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

Article abstract of DOI:10.1134/S0036023607090124

Mixed-ligand m-hydroxybenzoate complexes of Co(II), Ni(II), Cu(II), and Zn(II) with nicotinamide were synthesized and characterized by elemental analysis, FT-IR spectrometry, solid state UV-vis spectrometry, and magnetic susceptibility measurements. The thermal behavior of the complexes was studied by simultaneous TG-DTA methods in static air atmosphere. The infrared spectral characteristics of the complexes are discussed and the mass spectra data are recorded. The complexes contain two water molecules, two m-hydroxybenzoato (m-hba), and two nicotinamide (na) ligands per formula unit. In these complexes, the m-hydroxybenzoate and nicotinamide behave as a monodentate ligand through acidic oxygen and nitrogen of the pyridine ring. The decomposition pathways and the stability of the complexes are interpreted in terms of the structural data. The final decomposition products were found to be the respective metal oxides.

Full text of DOI:10.1134/S0036023607090124

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2007, Vol. 52, No. 9, pp. 1384–1390. © Pleiades Publishing, Inc., 2007.
COORDINATION
COMPOUNDS
Synthesis and Characterization of bis(Nicotinamide)
m-Hydroxybenzoate Complexes of Co(II), Ni(II),
Cu(II), and Zn(II)1
Dursun Ali Köse
Hacettepe University, Department of Chemistry, Beytepe Campus, 06532 Ankara, Turkey
Received October 10, 2006
Abstract—Mixed-ligand m-hydroxybenzoate complexes of Co(II), Ni(II), Cu(II), and Zn(II) with nicotin-
amide were synthesized and characterized by elemental analysis, FT-IR spectrometry, solid state UV-vis
spectrometry, and magnetic susceptibility measurements. The thermal behavior of the complexes was
studied by simultaneous TG–DTA methods in static air atmosphere. The infrared spectral characteristics
of the complexes are discussed and the mass spectra data are recorded. The complexes contain two water
molecules, two m-hydroxybenzoato (m-hba), and two nicotinamide (na) ligands per formula unit. In these com-
plexes, the m-hydroxybenzoate and nicotinamide behave as a monodentate ligand through acidic oxygen and
nitrogen of the pyridine ring. The decomposition pathways and the stability of the complexes are interpreted in
terms of the structural data. The final decomposition products were found to be the respective metal oxides.
DOI: 10.1134/S0036023607090124
1
Nicotinamide is known as a component of the vita-
min B complex as well as a component of the coen-
zyme, nicotinamide adenine dinucleotide (NAD). It is
documented that heterocyclic compounds play a signi-
ficant role in many biological systems, especially
N-donor ligand systems, being a component of several
vitamins and drugs such as nicotinamide [1–3]. These
are highly important for transfer of hydrogen in cell
breathing. The presence of a pyridine ring in numerous
naturally abundant compounds, adducts of nicotin-
amide, is also of scientific interest. Therefore, the struc-
ture of nicotinamide has been the subject of many stu-
dies [4–7]. Also, nicotinamide itself plays an important
role in the metabolism of living cells and some of its
metal complexes are biologically active as antibacterial
or insulin-mimetic agents [8].
EXPERIMENTAL
Materials and Instrumentation
O
O
OH
NH
2
N
OH
m-hba
na
Scheme 1.
All chemicals used were analytical reagent pro-
ducts. CoSO4 · 6H2O, NiSO4 · 6H2O, CuSO4 · 5H2O,
ZnSO4 · 7H2O, m-hydroxybenzoic acid, and nicotin-
amide were obtained from Merck (Darmstadt, Ger-
many). Elemental analyses (C, H, N) were carried out
by standard methods (Tubitak Marmara Research Cen-
ter). Magnetic susceptibility measurements at room
temperature were performed using a Sherwood Scien-
tific MXI model Gouy magnetic balance. IR spectra
were recorded in the 4000–400 cm–1 region with a Per-
kin Elmer 1000 FT-IR spectrophotometer using KBr
pellets. Thermal analysis curves (TG–DTA) were
recorded simultaneously in a static air atmosphere with
a Schimadzu DTG 60 thermal analyzer. The samples
weighed approximately 10 mg and highly sintered
α-Al2O3 was used as a reference material. The heating
Phenolic antioxidants such as hydroxybenzoates are
an important class of natural antioxidants [9].
m-Hydroxybenzoic acid is widely used as an antimicro-
bial agent in foods, drugs, cosmetics, and toiletries
[10]. Metal complexes of biologically important
ligands are sometimes more effective than the free
ligands [11]. Structural reports of metal (Zn2+) nicotin-
amide complexes exist in [12].
In the present paper, we report the synthesis and
spectroscopic and thermal properties of some new
mixed-ligand complexes of Co(II), Ni(II), Cu(II), and
Zn(II) containing m-hydroxybenzoate-nicotinamide.
The structures of the ligands are shown in Scheme 1.
rate was 10°C min–1 and the DTG sensitivity was
0.05 mg s–1. We used for electronic spectra a Schi-
madzu 3600/UV-VIS-NIR Spectrophotometer. Mass
1
The text was submitted by the author in English.
1384

