Chelation and extraction of copper(II) with 5-pyrazolone-based Schiff bases

Article abstract of DOI:10.1080/00958972.2011.553675

Copper(II) chelates of the Schiff bases (H₂L), obtained by condensation of 4-butyryl-3-methyl-1-phenyl-pyrazoline-5-one (HBMPP) with o-phenylene diamine (H₂L¹) and p-phenylene diamine (H ₂L²), have be

Full text of DOI:10.1080/00958972.2011.553675

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Chelation and extraction of copper(II)
with 5-pyrazolone-based Schiff bases
N.J. Parmar a , H.A. Barad a , B.R. Pansuriya a & R.A. Patel a
a Department of Chemistry , Sardar Patel University , Vallabh
Vidyanagar – 388 120, Dist. Anand, Gujarat, India
Published online: 06 Feb 2011.
To cite this article: N.J. Parmar , H.A. Barad , B.R. Pansuriya & R.A. Patel (2011) Chelation and
extraction of copper(II) with 5-pyrazolone-based Schiff bases, Journal of Coordination Chemistry,
64:4, 688-698, DOI: 10.1080/00958972.2011.553675
To link to this article: http://dx.doi.org/10.1080/00958972.2011.553675
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Journal of Coordination Chemistry
Vol. 64, No. 4, 20 February 2011, 688–698
Chelation and extraction of copper(II) with 5-pyrazolone-based
Schiff bases
N.J. PARMAR*, H.A. BARAD, B.R. PANSURIYA and R.A. PATEL
Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar – 388 120,
Dist. Anand, Gujarat, India
(Received 23 July 2010; in final form 22 November 2010)
Copper(II) chelates of the Schiff bases (H2L), obtained by condensation of 4-butyryl-3-methyl-
1-phenyl-pyrazoline-5-one (HBMPP) with o-phenylene diamine (H2L1) and p-phenylene
diamine (H2L2), have been prepared and characterized by elemental analyses, thermogravi-
metric analyses, magnetic measurements, diffuse reflectance spectra, IR and mass spectra, and
conductance measurements. The extractability of copper(II) with H2L in chloroform was
examined. Effective extraction was observed with 1 ꢀ 10ꢁ3 mol dmꢁ3 of ligands at pH 6.5 using
H2L1 and pH 7.0 using H2L2. The nature of the extracted species was ascertained by the slope
analysis method. The ligand can effectively be used in solvent extraction of copper(II) from
aqueous phase to organic phase.
Keywords: Ligands; Extraction; Schiff bases; 5-Pyrazolones; Copper(II)
1. Introduction
Schiff bases are important chelating agents toward metal ions for reversibly binding
oxygen [1], catalytic activity [2, 3], DNA binding or cleavages [4], photochromic
properties [5], and extraction of heavy metals [6]. Compounds containing C¼N linkages
have significant antifungal, antibacterial, and anticancer properties [3, 7]. In addition,
solvent extraction of metal chelates has been used as a separation method, applicable to
both trace and macro levels of metals [8].
Copper(II) is one of the essential elements in various biological species. However,
larger concentration in the environment severely affects aquatic and human life. There
are many extractants with special reference to ꢀ-diketones as chelating agents for metal
ions. Acetyl acetone, dibenzoylmethane, and thenoyltrifluoroacetate have been exten-
sively studied [9, 10]. Also five-membered heterocyclic ꢀ-diketones, particularly
monothiobenzoylmethane and dithiocarboxylate derivatives of 2-pyrazoline-5-one
[11], have been used. Metal complexes of Schiff bases derived from substituted
salicylaldehydes and various amines have been widely investigated [12–15].
4-Acyl-3-methyl-1-phenyl-pyrazoline-5-ones and related compounds are good extrac-
tants toward a wide variety of metal ions [16, 17]. To the best of our knowledge,
*Corresponding author. Email: njpchemdeptspu@yahoo.co.in
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2011 Taylor & Francis
DOI: 10.1080/00958972.2011.553675

