Some new Cu(II) complexes containing an on donor Schiff base: Synthesis, characterization and antibacterial activity

Article abstract of DOI:10.1016/j.poly.2010.10.001

Six new copper(II) complexes, CuLCl·H₂O (1), CuL(NO ₃)·2H₂O (2), [Cu(L)₂] (3), CuL(SCN)·2H₂O (4), CuL(ClO₄)·2H₂O (5) and (CuL)₂(SO₄)·4H₂O (6), wh

Full text of DOI:10.1016/j.poly.2010.10.001

Polyhedron 30 (2011) 154–162
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Some new Cu(II) complexes containing an ON donor Schiff base: Synthesis,
characterization and antibacterial activity
b
a
c
d
e
Tudor Rosu a, , Elena Pahontu , Catalin Maxim , Rodica Georgescu , Nicolae Stanica , Aurelian Gulea
⇑
a University of Bucharest, Faculty of Chemistry, Inorganic Chemistry Laboratory, 23 Dumbrava Rosie Street, 020464 Bucharest, Romania
b University of Medicine and Pharmacy, Faculty of Pharmacy, Organic Chemistry Department, 6 Traian Vuia Street, 020956 Bucharest, Romania
c ‘‘Horia Hulubei” National Institute of Physics and Nuclear Engineering IRASM, Radiation Processing Center, 407 Atomistilor Street, P.O. Box MG-6, Bucharest-Magurele, Romania
d ‘‘Ilie Murgulescu” Institute of Physical Chemistry, Romanian Academy, 202 Splaiul Independentei, 060021 Bucharest, Romania
e Coordination Chemistry Department, Moldova State University, 60 Mateevici Street, Kishineu, Republic of Moldova
a r t i c l e i n f o
a b s t r a c t
Article history:
Six new copper(II) complexes, CuLClꢀH2O (1), CuL(NO3)ꢀ2H2O (2), [Cu(L)2] (3), CuL(SCN)ꢀ2H2O (4), CuL(-
ClO4)ꢀ2H2O (5) and (CuL)2(SO4)ꢀ4H2O (6), where HL = 1-phenyl-2,3-dimethyl-4-(N-2-hydroxy-4-meth-
oxy-benzaldehyde)-3-pyrazolin-5-one, have been synthesized. The characterization of the newly
formed compounds was done by 1H NMR, UV–Vis, IR, ESR spectroscopy, elemental analysis and molar
electric conductivity. The crystal structure of 1-phenyl-2,3-dimethyl-4-(N-2-hydroxy-4-methoxy-benz-
aldehyde)-3-pyrazolin-5-one has been determined by X-ray diffraction studies, as well as the crystal
structure of one of its copper(II) complexes, [Cu(L)2] (3). The copper atom is coordinated to two nitrogen
and two oxygen atoms of the Schiff base ligand. The in vitro antibacterial activity against Klebsiella pneu-
moniae ATCC 100131, Staphylococcus aureus var. Oxford 6538, Pseudomonas aeruginosa ATCC 9027 and Esch-
erichia coli ATCC 10536 strains was studied and compared with that of free ligand. The anti-microbial
activity was dependent on the microbial species tested and the metal salt anion used.
Received 30 August 2010
Accepted 4 October 2010
Available online 14 October 2010
Keywords:
Copper(II) complexes
Schiff bases
Anti-microbial activity
1-Phenyl-2,3-dimethyl-4-(N-2-hydroxy-4-
methoxy-benzaldehyde)-3-pyrazolin-5-one
1-Phenyl-2,3-dimethyl-4-amino-3-
pyrazolin-5-one
Ó 2010 Elsevier Ltd. All rights reserved.
Crystal structure
2-Hydroxy-4-methoxy-benzaldehyde
1. Introduction
hyde. The complexes and ligand were also tested for their
in vitro antibacterial activity against K. pneumoniae, S. aureus, P.
Pyrazolones constitute a group of organic compounds that have
been extensively studied due to their properties and applications.
On the other hand, pyrazolone-based Schiff base chemistry is less
extensive. Some groups have reported the synthesis and character-
ization of pyrazolone-based Schiff base ligands and their Cu(II)
complexes [1–4]. The Schiff base of 4-aminoantipyrine and its
complexes have a variety of applications in biological, clinical, ana-
lytical and pharmacological areas [5–7]. Studies of a new kind of
chemotherapeutic Schiff base are now attracting the attention of
biochemists [8,9].
