Characterization and electrochemical studies of Mn(II), Co(II), Ni(II) and Cu(II) complexes with 2-mercapto-3-substituted-quinazolin-4-one and 1,10-phenanthroline or ethylenediamine as ligands

Article abstract of DOI:10.1016/j.saa.2008.11.004

Some mixed ligand complexes of the type [M(L¹ or L²)(phen or en)(H₂O)Cl], where M = Mn(II), Co(II), Ni(II) and Cu(II); HL¹ = 2-mercapto-quinazolin-4-one; HL² = 2-mercapto-3-phenyl-quinazolin-4-one; ph

Full text of DOI:10.1016/j.saa.2008.11.004

Spectrochimica Acta Part A 72 (2009) 663–669
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Characterization and electrochemical studies of Mn(II), Co(II), Ni(II) and Cu(II)
complexes with 2-mercapto-3-substituted-quinazolin-4-one and
1,10-phenanthroline or ethylenediamine as ligands
V.A. Sawant, S.N. Gotpagar, B.A. Yamgar, S.K. Sawant, R.D. Kankariya, S.S. Chavan∗
Department of Chemistry, Shivaji University, 416 004 Kolhapur (MS), India
a r t i c l e i n f o
a b s t r a c t
Some mixed ligand complexes of the type [M(L1 or L2)(phen or en)(H2O)Cl], where M = Mn(II),
Co(II), Ni(II) and Cu(II); HL1 = 2-mercapto-quinazolin-4-one; HL2 = 2-mercapto-3-phenyl-quinazolin-
4-one; phen = 1,10-phenanthroline; en = ethylenediamine have been prepared. All complexes were
characterized on the basis of elemental analysis, molar conductance, magnetic susceptibility measure-
ments, IR, UV–vis, ESR and powder X-ray diffraction studies. IR spectra of these complexes reveal that
the complex formation occurred through both nitrogen and sulphur atoms. On the basis of electronic
spectral data and magnetic susceptibility measurement octahedral geometry has been proposed for the
complexes. The ESR spectral data of the Cu(II) complexes showed that the metal–ligand bonds have con-
siderable covalent character. X-ray diffraction studies of Cu(II) complexes are used to elucidate the crystal
structure. The electrochemical behaviour of mixed ligand Ni(II) complexes was studied which showed
that complexes of phen appear at more positive potential as compared to those for corresponding en
complexes.
Article history:
Received 24 July 2008
Received in revised form 6 November 2008
Accepted 10 November 2008
Keywords:
Mixed ligands
Quinazoline derivatives
Ethylenediamine
1,10-Phenanthroline
ESR spectra
Cyclic voltammetry
© 2008 Elsevier B.V. All rights reserved.
report the mode of bonding of 2-mercapto-quinazolin-4-one (HL1),
2-mercapto-3-phenyl-quinazolin-4-one (HL2) as primary ligand
1. Introduction
Quinazolines are a class of fused heterocycles that contain the
pyrimidine nucleus in their structure. The presence of pyrimidine
nucleus in these compounds often leads to very interesting bio-
logical and pharmaceutical activities especially anti-inflammatory,
anticonvulsant, diuretic, antihypertensive, hypnotic, antimalarial,
etc. [1–6]. Recently the quinazolines have been found to possess
potent phosphodiesterase inhibitory activity, which is potentially
useful in the treatment of asthma [7]. Quinazolines especially
containing nitrogen and sulphur donor atoms play an impor-
tant role in anti-cancer and anti-viral activities. In addition, they
can form different types of coordination compounds due to the
several electron-rich donor centers with unusual structural and
chemical properties [8,9]. Because of the biological importance
of quinazoline derivatives and its ability to act as polyfunc-
tional ligand, many studies on its metal complexes have been
carried out [10–13]. Ethylenediamine and 1,10-phenanthroline
chelators also act as potential antitumor agents and they can
show better antitumor activity if they form water-soluble neu-
tral complexes with transition metal ions [14,15]. In this paper we
and 1,10-phenanthroline (phen), ethylenediamine (en) as sec-
ondary ligand with Mn(II), Co(II), Ni(II) and Cu(II). The complexes
prepared were characterized particularly by elemental analysis,
conductance, magnetic moment, X-ray crystallography and spec-
tral studies (IR, UV–vis and ESR). Electrochemical behaviour of these
complexes has also been discussed.
