Studies on the Effect of Tetramethylene Sulfoxide and Various Anions on the Stereochemistry of Lanthanide (III) Coordination Compounds of 4[N-(4’-Ethylbenzalidene) Amino]-Antipyrinesemicarbazone

 

Sajid Ali1* and Draksha2

1 Department of Chemistry, Vishveshwarya Institute of Engineering and Technology, Dadri -G. B. Nagar (U.P.)  203 207 India

2Department of Chemistry, S. S V. P. G. College, Hapur (U.P.)

*Corresponding Author E-mail: ali9402@gmail.com 

ABSTRACT:

The structural chemistry of the lanthanide (III) compounds has recently undergone considerable development and a wide variety of coordination numbers and geometries have been observed. The coordination numbers exhibited by the tripositive lanthanide ions usually vary from 6 to 10. However, other examples of lanthanide (III) complexes with more than 10- coordination number have also been reported in the literature. In the present studies the effect of tetramethylene sulfoxide (TMSO) on the stereochemistry of the coordination compounds of trivalent lanthanides derived from 4-[N-(4’-ethylbenzalidene)amino]antipyrine semicarbazone (EBAAPS) is reported. The general composition of these coordination compounds is LnX3.n (EBAAPS).TMSO (Ln = La, Pr, Nd, Sm, Gd, Tb, Dy or Ho; X = NO3 , n = 1, X = ClO4 or NCS, n =2). All these compounds were characterized by elemental analysis, molar mass, molar conductance, magnetic susceptibility, infrared and electronic spectra. The infrared studies reveal that the EBAAPS acts as a neutral tridentate (N,N,O), while TMSO is coordinated to the central metal ion via its lone oxygen atom. In nitrato complexes, the nitrates ions are bicovalently bonded, while thiocyanate is coordinated through hard N-atom. Perchlorato ions are not participating in coordination and are present outside the coordination sphere. From electronic spectral data, nephelauxetic effect (β), covalence factor (b1/2), Sinha parameter (δ %) and the covalence angular overlap parameter (η) has been calculated. Antibacterial properties of these compounds were also studied. Thermal studies of these compounds were studied by thermogravimetric analysis. The present studies reveal that the coordination number of lanthanide (III) in the present compounds is either 7 or 10 depending on the nature of anions.

 

KEYWORDS: Lanthanides, Semicarbazone, Diphenyl sulfoxide, Coordination compounds.

 

 

INTRODUCTION:

In quest of exploring the chelating behaviour of sone N,N,O and N,N,S donor semicarbazones and thiosemicarbazones in several metal complexes, we could acquire more information about their nature of coordination and related structural, spectral and biological properties (1-4). Amongst several Schiff bases, semicarbazones received much less attention. However semicarbazones are reported to possess versatile structural features (5) and very good antifungal and antibacterial properties (6,7). Less are known about metal complexes of semicarbazones (3,8,9). Because of their large size, the lanthanide ions are generally have higher coordination numbers than transition elements.

 

Lanthanide ions with their high positive charge and larger size are the best candidates to form stable complexes with high coordination numbers and generally coordination numbers of 6 to 10 are observed. In present studies we report the mixed ligand complexes of lanthanides (III) with 4[N-(4’-ethylbenzalidene) amino]antipyrine semicarbazone (EBAAPS) as primary ligand and tetramethylene sulfoxide (TMSO) as secondary ligand.

 

EXPERIMENTAL:

The lanthanide nitrates and oxides were obtained from Rare Earth Products Ltd. (India) and were used without further purification. The lanthanide perchlorates were prepared by heating the corresponding oxides with perchloric acid and evaporating off the excess of acid (10). The lanthanide isothiocyanates were prepared by adding a warm ethanolic solution of lanthanide nitrates to a warm ethanolic solution of KCNS. The precipitate of KNO3 rapidly coagulated.The volume of the solution was reduced on a water bath, cooled, filtered and the filtrate was used for complexation (11).The ligand EBAAPS was prepared by a known method (12). Tetramethylene sulfoxide was obtained from Merck and was used without further purification. The solvents used in this studies were obtained from Merck.

 

Synthesis of the complexes:

(1)    Ln(NO3)3(EBAAPS).TMSO (Ln=La, Pr, Nd,Sm, Gd, Tb, Dy or Ho) : An ethanolic solution of both ligands (EBAAPS and TMSO, 1 mmol each) was added withconstant stirring to a hot ethanolic solution of respective lanthanide (III) nitrate (1mmol) and the reaction mixture was refluxed on a water bath for 2 hrs. The yellow precipitate obtained was separated by filteration, washed with ethanol and finally dried at 110 oC in a vacuum oven.

(2)    Ln(NCS)32(EBAAPS).TMSO (Ln=La, Pr, Nd,Sm, Gd, Tb, Dy or Ho): All the complexes were prepared by the following general method. The corresponding metal salts and the ligands in required molar ratios (1:2:1) were added to ethanol and the reaction mixture was refluxed for 1-2 hrs. In each case the required solid product was obtained on cooling which was washed with the solvent and finally with diethyl ether and dried in vacuo over P4O10.

(3)    Ln(ClO4)32(EBAAPS).TMSO (Ln=La, Pr, Nd, Sm, Gd, Tb, Dy or Ho): The solution of corresponding lanthanide (III) perchlorate (1 mmol) and EBAAPS and TMSO (1:2:1 molar ratio) in hot methanol were mixed and stirred well. After fluxing the solution on a steam bath for 0.5 hr, the resulting solid was separated on cooling in an ice bath. After separating the complexes, washed with diethyl-ether and finally dried under reduced pressure.

