Spectral studies of copper(II) complexes of tridentate acylhydrazone ligands with heterocyclic compounds as coligands: X-ray crystal structure of one acylhydrazone copper(II) complex

Article abstract of DOI:10.1016/j.saa.2011.04.036

Six copper(II) complexes of 2-hydroxy-4-methoxybenzaldehyde nicotinoylhydrazone (H₂hmbn), 2-hydroxy-4-methoxyacetophenone nicotinoylhydrazone (H₂hman), 2-hydroxy-4-methoxybenzaldehyde benzoylhydrazone (H₂hmbb) and 2-hydrox

Full text of DOI:10.1016/j.saa.2011.04.036

Spectrochimica Acta Part A 79 (2011) 1154–1161
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Spectral studies of copper(II) complexes of tridentate acylhydrazone ligands with
heterocyclic compounds as coligands: X-ray crystal structure of one
acylhydrazone copper(II) complex
Nancy Mathew, Maheswaran Sithambaresan, M.R. Prathapachandra Kurup∗
Department of Applied Chemistry, Cochin University of Science and Technology, Kochi 682022, Kerala, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Six copper(II) complexes of 2-hydroxy-4-methoxybenzaldehyde nicotinoylhydrazone (H2hmbn), 2-
hydroxy-4-methoxyacetophenone nicotinoylhydrazone (H2hman), 2-hydroxy-4-methoxybenzaldehyde
benzoylhydrazone (H2hmbb) and 2-hydroxy-4-methoxyacetophenone benzoylhydrazone (H2hmab)
have been synthesized. The complexes viz. [Cu(hmbn)]2·2H2O (1), [Cu(hman)]2 (2), [Cu(hmbb)]2·2H2O
(3), [Cu(hmbb)phen]·1(1/2)H2O (4), [Cu(hmbb)(bipy)·H2O] (5) and [Cu(hmab)phen] (6) were charac-
terized by different physicochemical techniques. The crystal structure of [Cu(hman)phen] is obtained
and it has a distorted square pyramidal geometry with ꢀ–ꢀ stacking interactions and significant C–H ꢀ
interactions.
Received 4 February 2011
Received in revised form 22 March 2011
Accepted 15 April 2011
Keywords:
Acylhydrazones
Copper(II) complexes
Crystal structure
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
has been deepened by the findings of Johnson et al. which reveals
that the copper(II) complex of the most potent of the chelators,
Over the past few decades, there is growing interest in the study
of coordination chemistry of acylhydrazones and their metal com-
plexes, as they offer a wide spectrum of applications, including
analytical, biological and photochemical fields. The coordination
of bioactive ligands to metal might increase their activity while
some bioinactive ligands acquire activity through coordination.
Many complexes derived from hydrazones have potential biolog-
ical activities and hence they are pharmacologically important.
The presence of heterocyclic rings in the metal complexes play
an important role in their pharmacological properties [1,2]. Acyl-
hydrazones display radioprotective properties and a range of
acylhydrazones have been shown to be cytotoxic while copper
complexes of them show enhanced activity [3]. Among the different
transition metals, copper has gained a special position because of its
presence in biological systems, which are crucial to many biological
processes. Recently Chen et al. have shown that the copper com-
plexes of plumbagin (an extract from the plant Plumbago zeylanica
and used as traditional Chinese medicine) have higher anticancer
properties and are less toxic to healthy cells than commonly used
platinum-based drugs, such as cisplatin [4]. The biomimetic cat-
alytic activity of copper complexes towards the catechol oxidation
and aerobic oxidation of ascorbic acid is reported [5,6]. The inter-
est in the study of chemistry of copper complexes of hydrazones
salicylaldehyde benzoyl hydrazone exhibits appreciably greater
inhibitory activity than salicylaldehyde benzoyl hydrazone itself
[7]. There are so many reports on the studies of Cu(II) complexes
with ligands containing O, N and S donor atoms [8–10]. All the above
said facts stimulate our interest in the study of transition metal
complexes with O and N donor ligands and an extension of our work
on hydrazones [11–16], we report the synthesis and characteriza-
tion of some copper(II) complexes with four different ONO donor
ligands and some heterocyclic compounds as coligands. The crystal
structure of one of the copper(II) complexes is also discussed.
