New mixed ligand cobalt(II/III) complexes based on the drug sodium valproate and bioactive nitrogen-donor ligands. Synthesis, structure and biological properties

Article abstract of DOI:10.1016/j.molstruc.2017.04.048

New cobalt valproate complexes with different nitrogen based ligands were synthesized and characterized using various techniques such as IR, UV–Vis, single crystal X-ray diffraction as well as other physical properties. The general formula of the prepared

Full text of DOI:10.1016/j.molstruc.2017.04.048

Journal of Molecular Structure 1142 (2017) 40e47
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Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
New mixed ligand cobalt(II/III) complexes based on the drug sodium
valproate and bioactive nitrogen-donor ligands. Synthesis, structure
and biological properties
,
Hijazi Abu Ali* 1, Amani Abu Shamma 1, Shayma Kamel 1
Department of Chemistry, Birzeit University, West Bank, Palestine
a r t i c l e i n f o
a b s t r a c t
Article history:
New cobalt valproate complexes with different nitrogen based ligands were synthesized and charac-
terized using various techniques such as IR, UVeVis, single crystal X-ray diffraction as well as other
physical properties. The general formula of the prepared complexes is [Con(valp)m(L)z], (n ¼ 1, 2 …;
m ¼ 1, 2, …; Z ¼ 1, 2 …). The complexes [Co2(valp)4] (1), [Co(valp)2(2-ampy)2] (2) and [Co2(valp)4(quin)2]
(3) showed different carboxylate coordination modes. The crystal structures of the complexes 2 and 3
were determined using single crystal X-ray diffraction. Kinetic studies of hydrolysis reactions of BNPP
[bis-(p-nitrophenyl)phosphate] with complexes 2 and 3 were performed. The hydrolysis rate of BNPP
was studied at different temperatures, pH and concentrations by UVeVis spectrophotometric method.
The results showed that the hydrolysis rate of BNPP was 7.70 ꢀ 102 L molꢁ1 sꢁ1 for (3) and
2.60 ꢀ 10ꢁ1 L molꢁ1 sꢁ1 for (2).
Received 29 August 2016
Received in revised form
12 April 2017
Accepted 12 April 2017
Keywords:
Cobalt valproate complexes
Nitrogen donor ligands
Valproate coordination modes
© 2017 Elsevier B.V. All rights reserved.
1. Introduction
Valproic acid (2-propylvaleric or n-dipropylacetic or 2-
propylpentanoic acid) is a short chain fatty acid which is a car-
Co3þ ion can be found in different biological systems such as
vitamin B12 (cobalamin) which is a cofactor for many enzymes like
methyl transferases, and isomerases and it’s a key important in
biological system in the formation of blood and the normal func-
tioning of the nervous system and brain [1e5].
Cobalt ion has been widely used in therapeutic drugs because it
has a variety of geometries, coordination numbers and oxidation
states [6]. Moreover, it is less toxic than other metals like platinum
[5]. Among the most common ligands which were used to prepare
Co complexes as anticancer agents are phenanthroline and tri-
dentate N,O-donor ligands [7].
Nitrogen based ligands can be used in the synthesis and design
of compounds in biological, chemotherapy and pharmacological
applications such as anti-rheumatics and anti-histamines [8,9]. The
ligands 2-amino pyridine and quinoline exhibit anti-tumor, anti-
bacterial, anti-viral, anti-malarial and anti-fungal activities
[10e12].
boxylic acid [13e17]. Recently, valproic acid has a wide range
clinical uses such as antibiotic drugs for treatment of many diseases
such as epilepsy and bipolar disorder [13,15,17]. But it causes many
side effects in human organisms such as gastrointestinal distur-
bances and headache. Valproate complexation with metal may
reduce these side effects and enhance the biological activity
[15,17,18].
The transition metal with carboxylate complexes are used in
biological systems and industrial applications such as dirheniu-
m(III) dichlorotetraisobutyrate which inhibits cancer cells while
dirhodium(II) tetraacetate which is used as catalyst [19]. There are
many examples of metal valproate complexes such as copper,
cadmium(II), cobalt(II), zinc(II) and manganese(II) [20e23]. Tabrizi
and McArdle have studied cadmium (II), cobalt(II) and man-
ganese(II) valproate with 1,10-phenanthroline and imidazole. These
complexes were synthesized and characterized by using various
techniques. The complexes were tested for their biological activities
such as anti-bacterial activity by using agar diffusion method and
anti-cancer cells [23].