In a previous paper [10] we presented the synthesis of Cu(II)
complexes derived from the new Schiff base ligands obtained by
condensation of 4-amino-antipyrine with 2-hydroxybenzaldehyde,
terephthalic aldehyde, 4-hydroxy-5-methoxy-isophthalaldehyde,
4,5-dihydroxy-isophthalaldehyde and 3-formyl-6-methyl-chro-
mone. This paper is a continuation of our previous research and
it presents the synthesis and characterization of new complexes
of Cu(II) with a new Schiff base (Fig. 1) obtained by the condensa-
tion of 4-aminoantipyrine with 2-hydroxy-4-methoxy-benzalde-
aeruginosa and E. coli strains using the paper disc diffusion method
and the serial dilutions in liquid broth method [11,12].
2. Experimental
2.1. Materials
2-Hydroxy-4-methoxy-benzaldehyde (Aldrich) and 1-phenyl-
2,3-dimethyl-4-amino-3-pyrazolin-5-one (Merck) were used as re-
ceived. The metal salts CuCl2ꢀ2H2O, Cu(NO3)2ꢀ3H2O, CuSO4ꢀ5H2O,
Cu2(OAc)4ꢀ(H2O)2, Cu(ClO4)2ꢀ6H2O and KSCN (Merck) were used
as supplied. Solvents used for the reactions were purified and dried
by conventional methods [13]. Caution! Perchlorate complexes of
metals with organic ligands are potentially explosive and should
be handled with care.
2.2. Synthesis of the Schiff base 1-phenyl-2,3-dimethyl-4-(N-2-
hydroxy-4-methoxy-benzaldehyde)-3-pyrazolin-5-one (HL)
⇑
A solution of 1-phenyl-2,3-dimethyl-4-amino-3-pyrazolin-5-
one (0.203 g, 1 mmol) in ethanol (10 mL) was added to a solution
Corresponding author. Tel.: +40 0788249557; fax: +40 0213159249.
E-mail addresses: rosu.tudor@unibuc.ro, t_rosu0101@yahoo.com (T. Rosu).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.10.001

T. Rosu et al. / Polyhedron 30 (2011) 154–162
155
Fig. 1. Perspective view of the HL molecule, along with atom numbering scheme.
of 2-hydroxy-4-methoxy-benzaldehyde (0.152 g, 1 mmol) in etha-
nol (20 mL). The reaction mixture was stirred for 2 h at room tem-
perature, then heated to reflux for 2 h and kept at 4 °C for three
days. The characteristic yellow precipitate obtained was filtered
and recrystallized by dissolving in methanol. Fine yellow crystals
obtained upon slow evaporation at room temperature were char-
acterized, including single crystal X-ray diffraction.
(KBr, cmꢁ1):
O–Caliphatic) 1242, 1022;
1297;
t
(C@O) 1636;
t
(C@N) 1602;
t
(Ar–OH) 1117;
t
(Ar–
(OHꢁ) 3434;
t
5(NO3ꢁ) 1494;
t1(NO3
)
ꢁ
t
t
2(NO3ꢁ) 925. The complex is soluble in DMF and DMSO,
and is partially soluble in methanol.
2.3.3. [CuL2] (3)
Brown solid, X-ray quality single crystals were obtained. Yield:
83%; M.p. >220 °C; M.wt.: 735.5; Anal. Calc. for C38H36CuN6O6: C,
61.99; H, 4.89; N, 11.42; Cu, 8.63. Found: C, 62.28; H, 4.33; N,
Yield 76%; M.p.: 192–193 °C; M.wt.: 337; Anal. Calc. for
C19H19N3O3: C, 67.65; H, 5.63; N, 12.46. Found: C, 68.17; H, 5.22;
11.16; Cu, 8.48%. Main IR peaks (KBr, cmꢁ1):
t
(C@O) 1648;
N, 12.08%. The IR spectrum of the obtained ligand confirms the
occurrence of an absorption band at 1629 cmꢁ1 (st, intense), spe-
cific for the azomethinic group [14]. 1H NMR (CDCl3, d, ppm, J,
Hz): 2.35 (s, 3H, CH3-8); 3.15 (s, 3H, N–CH3-7); 3.76 (s, 3H,
OCH3); 6.42 (d, 8.5, 1H, H-17); 6.50 (d, 8.5, 1H, H-18); 7.32 (s 1H,
H-15); 7.42–7.50 (m, 5H, 1, 2, 3, 5, 6); 9.57 (s, 1H, H-12, CH@N);
13C NMR (DMSO-d6, d, ppm): 9.90 (C-8); 35.33 (C-7); 55.49
(OCH3); 132.83 (CH-15); 134.39 (C-4); 149.68 (C-10); 157.97
(C-16); 159.43 (C-12); 162.58 (C-14).
t(C@N) 1609; t(Ar–OH) 1121; t(Ar–O–Caliphatic) 1243, 1024. The
complex is soluble in chloroform, DMF and DMSO, and is partially
soluble in methanol.
