Metal complexes of antiuralethic drug: Synthesis, spectroscopic characterization and thermal study on allopurinol complexes

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Journal of Molecular Structure 888 (2008) 416–429 www.elsevier.com/locate/molstruc

Metal complexes of antiuralethic drug: Synthesis, spectroscopic characterization and thermal study on allopurinol complexes M.G. Abd El-Wahed a, M.S. Refat b,*, S.M. El-Megharbel a b

a Department of Chemistry, Faculty of Science, Zagazig University, Zagazig, Egypt Department of Chemistry, Faculty of Education, Suez Canal University, Port Said, Egypt

Received 3 September 2007; received in revised form 29 December 2007; accepted 7 January 2008 Available online 15 January 2008

Abstract Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) complexes of the allopurinol ligand, (H2L; Alp@(C5H4N4O)), were synthesized and characterized by microanalyses, magnetic susceptibility, conductance, infrared, electronic spectral and thermogravimetric (TGA/DTG) measurements. The ligand can be coordinated as a bidentate feature via pyrazole and/or pyrimidine rings. Spectroscopic and magnetic data are consistent with configuration of square planar geometry for the Mn(II), Co(II), Zn(II), Cd(II) and Hg(II) complexes while the Ni(II) and Cu(II) complexes are octahedral. From the thermal degradation curves, the uncoordinated water molecules are removed in a first stage while the decomposition of ligand beside coordinated water molecules occur in the second and subsequence steps. The kinetic thermodynamic parameters such as: E*, DH*, DS* and DG* are estimated from the DTG curves using Coats and Redfern (CR) and Horowitz–Metzger equations. Ó 2008 Elsevier B.V. All rights reserved. Keywords: Allopurinol; Pyrimidine and Pyrazole rings; Infrared spectra; Thermal analysis

1. Introduction The oxopurines hypoxanthine and xanthine are of biological importance, since they are metabolic intermediate products of purine metabolism. Hypoxanthine (1,7-dihydro-6H-purin-6-one), formed by degradation of nucleic acids, is oxidized by the molybdenum- and iron-containing enzyme xanthine oxidase via xanthine to uric acid, which subsequently is released from the active site of the enzyme [1]. Disturbances in purine metabolism result in an increase of the uric acid level and in the deposition of sodium hydrogenurate monohydrate crystals in joints. This disease, known as gout, is clinically treated by the drug allopurinol (pyrazolo[3,4-d]pyrimidin-6-one) (Fig. 1), which is also a substrate for xanthine oxidase [2]. Alloxanthine (pyrazolo[3,4-d]primidin-2,6-dione), the enzymatic oxidation product of the drug allopurinol, inactivates xanthine oxidase by *

Corresponding author. E-mail address: [email protected] (M.S. Refat).

0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2008.01.009

irreversible coordination to the reduced form of the molybdenum centre of the enzyme [3]. Therefore, the information of uric acid is inhibited, and patients receiving the drug allopurinol excrete much of their purines as hypoxanthine and xanthine. The metal co-ordination capability of allopurinol lies in great measure both in the existence of several electron donor atoms and their disposition in the framework. Many metal complexes involving allopurinol as an uncharged (neutral) ligand and metals, such as Zn(II), Co(II), Ni(II), etc. have been reported in the literature [4,5]. Generally, a monodentate metal co-ordination through the pyrazole nitrogen atom N(8) has been generally observed (Fig. 2), whereas a monodentate N(9) co-ordination of neutral Alp has been only reported for a rhodium carbonyl compound [6]. Under acidic conditions N(9) co-ordination of allopurinolium cation has been observed and a copper complex, having a chlorine-bridge polymeric chain structure, has been evidenced [7].

M.G. Abd El-Wahed et al. / Journal of Molecular Structure 888 (2008) 416–429

Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) allopurinol complexes. The Alp metal(II) complexes are new and are being reported for the first time. The spectral, magnetic and thermal of the new compounds are discussed.

O

8 N

NH

6

7

1

5

2

4

9

417

2. Experimental

N

N H

3

2.1. Materials and instrumentation

Fig. 1. Structure of allopurinol drug.

Recently interest in the trend of metal drug complexes, has increased in order to achieve an enhanced therapeutic effect in combination with decreased toxicity. It has been found that platinum or palladium complexes of purine derivatives show enhanced activity with respect to free ligand [8]. In addition, metal complexes of purine ring are of importance in view of their function as repository, slow-release or long-acting prodrugs for purine. However, information on allopurinol and their metal(II) complexes on the alkaline medium is very scanty. With the continuation of our previous studies [9–11] in the trend of metal drug complexes, we report herein the synthesis and characterization of the Mn(II), Co(II),

All chemicals used were of the purest laboratory grade (Merck) and allopurinol was presented from Egyptian international pharmaceutical industrial company (EIPICo.). Carbon and hydrogen contents were determined using a Perkin–Elmer CHN 2400. The metal content was found gravimetrically by converting the compounds into their corresponding oxides and carbides. Infrared spectra were recorded on Bruker FTIR Spectrophotometer (4000–400 cm1) in KBr pellets. The UV– vis, spectra were studied in the DMSO solvent with concentration (1.0  103 M) for the allopurinol and their complexes by help of Jenway 6405 Spectrophotometer with 1 cm quartz cell, in the range 800–200 nm. Molar conductivities of freshly prepared 1.0  103 mol/dm3 DMSO solutions were measured using Jenway 4010 conductivity meter. Magnetic measurements were carried out on a Sher-

HO O

O

NH

6

7 8 N

6

9 N H

7

1

5

2

4

HN

N

N

3

2

4

8 N

3

2

4

9

N

N H

N

3

enolic, N(9)-H

N(1)-H, N(8)-H

N(1)-H, N(9)-H

1

5

1

5 8 9

N

7

NH

6

Fig. 2. Tautomeric equilibrium of Alp compound.