The hydrolytic cleavage of phosphatediester bond is very diffi-
cult to occur, but the hydrolysis may be enhanced by using an
artificial catalyst which may be organic or inorganic compound.
* Corresponding author. Department of Chemistry, Birzeit University, P.O. Box 14,
West Bank, Palestine.
E-mail addresses: habuali@birzeit.edu, habuali1@yahoo.com (H. Abu Ali).
1
These authors have contributed equally to this work.
http://dx.doi.org/10.1016/j.molstruc.2017.04.048
0022-2860/© 2017 Elsevier B.V. All rights reserved.

H. Abu Ali et al. / Journal of Molecular Structure 1142 (2017) 40e47
41
The temperature, structure of the catalyst and the pH value are
1050, 803, 782, 735, 520, 467; UVeVis (MeOH,
l
(nm) (є/
factors affecting the hydrolysis of phosphatediester bond [24,25].
The hydrolysis of BNPP is very important in environmental, in-
dustrial and biological applications [26,27].
Lmolꢁ1cmꢁ1)): 213 (49030), 276 (9119), 366 (3.6), 520 (2.6).
2.4. X-ray crystallography
2. Experimental
Single crystal X-ray analysis of complexes 2 and 3 were carried
out by attaching single crystal to a glass fibber with epoxy glue, and
then it transferred to X-ray diffractometer system (Bruker SMART
APEX CCD) which is controlled by using Pentium-based PC running
the SMART software package [28e30]. The diffracted graphite-
2.1. Chemicals, materials and biological species
All reagents, chemicals and solvents were purchased from
commercial sources and were used without further purification.
monochromated (K
a
radiation
l
¼ 0.71073 Å) was detected on a
phosphor screen at ꢁ44 ꢂC and it held at 6.0 cm from the crystal. A
2.2. Physical measurements
detector array of 512 ꢀ 512 pixels (a pixel size̴ 120
mm) was used to
collect data [28]. Crystal data and structure refinements are sum-
Melting points were measured by using Electrothermal melting
point apparatus. IR spectra of cobalt complexes were taken on a
marized in Table 1.
Bruker Tensor II as KBr pellets in the region 200e4000 cmꢁ1
.
2.5. Kinetic measurements of BNPP hydrolysis
UVeVis spectra in MeOH solvent in the region 200e800 nm were
determined by using Agilent 8453 photodiode array (PDA) spec-
trophotometer. The magnetic susceptibility measurements of the
powder solid complexes were determined by magnetic suscepti-
bility, HgCo(NSC)4 complex (mercury cobalt-thiocyanate) was used
as a standard complex.
The kinetic experiments were performed at different tempera-
tures (25 ꢂC, 37 ꢂC and 40 ꢂC), different pH values (7.04, 7.48 and
7.91) and different catalytic concentrations from 1 ꢀ 10ꢁ3 to
1 ꢀ 10ꢁ6 M.
HEPES buffer, (4-(2-hydroxyethyl)-1-piperazineethanesulfonic
acid) was used to maintain a constant pH value. The buffer solu-
2.3. Synthesis of cobalt valporate complexes
tions were prepared by dissolving 50 mM of HEPES buffer in mini-
mum amount of deionized water then the pH of the solution was
adjusted with HCl or NaOH after that BNPP was dissolved in buffer
solution and the volume of the solution was adjusted to 100 ml in
the volumetric flask [31,32].
All cobalt valproate complexes were prepared at room temper-
ature (RT).
2.3.1. Synthesis of cobalt valporate [Co2(valp)4] (1)
Different concentrations of the cobalt complexes were prepared
in MeOH solution in order to use them as catalysis in the BNPP
hydrolysis process. The rate of p-nitrophenol formation was
Sodium valproate (2.00 g, 12.1 mmol) in water was slowly added
to a stirred aqueous solution of CoCl2$6H2O (1.42 g, 6.00 mmol),
then the formed purple solid was filtered from aqueous solution,
washed with cold water and air dried. The complex was charac-
terized by using IR-spectroscopy, UV-spectroscopy.
measured using UVevis spectrophotometer at
l
¼ 400 nm
(
3
¼ 13400 L molꢁ1 cmꢁ1) [32e34].
