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Studies of the S-Ethylthiosemicarbazoneswith Cu(I), Zn(II), Cd(II), Hg(II) ChlorideSaltsBahri Ülküseven aa University of Istanbul, Faculty of Chemical Engineering, 34850Avcilar, Istanbul, TurkeyPublished online: 23 Sep 2006.

To cite this article: Bahri lkseven (1995) Studies of the S-Ethylthiosemicarbazones with Cu(I), Zn(II),Cd(II), Hg(II) Chloride Salts, Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry, 25:9,1549-1560

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SYNTH. REACT. INORG. MET.-ORG. CHEM., 25(9), 1549-1560 (1995)

STUDIES OF T H E S-ETHYLTHIOSEMICARBAZONES WITH

Cu(I), Zn(II), Cd(II), Hg(1I)CHLORIDE SALTS

Bahri Ulkuseven

University of Istanbul, Faculty of Chemical Engineering, 34850 Avcilar, Istanbul, Turkey

SUMMARY

Thiosemicarbazone derivatives, R-C,H,-CH=N-N=(C-S-C2H5)-NH2 . HBr [R = H (L),

(CHJ2N (L’)], were prepared by a modified general method. Complexes of Cu(I),

Zn(I1). Cd(II), Hg(I1) chloride salts with ligands L and L’ were isolated in two

different solvents, and have the following stoichiometries: [Hg(L)C12], prepared in

CH2C12 and [Zn(L)C12] . 2H20, [Cd(L)CI2], . CdC1,. C,H,OH .4H20.

[Hg(L)Cl,] .1/2CzHSOH, [CU,(L)CI~], , [Cd(L’)CI,] . CdCl2. C2H5OH ‘ 2H20,

[Hg(L’ . HBr)]CI2 prepared in absolute ethanol. The complexes were characterized by

analytical data, UV, IR and ‘H NMR spectroscopy.

INTRODUCTION

Many “classical” complexes containing thiosemicarbazones as coordinated ligands.

with bidentate coordination through the sulphur and hydrazinic nitrogen atoms, have

been rep~rted’ .~. There are also reports of tridentate thiosemicarbazones where atoms

such as nitrogen and oxygen become part of the aromatic ring4. However, very few

papers describing complexes with monodentate sulphur coordination are available’.

1549

Copyright 0 1995 by Marcel Dekker, Inc

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Thiosemicarbazones have a wide range of pharmacological activity. Their biological

activity has been thought to improve selectively on certain biological systems. due to

their ability to chelate with trace metals6 '. The characterization of metal complexes of

S-alkylthiosemicarbazones has been limited. Most of the work done on this class of

compounds is connected with their medicinal properties . Some developments of

analytical aspects and structural information on these complexes have been

reported1°-12.

x 9

This communication reports on S-ethyl derivatives of trans configuration through the

N2=C bond13. The characterization of the series of complexes of Cu(I), Zn(II), Cd(I1)

and Hg(I1) with the ligands 2-phenylmethylene- and 2-(4-dimethylaminophenyl)-

methylene-S-ethylhydrazinecarbothioamide (Fig. 1) has been accomplished by means

of NMR, UV and IR spectroscopy.

EXPERIMENTAL

Chemicals and Apparatus

'H NMR spectra (200 MHz) were recorded on a Bruker WP 200SY spectrometer,

chemical shifts are referrenced to Me& IR spectra were recorded in KBr disks on a

Shimadzu FT-IR 8101 spectrometer, and UV spectra were recorded on a Hitachi

220A spectrometer. Analytical data were obtained with a Car10 Erba 1106 analyzer

(TUBITAK-Turkey). Halogens were determined by argentometric titration.

Reactions were carried out under nitrogen using standard Schlenk techniques.

Solvents were dried over powdered calcium oxide (EtOH), P205 (dichloromethane)

and Na-benzophenone (Et,O, petroleum ether) and freshly distilled under nitrogen.

Other chemicals were used as reagent grade.