Table 1 Elemental analysis and physical data of allopurinol complexes Complexes

[Mn2(Alp)2(Cl)(H2O)]2H2O (I, C10H11N8O5ClMn2) [Co2(Alp)2(Cl)(H2O)]4H2O (II, C10H15N8O7ClCo2) [Ni2(Alp)3(H2O)4]5H2O (III, C15H26N12O12Ni2) [Cu2(Alp)3(H2O)4]2H2O (IV, C15H20N12O9Cu2) [Zn2(Alp)2(Cl)(H2O)] (V, C10H7N8O3ClZn2) [Cd2(Alp)2(Cl)(H2O)] 2H2O (VI, C10H11N8O5ClCd2) [Hg(Alp)(Cl)(H2O)] (VII, C5H5N4O2ClHg)

Mwt.

468.60

Color

514.58

Deep brown Faint brown

683.71

Faint green

639.422 453.50

Deep blue White

583.54

White

389.20

White

Km (X1 cm1 mol1)

Content ((calculated) found) %C

%H

%N

% Cl

%M

(25.60) 25.20 (23.31) 23.50 (26.32) 26.40 (28.15) 27.78 (26.46) 26.30 (20.56) 20.32 (15.41) 15.32

(2.34) 2.36 (2.91) 3.20 (3.51) 3.60 (3.12) 3.32 (1.54) 1.49 (1.88) 1.72 (1.28) 1.54

(23.90) 23.98 (21.76) 21.20 (24.57) 25.30 (26.27) 26.82 (24.69) 24.88 (19.19) 18.89 (14.38) 13.99

(7.57) 7.72 (6.89) 6.40 –

(23.04) 23.66 (23.29) 23.90 (17.40) 16.90 (19.70) 19.74 (14.63) 14.22 (38.38) 38.04 (51.38) 51.42

– (7.82) 7.76 (6.08) 7.94 (9.12) 8.88

20 16 7.20 6.80 17.60 20 21

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3.5

3.5

B

A

3.0

3.0 2.5

Absorbance

Absorbance

2.5 2.0 1.5

2.0 1.5

1.0

1.0

0.5

0.5

0.0

0.0

200

300

400

500

600

700

200

800

300

400

500

600

700

Wave length (λ)

Wave length (λ) 3.5

3.5

D

3.0

3.0

2.5

2.5

Absorbance

Absorbance

C

2.0 1.5

2.0 1.5

1.0

1.0

0.5

0.5

0.0 200

0.0

300

400

500

600

700

200

800

300

400

500

600

700

3.5

3.5

E

F

3.0

3.0

2.5

2.5

Absorbance

Absorbance

800

Wave length (λ)

Wave length (λ)

2.0 1.5

2.0 1.5

1.0

1.0

0.5

0.5

0.0 200

800

0.0 300

400

500

600

700

800

200

Wave length (λ) 2+

300

400

500

600

700

800

Wave length (λ) 2+

Fig. 3. UV–visible spectra of (A) allopurinol, (B) Mn allopurinol, (C) Co allopurinol, (G) Cd2+ allopurinol and (H) Hg2+ allopurinol.

allopurinol, (D) Ni2+ allopurinol, (E) Cu2+ allopurinol, (F) Zn2+

M.G. Abd El-Wahed et al. / Journal of Molecular Structure 888 (2008) 416–429

3.5

419

3.5

H 3.0

2.5

2.5

Absorbance

Absorbance

G 3.0

2.0 1.5

2.0 1.5

1.0

1.0

0.5

0.5

0.0 200

300

400

500

600

700

800

0.0 200

Wave length (λ)

300

400

500

600

700

800

Wave length (λ) Fig. 3 (continued)

wood Scientific magnetic balance using Gouy method. Thermogravimetric analysis (TGA and DTG) were carried out in dynamic nitrogen atmosphere (30 ml/min) with a heating rate of 10 °C/min using a Schimadzu TGA-50 H thermal analyzer. 2.2. Synthesis of metal complexes 2.2.1. Manganese–Alp complex (I) Allopurinol (0.138 g, 1.0 mmol) was added to 30 ml distilled water and titrated against aqueous sodium hydroxide (0.1 M) to adjust pH at 8.00, then 10 ml aqueous solution of (1.00 g, 0.5 mmol) of MnCl2 4H2O was added with continuously stirring, after that the mixture was warmed at about 60 °C and then neutralized. Immediately, the brown precipitate was settle down and filtered off, washed several times by minimum amounts of hot methanol and dried under vacuo over anhydrous CaCl2. 2.2.2. Cobalt–Alp complex (II) A brown complex of cobalt(II) was prepared during the reaction of (1.0 mmol) allopurinol with (0.12 g, 0.5 mmol) of CoCl26H2O by a method similar to that described above. 2.2.3. Nickel–Alp complex (III) Like the above procedure of the preparation of complexes, aqueous solution of NiCl26H2O (0.119 gm, 0.5 mmol) was mixed with an equal volume of allopurinol solution (1.0 mmol) in methanol. The mixture was allowed to stay at room temperature for about 1 h with constant stirring and then heated on a water bath at 60 °C for 30 min. The faint green complex was filtered off, washed