SYNTHESIS AND CHARACTERIZATION OF BIS(NICOTINAMIDE)
Analytical data of the metal complexes
1385
Found (calcd.), %
H
Complex
M/g mol–1 Yield (%)
Color
d.p.a(°C)
µeff, µB.
C
N
[Co(m-hba)2(na)2(H2O)2] 613.45
67
72
73
80
50.80
(50.89)
51.20
4.22
(4.24)
3.83
9.14
(9.14)
9.20
pink
127
4.11
2.69
C26H26N4O10Co
[Ni(m-hba)2(na)2(H2O)2]
C26H26N4O10Ni
613.21
618.05
green
171
102
101
(50.92)
51.01
(4.20)
4.00
(9.14)
9.30
[Cu(m-hba)2(na)2(H2O)]
C26H26N4O10Cu
blue
1.51
(50.53)
49.95
(3.20)
4.47
(9.10)
9.03
[Zn(m-hba)2(na)2(H2O)2] 619.89
colorless
diamagnetic
C26H26O10Zn
(50.30)
(4.20)
(9.04)
a
Decomposition point.
spectrum data was recorded on anAgilent Technologies
5973 spectrophotometer using the DIP-MS method.
M(m-hba)2(H2O)n + 2na
M(m-hba)2(na)2(H2O)n
[M = Co(II), Ni(II), Cu(II), Zn(II)].
Preparation of m-hydroxybenzoate complexes
RESULTS AND DISCUSSION
At the first step, m-hydroxybenzoic acid sodium salt
was prepared according to the following equation:
Analytical results and compositions of the com-
plexes are given in Table 1. The complexes were syn-
thesized with high purity. The results of the elemental
analysis indicated that the complexes contain two
moles of m-hydroxybenzoato and nicotinamide ligands
per mole formula units. All of the complexes contain
two mole aqua ligands, and these are directly coordi-
nated to the metal ion. The presence of aqua ligands
was confirmed by the FT-IR spectra and mass loss and
endothermic peaks in the TG–DTA curves. In the com-
plexes with the aqua ligands, the octahedral coordina-
tion of the metal ion formed by two carboxylic oxygen
atoms from two m-hyroxybenzoates and two nitrogen
atoms from two nicotinamides. The elemental analysis
data in the Table confirm the proposed formula of the
complexes. Due to the low solubility, the electronic
spectrum of the complexes was taken in the solid state.
The electronic spectrum of the Co(II), Ni(II), and
Cu(II) complexes shows absorption bands at 595, 620,
and 670 nm, respectively [13, 14]. These peaks belong
to the d–d transitions in metals, which may be assigned
2m-hba + 2NaHCO3
At the second step, metal m-hba salts were synthe-
sized from Na(m-hba) salt by a substitution reaction:
2 Na(m-hba) + 2CO2 + 2H2O.
2Na(m-hba) + MSO4 ⋅ nH2O
M(m-hba)2 ⋅ nH2O + Na2SO4
[M = Co(II), Ni(II), Cu(II), 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 vacuum.
Synthesis of Mixed-Ligand Complexes
A solution of na (2 mmol) in distilled water
(30 mL) was added dropwise with stirring to a solu-
tion of M(m-hba)2(H2O)n (1 mmol) in hot distilled water
(50 mL). The solutions were heated to 50°C in a tempe-
rature-controlled bath and stirred for 4 h and then
cooled to room temperature and allowed 10–12 days
to 4A2g(F)
4T1g(F) for Co(II), 3T1g(F)
3A2g(F)
2
for Ni(II), and T2g
2Eg for Cu(II) transitions.
for crystallization. The crystals formed were filtered UV-visible peaks corresponding to the π
and washed with cold water and acetone and dried in sitions in the ligands were observed at 270 and 320 nm.
vacuo. The mixed-ligand complexes were prepared The peaks belonging to the π π* transitions are
according to the following equations: shifted to a longer wavelength as a consequence of
π* tran-
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 9 2007