2. Experimental
2.1. Materials and methods
All chemicals used were of the analytical reagents grade (AR)
and of highest purity available. Elemental analysis (C, H, N and S)
was performed on a Thermo Finnegan FLASH EA-112 CHNS ana-
lyzer. Electronic spectra were recorded on a Shimadzu UV-visible
NIR spectrophotometer. Magnetic susceptibility was measured on
Gouy balance at room temperature using Hg[Co(SCN)4] as calibrant.
Infrared spectra were recorded on Perkin Elmer FT-IR spectrometer
as KBr pellets in the 4000–400 cm−1 spectral range. ESR spectra of
the complexes were recorded at room temperature on Varian E-112
spectrometer using TCNE as the standard. X-ray powder analysis
was carried out by using Philips PW 3710 diffractometer oper-
ated at 40 kV and 30 mA generator using Cu K␣ line at 1.54056 Å
∗
Corresponding author. Tel.: +91 231 2609164; fax: +91 231 2691533.
E-mail address: sanjaycha2@rediffmail.com (S.S. Chavan).
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2008.11.004

664
V.A. Sawant et al. / Spectrochimica Acta Part A 72 (2009) 663–669
Fig. 1. Proposed molecular structure of mixed ligand complexes.
as the radiation source. Cyclic voltammetry measurements were
performed with a CH-400A Electrochemical Analyzer. A standard
three-electrode system, consisting of Pt disk working electrode, Pt
wire counter electrode and Ag/AgCl reference electrode containing
aqueous 3 M KCl were used. All potentials were converted to SCE
scale. Tetrabutyl ammonium perchlorate (TBAP) was used as sup-
porting electrolyte and all measurements were carried out in DMF
solution at room temperature with scan rate 50 mV s−1
.
2.2. Synthesis of HL1 and HL2 ligands
2-Mercapto-quinazolin-4-one (HL1) and 2-mercapto-3-phenyl-
quinazolin-4-one (HL2) were prepared by reported procedure
[16,17]. This was characterized by elemental analysis, infrared, 1H
NMR and mass spectra. Satisfactory results were obtained.
2.3. Preparation of mixed ligand complexes (Fig. 1)
The mixed ligand complexes of the ligands (HL1, HL2, phen, and
en) were prepared by the addition of hot ethanolic solution (60 ◦C)
of the appropriate metal chloride (1 mmol, 0.197 g, MnCl2·4H2O,
0.237 g, CoCl2·6H2O, 0.237 g, NiCl2·6H2O and 0.170 g, CuCl2·2H2O)
to the hot ethanolic solution of the ligands (1 mmol, 0.178 g, HL1 or
0.256 g, HL2 and 0.180 g, phen or 0.069 ml, en) while stirring. The
resultant mixtures were stirred for 2 h where upon the complexes
were precipitated. They were collected by filtration, washed with
1:1 ethanol:water mixture, and dried under vacuum over CaCl2
(Fig. 1).
3. Results and discussion
The results of the elemental analysis of the mixed ligand com-
plexes, which are recorded in Table 1, are in good agreement with
thoserequiredbythe proposedformula. The generalreactionfor the
preparation of the mixed ligand complexes of HL1 or HL2 (primary
ligand) and phen, or en (secondary ligand) is
MCl2·nH2O + HL1 or HL2 + phen or en
→ [M(L1 or L2)(phen or en)(H2O)Cl]
M = Mn(II), Co(II), Ni(II) and Cu(II) and n = 2–6; HL1 = 2-mercapto-
quinazolin-4-one, HL2 = 2-mercapto-3-phenyl-quinazolin-4-one;
phen = 1,10-phenanthroline, en = ethylenediamine.
3.1. IR spectral studies
The main stretching frequencies of the IR spectra of the lig-
ands and their mixed ligand complexes are presented in Table 2.
The ligands HL1 and HL2 are capable of exhibiting thione-thiol tau-

V.A. Sawant et al. / Spectrochimica Acta Part A 72 (2009) 663–669
665
Table 2
Infrared spectral data of the ligands and metal complexes.