 

Analysis:

The lanthanide metals content was estimated as its oxide by direct combustion in a platinum crucible. The estimation was further confirmed by dissolving the product of direct combustion in dilute HCl. The acid extract was transferred into a flask, pH was adjusted to 5.8-6.4 by the addition of acetic acid sodium acetate buffer and was then titrated against 0.1M EDTA using xylenol-orange as an indicator. The results from both the methods were compared and found within the experimental errors. Nitrogen was determined in the laboratory by the Kjeldahl method, while sulphur was estimated gravimetrically as BaSO4.The thiocyanate was determined by oxidizing the complex with bromine water to sulphate and subsequently precipitating it as BaSO4. The perchlorate was estimated by the method suggested Kurz et al (13). The molecular weight of the complexes was determined cryoscopically in freezing nitrobenzene using a Beckmann thermometer of accuracy ± 0.01 oC in the laboratory. The conductivity measurements were carried out using a Toshniwal Conductivity Bridge (type CL 01/01) and a dip type cell operated at 220 volts AC mains. All the measurements were performed at room temperature in PhNO2.The magnetic measurements were carried out at room temperature with a Gouy’s balance and anhydrous copper sulphate was used as a calibrant. The infrared spectra of the complexes were recorded on a Perkins Elmer infrared spectrophotometer model 521 in KBr or a polychlorotrifluoro ethylene mull in the range of 4000-200 cm-1. A Hilger Unispek spectrophotometer with 1cm-1 quartz cell was employed for recording the visible spectra of Pr3+, Nd3+ ,Sm3+ and Ho3+ complexes. Thermogravimetric analysis of present coordination compounds was carried out in static air, with open sample holder and small platinum boat, the heating rate was 6o min-1. The antibacterial activity of the ligand (EBAAPS and TMSO) and their corresponding lanthanide (III) complexes were studied against five bacteria Escherichia coli, Staphylococcus aureus, Bacillus subtilis, S.pneumoniae and Pseudomonas aeruginosa by cup-plate method  (14) . The zones of inhibition against all the microorganisms were measured in millimeter. The antifungal activity of these complexes were test against the pathogenic fungi Aspergillus niger and Pencillum notatum by cup plate method. The zone of inhibition was measured in millimeter for the particular test samples with each organism at 36 hrs interval.

 

RESULTS AND DISCUSSION:

The reaction of non-aqueous solutions of lanthanide(III) salts with 4[N-(4’ethylbenzalidene) amino] antipyrine semicarbazone (EBAAPS) as primary ligand and TMSO as secondary ligand resulting complexes of the general composition LnX3.n(EBAAPS).TMSO (X = NO3-, n =1, X = NCS- or ClO4-, n = 2; Ln = La, Pr, Nd, Sm, Gd, Tb, Dy or Ho). The complexes are anhydrous in nature, which is evident from their analytical, infrared and thermal studies. All the complexes of 4f -metal ions are quite stable and can be stored for long period except. The complexes are generally soluble in common organic solvents but insoluble in diethyl ether. All the metal-complexes are also soluble in weak coordinating solvents such as DMSO or DMF. The analytical data presented in Table 1-3 indicates that the complexes are pure and need no further purification. TG curves indicate no changes up to 130oC suggesting the absence of either coordinated or uncoordinated water molecule in these complexes. The molar conductances of 4f-metal complexes in nitrobenzene are presented in Tables 1-3. The molar conductance of nitrato and isothiocyanato complexes are too low to account for any dissociation, therefore, the complexes are non-electrolytes. The perchlorato complexes behave as 1:3 electrolytes in nitrobenzene. Data on the molecular weight of the complexes in nitrobenzene are presented in Tables 1-3 along with the values calculated on the basis of established formula of the complexes. The ratio of molecular weight observed for [Ln(NO3)3.(EBAAPS).TMSO] or Ln(NCS)3.2(EBAAPS).TMSO to that calculated is ~ 0.98 which shows that the complexes are monomeric in solution. In case of Ln(ClO4)3.2(EBAAPS).TMSO, the ratio is found to be 0.25. This data further support that four species are formed in the perchlorato complexes.

 

The magnetic moment values observed in 4f-metal coordination compounds are summarized in Tables 1-3 show that lanthanum complexes are diamagnetic in nature, as expected from its closed shell electronic configuration and absence of unpaired electrons.


Table-1: Analytical, conductivity, molecular weight and magnetic susceptibility data of lanthanide (III) nitrato complexes of EBAAPS and TMSO

Compounds

Elemental analysis (%): Found (Calcd.)

M.W. found (Calculated.)

Lm

(ohm-1 cm2 mol-1)

µeff (BM)

Ln

N

S

La(NO3)3·(EBAAPS)·TMSO

 

Pr(NO3)3·(EBAAPS)·TMSO

 

Nd(NO3)3·(EBAAPS)·TMSO

 

Sm(NO3)3·(EBAAPS)·TMSO

 

Gd(NO3)3·(EBAAPS)·TMSO

 

Tb(NO3)3·(EBAAPS)·TMSO

 

Dy(NO3)3·(EBAAPS)·TMSO

 

Ho(NO3)3·(EBAAPS)·TMSO

17.20

(17.41)

17.30

(17.51)

17.53

(17.79)

18.16

(18.40)

18.79

(19.09)

18.98

(19.29)

19.40

(19.63)

19.59

(19.87)

15.49

(15.67)

15.48

(15.65)

15.40

(15.57)

15.31

(15.46)

15.16

(15.32)

15.15

(15.29)

15.09

(15.22)

15.08

(15.18)

3.95

(3.98)

3.94

(3.97)

3.92

(3.95)

3.89

(3.92)

3.86

(3.89)

3.84

(3.88)

3.82

(3.86)

3.83

(3.85)

799.0

(804.0)

800.0

(805.0)

805.0

(809.0)

810.0

(815.0)

817.0

(822.0)

819.0

(824.0)

823.0

(827.5)

825.0

(830.0)

1.3

 

1.5

 

1.7

 

1.6

 

1.9

 

2.0

 

1.8

 

1.5

Diamag.

