Indian Journal of Chemistry Vol. 43A, October 2004, pp.2120-2125

Synthesis, characterization, biological and thermal properties of some new Schiff base

complexes derived from 2-hydroxy-5-chloroacetophenone and S-methyldithiocarbazate

J T Makode & A S Aswar*

Department of Chemistry, Amravati University, Amravati 444 602, India

Email: aswar2341 @rediff mail.com

Received 20 May 2003; revised 3 Jun e 2004

A new Schiff base derived from 2-hydroxy-5-chloroacetophenone and S-methyldithiocarbazate and its coordi­nation comp lexes with manganese(Il), iron(Il ) cobalt (ll ), nickei(Il), copper(ll ), zi nc( ll) , cadmium(fl) and oxovanadium(IV) have been sy nthesized. The resulting compl exes have been char­acterized on the basis of thei r elemental analyses, molecu lar weight, infrared spectra, re nectance spectra, magnetic suscepti ­bilities, molar conductance measurements and thermogravimetric analys is. The Schiff base acts as a tridentate diabasic donor and coord inating through the deprotonatcd phenolic oxygen, thi oeno­li c sulphur and azomethine nitrogen atoms. The antibac terial ac­tivities of the li gand and its compl exes have been screened against £. coli, S. aureus, Pr. mirabilis and S. typhi. Various kinetic and thermodynamic parameters have been eva luated from the thermo­grav imetric data and comparable va lues are obtained. Solid sta te conducti vit y of ligand and it s complexes have also been measured from room temperature to about 473 K, in the ir pellet forms and the che lates are found to show semicond ucting behaviour.

IPCode: Int. Cl. 7 C07 F 1/08; C07F 3/06; C07F 3/08: C07F 15/02: C07F 15/04; C07F I /06

Coordination metal complexes are gaining increasing importance in recent years particularly in the desi gn of repository, slow rel ease or long acting drugs in nu­trition and in the study of metabolism 1

• Metal ions are also known to accelerate drug action. The efficacy of a therapeutic agent is known2

. Metal complexes of the Schiff bases have also been widely studied due to their unusual magnetic properties, novel structural features and relevance to biological systems3

• A sur­vey of literature reveals that no work has been carried out on the synthesis of Schiff base (Scheme 1) and its metal complexes. The Schiff base has five potential donor sites with different coordination abilities which may lead to varied bonding and stereochemical be­haviour in complexes with different metal ions. ft

was, therefore thought to be worthwhile and logical to undertake the studies of transition metal complexes of Schiff base (Scheme 1) derived from substituted hydroxyacetophenone and S-methyldithiocarbazate.

OH OH

Cl JS:(C = N-N}~-S-CH ~ Cl JS(C = N-N = r_ S-CH CH/ '~ CH/ '

J J

Scheme I

l A (Keto Form) 1 B (Enol Form)

Experimental Manganese(Ir) acetate tetrahydrate, cobalt(ll) ace­

tate tetrahydrate, nickel(ll)acetate te trahydrate, cop­per(II) acetate monohydrate and p-chlorophenol were the products of Sarabhai M Chemicals. Zinc(II) ace­tatedihydrate, cadm ium chloride monohydrate and vanadylsulphate pentahydrate were obtained from E. Merck (India). All other chemicals and so lvents used were of AR grade. S-methyldithiocarbazate and 2-hydroxy-5-chloroacetophenone were prepared by re­ported methods4

·5

.

Synthesis of Schiff base The Schiff base (H2L) was prepared by the conden­

sation of S-methyldithiocarbazate with 2-hydroxy-5-chloroacetophenone in ethanol.

A hot ethanol solution (25 ml ) of 2-hydroxy-5-chloroacetophenone (1.70 gm, 0.01 mol) was added to a hot so lution of S-methylthiocarbazate ( 1.22 g, 0.0 I ml) in 25 ml ethanol and the react ion mixture was refluxed on a water bath for 3 h. After reducing the solvent to ca 20 ml the solution was a llowed to stand for overnight. The separated yellow so lid was filtered, washed with ethanol and dried at ambient tempera­ture. Finally, it was recrystallized from ethanol. Yield - 70 %, m.p. 185 OC.

