactions evident by the higher Vφ0IL values in salcn mixtures.
,
Table 2 shows that the Sv values decrease as the sequence salen > salpr > salcn, which is
the inverse of the order observed for the Vφ0IL values. This means that an increase in the soluteꢀ
,
solvent interactions is normally accompanied by a reduction in the soluteꢀcosolute interactions. It
is also clear that the experimental slopes increase with temperature. It seems that at high
temperatures, some loosely bound DMF molecules are released from the secondary solvation
shells of the ions, and hence the ILꢀligand interactions can become stronger with the increase of
temperature.
The values of partial molar expansibilities ( Eφ0 IL ) of the IL in ligand + DMF mixtures are
,
given in Table 2. Clearly, the Eφ0 IL values at all temperatures are negative that means the standard
,
partial molar volumes decrease with the increase of temperature (see Fig. 2). At high
temperatures, some of DMF molecules may be hydrolyzed back into formic acid and
dimethylamine, which causes to release a portion of the solvent molecules from the solvation
sphere of the IL.
The (∂2Vφ0IL /∂T 2 )P values of the IL in ligand + DMF mixtures are shown in Table 2.
,
These values are all negative showing that the IL acts as a structureꢀbreaker in the mixtures.
The coefficient of thermal expansion (
IL values are all negative and become more negative for salcn and salen but less negative for
salpr at higher temperatures. The fact that the coefficients of thermal expansion have a different
αIL ) are also given in Table 2. It is clear that
the
α
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order of magnitude for the ligand mixtures suggests a thermal behaviour practically dependent of
the ligand nature.
4.1.3 Effect of Schiff base complex structure on the volumetric properties
The standard partial molar volumes of the IL in the binary mixtures of DMF + vanadium Schiff
base complex (VO(3ꢀOMeꢀsalen), VO(salophen), and VO(salen)) at different temperatures are
given in Table 2. Surprisingly, it was observed that the Vφ0IL values increase with increasing
,
temperature (see Fig. 3), which this tendency is opposite the trend we previously observed in the
case of Vφ0 values in the Schiff base ligand mixtures. It is also clear that the Vφ0IL values in the
,
IL
,
complex mixtures follow the order VO(3ꢀOMeꢀsalen) > VO(salophen) > VO(salen), showing that
the standard partial molar volumes have greater values in the presence of larger VO complex.
The comparison of the experimental slopes of the complex solutions with those of the
ligand solutions, especially the salen ligand and its corresponding vanadium complex, reveals
their different thermal behavior in the studied mixtures. Table 2 shows that the Sv values of the
complex mixtures decrease with the increase of temperature, while these values for the ligand
mixtures increase with temperature. It seems that the coordination of vanadium to the Schiff base
ligand changes the thermal behavior of the obtained complex.
The values of partial molar expansibilities ( Eφ0 IL ) of the IL in DMF + complex mixtures
,
are given in Table 2. It is obvious that the Eφ0 IL values at all temperatures are positive that means
,
the standard partial molar volumes increase at higher temperatures. The (∂2Vφ0IL /∂T 2 )P values are
,
also given in Table 2. These values are negative showing that the IL behaves as a structureꢀ
breaker in DMF + complex mixtures.
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The coefficient of thermal expansion (
αIL ) were also calculated and reported in Table 2.
It is clear that the IL values are all positive and decrease for VO(3ꢀOMeꢀsalen) and VO(salen)
α
but increase for VO(salophen) at higher temperatures. Moreover, the greatest values of thermal
coefficient were obtained for VO(3ꢀOMeꢀsalen) at lower temperatures and for VO(salophen) at
higher temperatures.
4.2 Viscosity B-coefficients
Viscosity is one of the key transport properties of electrolyte solutions. The accurate viscosity
data (viscosity
solvent and ion–ion interactions. The
between the ions (ion– ion interactions) and can be theoretically calculated from Eq (11), and the
viscosity ꢀcoefficient reflects the variations of the solvation properties of ions in the solutions.