 

3.57

 

3.62

 

1.64

 

7.95

 

9.20

 

10.78

 

10.38

 

Table-2: Analytical, conductivity, molecular weight and magnetic susceptibility data of lanthanide(III) isothiocyanato complexes of EBAAPS and TMSO

Compounds

Elemental analysis (%): Found (Calculated.)

M.W. found (Calculated.)

Lm

(ohm-1 cm2 mol-1)

µeff (BM)

Ln

N

S

NCS

La(NCS)3·2(EBAAPS)·TMSO

 

Pr(NCS)3·2(EBAAPS)·TMSO

 

Nd(NCS)3·2(EBAAPS)·TMSO

 

Sm(NCS)3·2(EBAAPS)·TMSO

 

Gd(NCS)3·2(EBAAPS)·TMSO

 

Tb(NCS)3·2(EBAAPS)·TMSO

 

Dy(NCS)3·2(EBAAPS)·TMSO

 

Ho(NCS)3·2(EBAAPS)·TMSO

11.90

(11.96)

11.99

(12.04)

12.21

(12.26)

12.65

(12.71)

13.17

(13.22)

13.32

(13.37)

13.57

(13.62)

13.75

(13.80)

17.85

(17.94)

17.83

(17.93)

17.78

(17.88)

17.69

(17.79)

17.60

(17.69)

17.56

(17.66)

17.52

(17.61)

17.49

(17.57)

2.71

(2.73)

2.71

(2.73)

2.70

(2.72)

2.68

(2.71)

2.66

(2.69)

2.64

(2.69)

2.63

(2.68)

2.62

(2.67)

14.75

(14.87)

14.73

(14.85)

14.73

(14.82)

14.66

(14.74)

14.55

(14.65)

14.53

(14.63)

14.50

(14.59)

14.47

(14.56)

1165.0

(1170.0)

1166.0

(1171.0)

1170.0

(1174.0)

1175.0

(1180.0)

1182.0

(1187.0)

1184.0

(1189.0)

1187.0

(1192.5)

1190.0

(1195.0)

1.7

 

1.8

 

2.0

 

2.1

 

1.9

 

2.2

 

1.8

 

2.3

Diamag.

 

3.59

 

3.52

 

1.63

 

7.91

 

9.23

 

10.59

 

10.42

 

Table-3: Analytical, conductivity, molecular weight and magnetic susceptibility data of lanthanide(III) perchlorato complexes of EBAAPS and TMSO

Compounds

Elemental analysis (%): Found (Calculated.)

M.W. found (Calculated.)

Lm

(ohm-1 cm2 mol-1)

µeff (BM)

Ln

N

S

ClO4

La(ClO4)3·2(EBAAPS)·TMSO

 

Pr(ClO4)3·2(EBAAPS)·TMSO

 

Nd(ClO4)3·2(EBAAPS)·TMSO

 

Sm(ClO4)3·2(EBAAPS)·TMSO

 

Gd(ClO4)3·2(EBAAPS)·TMSO

 

Tb(ClO4)3·2(EBAAPS)·TMSO

 

Dy(ClO4)3·2(EBAAPS)·TMSO

 

Ho(ClO4)3·2(EBAAPS)·TMSO

10.76

(10.81)

10.79

(10.88)

10.99

(11.08)

11.41

(11.49)

11.89

(11.97)

12.01

(12.10)

12.23

(12.33)

12.39

(12.50)

12.89

(12.97)

12.88

(12.96)

12.85

(12.93)

12.82

(12.87)

12.74

(12.80)

12.73

(12.79)

12.70

(12.75)

12.68

(12.73)

2.43

(2.47)

2.43

(2.47)

2.42

(2.46)

2.42

(2.45)

2.39

(2.43)

2.39

(2.43)

2.38

(2.42)

2.38

(2.42)

22.86

(23.05)

22.85

(23.04)

22.62

(22.98)

22.57

(22.88)

22.49

(22.76)

22.48

(22.72)

22.41

(22.66)

22.38

(22.62)

330

(1294.5)

331

(1295.5)

332

(1298.5)

340

(1304.5)

342

(1311.5)

343

(1313.5)

344

(1317.0)

345

(1319.5)

76.9

 

79.0

 

77.3

 

78.3

 

78.0

 

76.8

 

78.9

 

78.4

Diamag.

 

3.59

 

3.1

 

1.61

 

7.92

 

9.19

 

10.73

 

10.38

 

Table-4: Key infrared spectral bands (cm-1) of lanthanide(III) complexes of EBAAPS and TMSO

Compounds

n (S=O)

n (C=N) azomethinic

n (C=N) hydrazinic

n (C=O)

n (Ln-O)/         n (Ln-N)

