Synthesis and structural investigation of mono- and polynuclear copper complexes of 4-ethyl-1-(pyridin-2-yl) thiosemicarbazide

Article abstract of DOI:10.1016/j.saa.2007.11.009

The reaction between 2-hydrazinopyridine and ethylisothiocyanate produced 4-ethyl-1-(pyridin-2-yl) thiosemicarbazide (HEPTS). Its reaction with copper fluoride, chloride, bromide, acetate, nitrate, perchlorate, sulfate, carbonate, hydroxide and copper met

Full text of DOI:10.1016/j.saa.2007.11.009

Available online at www.sciencedirect.com
Spectrochimica Acta Part A 71 (2008) 73–79
Synthesis and structural investigation of mono- and polynuclear copper
complexes of 4-ethyl-1-(pyridin-2-yl) thiosemicarbazide
a
b
b
b,∗
M.M. Hassanien , I.M. Gabr , M.H. Abdel-Rhman , A.A. El-Asmy
a
Chemistry Department, Industrial Education College, Beni-Suef University, Egypt
Chemistry Department, Faculty of Science, Mansoura University, Mansoura, Egypt
b
Received 18 August 2007; received in revised form 11 November 2007; accepted 15 November 2007
Abstract
The reaction between 2-hydrazinopyridine and ethylisothiocyanate produced 4-ethyl-1-(pyridin-2-yl) thiosemicarbazide (HEPTS). Its reaction
with copper fluoride, chloride, bromide, acetate, nitrate, perchlorate, sulfate, carbonate, hydroxide and copper metal produced 15 Cu(II) complexes.
The copper metal is easily oxidized in aqueous-ethanol solution of HEPTS giving [Cu (EPTS)(H O) (OH) ]EtOH. Different complexes for the
2 2 3 3
same anion were synthesized by controlling the heating time. Characterization by elemental, thermal, magnetic and spectral (electronic, IR, mass
and ESR) studies showed the formation of mono-, di-, tri- and tetra nuclear complexes. The room temperature solid state ESR spectra of the
2
x
2
complexes show an axial spectrum with d − y ground state, suggesting distorted tetragonal geometry around Cu(II) center. The kinetic and
thermodynamic parameters for the different decomposition steps in the complexes were calculated. HEPTS and its Cu(II) complexes showed high
3 2 2 4
activity against gram negative bacteria; [Cu (EPTS) (EtOH) Br ] has more activity.
©
2007 Elsevier B.V. All rights reserved.
Keywords: Copper complexes; Thiosemicarbazide; Electronic spectra; Infrared; ESR; Biological activity
1
. Introduction
rial and anticancer agents [18,19]. The crystal structure of
rhenium complexes of 4-t-butyl- and 4-phenyl-1-(pyridin-2-yl)
thiosemicarbazides showed that the phenyl derivative behaves
Complexes of iron, cobalt, nickel, palladium and plat-
1
inum with 2-hydrazinopyridine were reported [1]; the
coordination sites were the pyridine ring and NH2 group.
as binegative bidentate via S and N atoms where t-butyl deriva-
3
tive as mononegative tridentate via S, N and N-pyridine ring
2
-Hydrazinopyridine was found important in the synthesis
[20] and used for radiopharmaceutical application.
The present work aims to synthesize and characterize
complexes formed between 4-ethyl-1-(pyridin-2-yl) thiosemi-
carbazide (HEPTS) and different Cu(II) salts and examine their
thermal decompositions. Also, their antibacterial activity has
been tested.
of complexes used in the delivery of cytotoxin for therapy
or the delivery of radionuclide for imaging and/or therapy.