Extraction of copper(II)
689
there is no report on extraction ability of Schiff bases derived from 5-pyrazolones. The
derivatives of 5-pyrazolones have remained one of our focal points of research [18–20].
Therefore in this work we have synthesized two Schiff bases by the reaction of
4-butyryl-3-methyl-1-phenyl-pyrazoline-5-one with o- and p-phenylenediamines. Their
copper(II) chelates were synthesized by template effect from the reaction of 4-butyryl-
3-methyl-1-phenyl-5-pyrazolone (HBMPP) with corresponding aromatic diamines and
Cu(NO3)2 ꢂ 3H2O in ethanol. The extraction behavior of copper(II), from an aqueous
phase to non-aqueous phase with these Schiff-base ligands (H2L), was investigated.
2. Experimental
2.1. Reagents and solution
All the chemicals were analytical grade and used as received. The 4-butyryl-3-methyl-1-
phenyl-pyrazoline-5-one (HBMPP) was prepared from the reaction of butyrylchloride
with 3-methyl-1-phenyl-pyrazoline-5-one, Ca(OH)2 suspended in 1,4 dioxane as
reported in the literature [21]. The stock solution 0.04 mol dmꢁ3 in Cu2þ was prepared
by taking 1.25 g of acetone dried pure copper foil, dissolved in 5.0 mL of fuming nitric
acid with subsequent dilution to 1 L with doubly distilled water.
2.2. Physical measurements
Elemental analysis was carried out on a Perkin Elmer 2400 SERIES-II. Mass spectra
were obtained on a JEOL SX-102(FAB) mass spectrometer at Sophisticated
Instrumentation Center, CDRI, Lucknow, India. The gravimetric oxide method for
estimation of metal was employed. Conductivity measurements were made with a
‘‘SYSTRONICS 305 conductivity bridge’’ at room temperature. Magnetic susceptibility
measurements were made on a 7304 vibrating sample magnetometer, Lake Shore, USA.
The molecular weight of the chelate of the ligand derived from p-phenylenediamine was
determined using a K-7000 KNAUER vapor pressure osmometer in DMF, calibrated
with benzil (K ¼ 3000). The thermograms of all the compounds were obtained from
25ꢃC to 350ꢃC using nitrogen flux with a SDT 2960 TA thermoanalyzer. Diffuse
reflectance spectra (DRS) of solid compounds diluted with MgO (25%) were obtained
on a BECKMAN-DK-2A recording spectrophotometer from 350 to 1700 nm with
standard reflectance attachment. IR spectra of all the compounds were recorded with a
NICOLET-400 D spectrophotometer (400–4000 cmꢁ1) using KBr discs. 1H NMR
spectra were obtained in CDCl3 on a Hitachi R 1500 FT-NMR spectrometer. Shimadzu
160 A (Japan) UV-Vis recording spectrophotometer was used to measure the
absorbance of solution throughout the study. Photometric determination of
copper(II) was made on a HACH model DR/2500 spectrophotometer by standard
method. Elecon Digital pH meter was used to monitor the pH of solution.
2.3. Synthesis and characterization of Schiff-base ligands [H2L]
A solution of 5 mmol of aromatic diamine (0.54 g) in 50 mL absolute ethanol with a few
drops of acetic acid was added dropwise over 2 h to a stirred solution of HBMPP