I

II

III

TMSO

EBAAPS

La(NO3)3·(EBAAPS)·TMSO

Pr(NO3)3·(EBAAPS)·TMSO

Nd(NO3)3·(EBAAPS)·TMSO

Sm(NO3)3·(EBAAPS)·TMSO

Gd(NO3)3·(EBAAPS)·TMSO

Tb(NO3)3·(EBAAPS)·TMSO

Dy(NO3)3·(EBAAPS)·TMSO

Ho(NO3)3·(EBAAPS)·TMSO

1020vs

–

960s

955s

958s

962s

950s

955s

958s

960s

–

1615s

1590s

1592s

1595s

1585s

1590s

1592s

1590s

1590s

–

1660s

1625s

1630s

1632s

1625s

1630s

1625s

1622s

1632s

–

1700s

1650s

1645s

1652s

1640s

1642s

1645s

1640s

1642s

–

1565m

1533m

1528m

1532m

1530m

1535m

1532m

1530m

1532m

–

1350m

1330m

1335m

1332m

1330m

1328m

1330m

1325m

1332m

–

–

470m, 370w

465m, 385w

465m, 392w

468s, 390w

460m, 392w

465m, 387w

462m, 385w

468m, 385w

La(NCS)3·2(EBAAPS)·TMSO

Pr(NCS)3·2(EBAAPS)·TMSO

Nd(NCS)3·2(EBAAPS)·TMSO

Sm(NCS)3·2(EBAAPS)·TMSO

Gd(NCS)3·2(EBAAPS)·TMSO

Tb(NCS)3·2(EBAAPS)·TMSO

Dy(NCS)3·2(EBAAPS)·TMSO

Ho(NCS)3·2(EBAAPS)·TMSO

958s

958s

960s

962s

957s

958s

955s

950s

1592s

1587s

1590s

1588s

1590s

1588s

1585s

1592s

1628s

1625s

1630s

1632s

1628s

1630s

1633s

1628s

1645s

1640s

1650s

1645s

1640s

1642s

1640s

1647s

1533m

1530m

1535m

1532m

1530m

1533m

1535m

1530m

1330m

1332m

1335m

1330m

1332m

1325m

1328m

1330m

470m, 380w

465m, 382w

470m, 385w

450m, 378w

452m, 380w

460m, 365w

465m, 370w

472m, 375w

La(ClO4)3·2(EBAAPS)·TMSO

Pr(ClO4)3·2(EBAAPS)·TMSO

Nd(ClO4)3·2(EBAAPS)·TMSO

Sm(ClO4)3·2(EBAAPS)·TMSO

Gd(ClO4)3·2(EBAAPS)·TMSO

Tb(ClO4)3·2(EBAAPS)·TMSO

Dy(ClO4)3·2(EBAAPS)·TMSO

Ho(ClO4)3·2(EBAAPS)·TMSO

952s

965s

960s

958s

962s

955s

958s

955s

1595s

1592s

1595s

1590s

1587s

1592s

1588s

1592s

1630s

1630s

1628s

1622s

1632s

1625s

1630s

1625s

1648s

1652s

1642s

1645s

1640s

1650s

1645s

1642s

1535m

1530m

1528m

1532m

1530m

1533m

1535m

1532m

1332m

1335m

1332m

1330m

1335m

1330m

1332m

1328m

475m, 370w

465m, 380w

468m, 382w

455m, 380w

465m, 385w

475m, 372w

455m, 368w

462m, 372w

 

Table-5: Infrared absorption bands (cm-1) of NO3– in Ln(NO3)3·(EBAAPS)·TMSO

Complex

(n2+n5)

(n2+n6)

(n2+n5)- (n2+n6)

n4

n1

n2

n6

n3

n5

La(NO3)3·(EBAAPS)·TMSO

Pr(NO3)3·(EBAAPS)·TMSO

Nd(NO3)3·(EBAAPS)·TMSO

Sm(NO3)3·(EBAAPS)·TMSO

Gd(NO3)3·(EBAAPS)·TMSO

Tb(NO3)3·(EBAAPS)·TMSO

Dy(NO3)3·(EBAAPS)·TMSO

Ho(NO3)3·(EBAAPS)·TMSO

1782vw

1790vw

1785vw

1792vw

1778vw

1782vw

1780vw

1790vw

1732vw

1740vw

1745vw

1748vw

1738vw

1745vw

1740vw

1745vw

50

50

40

44

40

37

40

45

1508sh, 1490m

1515m

1498s,br

1510sh, 1490s

1525m, 1510w

1510sh, 1490m

1515m

1512sh, 1490m

1300m

1292m

1302m

1295m

1298m

1290m

1295m

1290m

1032m

1027m

1030m

1025m

1028m

1027m

1030m

1032m

827m

820m

817m

825m

822m

825m

830m

815m

740m

742m

737m

738m

740m

735m

740m

738m

685sh

698w

–

702w

695w

700w

685sh

680sh

 

Table-6: Infrared absorption frequencies (cm-1) of NCS– in Ln(NCS)3·2(EBAAPS)·TMSO

Complex

n (CN)

n (CS)

δ(NCS)

La(NCS)3·2(EBAAPS)·TMSO

Pr(NCS)3·2(EBAAPS)·TMSO

Nd(NCS)3·2(EBAAPS)·TMSO

Sm(NCS)3·2(EBAAPS)·TMSO

Gd(NCS)3·2(EBAAPS)·TMSO

Tb(NCS)3·2(EBAAPS)·TMSO

Dy(NCS)3·2(EBAAPS)·TMSO

Ho(NCS)3·2(EBAAPS)·TMSO

2050s

2040s

2045s

2035s

2045s

2038s

2040s

2042s

840m

837m

832m

838m

835m

842m

845m

840m

465w

470w

462m

468w

460w

470w

472w

465w

 

Table-7: Infrared absorption frequencies (cm-1) of ClO4– in Ln(ClO4)3·2(EBAAPS)·TMSO

Complex

n3

n4

La(ClO4)3·2(EBAAPS)·TMSO

Pr(ClO4)3·2(EBAAPS)·TMSO

Nd(ClO4)3·2(EBAAPS)·TMSO

Sm(ClO4)3·2(EBAAPS)·TMSO

Gd(ClO4)3·2(EBAAPS)·TMSO

Tb(ClO4)3·2(EBAAPS)·TMSO

Dy(ClO4)3·2(EBAAPS)·TMSO

Ho(ClO4)3·2(EBAAPS)·TMSO

1090s

1095s

1092s

1100s

1095s

1100s

1098s

1090s

630s

625m

635s

640s

635s

628s

632s

642s

 

