Synthesis, structural characterization, thermal and electrochemical studies of Mn(II), Co(II), Ni(II) and Cu(II) complexes containing thiazolylazo ligands

Article abstract of DOI:10.1016/j.molstruc.2009.11.010

Some thiazolylazo derivatives and their metal complexes of the type [M(L)(H₂O)Cl]; M = Mn(II), Co(II), Ni(II), Cu(II) and L = 6-(2′-thiazolylazo)-2-mercapto-quinazolin-4-one (HL₁), 6-(4′-phenyl-2′-thiazolylazo)-2-mercapto-quinazolin-4-one (HL₂), 6-(2′-thiazolylazo)-2-mercapto-3-(m-tolyl)-quinazolin-4-one (HL₃) and 6-(4′-phenyl-2′-thiazolylazo)-2-mercapto-3-(m-tolyl)-quinazolin-4-one (HL₄) have been prepared. All the complexes were characterized on the basis of elemental analysis, molar conductance, magnetic moment, IR, UV-vis, ESR, TG-DTA and powder X-ray diffraction studies. IR spectra of these complexes reveal that the complex formation occurred through thiazole nitrogen, azo nitrogen, imino nitrogen and sulfur atom of the ligands. On the basis of electronic spectral data and magnetic susceptibility measurement octahedral geometry has been proposed for the Mn(II), Co(II) and Ni(II) complexes and distorted octahedral geometry for the Cu(II) complexes. Electrochemical behavior of Ni(II) complexes exhibit quasireversible oxidation corresponding to Ni(III)/Ni(II) couple along with ligand reduction. X-ray diffraction study is used to elucidate the crystal structure of the complexes.

Full text of DOI:10.1016/j.molstruc.2009.11.010

Journal of Molecular Structure 965 (2010) 1–6
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, structural characterization, thermal and electrochemical studies
of Mn(II), Co(II), Ni(II) and Cu(II) complexes containing thiazolylazo ligands
*
S.S. Chavan , V.A. Sawant
Department of Chemistry, Shivaji University, Kolhapur (MS) 416 004, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 August 2009
Received in revised form 28 October 2009
Accepted 1 November 2009
Available online 6 November 2009
Some thiazolylazo derivatives and their metal complexes of the type [M(L)(H2O)Cl]; M = Mn(II), Co(II),
Ni(II), Cu(II) and L = 6-(20-thiazolylazo)-2-mercapto-quinazolin-4-one (HL1), 6-(40-phenyl-20-thiazoly-
lazo)-2-mercapto-quinazolin-4-one (HL2), 6-(20-thiazolylazo)-2-mercapto-3-(m-tolyl)-quinazolin-4-one
(HL3) and 6-(40-phenyl-20-thiazolylazo)-2-mercapto-3-(m-tolyl)-quinazolin-4-one (HL4) have been pre-
pared. All the complexes were characterized on the basis of elemental analysis, molar conductance, mag-
netic moment, IR, UV–vis, ESR, TG-DTA and powder X-ray diffraction studies. IR spectra of these
complexes reveal that the complex formation occurred through thiazole nitrogen, azo nitrogen, imino
nitrogen and sulfur atom of the ligands. On the basis of electronic spectral data and magnetic suscepti-
bility measurement octahedral geometry has been proposed for the Mn(II), Co(II) and Ni(II) complexes
and distorted octahedral geometry for the Cu(II) complexes. Electrochemical behavior of Ni(II) complexes
exhibit quasireversible oxidation corresponding to Ni(III)/Ni(II) couple along with ligand reduction. X-ray
diffraction study is used to elucidate the crystal structure of the complexes.
Keywords:
Azo complexes
ESR spectra
Thermal analysis
Electrochemistry
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
polyfunctional ligand many studies on their metal complexes have
been carried out [15–18].