several times with hot methanol, dried under vacuo over anhydrous CaCl2. 2.2.4. Copper–Alp complex (IV) The copper (II) allopurinol complex was prepared by the same method which used for preparation of the Mn(II) and Co(II) complexes. The weight of CuCl2H2O was (0.076 g, 0.5 mmol) and mixing with allopurinol by (1:2) molar ratio in water as solvent. 2.2.5. Zinc–Alp complex (V) Zinc complex was prepared by mixing equal volumes (30 ml) of allopurinol (1.0 mmol) with ZnCl2 (0.068 g, 0.5 mmol). The mixture was neutralized by titrated with NaOH to adjust pH at 9.13 and then heated on a water bath at 60 °C with constant stirring for about 45 min. A white solid complex was precipitated and its amount increasing with increasing the time of heating. The obtained precipitate was separated, washed several times with hot water and then dried in vacuo over anhydrous CaCl2 and recrystalization occurs using a mixture of water and methanol (1:1). 2.2.6. Cadmium–Alp (VI) and Mercruy–Alp (VII) complexes Preparation of these two complexes followed essentially the same procedure as preparation of (I), but the weight of CdCl2 and HgCl2 were (1.0 g, 0.5 mmol) and (0.136 g, 0.5 mmol), respectively. The pH was adjusted at 9.00 and 8.23, respectively. 3. Results and discussion The seven reactions of allopurinol (Alp) with transition metal chlorides (Mn(II), Co(II), Ni(II), Cu(II), Zn(II),

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Fig. 4. IR spectra of (A) allopurinol, (B) Mn2+ allopurinol, (C) Co2+ allopurinol, (D) Ni2+ allopurinol, (E) Cu2+ allopurinol, (F) Zn2+ allopurinol, (G) Cd2+ allopurinol and (H) Hg2+ allopurinol.

Cd(II) and Hg(II)) gave a colored complexes in moderate to good yields (45–70%). The physical and analytical data, colors, percentage yields, melting/decomposition temperatures and room temperature magnetic moments of the compounds are presented in Table 1. The found and calculated percentages of CHN are in a well agreement with each other and prove the suggested molecular formula of the resulted Alp complexes. The complexes have higher melting points above >300 °C. The molar conductivities

of the compounds in DMSO were ranged 7–35 X1 cm2 mol1, showing that they were non-electrolytes in the solvent. The Alp ligand behaves as a dinegative ligand and coordinated to the metal ions through the carbonyl group and N(1)–H in case of pyrimidine ring and so, on the other side (pyrazole ring) also can be coordinated with metal ions via lone pair of electron on N(8) and N(9)–H. The isolated Alp complexes are 1:1 and 2:3 molar ratio of (M:Alp). All the

M.G. Abd El-Wahed et al. / Journal of Molecular Structure 888 (2008) 416–429

421

Fig. 4 (continued)

complexes are located as square planner geometry except Ni(II) and Cu(II) complexes which have an octahedral configuration. 3.1. Magnetic moments Magnetic measurements were carried out according to the Gauy method. The calculations were evaluated by applying the equations: pffiffiffiffiffiffiffiffiffi clðR  R0 Þ vg vm ¼ vg MWt: leff ¼ 2:828 vm T 9 10 M where v is mass susceptibility per gm sample

c is the calibration constant R is the balance reading for the sample and tube R0 is the balance reading for the empty tube M is the weight of the sample in gm A moment of 5.92 B.M. is usually observed for the Mn(II) compounds, regardless of stereochemistry [12,13]. Because of the A ground term, with no higher T term of the same multiplicity, the orbital contribution is nil. Consequently, the Mn(II) complex is high spin and give the spin only square planer (sp3) moment at 5.93 B.M. Square planner, dsp2, cobalt(II) complexes are expected to have effective magnetic moment in the range

422

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Fig. 4 (continued)

1.73–2.73 B.M. The cobalt(II)–Alp complex studied has magnetic moment at 1.81 B.M.; thus the Co(II) complex is square planner. Generally, square planar complexes of Ni(II) are diamagnetic while tetrahedral complexes have moments in the range 3.20–4.10 B.M. and octahedral complexes should have moments between 2.90–3.30 B.M. [14,15]. Ni(II)–Alp gave a moment of 3.06 B.M. and hence assigned as octahedral. The magnetic moments of the copper(II)–Alp complex is 2.10 B.M. expectedly higher that the spin only moment due to spin-orbit coupling; thus the Cu(II) complex is octahedral.

3.2. Molar conductivities The molar conductivity values for the free ligand in DMSO solvent (1.0  103 mol) was at 7.00 X1 cm1 mol1, but the molar conductivity values for their complexes were in the range (7.00–35.00) X1 cm1 mol1. All the measurements in the range suggesting them to be non-electrolytes nature (Table 1), but the higher values of the complexes than that of the corresponding ligands indicated the formation of complexes and the presence of Cl ion. Conductivity measurements have frequently been used in predicts the structural of metal chelates

M.G. Abd El-Wahed et al. / Journal of Molecular Structure 888 (2008) 416–429

423

Fig. 4 (continued)

within the limits of their solubility. They provide a method of testing the degree of ionization of the complexes, the molecular ions that a complex liberates in solution (in case of presence anions outside the coordination sphere), the higher will be its molar conductivity and vice versa [16]. It is clear from the conductivity data that the complexes present seem to be non-electrolytes. Hence the molar conductance values indicate that the chloride ions may be exhibits inside or absent. The obtained results were strongly matched with the elemental analysis data where Cl ions are detected in case of Mn(II), Co(II), Zn(II), Cd(II) and Hg(II) complexes.

