Synthesis and Spectroscopic Studies of Mixed 2-(N-Salicylidene)-5-Chlorobenzophenone Dialkyldithiophosphato Derivatives of Antimony(III)

 

K. Prasada Rao1*, M. S. Singh2 and K. Santhakumari1

1Dept. of Chemistry, Bapatla Engineering College, Bapatla (Autonomous)-522101, Andhra Pradesh, India.

2Professor, Banarus Hindu University, Varanasi, (U.P.) India.

*Corresponding Author E-mail: prasad17467@gmail.com

 

 

ABSTRACT:

Some Antimony(III) derivatives of schiff base derived from 2-(N-salicylidene)-5-chlorobenzophenone have been synthesized by the reaction of dichloro and chlorobis 2-(N-salicylidene)-5-chlorobenzophenone antimony(III) with ammonium dialkyldithiophosphates in benzene (prepared insitu) in 1:2 and 1:1 molar ratios, respectively. All these compounds are characterized by elemental analysis, molecular weight measurements and spectroscopic (IR, 1H and 31P NMR) studies.

 

KEY WORDS: Schiff base ligands, alkyldithiocarbonate, dialkyldithiophosphato

 

 

INTRODUCTION:

Metal chelate Schiff complexes have continued to play the role of the most important steriochemical model in main group co-ordination chemistry due to their preparative accessibility, diversity and structural variability. The complexes of Antimony (III) with Schiff base ligands containing sulphur and nitrogen as donor ligands have been studied extensively1-4. The metal complexes derived from 2-(N-salicylidene)-5-chlorobenzophenone are reported to act as potential antianxiety5, 6 and antiepileptic7 agents. Previously we have reported mixed 2-(N-salicylidene)-5-chlorobenzophenone alkyldithiocarbonate derivatives of antimony (III) 4. In continuation of earlier work, we report here in the synthesis and characterization of some mixed 2-(N-salicylidene)-5-chlorobenzophenonedialkyldithiophosphato derivatives of antimony (III). These complexes are very interesting due to their fascinating structure8.A few antimony compounds are known for their technical uses in catalytic prossess9, 10.

 

MATERIALS AND METHODS:           

The mixed ligand complexes of antimony (III) have been synthesized by the reaction of chloro derivatives of [2-(N-salicylidene)-5-chlorobenzophenone] antimony (III) with ammonium salt of dialkyldithiophosphates.

 

Reaction between chlorobis [2-(N-salicylidene)-5-chlorobenzophenone] antimony (III) and ammonium salt of diethyldithiophosphate in 1:1 molar ratio:

The chlorobis [2-(N-salicylidene)-5-chlorobenzophenone] antimony (III) (1.50g, 3.95mmol)  and ammonium salt of diethyldithiophosphate (0.38g, 3.95 mmol) are mixed in dry benzene and stirred with heating on magnetic stirrer fitted with a heating plate for about 2hours. Precipitated ammonium chloride was removed by filtration, followed by removal of the solvent under reduced pressure giving the desired product (yield 1.40g). These yellow solids are purified by crystallization from benzene-petroleum ether (40-600C) mixture.

 

All the other mixed derivatives of antimony (III) are synthesized by the same route. The pertinent data of these complexes is listed in table 2.

 

Where n=1, R=Et, Compd. (1); n=2, R=Et, Compd. (2); n=1, R=i-Pr, Compd. (3); n=2,R= i-Pr, Compd. (4); n=1, R= i-Bu, Compd. (5); n=2, R= i-Bu, Compd. (6).

 

 

RESULT AND DISCUSSION:

The mixed derivatives are synthesized by the reaction of dichloro and chlorobis 2-(N-Salicylidene)-5-chlorobenzophenone antimony (III) with ammonium dialkyl ditiophosphates in benzene in 1:2 and 1:1 molar ratios, respectively.

 

The mixed derivatives are synthesized by stirring the reactions in dry benzene for about 3 hours. The NH4Cl was filtered off and the compound was isolated and purified by crystallization from benzene-petroleum ether mixtures. All these complexes are yellow crystalline solids, soluble in common organic solvents and are monomeric in benzene.