Diagnostic radiopharmaceuticals were used in majority of the
diagnostic scans [2,3]. Schiff bases of 2-hydrazinopyridine
with diacetylmonoxime [4], 2,3-butanedione [5], benzyl
[
6], phenanthraquinone [6], o-aminobenzaldehyde [7], 1-
isoquinolinaldehyde [8], 2-quinoxalinecarboxaldehyde [8],
-thiophenealdehyde [9], and 2,9-diformyl phenanthroline [10]
2. Experimental
2
were reported. Thiosemicarbazides are interesting because they
form highly stable and intensely colored complexes which
are used for spectrophotometric determination of metal ions
in different media [11–15] and showed catalytic activity
2
.1. Apparatus and reagents
The IR absorption spectra were recorded on a Mattson 5000
FTIR Spectrophotometer. The electronic spectra were measured
on a Unicam UV-Vis Spectrometer UV2. Thermogravimetric
analysiswasperformedusinganautomaticrecordingthermobal-
ance, type 951 DuPont instrument. Samples were subjected to
[
16,17]. Also, they have potentially beneficial as antibacte-
◦
◦
1
∗
heat on a rate of 10 C/min (25–800 C) in N . H NMR spec-
Corresponding author. Tel.: +20 101645966.
2
E-mail address: aelasmy@yahoo.com (A.A. El-Asmy).
trum of HEPTS in CD3Cl was recorded on EM-390 (200 MHz)
1
386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.11.009

7
4
M.M. Hassanien et al. / Spectrochimica Acta Part A 71 (2008) 73–79
Spectrometer. Mass spectra of some solid complexes were
recorded on a Varian MAT 311 Spectrometer. Carbon and hydro-
gen content for the ligand and its complexes was determined at
the Microanalytical Unit, Mansoura University, Egypt. Cu(II),
salt and 6 h in case of the metal. The dark green precipitate is
filtered hot, washed with EtOH then Et2O, dried and preserved.
2.4. Antibacterial activity
−
−
2−
halides (Cl and Br ) and SO4 contents in the complexes
were determined by the well known standard methods [21]. ESR
spectra were obtained on a Bruker EMX Spectrometer working
in the X-band (9.78 GHz) with 100 kHz modulation frequency.
The microwave power was set at 1 mW and modulation ampli-
tude was set at 4 Gauss. The low field signal was obtained after
four scans with a 10-fold increase in the receiver gain. A powder
spectrum was obtained in a 2 mm quartz capillary at room tem-
perature. The Cu(II) salts were pure (Fluka, Aldrich or Merck).
Copper metal was supplied, as powder, from Edwic.
The ligand and their complexes were tested as antibacterial
agents at the Department of Microbiology, Faculty of Pharmacy,
Mansoura University. The seeded agar plates were prepared by
putting 50 ml portion of inoculated agar into 15 cm Petri dishes
and allowed to solidify. Cups were made to receive 25 ␮l of the
◦
reagent solution and allow to diffusing and incubated at 37 C
for 24 h. Inhibition zone was measured [22] and compared with
that of gentamicin (commercial antibiotic, Memphis Co., Egypt,
1000 ␮g/ml). The experiment control was DMF.
3. Results and discussion
2
.2. Preparation of the ligand
The elemental analyses showed different stoichiometries for
HEPTS was prepared by heating under reflux a mixture of
-hydrazinopyridine (10.9 g, 0.1 mol) and ethylisothiocyanate
8.7 ml, 0.1 mol) in 20 ml absolute ethanol for 2 h. On cool-
the isolated complexes (Table 1). They have high melting points
2
(
◦
(
>300 C), insoluble in most common organic solvents and some
are soluble in DMF and DMSO.
ing, pale yellow crystals were formed, filtered off, washed with
◦
EtOH and Et2O and recrystallized from EtOH (m.p. 171 C;
3
3
.1. Spectral studies
yield 90%). The purity of the compound was checked by TLC.
1
.1.1. IR and H NMR
1
The H NMR spectrum of HEPTS in CD3Cl showed signals
due to the protons of CH3 (δ 1.75, t, 3H) and CH2 (δ 3.63, q,
1
2
H) [23]. The N H, overlapped with one of the pyridine CH
and observed at 8.09 (m, 2H) while the other pyridine signals
are observed at δ 6.87 (m, 2H), 7.62 (m, 1H) [24]. Its IR spec-
−
1
2
.3. Preparation of the complexes
trum showed bands at 3239, 3154 and 773 cm assigned to
4
2
1
ν(N H) [25], ν(N H) + ν(N H) [26] and ρ(NH) [27], respec-
On mixing 0.01 mol of HEPTS and 0.01 mol each
tively. The spectrum also displayed bands at 1604, 1519, 1446
and 798 cm assigned to ν(C N)Py [23] and thioamide (I, III
−
1
of CuCl2·2H2O, CuBr2, CuF2·3H2O, Cu(OAc)2·H2O,
CuSO4·5H2O, Cu(NO3)2·2.5H2O or Cu(ClO4)2·6H2O, in
EtOH and/or H2O, dark blue or green precipitate was immedi-
ately formed. For the preparation of [Cu(EPTS)F]2·EtOH·H2O,
and IV) [27], respectively, indicating thione form.