3.3. UV–vis spectra The electronic absorption spectra (Fig. 3) of Alp as a free ligand and the Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) chelates, respectively, in dimethylsulfoxide (DMSO) at wavelength within the range of 200– 800 nm against the same solvent as a blank show that allopurinol gives three essential maximum peaks at 240, 280 and 305 nm. The band at 240 nm may be attributed to p–p* transition (e = 377 mol1 cm1) while the two other bands (k = 280 and 305 nm) can be assigned to n–p* transitions (e = 96 and 3000 mol1 cm1, respectively)

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respecting Alp molecule. It is clearly obviously that the absorption spectra obtained from the Alp complexes give the same behavior with changing in the absorbance intensities with small shifted in the peak positions. The earlier bands in Alp at less than 240 nm are still remaining in the same position in all the complexes indicating that they are not affected by metal complexation. The medium strong band observed at 280 nm in DMSO solvent may be assigned to n–p* transition within the C@O group of the pyrimidine ring in the free Alp ligand. This band is blue shifted, this revealing the participating of the C@O of pyrimidine ring in the complexation. The second within the Alp moiety exhibited at k = 305 nm which attribute to the pyrimidine-N and/or pyrazole-N. During the complex formations, this band was affected (M–N) [17]. The shifted in n–p* transitions led to pronounced that N(1)–H and N(9)–H involved in the complexations. 3.4. Infrared spectra Alp ligand has various potential donor sites that are containing two rich donating groups (pyrazole and pyrim-

idine rings). A comparison between the IR spectra of Alp and their transition metal complexes (Fig. 4 and Table 2) provide an idea respecting of the coordination sites in the Alp complexes. The IR spectra of all Alp complexes show the asymmetric stretching vibrations of the coordinated H2O mas (OAH) is assigned to the band with broadening at the range 3450 cm1 while the corresponding symmetric vibration is assigned as expected to the weak intensity band at about 3150 cm1. It is known that the symmetric vibration is associated with little change in the dipole moment value of the bond displaying weaker band intensity in agreement with our assignment for H2O vibrations. The observation of the two bond vibrations for H2O supports our molecular structures with coordinated water molecules. The stretching vibration of OH group m(OAH) is occurred as expected [18] at 3500 cm1. The angular deformation motions of the coordinated water in Alp transition metal(II) complexes can be classified into four types of vibrations: db(bend), dr(rock), dt(twist) and dw(wag). The assignments of these motions in all isolated complexes are as follows. The bending motion, db(H2O),

Table 2 IR frequencies (cm1) of allopurinol and its metal complexes Assignments

Compound Alp

I

mas(OAH) m(NAH) m(CAH) ms(OAH)

– 3166 3082 3042 2291 2944 2873 1699 1588

3422 3166 3082 2938 2878

m(C@O) m(C@N) d(NH), pyrazole m(pyrazole ring) m(C@C) m(pyrazole ring)

w w w w w m s s

1478 s

II

III

3381 3170 3090 2920 2875

sbr w vw vw vw

IV

3374 3150 3065 2940 2875

sbr vw vw vw vw

V

3346 3139 3037 2948 2867

sbr w vw w w

3490 3245 3133 2939 2859

VI s s vw w w

VII

3420 3169 3086 2938 2880

sbr w w w w

3341 3180 3089 2940 2885

sbr sh vw vw vw

1701 vs 1598 s

1682 vs 1599 vs

1673 vs 1599 s

1684 vs 1599 s

1689 vs 1590 vs

1699 vs 1600 vs

1638 w 1600 w

1526 1507 1407 1388 1365

vw ms vw vw vw

1524 s

1505 vs

1507 vs

1501 vs

1395 ms 1328 ms

1399 s 1315 vw

1409 vs

1548 1523 1386 1330

s w vw ms

1250 s 1122 s 1002 mw

1249 vs 1104 s 1062 w

1255 1146 1082 1059

948 853 782 734 619 543

986 933 849 781 616 578 544

993 927 855 777 729 619 541

1528 vw 1502 vs 1434 w 1405 s 1362 vw 1322 vw 1253 vs 1220 ms 1109 s 1078 s 1016 w 995 w 924 ms 847 ms 778 vs 726 vw 617 vs 575 vw 547 s 522 vw 420 s

m(Pyrimidine ring)

1387 s 1363 s

m(CAN); pyrazole m(CAC) In-plane-def. CH-deformation

1231 vs 1156 ms 1080 vs

1248 1141 1103 1063

Ring breath CH-out of plane NH-out of plane

954 912 885 813 779 703 602 535

m(M–N)

–

986 954 916 884 812 782 705 640 541 465

vs w w ms ms vs vs vs

sbr vw w w ms

mw mw ms w vw s vw s s sh

w vw s vw s s

471 vw

s = strong, w = weak, m = medium, sh = shoulder, v = very, br = broad.

