Synthesis and characterization of bis(nicotinamide) m-hydroxybenzoate complexes of Co(II), Ni(II), Cu(II) and Zn(II)

Article abstract of DOI:10.1007/s10973-007-8712-5

The mixed-ligand m-hydroxybenzoate complexes of Co(II), Ni(II), Cu(II) and Zn(II) with nicotinamide were synthesized and characterized. The chemical, FT IR and UV-vis spectrophotometric, thermal and mass spectral analyses, magnetic susceptibility measurements revealed that the compounds contain two water molecules, two m-hydroxybenzoate (m-hba) and two nicotinamide (na) ligands per formula unit. m-Hydroxybenzoate and nicotinamide ligands bind to the metal atoms monodentately through their acidic oxygen and pyridinic nitrogen atoms, respectively. The thermal decomposition pathways and the stability of the complexes are interpreted in the terms of the structural data.

Full text of DOI:10.1007/s10973-007-8712-5

Journal of Thermal Analysis and Calorimetry, Vol. 93 (2008) 2, 509–514
SYNTHESIS AND CHARACTERIZATION OF bis(NICOTINAMIDE)
m-HYDROXYBENZOATE COMPLEXES OF Co(II), Ni(II), Cu(II) AND Zn(II)
D. A. Köse1* and H. NecefoÈlu2
1Hacettepe University, Department of Chemistry, Beytepe Campus, 06532 Ankara, Turkey
2Kafkas University, Department of Chemistry, Pasacayiri, 36100 Kars, Turkey
The mixed-ligand m-hydroxybenzoate complexes of Co(II), Ni(II), Cu(II) and Zn(II) with nicotinamide were synthesized and
characterized. The chemical, FT IR and UV-vis spectrophotometric, thermal and mass spectral analyses, magnetic susceptibility
measurements revealed that the compounds contain two water molecules, two m-hydroxybenzoate (m-hba) and two nicotinamide
(na) ligands per formula unit. m-Hydroxybenzoate and nicotinamide ligands bind to the metal atoms monodentately through their
acidic oxygen and pyridinic nitrogen atoms, respectively. The thermal decomposition pathways and the stability of the complexes
are interpreted in the terms of the structural data.
Keywords: m-hydroxybenzoate, metal complexes, nicotinamide, thermal decomposition, transition metals
Introduction
Nicotinamide is known as a component of the vita-
min B complex as well as a component of the
coenzyme,
nicotinamide
adenine
dinu-
cleotide (NAD). It is documented that heterocyclic
compounds play a significant role in many biological
systems, especially N-donor ligand systems being a
component of several vitamins and drugs such as
nicotinamide [1–3]. The presence of pyridine ring in
numerous naturally abundant compounds, are also of
scientific interest. Nicotinamide itself plays an impor-
tant role in the metabolism of living cells and some of
its metal complexes are biologically active as antibac-
terial or insulin–mimetic agents [4]. Therefore, the
structure of nicotinamide has been the subject of
many studies [5–8].
Scheme 1
Experimental
Materials
All chemicals used were analytical reagent products.
CoSO4·6H2O,
ZnSO4·7H2O,
NiSO4·6H2O,
CuSO4·5H2O,
acid and
m-hydroxybenzoic
nicotinamide were obtained from Merck.
On the other hand, phenolic antioxidants such as
hydroxybenzoates are important classes of natural an-
tioxidants [9]. m-Hydroxybenzoic acid is widely used
as antimicrobial agents in foods, drugs, cosmetics and
toiletries [10]. It is known that metal complexes of bi-
ologically important ligands are sometimes more ef-
fective than the free ligands [11]. Structural reports
on metal (Zn2+) nicotinamide complexes exist in [12].
In the present paper, we report the synthesis,
spectroscopic and thermal properties of new
mixed-ligand complexes of Co(II), Ni(II), Cu(II) and
Zn(II) containing m-hydroxybenzoate (mhba) and
nicotinamide (na). The molecular structures of the lig-
ands are shown in Scheme 1.
Synthesis of mixed-ligand complexes
An aqueous solution of na (2 mmol, 30 mL) was
added dropwise to stirred solution of
a
M(m-hba)2(H2O)n (1 mmol) in hot distilled water
(50 mL). The resulting solution was heated to 50°C in
a temperature-controlled water bath and stirred for 4 h
and then cooled to room temperature and allowed
10–12 days for crystallization. The crystals formed
were filtered and washed with cold water and acetone
and dried in vacuo. The mixed-ligand complexes
were prepared according to the following equations:
M(m-hba)2(H2O)n+2na®
M(m-hba)2(na)2(H2O)n
(1)
*
Author for correspondence: dkose@hacettepe.edu.tr
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2008 Akadémiai Kiadó, Budapest