The viscosity ꢀcoefficient includes all solute–solvent and solute–solute structural interactions
that were not accounted by the ꢀ and ꢀcoefficients at high concentrations, such as high terms of
A
ꢀ and
B
ꢀcoefficients) is known to give valuable information regarding ion–
A
ꢀcoefficient depends on the Coulombic interactions
B
D
A
B
the Coulombic forces, high term hydrodynamic effect, and interactions arising from changes in
solute–solvent interactions with concentration.23 According to Donald and Jenkins24, for most
solutes, the
D
ꢀcoefficient is unimportant at
c
< 0.5 mol dmꢀ3, and the
< 0.05 mol dmꢀ3) are
Aꢀcoefficient can be
obtained if highly accurate data at sufficiently low concentrations (
c
available. The concentration range studied here overlaps the range where only the
essential. Therefore, in this work, the ꢀ, ꢀ, and ꢀviscosity coefficients were calculated and
reported in Table 4, but only the viscosity ꢀcoefficient was discussed.
4.2.1 Effect of solvent structure on the viscosity B-coefficient
Bꢀcoefficient is
A
B
D
B
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The values of viscosity
B
ꢀcoefficient of [HMIm]Cl in binary mixtures of BPIC +
values are positive
C2H6O/C3H8O/C4H10O at 298.15 K are reported in Table 4. Obviously, the
B
and increase with increasing the alkyl chain length of alcohol, which is consistent with the
observed trend in the Vφ0IL values. The viscosity
B
ꢀcoefficient provides information about ionꢀ
,
solvent interactions and their effect on the solvent structure in the vicinity of the ions. The
obtained positive values demonstrate the presence of ionꢀsolvent interactions, and these
B
interactions are stronger for C4H10O relative to C3H8O and C2H6O. This trend is probably
attributed to the increased nonpolarꢀnonpolar interactions of the IL with the longer butyl chain of
the C4H10O alcohol.
The solvation number of the IL is a better tool to study its solvation behavior. When the
IL [HMIm]Cl dissolves in alcohol, the alcohol molecules cluster around the separated ions. This
process is called solvation. Alcohol frequently attaches to the cation ions by coꢀordinate bonds (a
shared pair of electrons in which both electrons come from the same atom) and attaches to the Clꢀ
anions using hydrogen bonds. The values of solvation number are given in Table 4. It is clear
from this table that the solvation numbers of the IL in the presence of alcohols has the sequence
C4H10O > C3H8O > C2H6O. Although the solvation number of the IL does not show the exact
number of solvent molecules attached to the IL (because the solvation sphere of the ions in the
studied ternary mixtures may not include alcohol molecules only), the resulted order for the
solvation numbers indicates that the number of C4H10O molecules solvate each ion is more than
that of the other two alcohols. Due to the larger volume of C4H10O molecule and its greater
number in the solvation sell of the IL, the radius of the solvation sphere of the ions must be larger
in the C4H10O mixtures, which is demonstrated by the greater Vφ0IL values of the IL in the
,
presence of C4H10O.
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4.2.2 Effect of the structures of ligand and complex on the viscosity B-coefficient
The values of the viscosity ꢀcoefficient of [HMIm]Cl in the binary mixtures of DMA + ligand
(salcn/salpr/salen) and DMA + complex (VO(3ꢀOMeꢀsalen)/VO(salophen)/VO(salen)) at 298.15
K are reported in Table 4. This table shows that the values of the IL in the ligand mixtures
follow the order salcn > salpr > salen, which verifies the obtained volumetric results. Table 4 also
indicates that the viscosity ꢀcoefficients of the IL in the complex mixtures increase with the size
of complex as the order VO(3ꢀOMeꢀsalen) > VO(salophen) > VO(salen), which again confirms
the volumetric results. It is also clear that the viscosity ꢀcoefficient in pure DMF is greater than
B
B
B
B
that in the mixed solvents. This shows that the solvation of the ions decreases in the presence of
the Schiff base ligand or complex.
4.3 Conductivity
The conductance studies of electrolytes in solutions are of great importance for obtaining
information about the intermolecular interactions existing in the solutions.