Table-8: Electronic spectral data (cm-1) and related bonding parameters of Ln(NO3)3·(EBAAPS)·TMSO

Complex

Ln(NO3)3 spectral bands

Complex electronic spectral bands

Energy levels

(1-β)

β

b½

δ %

h

Pr(NO3)3·(EBAAPS)·TMSO

22470

21325

20750

17000

22380

21220

20620

16880

3H4  ® 3P2

        ® 3P1

        ® 3P0

        ® 1D2

0.00400

0.00492

0.00626

0.00705

0.99599

0.99507

0.99373

0.99294

0.04472

0.04959

0.05594

0.05937

0.40161

0.49443

0.62994

0.71001

0.00201

0.0248

0.00314

0.00354

Nd(NO3)3·(EBAAPS)·TMSO

19600

17380

13680

12470

19500

17270

13630

12430

4I9/2 ® 2G9/2

       ® 2G9/3, 2G7/2

        ® 2S3/2, 2F9/2

       ® 4F5/2, 4H9/2

0.00510

0.00632

0.00365

0.00320

0.99489

0.99367

0.99634

0.99679

0.05049

0.05621

0.04272

0.04000

0.51261

0.63602

0.36634

0.32103

0.00256

0.00318

0.00183

0.00160

Sm(NO3)3·(EBAAPS)·TMSO

24870

24000

21550

24750

23700

21500

4H9/2 ® 4F9/2

        ® 6P5/2

       ® 4I13/2

0.00482

0.01250

0.00232

0.99518

0.98750

0.99767

0.04909

0.07905

0.03405

0.48433

1.26580

0.23254

0.00241

0.00630

0.00116

 

Table-9: Electronic spectral data (cm-1) and related bonding parameters of lanthanide(III) isothiocyanato complexes of EBAAPS and TMSO

Complex

Ln(NCS)3 electronic spectral bands

Complex electronic spectral bands

Energy levels

(1- β)

β

b½

δ %

h

Pr(NCS)3·2(EBAAPS)·TMSO

22400

21230

20800

16900

22250

21050

20620

16720

3H4 ® 3P2

       ® 3P1

       ® 3P0

       ® 1D2

0.00669

0.00847

0.00865

0.01065

0.99330

0.99152

0.99134

0.98934

0.04089

0.04601

0.04650

0.05159

0.67351

0.85424

0.87255

1.07647

0.00710

0.00426

0.00435

0.00534

Nd(NCS)3·2(EBAAPS)·TMSO

19400

17400

13400

12500

19200

17200

13240

12240

4I9/2 ® 2G9/2

       ® 4G5/2, 2G7/2

       ® 2S3/2, 4F7/2

       ® 4F5/2, 4H9/2

0.01030

0.01149

0.01194

0.02080

0.98969

0.98850

0.98805

0.97920

0.05074

0.05359

0.05463

0.07211

1.04072

1.16236

1.20844

2.11418

0.00519

0.00580

0.00602

0.01056

Sm(NCS)3·2(EBAAPS)·TMSO

24900

24000

21600

24700

23820

21440

4H5/2 ® 4F9/2

       ® 6P5/2

       ® 4I5/2

0.00803

0.00750

0.00740

0.99196

0.99250

0.99260

0.04480

0.04330

0.04301

0.80950

0.75566

0.74552

0.00404

0.00377

0.00372

 

Table-10: Electronic spectral data (cm-1) and related bonding parameters of lanthanide(III) perchlorato complexes of EBAAPS and TMSO

Complex

Ln(ClO4)3 electronic spectral bands

Complex electronic spectral bands

Energy levels

(1- β)

β

b½

δ %

h

Pr(ClO4)3·2(EBAAPS)·TMSO

22470

21325

20750

17000

22340

21200

20620

16850

3H4 ® 3P2

     ® 3P1

      ® 3P0

      ® 1D2

0.0057

0.0058

0.0062

0.0068

0.9943

0.9942

0.9938

0.9912

0.0380

0.0382

0.0395

0.0469

0.5813

0.5894

0.6299

0.8898

0.0023

0.0029

0.0031

0.0044

Nd(ClO4)3·2(EBAAPS)·TMSO

19600

17380

13680

12470

19450

17250

13580

12380

4I9/2 ® 2G9/2

     ® 4G5/2, 2G7/2

      ® 2S3/2, 4F7/2

      ® 4F5/2, 4H9/2

0.0076

0.0074

0.0073

0.0072

0.9924

0.9926

0.9927

0.9928

0.0437

0.0432

0.0427

0.0424

0.7709

0.7526

0.7353

0.7262

0.0038

0.0037

0.0036

0.0036

Sm(ClO4)3·2(EBAAPS)·TMSO

24870

24000

21550

2470

23800

21450

6H5/2 ® 4F9/2

      ® 6P5/2

      ® 4I13/2

0.0052

0.0083

0.0046

0.9948

0.9917

0.9954

0.0361

0.0456

0.0340

0.5247

0.8400

0.4661

0.0026

0.0041

0.0023

 

Table-11: Thermoanalytical results of some mixed ligands complexes of lanthanide(III) nitrates with EBAAPS and TMSO

Complex

Sample wt. (mg)

Residual wt. (mg)

Ligand mass loss (%)

Residual (%)
~ 830ºC

140-170 ºC

250-370ºC

Theor.a

Exp.

Theor.b

Exp.

Theor.c

Exp.