Arylazo compounds are interesting because they are involved in
many biological reactions [1,2]; and in analytical chemistry as
complexing agents for the determination of some metal ions, spec-
trophotometrically [3,4]. They are important in drugs and show a
variety of interesting biological activities including antimicrobial
activities [5–7], anti-inflammatory activities [8] and pesticidals
activities [9]. Due to presence of the azo (AN@NA) group these
compounds possess several distinctive properties including aggre-
gation, optical data storage and tautomerism which define as a
distinct class of dyestuffs [10,11]. Among various azo compounds
thiazolylazo derivatives have attracted much attention as analy-
tical reagents owing to their high sensitivity and selectivity
[12,13]. They are used in chemical and analytical methods includ-
ing spectrophotometry, solid phase extraction, liquid chromatogra-
phy and electrochemistry [14]. The use of thiazolylazo derivatives
in spectrophotometry is based on the coloured compounds result-
ing from their reaction with most of the transition metals. They can
form different types of coordination compounds particularly with
transition metals due to the several electron rich donor centers
with unusual structural and chemical properties. Because of the
importance of thiazolylazo derivatives and their ability to act as
In this paper we report the synthesis of new thiazolylazo ligands
6-(20-thiazolylazo)-2-mercapto-quinazolin-4-one (HL1), 6-(40-phe-
nyl-20-thiazolylazo)-2-mercapto-quinazolin-4-one (HL2), 6-(20-
thiazolylazo)-2-mercapto-3-(m-tolyl)-quinazolin-4-one (HL3) and
6-(40-phenyl-20-thiazolylazo)-2-mercapto-3-(m-tolyl)-quinazolin-
4-one (HL4) and their legation behavior with Mn(II), Co(II), Ni(II) and
Cu(II). The complexes prepared were characterized on the basis of
elemental analysis, conductance, magnetic moment, TG-DTA,
X-ray crystallography and spectral (IR, UV–vis and ESR) studies.
Electrochemical behavior of these complexes was discussed.
2. Experimental
2.1. Materials
All the chemicals used were pure and of analytical reagents
grade. 4-Phenyl-2-aminothiazole [19], 2-mercapto-quinazolin-4-
one [20] and 2-mercapto-3-(m-tolyl)-quinazolin-4-one [21] were
synthesized by reported method. Solvents were purified and dried
according to standard procedure.
2.2. Physical measurements
Microanalysis (C, H, N and S) were performed on a Thermo
Finnigan FLASH EA-112 CHNS analyzer. Electronic spectra were re-
* Corresponding author. Tel.: +91 231 2609164; fax: +91 231 2691533.
E-mail address: sanjaycha2@rediffmail.com (S.S. Chavan).
0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.11.010

2
S.S. Chavan, V.A. Sawant / Journal of Molecular Structure 965 (2010) 1–6
one (HL2), 6-(20-thiazolylazo)-2-mercapto-3-(m-tolyl)-quinazolin-
R
4-one (HL3) and 6-(40-phenyl-20-thiazolylazo)-2-mercapto-3-(m-
tolyl)-quinazolin-4-one (HL4) were synthesized by diazotization
of substituted 2-aminothiazole using H2SO4 and NaNO2 according
to a procedure analogous to that described earlier [22]. The diazo-
tized solution so formed was coupled with 2-mercapto-quinazolin-
4-one (0.178 g, 1 mmol) or 2-mercapto-3-(m-tolyl)-quinazolin-4-
one (0.268 g, 1 mmol) in 30 mL of ethanol below 5 °C. The product
formed was collected by filtration, washed well with water and
recrystalized from ethanol.
S
H2O
Cl
H2O
Cl
N
N
N
O
N
M
N
M
R'
S
N
S
N
N
N
R'
Cl
M
N
2.4. Preparation of metal complexes (Fig. 1)
H2O
O
The complexes of Mn(II), Co(II), Ni(II) and Cu(II) were prepared
by mixing ethanolic solution (5 mL) of the organic ligand
(1 mmol, 0.289 g, HL1, 0.365 g, HL2, 0.379 g, HL3, 0.455 g, HL4)
with solution (5 mL) of appropriate metal chloride (1 mmol,
0.197 g, MnCl2.4H2O, 0.237 g, CoCl2ꢁ6H2O, 0.237 g, NiCl2ꢁ6H2O
and 0.170 g, CuCl2ꢁ2H2O) in ethanol. The resultant mixture was re-
fluxed for 2 h on a water bath and the solid complex precipitated
was collected by filtration, washed several times with 1:1 etha-
nol:water mixture and dried under vacuum over CaCl2 at room
temperature .
S
R
R = H, C6H5; R' = H, m-tolyl; M = Mn(II), Co(II), Ni(II) and Cu(II)
Fig. 1. Proposed structure for the metal complexes.
corded on
a Shimadzu-3600 UV–vis-NIR spectrophotometer.
Magnetic susceptibility was measured on Gouy balance at room
temperature using a Johnson Matthey Alfa MKI magnetic suscepti-
bility balance, with Hg[Co(SCN)4] as calibrant. Molar conductance
3. Results and discussion
(KM) was measured on the ELICO (CM-185) conductivity bridge
using ca. 10ꢀ3 M solution in DMF. Infrared spectra were recorded
on Perkin-Elmer FT-IR-100 spectrometer as KBr pellets in the
4000–400 cmꢀ1 spectral range. ESR spectra of the complexes were
recorded at room temperature on Varian E-112 spectrometer using
TCNE as the standard. Cyclic voltammetry measurements were
performed with Electrochemical Quartz Crystal Microbalance
CHI-400. 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. X-ray powder
analysis were carried out by using Philips PW 3710 diffractometer
The results of the elemental analysis of ligands HL1-4 and their
Mn(II), Co(II), Ni(II) and Cu(II) complexes are recorded in Table 1.