4.3.1 Effect of solvent on the limiting molar conductivities
The values of limiting molar conductivity ( Λ0 ) of [HMIm]Cl in the binary mixtures of BPIC +
C2H6O/C3H8O/C4H10O and also in the pure alcohols at 298.15 K are given in Table 6. This table
shows that the limiting molar conductivities of the studied IL in pure alcohols are generally
greater than those in the mixed solutions. This behavior is due to the fact that the viscosity of
medium increases as BPIC is added to the solution. Moreover, the solvated radii of the ions get
larger due to the interactions with the Schiff base. Both of theses reasons make the ionic mobility
decrease, and consequently the molar conductivity of the IL reduces in the presence of the Schiff
base. It is also obvious that the
Λ0 values of the IL decrease as the alcohol chain length increases
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in the order C2H6O > C3H8O > C4H10O. This observation is because of the fact that the nonpolarꢀ
nonpolar interactions between the alkyl chain of the IL and the chain of alcohol are strengthened
as the chain length of alcohol increases. This results in the more association of the ions and the
alcohol, which reduces the ions mobility leading to the lower
Λ0 values.
4.3.2 Effect of the structures of ligand and complex on the limiting molar conductivities
The values of limiting molar conductivity of [HMIm]Cl in the binary mixtures of DMF + ligand
(salcn/salpr/salen) and DMA + complex (VO(3ꢀOMeꢀsalen)/VO(salophen)/VO(salen)) at 298.15
K are reported in Table 6. Clearly, the
Λ0 values of the IL decrease with increasing the size of
ligand and complex. This behavior may be due to the higher viscosity of the mixture containing
the larger complex or ligand, which results in a reduction in the ionic mobility. Moreover, it can
be related to the fact that the ionic mobility decreases as the size of ligand or complex existing in
the solvation sphere of the ions increases, which results in lower limiting molar conductivities.
5. Conclusions
The study of solvent effect on the ionꢀsolvent interactions indicated that the ILꢀalcohol
interactions are strengthened as the alcohol chain length increases. It was also revealed that the
nonpolarꢀnonpolar interactions between the alkyl chain of the IL cation and the chain of alcohol
predominates over other types of ILꢀalcohol interactions. The effect of Schiff base ligand
structure on the ILꢀligand interactions was also examined, and the results showed that theses
interactions for the ligands are in the order salcn < salpr < salen, indicating that the ILꢀligand
interactions are weakened with the increase of the ligand size. This behavior was attributed to the
higher steric strain of the larger ligand that does not allow getting close enough to the IL and
interacting with it. The same trend was observed for the ILꢀcomplex interactions and this type of
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interaction decreases as the size of complex gets larger. Surprisingly, it was found that the
thermal behavior of the studied Schiff base ligands and their complexes are different. The ILꢀ
ligand interactions are strengthened with the increase of temperature, while the ILꢀcomplex
interactions are weakened at higher temperatures. It seems that the coordination of transition
metal to the Schiff base ligand changes the thermal behavior of the obtained complex.
References
1 Z. Cimernman, N. Galic and B. Bosner, Anal. Chim. Acta, 1997, 343, 145.
2 N. Chantarasiri, T. Tuntulani, P. Tongraung, R. Seangprasertkitꢀ Magee and W. Wannatong,
Eur. Poly. J., 2000, 36, 695.
3 R. Pignatello, A. Panicol, P. Mazzone, M. Pinizzotto, A. Garozzo and P. Furneri, Eur. J. Med.
Chem., 1994, 29, 781.
4 L. Guofa, S. Tongshun and Z. Yonghian, J. Mol. Struct., 1997, 412, 75.
5 H. Ju, Z.P. Kai and Y. Li, Corros. Sci., 2008, 50 (3), 865.
6 H. Derya Lece, K.C. Emregül and O. Atakol, Corros. Sci., 2008, 50 (5), 1460.
7 R.A. Prabhu, T.V. Venkatesha, A.V. Shanbhag, G.M. Kulkarni and R.G. Kalkhambkar, Corros.
Sci., 2008, 50 (12), 3356.