2. Experimental
2.1. Materials
2-Hydroxy-4-methoxyacetophenone (Aldrich), 2-hydroxy-
4-methoxybenzaldehyde (Aldrich), nicotinic acid hydrazide
(Aldrich), benzhydrazide (Aldrich), copper (II) acetate
monohydrate (Qualigens), 2,2ꢀ-bipyridine (Qualigens), 1,10-
phenanthroline (Ranchem) were used without further purification.
Solvent used was methanol.
2.2. Synthesis of acylhydrazones
The acylhydrazones were synthesized by earlier reported meth-
ods [15,16]. Scheme 1 describes the syntheses of acylhydrazones.
∗
Corresponding author. Tel.: +91 484 2862423; fax: +91 484 2575804.
E-mail addresses: mrp k@yahoo.com, mrp@cusat.ac.in (M.R.P. Kurup).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.04.036

N. Mathew et al. / Spectrochimica Acta Part A 79 (2011) 1154–1161
1155
O
OH
R
H2N
O
O
OH
R
reflux 4 h
methanol
H3C
O
H3C
NH
+
N
-H2O
O
NH
X
X
R = H & X=N; H2hmbn
R = CH3 & X= N; H2hman
R = H & X=C; H2hmbb
R = CH3 & X=C; H2hmab
Scheme 1. Syntheses of acylhydrazones.
2.3. Synthesis of complexes
The trial structure was solved using SHELXS-97 and refinement
was carried out by full-matrix least squares on F2 using SHELXL-97
[19] and all the hydrogen atoms were fixed in calculated positions
for compound 6. The molecular graphics employed was DIAMOND
[20].
The complexes [Cu(hmbn)]2·2H2O (1), [Cu(hman)]2 (2) and
[Cu(hmbb)]2·2H2O (3) were prepared by refluxing 1 mmol of
Cu(OAc)2·H2O and 1 mmol of the corresponding ligand (H2hmbn,
H2hman or H2hmbb) in alcoholic medium for 3–5 h. The com-
plexes [Cu(hmbb)phen]·1(1/2)H2O (4), [Cu(hmbb)(bipy)·H2O] (5)
and [Cu(hmab)phen] (6) were prepared by refluxing 1 mmol each of
Cu(OAc)2·H2O, heterocyclic base (bipy/phen) and the correspond-
ing ligand (H2hmbb or H2hmab) in alcoholic medium for about
3–5 h. We tried to prepare the heterocyclic analogous of the lig-
ands (H2hmbn and H2hman) with copper, but our attempts failed.
Complex [Cu(hmab)phen] (6) crystallized from methanol and its
structure has been determined by single crystal X-ray diffraction
studies.
3. Results and discussion
In all the complexes the acylhydrazones are in the doubly
deprotonated form. The colors, magnetic susceptibility and partial
elemental analyses of the complexes are presented in Table 2. The
elemental analyses values are in good agreement with the general
formula of the complexes. Complexes 1, 2 and 3 show substantial
low magnetic moment in the range of 1.05–1.2 ␮ may be due to
B
the coupling of two magnetic centers suggesting dimeric nature to
these complexes [21]. The observed magnetic susceptibility values
of the complexes 4, 5 and 6 are in close agreement with the spin
only value for a d9 copper system.
2.4. Physical measurements
Elemental analyses of the acylhydrazones and their copper(II)
complexes were carried out using a Vario EL III CHNS analyzer at
SAIF, Kochi, India. Infrared spectra were recorded on a JASCO FT/IR-
4100 type A spectrometer in the range 4000–400 cm−1 using KBr
pellets. Electronic spectra were recorded on a Cary 5000 version
1.09 UV–vis spectrophotometer using acetonitrile as the solvent.
Magnetic susceptibility measurements at room temperature were
made using a vibrating sample magnetometer at IIT Roorkee, India.