Synthesis of complexes To a ethanolic solution (25 ml) of the Schiff base

(0.0 1 mol), a solution of appropriate metal (H) salt (0.01 mol) in hot methanol (25 ml), was added with constant stining. fn case of Cu(II), Zn(ff), Cd(ll) and Fe(II) complexes absolute ethanol (25 ml) was used in

NOTES 2121

place of methanol. To this solution, whi le heating a solution of ammonium acetate (2 M) was added. The reaction mixture was refluxed on water bath fo r about 3-4 h. The respective metal complexes separated were filtered, washed thorough ly with hot water, ethanol and methanol and dried in vacuo in a desiccator over anhydrous calcium chloride at room temperature.

The carbon, hydrogen and nitrogen ana lyses were performed by the microanalytical section of RSIC, Punjab University, Chandigarh, India. Ch loride and su lphur were estimated by standard methods6

. Melting point was recorded on a KSW melting point apparatus and is uncorrected. Metal contents were determined by gravimetrically/volumetrica lly and atomic absorp­tion technique. Diffuse reflectance spect ra were re­corded on a carry 2390 spectrophotometer using MgO as reference. J R spectra were scanned as KBr pe llet on a Perkin-E lmer model 1601-IT-IR spectropho­tometer 1H NMR spectrum of ligand was recorded on a Bruker WH-90 spectrometer in DMSO-d6 using TMS as an inte rnal standard. Magnetic measurements were carried out at room temperature by Gouy method using Hg [Co(SCN)4] as a calibrant. The con­ductivity measurements were made using systronic conductivity meter with a dip type cel l, using ap­proximately I o·3 M soluti on of the complexes in DMF. Molecular weight of the complexes were de­termined by Rast method using camphor as a solvent. A laboratory set up instrument was used to record thermogram of the complexes. All measurements were carried out in a quartz cup under a static ai r at­mosphere. Instrument was calibrated with crystalline copper su lphate pentahydrate. The antibacteria l ac­tivities were evaluated by agar disc diffusion method. The soi ld state electrical conductivity of the ligand and its complexes was measured by vo ltage drop method using a systronic microvoltmeter as a function of temperature in the range 398-473 K.

Results and discussion The analytical data (Table I) indicate that the metal

: ligand stoich iometry is I : I in all the complexes. All the complexes are coloured solids, insoluble in water and common organic so lvents but soluble in DMF and DMSO. All the complexes show very low molar con­ductance values ( - 18.0 ohm·' cm2 mor') in DMF/DMSO indicating their non-electrolytic natu re.

The 1H NMR spectrum of the Schiff base in DMSO-d6 shows signals at 9.60 and 13.38 ppm due to

the -NH and phenolic protons, respectively. The Schiff base displays a multiplet at 6.80 - 7.55 ppm due to the aromatic protons . The Schiff base also ex­hibits signals at 2.44, 2.20 and 2.63 ppm due to the CH3, C H3-C=N and S-CH3 protons, respectively .

The !R spectrum of li gand shows band at 3180 em· '

due to the uNH stretch . Absence of this band in the

metal complexes indicates the proton on the a­nitrogen atom is lost upon chelation with metal ions. The IR spectrum of the li gand does not display the

uS H band in the 2450-2600 em· ' region suggesting that in the so lid state, Sch iff base remains in the thio­keto form JA , but in solution it may remain as an equi librium mixture of both the thioketo JA and thiol 1 B tautomeric forms. A sharp band at I 060 em·' in the !R spectrum of Schiff base is a characteristic of -NH­C=S (thioamide) group. Thi s band di sappears in all the complexes which indicates complexation by re­placing proton from -NH- group of the li gand by tautomeric fo rm lB . Hence, the proton from -SH (thio l) group is removed by chelation. A strong band

at 1630 em·' is assigned to the uC= N stretch and this band undergoes a negative shift ( 10-15 cm-1

) in the complexes indicating the participation of the azome­thine nitrogen in coordinat ion7

. IR spectrum of the li gand shows a medium band at 2990 em· ' due to in­

tramolecular hydrogen bonded uOH group . Thi s band is absent in the spectra of the complexes, indicating the dissociation of the phenolic proton on complexa­tion. Moreover, the strong band at 1250 em·' due to

uC-0 (phenolic) in the ligand has been shifted to the 1270- 1290 em·' in the spectra of comp lexes. This sh ift in wave number towards hi gher frequency also suggests the formation of M-0 bond. The mode of coordination through the deprotonated phenolic oxy­gen, azomethine nitrogen and thienolic sulphur atoms is furt her manifested by the appearence of new bands in the region 550-590, 410-520 and 320-360 em·' due

to uM-0, uM-N and uM-S vibrations, respcctivell. T he strong band at 971 em·' in the oxovanadium comp lex is due to the presence of V=O group9

. The presence of a broad band at 3400 cnf 1 in the spectra of all complexes indicati ng the presence of water molecules, which is further supported by the presence of bands at -850 and 1530 em· ' which are ascribed to rock ing and bending vibrations of coordinated water. Thus, IR data and valence requirement of the metal io n indicate that the Schiff base behaves as a triden­tate ligand and coord inating through phenolic oxygen , azomethine nitrogen and thienolic sulph ur atoms.

