Synthesis, spectral and thermal properties of macrocyclic zinc(II) complexes

Article abstract of DOI:10.1023/B:JTAN.0000027808.60599.71

The new zinc ternary complexes [Zn(cyclen)NO₃]ClO₄ (I), [Zn₂(cyclen)₂( -nic)](ClO₄)₃ (II), [Zn₂(cyclen)₂( -pic)](ClO₄)₃ (III) (cyclen=1,4,7,10-te

Full text of DOI:10.1023/B:JTAN.0000027808.60599.71

Journal of Thermal Analysis and Calorimetry, Vol. 76 (2004) 97–105
SYNTHESIS, SPECTRAL AND THERMAL PROPERTIES
OF MACROCYCLIC ZINC(II) COMPLEXES
Z. Vargová, K. Györyová* and V. Zele×ák
University of P. J. Šafarik, Faculty of Sciences, Department of Inorganic Chemistry,
041 54 Košice, Slovakia
Abstract
The new zinc ternary complexes [Zn(cyclen)NO3]ClO4 (I), [Zn2(cyclen)2(m-nic)](ClO4)3 (II),
[Zn2(cyclen)2(m-pic)](ClO4)3 (III) (cyclen=1,4,7,10-tetraazacyclododecane; nic=nicotinic acid;
pic=picolinic acid) were synthesized and their spectral and thermal properties were investigated.
The compounds were characterized by elemental analysis, IR spectroscopy and TG/DTG, DTA
methods. Moreover, the way of coordination of pyridinecarboxylate anions was proposed on the
basis of the spectral data and consequently proved with results of X-ray structure analysis.
Keywords: infrared spectroscopy, macrocyclic complexes, thermal behaviour,
zinc(II) pyridinecarboxylate
Introduction
The pyridinecarboxylic acids belong to ligands occurring in biological systems. Nic-
otinic acid and nicotinamide are present in cells as the pyridine nucleotides (NAD+,
NADP+), which belong to the coenzymes and vitamins and are necessary for their
metabolisms. Nicotinamide transfers reversible hydride anion from alcohols to
nicotinamide adenosine dinucleotide (NAD+). Few models of zinc(II) enzymes were
built up to understand the interaction between enzymes, coenzymes and the substrate
itself. One of these models are macrocyclic polyamines. Kimura [1–3] has described
the 1,5,9-triazacyclododecane–Zn–OH species as a new alcohol dehydrogenase and
carbonic anhydrase models. Moreover, he reported the syntheses and characteriza-
tion of zinc(II) cyclen complexes and their various pendant derivatives [4–7]. Such
compounds have been extensively studied as the enzyme models and artificial carri-
ers for thymidine and uridine nucleosides useful in antiviral chemotherapy [8]. Some
of zinc(II) complexes show antimicrobial activity and fungistatic effect [9–11].
This paper reports the synthesis, spectral and thermal properties of the new
compounds [Zn(cyclen)(NO3)](ClO4) (I), [Zn(cyclen)-nic-Zn(cyclen)](ClO4)3 (II),
[Zn(cyclen)-pic-Zn(cyclen)](ClO4)3×H2O (III).
*
Author for correspondence: E-mail: gyoryova@kosice.upjs.sk
1388–6150/2004/ $ 20.00
Akadémiai Kiadó, Budapest
© 2004 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

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Experimental
Synthesis of the compounds
The following A.R. grade chemicals were used for the preparation of the compounds
under study: Zn(ClO4)2×6H2O (Lachema Neratovice), HNO3 68%, cyclen (1,4,7,10-tetra-
azacyclododecane, m.p. 110–113°C, F.W. 172.28), nicotinic acid 99% (m.p. 236–239°C,
F.W. 123.11), picolinic acid 99% (m.p. 139–142°C, F.W. 123.11), (Sigma).