Preparation of 2-Phenylmethylene-S-ethylhvdrazinecarbothioamide Hvdrobromide

(L . HBr). The thiosemicarbaz,ones were prepared by the literature neth hod'^. The

ligand was prepared with small modifications of general methods''.'' given below,

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S-ETHYLTHIOSEMICARBAZONE COMPLEXES 1551

R

Fig. 1. R = H (L), -N(CH3) (L')

obtaining slightly improved yields. To benzaldehydethiosemicarbazone (3.6 g,

0.02 mole) in ethanol (30 mL) was added an excess of ethybromide (2 mL, 0.03 mole)

and the mixture gently refluxed for 6 hrs. After cooling to room temperature, light

petroleum ether (5 mL) was added and the solution mixture was allowed to stand

at -5 "C overnight. The precipitated colourless solid product was filtered, recrystalized

from ethanol-petroleum ether (1 : l) , washed with petroleum ether (b.p. 60-80 "C) and

dried in vucuo (yield 5.2 g, 88 %).

Preparation of I 2-~4-Dimethvlaminophen~l~meth~lene-S-eth~lh~drazinecarbothio-

amide hydrobromide] (L' . HBr). The yellow Iigand was obtained in a similar manner

when 4-dimethylaminobenzaldehydethiosemicarbazone (3.45 g, 0.02 mole) and

ethylbromide (2 mL, 0.03 mole) in ethanol (30 mL) were refluxed for 6 hrs.

(yield 5.4 g, 82 %) .

Preparation of CZn(L)Cl,], (1) in Dichlormethane at Room Temperature.

A suspension of anhydrous ZnC1, (0.68 g, 5 .1 0-3 mole) and L . HBr ligand ( I .44 g.

5 mole) in dry, degassed dichlormethane (20 mL) in a sealed reaction tube under

nitrogen was stirred at room temperature overnight. After this period of time, the

resulting white precipitate was collected by filtration. The solid product was washed

with a mixture of dichlormethane-ether (1 : 1, 20 mL) and dried under vucuo over P,05

(yield 1.5 g. 88 YO).

The complexes (11) and (111) were prepared in a similar manner with anhydrous metal

chlorides giving crystals of the complexes (11) (yield 85 YO) and (111) (yield 75 YO),

respectively.

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Preparation of [Zn(L)CI,l . 2H,O f1V) in Absolute Ethanol at HiFh Temperature.

A solution of anhydrous ZnCI, (0.68 g, 5 .lo” mole) and L . HBr (1.44 g, 5

mole) in 20 mL of dry, degassed absolute ethanol in a sealed reaction tube under

nitrogen was stirred vigorously. The solution mixture was gently brought up to about

65°C and allowed to stand (with stirring) for about 6 hrs. After this period of time the

solvent was reduced to half of its volume under vacuum and a small amount of

petroleum ether was added. The mixture then was allowed to stand at O°C overnight to

give a white solid product. This was then filtered quickly, washed with petroleum

ether. Recrystalization of this solid product was carried out using ethanoVether in the

ratio of 1.3 to give white crystals of Zn(L)CI, . 2H20. The product was washed with

petroleum ether and dried under vacuo over P205 (yield 0.77 g, 37%).

The complexes (V), (VI) and (IX) were prepared with anhydrous metal chlorides in a

similar manner as above; yields were 25, 20 and 23 YO, respectively.

Preparation of ICu,(L)CI,J (VII) at Room Temperature. As above, a solution of

CyCI, (1 g, 5 mole) in degassed absolute ethanol (20 mL) was treated with

L . HBr (1.44 g, 5 mole) in a sealed reaction tube. The reaction mixture was

stirred vigorously for 30 min.. a white solid product precipitated. This was then

filtered, washed with petroleum ether and recrystalized under nitrogen in absolute

ethanol giving white crystals of Cu2(L)Cl2 (yield 1.95 g, 80 YO).