690
N.J. Parmar et al.
(10 mmol, 2.44 g), Na2SO4 (24 mmol, 3.41 g) in 50 mL warm absolute ethanol and
refluxed for 12 h. The colored product separated on cooling, after removing Na2SO4
and kept overnight. It was then filtered, washed with ether, and recrystallized from
absolute ethanol.
[H2L1]: Yield: 2.1 g (75%), color: yellow, m.p.: 187–189ꢃC. IR (cmꢁ1) :1629 ꢁ(C¼N)
(azomethine), 1595 ꢁ(C¼N) (cyclic), 1320 ꢁ(C–O), 1240 ꢁ(O–H). 1H NMR (ppm):
ꢂ ¼ 6–7.8 (phenyl multiplets) (m, 14H), ꢂ ¼ 0.6–2.5(CH2CH2CH3,–CH3) (m, 20 H),
ꢂ ¼ 12(enolic OH) (s, 2H). Anal. Calcd for C34H36N6O2 (%): C, 72.83; H, 6.47; N,
14.99. Found (%): C, 72.78; H, 6.39; N, 14.91. FAB MS: (m/z) (%) ¼ 560 av.
Calcd 560.69.
[H2L2]: Yield: 2.0 g (72%), color: almond black, m.p.: 250ꢃC. IR (cmꢁ1): 1630 ꢁ(C¼N)
(azomethine), 1595 ꢁ(C¼N) (cyclic), 1305 ꢁ(C–O), 1240 ꢁ(O–H). 1H NMR (ppm):
ꢂ ¼ 6 ꢁ 7.5 (phenyl multiplets) (m, 14H), ꢂ ¼ 0.4–2.8(–CH2CH2CH3,–CH3) (m, 20H),
ꢂ ¼ 11.8(enolic OH) (s, 2H). Anal. Calcd for C34H36N6O2 (%): C, 72.83; H, 6.47;
N, 14.99. Found (%): C, 72.76; H, 6.39; N, 14.82. FAB MS: (m/z) (%): 560 av.
Calcd 560.69.
2.4. Synthesis and characterization of copper(II) chelates
To a stirred solution of HBMPP (3.0 mmol, 0.72 g) and 1.5 mmol of diamine (0.162 g) in
50 mL of absolute ethanol was added dropwise the hydrated copper nitrate in absolute
ethanol (50 mL) followed by the addition of sodium acetate (10 mg). After the addition
was complete, stirring was continued under reflux for 3 h. A dark green precipitate was
filtered and washed several times with water, diethyl ether, and then finally the product
was dried in an oven at 60ꢃC.
[Cu(L11)(H2O)2]: Yield: 0.56 g (65%), color: blackish green, m.p.: 230ꢃC. IR (cmꢁ1):
3100–3500 (m, H2O) (coord.), 712(m, ꢃwH2O), 995(m, ꢃw H2O), 1240(w, ꢂOH), 1330(sh,
ꢁC–O), 1625(w, ꢁC¼N)(azomethine), 1595(m, ꢁC¼N)(cyclic). Anal. Calcd for
C34H38CuN6O4 (%): C, 62.04; H, 5.82; Cu, 9.65; N, 12.77. Found (%): C, 62.10; H,
5.90; Cu, 9.80; N, 12.78. FAB MS: (m/z) (%): 657.12 av. Calcd 658.25.
L ¼ 13.6 ꢀꢁ1 molꢁ1 cm2, ꢄeff ¼ 1.95 B.M.DRS: 15,384 cmꢁ1
,
24,096 cmꢁ1 (charge
transfer), 10 Dq (Calcd): 7692 cmꢁ1
.
[Cu(L22)(H2O)2]2: Yield: 0.51 g (59%) color: green, m.p.: 230ꢃC. IR (cmꢁ1): IR (cmꢁ1):
3100–3500(m, H2O)(coord.), 713(m, ꢃwH2O), 993(m, ꢃwH2O), 1240(w, ꢂOH),
1330(sh, ꢁC–O), 1625(w, ꢁC¼N)(azomethine), 1595(m, ꢁC¼N)(cyclic). Anal. Calcd
for C68H76Cu2N12O8 (%): C, 62.04; H, 5.82; Cu, 9.65; N, 12.77. Found (%): C, 62.09;
H, 5.88; Cu, 9.70; N, 12.80. FAB MS: (m/z) (%): 1318 av. Calcd 1317.
L ¼ 22.8 ꢀꢁ1 molꢁ1 cm2ꢁ, ꢄeff ¼ 1.94 B.M. DRS: 16,393 cmꢁ1, 24,449 cmꢁ1 (charge
transfer), 10 Dq (Calcd): 8196 cmꢁ1
.
2.5. Extraction and analytical procedures
Equal volumes (25 mL) of chloroform, containing 1 ꢀ 10ꢁ3 mol dmꢁ3 of Schiff base
(H2L), and aqueous solution containing 1 ꢀ 10ꢁ3 mol dmꢁ3 of Cu2þ, 1 ꢀ 10ꢁ1 mol dmꢁ3
of perchlorate, and required buffer (1 ꢀ 10ꢁ1 mol dmꢁ3 acetic acid, 1 ꢀ 10ꢁ2 mol dmꢁ3

