Synthesis, crystal structure, spectroscopic, thermal, catechol oxidase and catalase-like studies: New copper(II) complexes of 2-benzoylbenzoate and 2-pyridilpropanol ligands

Article abstract of DOI:10.1016/j.ica.2012.11.028

Two novel copper(II) complexes, mononuclear [Cu(bba)₂(pypr) ₂] 1 and dinuclear [Cu₂(bba)₂(pypr) ₂] 2, have been synthesized by reactions of 2-pyridilpropanol with CuSO₄·5H₂O or Cu(CH₃COO) ₂·2H₂O metal salt in the presence of 2-benzoylbenzoic acid. The copper(II) ion has a distorted octahedral geometry in 1 and distorted square pyramidal geometry in 2. 1 crystallizes in space group P1?, while 2 crystallizes in the monoclinic crystal system with the space group P2₁/n. 2-Benzoylbenzoate behaves as a monodentate in 1, bidentate in 2. 2-pyridilpropanol ligand acts as a bidentate in 1 and bridging in 2. Both complexes were characterized by elemental analysis, mass and IR spectroscopy. Their molecular structures were determined by X-ray crystal structure analysis and their thermal stabilities were confirmed by TG/DTA/DTG techniques. Dinuclear compound shows high catalytic activity regarding the oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone exhibiting saturation kinetics at high substrate concentrations. In addition, dinuclear compound demonstrates significantly catalase-like activity. But mononuclear complex shows neither catalase-like nor catechol oxidase activity.

Full text of DOI:10.1016/j.ica.2012.11.028

Inorganica Chimica Acta xxx (2013) xxx–xxx
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, crystal structure, spectroscopic, thermal, catechol oxidase
and catalase-like studies: New copper(II) complexes of 2-benzoylbenzoate
and 2-pyridilpropanol ligands
a
a
a
b
c
Sema Caglar a, , Ekrem Adıgüzel , Bulent Caglar , Tuba Saykal , Ertan Sahin , Orhan Büyükgüngör
⇑
a Department of Chemistry, Faculty of Arts and Sciences, Erzincan University, 24100 Erzincan, Turkey
b Department of Chemistry, Faculty of Arts and Sciences, Atatürk University, Erzurum 25240, Turkey
c Department of Chemistry, Faculty of Arts and Sciences, Ondokuz Mayis University, 55200 Atakum, Samsun, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 June 2012
Received in revised form 21 November 2012
Accepted 28 November 2012
Available online xxxx
Two novel copper(II) complexes, mononuclear [Cu(bba)2(pypr)2] 1 and dinuclear [Cu2(bba)2(pypr)2] 2,
have been synthesized by reactions of 2-pyridilpropanol with CuSO4ꢀ5H2O or Cu(CH3COO)2ꢀ2H2O metal
salt in the presence of 2-benzoylbenzoic acid. The copper(II) ion has a distorted octahedral geometry
ꢀ
in 1 and distorted square pyramidal geometry in 2. 1 crystallizes in space group P1, while 2 crystallizes
in the monoclinic crystal system with the space group P21/n. 2-Benzoylbenzoate behaves as a monoden-
tate in 1, bidentate in 2. 2-pyridilpropanol ligand acts as a bidentate in 1 and bridging in 2. Both com-
plexes were characterized by elemental analysis, mass and IR spectroscopy. Their molecular structures
were determined by X-ray crystal structure analysis and their thermal stabilities were confirmed by
TG/DTA/DTG techniques. Dinuclear compound shows high catalytic activity regarding the oxidation of
3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone exhibiting saturation kinetics at high substrate con-
centrations. In addition, dinuclear compound demonstrates significantly catalase-like activity. But mono-
nuclear complex shows neither catalase-like nor catechol oxidase activity.
Keywords:
Dinuclear copper(II) complex
2-Benzoylbenzoic acid
Crystal structure
Catechol oxidation
Catalase activity
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
Catalase, which is the sensible protective enzymes, plays an
important role in the conversion of hydrogen peroxide to less
Metal–organic frameworks are gaining intensive attention due
to their wide practical utility as dyes, extractants, drugs, pesticides,
catalysts, magnetism, host–guest chemistry [1–5]. Usually, multid-
entate organic ligands containing coordination sites of N and/or O
donors play key roles in construction of novel metal–organic
frameworks [6].