Compound
ꢂ(H2O)
ꢂ(NH)2
ꢂ(NH)
ꢂ(C O)
Thioamide bands
I
ꢂ(M–N)
II
III
IV
HL1
3081
3060
3065
3060
3056
3063
3056
3059
3060
3245
1686
1690
1689
1697
1700
1690
1700
1690
1697
1680
1686
1682
1698
1686
1698
1702
1695
1700
1568
1307
1299
1300
1295
1327
1323
1319
1329
1295
1339
1316
1298
1320
1303
1320
1316
1320
1305
978
978
978
980
976
977
979
977
980
988
989
988
991
985
986
990
991
977
870
857
865
860
863
857
860
857
863
842
835
837
832
836
835
837
832
837
[Mn(L1)(phen)(H2O)Cl]
[Co(L1)(phen)(H2O)Cl]
[Ni(L1)(phen)(H2O)Cl]
[Cu(L1)(phen)(H2O)Cl]
[Mn(L1)(en)(H2O)Cl]
[Co(L1)(en)(H2O)Cl]
[Ni(L1)(en)(H2O)Cl]
[Cu(L1)(en)(H2O)Cl]
HL2
3445
3460
3478
3432
3436
3440
3478
3421
1567, 1505
1568, 1507
1560, 1507
1549, 1505
1554, 1504
1540, 1505
1558, 1504
1560, 1507
1533
1566, 1540
1560, 1538
1579, 1540
1566, 1541
1573, 1540
1566, 1543
1570, 1541
1573, 1543
461
459
465
455
469
459
461
460
3235, 3300
3230, 3298
3240, 3296
3232, 3300
[Mn(L2)(phen)(H2O)Cl]
[Co(L2)(phen)(H2O)Cl]
[Ni(L2)(phen)(H2O)Cl]
[Cu(L2)(phen)(H2O)Cl]
[Mn(L2)(en)(H2O)Cl]
[Co(L2)(en)(H2O)Cl]
[Ni(L2)(en)(H2O)Cl]
[Cu(L2)(en)(H2O)Cl]
3442
3435
3447
3436
3460
3430
3420
3433
465
454
460
463
465
458
470
459
3232, 3300
3237, 3296
3240, 3300
3232, 3299
Thioamide bands: band-I (␦NH + ␦C–N); band-II (ꢂC N + ␦NH + ␦CH + ꢂC S); band-III (ꢂC S + ꢂC N); band-IV (ꢂC S).
tomerism. In the IR spectra of HL1 and HL2, ꢂ(NH) band appeared
at 3081 and 3248 cm−1 respectively and absence of ꢂ(SH) band
near 2600 cm−1 indicates the thione structural form of the lig-
ands in solid state. The shifting of ꢂ(NH) band to lower frequency
(3065–3056 cm−1) in the complexes of HL1 and disappeared in the
complexes of HL2, providing a strong evidence for involvement of
ligand coordination in deprotonated form. This is also supported by
the appearance of ꢂ(M–N) band at 470–459 cm−1 in the complexes.
The characteristic ꢂ(C O) frequency of ligands HL1 and HL2 occurs
at 1686 and 1680 cm−1 remains unaltered in all complexes, indi-
cates absence of bonding through carbonyl oxygen of HL1 and HL2
[18].
band-III observed at 978 and 988 cm−1 in HL1 and HL2 reduced
in intensity on coordination with metal ion [19]. In the spectra of
mixed phen complexes the bands of phen-free ligand at 740 cm−1
are shifted to higher frequencies around 777 cm−1 in the complexes.
The spectra of mixed en complexes show two characteristic bands
at 3232 and 3300 cm−1 assigned to ꢂsym and ꢂasym vibration of NH2
suggesting coordination through NH2 [20]. The presence of a broad
weak band around 3440 cm−1 in the spectra of all complexes is
associated with coordinated water molecules [21].