Extraction of copper(II)
691
C H
3
7
C H
3
7
C H
3
7
X
NH
X
2
O
N
N
EtOH
+
2 N
Reflux
N
HO
OH
N
N
OH
N
NH
2
N
Ph
Ph
Ph
Where X=–C H (para)–, –C H (ortho)–
6
4
6 4
Scheme 1. Synthesis of Schiff base (H2L).
acetate and hydrochloric acid or ammonia to adjust pH) were introduced into a
stoppered flask and shaken for 0.5 h at 25 ꢄ 0.1ꢃC. This period of shaking was enough
to establish equilibrium between the two phases. The ionic strength (I) of the aqueous
phase was kept at 0.1 mol dmꢁ3 using appropriate amount of perchlorate. Two phases
were separated by centrifuging and then the pH of the aqueous phase was determined
and used in the calculation. The copper(II) ion content in equilibrated aqueous phase
was determined spectrophotometrically by the HACH model DR/2500 spectro-
photometer using CuVerÕ powder as standard reagent. The extracted species
(ꢅmax ¼ 472 nm, " ¼ 29,775 dm3 molꢁ1 cmꢁ1) in the non-aqueous phase was also
measured in the same way after stripping with 2 mol dmꢁ3 HCl solution.
3. Results and discussion
3.1. Analytical data
The formation of the Schiff bases, synthesized, and characterized by elemental analysis,
IR, electronic spectra, magnetic measurements, molar conductivity, and mass spectra,
can be expressed as shown in scheme 1.
3.2. IR spectra
IR spectra of free ligands show OH stretching frequency displaced to 3350–2800 cmꢁ1
due to internal hydrogen bonding of OH with N¼C [22, 23]. The ligands are relatively
planar with intermolecular distance favoring hydrogen bond formation [23]. The
electron donating groups on nitrogen also favor intra- or inter-molecular hydrogen
bonding [23], suggesting that the ligands exist in enol form (scheme 1). The shifting of
C¼N band (1629–1635 cmꢁ1) in the ligands to a lower value (1610–1630 cmꢁ1) in all the
copper complexes suggests coordination might occur through ketimino nitrogen
[24–26]. While the unaltered position of band (1595 cmꢁ1, due to cyclic C¼N of
pyrazolone) observed in all the ligands in their corresponding copper chelates indicates