1386
DURSUN ALI KÖSE
TGA %
DTA uV
20
100
a
80
0
60
–20
–40
40
b
c
20
0
200
400
600
800
Temp (C)
Fig. 2. TG–DTA curve of the [Co(m-hba) (na) (H O) ].
2
2
2
2
vibrations of free nicotinamide at 1580 cm–1 shift to
lower frequencies in the spectrum of the metal complexes.
These shifts are shown in the range of 1443 cm–1; this
may indicate that the pyridine ring is coordinated. The
main difference in the spectrum of m-hydroxybenzoic
acid is that the C=O stretching vibration of the carboxyl
group at 1718 cm–1 is shifted to a lower frequency in all
the metal complexes. The absorption bands of carboxylate
in the metal complexes occur in the range of 1543 cm–1.
This shows that the coordination takes place through
the carboxyl group [15]. 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 vibrations [16, 17].
d
4000 3500 3000 2500 2000 1500 1000 500
Wavenumbers
Fig. 1. FT-IR spectra of the complexes. (a) Cu(II),
(b) Ni(II), (c) Co(II), and (d) Zn(II).
coordination when binding with metal, confirming the
formation of m-hba–na metal complexes. According to
magnetic susceptibility results, the metal complexes are
high-spin type and paramagnetic, except for the Zn(II)
complexes. As expected, the Zn(II) complexes are dia-
magnetic. All of the complexes may be thought to have
octahedral coordination around the metal ions.
Thermal Data
[Co(m-hba)2(na)2(H2O)2]. The coordination waters
of the Co(II) complex are dehydrated in the two-step tem-
perature ranges of 116–145°C and 148–179°C (Fig. 2).
The endothermic DTA peaks at 142°C and 162°C cor-
respond to the liberation of two water molecules that
are coordinated to the metal ion. In the next stage, two
mole nicotinamide ligands decompose in the tempera-
ture range of 190–305°C (exp. 38.97%; cal. 39.8%).
The related endothermic DTA peak is at 285°C. This
type of behavior of neutral ligands has been reported
earlier [16–18]. Consequently, the decomposition of
the m-hydroxybenzoato 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 relevant to the decomposition of m-
hydroxybenzoato ligands. The final decomposition
product is CoO (exp. 12.92%; calc. 12.31%).
FT-IR Spectra
The FT-IR spectra of the complexes are given in Fig. 1.
The absorption bands in the range of 3350–2900 cm–1 in
the complexes correspond to the asymmetric and sym-
metric stretching vibration 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 range of 3476–3186 cm–1 in all of the
complexes and assigned them to asymmetric and sym-
metric stretching vibrations of NH2. Also, a N–H bend-
ing peak of the complexes is shown approximately in
the range of 1599 cm–1. The na complexes give rise to
strong bands responsible for the C = O stretching. Con-
jugation 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
amide group of the free na ligand, so the na ligand did
[Ni(m-hba)2(na)2(H2O)2]. The thermal dehydration
of the Ni(II) complex occurred in two steps by giving
endothermic DTA peaks at 170°C and 188°C corre-
sponding to the liberation of two water molecules that
not coordinate to the amide group. The pyridine ring are coordinated to the metal ion (Fig. 3). The tempera-
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 9 2007