All the metal complexes are coloured, non-hygroscopic and are
fairly stable at room temperature. They are found to be insoluble
in common organic solvents like methanol, ethanol, dichlorometh-
ane, acetonitrile except DMF and DMSO. The molar conductance
data (Table 1) of the complexes in DMF at 10ꢀ3 M is in the range
13–36
X
ꢀ1 cm2 molꢀ1, which indicates nonelectrolytic nature of
the complexes suggesting that the Clꢀ anion is coordinated to me-
tal ion. This is further supported by proposed general formulae of
the complexes as suggested depending upon the results of elemen-
tal analysis and IR spectra.
operated at 40 kV and 30 mA generator using CuK
a line at
1.54056 Å as the radiation source.
2.3. Synthesis of HL1-4 ligands (diazotization and coupling)
3.1. IR spectral studies
The ligands 6-(20-thiazolylazo)-2-mercapto-quinazolin-4-one
(HL1), 6-(40-phenyl-20-thiazolylazo)-2-mercapto-quinazolin-4-
The main stretching frequencies of the IR spectra of ligands
(HL1-4) and their complexes are listed in Table 2. The IR spectra
Table 1
Analytical and physico-chemical data of the ligands and their metal complexes.
Complex
M. F. (colour)
Yield M.P. (°C) Analytical data % found (calculated)
KM
(X )
ꢀ1 cm2 molꢀ1
M
C
H
N
S
HL1
C11H7N5OS2 (brown)
73
148
45.30 (45.66) 2.28 (2.44) 24.35 (24.20) 21.98 (22.16)
[Mn(L1)(H2O)Cl] C11H8N5O2S2ClMn (yellow brown) 64
>300
>300
>300
>300
154
>300
>300
>300
>300
179
13.72 (13.85) 33.12 (33.30) 1.89 (2.03) 17.81 (17.65) 16.02 (16.16) 36
14.68 (14.71) 32.76 (32.97) 2.13 (2.01) 17.52 (17.48) 15.83 (16.00) 30
14.36 (14.66) 32.84 (32.99) 1.94 (2.01) 17.59 (17.49) 16.08 (16.01) 15
15.53 (15.68) 32.46 (32.59) 1.79 (1.99) 17.04 (17.28) 15.96 (15.82) 34
55.59 (55.87) 2.89 (3.03) 19.32 (19.16) 17.38 (17.55)
11.52 (11.62) 43.12 (43.18) 2.47 (2.56) 14.97 (14.81) 13.44 (13.56) 29
12.24 (12.36) 42.67 (42.82) 2.49 (2.54) 14.78 (14.69) 13.37 (13.45) 14
12.26 (12.32) 42.73 (42.84) 2.61 (2.54) 14.83 (14.69) 13.32 (13.46) 19
13.15 (13.20) 42.33 (42.41) 2.39 (2.51) 14.63 (14.55) 13.27 (13.32) 32
56.83 (56.97) 3.54 (3.45) 18.84 (18.46) 16.53 (16.90)
[Co(L1)(H2O)Cl] C11H8N5O2S2ClCo (brown)
[Ni(L1)(H2O)Cl] C11H8N5O2S2ClNi (pale brown)
[Cu(L1) (H2O)Cl C11H8N5O2S2ClCu (dark brown)
HL2 C17H11N5OS2 (violet)
65
70
66
69
70
65
66
68
65
[Mn(L2)(H2O)Cl] C17H12N5O2S2ClMn (brown)
[Co(L2)(H2O)Cl] C17H12N5O2S2ClCo (brown)
[Ni(L2)(H2O)Cl]
[Cu(L2)(H2O)Cl] C17H12N5O2S2ClCu (dark brown)
HL3 C18H13N5OS2 (brown)
C17H12N5O2S2ClNi (pinkish violet)
[Mn(L3)(H2O)Cl] C18H14N5O2S2ClMn (yellow brown) 70
>300
>300
>300
>300
186
>300
>300
>300
>300