The kinetic experiments were carried in triplicates by adding
Yield ¼ 86.50%; m. p ¼ 58 ꢂC; IR (KBr, cmꢁ1): 2959, 2872, 1556,
1.5 ml of the cobalt complex into 1.5 ml of BNPP solution in a quartz
cell at constant temp, then the solution was immediately mixed and
the kinetic measurement was performed [32,33]. The initial rate
(Vo) was calculated from the slope of the linear plot of p-nitro-
1450, 1419, 1330, 753, 469; UVeVis (MeOH,
l (nm) (є/
Lmolꢁ1cmꢁ1)): 270 (7576.5), 492 (43.6).
2.3.2. Synthesis of cobalt valporate 2-aminopyridine complex
[Co(valp)2(2-ampy)2] (2)
phenol concentration against time; [(rate)0 ¼ (dc/dt)0 ¼ (dA/dt)0/
3
[26].
2-ampy (0.96 g, 10.2 mmol) in MeOH was slowly added to a
stirred MeOH solution of complex 1 (0.93 g, 2.6 mmol), the solution
was then stirred for 3.5 h, the solvent was evaporated and a pink
precipitate was obtained. The complex was characterized by using
IR-spectroscopy, UV-spectroscopy, magnetic moment and single
crystal X-ray diffraction. Recrystallization from methanol produced
suitable crystals for X-ray structure determination.
3. Results and discussion
3.1. Synthesis of cobalt complexes
Cobalt valproate complex [Co2(valp)4] (1) was prepared by
adding 2 equivalents of sodium valproate to 1 equivalent of CoCl2 as
shown in Scheme 1. The purple solid product was obtained in
86.50% yield.
Cobalt valproate complexes 2 and 3 with different molar ratios
of the N-donor ligands were synthesized as shown in Scheme 2. The
physical properties of complexes 2 and 3 are listed in Table 2.
Yield ¼ 79.85%; m. p ¼ 121e125 ꢂC; IR (KBr, cmꢁ1): 3413, 3331,
3080, 3070, 2959, 2930, 2870, 1651, 1565, 1495, 1448, 1329, 1270,
1226, 1156, 1113, 1066, 1003, 864, 769, 740, 657, 518, 451; UVeVis
(MeOH,
l
(nm) (є/Lmolꢁ1cmꢁ1)): 235 (20072), 295 (8022.1), 520
(20.2); meff ¼ 4.83 BM.
2.3.3. Synthesis of cobalt valporate quinoline [Co2(valp)4(quin)2]
(3)
3.2. Crystallographic study
Quin (0.91 ml, 0.98 g, 7.6 mmol) was slowly added to a stirred
MeOH solution of complex 1 (1.4 g, 3.8 mmol), then the solution
was stirred for 5 h, the solvent was evaporated and a green pre-
cipitate was obtained. The complex was characterized by using IR-
spectroscopy, UV-spectroscopy, magnetic moment and single
crystal X-ray diffraction. Recrystallization from methanol produced
suitable crystals for X-ray structure determination.
3.2.1. Crystal structure of complex 2 [Co(valp)2(2-ampy)2]
The crystal structure of complex 2 is shown in Fig. 1. The
mononuclear [Co(valp)2(2-ampy)2] complex crystallizes in triclinic
crystal system and P-1 space group. For the four molecules per unit
cell, the asymmetric unit (one molecule) consists of one Co(III)
cation, two bidentate chelating valp groups and two monodentate
2-ampy ligands forming distorted octahedral geometry; (O(2)
eCo(1)eO(1) ¼ 59.5(2)ꢂ, O(1)eCo(1)eO(3) ¼ 95.6(3)ꢂ, O(4)eCo(1)
eO(3) ¼ 103.5(3)ꢂ, O(4)eCo(1)eN(3) ¼ 103.5(3)ꢂ, N(1)eCo(1)
Yield ¼ 26.23%; m. p ¼ 110e111 ꢂC; IR (KBr, cmꢁ1): 3100, 3050,
2956, 2930, 2870, 1613, 1560, 1510, 1450, 1417, 1241, 1145, 1110,

42
H. Abu Ali et al. / Journal of Molecular Structure 1142 (2017) 40e47
Table 1
Crystallographic data and structure refinements for complex 2 and 3.