2.3.4. CuL(SCN)ꢀ2H2O (4)
Green solid. Yield: 78%; M.p. >220 °C; M.wt.: 493.5; Anal. Calc.
for C20H22CuN4O5S: C, 48.63; H, 4.45; N, 11.34; Cu, 12.86. Found:
C, 49.08; H, 4,22; N, 11.07; Cu, 12.60%. Main IR peaks (KBr,
cmꢁ1):
phatic) 1241, 1029;
t
(C@O) 1632;
t(C@N) 1610; t(Ar–OH) 1120; t(Ar–O–Cali-
t
(OHꢁ) 3437. The complex is soluble in DMF,
2.3. General procedure for the preparation of the metal complexes
(1–6)
DMSO and chloroform, and is partially soluble in methanol.
Complexes 1–3, 5 and 6 were prepared by the direct reaction
between the ligand and the corresponding metal salts. Complex 4
was obtained by refluxing a mixture of CuCl2ꢀ2H2O and 1-phenyl-
2,3-dimethyl-4-(N-2-hydroxy-4-methoxy-benzaldehyde)-3-pyraz-
olin-5-one with addition of KSCN [15].
2.3.5. CuL(ClO4)ꢀ2H2O (5)
Green solid. Yield: 72%; M.p. >220 °C; M.wt.: 535; Anal. Calc. for
C
19H22CuN3O9Cl: C, 42.61; H, 4.11; N, 7.85; Cu, 11.86. Found: C,
43.14; H, 3.88; N, 7.55; Cu, 11.47%. Main IR peaks (KBr, cmꢁ1):
(C@O) 1637; (C@N) 1605; (Ar–OH) 1120; (Ar–O–Caliphatic
1240, 1027;
(OHꢁ) 3440. The complex is soluble in DMF, DMSO
t
t
t
t
)
t
and chloroform, and is partially soluble in methanol.
2.3.1. Synthesis of the complex CuLClꢀH2O (1)
An ethanol solution of CuCl2ꢀ2H2O (2 mmol, 15 mL aqueous/
ethanol 1:2 v/v) was added dropwise to a stirred ethanol solution
of the Schiff base ligand HL (2 mmol, 15 mL). The resulting solution
was stirring for 3 h at room temperature. The green–brown colored
solid was filtered, washed with hot water, then ethanol followed
by ether and dried in vacuo. Yield: 77%; M.p. >220 °C; M.wt.:
453; Anal. Calc. for C19H20CuN3O4Cl: C, 50.33; H, 4.41; N, 9.27;
Cu, 14.01. Found: C, 50.72; H, 4.27; N, 8.98; Cu, 13.92%. Main IR
2.3.6. (CuL)2(SO4)ꢀ4H2O (6)
Dark-green solid. Yield: 83%; M.p. >220 °C; M.wt.: 967; Anal.
Calc. for C38H44Cu2N6O14S: C, 47.15; H, 4.55; N, 8.68; Cu, 13.13.
Found: C, 47.63; H, 4.31; N, 8.36; Cu, 12.76%. Main IR peaks (KBr,
cmꢁ1):
phatic) 1243, 1024;
t
(C@O) 1636;
t
(C@N) 1606;
t
(Ar–OH) 1119;
t(Ar–O–Cali-
t(OH) 3436,
t
3(SO4ꢁ2) 1113;
t
4(SO4ꢁ2) 616.
The complex is soluble in chloroform, DMF and DMSO, and is par-
tially soluble in ethanol and methanol.
peaks (KBr, cmꢁ1):
(Ar–O–Caliphatic) 1240, 1025,
t
(C@O) 1636;
t(C@N) 1607; t(Ar–OH) 1120;
t
t
(OHꢁ) 3450. The complex is soluble
in DMF and DMSO, and is partially soluble in chloroform and
methanol.
2.4. Physical measurements
C, H and N analyses were performed with a Carlo-Erba LA-118
microdosimeter whereas an AAS-1 N Carl-Zeiss-Jena spectrometer
was used for the determination of Cu(II). Physico-chemical analy-
ses were performed after drying the complexes at 105 °C. Infrared
spectra (4000–400 cmꢁ1) were recorded on a BioRad FTS 135
2.3.2. CuL(NO3)ꢀ2H2O (2)
Dark-green solid. Yield: 89%; M.p. 220 °C; M.wt.: 497.5; Anal.
Calc. for C19H22CuN4O8: C, 45.83; H, 4.42; N, 11.25; Cu, 12.76.
