bis(nicotinamide) and bis(N,N-diethyl nicotinamide) p-hydroxybenzoate complexes of Ni(II), Cu(II) and Zn(II) spectrothermal studies

Article abstract of DOI:10.1023/B:JTAN.0000032269.12381.42

The mixed-ligand p-hydroxybenzoate complexes of Ni(II), Cu(II) and Zn(II) with nicotinamide and N,N-diethylnicotinamide were synthesized and characterized by elemental analysis, magnetic susceptibility measurements and mass spectrometry. The thermal behavior of the complexes was studied by simultaneous TG, DTG and DTA methods in static air atmosphere. The infrared spectral characteristics of the complexes are also discussed. The complexes contain two water molecules, two p-hydroxybenzoato (p-hba) and two nicotinamide (na) (or diethylnicotinamide (dena)) ligands per formula unit. In these complexes, all ligands are coordinated to the metal ion as monodendate ligands. In Zn(II)-na and Cu(II)-dena complexes, the p-hydroxybenzoate behaves as bidentate chelating ligand through carboxylic oxygen atoms. The decomposition pathways and the stability of the complexes are interpreted in the terms of the structural data. The final decomposition products were found to be the respective metal oxides.

Full text of DOI:10.1023/B:JTAN.0000032269.12381.42

Journal of Thermal Analysis and Calorimetry, Vol. 76 (2004) 837–851
bis(NICOTINAMIDE) AND bis(N,N-DIETHYL
NICOTINAMIDE) p-HYDROXYBENZOATE
COMPLEXES OF Ni(II), Cu(II) AND Zn(II)
Spectrothermal studies
H. Icbudak1*, Z. Heren1, D. Ali Kose2 and H. Necefoglu2
1Department of Chemistry, Faculty of Arts and Sciences, Ondokuz Mayis University,
55139-Kurupelit-Samsun, Turkey
2Department of Chemistry, Faculty of Arts and Sciences, Kafkas University, Kars, Turkey
(Received November 4, 2003; in revised form January 20, 2004)
Abstract
The mixed-ligand p-hydroxybenzoate complexes of Ni(II), Cu(II) and Zn(II) with nicotinamide and
N,N-diethylnicotinamide were synthesized and characterized by elemental analysis, magnetic sus-
ceptibility measurements and mass spectrometry. The thermal behavior of the complexes was stud-
ied by simultaneous TG, DTG and DTA methods in static air atmosphere. The infrared spectral
characteristics of the complexes are also discussed. The complexes contain two water molecules,
two p-hydroxybenzoato (p-hba) and two nicotinamide (na) (or diethylnicotinamide (dena)) ligands
per formula unit. In these complexes, all ligands are coordinated to the metal ion as monodendate
ligands. In Zn(II)-na and Cu(II)-dena complexes, the p-hydroxybenzoate behaves as bidentate che-
lating ligand through carboxylic oxygen atoms. The decomposition pathways and the stability of the
complexes are interpreted in the terms of the structural data. The final decomposition products were
found to be the respective metal oxides.
Keywords: diethylnicotinamide, metal complexes, nicotinamide, p-hydroxybenzoato,
thermal decomposition
Introduction
It is documented that heterocyclic compounds play a significant role in many biologi-
cal systems, especially N-donor ligand systems being a component of several vita-
mins and drugs such as nicotinamide [1–3]. Nicotinamide is known as a component
of the vitamin B complex as well as a component of the coenzyme, nicotinamide ade-
nine dinucleotide (NAD). These are more important for transfer of hydrogen in the
cell breath. The presence of pyridine ring in numerous naturally abundant com-
pounds, adducts of nicotinamide are also scientific interest. Therefore, the structure
of nicotinamide has been the subject of many studies [4–7].
*
Author for correspondence: E-mail: icbudak@omu.edu.tr
1388–6150/2004/ $ 20.00
Akadémiai Kiadó, Budapest
© 2004 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

