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Journal of the Chilean Chemical Society

versão On-line ISSN 0717-9707

J. Chil. Chem. Soc. vol.58 no.4 Concepción dez. 2013

http://dx.doi.org/10.4067/S0717-97072013000400012 

 

SYNTHESIS AND CHARACTERIZATION OF COPPER COMPLEXES: INTERACTION OF METALLICCARBOXYLATES WITH 1,3-THIAZOLE LIGAND

 

GLORIA V. SEGUEL*, BERNABÉ L. RIVAS, J. GUILLERMO CONTRERAS

Facultad de Ciencias Químicas, Universidad de Concepción, Casilla 160-C, Concepción, Chile
* e-mail: gseguel@ude.cl


ABSTRACT

Complexes were synthesized from aspirinate of Cu(II) and acetate of Cu(II) dihydrated with the ligand 1,3-thiazole and were characterized through elemental analysis, magnetic moment, FT-IR spectroscopy, and thermogravimetric analysis. Moreover, semiempirical structural PM6 of both compounds were carried out.

Ligand 1,3-thiazole coordinates with the Cu(II) ions through the nitrogen without break the dimeric unit Cu2 (RCOO)4 To coordinate with the aspirinate of Cu(II), the ligand must to break tridimensional arrangement and to coordinate with the acetate of Cu(II) dihydrated, it replaced the water molecules. In both compounds, Cu2(asp)4(Tz)2 and Cu2(acetate)4(Tz)2, the PM6 calculations corresponding to the Cu-Cu distances in the dimeric unit Cu2 (RCOO)4 presents a small difference 0.03A°, but the magnetic moments are very different. The complex with aspirinate presents a magnetic moment of 1.79 M.B and that with acetate is 1.4 MB.

Keywords: metallic aspirinates, metallic acetates, 1,3-thiazole


 

INTRODUCTION

Aspirine, acetil salicylic acid, it is very well known as antipiretic, analgesic, and anti-inflammatory agent [1]. It has been reported that the complex Cu2(aspirine)4 also shows interesting properties such as anticancerogenic, antimutagenic, bactericide, anticonvulsivant , and as potent antioxidant agent in biological systems [2]. It has been demonstrated that it is a better antioxidant than the salicylate of Cu(II) and acetate of Cu(II) [3].

The compound Cu2(aspirine)4 possesses a dimeric structure which is similar to that found in acetate of Cu(II) monohydrated. In both cases the two copper atoms are bridged by carboxylate groups [4,5]. The Cu-Cu distance in Cu2( acetate)42H2O is 2.63 A° and shows an non usual magnetic moment of 1.4 M.B. The antiferromagnetism has been explained by several authors through different mechanisms; one of them suggested a super exchange mechanism through the carboxylate groups [6-8].

Aspirinate of Cu(II) Figure 1 forms a polymeric chain where the Cu2(aspirine)4 units are associated via Cu-O (acetyl) bonds, with an average distance Cu-O of 2.963 A°. The distance Cu-Cu is 2.617 A° [9] and a magnetic moment of 2.04 M.B. has been reported [3].

 
Figure 1. Structure of aspirinate of Cu(II).

The pharmacological activity increases by the presence of ligands which coordinate through nitrogen donor atoms such as imidazoles, diimines, and pyridines. Mononuclear copper(II) complexes with nitrogen containing ligands i.e. bis(aspirinate)bis(2-methylimidazole) copper(II), Cu(asp)2(2-MeIm)2, have prepared by the reaction of 2-methylimidazole with binuclear Cu2(asp)4. [10]. On the other hand, the dinuclear compounds [Cu2(aspirinate)4 (L)2] (L = DMSO, DMF) have also been prepared and studied with regard and to their anticonvulsivant activities [11].

The thiazoles and their derivatives have a great biological importance as constituents of biomolecules like antibiotics. The pharmacological activities and their coordination properties are important features to prepare metal complexes with potential therapeutical activity or as model of metal-enzyme[13-16].

Thiazole (Figure 2) has both nitrogen and sulfur atoms as possible donor sites, and whereas the majority of complexes have been found to be nitrogen bonded, a case of sulfur coordination has been postulated [14].

 
Figure 2 : Structure of 1,3-thiazole.

The aim of this work is to study the interaction of 1,3-thiazole and Cu(II) complexes, Cu2(asp)4 and Cu2( acetate)42H2O .

EXPERIMENTAL

Materials

The metal salts, CuSO4, SH2O2 (acetate)42H2O and NaHCO3 were analytical grade (Merck). 1,3-thiazole was purchased from Aldrich.

