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

Article abstract of DOI:10.1134/S1070328407060073

Four novel mixed-ligand complexes of Co(II), Ni(II), Cu(II), and Zn(II) with m-hydroxybenzoate (m-Hba) and N,N-diethylnicotinamide (Dena) were synthesized and characterized on the basis of elemental analysis, FT-IR spectroscopic study, and solid state UV-Vis spectrophotometric and magnetic-susceptibility data. The thermal behavior of the complexes was studied by combined TG-DTA methods in static air atmosphere, and the mass spectra were recorded. The Co(II), Ni(II), and Zn(II) complexes, except for the Cu(II) complex, contain two molecules of coordinated water, two m-Hba, and two Dena ligands per formula unit. In these complexes, the m-Hba and Dena behave as monodentate ligands via acidic oxygen and nitrogen of the pyridine ring. In the Cu(II) complex, the m-Hba is coordinated as monoanionic bidentate ligand through acidic oxygen and carbonyl oxygen. Dena is bonded with Cu²⁺ as monodentate ligand by the nitrogen atom of the pyridine ring. The decomposition pathways and the stability of the complexes are interpreted in terms of the proposed structural data. The final decomposition products were found to be the respective metal oxides.

Full text of DOI:10.1134/S1070328407060073

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2007, Vol. 33, No. 6, pp. 422–427. © Pleiades Publishing, Ltd., 2007.
Synthesis and Characterization of Bis(N,N-diethylnicotinamide)
m-Hydroxybenzoate Complexes of Co(II), Ni(H),
Cu(II), and Zn(II)1
D. Ä. Kösea, Ä. Kayab, and H. Necefogˇlub
a Hacettepe University, Departmen of Chemistry, Beytepe Campus, Ankara, Turkey
b Kafkas University, Faculty of Art and Science, Department of Chemistry, Pasacayiri, Kars, Turkey
ˆ ˆ
e-mail: dkose@hacettepe.edu.tr
Received May 1, 2006
Abstract—Four novel mixed-ligand complexes of Co(II), Ni(II), Cu(II), and Zn(II) with m-hydroxybenzoate
(m-Hba) and N,N-diethylnicotinamide (Dena) were synthesized and characterized on the basis of elemental
analysis, FT-IR spectroscopic study, and solid state UV-Vis spectrophotometric and magnetic-susceptibility
data. The thermal behavior of the complexes was studied by combined TG–DTA methods in static air atmo-
sphere, and the mass spectra were recorded. The Co(II), Ni(II), and Zn(II) complexes, except for the Cu(II)
complex, contain two molecules of coordinated water, two m-Hba, and two Dena ligands per formula unit. In
these complexes, the m-Hba and Dena behave as monodentate ligands via acidic oxygen and nitrogen of the
pyridine ring. In the Cu(II) complex, the m-Hba is coordinated as monoanionic bidentate ligand through acidic
oxygen and carbonyl oxygen. Dena is bonded with Cu2+ as monodentate ligand by the nitrogen atom of the pyri-
dine ring. The decomposition pathways and the stability of the complexes are interpreted in terms of the pro-
posed structural data. The final decomposition products were found to be the respective metal oxides.
DOI: 10.1134/S1070328407060073
1
INTRODUCTION
have antibacterial activity. Benzoic acid is used in com-
bination with salicylic acid in dermatology as a fungi-
cidal treatment for fungal skin diseases [16]. Structural
reports of metal (Zn2+)complexes are available in [17].