The preparation of complex (VIII) was carried out with CdCI, . 2H20 in a similar

manner as above. Recrystalization from ethanol-ether (1 :3) gave an orange crystailine

solid (yield 80-85 %).

RESULTS AND DISCUSSION

The interaction of the ligands (L, L’) with MCI, in 1:l molar ratio in ethanol or

dichloromethane yielded stable solid complexes corresponding to the general formula

[M(L)CI,] {compound (I) and (111) where M = Zn, Hg}, [M(L)CI,] . X, {where

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S-ETHY LTHIOSEMICARBAZONE COMPLEXES 1553

X = H20, n = 2 compound (IV) and X = EtOH, n = 1/2 compound (VI)} and

complexes (11), (V), (VII), (VIII) and (IX). All of the complexes are very poorly

soluble in common organic solvents such as dichloromethane, but are very soluble in

donor solvents, such as dirnethylformamide (DMF), dimethylsulphoxide (DMSO) and

polar solvents, such as EtOH and MeOH. The analytical results and some physical

properties are given in Table 1. The IR spectral data in KBr disks are presented

in Table 2. The complexes are diamagnetic and their ‘H NMR spectral results are

shown in Table 3. Apart from the complex (VII) which is air and moisture sensitive

even in the solid state, the other complexes are stable in the solid form, but they do

decompose slowly in solution while exposed to air and moisture.

Representative equations for the complexation in dichloromethane the following.

L . HBr + ZnC1, --+ HBr + Zn(L)CI, (I)

L . HBr + 3 CdCl, + HBr + [Cd(L)CI,], . CdCI, (11)

and in ethanol:

L . HBr + 3 CdC1, + C,H,OH --+ HBr + [Cd(L)CI,], . CdCI,. C,HjOH (V)

L’ . HBr + 2 CdCl,. 2H20 + C2H,0H --+ HBr + [Cd(L’)CI,],. CdCI, . C2H50H .4H,O (VIII)

Reactions of CdCI, with ligwds L and L’ in CH,CI, and also in EtOH form

complexes(I), (11), (V) and (VIII), with satisfactory microanalytical and spectral data

(Tables 1-3). Reactions of these complexes with AgNO, in aqueous solution yielded a

precipitate of silver chloride immediately. In the case of complexes (11), (V) and

(VIII) the amount of white precipitate increases with time for a period of 1/2 hour.

This is evidence for the presence of coordinated and uncoordinated chloride ions in

these three complexes. Also the reaction of Cu,CI, with the ligand L yields

colourless crystals having the empirical formula [Cu,(L)CI,], in a few minutes.

Repeated treatment of this salt with L’ appeared to cause some changes (noticeably

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Table 1. Analytical Results and Some Physical Properties

Compound M.p. Analytical Data [%Found (calc.)] (‘C) C H N Me C1

41.56 4.95 14.52 --- 27.43’ 194.4 (41.67) (4.86) (14.48) --- (27.75)

35.32 3.82 12.1 I 19.24 20.92 172.5 (34.95) (3.78) ( 1 2.23) (19.04) (20.65)

25.01 2.78 8.63 35.12 22.23 >340a (24.89) (2.69) (8.71) (34.98) (22.06)

25.12 2.98 8.64 41.70 14.95 155-6 (25.07) (2.71) (8.77) (41.92) (14.81)

31.60 4.57 10.94 17.27 18.83 177-8 (3 I .63) (4.48) ( I 1.07) ( 1 7.23) ( 1 8.69)

26.22 4.09 8.27 33.09 21.57 (26.18) (3.96) (8.33) (33.44) (21.09)

26.44 3.37 8.25 39.45 14.52 162.5 (26.32) (3.19) (8.37) (39.99) (14.13)

29.78 3.44 10.22 16.02 17.18 (29.63) (3.20) (10.37) (15.68) (17.50)

43.47 5.86 16.84 --- 23.86’ 218.2 (43.51) (5.74)(16.92) --- (24.14)