Table !-The analytical , physical and electrical conductivity data of the ligand and its complexes

Sr. No. Compound Colour Mol.wt./ Elemental analysis found (calcd.)% found

(Calcd .) M c H N s CI

H2L Yellow 270.00 --- 42.96 3.75 9.85 22.97 12.90

C IOH II N20S2Cl (274.00) (43.71) (4.00) (10.10) (23 .31) (12.93)

[VO(L)(H20)h Pale red 706 00 13.97 34.93 3.03 7.35 17.35 9.77

(714.00) (14.26) (34.00) (3 .63) (7.83) (17.90) (9.93)

[Mn(L)(H20 )2h Light green 720.00 14.85 32.95 2.40 7.32 17.01 8.98

(726.00) , . c 1 f \ \ i J. J l ) (33.01) (2.47) (7.70) (17.60) (9.76)

[Fe (L) (H20)3) Greenish red 378.00 14.28 30.98 3.72 7.11 16.33 8.98

(382.00) (14.60) (31.38) (3.92) (7.27) (16.74) (9.21)

[Co(L)(H20 ) 2h Light pink ----- 14.95 32.40 2.33 7.32 16.93 8.97

(15.99) (32.57) (2.44) (7 .60) (17 .37) (8.63)

[Ni(L)(H20) 2h Pale yellow ----- 15 .71 32.43 2.22 7.43 16.98 8.92

(15.94) (32.59) (2.48) (7.83) (17 .38) (9.64)

[Cu(L)(H20] Pale green 342.00 16.96 33.69 2.95 7.25 17.93 9.87

(354.00) (17.94) (33.89) (3.11) (7 .90) (18.08) (10.03)

[Zn(L)(H20)] Pale red 349.00 18.07 33.10 2.88 7.35 !7.01 9.73

(355.00) ( 18.37) (33.72) (3 .09) (7.87) (17.95) (9 .95)

[Cd(L)(H20)] Pale orange 398.00 27.53 29.38 2.35 6.03 15.13 7.93

(402 .00) (27.90) (29.78) (2.73) (6.95) (15 .88) (8 .10)

(J

Ohm-1cm·1 at 373 K

1.06x l0-10

5.82 X 10' 11

1.16 x w - ll

1.43 x w -lo

1.94 X JO·IO

4.41 x w-9

3.95 x w-9

5.83 x lQ·II

6.59 x w -11

Ea (eV)

0.196

0.213

0.663

0.450

0.273

0.377

0.184

0.813

0.925

N

N N

z CJ

> z '-

n :r: tT1 3:: Cl'l tT1 n ?> 0 n -l 0 o; tT1 ;:o N 0 0 -!»

NOTES 2123

The reflectance spectrum of Mn(ll) complex shows three bands at 15,740,19,200 and 26,300 em·' due to h 6 4 (G 6 4 6 4 4 t e A18-t T18 }, A18-t Tzg(G), A1g-t A18 Eg(G)

transitions, respectively for an octahedral stereo­chemistry. The experimental room temperature mag­net ic moment value (5.14 B.M .) lies in the range required for an octahedral geometry 10. Lower value may be due to the presence of magnetic exchange and small traces of Mn(llf) species . The crystal field pa­rameters like Dq, B, ~and u2/u1 have been evaluated from the electronic spectral data . The reduction of Racah parameters B = 497 em·' and ~ = 0.51 from free ion value suggests appreciable amount of cova­len t character in the metal-li gand bond. The Fe(II) complex ex hibi ts bands at 10,947 ancl25 ,300 em·' clue to 5T2g( D }-t5 £8 and charge transfer transitions respec­tively. Its magnetic moment value is 5.62 B. M. corre­sponds to the hi gh spin octahedral formulation of the complex 11 with a 5T28 ground term. The various crystal field parameters Dq , B, C, ~and LFSE have been cal­culated and their values are Dq = I 094 em·', B = 591 em·' , C = 2361 em·' ~ = 0.574 and LFSE = 52.52 kJ mor' . The Co(ll) complex shows two bands at 8,728,