692
N.J. Parmar et al.
that there is no coordination via C¼N (cyclic) [27]. Similarly the displacement of band
due to C–O stretch (1305–1330 cmꢁ1) in complexation indicates the participation of OH
of 5-pyrazolone in the coordination [22]. All the chelates show a broad band at
3500–3100 cmꢁ1 due to the presence of water [28].
3.3. Thermogravimetric analysis
The thermograms of all the compounds were intended for finding out the nature and
number of the water molecules in this study. The weight loss of 5.4% for all the chelates
in the 110–190ꢃC range is assigned to two coordinated water molecules [29].
3.4. 1H NMR spectra
1H NMR spectra of the Schiff bases show phenyl multiplets at 6.6–7.40 ꢂ ppm. Three
signals (triplet, multiplet, and triplet) between 0.7 and 2.5 ppm are assigned to propyl
groups on pyrazolone. The enolic protons are observed at 12–14 ꢂ ppm.
3.5. Diffuse reflectance spectra
The presence of only one broad band at 16,000–20,000 cmꢁ1 is attributed to only one
2
spin allowed d–d transition 2Eg ! T2g in a regular octahedral field. Highly Jahn–Teller
unstable d9 configuration also leads to tetragonal distortion (D4h), which further splits
2
2
2
2
2
2Eg and T2g into B1g, A2g and B2g, Eg, respectively. Thus the transitions may lie
within one envelop or may resolve into two or three components. The broadness of the
band may be attributed to three transitions lying within one envelop. If the splitting of
the states due to tetragonal field follows barycentre rule, the approximate value of
10 Dq may be calculated from the expression: 10 Dq ¼ ꢁ3 ꢁ ½ꢁ1 ꢁ i(ꢁ3 ꢁ ꢁ2), where
ꢁ1 ¼ ꢁ2 ¼ ꢁ3 [30]. These values are 7692 and 8196 cmꢁ1 for H2L1 and H2L2, respectively.
The absence of a band below 10,000 cmꢁ1 ruled out the possibility of tetrahedral
structure in solid state. The green color of the chelates also confirms the distorted
tetragonal structure of Cu(II) chelates [18, 19, 30].
3.6. Magnetic and conductivity studies
The magnetic moment of all the chelates is in 1.94–1.95 B.M. range, which corresponds
to one unpaired electron [29]. The molar conductance (L) of all the chelates,
13.6–22.8 ꢀꢁ1 molꢁ1 cmꢁ2 range, indicates that the complexes are non-electrolytes [31].
3.7. Mass spectral characterization and V.P.O. study
The correlation of mass fragmentation pattern of all the Schiff bases and their
respective copper(II) chelate with its V.P.O. study were used to assign the structure of
the present compounds. It shows molecular ion peak at m/z ¼ 561 (R.I. ¼ 45%, Calcd
mol. wt ¼ 560) for ligand H2L1. The fragment at m/z ¼ 335 as base peak (R.I. ¼ 100%,
Calcd mol. wt ¼ 334.2) may be due to C20H22N4 ion. Rapture of different bonds inside

Extraction of copper(II)
693
(b) 100
(a)
100
80
60
40
20
0
80
60
40
20
0
0
2
4
6
8
10
0
2
4
6
8
10
pH
pH
Figure 1. Percentage extraction vs. pH: (a) using H2L1 and (b) using H2L2.
Table 1. The effect of pHa on degree of extraction/distribution ratio.
pH
%E
Db
pH
Dc
1.20
2.50
3.20
4.20
5.30
6.50
7.80
8.20
9.10
1.2
2.5
3.2
4.2
5.3
6.5
7.8
8.2
9
0.011
0.024
0.068
1
–
2.35
3.38
4.35
6.24
6.6
7.13
8
2.004
4.080
10.210
22.450
63.290
93.920
–
0.020
19.354
97.872
30.314
0.0100
0.01000
9
–
aThe concentration of the ligand and Cu2þ were 1 ꢀ 10ꢁ3 and 1 ꢀ 10ꢁ3 mol dmꢁ3, respectively.
bDistribution ratio; average calculated for data obtained from three independent extraction experiments using H2L1.
cDistribution ratio; average calculated for data obtained from three independent extraction experiments using H2L2.
the molecule resulted in different molecular ion peaks. One appeared dominantly at
m/z ¼ 227 with R.I. of 40% may be assigned to C14H15ON2 ion. Thus, there is a good
agreement in the mass spectra of the ligand with the structure shown in scheme 1. The
fragment in mass spectra of chelate of H2L1 at m/z ¼ 621 (R.I. ¼ 8%, Calcd 621.5) may
be assigned to C68H72Cu2N12O6 (M-2 H2O) due to the elimination of water molecules.
For the complex of H2L2, the peak at m/z ¼ 1318 (R.I. ¼ 7%, Calcd mol. wt ¼ 1317)
due to C68H76Cu2N12O8 ion confirms the dimer nature of the chelate. The base peak at
m/z ¼ 550 with R.I. of 100% may be due to C24H22Cu2N6O2 ion (M–H2O–L2–propyl–
Ph–Me). Also, in the V.P.O. measurements, the found molecular weight (1319) is very
close to the calculated value, suggesting 2 : 2 metal to ligand stoichiometry.
3.8. Extraction studies
3.8.1. Distribution of copper(II). A plot of percentage extraction (%E) versus pH is
shown in figure 1. The results are also expressed as distribution ratio (table 1).
Assuming that no aqueous counter-ion ligands are involved in extraction, the probable
extracted species can be designated as CuL1. The distribution ratio of divalent