KÖSE, NECEFO(LU
Preparation of m-hydroxybenzoate complexes
Result and discussion
In the first step, m-hydroxybenzoic acid sodium salt
was prepared according to the following equation:
Effective magnetic moments, elemental analysis data
and compositions of the complexes are given in Ta-
ble 1. There is agreement with literature values for
similar complexes [13, 14]. The complexes were syn-
thesized with high purity. The results of the elemental
analysis indicated that the complexes contain two
moles of m-hydroxybenzoate and nicotinamide lig-
ands per mole formula unit.
2m-hba+2NaHCO3®
2Na(m-hba)+2CO2+2H2O
(2)
In the second step, metal m-hba salt was synthe-
sized from Na(m-hba) salt by the following substitu-
tion reaction:
All of the complexes contain two moles of aqua
ligand that are directly coordinated to metal ions. The
octahedral coordination of the metal ions are completed
by two carboxylic oxygen atoms from two
m-hydroxybenzoates and two nitrogen atoms from two
nicotinamides. Octahedral structure is confirmed by
magnetic data. Due to the low solubility of the com-
plexes, the electronic spectrum of the complexes were
taken in the solid-state. The electronic spectra showed
two absorption bands and d–d transition at 7000 cm–1
2Na(m-hba)+MSO4·nH2O®
M(m-hba)2·nH2O+Na2SO4
(3)
where M=Co(II), Ni(II), Cu(II) and Zn(II).
The M(m-hba)2·nH2O solution was allowed
5–7 days for crystallization at room temperature. The
crystals formed were filtered and washed with cold
distilled water and acetone and dried in vacuo.
Instrumentation
4
4
(4T1g® T2g) and 20000 cm–1 (4T1g® T1g)(4P) for Co(II)
Elemental analyses (C,H,N) were carried out by stan-
dard method (Tubitak Marmara Research Center).
Magnetic susceptibility measurements were per-
formed at room temperature using a Sherwood Scien-
tific MXI model Gouy magnetic balance (England).
IR spectra were recorded in the 4000–400 cm–1 region
with a Perkin Elmer 1000 FT-IR spectrophotometer
using KBr pellets. Thermal analysis curves
(TG-DTA) were recorded simultaneously in an inert
gas (N2) atmosphere with a Schimadzu DTG 60 ther-
mal analyzer. The sample weighed approximately
10 mg and sintered a-Al2O3 was used as a reference
material. The heating rate was 10°C min–1. Electronic
complex; three absorption bands and d–d transition at
3
3
7800 cm–1 (3A2g® T2g), 15600 cm–1 (3A2g® T1g)(3F)
3
and 25500 cm–1 (3A2g® T1g)(3P) for Ni(II) complex re-
spectively. In the Cu(II) complex multiple absorption
band is observed at about 10700–17000 cm–1 but they
are overlapped. Because, octahedral complexes of
Cu(II) are observable distorted by Jahn–Teller effect
and the structure of complex is to name pseudo-octahe-
dral. It was to taken notice of top of the peak as absorp-
tion band and d–d transition at about 13000 cm–1
2
(2Eg® T2g) for Cu(II) complex. UV-visible peaks corre-
*
sponding to the the p®p transitions in the ligands were
observed at 270 and 320 nm [15, 16]. The peaks belong-
*
ing to p®p transitions are shifted to a higher
spectrum
was
recorded
by
a
Schimadzu 3600/UV-VIS-NIR Spectrophotometer.
Mass spectral data were recorded Agilent Technolo-
gies 5973 spectrophotometer using DIP-MS method.
wawelength as a consequence of coordination when
binding with metal, confirming the formation of
m-hba–na metal complexes. According to the magnetic
susceptibility results, the Zn(II) complexes are diamag-
netic as expected. All of the complexes may be thought
octahedral coordination around the metal ions.
Table 1 Characteristic data of the metal complexes
C/%
H/%
N/%
MA/
g mol–1
Yield/
%
d.p.a/
°C
meff./
Complex
B.M
found (calculated)
4.22 (4.24)
[Co(m-hba)2(na)2(H2O)2]
C26H26N4O10Co
613.45
613.21
618.05
619.89
67
72
73
80
118
141
131
91
4.11
50.80 (50.89)
51.20 (50.92)
51.01 (50.53)
49.95 (50.30)
9.14 (9.14)
9.20 (9.14)
9.30 (9.10)
9.03 (9.04)
[Ni(m-hba)2(na)2(H2O)2]
C26H26N4O10Ni
2.69
1.83
3.83 (4.20)
4.00 (3.20)
4.47 (4.20)
[Cu(m-hba)2(na)2(H2O)]
C26H26N4O10Cu
[Zn(m-hba)2(na)2(H2O)2]
C26H26N4O10Zn
diamag.
adecomposition point
510
J. Therm. Anal. Cal., 93, 2008