1
The IR data (Table 2) reveal a mononegative bidentate (N H
1
and C S) of HEPTS. The ν(N H) is shifted to higher wavenum-
−
1
[
(
[
(
Cu4(EPTS)3(H2O)(EtOH)(OH)Cl4]2H2O,
[Cu2(EPTS)-
ber (3164–3190 cm ) in all complexes [28] while the ν(C S)
2
H2O)3(OAc)3]EtOH,
Cu4(EPTS)2(H2O)4(SO4)3]EtOH,
NO3) ]H2O and [Cu3(EPTS)2(H2O)4(ClO4)4]3EtOH, the
[Cu4(EPTS)3(H2O)(EtOH)Br ]H2O,
and ν(N H) disappear with the appearance of ν(C S) and
ν(C N ) at ca 700 and 1640–1630 cm [27], respectively. The
ν(N H) and ν(C N)Py appear more or less at the same posi-
tion. In [Cu3(EPTS)2(EtOH)4Br4], the ν(C N ) and ν(C N)Py
shifted to 1612 and 1585 cm , respectively, due to their par-
ticipation in coordination [25] and the ν(N H) shifted to higher
5
2
−1
[Cu3(EPTS)(H2O)2-
4
5
2
mixture is heated for 1 h on a water bath. The precipitate
was filtered off after cooling, washed successfully with EtOH
−
1
◦
1
then Et2O, dried at 110 C in an oven for 30 min and finally
preserved in a vacuum desiccator. [Cu3(EPTS)2(EtOH)2Br4],
wavenumber due to hydrogen bonding.
[
Cu2(EPTS)3(NO3)2]2H2O, [Cu(EPTS)(H2O)(ClO4)]EtOH
The spectrum of the carbonato complex showed two bands
−
1
and [Cu2(EPTS)2(H2O)2(SO4)]EtOH were prepared by
heating the mixture for 2 h and the formed precipitate fil-
tered after cooling, washed with EtOH then Et2O, dried
and preserved. Applying the methods on CuCl2·2H2O,
CuF2·3H2O and Cu(OAc)2·H2O gave the same com-
plexes. [Cu(EPTS)Cl]2·2H2O was prepared by heating
at 1467 and 1040 cm
assigned to νas(CO3) and νs(CO3)
[26] while the sulfato complexes showed four bands at
−
1
1186–986 cm
[26] indicating that the two anions behave
as bidentate and/or bridged bidentate ligands. The perchlorate
complexes showed three bands at ca 1140, ca 1050 (ν3) and
−
1
ca 975 cm (ν ) consistent with a monodentate ligand [29].
6
−1
1
:1 (HEPTS:CuCl2·2H2O) in DMSO for 1 h; a green precipitate
The acetato complex showed bands at 1665 and 1467 cm
assigned to νas(OAc) and νs(OAc), respectively, with difference
is obtained, filtered, washed with EtOH then Et2O, dried and
−
1
finally preserved. In CuCO3·Cu(OH)2, Cu(OH)2 and Cu metal,
of 198 cm indicating monodentate manner [26]. The spec-
trum of [Cu3(EPTS)(H2O)2(NO3) ]H2O showed bands due to
0
.01 mol of each was added to 0.02 mol EPTS in EtOH, and
5
−
the NO vibrations at 1419 (ν ), 1109 (ν1) and 981(ν2) cm with
5
1
heated under reflux for 3 h to dissolve completely the insoluble

M.M. Hassanien et al. / Spectrochimica Acta Part A 71 (2008) 73–79
75
Table 1
Color, melting points and elemental analysis of HEPTS and its isolated complexes
◦
No.
Compound
Color
M.p. ( C)
%Found
C
%Calcd.