3.2. Molar conductivity
Both the HL1 and HL2 contain a thioamide group (H–N–C S)
and give rise to four characteristic bands (I–IV) at 1568, 1307,
978, 870 and 1533, 1339, 988, 842 cm−1 in their infrared spectra
respectively [18]. The thioamide band-I [␦(NH) + ␦(C–N)] observed
at 1568 and 1533 cm−1 respectively in HL1 and HL2, splits up in the
spectra of the complexes also suggests the coordination through
imino nitrogen atom of HL1 and HL2. The two bands appearing
at the frequency 1307, 1339 cm−1 [ꢂ(C N) + ␦(NH) + ␦(CH) + ꢂ(C S)]
thioamide band-II and 870, 842 cm−1 [ꢂ(C S)] thioamide band-IV
respectively in the spectra of HL1 and HL2 have been shifted to lower
frequencies in the ranges 1329–1295 cm−1 and 865–832 cm−1
indicating coordination of thione/thiolato sulphur. The thioamide
The solubility of the complexes in DMF permitted calculation
of the molar conductivity of 10−3 M solutions at 25 ◦C and, by
comparison, the electrolytic nature of each complex (Table 1). The
complexes are found to be non-electrolytic in DMF solution, imply-
ing the coordination of halide anion. Elemental analysis identified
the complexes as [M(L1 or L2)(phen or en)(H2O)Cl].
3.3. Magnetic moments and electronic spectra
Magnetic moments and electronic spectra of the metal com-
plexes are listed in Table 3. In all metal complexes, the absorption
bands at 45,454, 40,816, 35,842, 34,013, 31,347 and 44,444, 40,816,
Table 3
Electronic spectral data and magnetic moment values of the metal complexes.
Compound
ꢃeff (ꢃB)
␲ → ␲* and n → ␲* transitions and charge transfer transitions (cm−1
)
d → d transitions (cm−1
)
HL1
45,454, 40,816, 35,842, 34,013, 31,347
37,453, 34,602, 28,571
38,167, 34,364, 28,735
38,022, 34,482, 29,673
37,735, 34,965, 28,571
38,461, 34,602, 29,673
37,735, 34,482, 29,850
38,022, 34,843, 29,411
37,037, 34,482, 29,239
44,444, 40,816, 36,363, 34,013, 28,818
38,022, 34,965, 27,777
36,496, 33,783, 27,247
36,764, 33,898, 27,472
37,397, 34,843, 27,624
37,453, 34,482, 27,027
37,037, 34,482, 27,397
36,496, 33,898, 27,247
39,215, 34,482, 27,472
–
[Mn(L1)(phen)(H2O)Cl]
[Co(L1)(phen)(H2O)Cl]
[Ni(L1)(phen)(H2O)Cl]
[Cu(L1)(phen)(H2O)Cl]
[Mn(L1)(en)(H2O)Cl]
[Co(L1)(en)(H2O)Cl]
[Ni(L1)(en)(H2O)Cl]
[Cu(L1)(en)(H2O)Cl]
HL2
5.86
4.85
2.76
1.84
5.90
4.88
2.88
1.79
19,801, 16,000, 14,005
20,876, 15,267
15,380
15,748
20,000, 16,129, 13,888
21,276, 15,386
16,025
15,873
–
19,531, 16,025, 13,947
20,876, 14,727
16,000
[Mn(L2)(phen)(H2O)Cl]
[Co(L2)(phen)(H2O)Cl]
[Ni(L2)(phen)(H2O)Cl]
[Cu(L2)(phen)(H2O)Cl]
[Mn(L2)(en)(H2O)Cl]
[Co(L2)(en)(H2O)Cl]
[Ni(L2)(en)(H2O)Cl]
[Cu(L2)(en)(H2O)Cl]
5.89
4.73
2.82
1.89
5.92
4.74
2.98
1.80
15,384
19,607, 16,660, 13,908
21,505, 14,925
15,830
14,738

666
V.A. Sawant et al. / Spectrochimica Acta Part A 72 (2009) 663–669
Table 4
Spin Hamiltonian parameters of polycrystalline Cu(II) complexes.