838
ICBUDAK et al.: DIETHYLNICOTINAMIDE
Phenolic antioxidants such as hydroxybenzoates are important classes of natural
antioxidants [8]. p-hydroxybenzoic acid is widely used as antimicrobial agents in
foods, drugs, cosmetics and toiletries [9]. Metal complexes of biologically important
ligands are sometimes more effective than the free ligands [10]. Structural reports of
metal (Zn2+) nicotinamide complexes exist in [11].
In the present paper, we report the synthesis, spectroscopic and thermal proper-
ties of some new mixed-ligand complexes of Ni(II), Cu(II) and Zn(II) containing
p-hydroxybenzoate-nicotinamide and -diethylnicotinamide. The structures of the lig-
ands are shown in Scheme 1.
Experimental
Scheme 1
Materials and instrumentation
All chemicals used were analytical reagent products. NiSO4×6H2O, CuSO4×5H2O,
ZnSO4×7H2O, p-hydroxybenzoic acid and nicotinamide were obtained from Merck
(Darmstadt, Germany). Diethylnicotinamide was purchased from Darmitsa Chemi-
cals Union (Kiev, Ukraine). Elemental analyses (C, H, N) were carried out by stan-
dard methods (Tubitak Marmara Research Center). Magnetic susceptibility measure-
ments at room temperatures were performed using a Sherwood Scientific MXI model
Gouy magnetic balance. IR spectra were recorded in 4000–400 cm–1 region with a
Mattson 1000 FT-IR spectrometer using KBr pellets. Thermal analysis curves
(TG-DTG and DTA) were recorded simultaneously in a static air atmosphere with a
Rigaku TG8110 thermal analyzer. The samples weighed approximately 10 mg and
highly sintered a-Al2O3 was used as a reference material. The heating rate
was 10°C min–1 and the DTG sensitivity was 0.05 mg s–1. The mass spectrum was re-
corded by Tubitak Marmara Research Center.
Preparation of p-hydroxybenzoate complexes
At the first step, p-hydroxybenzoic acid sodium salt was prepared according to the
following equation:
2p-hba+2NaHCO3 ®2Na(p-hba)+2CO2+2H2O
J. Therm. Anal. Cal., 76, 2004

ICBUDAK et al.: DIETHYLNICOTINAMIDE
839
At the second step, metal p-hba salts were synthesized from Na(p-hba) salt by
substitution reaction:
2Na(p-hba)+MSO4×nH2O ® M(p-hba)2×nH2O+Na2SO4 [M=Ni(II), Cu(II), Zn(II)]
The M(p-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.
Synthesis of mixed-ligand complexes
A solution of na and dena (2 mmol) in distilled water (30 mL) was added dropwise
with stirring to a solution of M(p-hba)2(H2O)n (1 mmol) in hot distilled water
(50 mL). The solutions were heated to 80°C in a temperature-controlled bath and
stirred for 4 h and then cooled to room temperature and allowed 7–8 days for crystal-
lization. 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 fol-
lowing equations:
M(p-hba)2(H2O)n+2na ® M(p-hba)2(na)2(H2O)2 [M=Ni(II), Cu(II)]
Zn(p-hba)2(H2O)n+2na ® Zn(p-hba)2(na)2+nH2O
M(p-hba)2(H2O)n+2dena ® M(p-hba)2(dena)2(H2O)2×nH2O [M=Ni(II), Zn(II)]
[Cu(p-hba)2(H2O)n]+2dena ® Cu(p-hba)2(dena)2+nH2O
Result and discussion
Analytical results and compositions of the complexes are given in Table 1. The
complexes were synthesized with high purity. The results of the elemental analysis
indicated that the complexes contain two moles of p-hydroxybenzoato and nicotin-
amide ligands per mole formula units. The Ni(II)-na, Cu(II)-na and Ni(II)-dena and
Zn(II)-dena complexes also include two moles of aqua ligands. Furthermore, the
Ni(II)-dena and Zn(II)-dena complexes contain two moles of crystallization water per
formula unit. The presence of aqua ligand was confirmed by the FT IR spectra and
mass loss and endothermic peaks in the DTA curves. In the complexes with the aqua
ligands, the octahedral coordination of the metal ion formed by two carboxylic oxygen
atoms from two p-hyroxybenzoates and two nitrogen atoms from two nicotinamides
(or diethylnicotinamides). In the Zn(II)-na and Cu(II)-dena complexes, the p-hydroxy-
benzoate behaves as bidentate chelating ligand through carboxylic oxygen atoms. The
elemental analysis data in Table 1 confirm the proposed formulae of the complexes.
Due to the low solubility, it was not possible to record satisfactory UV-Vis spec-
tra for the complexes. The metal complexes are of the high-spin type and paramag-
netic, except for Zn(II) complexes. As expected, the Zn(II) complexes are diamag-
netic. These values suggest octahedral coordination around the metal ions.
J. Therm. Anal. Cal., 76, 2004

