Indian Journal of Chemistry Vol. 38A, November 1999, pp.11 50- 1158

Stereochemical, thermal and biochemical aspects of dioxomolybdenum(VI) and manganese(II) complexes

Ran Vir Singh' , Neeti Gupta & Nighat Fahmi Department of Chemi stry, Uni versi ty of Rajasthan, Jaipur 302 004, India

Received 19 April 1999; revised 24 August 1999

Stereochemical, thermal and biochemical studies of molybdenum(VI ) and manganese(II ) complexes prepared by the reactions of dioxobi s (2,4-pentanedionato) molybdenum(VI ) and hydrated manganese dichloride with 2-hydroxy-N-phenylbenzamide, 1-[2-hy­droxy-pheny l)-l-N-phenylamino]hydrazine carboxa mide and 1-[2-hydroxyphenyl)- I-N-phenylamino]hydrazine carbo-thioamide in different stoichiometri es have been reported. An attempt has been made to establi sh the structures of the resulting complexes on the basis of elemental analysis , mo lecular weight determi nations magneti c measurements, IR , IH and IJC NMR, UV and ESR spectral studi es.The resu lts of thermogravimetric and dilTerential thermal analysis of the compl exes suggest first order reaction. The X-ray powder diffraction pattern of representative compounds confirm the orthorhombic crystal system. The ant imicrobia l screening data of ill vitro studi es indicate that the metal chelates are more potent than the parent ligands. The ill vivo studies orthe representative ligands and their corresponding metal derivatives indicate them to be effective in cont rolling the leaf spot disease of brinjal plant caused by A.

alternata . The antifertility screening data indicate the anti-androgenic natu re of the complexes.

In dioxo compl exes of dO transition metals, favourable pn-dn orbi tal interactions between the n-base oxoligands and 1t-ac id metal centers are opti mi zed when a cis ge­ometry is adopted; accordingly, a ll such compl exes ex­hibit cis geometries l

.2 . The cis-[Mo02F+ center domi­

nates the c hemi stry of dO Mo(VI) complexes' and par­ticipates in many oxygen a tom transfer reac tion s46

.

Molybdenum has a major role as trace e lement7 and is an indispensable constituent of enzymes that are involved in the function of nitrogen fixing nitrogenaseR

• On the other hand , the coordin ation chem istry of manganese complexes with nitrogen and sulphur/oxygen donor moi­e ti es is of inte res t as these complexes give information about the functional ro le of manganese(JI) in biological systems9. IO. Several manganese co mplexes are known to ex hibit ant ifunga l act ivity, e.g., Maneb (manganous eth­ylene bisdithiocarbamate) has been successfully used aga in st a wide variety of diseases, particularly of fruits and vegetables I I. The ro le of metal chel ates in a ll as­pects of biological studies has ga ined considerable im­portance, as they provide valuable approaches to the metabolic studi es, ox idative phosphorylation, transm­ethylation and principles of chemotherapy. Azomethines, bonding through nitrogen and oxygen or sulphur atoms to the centra l metal ion form an important class of bio­logically active ligand s and provide model s for metal­ligand binding sites in several enzymes l2

. Thus, the strik-

ing structural features, d iverse stereochemistry and ap­preciable biochemical as well as com merc ial applica­tions of dioxomolybdenum (VI) as well as manganese(II) complexes have stimul atedl us to synthesize and charac­terize their chelates with 2-hydroxy-N-phenylbenzam ide (HPOH), 1-[(2-hydroxyphenyl )-I-N-phenylamino» hy­dra z in e -c a rb oxa mid e (HOnNnOH )and 1-[(2 -

hydroxypheny I)-I-N-pheny lamino ]hydrazine-ca rbo­thioamide (HonNnSH)].

rQY0H

~c=o I

NH

I

@

HI'OH -~ -.;:--

SINGH e/ al.: STUDIES ON Mo(VI) & Mn(" ) COMPLEXES 115 !

Materials and Methods Glass apparatus with standard quick- fit joints was

used throughout. Adequate precautions were taken to exclude moisture from the system particularly for the synthes is of molybdenum(VI) compl exes. The chemi­cals and solvents used were dried and purified by stan­dard meth ods before u se. Oioxobis (2,4-pentanedionato)molybdenum(VI) was prepared accord­ing to the literature method 13.