It is well documented that heterocyclic compounds
play a significant role in many biological systems, espe-
cially N-donor ligand systems, being a component of
several vitamins and drugs [1–4]. It is not surprising;
therefore, many authors have investigated heterocyclic
compounds and also examined them as ligands in coor-
dination compounds of several central atoms. Metal
In the several coordination compounds of Co, Cu,
and Zn with aryl carboxylic acids, the bonding occurs
by the acidic OH group of carboxylic acid as monoden-
tate [18]. According to X-ray structures in literature,
complexes of biologically important ligands are some- thephenolic OH group of aryl carboxylic acid does not
participate in coordination and remains free [19–21]. In
some metalcarboxylate complexes, coordination
becomes as chelate by the carbonyl oxygen atom and
acidic OH group of carboxylic acid [22]. The Dena
ligand is coordinated by the nitrogen heteroatom of the
pyridine ring. These type complexes resemble those
described in literature [19]. The thermal decomposition
curves of title compounds are compatible with pub-
lished data [6, 23–25].
times more effective than the free ligands [5]. N,N-
Diethylnicotinamide (Dena) is a derivative of nicotina-
mide (vitamin B) used as exhalation agent in respira-
tory systems in medicine [6]. The presence of the pyri-
dine ring in numerous naturally abundant compounds,
adducts of Dena are also of scientific interest. There-
fore, the structure of Dena has been the subject of many
studies [7–13]. Phenolic antioxidants such as hydroxy-
benzoates are important classes of natural antioxidants
[14]. Benzoic acid and derivatives are widely used as
antimicrobial agents in foods, and drugs [15]. Some
carboxylate compounds (e.g., benzoates) are known to
In the present paper, we report the synthesis and spec-
troscopic and thermal properties of some new mixed-
ligand complexes of Co(II), Ni(II), Cu(II), and Zn(II) con-
taining m-hydroxybenzoate (m-Hba)-diethylnicotina-
mide. The structures of the ligands are shown below:
1
The article was submitted by the authors in English.
422

SYNTHESIS AND CHARACTERIZATION
423
dropwise with stirring to
a
solution of
O
M(m-çb‡)2(H2O)n (1 mmol) in hot distilled water
(50 ml). The prepared solution was heated to 50°C in a
temperature-controlled bath, stirred for 4 h, and then
cooled to room temperature and allowed to stand for
10–12 days for crystallization. The crystals formed
were filtered off, washed with cold water and acetone,
and dried in vacuo. The mixed-ligand complexes were
prepared according to the following reaction:
O
OH
C H
2
5
5
N
C H
2
OH
(m-Bba)
N
(Dena)
M(m-Hba)2(H2O)n + 2Dena
M(m-Hba)2(Dena)2(H2O)n
EXPERIMENTAL
Materials and instruments. All used chemicals
were analytical reagent products. CoSO4 · 6H2O,
NiSO4 · 6H2O, CuSO4 · 5H2O, ZnSO4 · 7H2O, and
m-hydroxybenzoic acid were obtained from Merck
(Darnstadt, Germany). Diethylnicotinamide was pur-
chased from Darnitsa Chemicals Union (Kiev,
Ukraine). Elemental analyses (C, H, N) were per-
formed by standard methods at the TUBITAK Labora-
tory (Scientific and Technical Research Council of Tur-
key). Magnetic susceptibility measurements at room
temperature were determined on a Sherwood Scientific
MXI model magnetic balance (Gouy method) using
Hg[Co(SCN)4]. IR spectra were recorded in the 4000–
(M = Co(II), Ni(II), Cu(II), and Zn(II)).
RESULTS AND DISCUSSION
Analytical results and compositions of the com-
plexes are given in table. The complexes were synthe-
sized with high purity. The results of elemental analysis
indicated that the complexes contain two moles of
m-Hb‡ and Dena ligands per mole formula units.
Except for the Cu(II) complex, other complexes also
include two moles of aqua ligands. The Cu(II) complex
has no water ligand. The presence or absence of aqua
ligands was confirmed by the FT-IR spectra and mass
loss and endothermic peaks in the TG–DTA curves. In
the Co(II), Ni(II), and Zn(II) complexes with the aqua
ligands, the octahedral coordination of the metal ion is
formed by carboxylic acid oxygen atoms from two m-
Hba and two nitrogen atoms from two Dena. However,
in the anhydrous Cu(II) complex m-Hba behaves as
monoanionic bidentate chelating ligand through car-
boxylic oxygen atoms. The elemental analysis data in
table confirm the proposed formula of all investigated
complexes.