 

Characteristic bands in the IR spectra of the present mixed ligand complexes have been assigned by comparison with the spectra of the corresponding tris-(dialkylditiophosphate) antimony (III) 11 and tris 2-(N-salicylidene)-5-chlorobenzophenone antimony(III) complexes. The bands in the region 1025-950 cm־1 are assigned to (P)-O-C and P-O-(C) stretching modes, respectively11. A strong band observed in the region 670-625 cm־1 due to υ (P=S) in the spectra of dialkyldithiophosphoric acids and their ammonium salts is shifted to the lower frequencies (by ~25 cm־1) in the corresponding antimony (III) derivatives. This indicates a strong bidentate chelation of ligand with antimony (III).11 IR studies on tris [2-(N-salicylidene)-5-chlorobenzophenone] antimony (III) showed that the bands present in the region 460-455 cm־1 and 355 cm־1 and 1600 cm־1 assignable due to co-ordination of (-OH) and (C=N) groups to antimony, indicate bidentate nature of this moiety.

 

The 1H NMR spectra of these complexes in CDCl3 show characteristic resonances due to alkoxy and phenyl protons (Table 1). A singlet observed at δ 3.10 -3.60 ppm in the parent dithio acid assigned for –SH proton, found to be absent in spectra of the corresponding mixed ligand antimony (III) complexes indicating deprotanation of –SH group and formation of Sb-S bond12. The ethyl protons exhibit a triplet at δ 1.40 ppm due to CH3 protons and a quarte at δ 4.25 ppm due to –OCH2 protons showing integration for three protons and a septet centered at δ 4.75 ppm due to –OCH protons. The isobutyl group displays as a doublet at δ 0.98 ppm due to CH3 protons, a multiplet centered at δ 1.95 ppm due to CH protons and a doublet at δ 3.90 ppm due to –OCH2 protons. A multiplet of phenyl protons is present in region δ 6.80-8.10 ppm integrated for twelve protons.

 

The number of 13C NMR signals corresponds to the number of chemically different carbon atoms present in these compounds. There is no significant chemical shift for the various 13C signals present in the mixed ligand complexes of antimony(III) as compared to the corresponding tris(alkyldithiocarbonate) antimony(III)and tris[2-(N-salicylidene)-5-chlorobenzophenone] antimony (III) complexes3. The resonance at δ 160.0 ppm has been assigned to azomethine carbon. The resonances at δ 47.43, δ 15.93 ppm are displayed due to OCH2 and CH3 carbons of ethyl group and at δ 64.78, δ 18.05 ppm due to OCH and CH3 carbons of isopropyl group. The resonances due to OCH2, CH and CH3 carbons of isobutyl group have been assigned at δ 47.41, δ 28.74 and δ 18.35ppm respectively.

 

Thus based on the elemental analysis molecular weight measurements and spectroscopic studies a bidentate mode of attachment of the both types of ligands to the metal atom is proposed.

 

Fig.-1 Compound-5

 

The mixed derivatives show a distorted octahedral geometry if the presence of the stereochemically active lone pair is also considered in the capping position (Fig. 1 and 2) with pseudo seven coordinated structures.

 

Fig.-2 Compound-6

 

Table 1: NMR spectral data of mixed 2-(N-salicylidene)-5-chlorobenzophenone dialkydithiophosphate derivatives of Antimony (III)

S. No

Compounds

1H NMR (δ ppm)

31P NMR(δ ppm)

1

[(C2H5O)2PSS]2Sb[(OC6H4C(H)=NAr]

6.90-7.85(m, 12H. Ph); 4.0(s, 1H, =CH);

1.45, (t, 12H, CH3); 4.32 (q, 8H. OCH2).

92.5

2

[(C2H5O)2PSS]Sb[(OC6H4C(H)=NAr]2

7.0-7.80(m, 24H. Ph); 3.90(s, 2H, =CH);

1.48, (t, 6H, CH3); 4.28(q, 4H. OCH2).

93.0

3

[(i-C3H7O)2PSS]2Sb[(OC6H4C(H)=NAr]

6.85-8.10(m, 12H. Ph); 3.85(s, 1H, =CH);

1.64, (d, 24H, CH3); 4.74 (m, 4H. OCH).

92.8

4

[(i-C3H7O)2PSS]Sb[(OC6H4C(H)=NAr]2

6.80-8.0(m, 24H. Ph); 3.92(s, 2H, =CH);

1.62, (d, 12H, CH3); 4.70 (m, 2H. OCH).