Synthesis of copper(II) aspirinate Cu2(asp)4

It was synthesized according to the literature [1,9]-The aspirine (1,0g) was suspended in water and dissolved by adding slowly an aqueous solution of sodium bicarbonate (0,29g), the aspirine must be in excess. There is an evolution of gas, and after the reaction finish, it was filtered. An aqueous solution of CuSO45H2O (0,7g) was prepared. Both are mixed under slow stirring. Immediately, the formation of a blue precipitate was observed. The stirring was continued for couple of min and then it was filtered and washed with water.

Synthesis of Cu2(asp)4־(Tz)2 and Cu2(acetate)4(Tz)2.

The complexes Cu2(asp)4(Tz)2 and Cu2(acetate)4(Tz)2 were synthesized from Cu2(asp)4 and Cu2 (acetate)42H2O, respectively.

The compounds of Cu(II) were suspended in ethanol and an stoichiometric amount of 1,3-thiazole was added. After several hours under stirring a change of color of the solid fraction was observed. It was filtrated, washed with ethanol, and dried at oven at 50°C. A yield of 65% was obtained.

Cu2(asp)4(TZ)2
Elemental analysis: (Found: Cu: 12.7 %, N: 4.4 %, C: 44.2%, H:3.5 %. Calcd.: Cu: 12.5 %, N: 2.8 %, C: 49.7 %, H: 3.7 %).
Cu2(acetate)4(Tz).
Elemental analysis: (Found: Cu: 23.4 %, N: 5.7 %, C: 32.5%, H: 3.3 %.
Calcd.: Cu: 23.8 %, N: 5.2 %, C: 31.5 %, H: 3.4 %

Measurements

Cu(II) was analyzed by atomic absorption spectrometry with a Perkin Elmer model 5300 DV and the elemental analysis C,H,N in an EA 1108 Analyzer Elemental, Fision Instruments.

FT IR spectra were recorded on a Magna Nicolet 550 and Nicolet Nexsus spectrophotometers. The magnetic susceptibility measurements were performed at room temperature on a Sherwood Auto Magnetic Susceptibility Balance by the Gouy method using Hg[Co(SCN)4] as the calibration standard . From the observed susceptibility, the magnetic moment, μeff was calculated using the following formula: μeff = 2.824 -. The diamagnetic contribution due to the core electrons was estimated using Pascal constants and subtracted from the experimental values.

Thermogravimetric analysis was carried out in a Netzsch model TG 209 F1, Iris.N2(g) of high quality was used with a flux of 250 mL/ min, heating rate was10°C/min in a temperature range from 30°C to 550°C.

Quantum Chemical Calculations

PM6 semi-empirical calculations were carried out using GAUSSIAN98 package. The compounds were created graphically with support of the HyperChem Program. It was optimized by molecular mechanical and subsequently by the PM6 calculation method.

RESULTS AND DISCUSSION

For the aspirinate of Cu(II) the Cu2(asp)4 units are forming a polymeric chain and the coordination of 1,3-thiazole group through the nitrogen to each Cu(II) ion in axial position obtaining as product the Cu2(asp)4 (Tz)2 complex. (Figure 3). The ligand break the intermolecular Cu-O (acetyl).

 
Figure 3: PM6 calculated structure of Cu2(asp)4 (Tz)2

To react the 1,3-thiazole with Cu2( acetate)42H2O, changing the water molecules and coordinating to the Cu(II) ions through the nitrogen atoms yielding Cu2(CH3COO)4 (Tz)2 complex. (Figure 4).

 
Figure 4: PM6 calculated structure of Cu2(CH3 C00)4 (Tz)2

In the FTIR spectrum, (Table 1) the stretching vibration of acetyl group in the free aspirine is observed at 1759 cm-1, and in the Cu(II) aspirinate are observed two absorption bands at 1761 and 1725 cm-1, and in the complex with the thiazole only one at 1750 cm-1. The symmetric and unsymmetric stretching vibrations of carboxylic acid group present in the aspirine at 1689 and 1455 cm-1 are shifted at lower frequency by effect of the coordination. In the Cu(II) aspirinate are shifted at 1618 and 1408 cm-1 and those aspirinates and thiazole complexes are shifted at 1608 and 1373 cm-1. In the spectrum of Cu2(asp)4 (Tz)2 complex, it is observed an absorption band at 1449 cm-1 attributed to stretching vibration í (C=N) of thiazole group.