Scheme 1
Preparation of [Zn(cyclen)(NO3)]ClO4 (I)
A solution of 345 mg cyclen (2.00 mmol) soluble in 20 mL water was added to
the 20 mL aqueous solution containing 378 mg HNO3 (6.00 mmol). Subsequently zinc
perchlorate (745 mg 2.00 mmol) was added to the mixture. 1 M NaOH solution were
necessary to add to adjust pH to 5.8–6.0. The mixture was allowed to stand in covered
vessel 24 h at room temperature. Then ethanol was added to the mixture in ratio
water:ethanol=1:1. The solution was left to stand in the air and after few days colorless
crystals were obtained.
Preparation of [Zn(cyclen)-nic-Zn(cyclen)](ClO4)3 (II)
86 mg zinc perchlorate (0.232 mmol) soluble in 3 mL water was added to the 7 mL
aqueous solution containing 40 mg cyclen (0.232 mmol). Reaction mixture was al-
lowed to stand in covered vessel 24 h. Equimolar amount of 10 mL aqueous solution
of 29 mg nicotinic acid (0.232 mmol) was added to the mixture that was left to stand
at room temperature in the air (pH=4.3). After several days colorless and pellucid
crystals were obtained from the aqueous solution.
Preparation of [Zn(cyclen)-pic-Zn(cyclen)](ClO4)3×H2O (III)
The 5 mL aqueous solution of 172 mg zinc perchlorate (0.462 mmol) was slowly
added to the 5 mL aqueous solution of 80 mg cyclen (0.462 mmol). Reaction mixture
was allowed to stand in covered vessel 24 h. Then equimolar amount of 58 mg
picolinic acid (0.462 mmol) in 5 mL water was added to the reaction mixture. After
two hours pH of solution was adjusted by 1 M NaOH from 4.49 to 5.55. The solution
was left to stand and after 24 h 10 mL acetone was added to the solution. After few
days colorless crystals were obtained.
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Instrumentation
Infrared spectra were recorded on a Perkin Elmer spectrophotometer in the
range 4000–400 cm–1 using KBr discs.
The content of C, H, N in prepared compounds was determined by means of
Perkin Elmer 2400 CHN analyzer and zinc content complexometrically, using
Complexone III as an agent and Eriochrome black as an indicator.
The TG/DTG and DTA measurements were carried out using TA instruments
Setaram TG-DTA. The mass of the used samples was within 5.68–7.87 mg range.
The samples have been heated in air atmosphere in the temperature range to 1000°C.
Results and discussion
Spectral behaviour
The prepared compounds are colorless, lightproof and stable in the air. The results of
elemental analysis are in a good agreement with the calculated ones.
The IR spectra were used for determination of the presence of characteristic ab-
sorption bands. The observed absorption bands of prepared complexes are given in
Table 1 and Fig. 1.
Fig. 1 Characteristic absorption bands of ternary complexes [Zn(cyclen)NO3]ClO4 (I),
[Zn2(cyclen)2(m-nic)](ClO4)3 (II), [Zn2(cyclen)2(m-pic)](ClO4)3 ×H2O (III)
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101
Infrared spectra are in good accordance with [12]. The presence of nitrato ligand
and perchlorate anion was confirmed by characteristic stretching vibration at 1380 and
1090 cm–1. Picolinate and nicotinate anions show characteristic absorption bands in the
range 1630–1200 cm–1 [13]. Asymmetric stretching vibration of carboxylate anion
shows at 1590 and 1550 cm–1 in complex (II) and at 1610 and 1570 cm–1 in the case of
complex (III). Moreover, the presence of wide absorption band in the
range 1630–1610 cm–1 assume the overlap of asymmetric stretching vibration of
carboxylate anion with deformation vibration of water molecule. The presence of water
in this complex was really confirmed by X-ray structural analysis [14]. Therefore, the
value 1630 cm–1 we have assigned to deformation vibration of water molecule. The
values 1440 and 1450 cm–1 respond to symmetric vibration of carboxylate anion in
complex (II) and (III). The symmetric stretching vibrations n(C–C) and n(C–N) of
pyridine ring were spotted at 1480 cm–1 in both complexes. The other characteristic
absorption bands for the compounds (II) and (III) are in the range 1400–1000 cm–1.