Preparation of ligands Hydrazine carboxamide and hydrazin e

carbothioamide of2-hydroxy-N-phenylbenzamide were pre pared 14 by the condensation of HPOH with semicarbazide hydrochloride (in presence of sodium ac­etate) and thiosemicarbazide respectively in I : I molar ratio in refluxing ethanolic medium. On cooling, the crystals formed were filtered, recrystallised in the same solvent and finally dried in vacuo. HPOH, brown solid , m.pt., 134 °C; HOnW'OH, off white solid, m.pt. , 110 °C and HonNnSH, light pink solid, m.pt., 125 °C.

Synthesis of the complexes The unimolar and bimolar reac tions of hydrated man­

ganese dichloride with monofunctional bidentate ligand HPOH and unimolar reaction with bifunctional triden­tate ligands (HonNnOH and HonNnSH) were carried out in methan ol. To a weighed amount of MnCI 7 .4H1 0 (0.30-0.60 g, 1.51-3.03mmol) in methanol (50ml), w-as added the calculated amount of the li gand (0.32-1.29 g, 1.50-6.05 mmol) in I: I or 1:2 molar ratio.

For the molybd enum(VI) complexes, a weighed amount of dioxobis(2,4-pentaned ion ato) molybdenum (VI) (0.24-0.50 g, 0.73 - 1.53 mmol) and ligand (0.31-0.45 g, 1.45-2.11 mmol) in 1:2 or I: I molar ratios were mixed in dry methanol (50ml). The reaction mixture was refluxed for 12-14 h on a fractionating column. After the completion of the reaction , the excess solvent was

distilled off and the product was dried in vacuo . The complexes were washed with cyclohexane and recrystallised from methanol to obtain the pure product.

Conductivity measurements in dry OMF were made on a Systronics Conductivity Bridge type 305 and mo·· lecular weights were determined by the Rast camphor method. IR spectra (as KBr di sc) were recorded on a Perkin-Elmer 577 grating spectrophotometer in the range 4000-200 cm-I. The electronic spectra were recorded in methanol on a UV -160A, Shimadzu spectrophotometer in the range 200-600nm. IH NMR spectra were recorded on a Jeol FX-90Q spectrometer in OMSO-d

6 using TMS

as the internal standard . i3C NMR spectra were recorded in MeOH at 22.49 MHz. The magnetic susceptibilities of the powdered samples were recorded on a vibrating magnetometer mode l 155 . The ESR spectra of the samples were recorded on a Varian -E-UX band spec­trometer at room temperature . The thermal studies (TG and OTA) were recorded using Rigaku - 8150 therma l analyser attached to NEC minicomputer for data pro­cess ing. The heating rate was 10K min-I in a static air atmosphere. For OTA, a Pt crucible was used with oc-alumina (99 % pure) as the reference material. Pow­der XRO measurements were performed on powder samples using Phillips X-ray diffractometer (mode PW 1730) having Cu-Ku target operated at 30 KV and 20 MA. Filtered Cu-Ku radiation was used to obtain the diffraction patterns for most of the samples . The diffrac­tion data were refined using a least-squares refinement computer program to obtain structural parameters. The program essentially uses the least-squares method of fit­ting of d"kf values for the different reflections. The inten­sity of Cu-Ku radiation diffracted from the powder speci­men was detected by a solid state detector and recorded as a function of 28, where 8 is the angle of incidence.

Molybdenum(VI) was determined gravimetrically as bis(8 -hydroxyqu i nol i nato) dioxomo I ybdenu m(VI). Manganese(II) was estimated complexometrically with EOTA using Eriochrome Black T as an indicator. Nitro­gen and sulphur were determined by the Kjeldahl 's and Messenger's methods, respective ly. Chlorine was est i­mated by Volhard's method.

Antimicrobial screening Bioefficacy of the parent ligands and their complexes

was tested in vitro for the growth inhibiting potential against various fungal and bacterial strains using spore germination method l 5 and paper disc technique l6 respec­tively. Fungal s trains Alternaria alternata ,

11 52 INDI AN J CHEM, SEC. A, NOVEMB ER 1999

Table I - Physical properties and analyt ica l data of the co mpl exes

Complex Colou r Found (Calc.) % Mol Wl.