400 cm–1 region with a Perkin Elmer 1000 FT-IR spec-
trophotometer using KBr pellets. Thermal analysis
curves (TG–DTA) were recorded simultaneously in a
static air atmosphere with a Schimadzu DTG 60 ther-
mal analyzer. The sample weight was approximately
10 mg, and highly sintered α-Äl2é3 was used as a ref-
erence material. The heating rate was 10 K min–1, and
the DTG sensitivity was 0.05 mg s–1. We used a Schi-
madzu UV3600/UV-VIS-NIR model spectrophotome-
ter for solid-state UV-Vis range studies. Mass spectra
data were recorded Agilent Technologies 5973 spectro-
photometer using the DIP-MS method.
Due to the low solubility, we studied a solid sample,
recording satisfactory UV-Vis spectra for the com-
plexes. The electronic spectra of the Co(II), Ni(H), and
Cu(II) complexes show absorption bands at 550, 610,
and 590 nm, respectively [26, 27]. These peaks belong
to the d–d transitions in metals that can be assigned to
Synthesis of p-hydroxybenzoate complexes. In
the first step, m-hydroxybenzoic acid sodium salt was
prepared according to the following reaction:
2m-Hba + 2NaHCO3
2Na(m-Hba)
+ 2CO2 + 2H2O.
4A2g(F)
4T1g(F) for Co(II), 3T1g(F)
3A2g(F) for
2
Ni(II), and T2g
2Eg for Cu(II) transitions. The
In the second step, metal m-Hba salts were synthe-
sized from Na(m-Hba) salt by the substitution reaction:
UV-Vis peaks corresponding to the π
tions in the ligands were observed at 260 and 340 nm.
The peaks belonging to the π π* transitions are
π* transi-
2Na(m-Hba) + MSO4 ⋅ nH2O
M(m-Hba)2 ⋅ nH2O + Na2SO4
shifted to a longer wavelength as a consequence of
coordination when binding with metal, confirming the
formation of m-Hba–Dena metal complexes. The metal
complexes are of the high-spin type and paramagnetic,
except for the Zn(II) complexe, which is diamagnetic.
The values of µeff suggest octahedral coordination
around the metal ions.
˙
(M = Co(II), Ni(II), Cu(II), and Zn(II)).
An M(m-Hba)2 · nH2O solution was allowed to
stand for 5–7 days for crystallization at room tempera-
ture. The crystals formed were filtered off, washed with
cold distilled water and acetone, and dried in vacuo.
In FT-IR spectra of the Co(II), Ni(II), and Zn(II)
Synthesis of mixed-ligand complexes. A solution complexes, except of the Cu(II) complex, OH absorp-
of Dena (2 mmol) in distilled water (30 ml) was added tion bands of aqua ligands are present in a range of
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 33 No. 6 2007

424
KÖSE et al.
Analytical data of the metal complexes
Contents (found/calcd), %
Complex
M
Yield, %
Color
D.p., °C*
µ
eff., µB
C
H
N
[Co(m-Hba)2(Dena)2(H2O)2] 725.45
70
75
80
82
55.90/56.27 5.70/5.79 7.72/7.72 Pink
103
3.97
2.70
1.49
Dia
C34H42N4O10Co
[Ni(m-Hba)2(Dena)2(H2O)2]
725.21
730.05
55.95/56.32 5.55/5.79 7.78/7.72 Light-green 119
C34H42N4O10Ni
[Cu(m-Hba)2(Dena)2]
C34H38N4O8Cu
59.00/58.90 6.01/5.50 8.07/8.07 Light-blue
55.74/55.78 6.17/5.80 7.69/7.67 Colorless
102
101
[Zn(m-Hba)2(Dena)2(H2O)2] 731.89
C34H42N4O10Zn
* Decomposition point.
3300–3000 cm–1 corresponding to asymmetric and
symmetric stretching vibrations of water molecules.
These results indicate no aqua ligand in the Cu(II) com-
plex, while the other complexes have the water ligand.