The EPR spectra of the complexes in the solid state at 298 K, in
DMF at 298 K and at 77 K were recorded on a Varian E-112 spec-
trometer using TCNE as the standard, with 100 kHz modulation
frequency, modulation amplitude 2 G and 9.1 GHz microwave fre-
quency at the SAIF, IIT Bombay, India. The spectra of the complexes
were simulated using Easy Spin package [17]. TG-DTG analyses of
the prepared complexes were carried out on a Perkin Elmer, Dia-
mond thermogravimetric analyzer. The heat flow was 10 ◦C per
minute under nitrogen atmosphere over a temperature range of
50–1000 ◦C.
Table 1
Crystal data and structure refinement parameters for [Cu(hmab)phen] (6).
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
C28H22CuN4O3
526.04
100(2) K
˚
0.71073 A
Monoclinic
P21/c
˚
Unit cell dimensions
a = 16.0239(14) A
˚
b = 10.4971(6) A
˚
c = 14.4246(12) A
˛ = 90◦
ˇ = 106.347(9)◦
ꢂ = 90◦
2328.2(3) A
3
˚
Volume
Z
4
Density (calculated)
Absorption coefficient
F(0 0 0)
1.501 Mg/m3
0.978 mm−1
1084
Crystal size
ꢃ Range for data collection
Index ranges
0.11 mm × 0.08 mm × 0.05 mm
2.94–25.00◦
2.5. X-ray crystallography
−19 ≤ h ≤ 19,
−12 ≤ k ≤ 12,
Single crystals of the compound [Cu(hmab)phen] (6) suitable
for X-ray diffraction studies having approximate dimensions of
0.11 mm × 0.08 mm × 0.05 mm obtained by slow evaporation of the
solution of compound in CH3OH over two days was selected and
mounted on a CrysAlis CCD, Oxford Diffraction Ltd. diffractometer
[18], equipped with a graphite crystal, incident-beam monochro-
−17 ≤ l ≤ 17
Reflections collected
19,930
Independent reflections
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2ꢄ(I)]
R indices (all data)
4100 [R(int) = 0.1638]
Full-matrix least-squares on F2
4100/0/327
1.020
R1 = 0.0832, wR2 = 0.1611
R1 = 0.1633, wR2 = 0.2004
1.374 and −0.521 e.A−3
˚
mator, and a fine focus sealed tube, Mo K␣ (ꢁ = 0.71073 A) X-ray
Largest diff. peak and hole
source at a temperature of 100(2) K at the National Single Crystal
X-ray diffraction Facility, IIT, Bombay, India. The crystallographic
data along with details of structure solution refinements are given
in Table 1.
R1 = ꢅ||Fo| − |Fc||/ꢅ|Fo|
ꢀ
ꢁ
1/2
2
2
˙w(F −F
o
2
)
c
wR2
=
2
2
˙w(F
)
o

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N. Mathew et al. / Spectrochimica Acta Part A 79 (2011) 1154–1161
Table 2
Colors and partial elemental analyses data of copper(II) complexes.
Compound
Color
ꢆeff (B.M)
Found (calculated) %
C
H
N
[Cu(hmbn)]2·2H2O (1)
[Cu(hman)]2 (2)
[Cu(hmbb)]2·2H2O (3)
[Cu(hmbb)phen]·1(1/2)H2O (4)
[Cu(hmbb)(bipy)·H2O] (5)
[Cu(hmab)phen] (6)
Green
Dark green
Green
Green
Green
1.27
1.34
1.05
1.90
1.95
1.96
48.33(47.93)
52.50(51.95)
51.87(51.50)
60.20(60.16)
59.18(59.34)
63.37(63.93)
4.19(3.74)
3.68(3.78)
4.30(4.03)
3.78(4.30)
3.85(4.38)
3.87(4.22)
11.98(11.98)
12.16(12.12)
8.45(8.01)
10.82(10.39)
11.40(11.07)
10.74(10.65)
Green
3.1. Crystal structure of [Cu(hmab)phen] (6)
The crystal structure of the compound along with atom num-
bering scheme is given in Fig. 1. The complex crystallizes into
a monoclinic P21/c space group. In this complex the dinegative
ligand, 2-hydroxy-4-methoxyacetophenone benzoylhydrazone is
coordinated to Cu(II) through the phenolic oxygen O2, azomethine
nitrogen N1 and deprotonated enolate oxygen O3, forming five and
six membered chelate rings. The heterocyclic base phenanthroline
is coordinated to the central metal ion through two nitrogen atoms
N3 and N4 and forms a five membered chelate ring.