8 C. Küstü, K.C. Emregül and O. Atakol, Corros. Sci., 2007, 49 (7), 2800.
9 M. Elayyachy, A. El Idrissi and B. Hammouti, Corros. Sci., 2006, 48 (9), 2470.
10 A.W. Adamson, Physical Chemistry of Surfaces, John Wiley & Sons, New York, NY, USA,
1990.
11 P. Wasserscheid and T. Welton, Ionic Liquids in Synthesis. Weinheim: WileyꢀVCH, 2003.
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12 R. D. Rogers and K. R. Seddon, editors. Ionic Liquids IIIA: Fundamentals, Progress,
Challenges, and Opportunities: Properties and Structure. Washington, DC: American Chemical
Societ
13 R. Bernini, A. Coratti, G. Provenzano, G. Fabrizi and D. Tofani, Tetrahedron, 2005, 61, 1821.
14 C. Baleizao, B. Gigante, H. Garciab and A. Corma, Green Chem., 2002, , 272.
y, 2005. ACS symposium series, 901.
4
15 M.S. Masoud, A. Akelah and S.S. Kandil, Indian J. Chem., 1985, 24A, 855.
16 A.G. Ligtenbarg, R. Hage, A. Meetsma and B.L. Feringa, J. Chem. Soc. Perkin Trans., 1999,
2
, 807.
17 Gupta A and Yan DS. Viscosity of pure water 0–100. Mineral processing design and
operation; 2006, p. 690.
18 I. M. Abdulagatov, A. B. Zeinalova and N. D. Azizov, J. Mol. Liq., 2006, 126, 75.
19 M. BešterꢀRogač, N. Hauptman and J. Barthel, J. Mol. Liq., 2007, 131–132, 29.
20 K. Noack, A. Leipertz and J. Kiefer, J. Mol. Stru., 2012, 1018, 45.
21 H. Shekaari, A. Bezaatpour and M. Khoshalhan, J. Chem. Eng. Data, 2011, 56, 4164.
22 S. Cabani, G. Conti and E. Matteoli, J. Solution Chem., 1976, 5, 751.
23 I. M. Abdulagatov, A. B. Zeinalova and N. D. Azizov, J. Mol. Liq., 2006, 126, 75.
24 H. Donald and B. Jenkins, Chem. Rev., 1995, 95, 2695.
25 R. Sadeghi and N. Ebrahimi, J. Phys. Chem. B, 2011, 115, 13227.
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Figure Captions
Fig. 1 Standard partial molar volumes (Vφ0IL ) of the IL [HMIm]Cl in the mixtures of BPIC Schiff
,
base ligand + alcohol (●C2H6O, ■C3H8O, and ▲C4H10O) at T = 298.15ꢀ313.15 K.
Fig. 2 Standard partial molar volumes (Vφ0IL ) of the IL [HMIm]Cl in the mixtures of DMA +
,
Schiff base ligand (●salen, ■salpr, and ▲salcn) at T = 298.15ꢀ313.15 K.
Fig. 3 Standard partial molar volumes (Vφ0IL ) of the IL [HMIm]Cl in the mixtures of DMA +