Copper(II) ion plays an important role in biological systems,
supramolecular chemistry [7–11] and various enzymatic reactions,
such as catechol oxidase [12–22] and catalase like activity.
Catechol oxidase has been successfully conducted by Krebs and
co-authors since 1998 [23]. Catechol oxidase, in other words the
polyphenol oxidases, oxidizes phenolic compounds in the presence
of dioxygen to the corresponding quinone [24]. Dioxygen reduction
to water is coupled to the oxidation of two catechol molecules in
these processes. The analysis revealed that the active site consists
of mainly dinuclear copper(II) center. The catalytic activity of
[Cu2(bba)2(pypr)2] for the oxidation of 3,5-di-tert-butylcatechol
to the corresponding o-quinone in methanol solvent has been
studied by UV–Vis spectroscopic technique (Fig. 1).
harmful dioxygen and water (2H2O2 ? 2H2O + O2) [25]. Several
studies have been carried out on metal complexes to act as cata-
lase-like [26–29]. In this paper, the dinuclear copper(II) complex
and its catalase-like activity towards disproportionation of H2O2
is reported.
2-Pyridilpropanol ligand is water-soluble and shows a variety of
coordination modes. Because it has oxygen and nitrogen atoms as
potential donor, 2-pyridilpropanol has had much attraction from
the field of coordination chemistry. 2-benzoylbenzoate anion
[bba = (C14H9O3)ꢁ], which is deprotonated form of 2-benzoylben-
zoic acid (Hbba = C14H10O3), is a versatile ligand that can coordi-
nate since the presence of the negatively charged carboxylate
and carbonyl oxygen atoms. There are few studies relating to metal
complexes of bba in the literature [30–39]. This ligand and its
derivatives have had application in supramolecular coordination
compounds [30], in the preparation of electron-transport materials
[30], and in sweeteners [31].
In our previous studies, we prepared and structurally character-
ized a series of cobalt(II), nickel(II), copper(II), mercury(II) and
zinc(II) complexes containing the bba, 1,10-phenanthroline,
3-picoline or N,N0-bis(3-aminopropyl)ethylenediamine [40–44].
Especially, a systematic investigation of the impact of changes in
⇑
Corresponding author. Tel.: +90 446 224 30 97; fax: +90 446 224 30 16.
E-mail address: semacaglar2002@hotmail.com (S. Caglar).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.11.028
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2
S. Caglar et al. / Inorganica Chimica Acta xxx (2013) xxx–xxx
Fig. 1. Oxidation of the 3,5-di tert-butyl catechol by the catalyst.
the metal salt on the structure of the complexes was carried out. In
the present study, the syntheses, crystal structures, spectroscopic
and thermal properties of two new [Cu(bba)2(pypr)2] 1 and
[Cu2(bba)2(pypr)2] 2 complexes were investigated. Also, catechol
oxidase activity and catalase-like activity of dinuclear [Cu2(bba)2
(pypr)2] 2 have been discussed in detail.
2.2. Synthesis of [Cu(bba)2(pypr)2]
CuSO4ꢀ5H2O (0.075 g, 0.3 mmol) and 2-Hbba (2-benzoylbenzoic
acid) ligand (0.136 g, 0.6 mmol) were dissolved in ethanol (40 cm3)
with continuous stirring at 50 °C. Then 5 mL ethanol solution of 2-
pyridilpropanol (0.085 g, 0.6 mmol) was added. The resulting solu-
tion was allowed to evaporate slowly at room temperature, blue
colored crystals appeared after one week.
2. Experimental
Yield: 60%. Anal. Calc. for C44H40N2O8Cu: C, 66.98; H, 5.07; N,
3.55. Found: C, 67.08; H, 5.09; N, 3.58%.
2.1. Methods of sample characterization
2.3. Synthesis of [Cu2(bba)2(pypr)2]
All reactions were performed with commercially available re-
agents and they were used without further purification, and the
solvents were distilled and dried by standard procedures. Infrared
spectra of the complex salts were recorded with a Spectrum-100
FT-IR spectrophotometer in frequency range 4000–450 cmꢁ1 at a
resolution 4 cmꢁ1 by using KBr pellet. UV–Vis spectra were re-
corded on PG 80+ in the 200–900 nm range in methanol. Elemental
analyses (carbon, hydrogen and nitrogen) were determined with
an Elementar Micro Vario CHNS. The TG and DTA curves were
scanned using a PRIS Diamond TG/DTG apparatus in a nitrogen
atmosphere (heating rate: 10 °C minꢁ1, platinum crucibles, mass
ꢂ10 mg and temperature range 30–1000 °C). The electrospray
mass spectrum (ES-MS) was determined on an Agilent Quantum
Access Max and the concentrations of the samples were about
1.0 mM.