SYNTHESIS AND CHARACTERIZATION OF BIS(NICOTINAMIDE)
1387
DTA uV
DTA uV
20
TGA %
100
TGA %
100
20
80
60
40
20
80
0
0
60
40
20
–20
–40
–20
–40
0
200
400
600
800
T, °C
0
200
400
600
800
T, °C
Fig. 3. TG–DTA curve of the [Ni(m-hba) (na) (H O) ].
2
2
2
2
Fig. 4. TG–DTA curve of the [Cu(m-hba) (na) (H O) ].
2 2 2 2
ture ranges of these steps are 155–174°C and
175−204°C. In the second stage, two mole nicotin-
amide ligands decompose and are removed in the tem-
perature range of 215–307°C by giving an endothermic
DTA peak at 284°C (exp. 40.72%; cal. 39.80%).
Finally, the decomposition of the m-hydroxybenzoato
ligands starts and the loss of the weight-continuous
complex is obtained in the temperature ranges of
208−452°C (DTA peaks at 313, 391, 402, and 425°C).
The final decomposition product, namely NiO, was
identified (exp. 11.71%; calc. 12.23%) by IR spectros-
copy with the corresponding spectra obtained under the
same conditions as the pure oxides.
According to the mass loss, the final product is ZnO
(exp. 85.97, calcd. 86.87%) at 576°C (Fig. 5).
All of the complexes contain two moles of coordina-
tion water. In these complexes, the first stage from
approximately 92 to 196°C corresponds to dehydration.
The experimental values for the mass loss of the dehy-
dration stage are consistent with the calculated values.
Regardless of the coordination, the decomposition of
the complexes starts with a dehydration process. The
results indicate that the metal–water bond strength is
almost the same for all of the water molecules. The
complexes of Co(II) and Ni(II) lose water molecules in
two steps, whereas those of Cu(II) and Zn(II) lose water
in one step. This behavior was also observed in previ-
ous studies and this may be attributed to the electron
density of the Cu(II) and Zn(II) ions [21]. By the loss of
two coordinated the originally octahedral complexes
convert into a new arrangement. After the dehydration
process, the decomposition stages of the anhydrous
complexes are related to the release of nicotinamide
and the partial decomposition of m-hydroxybenzoate
involving the release of CO2. Previous studies show
[Cu(m-hba)2(na)2(H2O)2]. The TG–DTA curves
for the Cu(II) complex are given in Fig. 4. The first
stage of the thermal decomposition of Cu(II) nicotina-
mide m-hydroxybenzoate starts at the 110–196°C tem-
perature range with the release of the two aqua ligands
(exp. 6.76%; calc. 5.99%). The decomposition occurs
in one step, giving an endothermic DTA peak at 191°C.
The anhydrous complex, [Cu(m-hba)2(na)2], is not sta-
ble in air and begins to decompose with the removal of
the water molecules. At the 205 and 272°C DTA peaks,
na and m-hba ligands decompose in the temperature
range of 197–880°C. Similar behavior was observed in
the nicotinamide–acetylsalicylato and nicotinamide–p-
hydroxybenzoato mixed-ligand complexes of Cu(II)
[18, 19]. At the result of the removal of ligands, CuO is
produced (exp. 12.63%; calc. 12.87%).
DTA uV
20
TGA %
100
80
60
40
20
0
[Zn(m-hba)2(na)2(H2O)2]. Decomposition of the
Zn(II) complex is similar to that of the Cu(II) complex.
Firstly, two mol water are removed from the complex
structure in one step (92–126°C). Water decomposition
is given at the DTA peak at 117°C. This behavior was
also observed in our earlier studies with Zn(II) com-
plexes [18–20]. The following stage is related to
decomposition of the diethylnicotinamide and
p-hydroxybenzoate ligands (127–585°C) and the
decomposition DTA peaks are 277, 320, 560°C.
–20
–40
0
200
400
600
800
T, °C
Fig. 5. TG–DTA curve of the [Zn(m-hba) (na) (H O) ].
2
2
2
2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 9 2007

1388
DURSUN ALI KÖSE
O
OH
NH
2
O
N
O
OH
2
M
N
H O
2
O
O
H N
2
O
OH
Fig. 6. Suggested structure of the complexes.
that the benzoate–metal complexes decompose by
releasing CO2 [21–26]. In complexes, all ligands are
coordinated to the metal ion as monodendate ligands.
The IR spectra of the intermediate products show simi-
lar results. The final decomposition products were
found to be the respective metal oxides in the 450–
600°C temperature intervals. The thermal stabilities of
the complexes increase in the following order:
Mass Spectra
To conclude, the thermal decomposition pathway of
the [Ni(m-hba)2(na)2(H2O)2] complex mass spectrum
was recorded (Fig. 7) using the method of direct inser-
tion probe pyrolysis mass spectrometry. The molecular
ion peak is not detected in the mass spectrum recorded.
The obtained mass spectrum is relatively complex and
exhibits a large number of peaks that extend to the m/z
value above 612. These peaks belong to the decompo-
sition products of the complex and ligands.A schematic
representation including the main fragmentation pro-
cess for the [Ni(m-hba)2(na)2(H2O)2] complex and
ligands is given in Scheme 2.
Zn(II) < Cu(II) < Co(II) Ni(II) – m-hba–na.
The suggested structure of the complexes is given in
Fig. 6.
Abundance
122
90000
106
80000
70000
78
60000
50000
40000
30000
51
138
20000
177
93
10000
65
39
163
151
27
193 207 227239251 264 284 299 313325 339 355368 383 399 413
0
20
60
100 140 180 220 260 300 340 380 420
m/z
Fig. 7. Mass Spectrum of [Ni(m-hba) (na) (H O) ] complex.
2
2
2
2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 9 2007

SYNTHESIS AND CHARACTERIZATION OF BIS(NICOTINAMIDE)
O
1389
NH2
HO
O
N
O
H2O
O
N
H2O
OH
O
H2N
O
m/z 612
+
+
+
O
O
NH
N
2
OH
OH
O
O
HO
N
O
Ni
O
m/z 122
m/z 138
O
O
m/z 411
+
+
+
O
O
O
O
O
O
Ni
O
O
O
m/z 121
m/z 299
N
m/z 106
+
+
Ni
+
m/z 283
HO
m/z 93
+
N
O
m/z 78
O
Ni
O
+
m/z 190
+
O
m/z 77
O
Ni
m/z 162
Scheme 2. Mass spectral fragmentation pattern of the [Ni(m-hba) (na) (H O) ].
2
2
2
2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 9 2007

1390
DURSUN ALI KÖSE
15. H. Icbudak, H. Olmez, O. Z.Yesilel, et al., J. Mol. Struct.
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