The five coordinated complex adopts a square pyramidal geom-
etry, and the basal coordination positions are occupied by O2, N1,
O3 and N3 atoms. The Cu–N4 bond distance is larger when com-
pared with others suggests that N4 occupies an apical position.
This complex is somewhat distorted to square pyramidal geome-
try with the angular structural parameter ꢇ = 0.1366 [22]. The mean
plane deviation calculations show that the atoms O2, N1, O3 and
˚
N3 are nearly planar with a mean plane deviation of 0.2059 A. The
Fig. 2. Quadruple cell packing of the compound [Cu(hmab)phen)] (6) viewed along
the b axis.
significant deviation from regular square pyramidal geometry is
evident from the observed values of bond angles and bond lengths
summarized in Table 3.
phenanthroline rings Cg(5) and Cg(8) are involved in ꢀ–ꢀ stack-
A beautiful arrangement of molecules in the crystal system
in a quadruple cell along b axis is shown in Fig. 2. The ꢀ–ꢀ
interactions play an important role in controlling the packing or
assembly of compounds. Analyses of complexes with nitrogen
containing heterocyclic compounds reveal that ꢀ–ꢀ stacking is
usually an offset or slipped facial arrangement of the rings. Here
packing of the compound is stabililized by ꢀ–ꢀ stacking interac-
tions and C–H· · ·ꢀ interactions. The interchain stacking interaction
between the phenanthroline rings in the compound is remarkably
strong and it may be due to larger ␲ system in phenanthro-
line ligand [23]. In this compound all the phenanthroline rings
are arranged parallel to each other within the unit cell and the
˚
ing with a distance of 3.507 A. Fig. 3 shows the ꢀ–ꢀ stacking
in [Cu(hmab)phen]. In addition to the ꢀ–ꢀ stacking interactions
significant C–H· · ·ꢀ interactions are also present in the unit cell,
they are C15–H15· · ·Cg(3) and C21–H21· · ·Cg(6). These interaction
parameters are listed in Table 4. Weak intramolecular hydrogen
bonding is observed between C(9)–H(9C)· · ·N(2) [with a H· · ·N dis-
◦
˚
tance of 2.19 A and an angle of 111 ]. Intermolecular hydrogen
˚
bonding is C(17)–H(17)· · ·O(1) [with a H· · ·O distance of 2.51 A and
an angle of 120◦] and C(19)–H(19)· · ·O(2) [with a H· · ·O distance of
◦
˚
2.58 A and an angle of 167 ].
3.2. Infrared and electronic spectral studies
The vibrational bands of the free ligands and their copper com-
plexes, which are useful for determining the mode of coordination
of the ligands, are given in Table 5. In the IR spectra of the free
ligands, the carbonyl and azomethine bands are observed in the
Fig. 1. Structure and labeling scheme for [Cu(hmab)phen)] (6).
Fig. 3. ꢀ–ꢀ stacking of [Cu(hmab)phen)] (6).

N. Mathew et al. / Spectrochimica Acta Part A 79 (2011) 1154–1161
1157
Table 3
Selected bond lengths (Å) and bond angles (◦) for the compound [Cu(hmab)phen] (6).