This complex was prepared in a similar manner to 1 using
Cu(CH3COO)2.2H2O. Yield: 80%. Anal. Calc. for C44H38N2O8Cu2: C,
62.13; H, 4.47; N, 3.29. Found: C, 62.20; H, 4.51; N, 3.32%.
2.4. X-ray crystallography
For the crystal structure determination, the single-crystals of
the Cu(II) complexes 1 and 2 were used for data collection on a
four-circle Rigaku R-AXIS RAPID-S diffractometer (equipped with
a two-dimensional area IP detector). The graphite-monochroma-
tized MoK
nique with
a
D
radiation (k = 0.71073 Å) and oscillation scans tech-
= 5° for one image were used for data collection.
x
The lattice parameters were determined by the least-squares
Table 1
Crystal data and structure refinement parameters for (1) and (2) complexes.
(1)
(2)
Empirical formula
Formula weight
T (K)
C
44H40N2O8Cu
C44H38N2O8Cu2
849.84
293
788.33
293
k (Å)
0.71073
triclinic
0.71073
monoclinic
P21/n
Crytal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
ꢀ
P1
8.4849(4)
10.2733(4)
11.8111(5)
89.973(3)
90.088(4)
111.135(3)
960.29(7)
1
10.821(5)
15.026(5)
12.219(5)
90
99.168(5)
90
1961.4(14)
2
1.141
a
(°)
b (°)
c
(°)
V (Å)3
Z
Absorption coefficient (mmꢁ1
)
0.626
1.363
Dcalc (mg mꢁ3
)
1.439
Crystal size (mm)
0.290 ꢃ 0.307 ꢃ 0.340
0.12 ꢃ 0.13 ꢃ 0.15
r
(°)
2.13–26.49
2.2–26.4
Measured reflections
Independent reflections (Rint
Absorption correction
Refinement method
14649
3978
41259
)
4025
integrationa
full-matrix least-squares on F2
0.0405
multi-scanb
full-matrix least-squares on F2
Final R indices[F2 > 2
r
(F2)]
0.0497
1.05
ꢁ0.34 and 0.28
Goodness-of-fit (GOF) on F2
1.045
ꢁ0.40 and 0.57
Largest difference peah and hole (e Å3)
a
Stoe and Cie [47].
Blessing [47].
b
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S. Caglar et al. / Inorganica Chimica Acta xxx (2013) xxx–xxx
3
Fig. 2. ORTEP III diagram and atom numbering scheme of 1. Displacement ellipsoids are drawn at the 20% probability level.
Table 2
Selected bond distances (Å) and angles (°) for 1 and 2.
methods on the basis of all reflections with F2 > 2 (F2). Integration
r
(1)
of the intensities, correction for Lorentz and polarization effects
and cell refinement was performed using Crystal Clear (Rigaku/
MSC Inc., 2005) software [45]. The structures were solved by direct
methods using SHELXS-97 [46] and refined by a full-matrix least-
squares procedure using the program SHELXL-97 [46]. H atoms were
positioned geometrically and refined using a riding model. The
final difference Fourier maps showed no peaks of chemical signif-
icance. The detail of data collection, refinement and crystallo-
graphic data are summarized in Table 1.