2
Complex
g
||
g
⊥
gavg
A (×10−4 cm−1
)
A
(×10−4 cm−1
⊥
)
˛
ˇ2
G
||
[Cu(L1)(phen)(H2O)Cl]
[Cu(L1)(en)(H2O)Cl]
[Cu(L2)(phen)(H2O)Cl]
[Cu(L2)(en)(H2O)Cl]
2.271
2.155
2.224
2.155
2.073
2.053
2.060
2.066
2.139
2.087
2.114
2.095
168
196
168
196
65
56
58
47
0.737
0.593
0.707
0.599
0.873
0.619
0.728
0.569
3.71
2.92
3.73
2.35
36,363, 34,013, 28,818 cm−1 due to ␲ → ␲* and n → ␲* transitions
that are observed in the spectra of the free ligands HL1 and HL2
shifted to blue or red frequencies due to the coordination of the
ligand with metal ions.
The electronic spectra of Cu(II) mixed complexes show a broad,
low intensity shoulder band centered at 15,873–14,738 cm−1 that
2
forms part of the charge transfer band. The 2Eg and T2g states of
the octahedral Cu(II) (d9) split under the influence of tetrahedral
distortion and distortion can be such as to cause three transition
The Mn(II) complexes exhibit three weak absorption bands
2
2
2
2
2B1g → B2g
,
2B1g → Eg and B1g → A1g to remain unresolved in
at 14,005–13,888, 16,660–16,000 and 20,000–19,531 cm−1
6
4
6
4
6
4
the spectra [26]. It is concluded that, all three transitions lie within
the single broad envelope centered at the same range. This assign-
ment is in agreement with the general observation that Cu(II) d–d
transitions are normally close in energy. The octahedral geometry
of Cu(II) ion in all complexes is confirmed by the measured mag-
netic moment values in the range 1.79–1.89ꢃB which is in harmony
with the reported value [27].
attributed to A1g → T1g(ꢂ1), A1g → T2g(ꢂ2) and A1g → Eg,
4A1g(ꢂ3) transitions respectively. These absorptions are consistent
with an octahedral geometry around Mn(II) in all complexes.
The magnetic moment values of Mn(II) complexes in the
range 5.86–5.92ꢃB are an indicative of octahedral geometry
[22].
The electronic spectra of Co(II) complexes display two bands
in the range of 15,386–14,727 and 21,505–20,876 cm−1 may
be assigned to 4T1g(4F) → A2g(4F) and 4T1g(4F) → T1g(4P)
indicating octahedral configuration around Co(II) ion. Three
spin allowed transition for octahedral Co(II) complexes is
4
4
3.4. ESR spectral study
To obtain further information about the stereochemistry and
the site of the metal ligand bonding and to determine the mag-
netic interaction in the metal complexes, the X-band ESR spectra
of all copper(II) complexes have been recorded in the polycrys-
talline state. The spin Hamilton parameters of the complexes were
calculated and are summarized in Table 4.
4
4
expected:
4T1g(4F) → T2g(4F)(ꢂ1),
4T1g(4F) → A2g(4F)(ꢂ2),
4T1g(4F) → T1g(4P)(ꢂ3). The first band appeared in the
4
region 8080–8050 cm−1 usually in the IR region, so ꢂ1 tran-
4
sition due to transition 4T1g(4F) → T2g(4F) could not be
observed in all the complexes [23]. The ꢃeff value mea-
sured for the Co(II) complexes are in the range 4.73–4.88ꢃB
respectively which is fairly close to those reported for the
unpaired electrons of Co(II) ion in an octahedral environment
[24].
The room temperature polycrystalline ESR spectra of all Cu(II)
complexes (Fig. 2) are quite similar and exhibit an auxiliary sym-
metric g-tensor parameters with g > g > 2.0023 indicating that the
||
⊥
copper site has a dx
ground state characteristic of octahedral
2
2
−y
In the electronic spectrum of Ni(II) complexes
a broad
geometry [28]. According to Hathaway [29,30], if the value of G is
greater than four, the exchange interaction between copper(II) cen-
ters in the solid state is negligible, whereas when is less than four, a
considerable exchange interaction is indicated in the solid complex.
The calculated G values are given in Table 4. The G values within the
range 2.35–3.73 for all copper complexes are consistent with dx
absorption band at 16,025–15,380 cm−1 which may be
3
assigned to 3A1g(F) → T2g(F), while the absorption band
3
due to 3A2g(F) → T1g(P), is overlapped with the ligand
absorption bands. This indicates that the Ni(II) has an octa-
hedral geometry. The room temperature magnetic moment
values of Ni(II) complexes are 2.76–2.98ꢃB, which are in
normal range observed for octahedral Ni(II) complexes
[25].