N S M CI Found

(Ca lc.)

MnCI(HPO) HP (C11HIIP 2N) Li ght brow n 120 4.25 (4.37) 16.90 ( 17.04) 11.1 4 ( 11.09) 339 (320)

Mn (HPO)2 (C2(,H2cP4N) Dark brown 127 5.62 (5.84) I I. 19 ( I U 8) 495 (479)

Mn(Hp)(O"N"O) (CI4H1P2N4) Li ght brown 145d 16.27 ( 16.43) 15.7 1 ( 15.99) 362 (341)

Mn(Hp )(O"N"S) (C 1. H1P1N.) Choco late 130 15.24 ( 15.69) 8.6 1 (8.98) 14.93 ( 15.27 ) - 372 (357)

MoO/ HPO)z Green 233d 4 .88 (5.07) 16.99 ( 17.38) 563 (552)

Mo02(O"N"O) Li ght green 220d 13.63 ( 14. 14) 23.75 (24.22) 4 10 (396)

MoOZ<O" N" S) Brown black 225 13. 16 ( 13.59) 7.59 (7. 78) 23.02 (23.28) - 428(4 12)

Helminthosporeum gramineum and bacte ria l stra ins Sta­phylococcus en/reus and Xa nthomonas compestris were used . After assess ing ill vitro resu lts of antifungal screen­ing data of li gands and the ir metal compl exes some rep­resentati ve ligands and the ir respect ive complexes have a lso been screened ill vivo to study the ir potency on crop p lants, e.g., brinja l (leaf spot caused by A. alternata) using Percent Di sease Inc idence (POI) technique l

) . T he data were ana lysed stati sti cally and di sease contro l %

was assessed .

Sum o f score of in fec led leaves x 100 PDI =

TOla l nu mber of leaves observed x Maxillluill rali ng o f Ihe sca le

In thi s method, observations were recorded by di ffe r­ent plots. For studying the effi cacy of the I igand and its

complex under in vivo conditi on, fi e ld experiments were laid out in randomi zed block des ign with three replica­tions. T he brinj a l plants were ra ised in each plot. Three compounds with a standard fung ic ide, viz ., Bovistin [2-(methoxycarbamoy l)benzimidazole] were tried in addi­tion to negati ve control (water spray).

Thirt y fi ve d ays aft e r sow in g, th e pl a nt s we re innocul ated artifi c ia ll y by spray ing half litre o f coni d ia l suspension per plo t. The conidi a l suspension was pre­pared by cru shing infected leaves in one litre of water. The innocul ati on was done late in the evening. The first spray o f respecti ve fung ic ide was given when the d is­ease sy mptoms were first seen and the spray was repea ted afte r 10 days. Disease intens ity was recorded 10 days after first spray by us ing a d isease scale oro-so The data were ana lysed stati stica ll y and d isease contro l (%) was

assessed .

Antifertility aCTivity Animals were housed in po lypropylene cages mea­

suring 12"x I 01x8" under controlled environmental con­

ditions and fed with rat feed pellets and free access to watch. The first group (A) served as veh icle (o li ve o il)

treated contro ls. In the second g roup (B) the ligand (HPOH) (SOmg/kg body weigh t suspended in 0 .2 ml o l­ive oil ) was given orall y fo r a period o f sixty days. T he a nim a ls of third , fourth , fifth , s i xth a nd seventh (C ,D,B,F,G) groups were g iven the same dose of com­

p ound s, Mn (HPO)2' M o02( HPO) 2' HonNnS H , Mn(Hp)(OnNnS) and M oOo(onNns ) fo r the similar

period. The animals were screened fo r fe rti lity test and autopsied for deta iled patholog ical and b iochemica l stud­ies . Reproducti ve organs were excised , b lotted free of blood , weighed and f ixed in Bouin 's fl uid for hi sto logi­

cal studies.