Martini studied spectral properties of some carboxylates and found out, that D
value (D=nas(OCO–)–ns(OCO)) for acetates changes in the following order [15]:
Dunidentate >Dionic >Dbridging bidentate
<190 cm–1 170–160 cm–1 <140 cm–1
>Dchelating bidentate
<140 cm–1
In our complexes, for the compound [Zn2(cyclen)2(m-nic)](ClO4)3 (II) D value is
150 cm–1 and for [Zn2(cyclen)2(m-pic)](ClO4)3 (III) is D value 160 cm–1. The solved
crystallographic data confirm monodentate coordination in the complex (II) through
oxygen of carboxylate group and in (III) bridging bidentate coordination to two Zn(II)
ions [14]. There are two independent zinc atoms in the structure (II). Both are co-
ordinated by four nitrogen atoms of the cyclen subunit. The fifth coordination position is
occupied by oxygen atom of unidentate nicotinate carboxylate anion (O1–Zn2=
1.9240(19) ) or the nitrogen atom of nicotinate pyridine ring (N1–Zn1=2.026(2) ),
respectively. In the case of complex (III), the monomeric unit also contains two
independent zinc atoms, so two different chromophores are present (Zn(2)N4O and
Zn(1)N5O). The first coordination polyhedron adopts the shape of a distorted tetragonal
pyramid and the second a distorted octahedron.
Thermal behaviour
The TG/DTG and DTA curves of compound [Zn(cyclen)NO3]ClO4 (I) are depicted
in Fig. 2. The first step of the thermal decomposition belongs to the release of cyclen
molecule. This process is accompanied by strong exothermic effect at 330°C. The
following course of the DTA curve displays one exothermic peak with the maximum
at 420°C. This effect corresponds to the evaluation of oxygen and ZnO was found as
a final product of thermal decomposition. The following reaction was proposed for
the mechanism of the thermal decomposition:
2[Zn(cyclen)NO3]ClO4® 2cyclen+4O2+N2O5+ZnCl2+ZnO
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Fig. 2 TG/DTG and DTA curves of [Zn(cyclen)NO3]ClO4 (I)
As it is obvious from the TG, DTG and DTA curves in Fig. 3, the complex
[Zn2(cyclen)2(m-nic)](ClO4)3 (II) is thermally stable up to 340°C. Above this temper-
ature the sample loses cyclen, as demonstrated the mass loss on the TG curve and the
exothermic effect on DTA curve at 355°C. At the next step of thermal decomposition
pyridine, CO2, ClO3 and oxygen are released with an exothermic peak at 550°C.
Above 600°C the thermal decomposition continues by release of zinc chloride and
zinc oxide is the final product of thermal decomposition. The mechanism of the ther-
mal decomposition can be proposed in this way:
[Zn2(cyclen)2(m-nic)](ClO4)3 ® 2cyclen+pyridine+CO2+4O2+ClO3+ZnCl2+ZnO
It was interested to compare thermal decomposition of [Zn2(cyclen)2(m-
nic)](ClO4)3 (II) compound with Zn(nic)2(H2O)4 studied by Allan [16]. The compound
Zn(nic)2(H2O)4 is stable to 93°C. Above this temperature dehydration process was
observed. The complex then decomposes at 140°C with loss of organic ligand and the
formation of zinc oxide. In the DTA curve this decomposition process corresponds to
an exothermic effect at 390°C [16]. In our case the thermal decomposition of nicotinate
anion in complex [Zn2(cyclen)2(m-nic)](ClO4)3 (II) is also accompanied by exothermic
effect at higher temperature (550°C). The higher thermal stability is caused by different
way of zinc coordination in complex compounds. In the case of compound (II) zinc is
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Fig. 3 TG/DTG and DTA curves of [Zn2(cyclen2(m-nic)](ClO4)3 (II)
Fig. 4 TG/DTG and DTA curves of [Zn2(cyclen2(m-pic)](ClO4)3 (III)
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surrounded by four nitrogen atoms from cyclen and oxygen or nitrogen atom from
nicotinate anion [12]. On the other hand, zinc in complex [Zn(nic)2(H2O)4] is co-
ordinated only through two nitrogen atoms [16].