11.16 (11.28) 44.36 (44.41) 2.79 (2.90) 14.56 (14.38) 13.08 (13.17) 26
11.97 (12.01) 44.13 (44.04) 2.92 (2.87) 14.36 (14.27) 12.93 (13.07) 30
11.85 (11.96) 43.87 (44.07) 2.78 (2.88) 14.51 (14.27) 13.12 (13.07) 20
12.73 (12.83) 43.51 (43.63) 2.69 (2.85) 14.29 (14.13) 13.04 (12.94) 18
63.07 (63.28) 3.69 (3.76) 15.43 (15.37) 13.94 (14.08)
[Co(L3)(H2O)Cl] C18H14N5O2S2ClCo (brown)
[Ni(L3)(H2O)Cl] C18H14N5O2S2ClNi (pinkish violet)
[Cu(L3)(H2O)Cl] C18H14N5O2S2ClCu (dark brown)
HL4 C24H17N5O2S2 (violet)
68
66
69
76
66
71
68
70
[Mn(L4)(H2O)Cl] C24H18N5O2S2ClMn (light brown)
[Co(L4)(H2O)Cl] C24H18N5O2S2ClCo (brown)
9.62 (9.76)
51.13 (51.20) 3.18 (3.22) 12.66 (12.44) 11.27 (11.39) 22
10.27 (10.39) 50.67 (50.84) 3.24 (3.20) 12.49 (12.35) 11.37 (11.31) 13
10.24 (10.36) 50.74 (50.87) 3.13 (3.20) 12.27 (12.36) 11.53 (11.32) 26
11.07 (11.12) 50.34 (50.43) 3.12 (3.17) 12.48 (12.25) 11.17 (11.22) 30
[Ni(L4)(H2O)Cl]
C24H18N5O2S2ClNi (pinkish violet)
[Cu(L4)(H2O)Cl] C24H18N5O2S2ClCu (dark brown)

S.S. Chavan, V.A. Sawant / Journal of Molecular Structure 965 (2010) 1–6
3
Table 2
Infrared spectral data of the ligands and metal complexes.
Compound
mH2O
m
NH
m
(C@N)
m
(N@N)
m
C@O
Thioamide bands
I
m M–N
II
III
IV
HL1
3081
3060
3065
3060
3056
3087
3063
3056
3059
3060
3245
–
–
–
–
3248
–
–
–
–
1624
1610
1618
1615
1611
1620
1613
1609
1611
1608
1618
1593
1603
1598
1601
1624
1614
1609
1603
1597
1458
1424
1421
1415
1418
1448
1432
1425
1428
1420
1445
1424
1415
1420
1412
1453
1438
1442
1428
1435
1686
1690
1689
1697
1700
1685
1690
1700
1690
1697
1680
1686
1682
1698
1686
1687
1698
1702
1695
1700
1568
1307
1299
1300
1295
1327
1327
1313
1319
1309
1295
1339
1316
1298
1320
1303
1342
1320
1316
1320
1305
978
978
978
980
976
977
977
979
977
980
988
989
988
991
985
990
986
990
991
987
870
857
865
860
863
874
857
860
857
863
842
835
837
832
836
848
835
837
832
837
[Mn(L1)(H2O)Cl]
[Co(L1)(H2O)Cl]
[Ni(L1)(H2O)Cl]
[Cu(L1) (H2O)Cl
HL2
[Mn(L2)(H2O)Cl]
[Co(L2)(H2O)Cl]
[Ni(L2)(H2O)Cl]
[Cu(L2)(H2O)Cl]
HL3
[Mn(L3)(H2O)Cl]
[Co(L3)(H2O)Cl]
[Ni(L3)(H2O)Cl]
[Cu(L3)(H2O)Cl]
HL4
[Mn(L4)(H2O)Cl]
[Co(L4)(H2O)Cl]
[Ni(L4)(H2O)Cl]
[Cu(L4)(H2O)Cl]
3445
3460
3478
3432
1567, 1505
1568, 1507
1560, 1507
1549, 1505
1562
1554, 1504
1540, 1505
1558, 1504
1560, 1507
1533
1566, 1540
1560, 1538
1579, 1540
1566, 1541
1538
1573, 1540
1566, 1543
1570, 1541
1573, 1543
461
459
465
455
3436
3440
3478
3421
469
459
461
460
3442
3435
3447
3436
465
454
460
463
3460
3430
3420
3433
465
458
470
459
Thioamide bands: Band-I (dNH + dC–N); Band-II (
mC@N + dNH + dCH +
mC@S); Band-III (mC = S + mC@N); Band-IV (mC@S).