,
Schiff base complex (●VO(salen),
313.15 K.
■VO(salophen), and ▲VO(3ꢀOMeꢀsalen)) at T = 298.15ꢀ
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Table 1 Densities (
d) and apparent molar volumes (Vφ IL ) of the IL [HMIm]Cl in binary mixtures
,
of Schiff base (0.05 mol kgꢀ1) + organic solvent at
T
= 298.15ꢀ313.15 K
mIL
T = 298.15 K
T = 303.15 K
T = 308.15 K
T = 313.15 K
mol kgꢀ1
d
d
d
d
Vφ
Vφ
Vφ
Vφ
,IL
,IL
,IL
,IL
g cmꢀ3
g cmꢀ3
g cmꢀ3
g cmꢀ3
cm3 molꢀ1
cm3 molꢀ1
cm3 molꢀ1
cm3 molꢀ1
[HMIm]Cl + BPIC + C2H6O
0.0000
0.0242
0.0419
0.0599
0.0823
0.1019
0.1218
0.1449
0.1629
0.1772
0.2061
0.79130
0.79302
0.79425
0.79550
0.79703
0.79834
0.79965
0.80114
0.80229
0.80319
0.80499
0.78799
0.78970
0.79093
0.79217
0.79370
0.79501
0.79631
0.79780
0.79896
0.79986
0.80165
0.78467
0.78638
0.78760
0.78884
0.79036
0.79168
0.79298
0.79447
0.79562
0.79652
0.79831
0.78135
0.78305
0.78427
0.78551
0.78702
0.78833
0.78964
0.79112
0.79227
0.79317
0.79496
142.32
143.12
143.53
143.90
144.60
145.18
145.91
146.44
146.82
147.56
143.11
143.63
144.20
144.43
145.05
145.72
146.40
146.80
147.17
147.97
143.23
144.15
144.60
144.96
145.35
146.00
146.66
147.16
147.51
148.30
144.02
144.66
145.00
145.50
145.98
146.42
147.16
147.62
147.95
148.70
[HMIm]Cl + BPIC + C3H8O
0.0000
0.0242
0.0419
0.0599
0.0824
0.0986
0.1193
0.1416
0.1605
0.1797
0.2069
0.80034
0.80201
0.80321
0.80443
0.80592
0.80699
0.80832
0.80972
0.81090
0.81209
0.81374
0.79711
0.79877
0.79997
0.80118
0.80266
0.80373
0.80507
0.80648
0.80766
0.80883
0.81050
0.79387
0.79552
0.79672
0.79793
0.79941
0.80047
0.80181
0.80323
0.80441
0.80560
0.80727
0.79064
0.79229
0.79348
0.79469
0.79617
0.79723
0.79856
0.79998
0.80117
0.80237
0.80403
145.21
145.75
146.03
146.59
146.82
147.44
148.15
148.61
149.01
149.70
146.01
146.28
146.71
147.32
147.47
147.87
148.44
148.89
149.46
149.97
146.82
146.81
147.14
147.68
147.96
148.31
148.73
149.17
149.56
150.08
146.98
147.35
147.56
148.04
148.29
148.75
149.13
149.45
149.74
150.35
[HMIm]Cl + BPIC + C4H10O
0.0000
0.0217
0.0415
0.0622
0.0820
0.1013
0.1203
0.1415
0.1601
0.1820
0.2014
0.81125
0.81270
0.81400
0.81534
0.81663
0.81783
0.81905
0.82035
0.82148
0.82282
0.82400
0.80801
0.80945
0.81075
0.81210
0.81338
0.81460
0.81580
0.81713
0.81828
0.81963
0.82080
0.80477
0.80621
0.80751
0.80886
0.81014
0.81137
0.81258
0.81391
0.81507
0.81643
0.81761
0.80153
0.80297
0.80427
0.80562
0.80691
0.80815
0.80936
0.81071
0.81188
0.81325
0.81445
148.07
148.77
149.26
149.21
149.94
149.90
150.45
150.89
151.14
151.31
148.96
149.33
149.46
149.59
149.99
150.23
150.44
150.72
150.93
151.22
149.15
149.52
149.65
149.79
150.04
150.18
150.43
150.63
150.79
151.05
149.34
149.71
149.84
149.79
149.93
150.12
150.19
150.34
150.48
150.63
[HMIm]Cl + salen + DMF
0.0000
0.0204
0.0448
0.0630
0.0880
0.1014
0.1270
0.1367
0.1604
0.1795
0.2061
0.94528