Bond lengths
Bond angles
Bond angles
Cu(1)–O(2) 1.902(5)
Cu(1)–N(1) 1.940(6)
Cu(1)–O(3) 1.950(5)
Cu(1)–N(3) 2.012(6)
Cu(1)–N(4) 2.350(6)
O(2)–C(2) 1.300(8)
O(3)–C(10) 1.308(9)
N(1)–C(8) 1.306(9)
N(1)–N(2) 1.400(8)
N(2)–C(10) 1.327(9)
C(1)–C(8) 1.425(10)
O(2)–Cu(1)–N(1) 92.6(2)
O(2)–Cu(1)–O(3) 163.5(2)
N(1)–Cu(1)–O(3) 82.7(2)
O(2)–Cu(1)–N(3) 90.4(2)
N(1)–Cu(1)–N(3) 171.7(2)
O(3)–Cu(1)–N(3) 92.3(2)
O(2)–Cu(1)–N(4) 97.3(2)
N(1)–Cu(1)–N(4) 111.0(2)
O(3)–Cu(1)–N(4) 99.2(2)
N(3)–Cu(1)–N(4) 76.2(2)
C(4)–O(1)–C(5) 117.6(6)
C(2)–O(2)–Cu(1) 127.2(5)
C(10)–O(3)–Cu(1) 109.5(5)
C(8)–N(1)–Cu(1) 128.1(5)
N(2)–N(1)–Cu(1) 112.8(4)
C(10)–N(2)–N(1) 111.0(6)
C(28)–N(3)–Cu(1) 120.0(5)
C(17)–N(3)–Cu(1) 122.3(5)
C(26)–N(4)–Cu(1) 134.3(5)
C(27)–N(4)–Cu(1) 107.9(5)
C(8)–C(1)–C(2) 125.0(7)
O(2)–C(2)–C(1) 124.0(7)
Table 4
Interaction parameters of the compound [Cu(hmab)phen] (6).
ꢀ–ꢀ interactions
Cg(I)· · ·Cg(J)
Cg–Cg (Å)
˛ (◦)
ˇ (◦)
ꢂ (◦)
Cg(I)
Cg(J)
⊥
⊥
Cg(2)· · ·Cg(5) a
Cg(4)· · ·Cg(5) b
Cg(5)· · ·Cg(5)a
Cg(5)· · ·Cg(8)a
3.981(4)
3.676(4)
3.738(4)
3.507(4)
2.21
17.11
0.00
32.53
27.76
24.50
14.21
31.42
11.70
24.50
14.16
3.397
3.600
3.402
3.401
3.356
3.253
3.401
3.400
0.85
C–H· · ·␲ interactions
C· · ·H(I) Cg(J)
H· · ·Cg (Å)
C–H· · ·Cg (◦)
C· · ·Cg (Å)
C(15)–H(15)· · ·Cg(3)c
2.90
2.65
141
157
3.666
3.526
C(21)–H(21)· · ·Cg(6)d
Equivalent position codes: a = 1 − x, −y, −z; b = 1 − x, 1/2 + y, 1/2 − z Cg(2) = Cu(1) N(3), C(28), C(27), N(4); Cg(4) = N(3), C(17), C(18), C(19), C(20), C(28) Cg(5) = N(4), C(26),
C(25), C(24), C(23), C(27); Cg(8) = C(20), C(21), C(22), C(23), C(27), C(28); c = x,1/2 − y, −1/2 + z; d = 1 − x,1/2 + y,1/2 − z Cg(3) = Cu(1), O(2), C(2), C(1), C(8), N(1); Cg(6) = C(1),
C(2), C(3), C(4), C(6), C(7).
Table 5
Selected IR bands (cm−1) with tentative assignments of copper(II) complexes.