>340

- -a

[Cd(L1)C12]CdC12. EtOH ’4H2O (VIII) 22.80 4.39 17.44 30.28 19.70 ( C I ~ H X C ~ ~ N ~ O ~ S C ~ ~ ) 222-4a (22.86) (4.35) ( 1 7.62) (30.60) (19.30)

[Hg(L’ HBr) 2]C12 (IX) 30.78 4.35 11.89 21.35 25.27‘ ( C ~ J H X B ~ ~ C ~ ~ N ~ S ~ H ~ 157-9a (30.85) (4.07) (12.00) (21.49) (24.71)

a: decomp., b: Br %, c: CI+Br % L ’ HBr, (I) - (VII) colourless, L’ . HBr yellow, (VIII) orange, (IX) red D

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S-ETHYLTHIOSEMICARBAZONE COMPLEXES 1555

Table 2. IR Spectra data (crn-') and Selective Band Assignments of L and L' and Their Complexes

Compounds v(N2=C) v(C=N1) v(N-N) v(C-S) v(S-C,H,)

1620s 1570s 1623s 1564s 1628s 1560s 1625s 1560s 1622s 1562s 1630s 1560s 1628s 1560s 1630s 1575s 1625s 1540s 1628s 1534s 1627s 1529s

965m 960m 954m 957m 960m 950m 958m 945m 980m 965w 970w

690m 696w 694w,br 690w 692w 690w,br 692w 680w 730m 743w,br 740w

670w 662w 660w 658w 662w 650w 660w 650w 670w 632w 640w

s: strong, m: medium, w: weak, br: broad

Table 3. IH NMR Data of Ligands and Complexes

Ethyl-group Sppm (J)Hz Benzylidene Thioamide Others Compound

-CH3 -CH2- -CH= S-C-NH2

L .HBr 1.34t (7.30) 3.38q(7.22) 8.45s 9.68s 1.34 (7.30) 3.34 (7.30) 8.39 9.61 ---

_-- (I) (11) 1.33 (7.26) 3.33 (7.31) 8.35 9.64 (111) 1.33 (7.24) 3.34 (7.31) 8.37 9.67 (IV) 1.34 (7.33) 3.37 (7.50) 8.44 9.68 3.45s(H20)

---

(V) 1.33 (7.28) 3.34 (7.36) 8.35 9.60 [C2H,OHIb 1.05 (6.98) 3.45 (6.99)

(W 1.33 (7.28) 3.34 (7.36) 8.43 9.62 3.46s(H20) [C2H,OHIb 1.05 (7.00) 3.45 (6.99)

(VW 1.34 (7.28) 3.32 (7.13) 8.37 9.53 _-- L' .HBr 1.32t(7.27) 3.32q(7.27) 8.22s 9.44s 6H(3,01s)-N(CH,),

(VIII) 1.32 (7.30) 3.30 (7.30) 8.20 9.36 3 .47s(H20) [C2H,OHIb 1.06 (7.00) 3.33 (7.29)

(W 1.32 (7.27) 3.33 (7.29) 8.24 9.49 H(12.91s)2HBr

s: singlet, d: doublet, q: quartet, m: multiplet. All aromatic rings appears at 6.76-7.73 as multiplet a: spectra recorded in DMSO-dB. b: coordinated ethanol.

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in the colour of the solution) but no pure and microanalytically satisfactory adduct

could be isolated.

IR Spectra

In the IR spectra of the complexes (IV), (V) and (VI), v(0H) bands are observed at

around 3350 cm-'. These are of considerably lower energy than for a coordinated

water molecule'*, which are generally around 3600-3550 cm-'. The studies of IK

spectra of the complexes show that the strong v(C(H)=N) band at 1570 cm-l in the

free ligand L is shifted to lower frequency in their metal complexes. These shifts are

in agreement with the same basic mode of coordination, which has previously been

reported" 2". Therefore, the coordination of these ligands through the azomethine

nitrogen is most likely. On the other hand the possibility of coordination through the

