r, Indian Journal of Chemistry

Vol. 28A, December 1989, pp. 1070-1073

Complexes of oxovanadium(IV) and di-u-oxo-oxornolybdenumrv )with2-methylpiperazine and diethylenetriamine dithiocarbamates

Pradip K Gogoi" & Deba P PhukanDepartment of Chemistry, Dibrugarh University, Dibrugarh 786004

Received 2 August 1988; revised 29 December 1988; accepted 20 February 1989

Oxovanadium(IV) and di-u-oxo-oxomolybdenurnrv ) complexes of the types of VO~, VOL',M0204~ and M0204L' where L= 2-methylpiperazme dithiocarbamate and L'= diethylenetriaminebis(dithiocarbamate) have been synthesised and characterised on the basis of elemental analysis, magne-tic, IR, electronic and ESR spectral datil.

The chemistry of metal dithiocarbamates has beenwidely investigated due to their wide applications,interesting structural properties and biocidal act iv-ityl-3. The coordination compounds of molybde-num (IV, V and VI) with sulphur ligands are alsoimportant because of their role in metabolic pro-cesses and as possible models for molybdenumcontaining enzymes'>, Metal-metal interaction di-splayed by the polynuclear molybdenum com-pounds of this type is also a subject of intensivestudies". However, compared to N,N-dialkyldithio-carbamates, heterocyclic dithiocarbamates of oxo-metal cations are less studied. We report here thesynthesis and characterisation of oxovanadium(IV)and di-u-oxo-oxomolybdenumt'V ) complexes with2-methylpiperazine and diethylenetriamine dithio-carbamates.

Experimental

Synthesis of the ligandsThe sodium salt of 2-methylpiperazine dithio-

carbamate was prepared by reacting 10 g (0,1 mol)of the amine in diethylether with 7.6 g (0.1 mol) ofCS2 and 4 g (0.1 mol) of NaOH; the NaOH solu-tion was added over a period of 2 hr accompaniedby vigorous stirring. The precipitated product wasrecrystallised from isopropanol to get yellowishneedles.

To prepare the sodium salt of diethylenetria-mine bis (dithiocarbamate), 10.3 g (0.1 mol) of theamine dissolved in 50 ml of water was reactedwith 15.2 g (0.2 mol) of CS2 under vigorouslystirring conditions over a period of 1 hr. To theresulting reaction mixture, a solution of NaOH (8g; 0.2 mol) was added slowly maintaining the tem-perature below 30°C. The white crude product

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thus obtained was recrystallised from H20 - EtOH(1:1) to get the hexahydrate.

Preparation of the complexesBii.,2-methylpiperazine dithiocarbamatoioxovana-diuni,IV)

It was prepared by reaction in 2:1 molar ratioof the sodium salt of the ligand (in ethanol) andvigorously stirred aqueous ethanolic solution ofVOS04·2H20. The green precipitated productwas filtered, washed with absolute ethanol severaltimes and dried in vacuo over fused CaCI2•

Diethylenetriamine bis;dithiocarbamato )oxovana-diunilV)

This grey coloured compound was prepared byreacting the sodium salt of the ligand with a solu-tion of VOS04' 2H20 in- 1:1 molar ratio in thesame way as described for the 2-methylpiperazineanalogue.

Di-u-oxo- bis;2- methylpiperazine dithiocarbamatoi-oxomolybdenum; V)

1.77 g of (NH4)6M07024 '4H20 dissolved in 40ml water was depolymerised with cone. ammoniaand treated with vigorously stirred solution of thesodium salt of the ligand (2.34 g in ethanol) fol-lowed by the addition of a freshly prepared sodi-um dithionite solution (0.5 g in 20 ml water). Theresulting reaction mixture was acidified by drop-wise addition of glacial acetic acid till the pH was4. Finally, it was refluxed until the initial purpleprecipitate turned pale yellow. The product wasfiltered, washed with ethanol and dried in vacuoover fused CaCl2.

..

GOGO! et al: COMPLEXES,OF OXOVANADlUM(IV) & OXOMOLYBDENUM(V)

Table I - Analytical data of the compounds

Compound Found (Calc.) %

M C H N S

ChHIIN~S~Na'2H~O 30.48 6.28 12.03 27.22(30.75) (6.40) ( 11.96) (27.39)

C"H IIN3S~Na,' 6H~O 17.74 5.48 10.24 31.26( 17.68) (5.64) (10.31 ) (31.49)

CI,H22N4S~VO 12.37 34.24 5.19 13.33 30.48(12.21 ) (34.51) (5.27) ( i3.42) (30.73)

'ChHIIN-,S~VO 15.78 22.53 3.31 13.03 39.92(15.90) (22.48) (3.43) (13.12) (40.05)

CI~H22N~S4Mo,O~ 31.98 23.68 3.55 9.29 21.21(31.65) (23.75) (3.63) (9.23) (21.15)