Cu1–N1
Cu1–O1
Cu1–O2
2.0420(13)
2.5503(14)
1.9672(10)
93.07(5)
86.93(5)
92.71(2)
O2–Cu1–N1
O1–Cu1–N1ii
N1–Cu1–N1ii
O2–Cu1–O2ii
O1–Cu1–O2
86.93(5)
88.59(5)
180.00
180.00(6)
87.29(4)
O2–Cu1–N1ii
O2ii–Cu1–N1ii
O1–Cu1–O2ii
(2)
Cu1–N1i
1.990(3)
1.958(2)
1.921(2)
2.586(3)
76.80(3)
172.76(10)
96.42(10)
96.20(11)
92.67(9)
99.30(10)
Cu1i–O4
Cu1i–O4i
Cu1–O4i
1.920(2)
1.921(2)
1.920(2)
Cu1–O1
Cu1–O4
Cu1–O2
O4i–Cu1–O4
O4i–Cu1–O1
O4–Cu1–O1
O4i–Cu1–N1i
O2–Cu1–O4
O2–Cu1–N1i
O4–Cu1–N1i
O1–Cu1–N1i
Cu1i–O4–Cu1
O1–Cu1–O2
O2–Cu1–O4i
168.01(11)
90.91(11)
103.20(2)
56.30(9)
2.5. Methodology for catechol oxidase activity of 2
The catalytic oxidation of substrate 3,5-di-tert-butylcatechol
(DTBCH2) by [Cu2(bba)2(pypr)2] complex was evaluated in dioxy-
gen saturated methanol at room temperature. The reaction was
performed spectrophotometrically by choosing the strongest
absorbance value. Because, the oxidation product (3,5-di-
tert-butylquinone (3,5-DTBQ)) is significantly stable and has a
strong absorption at 400 nm. It was found that only dinuclear
complex shows catechol oxidase activity. The initial reaction rate
was determined from the slope of the trace at 400 nm first 1 min
of the reaction. While the initial rate was being determined, differ-
ent ratios of complex and substrate were studied. The minimum
complex to substrate rate was 1:10, the maximum complex to sub-
strate rate was 1:50. Km, Vmax and kcat values were determined by
Lineweaver–Burk plots and Michaelis–Menten equation.
120.80(9)
Symmetry code: (i) 2ꢁx, ꢁy, 2ꢁz; (ii) 1ꢁx, 1ꢁy, 1ꢁz.
Table 3
Hydrogen-bonding geometries for 1 and 2 (Å, °).
D–Hꢀ ꢀ ꢀA
D–H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D–Hꢀ ꢀ ꢀA
(1)
O1–H1Aꢀ ꢀ ꢀO3
C1–H1ꢀ ꢀ ꢀO1i
C6–H6Bꢀ ꢀ ꢀO2i
(2)
0.75(3)
0.93
0.97
1.94(3)
2.52
2.33
2.6657(17)
3.054(2)
3.174(3)
162(3)
117
145
C6–H6ꢀ ꢀ ꢀO2ii
C19–H19ꢀ ꢀ ꢀO3iii
C-20–H20ꢀ ꢀ ꢀO2iii
0.93
0.93
0.93
2.54
2.58
2.52
3.394(5)
3.440(6)
3.304(5)
153
154
142
2.6. Methodology for catalase-like activity of 2
Symmetry code: (i) 1ꢁx, 1ꢁy, 1ꢁz; (ii) ꢁ1/2 + x, 1/2ꢁy, ꢁ1/2 + z; (iii) ꢁx, 1ꢁy, 1ꢁz.
The catalase-like activity of the dinuclear [Cu2(bba)2(pypr)2]
complex in methanol was measured volumetrically at 25 °C, under
air. Firstly, 50 cm3 two-necked reactors containing of the complex
(10 ml, 0.1 mM) was placed in a water bath. The reactor was con-
nected to burette filled with water and other neck was stoppered
by a rubber septum. While the solution was stirring, H2O2 (com-
mercial 35% aqueous solution) (1.2 ml) was injected into it through
rubber septum using a micro syringe. The evolved dioxygen was
measured volumetrically at 1 min time. Before the addition of
H2O2, imidazole (50 mg) was added (in the absence of the imidaz-
ole the complex was either inactive or very weak catalysts for this
reaction).
3. Result and discussion
3.1. Crystal structure of [Cu(bba)2(pypr)2]
A molecular view of [Cu(bba)2(pypr)2] with the atom number-
ing scheme is shown in Fig. 2. The selected bond lengths and angles
are given in Table 2. Mononuclear complex, which is synthesized
ꢀ
with CuSO4.5H2O precursor material, has a P1 space group. Struc-
ture analysis of [Cu(bba)2(pypr)2] demonstrates that the complex
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4
S. Caglar et al. / Inorganica Chimica Acta xxx (2013) xxx–xxx
Fig. 3. A crystal packing diagram of 1.
consists of two bba and two pypr ligands. Cu(II) is coordinated by
four oxygen (O1, O1i, O2 and O2i) atoms. Four oxygen atoms are
originated from carboxylato group of two bba ligands and hydroxyl
oxygen atoms of two pypr ligands. And also copper(II) ion is coor-
dinated two nitrogen atoms of two pypr ligands, resulting in an
octahedral geometry.