2
2
−y
ground state.
Apart from this, the covalency parameters ˛2 (covalent in-plane
␴-bonding) and ˇ2 (covalent in-plane ␲-bonding) were calculated
Table 5
X-ray diffraction data of [Cu(L1)(en)(H2O)Cl].
d (Å)
I/I0
28.2
100
7.2
8.4
5.8
5.2
Observed sin2
ꢄ
Calculated sin2
ꢄ
h k l
Observed 2ꢄ
Calculated 2ꢄ
13.820
8.238
6.830
5.095
4.856
4.605
4.390
4.124
3.620
3.500
3.427
3.211
3.026
2.877
2.717
2.488
2.443
2.200
1.930
31.1
87.4
31.1
87.4
0 1 0
1 0 0
1 1 0
0 1 1
−1,0,1
−1,1,1
1 0 1
6.39
10.73
12.95
17.39
18.25
19.25
20.21
21.52
24.57
25.42
25.98
27.75
29.49
31.06
32.93
36.06
36.75
40.98
47.03
6.39
10.73
12.95
17.39
18.25
19.25
20.17
21.56
24.60
25.48
25.99
27.80
29.56
30.95
32.87
36.11
36.73
41.00
47.04
127.2
228.5
251.5
279.7
307.8
348.7
452.5
484.3
505.1
575.3
647.8
716.6
803.3
957.7
993.7
1225.3
1591.6
127.2
228.5
251.5
279.7
306.7
349.7
453.8
486.2
505.7
577.2
650.8
711.9
800.4
960.6
992.8
1226.6
1592.5
24.1
7.9
6.5
2 0 0
0,−3,1
−2,0,−1
−2,1,1
−2,3,0
2 1 1
21.6
10.3
5.0
11.8
18.0
11.2
14.4
6.5
0 4 1
−2,−3,1
1 1 2
1,−2,2
2 0 2
4 2 0
5.0
5.4

V.A. Sawant et al. / Spectrochimica Acta Part A 72 (2009) 663–669
667
Fig. 3. Cyclic voltammogram of HL1.
hedral geometry is proposed for the complexes. The ESR study of the
copper(II) complexes has provided supportive evidence to the con-
clusion obtained on the basis of electronic spectrum and magnetic
moment value.
Fig. 2. X-band polycrystalline ESR spectra of the complexes [Cu(L1)(Phen)(H2O)Cl]
(a), [Cu(L1)(en)(H2O)Cl] (b), [Cu(L2)(phen)(H2O)Cl] (c), and [Cu(L2)(en)(H2O)Cl] (d).
using the following equations [31–33]. Where ˛2 = 1.0 indicates
complete ionic character whereas ˛2 = 0.5 denoted 100% covalent
bonding, with assumption of negligible small values of the overlap
integral.
A
g
3
7
||
||
2
˛
= −
+
+
2.0023
(g⊥ − 2.0023) + 0.04
0.036
(g|| − 2.0023)E
−8ꢅ ˛2
ˇ2
=
where ꢅ = −828 cm−1 for free copper ion and E is electronic transi-
tion energy. From Table 4, the ˛2 and ˇ2 values indicate that there
is a substantial interaction in the in-plane ␴-bonding whereas the
in-plane ␲-bonding is almost ionic. The lower value of ˛2 compared
to ˇ2 indicates that the in-plane ␴-bonding is more covalent than
in-plane ␲-bonding. These data are well in accordance with other
reported values [34]. Based on these observations, a distorted octa-
Fig. 4. Cyclic voltammogram of [Ni(L1)(en)(H2O)Cl].