C=N2 nitrogen atom is most unlikely because of the conjugated backbone of the

ligand and involvement of this nitrogen atom with the azomethine nitrogen in this

conjugated system. However, the band at 1620 cm-l is shifted to higher frequency by

5-10 cm-l. The band of v(S-CH,) is shifted to lower frequencies in all the complexes

with the ligand L by 10-15 cm-l. This is also observed, with significantly larger

shifts, in the complexes with the ligand L' (Table 2). IR spectra of the complexes

(I), (111) and (VI) show a band at ca. 3400 cm-' which is assignable to v(NH) of the

terminal -NH2 group. This band is unaffected on complexation, which shows that the

terminal -NH2 group does not participate in coordination.

UV Spectra

The studies of UV spectra in ethanol indicate that the conjugated double bonds of the

ligands do not take part in complex formation, since there are no significant changes

observed in the UV spectra of the complexes compared with the free ligands.

Ligand L absorbs at h, = 225 nm (cl = 1.56 .lo4), h2= 308 nm (c2= 2.38 .lo4), and

Ligand L' at h, = 235 nm = 0.98 .lo4), h,= 347 nm (c2= 2.92~104dm3mol~' cm-I).

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S-ETHYLTHIOSEMICARBAZONE COMPLEXES 1557

Me” m n X

(I) Zn 0 0 not determined (111) Hg 0 0 not determined (IV) Zn 0 2 1 (VI) Hg 1/2 0 1

Fig. 2. [Me”(L)CI,], . m C2H50H . n H 2 0

I -H.NMR Spectra

The ‘H NMR spectra of the complexes (V), (VI) and (VIII) show evidence for

coordinated EtOH molecules (Table 3) (uncoordinated ethanol gives resonances

at 1.22 and 3.70, respectively). The C(H)=N resonances in all of the complexes are

shifted to lower frequencies compared to the free ligand. The evidence of the

coordination through sulphur is not clear-cut, but the change in the chemical shift and

coupling constant of the S-CH, protons (Table 3) indicates a change in the chemical

environment in this region and may be attributed to coordination through the sulphur

atom. There is a change in the chemical shift of the proton NMR signal of -NH, in the

complexes. This is may be due to a concentration effect.

Numerous previous studies of the thiosemicarbazone complexes with transition metal

salts have shown that the ligands coordinate through the sulphur and azomethine

nitrogen atoms’-3 In the majority of these complexes the bidentate thiosemicarbazone

ligands are coordinated through the sulphur atom, with either C=S or with

deprotonized C-S- ’ ”. The analytical and spectral data taken together lead to the

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Ligand m n X

(11) L 0 0 2 (V) L 1 0 2

(VIII) L' I 4 1

Fig. 3. [Cd(Ligand)CI,], . CdCl, . m C2H,0H . n H 2 0

conclusion that coordination occurs through the azomethine nitrogen and sulphur

atoms with S-ethylthiosemicarbazone in the trans configuration about the N2=C bond.

Therefore, the tentative structure for these type of complexes may be proposed

as shown in Figs. 2 and 3 .

The presence of HBr in the complex (IX) (evidence from analytical and

spectroscopic data, Tables 1 and 3) may be caused through the increase of electron

density in the thioamide region. This is because, the Hg(I1) is a rather soft ion and

can be easily polarized2'. Therefore, the 'H NMR spectrum of this complex shows

some differences in the chemical shifts in the CH=N and S-CH, regions compared

with the other complexes.

With these limited data in hand, we suggest a tentative structural formula for these

type of the complexes as shown in Figs.2-3. For the full structural determination

X-ray crystal studies are in progress.

ACKNOWLEDGMENT

We thank Dr. Naz Agh-Atabay (Heriot-Watt University. Edinburgh, Scotland) for his

useful discussions.

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S-ETHY LTHIOSEMICARBAZONE COMPLEXES 1559

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Received: 23 August 1994 Referee I: D. X. West Accepted: 8 June 1995 RefereeII: R. F. WiIson

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