C"HIIN.,S4Mo20~ 37.38 14.28 2.09 8.16 25.11(37.68) (14.14) (2.16) (8.24) (25.18)

Table 2 - Magnetic and electronic spectral data of the complexes (ern - 1)*

Compound !-lelL (B.M.) Ama, Dq Ds Dt Assignment

VOL2 1.75 13220 282-2£

16430 1643 -2862 926 282-281

23250 2B2-2AI

34450 Intraligand(rc - n")

VOL' 1.78 13300 '8,-'£16480 1648 -2874 935 '8,-'8123310 '82-'AI

34525 intraligand(rt - n")

Mop~L.! 0.36 19750 '82-~8128320 Charge-transfer34400 intraligand

Mo,O~L' 0.42 f9820 282-281

27955 Charge-transfer34530 intraligand

"Diffuse reflectance spectra.

Di-u-oxodiethylenetriamine bis;dithiocarbamatos-oxomolybdenum; V)

This pale yellow compound was prepared byreacting 1.77 g of (NH4)oM07024'4H20 with a so-lution of 2.03 g of sodium salt of the ligand in asimilar procedure as adopted for the -2-methylpip-erazine analogue. -

The elemental analyses for C, Hand N werecarried out at RSIC, CDRI, Lucknow. Metal andsulphur were determined by the reported standardmethods 7. IR spectra (4000-200 ern - I) were re-corded with a Perkin-Elmer 297 spectrophotome-ter at RSIC, NEHU, Shillong. The electronicspectra of the solid compounds were recordedwith a Shimadzu UV-240 spectrophotometer usingBaS04 as the reference material. ESR spectra of

(

powdered samples at liquid nitrogen temperaturewere recorded at RSIC, lIT, Bombay on a VarianE-112 ESR spectrometer (Xvband) by usingTCNE (g= 2.00277) as the g marker. The. roomtemperature magnetic moments were measured bythe Gouy method using Hg[Co(SCN)4] as the cali-brant. The thermogravimetric analyses were carri-ed out in air on a Shimadzu DT-30 thermal ana-lyzer with a scan rate of lOoC min - I.

Results and DiscussionAnalytical data of the complexes are in good

agreement with the proposed molecular formulae(Table 1). Oxovanadium(IV) complexes werestable only under dry nitrogen or in vacuum whilethe oxomolybdenum(V) complexes were quite

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INDIAN J CHEM, SEC A, DECEMBER 1989

stable in air. All the complexes were insoluble incommon organic solvents but soluble i~ stronglycoordinating solvents like qMF and DMSO. Theroom temperature magnetic moments (Table ,2) ofoxovanadium(IV) complexes are close to the spinonly value of 1.73 B.M. corresponding to one un-paired electron". The di-u-oxo-oxomolybdenum(V) complexes were only feeblyparamagnetic (Table 2) which may be due to weakmetal-metal interaction because of spin polariza-tion and super exchange through the oxygenbridge". However, absence of direct metal-metalbonding was indicated by the ESR spectra of thepowder samples which showed g.l values in therange 1.978-1.982 and &1values in the range 1.99-2.01.

The electronic spectra of the present oxovana-dium(IV) complexes exhibited three bands around13300, 16500 and 23300 em -I which are similarta those observed in other five coordinated oxova-nadium(IV) complexes and are assigned to'B )E 'B 'B d 'B 'A ..- 2 ...• - , - 2 ...• - I an - 2 ...• - I transinons re-spectively. The spectral data (Table 2) are indica-tive of square-pyramidal geometry for the com-plexes'". Another band observed around 34500em - I could be due to intraligand charge transferand is assigned to rt ...•Jt* transition II.

The ESR spectra of powdered samples at liquidnitrogen temperature [VOL:,: g.l' 1.982, gll, 1.94;(g), 1.968; All, 190G; A.l' 60G; (A) 103G; A, 138cm -I. VOL': g.l' 1.994; &1' 1.962; (g), 1.983; All,105G; A.l' 68G; (A), 80G] showed a typical eightline splitting pattern as expected for 51 V (I = 7/2)giving rise to (g) values very nearly 2 where (g) isdefined as,

1(g) = "3 (2g1 + gll)

The average hyperfine coupling constant, (A), va-lues are in the range expected far vanadyl com-plexes!'. The comparatively smaller (A) value fardiethylenetriamine analogue could be due to in-creased metal-ligand covalency!'. By correlatingthe ESR and electronic spectral data for 2-methyl-piperazine derivative the spin-orbit coupling con-stant, A, was calculated from the expressions 1.1,

(A ~ )gl = 2.0023 1 -, y ,

- B~...•-E

( 4Aa~)&1= 2.0023 1- , ,-B

2•..• -B

I

where the constants y2 and a2 are equal to unityfor weak covalent bonding. This value is in good

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agreement with those observed for other VOl +

complexes!'.