bis(NICOTINAMIDE) m-HYDROXYBENZOATE COMPLEXES
Table 2 Characteristic FTIR peaks of metal complexes
Gruplar
m-hba
Co(II)
Ni(II)
Cu(II)
Zn(II)
n(–OH)
n(–OH)
2860–3100
–
–
3530–3100
3476
1676
1545
1393
152
–
3550–3060
3477
1670
1544
1392
152
–
3500–3050
3471
1685
1552
1390
162
–
3500–3000
3474
1679
1548
1395
153
H
O
2
n(NH)
n(C=O)
1718
1602
1461
141
1190
1374
–
ester
n
n
(COO–
)
)
as
s
(COO–
Dn
n(C–O–C)
1135
1390
667
1137
1391
666
1198
1384
678
1144
1399
672
n(C– H)
CH
3
n(C– N)
py
n(C– N)
–
1253
1632
563
1254
1630
564
1229
1685
599
1251
1629
564
amid
n(C=O)
–
amid
n(M–N)
n(M–O)
–
–
424
430
451
424
FTIR spectra
Thermal data
Characteristic FTIR peaks of the complexes are given in
Table 2. The absorption bands in the range of
3350–2900 cm–1 correspond to the asymmetric and
symmetric stretching vibrations of water molecules. The
peaks for the N–H stretches of primary amides are
strong in the range of 3370–3170 cm–1. We observed
two bands in the 3476–3186 cm–1 range for all com-
plexes and assigned these peaks to asymmetric and sym-
metric stretching vibrations of NH2. Also N–H bending
vibrations appear approximately in 1599 cm–1. The na
complexes give rise to strong bands responsible from
the C=O stretching. Conjugation between the carbonyl
group and the amide nitrogen causes small frequency
shifts. The strong bands observed at around 1680 cm–1
are assigned to this mode. This band remained almost in
the same range as the amide group of the free na ligand,
indicating that the na ligand does not coordinate through
amide group. Pyridine ring vibration of free
nicotinamide at 1580 cm–1 shifts to 1443 cm–1 in the
complexes indicating that the pyridine ring is coordi-
nated. The main difference in the spectrum of
m-hydroxybenzoic acid is that the C=O stretching vibra-
tion of the carboxyl group at 1718 cm–1 shifts to lower
frequency in all the metal complexes. The carboxylate
peaks in the metal complexes appear in 1543 cm–1. This
shows that the coordination takes place through the car-
boxyl group [17]. The –OH bending peak for the
m-hydroxybenzoic acid remained almost in the same
position at around 1259 cm–1 in all metal complexes.
The low intensity bands in the region of 600–400 cm–1
are attributed to M–N and M–O vibration [18, 19].
[Co(m-hba)2(na)2(H2O)2]
The coordinating water molecules of Co(II) complex are
dehydrated in the two steps in the temperature ranges of
118–145 and 148–179°C (Fig. 1). The corresponding
endothermic DTA peaks at 142 and 162°C confirm the
release of the the water molecules. In the next stage, two
moles of nicotinamide decompose in the temperature
range of 190–305°C (exp. 38.97%; calc. 39.8%). Re-
lated endothermic DTA peak is at 285°C. This type of
behavior of neutral ligands has been reported earlier
[19, 20]. Consequently, the decomposition of the
m-hydroxybenzoate ligands starts with the release of
CO2 molecules. The descending continuous TG curve is
obtained in the temperature range of 306–575°C (DTA
peaks at 345, 484, 518 and 556°C) and these are rele-
vant to the decomposition of m-hydroxybenzoato lig-
ands. The final decomposition product is CoO
(exp. 12.92%; calc. 12.31%).
Fig. 1 TG-DTA curve of the [Co(m-hba)2(na)2(H2O)2]
J. Therm. Anal. Cal., 93, 2008
511