La(NO3)3·(EBAAPS)·TMSO

Pr(NO3)3·(EBAAPS)·TMSO

Gd(NO3)3·(EBAAPS)·TMSO

Tb(NO3)3·(EBAAPS)·TMSO

14.52

16.90

18.30

20.70

2.91

3.54

3.98

4.65

12.92

12.88

12.63

12.60

12.78

12.60

12.40

12.33

59.62

59.47

58.32

58.18

59.30

59.26

58.09

57.93

20.24

21.10

21.99

22.66

20.10

20.98

21.76

22.49

aCalculated for loss of TMSO; bCalculated for loss of EBAAPS; cCalculated for lanthanide oxides (La2O3, Pr6O11, Gd2O3, Tb4O7)

 

 

All other tripositive lanthanide ions are paramagnetic due to the presence of 4f-electrons, which are effectively shielded by 5s2 and 5p6 electrons. The comparison of these observed values with those observed for 8-hydrated sulphate 14 and those calculated for uncomplexed ions16, indicates that the 4f-electrons do not participate in any bond formation in these complexes. The magnetic moments of these complexes reported herein are within the range predicted and observed in the compounds of paramagnetic ions as reported earlier17,18.

 

Infrared:

In the present complexes (Table 4) as expected the n(NH2) of the hydrazinic nitrogen of semicarbazide (~ 1622 cm-1) is absent in the infrared spectra of the  EBAAPS19. It has also been observed that the amide-II band is shifted towards the lower energy side compared to that of the semicarbazone. The effect is due to the electron density drift from the hydrazinic nitrogen20.The characteristic absorption of the carbonyl group in EBAAPS  is observed at ca. 1705 cm-121,22. In the complexes, this band is shifted toward lower energy in 1652-1645 cm-1 region (Table 4). The amide-II band in EBAAPS is observed at 1570 cm-1. In all the present complexes of lanthanides of EBAAPS, this band is also shifted towards lower wave numbers in 1540-1530 cm-1 region. This observation suggests coordination though the carbonyl oxygen atom. The strong band at 1605 cm-1 in the present EBAAPS apparently has a large contribution from the n(C=N) band in all the complexes as compared to the free ligand. Another strong band was observed at 1620 cm-1 due to azomethine (C=N) absorption. On complexation this band is shifted towards the lower frequency region, clearly indicating the coordination through the azomethine N-atom (23). In far infrared region the bands due to n(Ln-N)/ n(Ln-O) are also observed18,24.

 

Sulfoxides act as electron pair donor forming molecular adducts or complexes with a variety of acceptor molecules. Sulfoxides contain a “soft” sulfur and a “hard” oxygen, both of which can act as nucleophiles. Although both oxygen and sulfur coordinated sulfoxide complexes are known with transition and non-transition metal ions25, only oxygen coordinated sulfoxide coordination compounds are formed with the lanthanides26. In the infrared spectra of free TMSO, the (S=O) stretching vibration25-27 appears as a strong band at 1020 cm-1, while in the spectra of its coordination compounds it is shifted to 955-942 cm-1 (Table-4). The (C-S) stretching absorption in free TMSO occurs at 680 cm-1, which undergoes a slight positive shift on complexation. A negative shift of the (S=O) stretching frequency and a shift of the (C-S) stretching frequency towards a higher wave numbers are indicative of the decrease in the double bond character of the (S=O) bond and an electron shift from the aryl group to the sulfur atom of the ligand. The data thus suggests coordination from the oxygen atom to the TMSO. A very strong absorption attributed to phenyl stretching28 has been identified at 1079 cm-1 in the free ligand which does not undergo any significant change on complexation. It may be taken as an indication of the absence of coordination from the sulfur atom of the TMSO.

 

Anions:

In all the [Ln(NO3)3.(EBAAPS).TMSO] complexes, the occurrence of two strong absorptions at 1525-1505 cm-1 and 1295-1280 cm-1 region is attributed to n4 and n1 modes of vibration of the covalently bonded nitrate group, respectively suggesting that the nitrate groups lie inside the coordination sphere29,30. If the (n4 - n1) difference is taken as an approximate measure of the covalency of the nitrate groups30, a value of ~ 200 cm-1 for the complexes studied herein suggest strong covalency for the metal-nitrate bonding (Table-5). To identify the monodentate or bidentate nature of NO3- , we applied Lever separation method 31.A separation of 40-50 cm-1 in the combination bands (n1 + n4) in the 1800-1700 cm-1 region conclude the bidentate nitrate coordination. The bidentate nature of nitrato groups has been established by X-ray32 and neutron diffraction studies33. It is infrared, which indicates that the nitrate groups in these complexes are of bidentate nature. In case of [Ln(NCS)3.2(EBAAPS).TMSO]  complexes, it is difficult to establish unambiguously from the infrared spectra whether the thiocyanate group is N or S bonded to Ln3+ ions. According to the “soft” and “hard” concept of Pearson (34) one would expect the NCS- ion, in which ‘N’ is “hard”, to coordinate by that atom to “hard” acids like lanthanides , whereas S in the SCN- is “soft” and should therefore be the atom coordinated to class-B metals. The C-N stretching frequency in [Ln(NCS)3.2(EBAAPS).TMSO]complexes appears in 2050-2035 cm-1 region which lies on the border line for distinguishing between sulphur and nitrogen bonding in the thiocyanate, although the high relative intensity of the band in these cases suggests that the thiocyanate groups are N-bonded35,36. The C-S bond identified in 845-835 cm-1 region further confirms that the thiocyanate group is almost  N-bonded35,36. The (N-C-S) bending (n2) is also identified in these complexes (Table-6).The occurrence of two strong bands at ~ 1080 cm-1 and 620 cm-1 in the spectra of perchlorate complexes attributed to n3 and n4 vibrations of the ionic perchlorate suggest that the perchlorate group are present outside the coordination sphere in all the Ln(ClO4)3.2(EBAAPS).TMSO complexes. The presence of a very strong n3 band in the range of 1105-1085 cm-1 and strong narrow n4 band in 630-622 cm-1 in Ln(ClO4)3.2(EBAAPS).TMSO complexes is indicative of tetrahedral symmetry of the perchlorate ion which is not bonded to Ln3+ ions37,38. (Table 7).