Found: C, 46.14; H, 4.16; N, 11.02; Cu, 12.59%. Main IR peaks

156
T. Rosu et al. / Polyhedron 30 (2011) 154–162
spectrophotometer, using KBr pellets. The 1H NMR spectra were
recorded on a Bruker 400 DRX spectrometer in CDCl3 solution,
using TMS as the internal standard. Diffuse reflectance spectra
were recorded on a Jasco V-670 spectrophotometer, in diffuse
reflectance, using MgO dilution matrices. Electron paramagnetic
resonance (EPR) measurements were performed on polycrystalline
powders and DMSO solutions, at room temperature and 77 K, with
Table 2
Selected bond lengths (Å) and bond angles (°) of HL and compound 3.
HL
3
C10 N3
C12 N3
C11 O1
C16 O2
C19 O2
C8 C9
C9 N1
C9 C10
1.402(4)
1.284(4)
1.233(3)
1.373(4)
1.432(5)
1.484(4)
1.354(4)
1.371(4)
1.396(4)
1.440(4)
1.390(5)
1.363(4)
1.407(3)
1.428(4)
1.384(5)
1.467(4)
128.8(2)
120.7(3)
131.5(3)
104.8(2)
121.5(3)
106.9(2)
125.5(3)
118.2(2)
109.4(2)
122.4(2)
120.5(2)
123.6(3)
117.5(3)
C29 N1
C31 N1
C11 O3
C3 O1
C1 O1
C7 O2
1.426(8)
1.307(7)
1.226(8)
1.353(8)
1.442(8)
1.309(7)
1.297(7)
a
MiniScope MS200, Magnettech Ltd., X-band spectrometer
(9.3–9.6 GHz), connected to a PC equipped with a 100 kHz field
modulation unit. The magnetic susceptibility measurements were
carried at room temperature in the polycrystalline state on a Fara-
day magnetic balance (homemade). The complexes were studied
by thermogravimetry (TG) in static air atmosphere, with a sample
heating rate of 10 °C/min. using a DuPont 2000 ATG thermo
balance. The molar conductances of the complexes in dimethyl-
formamide solutions (10ꢁ3 M), at room temperature, were mea-
sured using a Consort type C-533 conductivity instrument.
C33 O4
C11 N2
Cu1 O4
Cu1 O2
Cu1 N2
Cu1 N1
1.901(4)
1.912(5)
1.966(4)
1.972(5)
C10 C11
C16 C17
C17 C18
N1 N2
C4 N2
C5 C6
C7 N1
N3 C10 C11
C12 N3 C10
O1 C11 C10
N2 C11 C10
N3 C12 C13
C9 N1 N2
C9 N1 C7
N2 N1 C7
C11 N2 N1
C11 N2 C4
N1 N2 C4
O1 C11 N2
C16 O2 C19
O4 Cu1 O2
O4 Cu1 N2
O2 Cu1 N2
O4 Cu1 N1
O2 Cu1 N1
N2 Cu1 N1
92.75(19)
144.3(2)
95.99(19)
95.64(18)
137.1(2)
2.5. X-ray crystallography
A summary of the crystallographic data and details of the data
collection of HL and 3 are given in Table 1. Selected bond lengths
and bond angles are given in Table 2. A crystal of suitable size
was selected from the mother liquor and immersed in paratone
oil, then mounted on the tip of a glass fiber and cemented using
epoxy resin. XRD data were collected on a STOE IPDS II image plate
101.06(19)
detector using graphite-monochromated Mo
K
a
radiation
(k = 0.71073 Å), at room temperature. Data collection: Stoe x-area.
Cell refinement: Stoe x-area [16a]. The structures were solved by
direct methods and refined with anisotropic displacement param-
eters based on F2, using SHELXS 97 [16b] and SHELXL 97 [16c] pro-
grams. Packing and H-bonding diagrams are generated by the
DIAMOND program. Non-hydrogen atoms were refined anisotropi-
cally until convergence was reached. The hydrogen atoms were
stereochemically fixed in their ideal positions with fixed isotropic
U values.
aeruginosa and E. coli strains using the paper disc diffusion method
[17a] (for the qualitative determination) and the serial dilutions in
liquid broth method [17b] (for determination of MIC). Streptomy-
cin was used as internal standard.
Suspensions of microorganisms in sterile peptone water were
adjusted to 0.5 McFarland. Muller–Hinton petri dishes of 90 mm
were inoculated using these suspensions. Paper disks (6 mm in
diameter) containing 10
lL of the substance to be tested (at a con-
2.6. Antibacterial activity
centration of 2048 g/mL in DMSO) were placed in a circular pat-
l
tern in each inoculated plate. Incubation of the plates was done at
37 °C for 24 h. The reading of the results was done by measuring
the diameters of the inhibition zones generated by the tested sub-
The free ligand and metal complexes were screened for their
in vitro antibacterial activity against K. pneumoniae, S. aureus, P.
stances, using a ruler. Determination of MIC (lg/mL) was done
Table 1
using the serial dilutions in liquid broth method. The materials
used were 96-well plates, suspensions of microorganism
(0.5 McFarland), Muller–Hinton broth (Merck) and solutions of
Crystallographic data, details of data collection and structure refinement parameters
for compound HL and 3.