Results and Discussion T he reac ti o ns o f d ioxob is(2,4-pe nt a ne di o na to)

molybdenum(V I) with monofu nct ional bidentate ligand (HPO H) in 1:2 molar rat ios and with bi functional tri­dentate ligands (HonNnOH and Ho nNnS H) in I : I mo­

lar rati o have been carri ed out in refluxi ng methanol. T he reacti on proceeded with the li beratio n of two mol­ecules of 2,4-pentaned ione. However, the reactions be­tween manganese d ichl ori de tetrahydrate and monofu nc­tional bidentate ligand (HPOH) in I: I and 1:2 molar ra­tios and with bifuncti onal tridentate ligands (Ho nNnOH and HonNnS H) in I : I molar ratio resu lted in the suc­cessive replacement of chl orine by the ligands . The re­sulting so lids are non-elec tro lytes as evidenced by their

.101.-

--.(

SINGH el al .: STUDIES ON Mo(VI) & Mn (lI ) COMPLEXES 115 3

Table 2 - 'H and iJC NMR spectra l data (8, ppm) or li gands and their metal complexes

' 1/1 ." IV ~

Compo -OH (bs) 0-N H(bs)

HPOH 12.08 10.56

MoO/ HPO)2 10.50

HonNnOH 12. 16 10.42

Mo%nNno) 10.88

HonNnSH 12.24 10.60

Mo02(on Nn S) 10.80

AmidorThio10 carbon >C=N

HonNnOH 168.60 157 .72

Moo2(onNno) 16 1. 5 149.82

HonNnSH 175.82 162.9 1

Mo%nNns) 168.78 155 .76

o 100 200 300 400 500

. Temp. I 0 ( )

Fi g. 1 - TGA Curv~s (a) Mn(H20 )(O"NnS) , and (b) MoO/ onN" S)

molar conductance va lues of I 0-15 ohm-I cm2 mol -I of

their 10-3 M soluti ons in dry DMF. These are solubl e in MeOH, DMSO and DMF. The magnetic moment va lues of manaanese derivatives were in the range 5.9 ± 0 . 1 <:>

BM, suggesting a high-spin state for these complexes. T he dioxomolybdenum(Vl) complexes were found to be diamagnetic as expected for 4cfO configurati on. The ir magnetic susceptibilities lied in the range (0.3-0.8 x 10-6) cgs units. The physical and analyt ical data of these

complexes are compiled in Table I .

-NH(bs) -N H2(bs) Aromatic(m)

8.40-6.80

8.64-7 . 12

10.00 2.70 R.24-6.96

2.45 8.56-6 .72

10.32 3.20 8.32-6.80

2.56 8.40-6.88

Aromati c carbon

160.36,137.70,1 35.72. 128. 12, 127.44,

126.06, 122.63 , 120.56, 118.52 , 11 6.4 1

154.45, 137.39, 133.60, 128.50, 127.15 ,

124.1 7, 120.76 , 11 9.02, 11 6.96 , 11 6.86

155.87 , 137.06 , 132.68 .. 129 .25, 128. 13,

123 . 19,121.40, 120.05,119.72, 118.59

146.62 , 137.23 , 132.84, 129. 15, 127.9 1,

123.4 1,120.22, 11 8.26,1 16.53 , 11 6.42 .

a

•

100 200 300 400 500 600

Ttmp. I • ( 1

Fig. 2 - DTA curves: (a) Mn(Hp)(OnNnS) , and (b) Mo0

2( O" N"S)

Spectral studies In the IR spectra of ligands broad bands observed at

3400-3200 cm-! are ass igned to the phenolic OH group .

These bands di sappeared in the case of complex es in­dicating the possible loss of proton on comple xat ion a nd subsequ e nt formation of M - O bond. The azomethine stretching frequency shi fted by -IScm-1 from 1620 cm-! to lower frequency region due to coordination of the azomethine nitrogen to the metal atom. For the I: I manganese complexes, the coordi­nated H 0 molecu le! 7 was identified by a broad OH

2

11 54 INDIAN J CHEM, SEC. A, NOVEMBER 1999

6 .2

5.8 f:;'1

~ 54 Y . ~ 5.0 a

~ 6A a

..J I 6.0

5.6

5.2

x- ~xis-20 division • 0.2 Y -ilxis-20 division • 0.2

4 ,8 L-L-L..-L-.L-L-'--'--L......L-'--'--L-

IA 1.6 1.8 2.0 2.2 2A 2.6

~x103 T

N

f--

1.9

- 5.5

-5.6

~ - 5.8

"" o .-J - 5 .9

lxlO~ T

2.0 2 .1 Z:2 2.3 2.4 2.5 2.6

" I I I ' I i

~(al ~

X-axis-2CI division = 0.1 ~ Y -axis-20 division = 0.1

- 6.0 (bl

- 6.1

Fig. 3 - Coats Redfern plots fo r (a) Mn (Hp)(O"N"S), and (b) Mo0

2( O"N"S)

- 6.2

Fig. 4 - Piloyan Nov ikova plot for (a) Mn(Hp)(O"N"S), and

(b) Mo02

( O"N"S)

Peak no.