Table 6
X-ray diffraction data of [Cu(L2)(en)(H2O)Cl].
d (Å)
I/I0
Observed sin2
ꢄ
Calculated sin2
ꢄ
h k l
Observed 2ꢄ
Calculated 2ꢄ
8.139
5.041
4.846
4.595
4.363
4.106
3.596
3.476
3.401
3.014
2.865
2.472
1.993
1.924
1.631
100
3.3
89.5
233.4
252.6
281.0
311.6
351.8
458.7
491.0
512.7
653.0
722.7
970.9
1493.6
1602.8
2229.4
89.5
233.4
252.6
281.0
311.6
351.8
460.6
492.4
517.1
654.4
722.5
968.6
1499.4
1609.6
2227.7
0 1 0
10.86
17.58
18.29
19.30
20.33
21.62
24.74
25.60
26.17
29.61
31.19
36.31
45.47
47.20
56.35
10.86
17.58
18.29
19.30
20.33
21.62
24.79
25.64
26.29
29.64
31.19
36.27
45.56
47.31
56.33
−1,1,0
3.6
5.1
2.7
3.6
2.0
12.3
6.1
6.9
4.6
14.4
2.1
4.5
1.9
1 1 0
0 1 1
−1,−1,1
−1,1,1
0,−2,1
−1,2,0
1 1 1
−1,0,2
2 1 0
−2,0,2
3 1 0
−1,3,2
−2,−3,3

668
V.A. Sawant et al. / Spectrochimica Acta Part A 72 (2009) 663–669
Table 7
Electrochemical data for ligands and nickel complexes.
Compound
Reduction potentials (V)
Oxidation potentials (V)
Epa
Epc
ꢆEp
E1/2
Epa
Epc
ꢆEp
E1/2
HL1
−0.90, −0.45
−0.72
[Ni(L1)(phen)(H2O)Cl]
[Ni(L1)(en)(H2O)Cl]
HL2
−0.95
−0.91
0.23
0.23
−0.83
−0.79
0.35
0.27
0.20
0.04
0.15
0.23
0.27
0.15
−0.68
−0.66, −0.28
−1.05
[Ni(L2)(phen)(H2O)Cl]
[Ni(L2)(en)(H2O)Cl]
−1.15
−0.36
0.10
0.31
−1.10
−0.52
0.67
0.33
0.55
0.05
0.12
0.28
0.61
0.19
−0.67
Supporting electrolyte: n-Bu4NClO4 (0.05 M); complex: 0.001 M; solvent: DMF; ꢆEp = Epa − Epc where, Epa and Epc are anodic and cathodic potentials, respectively;
E1/2 = 1/2(Epa + Epc); scan rate: 50 mV s−1
.
3.5. X-ray powder diffraction
and anodic regions. Since the ligands used in this work are not
reversibly oxidized or reduced in the applied potential range, the
redox processes are assigned to the metal centers only.
Single crystal X-ray crystallographic investigation is the most
precise source of information regarding the structure of the com-
plexes, the difficulty of obtaining crystalline complexes in proper
symmetric form has rendered the powder X-ray diffraction method
for such study. The X-ray diffraction pattern of the complexes
[Cu(L1)(en)(H2O)Cl] and [Cu(L2)(en)(H2O)Cl] indicates high crys-
tallinity of the complexes. The diffractogram of [Cu(L1)(en)(H2O)Cl]
complex records 19 reflections between 5◦ and 80◦ (2ꢄ) with maxi-
mum at 2ꢄ = 10.730◦ corresponding to value of d = 8.238 Å (Table 5).
The diffractogram of [Cu(L2)(en)(H2O)Cl] complex consists of 15
reflections with maxima at 2ꢄ = 10.860◦ corresponding to value of
d = 8.139 Å (Table 6). The main peaks of [Cu(L1)(en)(H2O)Cl] and
[Cu(L2)(en)(H2O)Cl] complexes have been indexed by using com-
puter software by trial and error method [35,36], keeping in mind
characteristics of various symmetry systems till good fit could be
obtain between observed and calculated 2ꢄ and sin2 ꢄ values. The
method also yielded h k l (miller indices) values. The relative inten-
sities corresponding to the prominent peaks have been measured.