of ligands and their complexes are found to be quite complex as
they in general exhibit large number of bands of varying intensi-
ties. However, all the ligands HL1-4 are capable of exhibiting thi-
3.2. Magnetic moments and electronic spectra
Magnetic moments and electronic spectra of the complexes are
listed in Table 3. The absorption spectra of ligands HL1-4 shows four
absorption bands in the UV and visible region. The first two bands
observed at 226–220 and 257–245 nm undoubtedly originate from
the perturbed local excitation of the phenyl group. The bands lo-
one–thiol tautomerism. In the IR spectra of ligands (HL1-4),
band appeared at 3081–3248 cmꢀ1 and absence of
(SH) band near
2600 cmꢀ1 shows the thione structural form of the ligands in solid
m(NH)
m
state. This
m(NH) band shifting to lower frequency (3056–
3065 cmꢀ1) in the complexes of HL1 and HL2 and disappearing in
the complexes of HL3 and HL4, provides strong evidence for involve-
ment of ligand coordination in deprotonated form. This is also sup-
cated at 328–319 and 466–453 nm corresponds to the p ? p
*
*
and n ?
p transitions of the azo group [28]. However, the spectra
of complexes shows bathochromic shift in comparison with free
ligands.
ported by the appearance of
complexes. The characteristic
m
(M–N) band at 454–470 cmꢀ1 in the
(C@O) frequency of ligands at
m
The Mn(II) complexes exhibit three weak absorption bands at
720–714, 625–600 and 512–500 nm attributed to 6A1g ? 4T1g
(4G), 6A1g ? 4T2g (4G) and 6A1g ? 4A1g, 4Eg transitions, respectively.
These are consistent with an octahedral geometry around Mn(II)
ion in all complexes. The magnetic moment values of Mn(II) com-
plexes in the range 5.71–5.83lB are an indicative of octahedral
geometry [29].
1680–1687 cmꢀ1 remainingunalteredin all the complexesindicates
the absence of bonding through carbonyl oxygen of the ligands [23].
The spectral region 1400–1630 cmꢀ1 is quite complicated due to
presence of
strong band observed at 1618–1624 cmꢀ1 in the spectra of all li-
gands (HL1-4) is due to (C@N) of thiazole nitrogen. This band shifted
m(C@C), m(C@N) and m(N@N) stretching frequencies. A
m
to lower frequencies in the complexes indicates involvement of thi-
azole nitrogen in coordination [24]. However, the band appearing at
the frequency range 1445–1458 cmꢀ1 in the spectra of ligands
assigned to -N@N- group shifted to lower frequency (1412–
1442 cmꢀ1) in the complexes indicates involvement of azo nitrogen
in coordination with metal ion [25].
Table 3
Magnetic moment and electronic spectral data of the complexes.
Compound
leff
lB
p
?
p
* and n ?
transitions
(nm) (kmax in DMF)
p
*
d ? d transitions
(nm) (kmax in
DMF)
(
)
HL1
220, 245, 319, 453
262, 337, 408
263, 348, 413
253, 350, 421
265, 340, 426
223, 248, 320, 458
260, 349, 410
270, 335, 418
267, 342, 414
267, 347, 420
225, 254, 326, 463
276, 360, 412
270, 351, 414
274, 362, 425
258, 365, 430
226, 257, 328, 466
264, 364, 408
267, 360, 418
274, 349, 420
272, 367, 427
All the four ligands contain a thioamide group (H–N–C@S) and
give rise to four characteristic bands (I, II, III and IV) at 1533–
1579, 1307–1342, 976–990 and 842–870 cmꢀ1 in their infrared
spectra [23]. The thioamide band-I [d(NH) + d(C–N)] observed at
ꢂ1540 cmꢀ1, splits up in the spectra of the complexes also suggest-
ing the coordination through imino nitrogen atom of the ligands.
[Mn(L1)(H2O)Cl] 5.73
505, 625, 714
543, 655
535, 679, 956
660
[Co(L1)(H2O)Cl]
[Ni(L1)(H2O)Cl]
[Cu(L1) (H2O)Cl
HL2
4.78
2.92
1.79
[Mn(L2)(H2O)Cl] 5.71
500, 620, 720
542, 650
536, 684, 957
659
[Co(L2)(H2O)Cl]
[Ni(L2)(H2O)Cl]
[Cu(L2)(H2O)Cl]
HL3
4.81
3.02
1.78
The two bands appearing at the frequency ꢂ1340 cmꢀ1
[m(C@N) +
d(NH) + d(CH) +
m
(C@S)] thioamide band-II and ꢂ845 cmꢀ1
[m(C@S)] thioamide band-IV in the spectra of ligands have been
[Mn(L3)(H2O)Cl] 5.79
512, 624, 717
542, 654
535, 687, 948
663
shifted to lower frequencies in the ranges 1292–1327 and 832–
865 cmꢀ1, respectively, indicating coordination of thione/thiolato
sulfur. The thioamide band-III observed at ꢂ980 cmꢀ1 in the ligands
HL1-4 reduces in intensity on coordination with metal ion [26]. In the
[Co(L3)(H2O)Cl]
[Ni(L3)(H2O)Cl]
[Cu(L3)(H2O)Cl]
HL4
4.93
2.92
1.78
spectra of all complexes
a broad band observed at around
[Mn(L4)(H2O)Cl] 5.83
510, 600, 719
541, 649
538, 690, 961
667
3440 cmꢀ1 together with new band at around 826 cmꢀ1 indicating
the presence of water molecules in coordination sphere of the
complexes [27].