840
ICBUDAK et al.: DIETHYLNICOTINAMIDE
J. Therm. Anal. Cal., 76, 2004

ICBUDAK et al.: DIETHYLNICOTINAMIDE
841
IR spectra
The absorption bands in the range of 3472–3431 cm–1 in complexes correspond to the
asymmetric and symmetric stretching vibration of water molecules. The wave num-
ber range for the N–H stretches of primary amides is 3370–3170 cm–1. We observed
two bands in the range of 3350–3245 cm–1 in the na complexes and assigned to asym-
metric and symmetric stretching vibration of NH2. The na complexes give rise to
strong bands responsible from the C=O stretching. Conjugation between the car-
bonyl group and the amide nitrogen causes small frequency shifts. The strong bands
observed at around 1680 cm–1 are assigned to this mode. Pyridine ring vibrations of
free nicotinamide at 1592 cm–1 shifts to higher frequencies in the spectrum of the
metal complexes. The shifts in the spectrum of the complexes may indicate that the
pyridine ring is coordinated. The main difference in the spectrum of p-hydroxy-
benzoic acid is that the C–O stretching vibration of the carboxyl group at 1676 cm–1
is shifted to lower frequency in all the metal complexes. The bands due to the asym-
metric and symmetric stretching of carboxylate in the metal complexes occur in the
range of 1579–1533 and 1401–1385 cm–1, respectively. This shows that the coordi-
nation takes place through the carboxyl group [12]. The Zn(p-hba)2(na)2 and
Cu(p-hba)2(dena)2 complexes are bidendate and only one strong peak for each com-
plex appears at 1384 and 1385 cm–1 with a small shoulder at 1579 and 1580 cm–1, re-
spectively [13]. The d(OH) bending peak for the p-hydroxybenzoic acid remained al-
most in the same position at around 1250 cm–1 in all metal complexes. The low
intensity bands in the region of 456–400 cm–1 are attributed to M–N and M–O
vibration [14, 15].
Thermal data
[Ni(p-hba)2(na)2(H2O)2]
The one-step dehydration of the Ni(II) complex occurs in the temperature range
of 110–161°C (Fig. 1). The endothermic DTA peak at 143°C corresponds to the lib-
eration of two water molecules that are coordinated to metal ion. In the second stage,
two mole nicotinamide ligands decompose in the temperature range of 198–296°C
(exp. 40.04%; calcd. 39.8%). This type of behavior of neutral ligands has been re-
ported earlier [16–18]. Consequently, the decomposition of the p-hydroxybenzoato
ligands starts with the release of two CO2 molecules (exp. 7.40%; calcd. 7.18%). The
IR spectra of the intermediate products show similar results. The descending continu-
ous TG curve is obtained in the temperature range of 297–464°C (DTG peaks
at 303, 339, 418°C) and these are relevant to the decomposition of p-hydroxy-
benzoato ligands. In the fifth stage, the residue decomposes vigorously followed by a
strong exothermic DTA peak at 418°C implying the redox nature of this process. The
final decomposition product, namely NiO was identified by IR spectroscopy with
corresponding spectra obtained under the same conditions as the pure oxides.
J. Therm. Anal. Cal., 76, 2004