C
H
M
X
H
M
X
1
2
3
4
5
6
7
8
9
HEPTS, C8H12N4S
Yellow
171
49.02
35.83
28.80
23.83
24.89
30.47
21.81
36.32
32.90
13.39
22.00
28.49
25.00
29.36
28.51
32.01
6.34
4.93
4.27
3.29
3.28
4.76
3.67
5.26
4.35
3.10
4.06
5.09
5.58
6.39
5.10
4.85
–
–
–
48.96
34.89
28.42
23.58
24.19
30.64
20.57
35.55
32.05
12.81
22.22
28.44
25.37
29.76
30.77
31.90
6.16
4.88
4.22
3.27
3.45
5.14
3.45
4.60
5.38
2.28
4.07
4.53
5.53
6.34
4.20
4.46
–
–
–
[Cu(EPTS)F]2·EtOH·H2O
Bulish violet
Dark blue
Dark green
Green
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
19.29
23.97
19.52
19.72
24.73
25.01
16.09
20.57
24.91
16.32
15.06
26.82
24.09
18.78
18.84
20.51
23.13
19.19
19.21
24.95
24.19
15.67
21.20
25.42
16.03
15.04
26.84
24.23
20.35
18.75
[Cu4(EPTS)3(H2O)(EtOH)(OH)Cl4]2H2O
[Cu4(EPTS)3(H2O)(EtOH)Br5]H2O
[Cu3(EPTS)2(EtOH)2Br4]
13.66
30.51
31.85
–
28.21
–
–
–
–
–
–
–
12.92
30.16
32.18
–
27.41
–
–
–
–
–
–
–
[Cu2(EPTS)(H2O)(EtOH)(OH)CO3]EtOH
[Cu4(EPTS)2(H2O)4(SO4)3]EtOH
[Cu2(EPTS)3(NO3)2]2H2O
[Cu2(EPTS)(H2O)3(OAc)3]EtOH
[Cu3(EPTS)(H2O)2(NO3)5]H2O
[Cu3(EPTS)2(H2O)4(ClO4)4]3EtOH
[Cu(EPTS)(H2O)ClO4]EtOH
Dark green
Dark blue
Dark blue
Dark green
Dark blue
Dark green
Greenish blue
Dark green
Dark green
Green
10
11
12
13
14
15
16
[Cu2(EPTS)(H2O)3(OH)3]EtOH
[Cu2(EPTS)(H2O)2(EtOH)2(OH)3]½EtOH
[Cu(EPTS)Cl]2·2H2O
11.00
13.88
11.37
14.17
[Cu2(EPTS)2(H2O)2(SO4)]EtOH
Dark blue
X: Cl, Br or SO4.
the difference of 300 cm 1 between ν and ν1 due to a mon-
−
and [Cu2(EPTS)3(NO3)2]2H2O, in Nujol, showed a band at
5
−
1
−
17123–13793 cm due to the d–d transition in a tetrahedral
odentate behavior of NO3 [30] in addition the bands at 1471,
146 and 1053 cm characteristic for a bridged and/or biden-
tate [26]. [Cu2(EPTS)3(H2O)(NO3)2]H2O, showed only bands
at 1382, 1271, 1018 and 836 cm indicating a monodentate
behavior [30]. The spectra of [Cu2(EPTS)(H2O)3(OH)3]EtOH
and [Cu2(EPTS)(H2O)2(EtOH)2(OH)3]½EtOH reveal the coor-
dination of OH to the metal by the appearance of 1203 and
−
1
structure [33]. The spectra of the other Cu(II) complexes
showed a broad band at 17182–15432 with a shoulder
1
−
1
2
2
−
1
at 13072–12225 cm
attributed to the B1g → Eg and
2
2
B1g → A transitions in a square-planar geometry [33].
lg
In DMF, the spectra of tetrahedral complexes in addition to
[Cu3(EPTS)2(EtOH)2Br4], [Cu2(EPTS)(H2O)(EtOH)(OH)]-
−1
EtOH, [Cu2(EPTS)2(H2O)2 (SO4)]EtOH and [Cu(EPTS)Cl]2·-
1
215 cm bands attributed to δ(M O H) [26].