2

3

4

5

6

7

8

9

10

11 12

13

14

15

16

17

18

19

20

2 1

22

23

24

25

26.

27

28

Tabl e 3 - X- ray powder diffrac ti on data of Mn Hp (O"N"S)

28, deg.

14.7

16. 1

18. 1

19.9

2.5

23.1

25.9

26.7

28.45

29.60

30.75

32.0

32.6

34.7

36. 1

38.25

40.0

41.2

42 .2

42.7

44.2

45 .9

47 .0

48.1

49 .9

53.2

54.2

56.6

d-Spacing

(obs.), A a

6.0209

5.5003

4 .8968

4.4578

4. 1296

3.8471

3.4372

3.3360

3 .1400

3.0 153

2.9 190

2.7945

2.7444

2.5830

2.4860

2.3540

2.2520

2. 1892

2.1 396

2. 11 57

2.0473

1.9754

1. 93 16

1. 890 1

1.8260

1.7173

1.6909

1.6247

h k

1 3

0 3

0 2

0 5

2

I

2 I

1 5

0 2

0 5

2

4 4

0 6

5

5 3

3 8

2

5 5

3 9

0 9

6 4

2 7

3 10

5

12

0 7

0 12

5 10

Refined va lues o f a = 13.0202(orthorhombic sys tem): b = 22.4247; c = 17.0650

2

3

5

3

4

4

3

5

4

5

I

4

5

0

0

7

2

4

0

6

2

6

I

8

4

3

-'l

SINGH et al. : STUDIES ON Mo(Y!) & Mn(ll ) COMPLEXES 11 55

Table 4 - Bactericidal screening data of li gands and their metal complexes

Compound Diameter of inhi bition zone, mm (A ngul ar values)

Staphylococcus aurell.\' Xan./homonas compestris

500ppm 1000ppm 500ppm 1000ppm

HPOH 6.0 (14. 18) 7.0 ( 15.32) 3.0 (9.97) 4.0 ( 11.54)

MnCI (HPO)HP 9.5 (17 95) 12.0 (20.27) 9.0 ( 17.46) 11.0 (19.37)

Mn(HPO)2 13.0 (2 1.1 3) 15.0 (22.79) 11.0 ( 19.37) 14.0 (2 1.97)

Mo02(HPO)2 10.0 ( 18.43) 11.5 (19.82) 6.5 ( 14.77) 7.5( 15 .89)

HO"NnOH 7.0 ( 15.32) 8.5 ( 16.83) 4.0 ( 11.54) 5.0 ( 12.92)

Mn(Hp)(OnNnO) 11.0 (19.37) 12.5 (20.7 1) 8.5 ( 16.83 ) 9.5 ( 17.95)

MoOi O" NnO) 9.0 ( 17.46) 9.5 ( 17.95) 8.0 ( 16.43) 9.0 ( 17.46)

HonNnS H 8.0 ( 1643) 9.0 ( 17.46) 4 .5 ( 12.25) 6.0 ( 14. 18)

Mn(Hp)(O" Nn S) 13.0(2 1.1 3) 16.0 (23 .58) 7.0( 15.34) 8.5 ( 16.95)

Moo 2(onNns) 11.0 (19.37) 13.0 (2 1.1 3) 7.0 ( 15 34) 9.0 ( 17.46)

StaeJ1l'lococcus aureus Xallthomollas compestris

Std. Error Mean Criti cal difference at 5% Std . Error Mean Critical difference at 5%