In the,lR spectra, a band around 1470 ern - I ischaracteristic thioureide band and is assigned tov(C :::.:N). Owing to lower tendency of the hetero-cyclic ring to release electrons the v(C::': N) modein 2-methylpiperazine derivative appeared at'slightly lower wave numbers as compared to theposition in diethylenetriamine analogue. Thestrong absorption at 1025 ± 5 em - I was assignedto v(C::': S). Absence of splitting in this region indi-cated chelating behaviour of the dithiocarbamategroup" and the quadridemate nature of the liganddiethyletriamine bis(dithiocarbamate). Thev(V=O) and v(V-,S) modes were observed at965 ± 5 and 360 ± 5 em - I respectively. Finally,the appearance of v(N - H) at 3355 ± 10 em - I

and b(N - H) at 1610 ± 5 ern - I is suggestive ofnon-involvement of - NH group in coordination.

From the above observations the complexesVOL:, and VOL' are suggested to contain the fol-lowing (structure I) arrangement around the V02+moiety,

o<, -1"'5"11/5",, ,//N-C~S/V'-....S)-C-N,

III

The IR spectral data of the present oxorno-lybdenum(V) compounds are in good agreementwith the presence of Mol03 + core in the com-plexes. Four characteristic IR bands, two due toterminal v(Mo = 0) and two due to v(Mo02Mo) areexpected for the M020} + moiety. Terminal(Mo = 0) group is expected to show two bandsaround 980 and 960 em - I while the bridged(Mo02Mo) group is expected to show bandsaround 740 and 430 cm-I due to the antisymmet-ric .and symmetric v(Mo - 0) modes respectively'.Two bands observed at 985 and 960 em - I for the2-methylpiperazine derivative are assigned to vasand v, (M=O) modes respectively. But only oneband is observed at 955 ern - I for diethylenetria-

. mine derivative which has been assigned tovs\Mo = 0) vibration. However, the presence ofthIS symmetric stretching mode is quite sufficientto indicate a cis disposition of the two terminalMo = 0 groups in dimeric complexes 1.\ The vsand vas modes due to Mo02Mo bridge were ob-served at 440 ± 5 and 730 ± 5 ern - I respectively.These assignments are consistent with those ob-served for the complexes having an MoO,Mobridge">" and provide the evidence for the pres-ence of M0204 core (structure II).

GOGO! et al: COMPLEXES OF OXOVANADIUM(IV) & OXOMOLYBDENUM(V)

o 0,,11./ 0"1 .// Mo"O/ Me"

(II)

The v(C ::.:N) band observed around 1475 ern - 1 isindicative of partial double bond character of theC - N bond. The strong band at 1020 ± 5 em - 1

due to v(C::': S) is suggestive of chelating behaviourof the dithiocarbamato group and quadridentatenature of the ligand diethylenetriamine bis(dithio-carbamate). The v(Mo - S) mode was observedaround 350 em - I. In view of the above observ-ations the complexes could be best represented asM0204~ and M0204L. The notable feature dis-played by the complex M0204L' is that the ligandL' forms another bridge connecting the two Moatoms at position trans to the terminal Mo =0,like that in the Mo(V) glutathion complex".

The electronic spectra of di-u-oxo-oxomolybdenum(V) complexes showed a weakband around 19700 em - 1 and a shoulder at27550 em -I. These two bands have been assignedto 2 B2 ....•.2 E and charge transfer transitions respect-ively and are indicative of square pyramidalgeometry for the complexes containing dioxobridges!". Both the complexes exhibited an intenseband around 34500 em - 1 attributable to intrali-gand charge transfer. These observations are com-parable with those observed previously for otherdithiocarbarnates and related compounds contain-ing di-u-oxo-bridges with a dinuclear moietyt+".

Thermal studiesThermogravimetric studies of oxovanadium(IV)

complexes showed no sharp decomposition andwere indicative of slow degradation of the organicmoiety. At 400-450°C, an intermediate, probablymetastable VO(SCNh, was formed which alsobroke down continuously until the formation ofVO took place at 650-690°C. The DTA of VO~showed an endothermic process around 140-180°C which might be due to quick volatilasationof organic radicals. On the other hand, the forma-tion of VO was accompanied by an exothermicprocess. TG studies of oxomolybdenum(V) com-plexes also showed no definite stable intermediate

(

stage indicating the gradual decomposition of theorganic part. At 550-nOoe the oxidised product,Mo03, was formed which was accompanied by anexothermic process. Another exothermic processobserved around 190-250°C was probably due tothe formation of CS2, SH2 and isothiocyanates "'.

AcknowledgementThe authors thank the RSIC, IIT, Bombay for

ESR spectra, NEHU, Shillong for IR spectra andCDRI, Lucknow for C, H, N analyses. One of theauthors (PKG) thanks the UGC, New Delhi, alsofor financial assistance.

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