Compound
ꢈ(C O)
ꢈ(C N)
ꢈ(N C)
ꢈ(Cu–N)
ꢈ(N–N)
Heterocyclic breathing
ꢈ(C–O)
H2hmbn·H2O
1643
1604
1594
1602
1591
1600
1588
1589
1588
1600
1590
–
1525
–
1531
–
1547
1532
1529
–
–
420
–
419
–
419
420
407
–
1027
1060
1024
1080
1031
1067
1089
1070
1025
1080
–
–
–
–
–
–
1284
1233
1262
1244
1286
1225
1214
1214
1265
1246
[Cu(hmbn)]2·2H2O (1)
H2hman
–
1638
–
1630
–
–
–
1650
–
[Cu(hman)]2 (2)
H2hmbb
[Cu(hmbb)]2·2H2O (3)
[Cu(hmbb)phen]·1(1/2)H2O (4)
[Cu(hmbb)(bipy)·H2O] (5)
H2hmab
1428, 728
1438, 774
–
[Cu(hmab)phen] (6)
1524
420
1425, 726
regions 1630–1650 cm−1 and 1600–1605 cm−1, respectively. The
O–H and N–H stretching frequencies are observed around 3250 and
the region 30,500–46,000 cm−1 due to ꢀ–ꢀ* transitions. The con-
jugation of azomethine chromophore with olefinic or aryl groups
change the spectrum significantly, since rather weak bands due
to n–ꢀ* transitions are submerged by strong absorptions associ-
ated with ꢀ–ꢀ* transitions [24]. These intraligand transitions were
slightly shifted on complexation. In all the complexes an intense
band at 25,670 cm−1 is assignable to the ligand to metal charge
transfer transition. The d–d bands of complexes except 1 appeared
as weak bands around 15,710 cm−1 [25].
3035 cm−1
.
In all the six copper(II) complexes the bands due to O–H and
N–H are absent which is a clear evidence for the coordination of
ligands in deprotonated form. In all the complexes the azomethine
bands are shifted to lower wavenumbers and the newly formed
–C N–N C– moiety gave bands between 1520 and 1550 cm−1
.
The bands around 415 cm−1 indicate the coordination of azome-
thine nitrogen to copper centre. A new band appears in the region
1230–1255 cm−1 in complexes was assigned to the ꢈ(C–O) mode,
which is also an evidence for the coordination of ligands in the
enolic form. The increase in ꢈ(N–N) bands in complexes, due to the
increase in double bond character is another proof for the coordi-
nation of the ligands through the azomethine nitrogen. There are
broad bands observed around 3400 cm−1 in all complexes except 2
and 6 indicate the presence of water in structures. In compounds
4, 5 and 6, bands due to heterocyclic breathing are observed in the
3.3. EPR spectra
The EPR spectral assignments of the complexes are presented in
Table 7.
The EPR spectra of the compounds recorded in polycrystalline
state at room temperature provide information about the coor-
dination environment of Cu(II) species in these complexes. In
polycrystalline state at room temperature complexes 2, 4 and 6
region 750–1450 cm−1
.
show typical axial symmetry with well defined g and g values
||
⊥
The electronic absorption bands of the free ligands and com-
plexes, recorded in acetonitrile are presented in Table 6. The
electronic spectra of all the four acylhydrazones show bands in
whereas the compounds 1 and 5 gave three g values g1, g2 and
g3 which indicate rhombic distortion in their geometry. In addi-
tion to this, a half field signal obtained for compound 1 (Fig. 4)

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N. Mathew et al. / Spectrochimica Acta Part A 79 (2011) 1154–1161
Table 6
Electronic spectral assignments (cm−1) of copper(II) complexes.
Compound
Intraligand transitions
LMCT
d–d
H2hmbn·H2O
30,450, 33,370, 40,860, 45,800
30,710, 33,810, 41,660, 45,720
30,630, 33,450, 41,920, 45,540
30,710, 33,890, 42,100, 45,800
30,350 (sh), 33,260 (sh), 37,680, 43,520
30,488, 38,020, 44,150
–
–
–
–
–
–
–
–
–
H2hman
H2hmbb
H2hmab
[Cu(hmbn)]2·2H2O (1)
[Cu(hman)]2 (2)
[Cu(hmbb)]2·2H2O (3)
[Cu(hmbb)phen]·1(1/2)H2O (4)
[Cu(hmbb)(bipy)·H2O] (5)
[Cu(hmab)phen] (6)
25,310
24,630
26,150
25,870
26,010
26,280
14,990
16,210
15,700
15,850
15,800
32,530, 37,310, 42,980
32,125, 37,490, 43,320
31,363 (sh), 36,310, 42,290
32,180 (sh), 37,490, 43,460
due to forbidden transition ꢉMs = 2 at 1600 G with g = 4.074, sug-
corresponding to MI = + 3/2 split into three with superhyperfine
coupling constant AN = 12.5 and 15 G, respectively indicating that
the azomethine nitrogen dominates the bonding in solution [30].