[Co(L4)(H2O)Cl]
[Ni(L4)(H2O)Cl]
[Cu(L4)(H2O)Cl]
4.86
2.89
1.76

4
S.S. Chavan, V.A. Sawant / Journal of Molecular Structure 965 (2010) 1–6
The electronic spectra of Co(II) complexes shows two d–d tran-
firming to the corresponding metal oxides even at 800 °C indicat-
ing that decomposition of organic moiety remains incomplete
even at this temperature. The Fig. 2 is a representative example
for thermal analysis of the metal complexes under study.
sitions at 655–649 and 543–541 nm that may be assigned to
4T1g(4F) ? 4A2g(4F) and 4T1g(4F) ? 4T1g(4P) transitions, respectively.
These transitions suggest an octahedral geometry around Co(II) ion
[30]. The leff value measured for the Co(II) complexes is in the
range 4.78–4.93lB, which is fairly close to those reported for
the three unpaired electrons of Co(II) ion in an octahedral
3.4. ESR spectra
environment [31].
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 Cu(II) complexes have been recorded in the polycrystalline
state. The ESR spectra of Cu(II) complexes exhibit a single broad
signal (Fig. 3) due to dipolar broadening and enhanced spin lattice
relaxation. The spectra of all Cu(II) complexes are quite similar and
The Ni(II) complexes exhibit three absorption bands at 961–
948, 690–679 and 538–535 nm attributed to A2g(F) ? 3T2g(F),
3
3A2g(F) ? 3T1g(F) and A2g(F)? 3T1g(P) transitions, respectively.
3
These results are compatible with the reported values for the octa-
hedral Ni(II) complexes [32]. The room temperature magnetic mo-
ment values of Ni(II) complexes are 2.89–3.02lB which is in
normal range observed for octahedral Ni(II) complexes [33].
The electronic spectra of Cu(II) complexes show a broad band
centered at ꢂ660 nm which could be attributed to 2Eg ? 2T2g tran-
sition characterized by Cu(II) ion in octahedral geometry [34]. The
octahedral geometry of Cu(II) ion in all complexes is confirmed by
the measured magnetic moment values in the 1.76–1.79lB range
which is in harmony with the reported value.
exhibit auxiliary symmetric g-tensor parameters with g|| > g\
>
2
2
2.0023 indicating that the copper site has a dx
ground state
-y
characteristic of octahedral geometry [35]. The observed g values
for all Cu(II) complexes are less than 2.3 and are in agreement with
the covalent character of the metal–ligand bond. No band corre-
sponding to
DMs = 2 transition is observed in the spectrum ruling
out any Cu–Cu interaction. The geometric parameter G, which is a
measure of exchange interaction between the copper centres in the
polycrystalline compounds, is calculated using the equation
G = (g|| ꢀ 2.0023)/(g\ ꢀ 2.0023). According to Hathaway [36,37], if
the value of G is greater than four, the exchange interaction be-
tween Cu(II) centers in the solid state is negligible, whereas when
it is less than four, a considerable exchange interaction is indicated
in the solid complex. The calculated G values are within the range
3.44–3.83 for all copper complexes indicating that the magnetic
interaction between the Cu(II) ions is negligible in the solid com-
plexes [38].
3.3. Thermal studies
The thermal decomposition of Mn(II), Co(II), Ni(II) and Cu(II)
complexes of the ligand HL1 was studied using the TG-DTA in the
temperature range 50–800 °C. In Mn(II) and Ni(II) complexes the
first decomposition step occurs within the temperature range
148–282 °C with an accompanying DTA peak at 233 °C for Mn(II)
and 258 °C for Ni(II) complex, estimated mass loss of 4.54% and
4.49%, respectively. The temperatures at which these losses are ob-
served suggest the presence of one coordinated water molecule in
the complexes. In Co(II) and Cu(II) complexes the first decomposi-
tion step occurs within the temperature range of 143–282 °C with
an estimated mass loss of 4.49% and 4.44%, respectively. An accom-
panying DTA peak observed for Co(II) and Cu(II) at 240 and 238 °C,
respectively, can be attributed to loss of one water molecule. Above
250 °C the complexes decompose in a gradual manner rather than
with the sharp decomposition which may be due to fragmentation
and thermal degradation of the organic moiety, as DTA curve
shows exothermic peak. All these complexes show residue not con-
Fig. 3. X-band polycrystalline ESR spectra of the complexes [Cu(L1)(H2O)Cl] (a),
Fig. 2. TG-DTA curve of [Co(L1)(H2O)Cl].