The TG/DTG and DTA curves of compound [Zn2(cyclen)2(m-pic)](ClO4)3 (III)
are given in Fig. 4. The first step of the thermal decomposition is the release of
cyclen, pyridine, CO2 and ClO3 as it is displayed on the DTA curve with a maximum
at 340°C. The next step of thermal decomposition is accompanied by weak exother-
mic effect on the DTA curve at temperature 525°C. It corresponds to the mass loss of
ClO3 and O2. Above 550°C the thermal decomposition is finished by formation of
zinc oxide. The scheme of the thermal decomposition can be proposed like this:
[Zn2(cyclen)2(m-pic)](ClO4)3® 2cyclen+pyridine+CO2+1/2O2+3ClO3+2ZnO
Conclusions
We have found that the compounds [Zn(cyclen)NO3]ClO4 (I), [Zn2(cyclen)2(m-
nic)](ClO4)3 (II), [Zn2(cyclen)2(m-pic)](ClO4)3×H2O (III) are stable in the air
atmosphere up to 300°C. When heated above this temperature, the release of cyclen
and the decomposition of pyridinecarboxylate anions takes place and O2, N2O5, ClO3
and ZnCl2 are evolved. The solid product of the thermal decomposition ZnO was
proved by X-ray powder diffraction.
The thermal stability of the prepared complexes increases in the following order:
[Zn(cyclen)NO3]ClO4 (I) – 330°C <
[Zn2(cyclen)2(m-pic)](ClO4)3×H2O (III) – 340°C <
[Zn2(cyclen)2(m-nic)](ClO4)3 (II) – 355°C
* * *
This work was supported by the Slovak Ministry of Education project VEGA No. 1/9247/02. This
financial support is gratefully acknowledged.
References
1 Eiichi Kimura, Progress in Inorganic Chemistry, 41 (1994) 443.
2 T. Koike, E. Kimura, I. Nakamura, Y. Hashimoto and M. Shiro, J. Am. Chem. Soc.,
114 (1992) 7338.
3 E. Kimura, T. Shiota, T. Koike, M. Shiro and M. Kodama, J. Am. Chem. Soc., 112 (1990) 5805.
4 T. Koike, M. Takamura and E. Kimura, J. Am. Chem. Soc., 116 (1994) 8443.
5 T. Koike, S. Kajitani, I. Nakamura, E. Kimura and M. Shiro, J. Am. Chem. Soc., 117 (1995) 1210.
6 X. Zhang and R. van Eldik, Inorg. Chem., 34 (1995) 5606.
7 M. Kalesse and A. Loos, Liebigs Ann., (1996) 935.
8 H. Fujioka, T. Koike, N. Yamada and E. Kimura, Heterocycles, 42 (1996) 775.
9 K. Györyová, E. Szunyogová, J. Kováéová, D. Hudecová, D. Mudro×ová and E. Juhaszová,
J. Therm. Anal. Cal., 72 (2003) 587.
J. Therm. Anal. Cal., 76, 2004

VARGOVÁ et al.: MACROCYCLIC ZINC(II) COMPLEXES
105
10 E. Szunyogova, K. Györyová, J. Kováéová, D. Hudecová, and E. Juhászova, J. Therm. Anal.
Cal., 71 (2003) 967.
11 E. Andogova, K. Györyová and F. A. Nour El-Dien, J. Therm. Anal. Cal., 69 (2002) 245.
12 T. Koike, M. Takamura and E. Kimura, J. Am. Chem. Soc., 116 (1994) 8443.
13 Z. Vargová, P. Hermann, I. Lukeš and K. Györyová, Chem. Listy, 97 (2003) 649.
14 Z. Vargová, P. Hermann, R. Gyepes, I. Císaéová, J. Rudovský and I. Lukeš, Eur. J. Inorg. Chem.,
prepared in press.
15 D. Martini, M. Pellei, C. Pettinari, B.W. Skelton and A. H. White, Inorg. Chim. Acta,
333 (2002) 72.
16 J. R. Allan, W. C. Geddes, C. S. Hindle and A. E. Orr, Thermochim. Acta, 153 (1989) 249.
J. Therm. Anal. Cal., 76, 2004