 

Electronic specta:

Typical spectral data for the solutions of the present 4f-metal coordination compounds investigated in CH3CN are recorded in Table 8-10 and for comparison; data for an aqueous salt solution are also given. Lanthanum(III) has no significant absorption in the visible region. The absorption bands of praseodymium(III), neodymium(III), samarium(III), gadolinium(III) and dysprosium(III) in the visible and near infrared region appear due to transitions from the ground levels 3H4, 4I9/2, 6H5/2, 8S7/2 and 6H15/2 to the excited J-levels of 4f-configuration, respectively. Some red shift or nephelauxetic effect is observed in CH3CN solution of these coordination compounds. This red shift is usually accepted as evidence of a higher degree of covalency than existing in the aquo compounds47,48. In all the complexes marked enhancement in the intensity of the bond has been observed. This red shift of the hypersensitive bands has been utilized to calculate the nephelauxetic effect (b) in these chelate complexes. From the b-values the covalence factors (b1/2), Sinha parameter (d%) (metal-ligand covalency, per cent) and the covalency angular overlap parameter (h) have been calculated using the following expression39-41.

b1/2 = ½ [(1-b)1/2]

d(%) = [(1-b)/b] x 100

h = [(1-b1/2)/b1/2

 

The positive values for (1-b) and d% in these coordination compounds (Tables 8-10) suggest that the bonding between the metal and the ligand is covalent as compared with the bonding between the metal and an aquo ion. The values of parameter of bonding (b1/2) and angular overlap parameter (h) were found to be positive indicating covalent bonding.

 

Thermal studies.

Ln(NO3)3.(EBAAPS).TMSO ( Ln = La, Pr , Gd or Tb):

The thermoanalytical results of these complexes are presented in Table 11. The pyrolysis curves of [Ln(EBAAPS).TMSO.(NO3)3] ( Ln = La, Pr, Gd or Tb) show that the complexes are anhydrous in nature. The weight losses in 130 – 160 oC temperature region is attributed to the loss of TMSO molecule. Further the thermal curves show that at ~ 240 oC, the complexes start to lose mass with a partial evaporation of organic ligand up to temperature of 380 oC. The residues obtained after heating at ~ 830 oC, the constant weight which is very close to that expected for lanthanide oxides (La2O3, Pr6O11, Gd2O3 or Tb4O7)42,43.

 

Ln(NCS)3.2(EBAAPS).TMSO ( Ln = La, Sm or Tb):

The thermal results of these complexes are presented in Table 12. The TG-curves of the complexes clearly indicate the absence of water molecule in these complexes. All the pyrolysis curves behave similarly and show that there is a weight loss in 125 – 160 oC which follow the loss of TMSO. At 220 – 250 oC, a loss of 44.10 – 45.82% is observed which corresponds to one mole of EBAAPS followed by a further loss of 73.10 – 74.40 % in 270 – 300 oC temperature region showing the complete loss of FAAPS. The lanthanide oxide (La2O3, Sm2O3 or Tb4O7) was finally formed at ~ 840 oC. Above this temperature , there is no measurable change in weight42,43.

 

Ln(ClO4)3.2(EBAAPS).TMSO ( Ln = Nd, Dy or Ho):

Thermoanalytical results of these complexes are summarized in Table 13. The thermograms of the complexes indicate that during 120 – 160 oC temperature region, the weight loss (15.42 – 15.58%) is due to complete evaporation of TMSO. At 210 – 235 oC, a loss of 40.70 – 41.26 % is observed which corresponds to one mole of the FFAAPS followed by a further loss of 66.08 – 67.24 % in 250 – 280 oC temperature region showing the complete loss of FFAAPS. The lanthanide oxide Ln2O3 ( Ln = Nd, Dy or Ho) was finally formed at ~ 835 oC. Above this temperature there is no measurable change in weight42,43

 

Antimicrobial studies:

Several workers have reported the antimicrobial properties of lanthanide (III) complexes44-53. The literature concerning 4-aminoantipyrine derived complexes is richer and more diverse than other pyrazole rings is the higher biological activity. 4-Aminoantipyrine derived complexes show antimicrobial,  antimalarial and antitumorous activity. Raman et al 3,45- 54 have reported the antimicrobial activityof Schiff bases of 4-aminoantipyrine derivatives . The complexes showed higher inhibitory activity than the ligands and have higher activity than ampicillin, except for K.pneumoniae and P.aeruginosa.. Less is known about the antimicrobial activity of lanthanide (III) complexes derived from semicarbazones.. Antibacterial and antifungal activities of some selected lanthanide (III) complexes of EBAAPS and TMSO are presented in Tables 14 and 15. The results show that the semicarbazone and lanthanide (III) complexes have inhibitory action against all the strains. Thus it is assumed that the coordination of metal ions with EBAAPS and TMSO varied the conjugated system of the ligand and antibacterial and antifungal activities changed. In other words, the complexes probably have enhanced activities when they enter microorganism cells to act with DNA in vivo55

 

Stereochemistry:

[Ln(EBAAPS)2.TMSO(NO3)3] (Ln = La, Pr, Nd, Sm, Gd, Tb, Dy or Ho):

The molar conductance data indicate that the nitrato complexes in nitrobenzene behave as non-electrolytes. Thus, all  the three NO3- ions are present in coordination sphere. The molecular weight measurements cryoscopically determined in freezing nitrobenzene indicate the monomeric nature of these coordination compounds. Infrared data reveals the bidentate nature of NO3- in these coordination compounds. The organic ligand EBAAPS behaves as neutral tridentate (N,N,O) and TMSO is oxygen-donor in these coordination compounds. Thus in these coordination compounds the central metal ion is surrounded by 8-oxygen atoms and 2-nitrogen atoms and thus produce a coordination number ten in these coordination compounds (26) (Fig.3a).