694
N.J. Parmar et al.
copper(II) may be expressed based on the following extraction reaction:
iCu2þ þ ð j þ kÞH2L
CuiðLÞ ðHLÞk,o þ ð2j þ kÞHþ
ꢁꢁꢁ*
ðoÞ )ꢁꢁꢁ
j
ðwÞ
½CuiðLÞjðHLÞkðoÞꢅ
D ¼
,
ð1Þ
½Cu2þꢅð1 ꢁ iÞ
where Cui (L)j (HL)k,(o) denotes extractable metal complex and i indicates the degree of
polymerization, j the number of ligands that coordinate with both 5-OH donor sites of
pyrazolone ring as a diprotic acid, k the number of ligands that coordinate with only
one side of the 5-OH donor site as a monobasic acid.
From the above equation the relation between the extractant constant, kex and the
distribution ratio, D can be expressed as
log D ꢁ ði ꢁ 1Þ log½Cu2þꢅ ¼ log kex þ ð j þ kÞ log½H2Lꢅ þ log i þ ð2j þ kÞpH:
ð2Þ
Evaluation of this equation by the slope analysis method allows the stoichiometry of
the extracted species to be elucidated for each Schiff-base ligand system [32]. The
following three partial derivative equations can be derived:
@ðlog DÞ=@ðlog½Cu2þꢅÞ ¼ i ꢁ 1,
ð3Þ
ð4Þ
ð5Þ
@ðlog D ꢁ ði ꢁ 1Þ log½Cu2þꢅÞ=@ðpHÞ ¼ 2j þ k,
@ðlog D ꢁ ði ꢁ 1Þ log½Cu2þꢅÞ=@ðlog½H2LꢅÞ ¼ j þ k:
Generally, during chelation Cu(II) reacts with ligand to form a square-planar
complex and is able to be extracted, depending upon the pH. As a tetradentate ligand,
H2L with two donor sites would affect mode and stoichiometry of the metal chelate.
For instance, H2L1, which has two 5-OH groups ortho to ketiminic carbon, is expected
to form complex via ONNO donors. In this study, the slopes of the plots of log D versus
log[Cu2þ], pH, and log[H2L1] are 0, 2, and 1, respectively. Consequently, the values of i,
j, and k were obtained as 1, 1, and 0, respectively. Substituting these values in equations
(1) and (2) yields:
2þ
þ
Cu þ H2L1ðoÞ
CuðLÞ þ 2H ,
ð6Þ
ð7Þ
ꢁꢁ*
)ꢁꢁ
o
ðwÞ
log D ¼ log kex þ log½H2Lꢅ þ 2pH:
According to equation (7), the plot of log D versus log[H2L1](o) at constant pH will
give a straight line of slope equal to one and intercept as log kex þ 2pH. Hence, from the
graph (figure 2) the extraction constant pkex has been calculated as 11.22. From the
results, the extraction equilibrium was found, as shown in equation (6). Thus, 1 : 1
Cu(II) to ligand stoichiometry is expected, as shown in figure 3. Both from quantitative
evaluation of the equilibrium data and Job’s method (figure 4), the chelates are 1 : 1 in
metal to ligand stoichiometry [CuL1].
Another type of complex was observed for H2L2 at low concentration of Cu(II). The
plot of log D versus log[Cu2þ] consists of two rectilinear sections with sharp
discontinuity in slope at 3.2 ꢀ 10ꢁ5 mol dmꢁ3 Cu2þ; the slope shifts from 0 to 1. In
order to confirm the composition of the complex, the slope analysis was made in lower