Complex 2
Complex 3
Empirical formula
Formula weight
Temperature
C26 H42 Co N4 O4
533.57
293(1) K
C50 H74 Co2 N2 O8
948.97
295(1) K
Wavelength
0.71073 Å
0.71073 Å
Crystal system
Space group
Unit cell dimensions
Triclinic
P-1
Orthorhombic
Pbca
a ¼ 9.810(2) Å
b ¼ 14.660(2) Å
c ¼ 21.820(4) Å
3000.5(8) Å3
4
a
b
g
¼ 74.032(3)ꢂ
¼ 89.287(3)ꢂ
¼ 84.123(3)ꢂ
a ¼ 20.541(3) Å
b ¼ 11.247(1) Å
c ¼ 22.443(3) Å
5184.7(1) Å3
4
a
b
g
¼ 90ꢂ
¼ 90ꢂ
¼ 90ꢂ
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to theta ¼ 26.00ꢂ
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indicesa [I > 2sigma(I)]
R indices (all data)
Largest diff. peak and hole
1.181 Mg/m3
0.606 mmꢁ1
1140
1.216 Mg/m3
0.690 mmꢁ1
2024
0.50 ꢀ 0.08 ꢀ 0.08 mm3
0.55 ꢀ 0.21 ꢀ 0.11 mm3
2.29e26.00ꢂ.
2.26e26.00ꢂ.
ꢁ12 ꢃ h ꢃ 12, ꢁ18 ꢃ k ꢃ 17, ꢁ26 ꢃ l<¼26
25036
ꢁ25 ꢃ h ꢃ 25,-13 ꢃ k ꢃ 13, 27 ꢃ l ꢃ 27
48124
11567 [R(int) ¼ 0.0835]
5070 [R(int) ¼ 0.0882]
98.3%
99.8%
Semi-empirical from equivalents
0.9531 and 0.7516
Full-matrix least-squares on F2
11567/4/568
Semi-empirical from equivalents
0.9280 and 0.7029
Full-matrix least-squares on F2
5070/4/214
1.132
1.397
R1 ¼ 0.1519, wR2 ¼ 0.3215
R1 ¼ 0.2611, wR2 ¼ 0.3809
0.718 and ꢁ0.636 e.Åꢁ3
P
R1 ¼ 0.2198, wR2 ¼ 0.4492
R1 ¼ 0.2352, wR2 ¼ 0.4579
1.097 and ꢁ0.684 e.Åꢁ3
P
P
P
a
R1 ¼ || Fo| e| Fc||/ | Fo and wR2 ¼ { [w(Fo2 e Fc2)2]/ [w(Fo2)2]}1/2
.
O
O
O
O
O
O
H2O
RT
2
CoCl2
+
Co
Co
NaO
O
O
O
1
Scheme 1. Synthesis of [Co2(valp)4] (1).
eN(3) ¼ 96.5(3)ꢂ, O(2)eCo(1)eN(1) ¼ 106.3(3)ꢂ). Selected bond
distances (Å) and bond angles (ꢂ) for complex 2 are reported in
Table 3.
The bond distances of CoeN and CoeO are ligand dependent,
the average bond distances of CoeN (2.077 Å) and CoeO (2.189 Å)
in complex 2 are longer than those found in [cis-Co(en)2(-
C8H7O2)2](C8H7O2$2H2O) (1.945 Å) and (1.910 Å) respectively,
where C8H7O2 is p-methyl benzoate and en is ethylene diamine
[35].
the complex geometry and in stabilizing the complex in the solid
state [9,36]. The hydrogen bonding in complex 2 are summarized in
Table 4. The data show four intermolecular hydrogen bonding;
(N(2)eH(2N2)/O(7)#2 ¼ 2.22 Å, N(4)eH(2N4)/O(6) ¼ 2.18 Å,
N(6)eH(2N6)/O(3) ¼ 2.19 Å and N(8)eH(2N8)/O(1)#1 ¼ 2.12 Å)
and two intramolecular hydrogen bonds (N(2)eH(1N2)/
O(4) ¼ 2.12 Å and N(4)eH(1N4)/O(2) ¼ 2.10 Å).
3.2.2. Crystal structure of complex 3 [Co2(valp)4(quin)2]
The N(1)eCo(1)eN(3) (96.5ꢂ) and O(1)eCo(1)eO(3) (95.6ꢂ)
bond angles in complex 2 are shorter than the same angles found in
[Zn(valp)2(2-ampy)2] complex (102.84ꢂ, 124.92ꢂ, respectively) [20].