 

[Ln(EBAAPS)2.TMSO(NCS)3] (Ln = La, Pr, Nd, Sm, Gd, Tb, Dy or Ho):

The conductance, molecular weight  and spectral data indicate that the lanthanide ion is surrounded by seven nitrogen atoms ( three of isothiocyanate ions and four from EBAAPS), two oxygen atoms of  >C=O moiety of EBAAPS and one oxygen of TMSO. Hence a coordination number ten for all these metal ion has been suggested in these coordination compounds (26) (Fig.3b).

Table 12: Thermoanalytical Results of Some Mixed Ligand Complexes of Lanthanide (III) Isothiocyanate with EBAAPS and TMSO

Complex

 

Sample wt.

(mg.)

Residual wt.

(mg)

Ligand Mass Loss (%)

Residual (%)

125 – 160oC

220-250oC

270-305oC

~ 830oC

Theor.a

Exp

Theor.b

Exp

Theor.c

Exp

Theor.d

Exp

 

La(NCS)3.2(EBAAPS).TMSO

14.60

1.96

16.96

17.28

43.34

44.10

73.71

74.40

13.68

13.42

Sm(NCS)3.2(EBAAPS)TMSO

12.40

1.76

16.80

17.08

44.92

45.82

73.04

73.68

14.47

14.19

Tb(NCS)3.2(EBAAPS).TMSO

17.10

2.59

16.68

16.88

44.59

45.20

72.50

73.10

15.44

15.16

a – Calculated for loss of TMSO; b – Calculated for loss of one mole of EBAAPS

c – Calculated for total loss of EBAAPS; d – Calculated for lanthanide oxides (La2O3,  Sm2O3,  Tb4O7)

 

Table 13:Thermoanalytical Results of Some Mixed Ligand Complexes of Lanthanide (III) Perchlorate with EBAAPS and TMSO

Complex

 

Sample wt.

(mg.)

Residual wt

(mg)

Ligand Mass Loss (%)

Residual (%)

130 – 160oC

210-235oC

250-280oC

~ 835oC

Theor.a

Exp

Theor.b

Exp

Theor.c

Exp

Theor.d

Exp

 

Nd(ClO4)3.2(EBAAPS)TMSO

12.60

1.57

15.29

15.58

40.89

41.26

66.48

67.24

12.72

12.48

Dy(ClO4)3.2(EBAAPS)TMSO

14.00

1.90

15.08

15.42

40.32

40.82

65.57

66.10

13.92

13.58

Ho(ClO4)3.2(EBAAPS)TMSO

15.80

2.18

15.05

15.40

40.25

40.70

65.44

66.08

14.08

13.84

a – Calculated for loss of TMSO; b – Calculated for loss of one mole of  EBAAPS

c – Calculated for total loss of EBAAPS; d – Calculated for lanthanide oxides, ( Nd2O3,  Dy2O3,  Ho2O3)

 

Table-14    Antibacterial activity of EBAAPS and  [Ln (EBAAPS)2.TMSO(NCS)3]

Compound

Escherichia coli,

Staphylococcus aureus,

Bacillus subtilis,

S.pneumoniae

Pseudomonas

aeruginosa

EBAAPS

+ +

+

+ +

+ +

+

[La(EBAAPS)2.TMSO (NCS)3]

+ +

+ +

+ + +

-

-

[Pr (EBAAPS)2.TMSO (NCS)3]

+ + +

+

+ +

+ + +

+

[Nd(EBAAPS)2.TMSO (NCS)3]

+ +

+

+ +

+ +

_

[Sm (EBAAPS)2.TMSO (NCS)3]

+ + +

++

+ +

+ + +

+

[Tb(EBAAPS)2.TMSO (NCS)3]

+ +

++

+ +

+ +

+

 

Table 15 Antifungal activity of EBAAPS and [Ln (EBAAPS)2.TMSO (NCS)3]

Compound

Penicillium notatum

Aspergillus niger

EBAAPS

+

+

[Pr(EBAAPS)2.TMSO (NCS)3]

+ +

+ +

[Tb(EBAAPS)2.TMSO (NCS)3]

+ +

-

[Dy(EBAAPS)2.TMSO (NCS)3]

-

+ +

 

 

[Ln(EBAAPS)2.TMSO](ClO4)3 (Ln = La, Pr, Nd, Sm, Gd, Tb, Dy or Ho):

These coordination compounds dissociate in nitrobenzene and behave as 1:3 electrolytes. This is due to poor coordinating ability of ClO4- toward the lanthanides. Infrared spectral data further confirm the ionic nature of perchloric ions, tridentate nature of EBAAPS and TMSO as oxygen donor ligand. Hence in these coordination compounds the trivalent lanthanide ions are bonded by four-nitrogen atoms and three oxygen atoms and produce a coordination number 7 in these compounds (26) (Fig,3c.).

 

Fig. 1. 4[N-(4'-Ethylbenzalidene)amino]antipyrine semicarbazone (EBAAPS)

 

Fig. 2. General structure of [Ln(EBAAPS).TMSO(NO3)3]

 

[Ln(EBAAPS)2(NCS)3.TMSO]

 

[Ln(EBAAPS)2.TMSO](ClO4)3]

Fig. 3. Proposed structures of  Lanthanide (III) complexes of EBAAPS and  TMSO

 

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Received on 13.02.2010        Modified on 02.03.2011

Accepted on 25.03.2011        © AJRC All right reserved

Asian J. Research Chem. 4(6): June, 2011; Page 908-916