−1
2
H2O, showed only one band at 13624–12500 cm similar
to that reported in an octahedral geometry [33] indicat-
ing that the tetrahedral complexes are affected by DMF.
The spectra of the other complexes, in DMF, showed
3
.1.2. Electronic, mass and ESR
The absorption spectrum of HEPTS, in DMF, showed bands
−
1
at 35460, 31950, 30870 and 24940 cm (Table 3) attributed
−
1
a broad band at16892–14749 cm
with a shoulder at
3793–12346 cm more or less similar to those recorded in
Nujol indicating that the structure is not affected by the solvent
to the (␲ → ␲*)Py, (␲ → ␲*)C S [23,31], (n → ␲*)Py and
−
1
1
(
n → ␲*)C S [23,32], respectively.
The spectrum of each [Cu(EPTS)F]2·EtOH·H2O, [Cu4-
[33].
(
EPTS)2(H2O)4(SO4)3]EtOH, [Cu3(EPTS)(H2O)2(NO3) ]H2O
5
Table 2
Infrared date of ligand and isolated solid complexes
4
1
ν(C N2)
No.
Compound
ν(OH)solv
ν(N H)
ν(N H)
ν(C N)Py
ν(C C)Py
Thioamides
1
2
3
4
5
6
7
8
9
HEPTS
–
3239
3259
3241
3266
3257
3261
3255
3257
3264
3238
3235
3245
3242
3240
3282
3263
3154
3182
3166
3180
3182
3188
3171
3185
3190
3170
3186
3161
3173
–
1604
1600
1607
1594
1585
1600
1604
1598
1602
1610
1608
1604
1598
1590
1602
1600
1577
1600
1590
1594
1575
1600
1604
1598
1602
1610
1589
1604
1598
1590
1602
1600
1519, 1446
1519, 1442
1540, 1440
1521, 1442
1518, 1450
1521, 1436
1523, 1446
1542, 1438
1538, 1436
1529, 1445
1544, 1436
1541, 1443
1534, 1466
1550, 1465
1525, 1454
1517, 1468
[Cu(EPTS)F]2·EtOH·H2O
3426, 3297
3442, 3365
3451, 3318
3444
3569, 3482, 3382
3409, 3388
3421
3417
3440, 3459
3426
3409
3450
3441, 3344
3432
3422
1635
1633
1641
1610
1637
1633
1635
1635
1635
1635
1637
1639
1635
1635
1635
[Cu4(EPTS)3(H2O)(EtOH)(OH)Cl4]2H2O
[Cu4(EPTS)3(H2O)(EtOH)Br5]H2O
[Cu3(EPTS)2(EtOH)2Br4]
[Cu2(EPTS)(H2O)(EtOH)(OH)CO3]EtOH
[Cu4(EPTS)2(H2O)4(SO4)3]EtOH
[Cu2(EPTS)3(NO3)2]2H2O
[Cu2(EPTS)(H2O)3(OAc)3]EtOH
[Cu3(EPTS)(H2O)2(NO3)5]H2O
[Cu3(EPTS)2(H2O)4(ClO4)4]3EtOH
[Cu(EPTS)(H2O)ClO4]EtOH
[Cu2(EPTS)(H2O)3(OH)3]EtOH
[Cu2(EPTS)(H2O)2(EtOH)2(OH)3]½EtOH
[Cu(EPTS)Cl]2·2H2O
10
11
12
13
14
15
16
3164
3183
[Cu2(EPTS)2(H2O)2(SO4)]EtOH

7
6
M.M. Hassanien et al. / Spectrochimica Acta Part A 71 (2008) 73–79
Table 3
Electronic spectra and magnetic moment date of the ligand and its complexes
Compound no.