The complexes give rise to strong bands responsible for
the C=O stretching. Conjugation between the carbonyl
group and amide nitrogen causes small frequency
shifts. The strong bands observed at ~1620 cm–1 are
assigned to this mode. Pyridine ring vibrations of free
dietylnicotinamide at 1580 cm–1 shifts to lower fre-
quencies in the spectrum of the metal complexes. These
shifts are shown in range of 1448–1443 cm–1, approxi-
mately this can indicate 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 is shifted to
lower frequency in all the metal complexes. The
absorption bands of carboxylate in the metal complexes
are observed in a range of 1646–1617 cm–1. This can be
a consequence of coordination that takes place through
the carboxyl group by deprotonation of the m-Hba mol-
ecule during coordination [23]. They νs(COO–) bands
salt, this result proves that bonding of the carboxylate
group is bidentate to the metal atom. The OH bending
peak for the m-hydroxybenzoic acid remained almost
in the same position at ~1259 cm–1 in all the metal com-
plexes. The low-intensity bands in a region of
600−400 cm–1 are attributed to the M–N and M–O
vibrations [6, 31–33].
The thermal data of the Co(II), Ni(II), and Zn(II)
complexes are given in Fig. 1. Among all complexes
investigated by us, [Co(m-Hba)2(Dena)2(H2O)2] is
more stable. Its thermal decompositions began at 85°C.
The coordination waters of the Co(II) complex are
dehydrated in the one-step temperature in a range of
endothermic DTA peak at 103°C (found 5.01%; calcd
4.98%).The decomposition of the complex is associ-
ated with the complete pyrolysis of the organic part of
the compound starts above this temperature. The ther-
moanalytical responses of the Co(II) complex are
shown in Fig. 1a. The organic part of the complex
decomposes with the release of CO2 molecules. The
descending continuous TG curve is obtained in a tem-
perature range of 185–605°C (endothermic DTA peaks
at 254, 455, 485, and 560°C). The final decomposition
product is CoO (found 9.00%; calcd 10.31%).
are located at 1541 cm–1 for the Co(II) complex,
1514 cm–1 for the Cu(II) complex, and 1542 cm–1 for
the Ni(II) and Zn(II) complexes. The νas(COO–) peaks
The thermal dehydration of [Ni(m-Hba)2(Dena)2
(H2O)2] occured in one-step by giving an endothermic
DTA peak at 119°C corresponding to the liberation of
two water molecules that are coordinated to the metal
ion (Fig. 1b) (found 5.05%; calcd 4.98%o). The tem-
perature range of this step is 85–135°C. The anhydrous
Ni(II) complex is stable in a range of 135–190°C. In the
second stage, all of the organic ligands decompose and
remove in a temperature range of 215–307°C by giving
exothermic DTA peaks at 361 and 418°C. The final
decomposition product, namely NiO, was identified
are observed at 1394 cm–1 for the Co(II), 1385 cm–1 for
Cu(II), 1399 cm–1 for Ni(II), and 1402 cm–1 for Zn(II)
complexes. The splitting of the νas and νs bands of the
COO– groups is almost identical for the Co(II), Ni(II),
and Zn(II) complexes (144–147 cm–1) and these bands
are shifted slightly than that for the sodium salt
(140 cm–1) [28], because the monodentate carboxylate
group exists [29, 30]. However, in the Cu(II) complex
this splitting band of the COO– group is almost identi-
cal (131 cm–1) and is smaller than that in the sodium (found 9.76%; calcd 10.32%) by IR spectroscopy with
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 33 No. 6 2007

SYNTHESIS AND CHARACTERIZATION
425
TGA, %
100
DTA, uV
TGA, %
DTA, uV
20 100
(a)
(b)
80
60
40
20
20
0
80
0
60
–20
–20
40
–40
–40
–60
20
0
0
–60
200
400
600
800
0
200
400
600
800
T, °C
T, °C
TGA, %
100
DTA, uV
TGA, %
100
DTA, uV
20
20
(c)
(d)
80
60
40
20
80
60
40
20
0
0
–20
–40
–60
–20
–40
–60
0
0
0
200
400
T, °C
600
800
200
400
T, °C
600
800
Fig. 1. TG-DTA curves of the complexes: (a) [Co(m-Hba) (Dena) (H O) ]; (b) [Ni(m-Hba) (Dena) (H O) ]; (c) [Cu(m-
2
2
2
2
2
2
2
2
Hba) (Dena) ], and (d) [Zn(m-Hba) (Dena) (H O) ].