Compound
HL
3
the substances to be tested (2048
concentrations of the substances to be tested were obtained in
the 96-well plates: 1024; 512; 256; 128; 64; 32; 16; 8; 4; 2 g/
lg/mL in DMSO). The following
Chemical formula
C
19H19N3O3
C38H36CuN6O6
736.27
293
0.71073
triclinic
P1
10.755(3)
13.083(3)
14.461(3)
105.997(18)
102.276(18)
110.404(18)
1722.4(7)
2
M (g molꢁ1
)
337.37
293
0.71073
monoclinic
C2/c
30.760(5)
6.9320(8)
17.077(3)
90
110.387(13)
90
3413.2(9)
8
1.313
0.091
1424
l
Temperature, (K)
Wavelength, (Å)
Crystal system
Space group
a (Å)
mL. After incubation at 37 °C for 24 h, the MIC for each tested sub-
stance was determined by macroscopic observation of microbial
growth. It corresponds to the well with the lowest concentration
of the tested substance where microbial growth was clearly
inhibited.
ꢀ
b (Å)
c (Å)
a
(°)
b (°)
3. Results and discussion
c
(°)
V (Å3)
The present Schiff base HL (Scheme 1) was prepared under the
method described elsewhere [10], by refluxing in ethanol (30 mL)
an equimolar mixture of 4-aminoantipyrine with 2-hydroxy-4-
methoxy-benzaldehyde. The structure of formed Schiff bases was
established by IR, 1H NMR and 13C NMR spectroscopies and by
X-ray crystallography.
All compounds were prepared by direct reaction between
ligand and the corresponding metal salts, while compound 4 was
prepared by using a mixture of CuCl2ꢀ2H2O and HL with addition
Z
Dcalc (g cmꢁ3
)
1.420
0.691
766
0.947
l
(mmꢁ1
)
F(0 0 0)
Goodness-of-fit on F2
0.948
Final R1, wR2 [I > 2
r
(I)]
0.0675,
0.1401
0.1476,
0.1670
ꢁ0.220, 0.272
0.0780, 0.1556
R1, wR2 (all data)
0.1429, 0.1766
Largest difference in peak and hole (e Åꢁ3
)
ꢁ0.933, 0.529

T. Rosu et al. / Polyhedron 30 (2011) 154–162
157
2
O
3.1. Structural characterization of HL and [Cu(L)2] (3)
3
15
OH
H31C9
16
14
The structure of the Schiff base ligand HL is shown in Fig. 1. This
ligand crystallizes in the monoclinic system, space group C2/c.
The OH bond is found to be disordered over two positions with
a site occupational factor (s.o.f.) refined to 0.7 (O3) and 00.3 (O3A).
The distance between the atoms C(12)–N(3) is 1.284(4) ÅA, suggest-
ing the formation of an azomethine bond. Also, the bite angle
[C(10)–N(3)–C(12) = 120.7(3)°] is proof of the sp2 hybridization at
the C(12) and N(3) atoms.
3
N
8
CH3
17
10
11
9
13
12
18
N1
1
O
2
N
7
CH3
4
5
3
2
6
A perspective view of the molecule and its association through
hydrogen bonds is represented in Fig. 2. In the crystal structure
two types of hydrogen bonds coexist. Intramolecular interactions
1
Scheme 1. Schiff base ligand HL (numbering similar to Fig. 1).
(70% molecules), Fig. 2a, are established between the O(3) and azo-
0
methine nitrogen atoms [O3A–N3 = 2.62 ÅA]. Intermolecular inter-
actions, dimers present only in a small quantity (<30%), are
established between the ligand molecules through O(1), the exocy-
clic ketonic oxygen of the antipyrine ring, and O(3A) of the 2-hy-
droxy-4-methoxy-benzaldehyde ring [O1ꢀ ꢀ ꢀO3A = 2.87 Å], Fig. 2b.
The packing of the molecules in the crystal, Fig. 3, is influenced
of KSCN. The obtained complexes are microcrystalline solids which
are stable in air and have melting points above 220 °C. They are
insoluble in organic solvents such as acetone, but soluble in
methanol, DMF and DMSO. The molar conductivity values
(8–12 ohmꢁ1 cm2 molꢁ1) of the complexes 1–5 in 10ꢁ3 M solution
DMF show that they are non-electrolytes and
6
(79 ohmꢁ1
by van der Waals’ interactions and
pꢁp contacts (3.34–3.83 Å),
cm2 molꢁ1) is electrolyte [18]. The elemental analyses data of the
Schiff base and complexes (reported in Section 2) are in agrement
with structure of the ligand and with structures of the complexes
(Scheme 2), respectively.
established between the phenyl ring from one molecule and the
antipyrine ring from another molecule. The 2-hydroxy-4-meth-
oxy-benzaldehyde ring is almost in the same plane with central
five-membered ring of the antipyrine moiety.