HEPTS
Electronic spectra (nm)
μeff. (BM)
282; 313, 324; 401
272; 300; 387; 413; 800; 725a
275; 330; 395; 605; 725; 625a
282; 316; 340; 496; 612; 648
286; 320; 348; 736; 600 , 796
–
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
Cu(EPTS)F]2·EtOH·H2O
1.33
0.00
0.00
0.00
1.23
0.80
0.99
1.34
0.91
1.2
Cu4(EPTS)3(H2O)(EtOH)(OH)Cl4]2H2O
Cu4(EPTS)3(H2O)(EtOH)Br5]H2O
Cu3(EPTS)2(EtOH)2Br4]
a
a
a
a
a
Cu2(EPTS)(H2O)(EtOH)(OH)CO3]EtOH
Cu4(EPTS)2(H2O)4(SO4)3]EtOH
Cu2(EPTS)3(NO3)2]2H2O
Cu2(EPTS)(H2O)3(OAc)3]EtOH
Cu3(EPTS)(H2O)2(NO3)5]H2O
Cu3(EPTS)2(H2O)4(ClO4)4]3EtOH
Cu(EPTS)(H2O)ClO4]EtOH
286; 310; 392; 714; 588 , 794
a
a
275; 330, 775; 594 ; 1000
a
262; 318; 330; 355; 400; 775; 713
282; 314; 370; 636; 588 , 800
280; 306; 370; 650; 584 , 1000
282; 310; 390; 630; 536 , 826
282; 314; 358, 394; 674; 602 , 810
282; 308; 370; 460; 680; 676 , 810
280; 312; 378; 702; 802; 670 ; 810
282; 334; 348; 360; 800; 596 ; 824
a
a
a
a
a
a
a
a
a
1.4
a
Cu2(EPTS)(H2O)3(OH)3]EtOH
Cu2(EPTS)(H2O)2(EtOH)2(OH)3]½EtOH
Cu(EPTS)Cl]2·2H2O
1.21
1.13
1.65
0.79
a
a
a
a
a
a
Cu2(EPTS)2(H2O)2(SO4)]EtOH
282; 308; 408; 734; 596 ; 818
a
Values in Nujol.
The solid state ESR spectra of some complexes exhibit axial
symmetric g-tensor parameters with g|| > g⊥ > 2.0023 indicating
that the copper site has a d
2
2
ground state characteristic of
x −y
tetrahedral, square-planar or octahedral stereochemistry [34].
The spin Hamiltonian parameters of these complexes were
calculated (Table 4). The G values (G = (g|| − 2)/(g⊥ − 2) = 4)
for [Cu2(EPTS)(H2O)3(OH)3]EtOH, [Cu4(EPTS)2(H2O)4-
(SO4)3]EtOH, and [Cu3(EPTS)2(EtOH)2Br4] are 3.25, 3.5
and 3.5, respectively, suggesting Cu–Cu exchange interactions
while in [Cu(EPTS)Cl]2·2H2O and [Cu(EPTS)F]2·EtOH·H2O,
the values are 6.6 and 5.0 indicating a negligible interaction.
In addition to the signals corresponding to ꢀMs = ± 1 allowed
transitions, a weak signal around 1600 G near g = 4 was
observed corresponding to the ꢀMs = ± 2 forbidden transition,
indicating a magnetic coupling between the two Cu(II) ions
in [Cu2(EPTS)(H2O)3(OH)3]EtOH which is not observed in
[Cu(EPTS)Cl]2·2H2Oand[Cu(EPTS)F]2·EtOH·H2O(Fig. 1A).
The same spectra were observed for bridged Cu(II) binuclear
complexes [35,36].
Scheme 1. Fragmentation pattern of [Cu4(EPTS)3(H2O)(EtOH)(OH)Cl4]
H2O.
2
The mass spectra of the chloro complexes provide
good evidence for their molecular formulae: [Cu4(EPTS)3-
H2O)(EtOH)(OH)Cl4]2H2O and [Cu(EPTS)Cl]2·2H2O (F.Wt.