Intramolecular hydrogen bonding within a molecule and inter-
molecular hydrogen bonding between molecules play a key role in
The crystal structure of complex 3 is shown in Fig. 2. The
dinuclear [Co2(valp)4(quin)2] complex crystallizes in orthorhombic
crystal system and Pbca space group. For the four molecules per
unit cell, the asymmetric unit (one molecule) consists of two Co
cations, four valp and two quin molecules. Selected bond distances

H. Abu Ali et al. / Journal of Molecular Structure 1142 (2017) 40e47
43
O
O
O
NH2
O
Co
H2N
N
OH
N
e
M
RT,
2
2-ampy
,
r
h
O
O
O
O
3.5
O
Co
Co
O
O
O
MeOH,
R
T
qui
n,
1
5
O
O
h
r
O
O
N
Co
Co
N
O
O
O
O
3
Scheme 2. Synthesis of complexes 2 and 3.
Table 2
Physical properties and %yields of complexes 1e3.
Complex
m.p (ꢂC)
% Yield
Solubility
CH3OH, ether, petroleum ether
CH3OH, ether, CH2Cl2, CH3CN, (CH3)2CO, C2H5OH, CHCl3
CH3OH, ether, CH2Cl2, CH3CN, (CH3)2CO, C2H5OH, CHCl3
Co2(valp)4 (1)
Co(valp)2(2-ampy)2 (2)
Co2(valp)4(quin)2 (3)
58
121e125
110e111
86.50
79.85
26.23
Fig. 1. X-ray structure of Co(valp)2(2-ampy)2 (2).

44
H. Abu Ali et al. / Journal of Molecular Structure 1142 (2017) 40e47
Table 3
and bond angles for complex 3 are listed in Table 5.
Selected bond distances (Å) and bond angles (ꢂ) for complex 2.
The distorted octahedral geometry around each Co center con-
sists of four oxygen atoms from four valproate bidentate chelating
ligands and one nitrogen atom from quinoline monodentate ligand;
O(1)eCo(1)eO(3) ¼ 86.7(4)ꢂ, O(3)eCo(1)eN(1) ¼ 94.5(4)ꢂ, O(2)#1-
Bond
Distance (Å)
Bonds
Angle (ꢂ)
Co(1)eN(1)
Co(1)eN(3)
Co(1)eO(1)
Co(1)eO(2)
Co(1)eO(3)
Co(1)eO(4)
C(9)eO(3)
C(9)eO(4)
C(22)eN(3)
C(26)eN(3)
C(17)eN(1)
C(21)eN(1)
C(1)eO(1)
C(1)eO(2)
2.072(9)
2.081(8)
2.292(7)
2.053(7)
2.367(8)
2.042(7)
1.233(11)
1.264(10)
1.353(11)
1.341(14)
1.362(11)
1.324(14)
1.217(12)
1.285(12)
O(2)eCo(1)eO(1)
O(1)eCo(1)eO(3)
O(2)eCo(1)eN(1)
N(1)eCo(1)eN(3)
O(4)eCo(1)eN(3)
O(4)eCo(1)eO(3)
C(17)eN(1)eCo(1)
C(26)eN(3)eCo(1)
C(9)eO(4)eCo(1)
C(9)eO(3)eCo(1)
C(1)eO(1)eCo(1)
C(1)eO(2)eCo(1)
O(3)eC(9)eO(4)
O(1)eC(1)eO(2)
59.5(2)
95.6(3)
106.3(3)
96.5(3)
103.5(3)
58.3(2)
126.9(7)
115.7(7)
97.8(6)
83.5(6)
85.8(7)
Co(1)eN(1)
¼
97.9(4)ꢂ, O(4)#1-Co(1)eN(1)
¼
102.2(4)ꢂ, O(3)
eCo(1)eCo(1)#1 ¼ 79.2(2)ꢂ and O(1)eCo(1)eCo(1)#1 ¼ 87.4(2)ꢂ.
The (CoeCo) bounding distance is 2.791(3) Å which is shorter
than ZneZn bond in [Zn2(valp)4(quin)2] (2.948(3) Å) [20]. The
average bond distances of CoeO (2.043 Å) and CoeN (2.106 Å) are
similar to previously reported values (2.07 Å and 2.090 Å, respec-
tively) [37].
95.0(7)
120.4(11)
119.8(11)
3.3. IR spectroscopy
The prepared cobalt complexes were characterized by
measuring their IR spectra in the range of 200e4000 cmꢁ1 as KBr
disk. The IR spectral data for Navalp [20,38e40] and complexes 1e3
are listed in Table 6. The IR spectra for complex 1 shows two
carboxylate stretching bands asymmetric, nas(COOꢁ) at 1556 cmꢁ1
and symmetric, ns(COOꢁ) at 1419 cmꢁ1. The difference between
nas(COOꢁ) and ns(COOꢁ) is Dn(COOꢁ) and its value (137 cmꢁ1) for
complex 1 is the same as in Navalp which may indicate bridging
bidentate coordination mode between cobalt and the valproate
carboxylic group [41,42].