The expected half field signal is not obtained in the frozen state
for compound 1. However, a four fold splitting in the parallel region
is obtained (Fig. 5). The spectrum obtained for complex 2 was
not good to interpret due to poor glass formation. The hyperfine
splitting is due to the interaction of the electron spin with the cop-
per nuclear spin (63,65Cu, I = 3/2). In all complexes g > g > 2.0023
gests a dimeric species [26] and the separation between these two
˚
metal centers is less than 3.5 A as there is an interaction between
these copper nuclei [27]. The compound 3 gave no EPR signal in
polycrystalline state at room temperature due to strong antiferro-
magnetic interactions between copper centers. The consistency of
these giso values with the gav values of the spectra in frozen solu-
tion show the existence of the same geometry in both states except
for the compound 3 for which we obtained no EPR signal at poly-
crystalline state. The geometric parameter G, which is a measure of
exchange interaction between copper centers, is calculated using
the equation
||
⊥
indicating the presence of dx
ground state. The g < 2.3 is an
2
2
||
−y
indication of significant covalent character to the M–L bond [31].
The EPR spectrum of compound 3 in DMF showed the presence of
two copper species in the system and we are unable to simulate
this spectrum. This may be due to the cleavage of the compound in
DMF and the coordination of solvent molecule to some copper cen-
ters [32]. In the EPR spectra of the compounds 4, 5 and 6 (Figs. 6–8)
expected superhyperfine splitting due to three nitrogen atoms are
g
|| − 2.0023
for axial spectra
G =
g⊥ − 2.0023
g3 − 2.0023
and G =
g
⊥ − 2.0023
absent. But g > g suggest a distorted square pyramidal geometry
||
⊥
and rules out the possibility of a trigonal bipyramidal structure.
where g = (g + g )/2 for rhombic spectra [28].
⊥
1
2
This is confirmed by the crystal structure of compound 6.
If G > 4.4, exchange interaction is negligible, and if it is less than
4.4 considerable exchange interaction is there [29]. G values for the
compounds 1, 2, 4 and 5 are less than 4.4 indicating considerable
exchange interactions, but for compound 6 the value exceeds 4.4
showing negligible exchange interactions.
The EPR parameters g , g , A and the energies of d–d transitions
||
⊥
||
were used to evaluate the bonding parameters ˛2, ˇ2 and ꢂ2 which
may be regarded as measure of covalency in the in-plane ␴-bonds,
in-plane ␲-bonds and out-of-plane ␲-bonds. The orbital reduc-
tion factors K and K were also used to calculate these bonding
The solution spectra of all complexes were recorded in DMF at
298 K. For all the complexes except 2 isotropic spectra are obtained
and this is due to the tumbling motion of molecules in DMF. All
the complexes in DMF solution clearly showed four well resolved
hyperfine lines (63,65Cu, I = 3/2). In complexes 3 and 5 the signal
||
⊥
parameters.
According to Hathaway [33] for pure ␴-bonding K ≈ K⊥ ≈ 0.77
||
and for in-plane ␲-bonding K < K , while for out-of-plane ␲-
||
⊥
bonding K < K . Here in compounds 3 in DMF and 6, it is observed
⊥
||
Table 7
EPR spectral assignments of copper(II) complexes in polycrystalline state at 298 K, in DMF solution at 298 K and in DMF solution at 77 K.