(
1
098.96 and 624.55). The spectrum of [Cu(EPTS)Cl]2·2H2O
showed the molecular ion peak at 624 indicating its dim-
mer nature. The mass spectrum of [Cu(EPTS)F]2·EtOH·H2O
showed the molecular ion peak coincides with its molec-
ular formula (Calcd. 619.46; found 620) indicating its
dimmer nature. On the other hand, the spectrum of
Zero-field splitting (ZFS) is the removal of spin microstate
degeneracy for systems with S > ½ in absence of applied field
as a consequence of molecular electronic structure and/or spin
density distribution. [Cu3(EPTS)2(EtOH)2Br4] showed a broad
band at low field (g = 5.0) due to the presence of ZFS of
S = 3/2 indicating the presence of three copper sites. The ten-
dency of A|| to decrease with increasing g|| is an index of
an increase of the tetrahedral distortion in the coordination
sphere of copper [37]. In order to quantify the degree of dis-
tortion of Cu(II) complexes, the f factor (g||/A||) obtained from
the ESR spectra was evaluated. The value is considered as an
empirical index of tetrahedral distortion (105–135 for square
planar complexes) [38], depending on the nature of the coor-
dinated atoms. In distorted tetrahedral structure, the value may
be much larger [37]. For the complexes [Cu(EPTS)Cl]2·2H2O
[
Cu4(EPTS)3(OH)(H2O)(EtOH)Cl4]2H2O showed a peak at
m/z = 551 corresponding to half of the complex molecule
549.48) and multi peaks corresponding to the successive degra-
(
dation of the other half. The proposed fragmentation patterns for
the mass spectra are illustrated in Schemes 1 and 2.
(Fig. 1B), [Cu2(EPTS)(H2O)3(OH)3]EtOH (Fig. 2) and
Scheme 2. Fragmentation pattern of [Cu(EPTS)Cl]2·2H2O.
[Cu3(EPTS)2(EtOH)Br4] (Fig. 3), f = 134, 129 and 130 support-

M.M. Hassanien et al. / Spectrochimica Acta Part A 71 (2008) 73–79
77
Table 4
ESR data of some copper(II) complexes at room temperature
A|| × 10− (cm
4
−1
)
g||/A||
G
α
2
β
2
Complex
g||
g⊥
[
[
[
[
[
Cu(EPTS)Cl]2·2H2O
2.36
2.30
2.26
2.21
2.28
2.06
2.06
2.08
2.06
2.08
175
170
175
170
160
134
142
129
130
142
6.60
5.00
3.25
3.50
3.50
0.89
0.87
0.82
0.74
0.79
1.00
0.79
0.69
0.70
0.86
Cu(EPTS)F]2·EtOH·H2O
Cu2(EPTS)(H2O)3(OH)3]EtOH
Cu3(EPTS)2(EtOH)2Br4]
Cu4(EPTS)2(H2O)4(SO4)3]EtOH
ing a square-planar geometry with no appreciable tetrahedral
distortion. For the other complexes, f is high demonstrating a sig-
nificant dihedral angle distortion in the xy-plane and indicating a
tetrahedral distortion from square-planar geometry. The spectral
results of [Cu4(EPTS)2(H2O)4(SO4)3]EtOH (Fig. 4) are consis-
tent with the other tetranuclear tetragonal geometry [39,40]. No
superhyperfine structure at higher fields excluding any interac-
tion of the nuclear spins of nitrogen (I = 1) with the unpaired
electron density on Cu(II). The absence of 14N hyperfine cou-
pling may be due to a relatively higher tetrahedral distortion
[
41].
Molecular orbital coefficients, α2 (covalent in-plane ␴-
2
bonding) and β (covalent in-plane ␲-bonding) were calculated
[
42,43]:
ꢀ
ꢁ
A||
.036
3
2
α = −
+ (g|| − 2.0023) + (g⊥ − 2.0023) + 0.04
0
7
(
g|| − 2.0023)E
2
β =
2
−8λα
−
1
2
2
λ = 828 cm
for the free ion and E is the B1g → A1g
2
transition. Complete ionic character for α = 1, and 100%
covalent for α = 0.5, with the assumption of negligibly
Fig. 1. ESR spectra of [Cu(EPTS)F]2·EtOH·H2O (A) and [Cu(EPTS)Cl]2-
2H2O (B).
2
·
Fig. 2. ESR spectrum of [Cu2(EPTS)(H2O)3(OH)3]EtOH.
Fig. 3. ESR Spectrum of [Cu3(EPTS)2(EtOH)2Br4].