The indexing of diffractogram of [Cu(L1)(en)(H2O)Cl] and
[Cu(L2)(en)(H2O)Cl] complexes is identical. Based on this it can be
proposed that these compounds belong to same structural class. A
comparison of values of 2ꢄ and sin2 ꢄ for the [Cu(L1)(en)(H2O)Cl]
and [Cu(L2)(en)(H2O)Cl] complexes reveals that, there is good
agreement between the calculated and observed values of 2ꢄ and
sin2 ꢄ on the basis of assumption of triclinic structure [37]. The small
difference in the observed d spacing can be attributed to difference
in unit cell dimensions. The structure of [Cu(L1)(en)(H2O)Cl] com-
plex yields values for lattice constant a = 8.311 Å, b = 13.874 Å, and
c = 5.598 Å; ˛ = 91.666◦, ˇ = 95.959◦, and ꢇ = 94.578◦; unit cell vol-
ume V = 639.56 Å3. However the structure of [Cu(L2)(en)(H2O)Cl]
complex yields values for lattice constant a = 6.392 Å, b = 8.202 Å,
and c = 6.268 Å; ˛ = 96.723◦, ˇ = 103.226◦, and ꢇ = 90.735◦; unit cell
volume V = 317.55 Å3. In conjugation with these lattice parameters
the conditions such as a =/ b =/ c and of ˛ =/ ˇ =/ ꢇ required for
the samples to be triclinic were tested and found to be satisfactory.
All the Ni(II) complexes exhibit both anodic and cathodic redox
potentials. In anodic potential region the reduction wave (Epc
,
0.04–0.55 V) corresponding to Ni(III)/Ni(II) reaction is obtained.
During the reverse scan the oxidation of Ni(II)/Ni(III) occurs in the
potential range (Epa, 0.27–0.67 V). In cathodic potential region the
reduction wave (Epc, −0.36 to −1.15 V) corresponding to Ni(II)/Ni(I)
reaction is obtained. During the reverse scan the oxidation of
Ni(I)/Ni(II) occurs in the potential range (Epa, −0.67 to −1.05 V).
However the values of the limiting peak-to-peak separation (ꢆEp)
ranging from 100 to 310 mV reveal that this process can be quassi-
reversible.
Further the redox process among the mixed ligand Ni(II) com-
plexes of phen appears at more positive potential (0.27 V) as com-
pared to those for corresponding en complex (0.15 V). This trend
may be due to the strong ␴-donor tendency of the ethylenediamine
moiety and the strong ␲-acceptor ability of 1,10-phenanthroline
ligand. These results are consistent with those reported in the lit-
erature [38]. In comparison with [Ni(L1)(en)(H2O)Cl] (0.15 V) the
respective response of [Ni(L2)(en)(H2O)Cl] (0.19 V) are shifted to
a more positive potential. This indicates that the coordination of
nickel to the ligand lessens its electron-withdrawing properties
[39].
4. Conclusion
A series of mixed ligand complexes of 2-mercapto-quinazolin-
4-one (HL1), 2-mercapto-3-phenyl-quinazolin-4-one (HL2) and
1,10-phenanthroline (phen), ethylenediamine (en) with Mn(II),
Co(II), Ni(II) and Cu(II) have been synthesized and characterized.
All complexes exhibit octahedral geometry by involvement of both
nitrogen and sulphur of HL1 and HL2 ligands in complex forma-
tion. All the Ni(II) complexes exhibit both positive and negative
redox potentials corresponding to Ni(III)/Ni(II) and Ni(II)/Ni(I) pro-
cesses respectively. Further, the redox potential of Ni(II) complexes
of phenanthroline is higher than Ni(II) complexes of ethylenedi-
amine. The complex crystallizes in the triclinic crystal system.
3.6. Electrochemical studies
Acknowledgements
Electrochemical properties of the ligands HL1 and HL2 and their
Ni(II) complexes were investigated in DMF solution containing
0.05 M n-Bu4NClO4 as supporting electrolyte by cyclic voltammetry
(Table 7). All the measurements were carried out in 10−3 M solu-
tions at room temperature in the potential range +1 to −1.5 V with
scan rate 50 mV s−1. Typical cyclic voltammogram (CV) of HL1 and
its [Ni(L1)(en)(H2O)Cl] complex are shown in Figs. 3 and 4 respec-
tively.
Authors are thankful to IISc, Bangalore for Elemental Analysis
and Regional Sophisticated Instrumentation Centre, IIT, Mumbai for
providing ESR facility.
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