distances and angles are given in Table 2. The dinuclear complex
crystallizes in the monoclinic crystal system with the space group
P21/n. The CuNO4 coordination sphere around each Cu(II) is dis-
torted square pyramidal as can be seen from the angles subtended
at the metal ion (Table 2) and distortion is effected considerably
from the Cu-carboxyl coordination. The structural distortion index
Cu–Npypr, Cu–Opypr and Cu–Obba bond distances are 2.0420(13),
2.5503(14) and 1.9672(10) Å, respectively. Cu–O(1)pypr bonds are
longer than Cu–O(2)bba and Cu–N(1)pypr bonds, this results in for-
mation of an elongated octahedral geometry along the O(1)pypr
atoms. The distortion in the copper(II) complex is a consequence
of the Jahn–Teller effect.
tau (
square pyramidal geometry for 2 (
spond to two angles showing tendency to linearity). The
s
) was calculated as 0.079 and clearly reflects a distorted
–b/60, where and b corre-
-values
s
=
a
a
s
of square-based-pyramidal and trigonal–bipyramidal extremes
are 0 and 1, respectively. (pypr)2 binds are in a chelating fashion
and the chelate angle is 96.21(9)°. The Cu–O2 distance of
2.586(3) Å lies in the normal range for Cu–O distances along the
axial Jahn–Teller axis [49]. The molecule shows a center of inver-
sion and the bridging parallelogram is constructed by Cu2O2
[O((pypr)2)] atom participation. The bridging angles for Cu–O4–
Cui and O4–Cu–O4i are 103.2(2)° and 76.80(3)°, respectively and
Cu–Cui distance is 3.010(4) Å. Distortion in the square pyramidal
constituted by Cu, N1, O1, O4, O4i is observed. In addition, the
dihedral angle between the chelate plane (Cu, N1, C15, O4) and
the bridged parallelogram (Cu, O4, O4i, Cui) is 14.8°.
The Cu–Npypr and Cu–Opypr bond distances are similar with
[Cu(pypr)2(sac)2] (2.010(3) and 2.544(3) Å) [48].
There is an intramolecular hydrogen bond between pypr and
bba (Table 3) so that C6–H6Bꢀ ꢀ ꢀO2i, C1–H1ꢀ ꢀ ꢀO1i and
O1–H1Aꢀ ꢀ ꢀO3 intramolecular hydrogen bonds stabilize this
arrangement. The chains are cross-linked by C–Hꢀ ꢀ ꢀ
p interactions
(C4i–H4iꢀ ꢀ ꢀCt1 (C9–C14); C4–H4ꢀ ꢀ ꢀCt1ii (2.9282 Å); i: 1ꢁx, 1ꢁy,
1ꢁz; ii: 2ꢁx, 1ꢁy, 1ꢁz) (Fig. 3).
The Cu–Opypr and Cu–Npypr bond distances are 1.921(2) and
3.2. Crystal structure of [Cu2(bba)2(pypr)2]
1.990(3) Å, respectively. The Cu–Opypr and Cu–Npypr bond distances
are similar to corresponding values found in [Cu2(
(1.9271(18), 1.9170(18), 1.982(2) Å) [48].
l-pypr)2(sac)2]
The single crystal structure of the dinuclear [Cu2(bba)2(pypr)2]
with the atom numbering scheme is shown in Fig. 4. Selected bond
Fig. 4. ORTEP III diagram and atom numbering scheme of 2. Displacement ellipsoids are drawn at the 20% probability level.
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S. Caglar et al. / Inorganica Chimica Acta xxx (2013) xxx–xxx
5
Fig. 5. A crystal packing diagram of 2.
The Cu–Obba (1.9672(10) Å (for 1); 1.958(2) Å (for 2)) bond dis-
tances are similar to the corresponding values found in [Cu(bba)2-
(benzimidazole)2] (1.95(13) Å) [39], [Cu(bba)2(phen)] (1.92(2),
1.96(2) Å [40] but shorter than the corresponding bond in
[Cu(bba)2(3-pic)2] (2.108(2) and 2.310(2) Å) [42]. The Cu–O2bba
(2.586(3) Å (for 2)) bond distance is longer than the corresponding
values found in the literature [39,40,42].