[Cu(L2)(H2O)Cl] (b), [Cu(L3)(H2O)Cl] (c), [Cu(L4)(H2O)Cl] (d).

S.S. Chavan, V.A. Sawant / Journal of Molecular Structure 965 (2010) 1–6
5
Table 4
Electrochemical data for Ni(II) complexes.
Compound
Reduction potentials
Oxidation potentials
Epa (V)
Epc (V)
E1/2 (V)
D
Ep (mV)
Epa (V)
Epc (V)
E1/2 (V)
D
Ep (mV)
Epa (V)
Epc (V)
E1/2 (V) DEp (mV)
[Ni(L1)(H2O)Cl]
[Ni(L2)(H2O)Cl]
[Ni(L3)(H2O)Cl]
[Ni(L4)(H2O)Cl]
ꢀ1.30
ꢀ1.22
ꢀ1.26
ꢀ1.18
ꢀ1.42
ꢀ1.34
ꢀ1.39
ꢀ1.30
ꢀ1.36 (119)
ꢀ1.28 (123)
ꢀ1.33 (131)
ꢀ1.24 (119)
ꢀ0.62
ꢀ0.56
ꢀ0.57
ꢀ0.53
ꢀ0.75
ꢀ0.70
ꢀ0.71
ꢀ0.67
ꢀ0.69 (136)
ꢀ0.62 (140)
ꢀ0.64 (136)
ꢀ0.60 (146)
+0.42
+0.39
+0.41
+0.39
+0.30
+0.28
+0.28
+0.27
+0.36 (124)
+0.34 (116)
+0.34 (129)
+0.33 (115)
Supporting electrolyte: n-Bu4NClO4 (0.05 M); complex: 0.001 M; solvent: DMF;
E1/2 = ½(Epa + Epc); scan rate:50 mV sꢀ1
D
Ep = Epa ꢀ Epc where, Epa and Epc are anodic and cathodic potentials, respectively;
.
Table 5
X-ray diffraction data of [Ni(L1)(H2O)Cl].
d (Å)
I/I0
10.1
sin2h Obs.
sin2h Calc.
hkl
2h Obs.
2h Calc
7.361
6.592
6.247
5.013
4.820
4.271
3.914
3.386
3.147
3.115
2.826
2.343
2.073
2.029
1.783
109.5
136.5
152.0
236.1
255.4
325.2
387.3
517.5
599.1
611.4
742.9
1080.7
1380.6
1441.1
1866.2
109.5
136.5
162.9
243.3
246.0
327.1
381.9
517.1
600.9
651.6
738.8
1082.8
1379.5
1434.3
1861.4
110
111
102
003
201
202
212
213
302
204
321
116
107
117
530
12.01
13.42
14.17
17.68
18.39
20.78
22.70
26.30
28.34
28.63
31.63
38.39
43.62
44.62
51.19
12.01
13.42
14.67
17.95
18.05
20.84
22.54
26.29
28.38
29.58
31.54
38.42
43.61
44.51
51.12
17.6
12.8
21.3
18.4
23.1
12.4
17.5
32.9
100.0
18.7
7.6
14.8
17.6
9.3
Fig. 4. Cyclic voltammogram of [Ni(L3)(H2O)Cl].
3.5. Cyclic voltammetry
Table 6
X-ray diffraction data of [Cu(L1)(H2O)Cl].
The electrochemical properties of all the Ni(II) complexes were
investigated in DMF solution (10ꢀ3 M) containing 0.05 M n-Bu4N-
ClO4 as supporting electrolyte by cyclic voltammetry. All the mea-
surements were carried out in the potential range +1.5 to ꢀ1.5 V
with scan rate 50 mV sꢀ1 and redox potentials are expressed with
reference to Ag/AgCl. The potentials are summarized in Table 4 and
representative voltammogram of [Ni(L3)(H2O)Cl] is shown in Fig 4.