Within doses 1.0 1 2.92 0.83 2.42

Interaction 0.54 1.56 0.44 1.29

Tab le 5 - Fungicidal screening of ligands and their metal complexes

Compound Helminthosporewn gral11illeulI1 Alternaria a/ternata

Conc. Total No. of No. of Total No. of No . of

ppm no. of germinated ungerminated no. of germinated ungerminated

spores spores spores spores spores spores

HPOH 500 12 2 10 10 I 9 250 12 4 8 10 3 7

125 12 5 7 10 6 4

62.5 12 7 5 10 6 4 I-IonNnS H 500 10 1 9 8 2 6

250 10 3 7 8 3 5 125 10 5 5 8 5 3 62.5 10 6 4 8 7

500 10 9 9 I 8 250 10 2 8 9 2 7 125 10 4 6 9 5 4 62.5 10 7 3 9 7 2 500 12 II 8 7 250 12 2 10 8 2 6 125 12 4 8 8 5 3

62.5 12 7 5 8 6 2

1156 INDIAN J CHEM, SEC. A, NOVEMBER 1999

Table 6 - Efficacy of ligands and their complexes against leaf spot of brinjal pl ant caused by A. a/lernala •

Camp Dose, ppm

HPOH 100

200

Mn(HPO)2 100

200

HCY'NnSH 100

200

Mn(J-lp)(OnNnS) 100

200

Bavistin (0.2%)

Std. Error Mean = 0.92

Criti ca l difference at 5% = 2.68

POI in untreated plants = 40

PDI in

treated plant

17

13

II

8

16

12

II

8

9

Disease

control , %

58 .0

68.0

73.0

80.0

60.0

70.0

73.0

80.0

78.0

absorption around 3520-3450 cm-I. In all the cases I : I

mol ybdenum complexes showed only a single stretch l8

at 9 15-930 cm l . A doublet in the spectra of 1:2 molyb­denum complexes at -900 cm-I is assigned to v (O=Mo=O) and v (O=Mo=O) vibrations indicat-

sym asym

ing the presence of cis Mo02 moiety. Several new bands in the spectra of complexes at -480, -310, -380, -650, -430 and -360 cm-I are due to v(Mn-O), v(Mn- CI) , V(MIH-N), v(Mo- O), v(Mof-N), and v(Mo- S), vibra­

tions, respec ti vely. The e lectronic spectra of the ligands and the ir metal

complexes were recorded in methanol. The e lec tronic spectra of ligands exhibit three bands at -230, -270 and -320 nm. The bands at -230 and -270 nm are due to 11:-11:* transitions within the benzene ring and that around 320 nm due to n- 11:* transitions of the azomethine group . However, in the metal complexes the first two bands re­main unaltered , whereas the third undergoes a blue shift due to the coordination of nitrogen to the central meta l

atom. The proton magnetic resonance spectra of ligands and

their molybdenum complexes have been recorded in DMSO-d

6 (Table 2) . In the spectra of the complexes the

disappearance of the -OH proton signal indicates the deprotonation and complexation through thi s functional group. The s ignal due to -NH proton attached to phenyl ring remains unaltered in the complexes. The disappear-

ance of the -NH resonance signals of the HorN'""'OH and

HO'""'N'""'SH ligands in the case of comp lexes provides evidence for the complexation through this functional group. The NH, proton signals remain almost unchanged . The i3C NMR spectra of the ligands and the ir complexes have also been recorded in Tab le 2. The considerab le shifts in the positions of the carbon atoms adjacent to the azomethine nitrogen and thiolo sulphur/amido oxy­gen further support the proposed coordination pattern .

The ESR spectra of manganese complexes at room temperature showed only one isotropic signal centered at g = 2.0 suggesting a four-coordinated geometry l9 for

these complexes.

Thermogravimetric analyses of Mn (Hp)(O'""'N'""'S) and Mo0

2(O'""'N'""'S) have also been carried out to evalu­

ate their thermal stability20. The TG curve (Fig I, curve

a) for the complex Mn(Hp)(O'""'N'""'S) shows first mass loss step from around 273K to 547K. T he subsequent

step shows mass loss up to 627K. If Mn02 is the fin a l product after decomposition , the calculated mass loss should be 55 .7%; it was found to be 50% from the ther­mogram which suggests complete conversion to oxide at 627K. The TG curve (Fig. I , curve b) for the comple x MoO/ O'""'N'""'S) shows procedural decomposition tem­perature (pdt) of about 473K. Thi s maj or thermal de­composition step continues upto 656K. Almost 65% mass loss occurs in thi s step. At thi s te mperature, MoO, is pre­sumed to be the end product (calculated mass loss =

65.05 %; found 65 %). The subsequent step shows minor mass loss upto 773K.