KÖSE, NECEFO(LU
[Ni(m-hba)2(na)2(H2O)2]
begins to decompose by eliminating na and m-hba lig-
ands that is occurred in the temperature range of
217–880°C (DTA: 272°C). A similar behavior was
observed in the nicotinamide–acetylsalicylato and
nicotinamide–p-hydroxybenzoato mixed-ligand com-
plexes of Cu(II) [20, 21]. Finally, the product was ob-
tained in CuO form (exp. 12.63%; calc. 12.87%).
The thermal dehydration of the Ni(II) complex
occurred in two-steps by giving two endothermic
DTA peaks at 170 and 188°C corresponding to the
liberation of two water molecules that are coordinated
to metal ion (Fig. 2). In the second stage, two moles of
nicotinamide ligands decompose and remove in the
temperature range of 215–307°C by giving an endo-
thermic DTA peak at 284°C (exp. 40.72%;
calc. 39.80%). Finally, the decomposition of the
m-hydroxybenzoate ligands starts and the mass loss
continues in the temperature range of 208–452°C re-
lated (DTA peaks are at 313, 391, 402 and 425°C).
The final decomposition product, namely NiO was
identified (exp. 11.71%; calc. 12.23%) by comparing
the IR spectrum with that of the pure oxide.
[Zn(m-hba)2(na)2(H2O)2]
Decomposition of the Zn(II) complex is different
from others. Firstly, two mol of aqua ligands are re-
moved from the complex structure in onestep
(91–126°C) (DTA: 117°C). This behavior was also
observed in our previous studies with Zn(II) com-
plexes [21–23]. The following stage is related to the
decomposition
of
the
nicotinamide
and
p-hydroxybenzoate ligands (127–585°C) (the related
DTA peaks are 277, 320, 560°C). According to the
mass loss, the final product is ZnO (exp. 85.97,
calc. 86.87%) at 576°C (Fig. 4) [24].
Fig. 2 TG-DTA curve of the [Ni(m-hba)2(na)2(H2O)2]
[Cu(m-hba)2(na)2(H2O)2]
TG-DTA curves for the Cu(II) complex are given in
Fig. 3. The first stage of the thermal decomposition of
Cu(II) nicotinamide m-hydroxybenzoate starts at
131°C with the release of two aqua ligands
(exp. 6.76%; calc. 5.99%) at two steps. This corre-
sponds to the endothermic DTA peaks at 191 and
205°C. The anhydrous complex, [Cu(m-hba)2(na)2]
Fig. 4 TG-DTA curve of the [Zn(m-hba)2(na)2(H2O)2]
All of the complexes contain two moles of coor-
dination water. In these complexes, the first stage
from approximately 91 to 215°C corresponds to dehy-
dration. The experimental values for the mass loss of
the dehydration stage are well consistent with the cal-
culated values. The results indicate that metal–water
bond strength is almost the same for all of the water
molecules. The complexes of Co(II), Ni(II) and Cu(II)
lose water molecules in twosteps whereas those of
Zn(II) lose water in onestep. This behaviour was also
observed in previous studies and this may be attrib-
uted to the electrostatic density of Zn(II) ion [24]. Af-
ter the dehydration process, decomposition stages of
the anhydrous complexes are related to the release of
nicotinamide and partial decomposition of
m-hydroxybenzoate with the release of CO2. Previous
studies showed that the benzoate-metal complexes
decompose by releasing of CO2 [23–28]. In com-
plexes, all ligands are coordinated to the metal ion as
Fig. 3 TG-DTA curve of the [Cu(m-hba)2(na)2(H2O)2]
512
J. Therm. Anal. Cal., 93, 2008

bis(NICOTINAMIDE) m-HYDROXYBENZOATE COMPLEXES
monodentate ligands. The IR spectra of the intermedi-
rolysis mass spectrometry method. The molecular ion
peak was not detected in the mass specrum recorded.
The obtained pattern is relatively complex and exhib-
its a large number of peaks that extend to m/z value
above 612 belonging to the decomposition products
of the complex and ligands. A schematic representa-
tion including the main fragmentation process for the
[Ni(m-hba)2(na)2(H2O)2] complex and ligands is
given in Scheme 2.
ate products showed similar results. The (COO–)sym.
peaks are located at 1545 cm–1 for Co(II), 1544 cm–1
for Ni(II), 1552 cm–1 for Cu(II) and 1548 cm–1 for
Zn(II) complexes. (COO–)asym. peaks are observed at
1393 cm–1 for Co(II), 1392 cm–1 for Ni(II), 1390 cm–1
for Cu(II) and 1395 cm–1 for Zn(II) complexes. The
shift (D) between of the nasym. and nsym. bands of COO–
groups are for all of the complexes almost identical
(162–152 cm–1) and more than for the sodium salt
m-hydroxybenzoic acid (141 cm–1) [29] that
monodentate carboxylate group exists [30, 31].
The coordination waters of Co(II) and Ni(II)
complexes are removed two steps, but Zn(II) and
Cu(II) complexes lose one step their coordination wa-
ters. According to the thermal stability of hydrated
and non-hydrated complexes follow the order ;
Cu(II)<Zn(II)<Co(II)<Ni(II)–m-hba–na
This order is followed Pearson’s arrangement of
2+ ions of metals.
The final decomposition products were found to
be the respective metal oxides formed in the
450–600°C temperature intervals.
Mass spectra
To conclude the thermal decomposition pathway of
the [Ni(m-hba)2(na)2(H2O)2] complex, mass spectrum
was recorded (Fig. 5) using direct insertion probe py-
Scheme 2 Mass spectral fragmentation pattern of the
[Ni(m-hba)2(na)2(H2O)2]
Fig. 5 Mass spectrum of [Ni(m-hba)2(na)2(H2O)2] complex
Suggested structure of the complexes are given
in Fig. 6.
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