s s mw s ms vw ms

477 vw

vs w w w

s s mw vs vw s s

468 vw

1401 w 1380 s

1296 1248 1101 1054 974 922 855 781 706 611 567 540

mw s s s

vw s w s w s vw s

417 s

ms vw vs sh

1283 vs 1226 ms 1185 vw 1113 vs 1058 ms 988 vs 940 ms 882 ms 787 vs 696 vw 582 mw 543 w

435 mw

M.G. Abd El-Wahed et al. / Journal of Molecular Structure 888 (2008) 416–429

is assigned to its characteristic band at 1670 cm1. The rocking motions, dr(H2O), is assigned at 750 cm1 and the wagging motion, dw(H2O), is observed at 600 cm1. The twisting motion, dt(H2O), is observed at 670 cm1. It should be mentioned here that these assignments for both the bond stretches and angular deformation of the coordinated water molecules fall in the frequency regions reported for related aquo-complexes [18]. The IR spectrum of the Alp reveals bands at 3166, 1699, 1588, 1478 and 1387 cm1 assigned to m(NAH), m(C@O), d(NH); pyrazole ring, m(pyrazole ring) and m(pyrimidine ring). These bands are decrease in the intensities and hypsochromic shift resulted from the coordination fashions via bidentate of (C@O of pyrimidine ring and N(1)–H) and (N(9)–H and the lone pair of electron on the N(8)). Beside of the change in m(C@O) frequencies, the m(C@N) of pyrazole ring (1588 cm1) in the free ligand is shifted to positive frequencies and decreasing in the intensities, clearly obviously occurs coordination through the pyrazole ring N(9) and N(8). The m(M–N) bonding is observed by the presence of weak to very weak bands at the range of 417–477 cm1 [18].

DrTGA mg/min

TGA, % 95

20

A

425

3.5. Thermal analysis The TGA curves (Fig. 5) for the Alp and their transition metal complexes were carried out within a temperature ranged from 50 to 800 °C. The calculated mass losses were estimated based on the TG data and agree quite well with the molecular formula of the suggested complexes (Table 1). The decomposition stages, temperature ranges, maximum decomposition peaks DTGmax, percentage losses in mass, and the assignments of decomposition moieties are given in Table 3, which deduced the following data. The allopurinol ligand melts at 350 °C with simultaneous decomposition, Fig. 5A. The thermal decomposition of Alp occurs completely in one step which was observed at 350 K. corresponding to the loss of 2C2H2 + CO + 2N2 molecules, representing a weight loss of (obs. = 99.98%, calc. = 100%). The Mn(II) complex of Alp gives two main stages of decomposition pattern. The first stage, within the temperature range of 50–150 °C, represents the loss of two water molecules of hydration (obs. = 7.96%, calc. = 7.68%). The activation energy of this dehydration step is 4.72  104 J mol1 (Table 4). The second stage (150–800 °C) is

DrTGA mg/min

TGA, % 95

20

B

10

10

75

75

0

0 55

-10 -20

35

55

-10 -20

35

-30 15

-40 -50

-5 50

-30 15

-40

-5

-50 50

150 250 350 450 550 650 750

150 250 350 450 550 650 750

Temp [oC]

Temp [oC] DrTGA mg/min

TGA, % 95

C

75

20

-10 -20

35

9

95

D

10 0

55

DrTGA mg/min

TGA, %

1 55 -3 35

-7

-30 15

-40

-5

-50 50 150 250 350 450 550 650 750

Temp [oC]

5

75

15

-11

-5

-15 50 150 250 350 450 550 650 750

Temp [oC]

Fig. 5. TGA and DrTGA of (A) Alp, (B) Mn2+ Alp, (C) Co2+ Alp, and (D) Ni2+ Alp compounds.

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M.G. Abd El-Wahed et al. / Journal of Molecular Structure 888 (2008) 416–429

Table 3 Thermal data of Alp and its complexes Compound

DTG peak (°C)

TG Weight loss (%) Calc.

Found

Alp [Mn2(Alp)2(Cl)(H2O)]2H2O (I, C10H11N8O5ClMn2)

350 75 298

100 7.68 38.09

99.98 7.96 36.94

[Co2(Alp)2(Cl)(H2O)]4H2O (II, C10H15N8O7ClCo2)

76 402

13.99 51.01

13.69 51.62

[Ni2(Alp)3(H2O)4].5H2O (III, C15H26N12O12Ni2)

88 451

13.16 59.08

14.01 58.22

[Cu2(Alp)3(H2O)4]2 H2O (IV, C15H20N12O9Cu2)

68 309 483

5.63 11.26 56.92

5.94 10.74 56.88

[Zn2(Alp)2(Cl)(H2O)] (V, C10H7N8O3ClZn2)

73 439 546

3.96 33.95 21.27

3.76 32.96 22.00

[Cd2(Alp)2(Cl)(H2O)]2H2O (VI, C10H11N8O5ClCd2)

124 390 578

9.25 18.67 24.93

10.21 19.24 23.90

[Hg(Alp)(Cl)(H2O)] (VII, C5H5N4O2ClHg)