O
H3C
O
N
N
H3C
H3C
N
O
N
O
CH3
CH3
H2O
Cu
N
CH3
N
Cl
;
Cu
N
O
O
O
O
H3C
CH3
CH3
N
O
N
1
3
2
+
O
H3C
O
OH
2 N
CH3
O
CH3
Cu
N
H2O
H O
2
O
N
CH3
O
H3C
N
O
O
N
H3C
H3C
OH2
N
Cu
Cu
H2O
N
SO4
;
H3C
N
X
N
O
OH2
X = NO3 , SCN , ClO4
CH3
O
2, 4, 5
6
Scheme 2. Proposed structures of the metal complexes.

158
T. Rosu et al. / Polyhedron 30 (2011) 154–162
Fig. 2. Hydrogen bonding interactions: (a) intramolecular (b) intermolecular in HL.
Fig. 3. Packing diagrams in the crystal HL.

T. Rosu et al. / Polyhedron 30 (2011) 154–162
159
The molecular structure of compound 3 is depicted in Fig. 4, and
representative bond length and bond angle values are collected in
Table 2. This compound crystallizes in the triclinic system, space
energies (1610–1602 cmꢁ1) in the spectra of the complexes, indi-
cating coordination via the azomethine nitrogen. This is confirmed
by bands in the range 467–463 cmꢁ1, which have been assigned to
ꢀ
group P1.
the m(Cu–N) band [4,14a,20]. The m(C@O) band of the ligand at
The copper atom is coordinated to two nitrogen and two oxygen
atoms of the Schiff base ligand. The dihedral angle h between the
two M(NO) planes is 53.74°. For a planar (local D2h) geometry h
would be 0°, and for pseudo-tetrahedral (local D2d) geometry h
would be 90°; the metal ion is therefore in a geometry that is
much closer to pseudo-tetrahedral than planar. The bite angles
O(1A)–Cu(1)–O(1) (92.75(19)°), N(3)–Cu(1)–O(1) (95.99(19)°),
N(3A)–Cu(1)–O(1A) (95.64(18)°), N(3A)–Cu(1)–O(1) (137.1°),
N(3)–Cu(1)–O(1A) (144.3°) and N(3)–Cu(1)–N(3A) (101.06°) also
support the distortion from the tetrahedral geometry.
1646 cmꢁ1, for the exocyclic carbonyl group, is shifted by 10–
14 cmꢁ1 to lower energies in the spectra of the complexes 1, 2,
4–6. This indicates that the exocyclic carbonyl oxygen is bonded
to the metallic ions [4,14,20]. In the IR spectrum for complex 3,
m(C@O) remains un-modified, indicating that the exocyclic ketonic
oxygen of the antipyrine ring is not involved in the coordination
[20].
In the IR spectrum of HL, a broad medium intensity band occurs
in the 3500–3390 cmꢁ1 range, along with a narrow band of med-
ium intensity (1135 cmꢁ1), ascribed to the
m(OH) vibration of the
The C(7)–O(1) and C(33)–O(1A) bond lengths in the coordinated
ligand are between the values for a double (1.23 Å) and single
hydroxymethyl group and H2O. In the IR spectra of complexes 1,
2, 4–6, a considerable peak observed in the 3450–3434 cmꢁ1 range
(1.43 Å) bond, which indicates significant delocalization of the
p
supports the presence of
m(H2O) in the complexes [21].
electrons of the 2-hydroxy-4-methoxy-benzaldehyde ring towards
the oxygen atoms O(1) and O(1A), respectively [19].
The phenolic m(C–O) stretching vibration in the free Schiff base
is observed at 1135 cmꢁ1 [17a], which is shifted by 14–18 cmꢁ1 to-
wards lower wavenumbers in the complexes, thus indicating coor-
dination of the phenolic oxygen to the Cu2+ ion [22].
The four independent Cu–N and Cu–O distances are in the range
1.901(4)–1.972(5) Å. The molecules are packed along the c-axis.
The interactions between the phenyl ring of one molecule and
the pyrazol moiety of another one reinforce crystal structure cohe-
sion in the molecular packing in the crystal lattice.
The nitrato complex 2 has two bands at 1494 and 1297 cmꢁ1
corresponding to m5 and
medium band at 925 cmꢁ1 assigned to m2 of the nitrato group.
The separation m5 m1 can be used as a near criterion to distinguish
m
1, with a separation of 197 cmꢁ1, and a
–
between the degree of covalence of the nitrate coordination. These
values indicating the presence of a terminal monodentate nitrato
group [14a,14b,23].