2
2
2
2
2
2
the corresponding spectra obtained under the same con- Similar decomposition behaviors are shown in litera-
ditions as the pure oxides.
ture [24, 25, 33].
Except for the Cu(II) complex, all the other com-
plexes contain two coordinated water molecules. The
aqua ligands of the complexes, the first stage from
approximately 55 to 160°C corresponds to dehydra-
tion. The experimental values for the mass loss of the
dehydration stage are well consistent with the calcu-
lated values. Regardless of coordination, the decom-
position of the complexes starts with a dehydration
process but the decomposition of the Cu(II) complex
starts with to be smashed of organic ligands. The
results indicate that the metal–water bond strength is
almost the same for all the water molecules. The
The TG–DTA curves for [Cu(m-Hba)2(Dena)2
(H2O)2] are given in Fig. 1c. There is no aqua molecule
in this complex and, hence, no aqua decomposition
peak is shown. The anhydrous complex is stable untill
to temperature of 185°C. After this temperature, the m-
Hba and Dena ligands start to decompose all together.
The decomposition occurs in a temperature range of
185–520°C in two steps by giving endothermic DTA
peaks at 213 and 269°C. As a result of the removing
organic ligands, CuO is produced (found 11.91%; calcd
10.97%).
The thermal decomposition of [Zn(m-Hba)2(Dena)2 Co(II), Ni(II), and Zn(II) complexes lose water mol-
ecules in one-step. By the loss of two coordinated
molecules the originally octahedral complexes con-
vert into a new arrangement. After the dehydration
process, decomposition stages of the anhydrous
complexes are related to release nicotinamide, and
the partial decomposition of m-hydroxybenzoate
involving the release of CO2 occurs. Previous studies
show that the benzoate–metal complexes decompose
by releasing CO2 [34, 35]. In the Co(II), Ni(II), and
(H2O)2] is given in Fig. 1d. The first stage of its thermal
decomposition starts at the 55–160°C temperature
range with the release of two aqua ligands (found
4.97%; calcd 4.92%). The decomposition occurs in two
steps by giving endothermic DTA peaks at 72 and
134°C. The anhydrous complex, [Zn(m-Hba)2(Dena)2],
is not stable in air and begins to decompose with
removing the water molecules. At 282, 400, and 502°C
DTA peaks of the Dena and m-Hba ligands decompose
in a temperature range of 161–555°C. The removing Zn(II) complexes, all ligands are coordinated to the
ligands produced ZnO (found 12.95%; calcd 11.15%). metal ion as monodendate (a) but, in the Cu(II) com-
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 33 No. 6 2007

426
KÖSE et al.
plex m-Hba ligands are coordinated as monoanionic tion products were found to be the respective metal
bidentate (b). This type bonding is present in litera- oxides in the 500–600°C temperature intervals. The
ture [36–38]. The IR spectra of the intermediate suggested structures of the complexes are given
products show similar results. The final decomposi- below:
O
O
C2H5
C2H5
C2H5
C2H5
OH
N
N
OH
N
M
N
N
M
N
O
O
OH2
O
O
O
O
H2O
O
O
H5C2
H5C2
OH
N
N
OH
H5C2
H5C2
O
O
(a)
(b)
M = Co(II), Ni(II), and Zn(II)
M = Cu(II)
To conclude the thermal decomposition pathway of
the [Ni(m-Hba)2(Dena)2(H2O)2] complex, the mass
spectrum was recorded (Fig. 2) using direct the inser-
tion probe pyrolysis mass spectrometry method. 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 722. These peaks belong
to decomposition products of the complex and ligands.
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