0 I 4 4 and 19,20 em· due to T1g( F}-t T28 (F) and "'T18(F}-t4 T1g(P) transitions respectively and the posi­tion of the bands is indicative of an octahedral struc­ture 12. The electronic spectral parameters are : Dq = I 059 em·', B = 822 em·', ~ =0.734, u2/u1 = 1.83 , ~8= 28.54 o/o and LFSE = 76.29 kJ mor '. The reduction of the Racah parameters (B) from the free ion value of 971 em·' and the ~ indicate the presence of covalent character. The Co(ll) complex has magnetic moment 4.86 BM also suggest an octahedral geometry. The magnetic moment of Ni(ri) complex is 2.86 BM which is in the range expected for octahedral Ni(ll) ion. Its reflectance spectrum shows three bands at I 0,550, 16,750 and 25,700 em·' due to the transitions 3A2g( F)-t3T2g( F) , 3 A2g( F)-t3T1g( F) and 3A2g(F)-t3T1g( P) respect ively, in an octahedral ge­ometry1 3. The u2/u1 ratio for the complex is 1.59 and thi s is in the usual range reported for octahedral Ni(ll) complexes. The crystal field parameters are Dq = 1055 em·', B = 720 em· ', ~ = 0.66, ~0 = 33 o/o and LFSE = 151 kJ mor'. The ~0 value and the reduction of B from the free ion value of 1056 em·' testify to the presence of strong metal li gand covalent bonding. The Cu(ll) complex ex hibits magneti c moment 1.78 B.M., which is sli ghtly higher than spin on ly value or one unpaired electron for square planar environment. The

electronic spectrum of Cu(Il) complex shows bands at 17,739, 19,592 and 24,611 em·' assignable to 2B18-t2A 18, 2B18-t2E8 and charge transfer transition respectively, indicative of square planar configura­tion14. The reflectance spectrum of YO(IY) , complex exhibited bands aL13157, 16500 and 23529 em·' due

. . 28 2£ ?B 28 d 28 2A to transitions 2-t , - 2-t 1 an 2-t 1 respec-tively towards octahedral geometry' 5

. The magnetic moment of oxovanadium(fV) complex is 1.58 B. M. is lower than the spin only value (1.73 B.M .). This lowing of the moment may perhaps be attributed to the binuclear nature of the complex. The Zn(ll) and Cd(lf) complexes do not exhibit any characteristic d-d transitions and are also found to be diamagnetic and may have tetrahedra l geometry. Although molecular weight measurements on the Ni(ll) and Co(ll ) com­plexes were not poss ible due to their inso lubility in common non-coordinatin g organic solvents but such measurement on Mn(ll) and YO(lY) complexes indi­cated their climeric structure (I) with octahedral ge­ometry for these complexes16·17 .

The results of electrical conductivity and activation energy of the ligand and its complexes are cited in Table 1. The electrical conductivity (cr) varies expo­nentially with the absolute temperature according to the relationship cr = cr0 exp (-Ea!KT), where cr0 is a constant, Ea is the activation energy and K is the Boltzmann constant. The plots of log cr vs I IT were found to be linear, suggesting the semiconducting nature of ligand and its complexes. The temperature

~

s "".f)o"' f)N ( /["/'"J N OH OH . ~ 2

M = Mn(ll), Co(ll) and Ni(ll)

OI-l , OH

(o""l! , / i""

N OH S ~

(0"" / 01-1,

M

/"" N S

~

M = Cu(ll ), Zn(ll) & Cd(ll)

(I)

2124 INDIAN J CHEM, SEC A, OCTOBER 2004

dependence of the conductivity curves of the com­plexes gave two region with two slopes. This agrees well with the report of Spiratos et a/. 18 that the activa­tion energy of Arrhenius plots approaches higher val­ues at high temperature suggesting intrinsic conduc­ti on, while those measured at lower temperature have much lower va lues due to ex trinsic conduction. Elec­trical conductivity of these compounds lies in the range 3.95 x 10·9 to 6.63 x 10· 11 ohm-1 cm-1 at 373 K. The results indicate that the e lectrical conductivi ty and energy of activation vary with the metal ions, which may be due to the incorporation of different metal ions in the complexes which increases the ioni­zat ion tendenc/ 9

.