3.2. Infrared spectra
The ligand and complexes have been characterized in detail by
recording their IR spectra. The proposed assignments are based on
The thiocyanato complex 4 exhibits a strong and sharp band at
2096 cmꢁ1, a weak band at 745 cmꢁ1 and another weak band at
previous results [10] and pertinent bibliography [24]. The m(C@N)
484 cmꢁ1 which can be attributed to
m(CN), m(CS) and d(NCS),
band of the ligand at 1629 cmꢁ1 is found to be shifted to lower
respectively. These values are typical for N-bonded thiocyanato
complexes [23a,23b].
The perchlorate complex 5 shows a single band at 1087 cmꢁ1
and a strong band at 628 cmꢁ1, indicating the presence of ionic
perchlorate. The band at 1087 cmꢁ1 is assignable to
m
3(ClO4) and
4(ClO4). The splitting of
these bands shows the presence of a coordinated perchlorate group
[14,24].The sulfato complex 6 has bands at 1113 and 616 cmꢁ1
assignable to m3 and 4, indicating the presence of a non-coordi-
the band at 628 cmꢁ1 is assignable to
m
,
m
nated sulfato group [14,25].
3.3. Electronic spectra
The significant electronic absorption bands in the spectra of the
ligand and all the complexes are presented in Table 3. The energy
values of the d–d transitions suggest a tetragonal geometry for
complexes 2, 4–6, a tetrahedral distorted geometry for complex 3
and a trigonal bipyramidal geometry for complex 1 [26]. The
charge transfer band for the complexes appeared at 26 300–
25 000 cmꢁ1 with a shoulder at 23 250–22 250 cmꢁ1[21].
The values of leff (1.76–2.06 BM) for complexes 1–5 suggest the
presence of an unpaired electron. Also, it indicates the existence of
monomeric species of copper(II). Complex 6 shows a very low
magnetic moment of 1.44 BM per copper center, measured at room
Fig. 4. Perspective view of complex 3 along with the atom numbering scheme.
Table 3
Electronic spectra (cmꢁ1) and magnetic moment (BM) of the complexes 1–6.
Metal complex molecular formula
Transitions d–d (cmꢁ1
)
leff MB
Geometry
[Cu(L)(H2O)Cl] (1)
[Cu(L)(NO3)(H2O)2] (2)
[Cu(L)2] (3)
[CuL(SCN)(H2O)2] (4)
[CuL(ClO4)(H2O)2] (5)
[Cu2(L)2(H2O)4]SO4 (6)
2A1g
2B1g
?
?
2B1g 11 900
2A1g
2B1g
?
?
2B2g 17 240
2B2g 13 550
2.06
1.89
1.97
1.76
1.78
1.44
Trigonal bipyramidal
Tetragonal
Tetrahedral (distortion)
Tetragonal
Tetragonal
Tetragonal
2A1g
-
2B1g
?
2Eg 18 310
2B2
?
2E-
2B2
?
2B1(2A1) 14710
2B1g
2B1g
2B1g
?
?
?
2A1g
2A1g
2A1g
-
-
-
2B1g
2B1g
2B1g
?
?
?
2Eg 17 880
2Eg 18 310
2Eg 18 510
2B1g
2B1g
2B1g
?
?
?
2B2g 13 250
2B2g 13 620
2B2g 13 790

160
T. Rosu et al. / Polyhedron 30 (2011) 154–162
temperature. The subnormal magnetic moment indicates that the
copper centers are antiferromagnetically coupled [27].
3.4. EPR spectra
The EPR spectra of polycrystalline samples at 298 K, and DMSO
solutions at 298 and 77 K were recorded in the X-band using 100-
kHz modulation and g factors were quoted relative to the standard
marker TCNE (g = 2.00277). EPR spectral assignments of the cop-
per(II) complexes and orbital reduction parameters are in Table
4. The EPR spectra of the complexes recorded in the polycrystalline
state provide information about the coordination environment
around copper(II). The EPR spectra of complexes 1–6 in the poly-
crystalline state at 298 K shows different types of geometrical spe-
cies. The spectrum of complex 1 (Fig. 5) shows three g values:
g3 = 2.236, g2 = 2.127, g1 = 2.055, which indicate a trigonal bipyra-
midal geometry [28]. In trigonal bipyramidal complexes the un-
2
2
paired electron lies in the dz orbital, giving A1g as the ground
state. The g and A// tensor values (g// = 2.405, g\ = 2.052, A// = 117
G) suggests that complex 3 has a distorted tetrahedral geometry,
which is in good agreement with the X-ray determined structure.