97 312 405 551

13.74 10.79 51.30 28.26

12.80 10.00 50.00 27.30

assigned to the loss of the other one coordinated water molecule and (2HCl, 2H2, 0.5O2 and 4N2) gaseous molecules (obs. = 36.94%, calc. = 38.09%) then leaving mixtures of manganese oxide and carbides as final residue. The thermogram of Co(II) complex shows that at a temperature of 50–150 °C, only the four water molecules of hydration are lost with mass loss of (obs. = 13.69%, calc. = 13.99%). The activation energy of the thermal dehydration of this complex is 6.47  104 kJ mol1. The second (150–800 °C) step involves the loss of C6H7N8O2Cl (organic moiety). The mass losses corresponding to these temperature ranges are (obs. = 51.62%, calc. = 51.01%), respectively. The thermal decomposition of the Co(II) complex together with its IR and solid reflectance spectra are correlated with the proposed structure shown in Fig. 5C, then leaving mixtures of cobalt oxide and carbides as final residue. The thermal decomposition of Nickel complex with the general formula [Ni2(Alp)3 (H2O)4]Cl25H2O is thermally decomposed in a successive two decomposition steps. The first estimated mass loss of (obs. = 14.01%) within the temperature range 50–140 °C may be attributed to the loss of five water molecules of hydration (calc. = 13.16%). The energy of activation of this step is 5.21  104 kJ mol1. The second step occurs within the temperature range 140–800 °C with a mass loss (obs. = 58.22%, calc. = 59.08%) is reasonably accounted for the decomposition of four coordinated water, and C11H8N12O2 mole-

Assignments

2C2H2 + CO + 2N2 2H2O H2O + HCl + 2H2 + 4N2 + 0.5O2 (MnO + MnC2 + 8C) residue 4H2O C6H7N8O2 Cl (organic moiety) (CoO + CoC2 + 2C) residue 5H2O 4H2O + C11H8N12O2 (NiO + NiC2 + 2C) residue 2H2O 4H2O C13H8N12O2(organic moiety) (CuO + CuC2) residue H2O C4H4N5O2(organic moiety) HCl + H2O + 1.5N2 (2ZnC2 + 2C) residue 3H2O C3H3N4O (organic moiety) C3H2N4OCl (organic moiety) (2CdC2) residue Cl + H2O Co + 0.5N2 (Hg) evaporate as vapor C4H4N3O

cules, leaving metal oxide and carbides as the residue of decomposition. The thermal degradation of the Cu complex occurs in mainly three degradation stages. The first stage of decomposition occurs at a temperature maximum of 68 °C. The found weight loss associated with this step is (obs. = 5.94%, calc. = 5.63%) and may be attributed to the loss of 2H2O. The energy of activation of this step is 7.21  104 kJ mol1. The second step of decomposition occurs at a temperature maximum of 309 °C. The weight loss found at this step equals to (obs. = 10.74%, calc. = 11.26%) corresponds to the loss of 4H2O molecules. The final step of decomposition occurs at a temperature maximum of 483 °C. The weight loss found at this step equals to (obs. = 56.88%, calc. = 56.92%) corresponds to the loss of C13H8N12O2 (organic moiety). The final thermal products obtained at 800 °C are copper oxide and carbides as the residue of decomposition. The TG curve of the Zn(II) complex indicates the decomposition of the complex in three steps. The first step within the temperature range of 50–125 °C corresponds to the loss of one coordinated water molecule with a mass loss (obs. = 3.76%, calc = 3.96%). It is found that, the value of the activation energy for this dehydration process is 6.40  104% kJ mol1. This is followed by another two successive decomposition steps within the temperature range 125–500 °C and 500–800 °C with a mass loss of (obs. = 32.96%, calc = 33.95%) and (obs. = 22.00%, calc = 21.27%). This corresponds to the loss of the

M.G. Abd El-Wahed et al. / Journal of Molecular Structure 888 (2008) 416–429

427

Table 4 Kinetic parameters using the Coats–Redfern (CR) and Horowitz–Metzger (HM) operated for the allopurinol and their complexes Complex

Alp

Stage

1st 2nd

I

1st 2nd

II

1st 2nd

III

1st 2nd

IV

1st 2nd

V

1st 2nd

VI

1st 2nd

VII

1st 2nd

Method

CR HM CR HM CR HM CR HM CR HM CR HM CR HM CR HM CR HM CR HM CR HM CR HM CR HM CR HM CR HM CR HM

Parameter E* (J mol1) 1.53  105 1.62  105 1.32  105 1.31  105 4.84  104 4.59  104 5.10  105 4.89  105 6.13  104 6.81  104 6.68  105 6.75  105 4.84  104 5.58  104 2.08  105 2.25  105 6.98  104 7.45  104 1.21  105 1.40  105 6.22  104 6.59  104 1.12  105 1.26  105 2.85  104 3.55  104 1.99  105 1.94  105 3.82  104 4.63  104 1.97  105 2.06  105

R A (s )

DS* (J mol1 K1)

DH* (J mol1)

DG* (J mol1)

1.17  1011 6.13  1011 2.39  107 2.17  107 8.46  104 2.34  104 6.67  1044 1.76  1043 9.25  106 1.91  108 9.29  1049 1.01  1051 5.54  104 1.80  106 6.03  1012 2.20  1014 5.61  108 2.83  109 4.46  108 2.17  1010 1.92  107 8.76  107 1.06  106 1.22  107 1.54  104 4.98  104 3.69  1013 2.54  1013 1.54  103 3.01  104 2.69  1015 3.58  1016

3.91  10 2.53  10 1.11  102 1.12  102 1.52  102 1.24  102 6.08  102 5.78  102 1.13  102 8.78  10 7.05  102 7.25  102 1.56  102 1.27  102 7.61  10 2.23  10 7.87  10 6.53  10 8.51  10 5.28  10 1.07  102 9.43  10 1.37  102 1.16  102 1.67  104 1.95  102 8.16 5.05 1.86  102 1.61  102 4.48  10 6.63  10