91.3

5

[(i-C4H9O)2PSS]2Sb[(OC6H4C(H)=NAr]

6.95-7.90(m, 12H. Ph); 3.70(s, 1H, =CH);

1.05, (d, 24H, CH3); 1.90 (m, 4H. CH);3.90, (q, 8H, OCH2)

93.2

6

[(i-C4H9O)2PSS]Sb[(OC6H4C(H)=NAr]2

7.05-8.10(m, 12H. Ph); 3.68(s, 2H, =CH);

1.0, (d, 12H, CH3); 1.92(m, 2H. CH);3.92,(q, 4H, OCH2)

92.6

 

Table 2: Reactions between chloroderivatives of [2-(N-salicylidene)-5-chlorobenzophenone]antimony (III) and dialkyl dithiophosphates in different stoichiometric ratios

S.

No

Reactants(g)

Molar

 ratio

Product* (g)

Yield

%

M.P  (0C)

Mol. Wt. Found/ (Calcd)

Analysis: % Found (Calcd)

Sb(III) Complexof L

Ligand

C

H

Sb

N

S

1

L2SbCl

(1.50)

H4NS2P

(OC2H5)2

(0.38)

1:1

L2Sb[S2P

(OC2H5)2]

(1.40)

95

126

970

(976.35)

53.08

(54.07)

3.61

(3.68)

12.22

(12.46)

1.34

(1.43)

06.51

(06.55)

2

LSbCl2

(1.10)

H4NS2P

(OC2H5)2

(0.86)

1:2

LSb[S2P

(OC2H5)2]2

(1.55)

92

120

822

(816.63)

40.76

(41.14)

4.00

(4.04)

13.81

(14.90)

1.69

(1.71)

15.70

(15.67)

3

L2SbCl

(1.75)

H4NS2P

(OC3H7)2

(0.50)

1:1

L2Sb[S2P

(OC3H7)2]

(1.82)

89

127

1014

(1004.41)

54.80

(54.95)

3.60

(3.98)

12.21

(12.11)

2.81

(2.79)

06.31

(06.37)

4

LSbCl2

(1.12)

H4NS2P

(OC3H7)2

(1.00)

1:2

L2Sb[S2P

(OC3H7)2]2

(1.76)

94

117

874

(886.07)

42.31

(43.33)

4.70

(4.62)

13.85

(13.79)

1.62

(1.58)

14.32

(14.50)

5

L2SbCl

(1.46)

H4NS2P

(OC4H9)2

(0.47)

1:1

L2Sb[S2P

(OC2H5)2]

(1.50)

96

119

1039

(1041.54)

54.30

(55.30)

4.19

(4.22)

11.50

(11.68)

1.27

(1.34)

06.01

(06.14)

6

LSbCl2

(1.10)

H4NS2P

(OC4H9)2

(1.12)

1:2

L2Sb[S2P

(OC2H5)2]

(1.64)

90

120

951

(956.94)

44.86

(45.14)

5.14

(5.12)

12.66

(12.72)

1.32

(1.46)

13.20

(13.37)

L= -OC6H4C (H) =NC6H4 (Cl) COC6H5                  * Yellow solid

CONCLUSION:

On the basis of the work citied above it becomes apparent that the field of antimony(III) Chemistry has enjoyed a very fast development in the last three decades. There is a rich coordination chemistry and a remarkable diversity of  structural types in this area. The sulphur ligands like dialkyldithiophosphates have been utilized as chelating agents in the synthesis of Sb(III). Emphasis is based on their synthesis, spectroscopic studies, reactivity and coordination patterns.

 

AKNOWLEDGMENT:

The Author is highly thankful to Prof. M.S. Singh, Banarus Hindu University, Varanasi for his valuable academic guidance throughout the work.

 

REFERENCES:

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7.       De Angelis L. 1979, Drugs of Today, 15, 107.

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9        Mc Auliffe C. A. in comprehensive coordination chemistry,eds. Wilkinson G., Gilla R. D. and Mc cleverty J. A., 1987, Pergaman, Oxford, 3.

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Received on 12.09.2012        Modified on 23.09.2012

Accepted on 27.09.2012        © AJRC All right reserved

Asian J. Research Chem. 5(10): October, 2012; Page 1225-1228