842
ICBUDAK et al.: DIETHYLNICOTINAMIDE
Fig. 1 The TG, DTG and DTA curves of [Ni(p-hba)2(na)2(H2O)2]
[Cu(p-hba)2(na)2(H2O)2]
The TG-DTG and DTA curves for the Cu(II) complex are given in Fig. 2. The first
stage of the thermal decomposition of Cu(II) nicotinamide p-hydroxybenzoate starts
at the 58–108°C temperature range with the release of the aqua ligands
(exp. 6.16%; 5.82%). The anhydrous complex, [Cu(p-hba)2(na)2] is stable in air up
to 196°C and begins to decompose with melting at 205°C (DTA curve). Similar be-
havior was observed in the nicotinamide-acetylsalicylato mixed-ligand complex of
Cu(II) [16]. In this consecutive stage (DTG peaks at 211, 227, 230 triplet), a number
of undefined processes take place in this range eventually produce CuO.
Fig. 2 The TG, DTG and DTA curves of [Cu(p-hba)2(na)2(H2O)2]
J. Therm. Anal. Cal., 76, 2004

ICBUDAK et al.: DIETHYLNICOTINAMIDE
843
[Zn(p-hba)2(na)2]
Thermal analysis curves (TG-DTG and DTA) of the complex are shown Fig. 3. Obvi-
ously, due to the absence of the crystal water, Zn(II) complex is the most stable of all
investigated nicotinamide-p-hydroxybenzoate complexes. The complex is thermally
stable up to 191°C. The thermal decomposition of the complex begins with melting
at 210°C (DTA peak) and reveals a 49.66% mass loss between 191–262°C. In this
stage, decomposition of the nicotinamide ligands and p-hydroxybenzoato ligand with
release of CO2 proceeds. A good agreement between the experimental and calculated
values was observed for the mass loss (exp. 49.66%; calcd. 49.35%). The IR spec-
trum of the intermediate product obtained in this step showed that the p-hydroxy-
benzoato ligand decomposes with release of CO2. The strong exothermic peak at
490°C is associated with the burning of the organic residue. Final decomposition
product is ZnO.
Fig. 3 The TG, DTG and DTA curves of [Zn(p-hba)2(na)2]
[Ni(p-hba)2(dena)2(H2O)2]×2H2O
The complex contains both of the crystallization and coordination water, different from
the Cu(II) nicotinamide p-hydroxybenzoate complex. The thermal dehydration of the
complex occurred in one step by giving endothermic effect at 107°C (Fig. 4). According
to the initial decomposition temperatures (Table 2), the thermal stability of the
[Ni(p-hba)2(dena)2(H2O)2]×2H2O is lower than that of the [Ni(p-hba)2(na)2(H2O)2]. Two
moles of crystallization and two moles of coordination water are removed at this stage
(exp. 9.75%; calcd. 9.46%). A color change from light-blue to green was noted by the
removal of the water molecules. After dehydration the crystal structure of the complex is
distorted, but on gradual heating the anhydrous complex shows a phase transition at
167°C (DTA peak) indicating rearrangement of species in the solid state. The anhydrous
complex is stable to 220°C and decomposes in the 220–406°C temperature intervals. The
J. Therm. Anal. Cal., 76, 2004

844
ICBUDAK et al.: DIETHYLNICOTINAMIDE
J. Therm. Anal. Cal., 76, 2004

ICBUDAK et al.: DIETHYLNICOTINAMIDE
845
J. Therm. Anal. Cal., 76, 2004

846
ICBUDAK et al.: DIETHYLNICOTINAMIDE
Fig. 4 The TG, DTG and DTA curves of [Ni(p-hba)2(dena)2(H2O)2]×2H2O
fourth mass loss process of the complex is vigorous and strongly exothermic (DTA peak
at 388°C), and related to the burning of the organic residue. The final product obtained at
406°C is NiO (exp. 90.93%; calcd. 90.18%).
[Cu(p-hba)2(dena)2]
The thermal analysis curves of this complex (Fig. 5) indicate that the complex is thermal-
ly stable to 175°C and begins to decompose with melting at 202°C (DTA curve). This
decomposition stage with multi-step is indicative of a very complex process. The DTG
curve of the complex displays five closely spaced peaks at 214, 226, 247, 256 and 266°C.
These peaks can be attributed to the decomposition of the diethylnicotinamide and
p-hydroxybenzoate ligands. The exothermic peaks at 443 and 470°C can be assigned to
Fig. 5 The TG, DTG and DTA curves of [Cu(p-hba)2(dena)2]
J. Therm. Anal. Cal., 76, 2004