1.48  105 1.57  105 1.26  105 1.25  105 4.55  104 5.20  104 5.06  105 4.85  105 5.84  104 6.51  104 6.62  105 6.69  105 4.54  104 5.28  104 2.02  105 2.19  105 6.69  104 7.17  104 1.16  105 1.35  105 5.93  104 6.29  104 1.06  105 1. 20  105 2.53  104 3.23  104 1.93  105 1.89  105 3.51  104 4.32  104 1.92  105 2.01  105

1.72  105 1.72  105 2.66  105 2.06  105 9.84  105 9.53  105 1.67  105 1.64  105 9.83  104 9.61  104 1. 87  105 1.81  105 1.01  105 9.82  105 2.08  105 2.03  105 9.43  104 9.44  104 1.67  105 1.67  105 9.70  104 9.62  104 2.04  105 2.03  105 8.92  104 1.07  105 1.88  105 1.85  105 1.04  105 1.03  105 1.65  105 1.62  105

1

C4H4N5O2 (organic moiety) and (HCl + H2O + 1.5N2) molecules and formation of metal carbides residue. The Cd(II) complex of Alp gives three main stages of decomposition pattern. The first stage, within the temperature range of 50–280 °C, represents the loss of three water molecules of hydration (obs. = 10.21%, calc. = 9.25%). The activation energy of this dehydration step is 1.19  105 J mol1 (Table 4). The second stage (280– 490 °C) is assigned to the loss of C3H3N4O (organic moiety) (obs. = 19.24%, calc. = 18.67%). The final decomposition stage (480–800 °C) is assigned to the loss of C3H2N4OCl (organic moiety) (obs. = 23.90%, calc. = 24.93%).Then leaving cadmium carbides as final residue. The thermal decomposition of mercury complex with the general formula [Hg(Alp)(Cl)(H2O)] is thermally decomposed in a successive four decomposition steps. The first estimated mass loss of (obs. = 12.80%) within the temperature range 50–200 °C may be attributed to the loss of (H2O + Cl) molecules of mass loss of (calc. = 13.74%). The energy of activation of this step is 4.22  104 kJ mol1. The second step occurs within the temperature range 200–350 °C with a mass loss (obs. = 10.00%, calc. = 10.79%) is reasonably accounted

0.9965 0.9975 0.9955 0.9981 0.9948 0.9996 0.9931 0.9965 0.9942 0.9970 0.9933 0.9970 0.9973 0.9979 0.9820 0.9984 0.9918 0.9972 0.9985 0.9940 0.9946 0.9957 0.9807 0.9949 0.9863 0.9943 0.9926 0.9976 0.9934 0.9974 0.9963 0.9980

for the decomposition of (CO + 0.5N2. the third step occurs at a maximum temperature of 405 °C with a mass loss (obs. = 50.00%, calc. = 51.30%) is reasonably accounted for the evaporation of Hg as vapor. The final decomposition stage occurs within the temperature range 500–800 °C may be attributed to the loss of C4H4N3O (organic moiety) without leaving metal oxide or carbides as the residue of decomposition.

3.6. Kinetic studies In recent years there has been increasing interest in determining the rate-dependent parameters of solid-state non-isothermal decomposition reactions by analysis of TG curves [19–25]. Most commonly used methods are the differential method of Freeman and Carroll [19] integral method of Coat and Redfern [21] and the approximation method of Horowitz and Metzger [24]. In the present investigation, the general thermal behaviors of the allopurinol complexes in terms of stability ranges, peak temperatures and values of kinetic parameters, are shown in Table 4. The kinetic parameters have been evaluated using the Coats–Redfern equation:

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M.G. Abd El-Wahed et al. / Journal of Molecular Structure 888 (2008) 416–429

O

N N

N

HN

Cl M

M

OH2

N

N

N

XH2O

N

O

Where M = Mn(II), Co(II), Zn(II) and Cd(II); x=0, 2 and 4 OH2

OH2 O

N N

N

HN

O N

M

NH

N

M

XH2O

N

N

N

N N

O

OH2

OH2

Where M = Ni(II) and Cu(II); x = 2 and 5 N N Cl

NH N

Hg O H2O

Fig. 6. Suggested structures of allopurinol complexes.

Z

a

0

da A n ¼ ð1  aÞ u

Z

T2 T1



E exp  RT

 dt

This equation on integration gives;     lnð1  aÞ E AR þ ln ¼ ln  uE RT T2

ð1Þ

1n

g=ð1  nÞ ¼ E h=2:303RT 2s

for n 6¼ 1 ð4Þ

ð2Þ

When n = 1, the LHS of Eq. (4) would be log[log(1  a)]. For a first-order kinetic process the Horowitz–Metzger equation may be written in the form: log½logðwa =wc Þ ¼ E h=2:303RT 2s  log 2:303

A plot of left-hand side (LHS) against 1/T was drawn. is the energy of activation in J mol1 and calculated from the slop and A in (s1) from the intercept value. The entropy of activation DS* in (J K1mol1) was calculated by using the equation: E*

DS  ¼ R lnðAh=k B T s Þ

log½f1  ð1  aÞ

ð3Þ

Where kB is the Boltzmann constant, h is the Plank’s constant and Ts is the DTG peak temperature [26]. The Horowitz–Metzger equation is an illustrative of the approximation methods.

where h = T  Ts, wc = wa  w, wa = mass loss at the completion of the reaction; w = mass loss up to time t. The plot of log[log(wa/wc)] vs h was drawn and found to be linear from the slope of which E* was calculated. The pre-exponential factor, A, was calculated from the equation: E =RT 2s ¼ A=½/ expðE =RT s Þ The entropy of activation, DS*, was calculated from Eq. (3). The enthalpy activation, DH*, and Gibbs free energy, DG*, were calculated from; DH* = E*  RT and DG* = DH*  TDS*, respectively.