The spectra of the complexes 2 and 4–6 show axial symmetry
with well-defined g// and g\ values. In these Cu(II) complexes, ten-
sor values of g// > g\ are consistent with a dx ꢁ y ground state
[29]. For complex 6, a half field signal at g = 4.187 was observed,
indicating a dimeric species [10d,24].
Fig. 5. (a) EPR spectrum of 1 in the polycrystalline state at 77 K; (b) second
derivative spectrum at 77 K.
2
2
The geometric parameter G, which is a measure of the exchange
interaction between copper centers in a polycrystalline compound,
is calculated using the equation G = (g// ꢁ 2)/(g\ ꢁ 2) for axial spec-
tra, and for rhombic spectra, G = (g3 ꢁ 2)/(g\ ꢁ 2) and g\ = (g1 + g2)/
2
2. G values less than 4.0 are consistent with a dx ꢁ y2 ground state
having a small exchange coupling (complexes 2, 4–6). If G is higher
than 4.0, the exchange interaction is negligible (complex 3) [30].
The EPR spectra of complex 1 in DMSO solution at 77 K, shows a
typical distorted tetrahedral geometry, with values: g// = 2.413 and
g\ = 2.080 and hyperfine splitting into four lines. The EPR spectra
of complexes 2–6 in DMSO solution at 77 K are axial. These show
four well defined hyperfine lines in the parallel region correspond-
ing to the electron spin-nuclear spin interaction. The EPR spectra of
complexes 1, 3 and 6 in DMSO solution at 77 K are given in Fig. 6.
The g// values are nearly the same for all the complexes, indicat-
ing that the bonding is dominated by the 4-amino-antipyrine moi-
ety. In all the complexes, g// > g\. The fact that g// values are less
than 2.3 is an indication of significant covalent character to the
M–L bond [29a,29c].
Fig. 6. EPR spectra of 1, 3 and 6 in DMSO solution at 77 K.
The EPR parameters g//, g\, A// (Cu) and the energies of the d–d
transition were used to evaluate the bonding parameters
a
2, b2 and
d2, which may be regarded as measures of the covalency of the in-
calculated using expressions reported elsewhere [32]. Hathaway
plane
r bonds, in-plane p bonds and out-of-plane p bonds
has pointed out that for pure
in-plane -bonding, K// < K\, while for out-of-plane
K// > K\ [33].
r
bonding, K// ꢂ K\ ꢂ 0.77 and for
[30a,31]. The orbital reduction factors K//
=
a2b2 and K\
=
a2d2 were
p
p-bonding,
The empirical factor f = g///A// cmꢁ1 is an index of tetragonal dis-
tortion. Values of this factor may vary from 105 to 135 for small to
extreme distortions in square planar complexes and it depends on
the nature of the coordinated atoms [34]. The f values of complexes
2–6 are found to be in the range 137–154, indicating significant
distortion from planarity.
Table 4
EPR spectral parameters of the copper(II) complexes 1–6.
1
2
3
4
5
6
Polycrystalline(298 K)
g//
g\
2.236(g3)
2.055(g1) 2.127(g2)
2.220
2.068
2.405
2.052
2.256
2.065
2.240
2.062
2.363
2.162
DMSO (77 K)
g//
g\
A//
a2
b2
d2
2.413
2.08
125
0.830
0.990
0.873
0.822
0.525
2.292
2.078
152
0.784
0.980
0.998
0.768
0.783
2.290
2.070
160
0.801
0.887
0.963
0.710
0.771
2.287
2.062
148
0.760
0.991
0.904
0.753
0.687
2.289
2.072
154
0.782
0.979
0.963
0.766
0.753
2.285
2.07
166
0.812
0.943
0.918
0.766
0.746
3.5. Anti-microbial activity
The free ligand and its metal complexes were screened for their
antibacterial activity. The results (Table 5) indicate that the ligand
does not have any significant activity, whereas its complexes
showed more activity against the some microorganisms under
identical experimental conditions.
K//
K\

T. Rosu et al. / Polyhedron 30 (2011) 154–162
161
Table 5
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Antibacterial activities of ligand HL and its Cu(II) complexes 1–6 as MIC values
(l
g/mL).
Compound
Gram-positive bacteriaa Gram-negative bacteriab
References
Kp
Sa. Oxf
Pa
Ec
HL
128
16
256
8
128
4
64
128
16
512
512
1024
1024
512
4
256
128
256
16
256
256
128
512
1024
1024
1024
1024
16
512
16
256
64
512
512
16
1024
1024
512
1024
512
8
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[Cu(L)(NO3)(H2O)2] (2) 128
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512
1024
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512
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[CuL(SCN)(H2O)2] (4)
[CuL(ClO4)(H2O)2] (5)
[Cu2(L)2(H2O)4]SO4 (6)
CuCl2ꢀ2H2O
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