The cyclic voltammogram of Ni(II) complexes displayed both
anodic and cathodic redox processes. In anodic region the reduc-
tion wave (Epc, +0.277 to +0.302 V) corresponding to Ni(III)/Ni(II)
process is obtained. During reverse scan the oxidation of Ni(II)/
Ni(III) occurs in the potential range (Epa, +0.392 to +0.426 V). The
oxidation observed is quasireversible in nature, characterized by
d (Å)
I/I0
9.1
sin2h Obs.
sin2h Calc.
hkl
2h Obs.
2h Calc.
7.823
7.312
6.491
5.712
4.861
3.987
3.468
3.095
2.762
2.134
2.089
2.019
1.737
96.9
111.0
140.8
181.8
251.1
373.2
493.3
619.4
777.7
1302.8
1359.5
1455.4
1966.4
96.9
111.0
138.72
180.2
249.7
360.6
498.7
622.8
776.2
1303.3
1359.4
1456.3
1969.1
1 0 1
2 0 0
2 1 0
2 0 1
3 0 0
3 2 0
2 2 2
0 0 3
3 3 2
6 1 2
7 0 0
5 5 1
6 5 2
11.30
12.09
13.63
15.50
18.23
22.28
25.67
28.82
32.39
42.32
43.27
44.85
52.65
11.30
12.09
13.53
15.43
18.18
21.89
25.81
28.90
32.35
42.32
43.27
44.87
52.69
13.4
17.8
19.3
11.2
13.5
16.2
13.3
34.7
100.0
21.9
9.6
14.8
a large peak-to-peak separation (
potential region, the complexes display two quasireversible redox
couples at ꢀ0.60 to ꢀ0.69 V ( Ep, 136–146 mV) and ꢀ1.24 to
DEp) of 115–129 mV. In cathodic
indicates high crystallinity of the complexes. The diffractogram
of [Ni(L1)(H2O)Cl] records 15 reflections between 5° and 80° (2h)
with maximum at 2h = 28.63° corresponding to value of d =
3.115 Å (Table 5). However, the diffractogram of [Cu(L1)(H2O)Cl]
consists of 13 reflections with maxima at 2h = 42.32° correspond-
ing to value of d = 2.134 Å (Table 6). The main peaks of [Ni(L1)-
(H2O)Cl] and [Cu(L1)(H2O)Cl] have been indexed by using
computer software by trial and error method, keeping in mind
characteristics of various symmetry systems until good fit could
be obtain between observed and calculated 2h and sin2h values.
The method also yielded hkl (Miller indices) values. The relative
intensities corresponding to prominent peaks have also been
measured.
D
ꢀ1.36 V (
DEp, 119–131 mV), may be assigned to reduction of the
azo group [(-N@N-)/(-N@N-)ꢀ] and [(-N@N-)ꢀ/(-N@N-)2ꢀ], respec-
tively, of the chelated ligand.
3.6. X-ray powder diffraction
Single crystal X-ray crystallographic investigation is the most
precise source of information regarding the structure of the com-
plexes, but 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
[Mn(L1)(H2O)Cl] and [Co(L1)(H2O)Cl] complexes are similar in nat-
ure having no peaks. The trend of the curves decreases from max-
imum to minimum intensity indicating that these complexes are
amorphous in nature in the present metal–ligand formation. The
X-ray diffraction pattern of [Ni(L1)(H2O)Cl] and [Cu(L1)(H2O)Cl]
The indexing of diffractogram of [Ni(L1)(H2O)Cl] and [Cu(L1)-
(H2O)Cl] are identical. Based on this it can be proposed that these
compounds belong to same structural class. A comparison of the
values of 2h and sin2h for the [Ni(L1)(H2O)Cl] and [Cu(L1)(H2O)Cl]
complexes reveals that, there is good agreement between the

6
S.S. Chavan, V.A. Sawant / Journal of Molecular Structure 965 (2010) 1–6
calculated and observed value of 2h and sin2h on the basis of
assumption of tetragonal structure [39]. The small difference in
the observed d spacing can be attributed to difference in unit cell
dimensions. The structure of [Ni(L1)(H2O)Cl] yields values for lat-
tice constant a = b = 10.410 Å, c = 14.810 Å and unit cell volume
V = 1605.32 Å3. However the structure of [Cu(L1)(H2O)Cl] yields
values for lattice constant a = b = 14.624 Å, c = 9.259 Å and unit
cell volume V = 1980.19 Å3. In conjugation with these lattice
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On the basis of physico-chemical characterization, the ligands
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the studied metal–ligand formation. However, Ni(II) and Cu(II)
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Acknowledgement
The authors express their sincere thanks to University Grants
Commission, New Delhi for financial assistance.
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