groups are acting as monodentate and bidentate ligands, respec-
tively [51]. The bands around at 1277 cmꢁ1 are due to
(C–O)
vibration. The bands around at 934 and 706 cmꢁ1 correspond to
the (C–H) vibration in-plane and out-plane bending for ligands.
m
m
3.4. Thermal analysis
The possible three HBs can be proposed as the following: C6–
Complex 1 shows two stages decomposition process and stable
up to 126 °C. The thermal decomposition of the complex begins
with melting at 140 °C (DTA peak) and this stage between 126
and 314 °C corresponds to the exothermic removal of two pypr li-
gands and bba ligand with release of CO2 proceed (DTA peak at
231 °C). A good agreement between the experimental and calcu-
lated values was observed for the mass loss (exp. 77.70%; calcd.
77.55%). In the next stages, occurs in the 314–546 °C range with
the exothermic DTA peaks at 410, 433 and 480 °C are associated
with the burning of the organic residue (exp. 13.6%; calcd.
14.27%). This results in the formation of CuO as the end product.
The experimental total mass loss value of 91.30% is consistent with
the calculated value 91.82%.
The thermal behavior of the dinuclear complex 2 was followed
up to 900 °C in a nitrogen atmosphere. Complex decomposes in
three stages. The first stage between 141 and 203 °C corresponds
to removal of 0.5 mol pypr ligand with the endothermic step in
DTA at 185 °C. The experimental mass loss of 8.5% agrees with
the calculated mass loss of 8.0% (DTGmax 180 °C). The degradation
of the remainder pypr ligands and bba ligand take place in the sec-
ond stage (203–320 °C, DTGmax 246 °C) with a mass loss of 61.70%
(calcd. 63.70%). In the third stage related to the burning organic
residue (320–534 °C found = 12.80%, calcd. = 13.23%; DTGmax
426 °C). The total experimental mass loss 83.10% agrees well with
the calculated mass loss of 84.93% and the final product obtained is
CuO.
H6ꢀ ꢀ ꢀO2ii, 3.394(5) Å; C19–H19ꢀ ꢀ ꢀO3iii, 3.440(6) Å; C–20–H20ꢀ ꢀ ꢀ
O2iii, and 3.304(5) Å (Table 3). C–Hꢀ ꢀ ꢀ
p interaction distances are
not less than the 3.5 Å. These weak HB interactions contribute to
the stability of the complex (Fig. 5).
3.3. IR spectra
Selected IR bands of Hbba ligand, complex 1 and 2 are listed in
Table 4. It is not observed that m(OH) vibration, which is appeared
in the Hbba ligand at 3445 cmꢁ1, is disappeared from the func-
tional region in complexes due to the loss of the proton of the car-
boxylic acid. The weak bands around at 3099 and 2846 cmꢁ1 are
assigned to the aromatic
m(C–H) of phenyl rings and aliphatic
m
(C–H) vibration of pypr ligand, respectively. The absorption band
of the carbonyl group of bba is observed at 1669 cmꢁ1 for two com-
plexes. The band around at 1579 (1) and 1562 (2) cmꢁ1 can be as-
signed that typical m(OCO)asym vibration of carboxylate anion. The
complex also demonstrates strong intensity bands at 1371 (1)
and 1370 (2) cmꢁ1, this band may be assigned to the symmetric
vibration (m(OCO)sym) of carboxylate group [50]. The calculated
D
(OCO) values {
m
(OCO)asym
ꢁ
m(OCO)sym} are 208 (1) and 192
(2) cmꢁ1, in agreement with the observation that the carboxyl
Table 4
Selected IR spectral dataa for the Hbba ligand, (1) and (2) complexes.
Hbba
(1)
(2)
3.5. ES-MS of the complexes
m
m
m
m
m
m
m
(OH)
aro(CH)
alf(CH)
3445m
–
–
3060w
–
1673vs
–
–
–
3099w
2937–2846w
1669vs
1579m
1371s
3053w
2916–2861w
1669vs
1562m
1370s
Electrospray mass spectrometry (ES-MS), which is a new tech-
nique for the characterization of unstable species and intermediate
in solution, allows ions in solutions to be transferred to the gas
phase with minimal fragmentation [52,53]. The positive-ion ES
mass spectrums of the complexes 1 and 2 in methanol are shown
in Fig. 6 and Fig. 7, respectively. The peaks can be appointed to new
species formed by solvation of the complex cation.