The dynamic TGA with the percentage mass loss at different steps have been recorded. The e limination o f lattice and coordinated water molecules take place in

the first step. The Mn(II) , Co(lf) and Ni(li) complexes lose their weight in the temperature range 160 -

21 OOC corresponding to two coordinared water mole­cules. In the case of Fe(II) complex loss of three co­ordinated water molecules has been observed, whereas the Cu(Il), Zn(Il), Cd(Il) and VO(IV) com­

plexes show weight loss at about 160°C correspond­ing to one coordinated water molecule. After the total loss of water, the organic moiety decomposes on fur­ther increment of temperature. Although decomposed fragments of the ligand could not be estimated due to continuous weight loss, the complete decomposition of ligand occurs at -700 OC and the observed res idue corresponds to the respective oxide20

. The thermal data of complexes was analysed by Freeman­Carroll21, Sharp-Wentworth22 and Coats-Redfern23

methods. It is observed from Table 2 that the degra­dation of complexes at e levated temperature is a com-

Table 2 - Thermal properti es of li gand and its complexes

Compounds 0 Method Ea (kJmor 1) -L\ S (JK-I mor I L\F(kJmor 1) Z (S- 1) Decomp. Temp ( C) Order n

H2L 185 FC 12.89 308.63 106.79 0.0 102 0.57

sw 12.23 211.20 83.34 0.0 106

CR 16.4 1 254.50 9607 0.0105

[VO(L)(H 0)] 200 FC 20.62 297 .02 11 3.59 0. 1260 2 2

0.60

sw 2 1.27 218.Q7 89.53 0. 1937

CR 17.67 248. 14 95.34 0.585

[Mn(L)(H2 0)2)

2 2 10 FC 16.28 309.52 11 3. 16 0.0873 0.72

sw 22.34 213.49 89.17 0.1129

CR 16.28 258.59 97.21 0.0827

[Fe(L)( H 0 ) ] 190 FC 16.41 303.33 111.35 0.0365 2 3

0.80

sw 14.34 219.81 83. 16 0.04 18

CR 21 .27 244.50 97.80 0.0892

[CoL(H20\]2

250 FC 13.40 300.42 107.43 0. 1029 0.58

sw 17.23 211.97 83.58 0.080

CR 2 1.06 236.34 95.64 0. 1307

[Ni (L)(H20hh 280 FC 17.55 302.57 11 2.26 0.0643 0.61

sw 19.15 219.91 85.16 0.0590

CR 17.41 245.22 95.41 0.0649

[Cu(L)(H20)) 200 FC 15.96 304.7 1 11 1.33 0.0115 0.75

SW 22.98 219.54 96.69 0.0 159

CR 15.90 255.31 95.86 0.0 115

[Zn(L)(H20)] 205 FC 14.89 307.15 111.03 0.0295 0.72

sw 14.10 226.03 84.86 0.02 11

CR 18. 18 248.62 96.00 0.0383

[Cd(L)(H2 0)] 195 FC 13.68 312.83 111 .59 0.0075 0.69

sw 15.32 219.79 84. 11 0.0 107

CR 17.4 1 255.69 97.44 0.0 149

FC =Freeman-Carroll ; SW =Sharp-Wentworth; CR = Coats-Reclfern

NOTES 2125

plex process as noted from the non-integer order of reaction and follows the first order kinetics. The val­ues of kinetic parameters obtained from different equations are reasonable and in good agreement sug­gests that a single mechanism will describe the kinet­ics. From the data of Table 2 it can be observed that the values of the thermodynamic properties are nearly the same for each complex. Thi s simi larity indicates a common reaction mode with regard to the abnormally low value of frequency factor (Z). It may be con­cluded that the reaction proceeds s l owll~. The

change of entropy (.1S) values for all complexes are nearly of the same magnitude and lie within the range (-265 to 293 JK' 1 mol" 1

) indicates that activated com­plex has more ordered structure than the reactant and that the reactions are slower than normal.

The free li gand and its metal complexes were screened against E. coli, E. aureus, Pr. mirabilis and S. typhi to assess their potential as ant imi crobial agents. The results reveal that the ligand is reactive towards all bacterial strains. The oxovanadium(II ) and Co(Il) complexes show very good activity against all strains. The Mn(ll), Fe(II) and Ni(Il) complexes show moderate activity against all strains except E. coli . While Cu(ll) , Zn(ll) and Cd(ll ) complexs are more active towards all strains exceptS. aureus. In general, the metal complexes are more potent than their ligand and hence may serve as vehicles for activation of the ligand as principal cytotoxic species25

.

Acknowledgement Authors are thankful to University authorities for

providing laboratory facilities. One of us (JTM) is gratefu l to UGC, WRO, Pune for the award of teacher fellowship.

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