The differential thermal analysis (DTA) profile (Fig2, curve a) for the complex Mn(H

20)(O'""'N'""'S) shows a

shallow and broad exothermic peak at 623 K due to the formation of intermedia te. A sharp exothermic peak at 813K indicates further reaction of the intermediate ac­companied by crystalline phase change. Similarly, the DTA curve (Fig.2, curve b) for Mo02(O'""'N'""'S) shows one endothermi c peak at around 403 K which is due to me lting transition; second endothermi c peak due to de­composit ion is observed at around 448K. An exother­mic peak at T = 750K corresponds to crystalline phase

max

change.

From the above curves the reaction order (n) for the first thermal decomposition step has been determined by the methods of Coats and Redfern (Fig.3) and Piloyan and Novikova (FigA).

The temperature dependent calibration constant was obtained from the Curel equat ion :-

-

,.

-'"

SINGH el al.: STUDIES ON Mo(VI) & Mn(II) COMPLEXES 11 57

Table 7 - Changes in the body weight and weights of reproducti ve organs along with seminiferous tubul e and Leydig cell nuclear diameter

after treatment with ligands and their manganese(II) and molybdenum(VI) complexes.

Group Compound tested Bod" weight, gm Testes Epididymis Seminal vesicle Ventral prostate Seminiferous Leydig cell

tubule, ~m nuclear

diameter, ~m

Ini tial Final mg! I 00 gm body weight

A. Control 17.0±)5.0 200.0±.12.0 11,00.0±.BO.50 4 10.0±.250 310.0±.2.S0 240 0±.30.70 215.0±.19 610±.O.95

B. HPOH I BS.O± 20.0 220.0± 15.0' B.'iOO±:lO.O" :l IO.O± 20.0" 250.0± 10.5' 200.0± 15.0' 150.0± 1.5" 4.9± 0.12'

c. Mn(HPO), 190.0± 15.0 2100± IB.O' 7S00± 200' 2500± 10.0' 212.0± 10.B' 175 0±.1 20' I 1O.0± 17' 4.0±.0 15'

D. MoO,(HPO), 200.0± 10.0 2:10.0±.170' 720.0± 10.0' 2200±.BO' 200.0± B.5' 1600± 15.0' II SO±.IS' 4.1± 0.I I'

E. HCY'N"SH mo± 110 190.0±, I 0.0' BIOO± 15.0' 290.0±S'{}' 210.0± 7.5" 170.0± 7.B' 160.0±1J ' S.O±OI '

F. Mn(H,o)(CY'N"S) I BO.O± 10.0 20S0± 110' 7000±. ISO' 20S.0± 15.8' 1700±S9" 1400± 5.6' 100.0± l.O' 3.9± 0.2'

G. MoO,(CY'N"S) 2 1O.0±S.0 23S0± 120' 6900± 110' 200.0±6S' ISOO±47" 120.0± 7.B' 10S.0± 10' 17±.O. I'

Values are Mean ± SE of six dctcnninalions ; (I =PS; 0.0.) Groups Band E compared with Group A.:!J =PS; 0.00 I Group B compared wilh Groups C and D.

c =P= NS Groups F and G compared wilh Group E.

Tablc 8 - Sperm dy namics and fert ility test after treatment wi th li gands and their metal complexes

Group Treatment Sperm moti I i ty Sperm densi ty, million/ml Fertili ty test, %

(Cauda epididymi s) Testes Epididymis

A. Control 75 .0 ± 5. 1 1.85 ± 0. 10 49 .5 ± 1.75 98% +ve

B. HPOH 55.0 ± 3. 1" 0.89 ± 0. 11" 37.5 ± 0.90" 7 1% -ve

C. Mn(HPO)l 35.0 ± 2. 1" 0.65 ± 0. 10" 3 1.5 ± 0. IO" 86% -ve

D. MoOz(HPO)l 30.0 ± 2.5" 0.50 ± 0. 1510 25.0 ± 0.20" 87% -ve

E. HO" N"SH 40.0 ± 4. 1" 0.70 ± 0. 10" 30.0 ± 0.95" 85% -ve

F. Mn(Hp )(O" N"S) 28.0 ± 3.5" 0.5 I ± 0.20" 20.0 ± 0.80" 90% -ve

G. MoO/ O"N"S) 21.0 ± 3.2" 0.40 ± 0. 15" 2 1.0 ± 0.80" 94% -ve

Values are Mean ± SE of six determ inati ons

a =P~ 0.05 Groups Band E compared wit h Group A.

h =p~ 0.05 Group B compal'ed wit h Groups C and D.