0.94591
0.94663
0.94715
0.94783
0.94818
0.94883
0.94906
0.94960
0.95000
0.95055
0.94051
0.94117
0.94192
0.94246
0.94316
0.94354
0.94419
0.94444
0.94504
0.94544
0.94602
0.93576
0.93644
0.93722
0.93778
0.93851
0.93888
0.93958
0.93984
0.94045
0.94088
0.94148
0.93084
0.93156
0.93238
0.93297
0.93374
0.93415
0.93488
0.93514
0.93578
0.93626
0.93688
179.73
180.46
180.89
181.54
181.90
182.50
182.79
183.48
184.12
184.81
178.80
179.67
180.19
181.00
181.19
182.08
182.29
182.74
183.54
184.24
178.39
179.12
179.64
180.43
180.91
181.55
181.77
182.33
183.07
183.82
177.48
178.39
178.95
179.76
180.04
180.83
181.19
181.79
182.39
183.26
[HMIm]Cl + salpr + DMF
0.0000
0.0203
0.0448
0.94622
0.94682
0.94752
0.94145
0.94208
0.94281
0.93669
0.93735
0.93811
0.93183
0.93251
0.93330
181.14
181.58
180.21
180.81
179.26
180.02
178.86
179.48
27

Physical Chemistry Chemical Physics
Page 28 of 37
View Article Online
DOI: 10.1039/C4CP04432K
Table 1
mIL
(continued)
T = 298.15 K
T = 303.15 K
T = 308.15 K
T = 313.15 K
mol kgꢀ1
d
d
d
d
Vφ
Vφ
Vφ
Vφ
,IL
,IL
,IL
,IL
g cmꢀ3
g cmꢀ3
g cmꢀ3
g cmꢀ3
cm3 molꢀ1
181.93
182.35
182.74
183.48
183.83
184.07
184.49
184.75
cm3 molꢀ1
181.44
181.70
182.37
182.74
183.34
183.60
184.17
184.45
cm3 molꢀ1
180.58
181.03
181.63
182.26
182.67
182.97
183.52
183.83
cm3 molꢀ1
178.87
179.48
179.89
180.35
180.76
181.39
182.23
182.56
0.0643
0.0809
0.1003
0.1212
0.1453
0.1578
0.1792
0.1925
0.94806
0.94850
0.94900
0.94949
0.95008
0.95037
0.95085
0.95114
0.94336
0.94383
0.94433
0.94488
0.94547
0.94577
0.94625
0.94655
0.93869
0.93917
0.93970
0.94025
0.94089
0.94120
0.94171
0.94202
0.93391
0.93441
0.93498
0.93556
0.93618
0.93650
0.93701
0.93733
[HMIm]Cl + salcn + DMF
0.0000
0.0206
0.0470
0.0607
0.0823
0.0970
0.1251
0.1452
0.1602
0.1803
0.2054
0.94658
0.94715
0.94786
0.94822
0.94879
0.94916
0.94987
0.95036
0.95073
0.95120
0.95178
0.94190
0.94249
0.94323
0.94361
0.94419
0.94459
0.94532
0.94582
0.94620
0.94669
0.94728
0.93718
0.93780
0.93857
0.93896
0.93956
0.93996
0.94071
0.94124
0.94163
0.94213
0.94274
0.93244
0.93308
0.93388
0.93428
0.93491
0.93532
0.93609
0.93664
0.93703
0.93754
0.93817
183.21
183.56
183.70
183.78
183.99
184.18
184.37
184.45
184.67
184.89
182.87
183.11
183.15
183.43
183.46
183.76
184.03
184.14
184.35
184.65
181.97
182.41
182.58
182.93
183.15
183.51
183.68
183.82
184.09
184.40
181.60
181.93
182.19
182.42
182.71
183.15
183.31
183.57
183.88
184.19
[HMIm]Cl + VO(salen) + DMF
0.0000
0.0202
0.0449
0.0607
0.0856
0.0989
0.1205
0.1415
0.1624
0.1779
0.1973
0.96023
0.96084
0.96156
0.96200
0.96267
0.96302
0.96357
0.96410
0.96459
0.96495
0.96538
0.95545
0.95606
0.95679
0.95724
0.95792
0.95828
0.95883
0.95936
0.95987
0.96023
0.96067
0.95071
0.95133
0.95205
0.95251
0.95321
0.95357
0.95413
0.95467
0.95519
0.95556
0.95601
0.94581
0.94643
0.94717
0.94763
0.94834
0.94870
0.94928