ICBUDAK et al.: DIETHYLNICOTINAMIDE
847
the burning of the organic residue formed in the previous stage. The final solid product of
thermal decomposition was identified as CuO (exp. 88.92%; calcd. 88.53%).
[Zn(p-hba)2(dena)2(H2O)2]×2H2O
Zn(II) diethylnicotinamide p-hydroxybenzoate complex contains both of the
crystallization and coordination waters similarly to [Ni(p-hba)2(dena)2(H2O)2]×2H2O.
But the thermal dehydration of the Zn(II) complex occurred in two steps by giving
endothermic effect at 54 and 114°C which is different from the other studied
complexes. Two moles of crystallization water are released in the first step of the
dehydration in the temperature range of 35–84°C. The dehydration temperature of
[Zn(p-hba)2(dena)2(H2O)2]×2H2O is lower than other all investigated complexes. In
the second step of dehydration, the coordinated waters are removed in the
temperature range of 93–143°C. This behavior was also observed in our early studies
with Zn(II) complexes [16, 19]. The following stage is related to decomposition of
the diethylnicotinamide and p-hydroxybenzoate ligands. According to the mass loss,
the final product is ZnO (exp. 90.78, calcd. 89.40%) at 495°C (Fig. 6).
Fig. 6 The TG, DTG and DTA curves of [Zn(p-hba)2(dena)2(H2O)2]×2H2O
The complexes of Ni(II) and Cu(II) p-hydroxybenzoate-nicotinamide, Ni(II)
and Zn(II) p-hydroxybenzoate-diethyl nicotinamide contain two and four moles of
water, respectively. In these hydrated complexes, the first stage from approx. 35
to 161°C corresponds to dehydration. The experimental values for the mass loss of
the dehydration stage are well consistent with the calculated values (Table 2). The
water molecules present in the complexes of Ni(II) and Zn(II) p-hydroxybenzoate-
diethyl nicotinamide can be divided into two groups. Two of them are directly
coordinated to the metal ion as ligands while the rest is present as crystallization
water. However, the results indicate that metal-water bond strength is almost the
same for all of the water molecules. By the loss of two coordinated and two
J. Therm. Anal. Cal., 76, 2004

848
ICBUDAK et al.: DIETHYLNICOTINAMIDE
crystallization waters the originally octahedral complexes convert into new arrange-
ment. This destabilizes the anhydrous complexes and a phase transition occurs
at 167°C to rearrange the present species in the solid state. The phase transition was
not observed in the other complex. Usually dehydration was followed by a color
change. In the Zn(II) p-hydroxybenzoate-diethyl nicotinamide, the dehydration take
places in two steps, different from the other complexes. After the dehydration
process, decomposition stages of the anhydrous complexes are related to release
nicotinamide (or decomposition of the diethyl nicotinamide) and the partial
decomposition of p-hydroxybenzoate involving the release of CO2. Previous studies
show that the benzoate-metal complexes decompose by releasing of CO2 [20–24].
The IR spectra of the intermediate products show similar results. The final
decomposition products were found to be the respective metal oxides in the
400–530°C temperature intervals.
Mass spectra
To deduce the thermal decomposition pathway of the [Ni(p-hba)2(na)2(H2O)2] com-
plex the positive-ion FAB mass spectrum was recorded (Fig. 7) to see if the thermal
and ionization processes somehow resemble each other. The mass spectrum shows
the fragmentation pattern and the most fragile points of the molecule. The obtained
mass spectrum is relatively complex and exhibits a large number of peaks that extend
to m/z value above 612. Beside the most abundant peaks, much fewer abundant peaks
observed on the spectrum depend probably on the nature of ligands. In the mass spec-
trum recorded, the molecular ion is not detected. A schematic representation includ-
ing the main fragmentation process for the [Ni(p-hba)2(na)2(H2O)2] complex is given
in Scheme 2.
Fig. 7 The mass spectrum of [Ni(p-hba)2(na)2(H2O)2]
J. Therm. Anal. Cal., 76, 2004