Table 4
Hydrogen bonds in complex 2.
D-H … A (Ǻ)
d(D-H) (Ǻ) d(H … A) (Ǻ) d(D … A) (Ǻ) <(DHA) (ꢂ)
N(8)eH(2N8)/O(1)#1 0.86
2.12
2.10
2.19
2.15
2.18
2.10
2.12
2.22
2.921(9)
154.6
159.7
152.8
160.7
160.8
161.8
162.5
155.0
N(8)eH(1N8)/O(5)
N(6)eH(2N6)/O(3)
N(6)eH(1N6)/O(8)
N(4)eH(2N4)/O(6)
N(4)eH(1N4)/O(2)
N(2)eH(1N2)/O(4)
0.86
0.86
0.86
0.86
0.86
0.86
2.925(10)
2.984(10)
2.980(11)
3.009(10)
2.931(11)
2.947(11)
3.019(10)
For complex 2, the nas(COOꢁ) at 1565 cmꢁ1 and ns(COOꢁ) at
1448 cmꢁ1 have been observed. The Dn value for complexes 2
(117 cmꢁ1) is less than Dn of Navalp (137 cmꢁ1) which indicates
bidentate chelating coordination mode.
N(2)eH(2N2)/O(7)#2 0.86
Symmetry transformations used to generate equivalent atoms: #1 x,yþ1,z #2 x,y-
1,z.
However, in complex
3
the nas(COOꢁ) was observed at
1560 cmꢁ1 and ns(COOꢁ) at 1450 cmꢁ1
,
Dn (COOꢁ) ¼ 110 cmꢁ1
which is smaller than Dn of Navalp supporting a bidentate bridging
coordination mode. Two primary amine NH absorption frequencies
at nas(NH2) ¼ 3413 cmꢁ1 and nas(NH2) ¼ 3331 cmꢁ1 were also
observed and suggest that the coordination mode with metal to be
through the pyridine nitrogen atom as supported by its X-ray
structure analysis.
3.4. Magnetic moments and UVeVis spectral data for cobalt
complexes
The electronic spectra of cobalt complexes were recorded in
MeOH solution. The electronic transition data for complexes 1e3
and their parent ligands are summarized in Table 7.
The magnetic moment of complex 2 was determined and
calculated by using the spin only formula. Table 8 shows the
magnetic properties for complex 2. On the other hand, the mag-
netic moments for complexes 1 and 3 couldn’t be measured due to
unsuccessful packing process.
Fig. 2. X-ray structure of Co2(valp)4 (quin)2 (3).
Table 5
The electronic spectrum of complex 1 exhibits two bands. The
band at 270 nm (7576.5 L molꢁ1 cmꢁ1) was assigned to the charge
transfer band with extinction coefficients larger than
Selected bond distances (Å) and bond angles (ꢂ) for complex 3.
Bond
Distance (Å)
Bonds
Angle (ꢂ)
1000
L
molꢁ1 cmꢁ1 whereas the band at 492 nm
Co(1)eCo(1)#1
Co(1)eN(1)
Co(1)eO(3)
Co(1)eO(2)#1
Co(1)eO(1)
O(2)eCo(1)#1
O(4)eCo(1)#1
C(17)eN(1)
C(21)eN(1)
C(9)eO(3)
2.791(3)
2.106(9)
2.055(9)
2.037(9)
2.046(9)
2.037(9)
2.034(8)
1.300(17)
1.371(16)
1.242(14)
1.245(13)
1.225(13)
1.249(13)
O(1)eCo(1)eO(3)
O(3)eCo(1)eN(1)
O(2)#1-Co(1)eN(1)
O(4)#1-Co(1)eN(1)
O(3)eCo(1)eCo(1)#1
O(1)eCo(1)eCo(1)#1
C(17)eN(1)eCo(1)
C(1)eO(1)eCo(1)
86.7(4)
94.5(4)
97.9(4)
102.2(4)
79.2(2)
(43.55 L molꢁ1 cmꢁ1) was assigned to the cobalt DMSO-d6
Table 6
87.4(2)
Assignment of IR bands and wave numbers for Navalp and 1e3 complexes.