7
8
M.M. Hassanien et al. / Spectrochimica Acta Part A 71 (2008) 73–79
The TG of the isolated complexes was taken as a proof
for the existing of H2O and/or EtOH molecules as well as the
anions to be outside and/or inside the coordination sphere. The
conductance was not measured due to the partial solubility of
the complexes in DMF and DMSO. The outside solvent (H2O
◦
and/or EtOH) lost at 70–120 C while those coordinated lost at
◦
120–270 C.
The complexes show thermal stability rather than the ligand
where the beginning of its decomposition shifts to higher tem-
◦
perature (240–438 C). In general, all complexes are thermally
stable; [Cu2(EPTS)(H2O)3(OAc)3]EtOH is the highest one. It
◦
lost the outside EtOH at 88 C (found 6.74; Calcd. 7.68), the
◦
coordinated water (3H2O) at 220 C (found 9.83; Calcd. 9.03)
and the acetate (3OAc) at 410 C (found 29.67; Calcd. 29.55)
◦
leaving Cu2(EPTS) (found 53.74; Calcd. 53.76). The data of the
different decomposition steps are shown in Table 5S (supple-
mental information).
To evaluate the kinetic and thermodynamic parameters for the
different thermal decomposition steps, the Coats–Redfern [46]
and Horowitz–Metzger [47] equations are employed. The data
of activation enthalpy (ꢀH* = E − RT); the activation entropy
(
ꢀS* = 2.303 [log(Zh/KT)]R) and the free energy of activa-
Fig. 4. ESR spectrum of [Cu4(EPTS)2(H2O)4(SO4)3]EtOH.
tion (ꢀG* = ꢀH* − TꢀS*) are determined and presented in
Table 6S (supplemental information), where Z, K and h are the
pre-exponential factor, Boltzman and Plank constants, respec-
tively. From the results, one can pointed out the following
remarks:
small values of the overlap integral. From Table 4, it is
clear that the in-plane ␴-bonding for [Cu(EPTS)Cl]2·2H2O
and [Cu3(EPTS)2(EtOH)2Br4] are more covalent than the
in-plane ␲-bonding. In [Cu2(EPTS)(H2O)3(OH)3]EtOH and
2
[
Cu(EPTS)F]2·EtOH·H2O, α value indicates slight ionic nature
2
of the metal–ligand ␴-bonding, and β indicate considerable in-
plane ␲-bonding contribution in metal–ligand ␲-bonding. These
data are well consistent with other reported values [43,44].
(i) The positive values of ꢀS suggest disorder of the decom-
posed fragments much more the undecomposed ones.
(ii) The positive sign of ꢀH indicates that the decomposition
stages are endothermic processes.
3
.2. Magnetic moments
(iii) The high values of E reveal high stability of the chelates
due to their covalent bond character.
Most Cu(II) complexes measured subnormal values (Table 3)
(iv) The negative sign of ꢀG for most investigated complexes
reveals that all the decomposition steps are spontaneous
processes.
except [Cu(EPTS)Cl]2·2H2O (1.65 BM) confirming an anti-
ferromagnetic interaction between the copper centers. Zero
values were measured for [Cu3(EPTS)2(EtOH)2Br4], [Cu4-
(
(
EPTS)3(H2O) (OH)(EtOH)Cl4]H2O and [Cu4(EPTS)3(H2O)-
EtOH)Br ]H2O attributed to high quenching due to the strong
5
antiferromagnetic copper–copper interaction in a polynuclear
structure [45]. Although, the fluoride complex has mononu-
clear structure, it showed subnormal value (1.33 BM) which
may be attributed to intermolecular copper–copper interac-
tion [45]. Structures for [Cu2(EPTS)(H2O)3(OH)3]EtOH,
[
Cu4(EPTS)3(H2O)(EtOH)Br ]H2O
and
[Cu3(EPTS)2-
5
(
EtOH)2Br4] are drawn.
3
.3. Thermal analysis
The TG curve of HEPTS indicates a thermal stability till
◦
◦
1
80 C which coincides with its melting point (171 C). The
◦
curve showed three decomposition steps at 210, 300 and 640 C
corresponding to loss of CSNHEt (found 46.6; Calcd. 44.9%),
pyridine ring (found 40.6, Calcd. 39.8%) and complete decom-
position of the ligand.

M.M. Hassanien et al. / Spectrochimica Acta Part A 71 (2008) 73–79
79
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