Extraction of copper(II)
695
y = 1x + 2.7714
R² = 1
0.35
0.15
–0.05
–0.25
–3.2
–3
–2.8
–2.6
–2.4
–2.2
–2
log[H2 L 1]
Figure 2. The plot of log D vs. log[H2L1].
Figure 3. Suggested structure of extracted copper(II) chelate of 1 : 1 H2L1 to Cu(II) stoichiometry.
[Cu2þ] range. Stoichiometry was deduced from the slope of the relevant section of plots
of log D versus log[Cu2þ], pH, and log[H2L] [32]. The slope of log D versus log[H2L2] is
shown as figure 5. The observed values of the slopes were 0, 2, and 2, respectively,
giving values of i, j, and k as 1, 0, and 2, respectively. Substituting these values in
equations (1) and (2) yields:
2þ
2
Cu þ 2H2L2ðoÞ
CuðHL Þ2ðoÞ þ 2Hþ,
ð8Þ
ð9Þ
ꢁꢁ*
)ꢁꢁ
ðwÞ
log D ¼ log kex þ 2 log½H2L2ꢅorg þ 2pH:

696
N.J. Parmar et al.
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
[Cu(II)]/[Cu(II)]+[H2L1]
Figure 4. Job’s method.
2
1
y = 1.9983x + 7.591
R² = 0.9913
0
– 4.5
– 4.3
– 4.1
– 3.9
– 3.7
– 3.5
– 3.3
– 3.1
Log[H2 L2 ]
–1
–2
Figure 5. Plot of log D vs. log [H2L2].
Accordingly, the nature of extracted species may be 1 : 2 Cu(II) to ligand
stoichiometry, where Cu(II) is coordinated through 5-OH donor of each of two ligands
as monobasic acid, as shown in figure 6. Higher concentration of Cu(II) results in
forming 2 : 2 type complexes, where the partial derivatives in equations (3)–(5) are 1, 4,
and 2, respectively. From the intercept of plot log D versus log[H2L2] the value of pkex is
calculated as 6.4.
This investigation at higher concentrations is not satisfactory, perhaps due to rigidity
of the molecules in the solution. However from the V.P.O. study, the solid chelate
derived from H2L2 is of type 2 : 2 metal to ligand stoichiometry. Thus our observation
shows that H2L1 forms 1 : 1 and H2L2 1 : 2 complexes with copper(II). The dimer of
H2L2 may be expected at higher concentration of copper(II).
4. Conclusion
From the elemental, physico-chemical, spectral, mass, TGA, V.P.O., and magnetic
measurements the general structure of solid copper(II) chelates may be expressed

Extraction of copper(II)
697
HO
Ph
C3H7
C3H7
N
N
N
N
N
X
N
Ph
Cu
O
O
Ph
N
X
N
N
N
N
N
C3H7
C3H7
Ph
OH
Figure 6. Suggested structure of extracted copper(II) chelate of 2 : 1 ligand to metal stoichiometry.
as [Cu(L)(H2O)2]n, where n ¼ 1 and 2 for H2L1 and H2L2, respectively. The same ligands
when employed for extracting copper from perchlorate aqueous medium into
chloroform at pH 6.5 and 7, respectively, are [Cui(L)j (HL)k], where i ¼ 1, j ¼ 1, k ¼ 0
and i ¼ 1, j ¼ 0, k ¼ 2 for complexes of H2L1 and H2L2, respectively.
Acknowledgments
The authors wish to thank Dr H.S. Patel, Head, Department of Chemistry, for his
constant encouragement and necessary facilities. One of the authors (NJP) gratefully
acknowledges financial support from UGC, New Delhi, India, under UGC scheme of
minor research project (letter no. F30-91/2004(SR), dated 28.10.2004).
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