114.1(9)
117.4(8)
127.8(8)
171.4(3)
122.0(8)
131.4(8)
120.7(11)
Assignments
Navalp
(cmꢁ1
Complex 1
Complex 2
Complex 3
)
(cmꢁ1
)
(cmꢁ1
)
(cmꢁ1
)
C(9)eO(3)eCo(1)
nas(COOꢁ
ns(COOꢁ)
)
1548
1411
137
e
1556
1419
137
e
1565
1448
117
3413
3331
1560
1450
110
e
N(1)eCo(1)eCo(1)#1
C(9)eO(4)eCo(1)#1
C(1)eO(2)eCo(1)#1
C(22)eC(21)eN(1)
C(9)eO(4)
C(1)eO(1)
C(1)eO(2)
Dn(COOꢁ)
nas(N-H)
ns(N-H)

H. Abu Ali et al. / Journal of Molecular Structure 1142 (2017) 40e47
45
Table 7
The electronic data for 1e3 complexes and their parent ligands.
Complex
lmax (nm)
Є (L molꢁ1 cmꢁ1
)
Pure ligands
lmax (nm)
Є (L molꢁ1 cmꢁ1
)
Co2(valp)4 (1)
270
492
235
295
520
213
276
366
520
7576.5
43.55
20072
8022.1
20.2
49030
9119
3.6
e
e
e
Co(valp)2(2-ampy)2 (2)
Co2(valp)4(quin)2 (3)
2-ampy
Quin
234
291
11479
5569.5
204
225
276
44107
41442
3605.9
2.6
Table 8
small shifts caused by Co coordination.
Magnetic properties for complex 2.
The magnetic moment of complex 2 is 4.50 BM. This value in-
dicates the presence of four unpaired electrons supporting a high
spin d6 octahedral geometry. The electronic spectrum of this
complex exhibits one DMSO-d6 transition band (520 nm). More-
over, high spin Co(III) octahedral complex 2 was obtained because
2-ampy ligand in the present case behaved as weak field ligand
[44].
Complex
Magnetic moments
# of unpaired
electrons (n)
(
meff) (BM)
Co(valp)2 (2-ampy)2 (2)
4.83
4
O
O
H2O
M
The electronic spectrum of complex 3 exhibits two DMSO-d6
L
L
transition bands at 366 nm (3.6 L molꢁ 1cmꢁ1) and 520 nm (2.6
OH2
BNPP
4
L molꢁ1 cmꢁ1) for complex 3 as a result of T1g
/
/
4T2g(F) and
HO
NO2
A
4T1g
4T1g(P) electronic transition bands. The third band
+
H3PO4
(4T1g
/
4A2g(F)) is embedded in the charge transfer bands and
(IV)
intra-ligand transition bands. The UVeVis spectral data for com-
plexes 3 is similar to those observed for [Co(2-ampy)2(dca)2] [8,45].
O
O
H
P
O
R
H
O
O
O
OR
M
B
H
O
M
L
O
L L
3.5. BNPP catalytic hydrolysis
D
O
OH
H
L
R
O
P
O
The rate of BNPP hydrolysis was studied at different
O
(III)
(II)
NO2
C
H2O
O
O
O
L
HO
M
O
P
O R
L
OH
Fig. 3. The possible mechanism of the BNPP catalytic cleavage.
Fig. 5. BNPP hydrolysis by complex 3 in MeOH/HEPEs buffer solution with different
temp values under the selected conditions (pH ¼ 7.91, [complex 3] ¼ 2 ꢀ 10ꢁ3 M and
[BNPP] ¼ 1 ꢀ 10ꢁ4 M).
Fig. 4. BNPP hydrolysis by complex 3 in MeOH/HEPEs buffer solution with different pH
values under the selected conditions (T ¼ 37 ꢂC, [complex 3] ¼ 2 ꢀ 10ꢁ3 M and
[BNPP] ¼ 1 ꢀ 10ꢁ4 M).
transition [43].
The bands between 213 and 295 nm for complexes 2 and 3 were
assigned to the intra-ligand transition bands in addition to charge
transfer bands. The results also showed similarities between the
cobalt complexes and their parent ligands and complex 1 with very
Fig. 6. Second order rate for complex 2 with different [BNPP] under the selected
conditions (pH ¼ 7.91, temp ¼ 25 ꢂC and [complex 2] ¼ 2 ꢀ 10ꢁ4 M).