1
2
3
4
5
6
Polycrystalline (298 K)
g
g1 = 2.050
g3 = 2.187
2.192
–
2.146
g1 = 2.047
g2 = 2.117
g3 = 2.163
2.221
||
g
2.060
2.104
3.288
–
–
–
2.080
2.102
1.849
2.066
2.163
5.584
⊥
giso/gav
G
2.108
2.748
2.109
2.016
DMF (298 K)
giso
Aiso
AN
2.115
73.3
–
–
–
–
2.117
83.3
12.5
2.118
75.0
–
2.117
80.0
15.0
2.109
76.7
–
a
DMF (77 K)
g
g
gav
A
˛
ˇ2
ꢂ2
K
K
2.235
2.055
2.115
198.0
0.817
–
–
–
–
–
–
2.209
2.038
2.095
210.0
0.845
0.841
0.782
0.711
0.661
2.256
2.074
2.135
200.0
0.879
0.881
0.937
0.775
0.824
2.223
2.058
2.113
195.0
0.826
0.879
0.883
0.727
0.730
2.146
2.012
2.056
163.0
0.641
0.914
0.475
0.585
0.304
||
⊥
a
–
–
–
–
–
–
||
2
||
⊥
Expressed in units of cm−1 multiplied by a factor of 10−4
.
a

N. Mathew et al. / Spectrochimica Acta Part A 79 (2011) 1154–1161
1159
Fig. 4. EPR spectrum of complex 1 in polycrystalline state at RT.
that K < K which indicates the presence of significant out-of-plane
show that the weight losses for lattice water are in the range of
50–130 ◦C and weight losses due to coordinated water molecules
are in the range of 130–250 ◦C [34,35]. Here in complexes 1, 3
and 4 there are weight losses in the region 90–130 ◦C indicate the
presence of lattice water molecules and weight loss is observed in
between 160 ◦C and 210 ◦C in compound 5 indicating the presence
of coordinated water molecule in structure. In compounds 2 and
6 there are no weight loss in these regions indicating the absence
of water molecules. All the complexes decompose in the temper-
ature range 250–550 ◦C. Above 550 ◦C a plateau is observed which
corresponds to the formation of CuO.
⊥
||
␲-bonding and the compounds 4 and 5 (K < K ) show in-plane
||
⊥
␲-bonding. The value of bonding parameters ˛2, ˇ2 and ꢂ2 < 1 con-
firms the covalent nature of complexes.
3.4. Thermal studies
Thermal analyses provide valuable information regarding the
thermal stability and nature of water molecules in complexes were
obtained. It helps us to distinguish the lattice water molecules and
coordinated water molecules present in the compound. Reports
Fig. 5. Experimental and simulated best fit EPR spectra of the complex 1 in DMF at 77 K.

1160
N. Mathew et al. / Spectrochimica Acta Part A 79 (2011) 1154–1161
Fig. 6. Experimental and simulated best fit EPR spectra of the complex 4 in DMF at 77 K.
Fig. 7. Experimental and simulated best fit EPR spectra of the complex 5 in DMF at 77 K.
Fig. 8. Experimental and simulated best fit EPR spectra of the complex 6 in DMF at 77 K.
Supplementary data
(CCDC), 12 Union Road, Cambridge, CB2, IEZ, UK; Fax: +44(0)1223-
336033; e-mail: deposit@ccdc.cam.ac.uk].
Crystallographic data for the structural analysis has been
deposited with the Cambridge Crystallographic Data centre, CCDC
696921 for compound [Cu(hman)phen]. Copies of this informa-
tion may be obtained free of charge at www.ccdc.cam.ac.uk/conts/
retrieving.html [or from Cambridge Crystallographic Data Centre
Acknowledgements
M.R.P. Kurup is thankful to the Kerala State Council for Sci-
ence, Technology and Environment, Thiruvananthapuram, Kerala,

N. Mathew et al. / Spectrochimica Acta Part A 79 (2011) 1154–1161
1161
India for financial assistance. Nancy Mathew is thankful to the
University Grants Commission, New Delhi, India for the award of
Senior Research Fellowship. Maheswaran Sithambaresan gratefully
acknowledges the Indian Council for Cultural Relations (ICCR) for
financial support. The authors are thankful to the Sophisticated
Analytical Instrumentation Facility, Cochin University of Science
and Technology, Kochi 22, India for elemental analyses and National
Single Crystal X-ray Diffraction Facility, IIT, Bombay, India for pro-
viding single crystal XRD data.
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