M.G. Abd El-Wahed et al. / Journal of Molecular Structure 888 (2008) 416–429

From the kinetic and thermodynamic data resulted from the TGA curves and tabulated in Table 4, the following outcome can be discussed as follows: 1. The thermodynamic data obtained with the two methods are in harmony with each other. 2. The higher values of activation energies of the Alp complexes led to thermal stability of the studied complexes. 3. The activation energy of Mn2+ and Hg2+ complexes is expected to increase in relation with decrease in their radii [27]. The smaller size of the ions permits a closer approach of the ligand. Hence, the E value in the first stage for the Mn2+ complex is higher than that for the other Hg2+ complex. 4. The correlation coefficients of the Arrhenius plots of the thermal decomposition steps were found to lie in the range 0.9820–0.9996, showing a good fit with linear function. 5. It is clear that the thermal decomposition process of all allopurinol complexes is non-spontaneous, i.e., the complexes are thermally stable. On the basis of the above interpretation, the following structures may be suggested for the allopurinol complexes (Fig. 6). 4. Conclusion The allopurinol (Alp) coordinates to the Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) ions using both of the pyrazole ring N and NH atoms and pyrimidine ring C@O and NH but in case of Hg(II) complex the coordination occurs through pyrimidine ring. The assignment of a square planar (four coordinated) geometry for the all metal Alp complexes and six coordinate, octahedral geometry for the nickel and copper complexes are discussed by magnetic, infrared and thermal measurements. In the absence of no suitable crystal for single crystal X-ray structure, the proposed coordination modes of the complexes are presented in Fig. 6. The Hg Alp complex is generally more biological

429

effective than the Zn Alp metal complex, which is themselves more sensitive than the ligand. References [1] E.J. Stiefel, Progr. Inorg. Chem. 22 (1977) 1. [2] R. Hille, V. Massey, Nucleic acid-metal interactions, in: T.G. Spiro (Ed.), Metals ions in Biology, vol. 7, Wiley, New York, 1985, p. 443. [3] T.R. Hawkes, G.N. George, R.C. Bray, Biochem. J. 218 (1984) 961. [4] G. Hangi, H. Shamalle, E. Dubler, Inorg. Chem. 27 (1988) 3131. [5] G. Hangi, H. Shamalle, E. Dubler, Acta Cryst. C47 (1991) 1609. [6] W.S. Sheldrick, B. Gunther, Inorg. Chim. Acta 151 (1988) 237. [7] W.S. Sheldrick, P. Bell, Z. Naturforsch, Teil B 42 (1987) 195. [8] S. Kishner, Y.K. Wei, D. Francies, S.G. Bergman, J. Med. 9 (1969). [9] M.G. Abd El-Wahed, M.S. Refat, S.M. El-Megharbel, Spectrochim. Acta Part A, in press. [10] M.G. Abd El-Wahed, M.S. Refat, S.M. El-Megharbel, Spectrochim. Acta Part A, submitted for publication. [11] M.G. Abd El-Wahed, M.S. Refat, S.M. El-Megharbel, J. Mol. Struct, submitted for publication. [12] A.B.P. Lever, Inorganic Electronic Spectroscopy, 4th ed., Elsevier, London, 1980, p. 481. [13] F.A. Cotton, G. Wilkinson, C.A. Murillo, M. Bochmann, Advanced Inorganic Chemistry, 6th ed., John Wiley, New York, 1999, P. 857. [14] A. Earnshaw, The Introduction to Magnetochemistry, Academic Press, London, 1980, p. 80. [15] L. Sacconi, Electronic structure and stereochemistry of Ni(II), in: R.L. Carlin, (Ed.), Transition Metal Chemistry: A Series of Advances, vol. 4, 1968 p. 199. [16] M.S. Refat, J. Mol. Struct. 842 (2007) 24. [17] M.M. Abd-Elzaher, J. Chin. Chem. Soc. 48 (2001) 153. [18] K. Nakamoto, Infrared Spectra of Inorganic and Coordination Compounds, Wiley Interscience, New York, 1970. [19] E.S. Freeman, B. Carroll, J. Phys. Chem. 62 (1958) 394. [20] A.W. Coats, J.P. Redfern, Nature 201 (1964) 68. [21] T. Ozawa, Bull. Chem. Sot. Jpn. 38 (1965) 1881. [22] W.W. Wendlandt, Thermal Methods of Analysis, Wiley, New York, 1974. [23] H.W. Horowitz, G. Metzger, Anal. Chem. 35 (1963) 1464. [24] J.H. Flynn, L.A. Wall, Polym. Lett. 4 (1966) 323. [25] P. Kofstad, Nature 179 (1957) 1362. [26] J.H.F. Flynn, L.A. Wall, J. Res. Natl. Bur. Stand. 70A (1996) 487. [27] N.K. Tunali, S. Ozkar, Inorganic Chemistry, Gazi University Publication, Pub. No. 185, AnKara, 1993.