46
H. Abu Ali et al. / Journal of Molecular Structure 1142 (2017) 40e47
Table 9
Kinetic parameters of the phosphate diester group hydrolysis for complexes 2 and 3 at different BNPP concentrations.
Kcat (sꢁ1
)
2nd-order rate
a
Concentration(M)
Complexes
V
o (mol/L s)
Vmax (mol/L s)
Km (mol/L)
1.9 ꢀ 10ꢁ3
6.5 ꢀ 10ꢁ6
KBNPP (L molꢁ1 sꢁ1
)
b
BNPP
2 (2 ꢀ 10ꢁ4
2 (2 ꢀ 10ꢁ4
2 (2 ꢀ 10ꢁ4
3 (2 ꢀ 10ꢁ6
3 (2 ꢀ 10ꢁ6
3 (2 ꢀ 10ꢁ6
)
)
)
)
)
)
1 ꢀ 10ꢁ3
2 ꢀ 10ꢁ4
1 ꢀ 10ꢁ4
1 ꢀ 10ꢁ3
1 ꢀ 10ꢁ4
1 ꢀ 10ꢁ5
3.0 ꢀ 10ꢁ8
1.0 ꢀ 10ꢁ8
5.0 ꢀ 10ꢁ9
1.0 ꢀ 10ꢁ8
9.0 ꢀ 10ꢁ9
6.0 ꢀ 10ꢁ9
1 ꢀ 10ꢁ7
5 ꢀ 10ꢁ4
5 ꢀ 10ꢁ3
2.60 ꢀ 10ꢁ1
7.70 ꢀ 102
1.0 ꢀ 10ꢁ8
a
Kcat ¼ Vmax/[complex].
b
KBNPP ¼ Kcat/Km
.
temperatures, pH and concentrations. The optimum condition for
BNPP hydrolysis was obtained by changing one of the above factors
while maintaining the other two constant. All cobalt valproate
complexes were used as catalysts. One possible mechanism of the
BNPP catalytic cleavage is shown in Fig. 3.
The rate of BNPP hydrolysis was studied by UVeVis spectro-
photometric method in order to determine the effect of cobalt
complexes on the phosphatase hydrolysis. The results showed that
the hydrolysis rate of BNPP was 7.70 ꢀ 102 L molꢁ1 sꢁ1 for (3) and
2.60 ꢀ 10ꢁ1 L molꢁ1 sꢁ1 for (2) and their values are higher than
other synthetic chemical models.
3.5.1. Effect of pH on BNPP catalytic hydrolysis
The pH value of 7.46 was selected in close agreement with the
physiological pH value. For comparison purposes, a lower value and
Acknowledgment
The authors thank the Office of Vice President for Academic
Affairs at Birzeit University for their financial support.
a
higher value of pH values were selected for further
experimentation.
Fig. 4 shows the Abs versus time relationship for complex 3 at
different pH values and constant temp and concentration of both
BNPP and complex. The initial rate (Vo) of BNPP hydrolysis was
calculated by measuring the absorbance of p-nitrophenol against
Appendix A. Supplementary data
CCDC 1488000 and 1488002 contain the supplementary crys-
tallographic data for 2 and 3, respectively. These data can be ob-
tained free of charge via http://www.ccdc.cam.ac.uk/conts/retrievi
ng.html, or from the Cambridge Crystallographic Data Center, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (þ44) 1223-336-033; or
e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated
with this article can be found, in the online version, at http:// …
time at 400 nm [32,33]. The Vo values (mol/L.S) are 1 ꢀ 10ꢁ8
,
3 ꢀ 10ꢁ9 and 5 ꢀ 10ꢁ9 at pH ¼ 7.91, 7.46 and 7.02, respectively for
complex 3. The maximum Vo was obtained at pH ¼ 7.91 for complex
3.
3.5.2. Effect of temperature on the BNPP catalytic hydrolysis
Fig. 5 shows the Abs versus time relationship for complex 3 at
different temp values and constant pH and concentration of both
BNPP and complex. The Vo values (mol/L.S) are 1.8 ꢀ 10ꢁ8 and
1.7 ꢀ 10ꢁ8 at 25 ꢂC and 37 ꢂC for complex 3. The maximum Vo was
obtained at 25 ꢂC for complex 3.
Complexes 2 and 3 showed similar trend in the hydrolysis of
BNPP. The hydrolysis of BNPP has been analyzed by using
MichaeliseMenten equation [46] (1/Vo ¼ 1/Vmax þ Km/Vmax[BNPP]
(Fig. 6).
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