(C@O)
asym(COOꢁ)
sym(COOꢁ)
(C–O)
1278s
1276s
w, weak; m, medium; s, strong; vs very strong.
Frequencies in cmꢁ1
.
a
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S. Caglar et al. / Inorganica Chimica Acta xxx (2013) xxx–xxx
Fig. 6. The ES-MS of 1 in methanol solution.
The peak at m/z = 512.81 (7.1%) is related to [Cu(bba)2]+ mole-
the loss of propanol group from the pypr ligand. The peak at
m/z = 344.05 (48%) is due to [Cu2(benzene)2(propanol)]+ molecule
ion (MWt = 343 g/mol) by the loss of pyridine group from the pypr
ligand. The peak at m/z = 328.01 (71%) is due to [Cu2(benzene)2-
(ethanol)]+ molecule ion (MWt = 328 g/mol).
cule ion (MWt = 512 g/mol) by the loss of two pypr ligands from
the complex 1 cation. The peak at m/z = 497.00 (8.0%) is due to
[Cu(bba-CO)2]+ molecule ion (MWt = 496 g/mol) by the loss of car-
bonyl group from the bba ligands. The peak at m/z = 287.00 (4%) is
related to [Cu(bba)]+ molecule ion (MWt = 287 g/mol). The peak at
m/z = 376.92 (30.0%) is due to [Cu(benzene)4]+ molecule ion
(MWt = 375 g/mol). The peak at m/z = 424.92 (4.1%) is related to
[Cu(bba)(pypr)]+ molecule ion (MWt = 425 g/mol) by the loss of
one 2-pypr and one bba ligands from the complex cation. The peak
at m/z = 365.00 (3.2%) is related to [Cu(bba)(pyridine)]+ molecule
ion (MWt = 365 g/mol) by the loss of propanol group from the pypr
ligand. The peak at m/z = 474.95 (25%) is related to [Cu(benzene)4-
(pypr-CH2OH)]+ molecule ion (MWt = 473 g/mol). The mass spec-
trum is dominated by the peak at m/z = 280.94 (100%), which
may result from the formation of [Cu(benzene)2(propanol)]+ mole-
cule ion (MWt = 279 g/mol).
3.6. Catalase-like activity
The catalytic activity studies of copper(II) complex towards the
disproportionation of hydrogen peroxide were performed in
the presence of heterocyclic base imidazole. We have measured
the disproportionation of H2O2 catalyzed by [Cu2(bba)2(pypr)2]
volumetric determination of the evolved O2. Experiments were re-
peated several times to ensure consistency of the results. The time
course of the dioxygen evolution is shown in Fig. 8. The studies
showed that, the complex itself is catalytically very weak without
the addition of heterocyclic base but the decomposition of H2O2 in-
creased with the addition of base such as imidazole, pyridine or 1-
methyimidazole. They have strong pi donating ability [25]. It
should be noted that heterocyclic base alone cannot catalyze the
disproportionation of H2O2. When the second coordinate metal
ion is present in structure, the catalytic reactivity greatly
enhances. Because, in the catalytic process the electron transfer
Complex 2 shows similar peaks like a complex 1 at m/z = 376.91
(100%), 424.89 (19%), 474.94 (57.3%) and 497.01 (21%). The differ-
ent peaks are also present in complex 2. The peak at m/z = 538.92
(14%) is related to [Cu2(benzene)2(pypr-CH2OH)]+ molecule ion
(MWt = 537 g/mol). The peak at m/z = 361.00 (68%) is due to
[Cu2(benzene)2(pyridine)]+ molecule ion (MWt = 360 g/mol) by
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S. Caglar et al. / Inorganica Chimica Acta xxx (2013) xxx–xxx
7
Fig. 7. The ES-MS of 2 in methanol solution.
of the mono and dinuclear complexes, and it was found that only
dinuclear complex displayed catechol oxidase activity in methanol
solution at room temperature. This substrate (3,5-DTBCH2) is com-
monly used in the studies of catechol oxidase activity, because 3,5-
DTBCH2 has a low potential in the presence of bulky substituent
and the quinone-catechol couple.
Time dependent increase in concentration is shown in Fig. 9.
5 ꢃ 10ꢁ5 M complex and 15 ꢃ 10ꢁ4 M substrate were stirring at
equal volumes and quinone formation was determined by moni-
toring the increase in concentration. In another study demonstrat-
ing the formation of quinone is shown in Fig. 10. In that study,
10ꢁ4 M complex and 10ꢁ3 M substrate were stirred at equal vol-
umes and quinone formation was determined by UV–Vis spectro-
photometer at 400 nm.