ICBUDAK et al.: DIETHYLNICOTINAMIDE
849
Scheme 2 Mass spectral fragmentation pattern of the [Ni(p-hba)2(na)2(H2O)2]
The structures of the synthesized complexes, which are presented in Fig. 8, are
consistent with their chemical, thermal and spectroscopic properties.
J. Therm. Anal. Cal., 76, 2004

850
ICBUDAK et al.: DIETHYLNICOTINAMIDE
Fig. 8 Suggested structures of the complexes
* * *
Our thanks are due to the Researhc Fund of Ondokuz Mayis University and the Research Fund of
Kafkas University for financial support.
References
1 U. Brühlmann and E. Hayon, J. Am. Chem. Soc., 96 (1974) 6169.
2 M. Kato and Y. Muto, Coord. Chem. Rev., 92 (1988) 45.
3 R. Nagar, J. Inorg. Biochem., 40 (1990) 349.
4 Y. Miwa, T. Mizuno, K. Tsuchiya, T. Taga and Y. Iwata, Acta Crystallogr., B55 (1999) 75.
5 B.Vogalsanger, R. D. Brown, P. D. Godfrey and A. P. Pierlot, J. Mol. Spectrosc., 145 (1991) 1.
6 P. Purcell, J. Phys. Chem., 68 (1964) 2666.
7 P. Purcell and A.J. Siger, J. Phys. Chem., 69 (1965) 4097.
8 C. A. Rice-Evans, N. J. Miller and G. Paganga, Free Radic. Biol. Med., 20 (1996) 933.
J. Therm. Anal. Cal., 76, 2004

ICBUDAK et al.: DIETHYLNICOTINAMIDE
851
9 A. Hossaini, J. J. Larsen and J. C. Larsen, Food and Chemical Toxicology, 38 (2000) 19.
10 J. R. J. Sorensen, Metal Ions in Biological Systems, H. Sigel (Ed.),Vol. 14, Marcel Dekker,
New York 1982, p. 77.
11 T. Hökelek and H. NecefoÈlu, Anal. Sci., 17 (2001) 1241.
12 H. Icbudak, H. Olmez, O. Z. Yesilel, F. Arslan, P. Naumov, G. Jovanovski, A.R. Ibrahim,
A. Usman, H. K. Fun, S. Chantrapromma and S.W. Ng, J. Mol. Struct., 657 (2003) 255.
13 K. Rissanen, J. Valkonen, P. Kokkonen and M. Leskela, Acta Chemica Scandinavica,
A41 (1987) 299.
14 K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds,
Wiley and Sons, New York, 1978, p. 197.
15 J. Zsakó, G. Pokol, Cs. Novák, Cs. Várhelyi, A. Dobó and G. Liptay, J. Therm. Anal. Cal.,
64 (2001) 843.
16 H. NecefoÈlu, H. Icbudak, D. A. Kose and A. Uyanik, Challenges for Coordination Chemistry
in the New Century, (Monograph, edited by M. Melnik and A. Sirota), Vol. 5, Slovak
Technical University Press, Bratislava 2001, p. 427.
17 P. Naumov, V. Jordonavska, O. Grupce, B. Boyanov and G. Jovanovski, J. Therm. Anal. Cal.,
65 (2001) 59.
18 K. Györyova, E. Szunyogova, J. Kovarova, D. Hudecova, D. Mudronova and E. Juhaszova,
J. Therm. Anal. Cal., 72 (2003) 587.
19 H. Icbudak, V. T. Yilmaz and H. Olmez, J. Thermal Anal., 53 (1998) 843.
20 P. Kokkonen, L. H. J. Lajunen, A. Jaakola and H. Ruotsalainen, Thermochim. Acta,
79 (1984) 289.
21 G. A. M. Hussein, H. M. Ismail and S. A. S. Mansour, J. Anal. Appl. Pyrolysis, 36 (1996) 17.
22 B. R. Srinivasan and S. C. Sawant, Thermochim. Acta, 402 (2003) 45.
23 W. Ferenc and B. Bocian, J. Therm. Anal. Cal., 74 (2003) 521.
24 M. Olczak-Kobza, R. Czylkowski and J. Karolak-Wojciechowska, J. Therm. Anal. Cal.,
74 (2003) 895.
J. Therm. Anal. Cal., 76, 2004