Table 1. FT-IR absorption signals (cm-1) for acetyl salicylic acid and complexes.
 

The FTIR spectrum of Cu2(CH3COO)4 2H2O (Table 2) shows the antisymmetric and symmetric stretching vibrations of the acetate group at 1608 and 1440 cm-1 [17]. The spectrum of the complex Cu2(CH3COO)4 (Tz)2 shows the same absorption bands at 1620 and 1436 cm-1 and the strength vibrations v (C=N) from thiazole group at 1496 cm-1.

Table 2. FT-IR absorption signals (cm-1) for Cu2(CH3COO)4 2H2O and Cu2(CH3COO)4 (Tz)2
 

Magnetic measurements

For the aspirinate of copper(II) different magnetic moments from 2.0 up to 1.35 M.B have been reported [3,8].

In the current work, the magnetic moments for the aspirinate of copper(II) and the complex with 1,3-thiazole were determined from the experimental data doing the corresponding corrections of the diamagnetism, yielding, 1.77 and 1.79 M.B respectively.

For those Cu2(CH3COO)4 2H2O and Cu2(CH3COO)4 (Tz)2 complexes the magnetic moments were determined and the value for both was 1.4 M.B.

Hermler and Meyer have reported for the Cu2(CH3COO)4 (1,3-benzothiazole)2 complex a value for the magnetic moment 1.42 M.B [19].

Thermogravimetric analysis

TGA of Cu2(asp)4 (Tz)2 complex shows the weight loss corresponding to the thiazole groups (16.7%) at 128°C, aspirinate group ((17%) at 161°C , a second aspirinate (17%) at 241°C, and then the loss of the other aspirinate groups (Figure 5).

 
Figure 5: TGA and DTG curves of Cu2(asp)4 (Tz)2

The sequence of decomposition reactions as deduced from TGA studies are summarized below:

Cu2(asp)4 (Tz)2
Cu2(asp)4
+
2 T z
         
Cu2(asp)4
Cu2(asp)3
+
asp
         
Cu2(asp)3
Cu2(asp)2
+
asp
         
Cu2(asp)2
Cu2(asp)
+
asp
         
Cu2(asp)
2CuO
+
asp

TGA of Cu2(acetate)4(Tz)2 shows the loss of thiazole group (32%) at 165°C and the weight loss of four acetate groups (44%) at 272°C.

The sequence of decomposition reactions as deduced from TGA studies are summarized below:

Cu2(acetate)4(Tz)2
Cu2(acetate)4
+
2Tz
 
     
Cu2(acetate)4
2CuO
+
4Acetates

For both compounds, semiempiric structural calculations PM6 were carried and they were compared with reported crystalline structures [7,9]. To analyze the PM6 data of Cu2(asp)4(Tz)2 complex, (Table 3) PM6 calculations for the complex Cu2(asp)4(DMF)2 were carried out considering that the crystalline structure was reported [11]. PM6 calculations of both compounds show only small differences.

Table 3: Selected PM6 structural parameters of Cu2(asp)4(Tz)2.
 
 

a)Ref.7 b)Ref.9

PM6 calculations (Table 4) complexes of Cu2(acetate)4(Tz)2 and Cu2( acetate)4 2H2O were carried out for Cu2( acetate)4 2H2Othat was reported the crystalline structure for other authors [4]. PM6 calculations show an important difference in the Cu-Cu distances.

Table 4. Selected PM6 structural parameters of Cu2(acetate)42H2O and Cu2(acetate)4(Tz)2
 

CONCLUSIONS

Accordingly to the experimental results it can be concluded that in both complexes, the dimeric Cu2(RCOO)4 does not break and the 1,3-thiazole ligand coordinates through the nitrogen.

The coordination of the ligand does not produce strong changes in the structure of the dimeric unit Cu2(RCOO)4.

The distances Cu-Cu in the aspirinates and acetates of Cu(II) are very similar, however, the magnetic moments are very different.

Cu-Cu distances of aspirinates are lower than those acetates of Cu(II), however, the magnetic moments of aspirinates are higher than those of acetates of Cu(II).

It can suggest that the Cu-Cu distance in the acetate of Cu(II) is not the more important effect for the not usual value 1.4 M.B obtained.

ACKNOWLEDGEMENTS

The authors thank to Vicerrectoria de Investigación y Desarrollo, Universidad de Concepción (Grant No 211.021.032-1.0) and PIA (Anillo ACT-130).

 

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(Received: May 30, 2013 - Accepted: September 9, 2013)

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