The kinetic study was performed by the initial rate method by
monitoring the absorption at 400 nm for the first 1 min. Constant
concentration of complex and different concentration of substrate
were prepared (complex: 5.10ꢁ5 M, substrate: 5–10–15–20–
25.10ꢁ4 M). A linear relationship for the initial rate and complex
concentration were observed which means a first-order depen-
dence on the catalyst concentration for the system. At low concen-
trations of 3,5-DTBCH2 a first-order dependence of the substrate
concentration was observed. Also saturation kinetics was found
Fig. 8. Time course of dioxygen evolution (ml) from the reaction of H2O2 (1.2 ml,
35%) with: (a) imidazole (50 mg) and 2 (10 ml,10ꢁ4 M), (b) just 2 (10 ml,10ꢁ4 M).
especially take place between homo dinuclear Mn and Cu com-
plexes or hetero dinuclear Mn-Cu complexes [54].
at high substrate concentrations [55]. The kinetic parameters Vmax
:
3.33 ꢃ 10ꢁ6 Msꢁ1, Km: 1.22 ꢃ 10ꢁ3 M and kcat 240 hꢁ1 were deter-
mined by using both the Michaelis–Menten equation (Fig. 11)
and a Lineweaver–Burk plot (Fig. 12).
3.7. Catechol oxidase activity
Some of the crucial factors are catalytic effect, redox potential,
geometry, steric factors and interaction between the substrate
The catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-
DTBCH2) was studied to investigate the catechol oxidase activity
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8
S. Caglar et al. / Inorganica Chimica Acta xxx (2013) xxx–xxx
Fig. 9. Time dependent oxidation of 3,5-DTBCH2 (15 ꢃ 10ꢁ4 M) by dinuclear
complex (5.10ꢁ5 M).
Fig. 12. Lineweaver–Burk plot for the catalysis by 2.
catalytic effect is the distance between the Cuꢀ ꢀ ꢀCu metal ions.
Dinuclear copper complexes are generally more reactive towards
the oxidation of catechols than the corresponding mononuclear
species [16,55,60] and these complexes catalyze oxidation if the
Cuꢀ ꢀ ꢀCu distance is <5 Å [16,55,61]. In our present study, Cuꢀ ꢀ ꢀCu
distance is 3.01 Å.
The turnover number is for catechol oxidase enzyme
8254.8 ꢃ 103 hꢁ1. Although dinuclear copper(II) complexes dis-
played much less turnover number compared to catechol oxidase
the result is quite comparable to reported in literature [55,62–65].
4. Conclusions
The newly synthesized mono and dinuclear Cu(II) complexes
have been characterized by elemental analyses, FT-IR, thermal
analyses and X-ray diffraction. X-ray crystal structure analysis
showed that copper(II) center has a distorted octahedral geometry
in 1, distorted square pyramidal geometry in 2. The intra or inter-
molecular hydrogen bonds are between pypr and bba ligand in 1
and 2 complexes. Additionally, the chains are cross-linked by C–
H interactions. Thermal analysis data shows that complex decom-
poses in two stages for 1 and three stages for 2. Catechol oxidase
activity of this complex has been investigated by using 3,5-DTBCH2
as substrate in methanol. Our study indicates that only dinuclear
complex displays both catechol oxidase and catalase-like activity.
Both enzyme activity results are quite acceptable compared to
the results obtained in literature. And also ionization procedures
of decomposition process for complexes are explained with elec-
trospray mass spectrometry (ES-MS).
Fig. 10. Oxidation 3,5-DTBCH2 by 2 monitored by UV–Vis spectroscopy.
Appendix A. Supplementary material
CCDC 882234 and 884195 contain the supplementary crystallo-
graphic data for complex 1 and 2. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.ica.2012.11.028.
Fig. 11. Dependence of the reaction rates on the 3,5-DTBCH2 concentrations for the
oxidation reaction catalyzed by 2. The reaction was performed in methanol under
room temperature.
and catalyst. No clear and direct correlation has been established
between the rates of reaction, redox potentials and electronic ef-
fect until now [16,56–59]. But other factors for example geometry,
steric factors, and interactions between catalyst and substrate can
also influence the overall efficiency [59]. Another factor for
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