Groups F and G compJred with Group E.

K = - 1.3 x 10'· x PeJk temp. + 0.2200 kJ cm·1

Th e kin e t ic pa ra m e te rs of th e co mpl e xe s Mn (Hp)(OnN"'S) and Mo02(o nNns) for the first step of the rmal decompos iti o n a re 0 . 11 43 Kl kJ cm,l and 0. 1225 KlkJ em,l respecti ve ly suggesting first order re­

action, n = 1. X- ray diffraction study o f the representative Mn(ll)

complex, M n(H,O) (onNns) has been carried out. The

resu lt shows that the compound belongs to the orthor-

ho mbic crysta l system, hav ing unit ce ll dimensions {/ =

13.0202A 0 , h = 22.4247 A 0, c = 17.0650A ° ; and oc = ~ = y = -90° and A = 1.5405. The interpl anar spac ing values (d in A 0), hkl values and 28 ang les are reported in Table 3.

O n the bas is of the above stud ies, a hexacoordinated structure for Mo02(HPO)2' pseudo-octahedral structu re fo r M o%nNno ) a nd M o%nN ns ) a nd a

tetracoordinated st ructure fo r manganese complexes have been es tabli shed .

1158 INDIAN J CHEM , SEC. A , NOVEMBER 1999

Alltimicrobial screening

It is ev ident from the antimicrobi al screening data (Tables 4, 5 and 6) that the metal chelates are more po­tent than the parent li gands. The increased potency of metal complexes may be ass igned to their increased li ­pophilic nature arisi ng due to chelation21. The represen­tati ve ligands and the corresponding meta l derivatives were found to be effective in controlling the leaf spot disease of brinjal plant caused by A. a/t em ata . It was observed that the % disease control of a ll the compounds is quite appreciab le as compared to the check, yet the superiority of the metal deri vatives can not be ruled out.

Mode of ac ti on of antimicrob ials may in vo lve vari­ous targets in microorganisms, e.g. , interference with cell wall synthes is, damage to the cytop lasmic membrane as a result of which cell permeabi lity may be altered or they may disorgani ze the li poproteins leading to ce ll death22 .

Antif ertility activit)'

Male alb in o rats were sc reened for the fertility test and autops ied fo r detailed pathological and biochemical studies in vivo with HPOH, Mn(HPO)2' Mo02(HPO)2' HonW"S H, Mn(Hp)(OnNnS) and Moo

2(onNns), re­

spective ly. The sperm motility and density of Cauda epi­didymal spermatozoa were assessed. The protein , siali c acid , fructose and enzy me act ivity of acid phosphatase were determined2J.

Organ we ights and body weights were not affected after the treatment with ligand or the Mo/Mn complexes. However, the weight of tes tes , epidid ymi s, se mina l ves icle and ventral prostate decreased sig nificantl y (Table 7). The fertility tes t was negat ive in animals. Cauda epididymal density, spermatozoa motility, diam­eter of sem iniferous tubul e and Leydig cell nuclear di­ameter declined significantl y in animals (Table 8). Bio­chemica l analys is showed that the sialic ac id content, concentration of ac id phosphatase and protein24 decrease significantly in reproductive organs of animals due to androgen depletion. The two li ga nd s, HPOH and HonNnSH, affect the pattern of sperm motility and bio­chemical parameters of reproductive organs and tubular dimensions. The molybdenum and manganese complexes of these ligands were found to be more effect ive fertility inhibitor in rats and their activity is due to the synergis­tic action25 It has been found that molybdenum spec ifi­ca ll y induce testicular degeneration and manganese may be critica l fo r lipid metabolism as a cofactor in steroid biosynthes is26 Any disturbance in steroid biosynthesis

may alter the reproductive physiology lead ing to in fer­ti Iity.

Acknowledgement The authors are thankful to CSIR New Delhi , for fi­

nancial ass istance.

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