0.94983
0.95034
0.95073
0.95120
178.22
178.75
179.14
179.74
180.01
180.43
180.72
181.18
181.46
181.84
178.95
179.24
179.52
180.09
180.30
180.81
181.16
181.52
181.84
182.20
179.12
179.97
180.06
180.43
180.70
181.18
181.51
181.85
182.15
182.50
179.87
180.23
180.45
180.80
181.12
181.48
181.80
182.28
182.48
182.76
[HMIm]Cl + VO(salophen) + DMF
0.0000
0.0203
0.0470
0.0614
0.0845
0.1002
0.1191
0.1446
0.1588
0.1805
0.1997
0.95087
0.95148
0.95226
0.95267
0.95331
0.95374
0.95424
0.95490
0.95527
0.95581
0.95628
0.94489
0.94551
0.94630
0.94672
0.94738
0.94781
0.94833
0.94901
0.94938
0.94993
0.95041
0.94008
0.94070
0.94150
0.94191
0.94257
0.94301
0.94353
0.94421
0.94458
0.94513
0.94561
0.93491
0.93553
0.93633
0.93675
0.93742
0.93786
0.93838
0.93907
0.93945
0.94002
0.94051
179.85
180.25
180.43
180.79
180.96
181.26
181.60
181.71
181.98
182.20
180.22
180.70
180.81
181.06
181.34
181.54
181.84
182.01
182.30
182.52
180.97
181.21
181.56
181.82
181.98
182.20
182.52
182.70
183.01
183.24
181.78
182.02
182.19
182.36
182.57
182.83
183.10
183.23
183.45
183.66
[HMIm]Cl + VO(3ꢀOMeꢀsalen) + DMF
0.0000
0.0281
0.0505
0.0674
0.0859
0.1079
0.1233
0.1440
0.1641
0.1807
0.2036
0.95057
0.95134
0.95194
0.95238
0.95285
0.95340
0.95378
0.95427
0.95474
0.95512
0.95563
0.94650
0.94727
0.94787
0.94832
0.94880
0.94935
0.94973
0.95024
0.95072
0.95111
0.95164
0.94109
0.94187
0.94248
0.94293
0.94341
0.94398
0.94437
0.94488
0.94537
0.94577
0.94631
0.93626
0.93705
0.93766
0.93812
0.93861
0.93919
0.93959
0.94011
0.94061
0.94101
0.94156
182.80
182.97
183.18
183.46
183.70
183.84
184.12
184.34
184.52
184.78
183.46
183.63
183.67
183.85
184.15
184.32
184.47
184.66
184.81
185.00
183.93
184.05
184.22
184.47
184.61
184.74
184.96
185.13
185.26
185.44
184.31
184.61
184.66
184.86
184.97
185.06
185.27
185.43
185.60
185.78
28

Page 29 of 37
Physical Chemistry Chemical Physics
View Article Online
DOI: 10.1039/C4CP04432K
Table 1
mIL
(continued)
T = 298.15 K
T = 303.15 K
T = 308.15 K
T = 313.15 K
mol kg
d
d
d
d
Vφ
Vφ
Vφ
Vφ
,IL
,IL
,IL
,IL
g cmꢀ3
g cmꢀ3
g cmꢀ3
g cmꢀ3
cm3 molꢀ1
cm3 molꢀ1
cm3 molꢀ1
cm3 molꢀ1
[HMIm]Cl + DMF
0.0000
0.0226
0.0468
0.0600
0.0797
0.1002
0.1216
0.1410
0.1621
0.1781
0.2012
0.94451
0.94513
0.94578
0.94610
0.94661
0.94711
0.94762
0.94807
0.94854
0.94888
0.94934
0.93977
0.94042
0.94111
0.94147
0.94200
0.94253
0.94307
0.94354
0.94403
0.94440
0.94490
0.93567
0.93636
0.93708
0.93746
0.93801
0.93858
0.93912
0.93963
0.94014
0.94051
0.94104
0.93157
0.93230
0.93306
0.93346
0.93404
0.93463
0.93522
0.93572
0.93627
0.93667
0.93722
183.73
183.95
184.62
184.69
185.04
185.35
185.63
185.97
186.28
186.77
182.99
183.01
183.31
183.60
183.99
184.34
184.70
185.12
185.38
185.84
181.62
181.95
182.24
182.67
182.92
183.58
183.80
184.29
184.67
185.12
180.22
180.61
180.95
181.43
181.83
182.31
182.88
183.28
183.62
184.14
29