Indi an Journal of Chemistry Vol. 40A, October 2001, pp. 1053-1063

Metal chelates of bioinorganic and catalytic relevance: Synthesis, magnetic and spectral studies of some mononuclear and binuclear oxovanadium(lV) and

dioxotungsten(VI) complexes involving Schiff bases derived from 4-butyryl-3-methyl-l-phenyl-2-pyrazolin-5-one and certain aromatic amines

R C Maurya*, H Singh, A Pandey & T. Singh

Coordination Chemi stry Laboratory , Department o f P G Studies and Research in Chemistry, R.D. University, Jabalpur 48200 I, India

Received 10 October 2000; revised 2 May 2001

Sy nthesis o f two seri es o f meta l chelates: (i) mononuclear chelates of composItIons, [VO(L l h].H20 and [W02(SCN)(C2H50HhCLI)], (where LI H = N-(4'-butyrylidene-3' -methyl-I '-phenyl-2'-pyrazolin-5'-one)-p-ani sidine (BUMPHP-PAH, I), N-(4 ' -butyry lidene- 3' -methyl-1 '-pheny l-2'-pyrazolin-5' -one)-o-phenitidine (BUMPHP-OPH , II) , N-(4' -butyrylidene-3' -methyl-I' -phenyl-2' -pyrazolin-5' -one)-III-phenetidine (B UMPHP-MPH , II I) or N-( 4' -butyrylidene-3'-methyl- I' -phenyl-2' -pyrazolin-5' -one)-III-toluidine (B UMPHP-MTH , IV) or N-( 4' -butyrylidene-3 ' -methyl-I' -pheny l-2'-pyrazo lin-5'-one)-p-tolui di ne (BUMPHP-PTH V), [VO(L2)].H20, and [W02(SCN)(L2H)] (where L2H2 = N,N'-bi s-(4'-butyrylidene-3' -methyl-I ' -phenyl-2' -pyrazolin-5 ' -one)-o-phenylenediamine (BUMPHP-OPHDH2, VI ) or N,N' -bi s-( 4'-butyry lidene-3' -methyl-I '-phenyl-2' -pyrazolin-5' -one)-III -phenylenediamine (BMPHP-MPHDH2, VII ) and VO(Lz')(H10)] (where L2' H2 N,N' -bi s( 4' -butyry lidene-3'-methyl- I' -phenyl-2' -pyrazolin-5'-one)-III -phenylenediamine (BMPHP-MPHDH2, VIl). and ( ii ) binuclear chelates o f compositions, [( VO(HzO)(OH) h L)] and [( W02(SCN)(H20) b (L) ], where L, H2 = N ,N' -bis-( 4-butyry lidene-3- methyl-l-phenyl-2-pyrazolin-5-o ne)-p-phenylenediamine (BMPHP-PPHDH 2, VIII ) or N.N'-bis-(4-butyrylidene-3-methyl-l-phenyl-2-pyrazolin-5-one)-benzidine (BMPHP-BZH 2, IX) are described. The resulting chelates have been characterized by elemental analyses, molar conductance, decomposition temperature and magnet ic measurements. electron spi n resonance/ I H-NMR, infrared and elec tronic spectral studies. The oxovanadium(lV) compou nds with ligands, BUMPHP-PPHDH 2 and BUMPHP-BZH 2 exhibit subnormal magnetic moments. Structures involving ... v=o··· V=O·· · chain for oxovanadium(lV) complexes, and tentative st ructures involving cis-W02 have been proposed for dioxotungsten(VI) complexes.

The chemistry of oxovanadium (IV) has received considerable attention t as the V02+ unit can readily

coordinate four, five and six donor atoms to form VOL4, VOLs and VOL6 type of complexes

2,

respectively. Additional interest has been generated due to the di scoveries of the increasing biological

importance of vanadiumJ . Several types of

invertebrate accumulate vanadium in their blood. Thus, the ascidian seaworm phallusioll malllmiiata has a blood concentration of vanadium up to 1900 ppm, which represents more than a 10-fold concentration with respect to the seawater in which it li ves4 . In this instance, vanadium is believed to play a role in the oxygen transport cycleS. Vanadium is al so known to be an essential nutrient in higher life fo rms3.6 where it IS in volved It1 phospholipid

oxidation, sulphur metabolism and cholesterol biosynthesis 7.

There is heightened interest in the biological chemi stry of vanadium due to the recent di scovery of

two types of vanadium enzymes8.9 vanadium nitrogenase and vanadium bromoperoxidase. A recent report indicates that there is a class of nitrogenase metalloenzymes hav ing vanadium at the active site which appears to shuttle between V(ll) and V(lV), and is possibly bound to an iron-sulphur cluster " . According to others l 2, in vanadium nitrogenase, VOII ) is at the active si te. One synthetic difficulty in modeling the active site is the problem of direct linking of iron-sulphur clusters and vanadium compounds. This requires functionality on vanadium atom, which can be synthetically manipulated. Thus, having new vanadium compounds with functionality is highly desirable. The di scovery that vanadium is invo lved in the nitrogenase and bromoperoxidase, as low molecular weight complex (amavadin) 13 led to renewed interest in the chemi stry of the model compounds with varying N/O coordination sites. In another report l4 , oxovanadium(V) with coordinated N, O-donor li gand was shown to be the active site in vanad ium bromoperox idasc.

1054 INDIAN J CHEM, SEC A, OCTOBER 2001

Since the seventies, vanadium has been a subject of investigation with regard to its association with insulin and its role in the bod/ 5. Control of glucose levels in plasma has been achieved, in vitro and in vivo, by means of vanadium administration in the form or inorganic salts 16. As these salts are poorly absorbed, the required high doses have been associated with undesirable side effects. In order to achieve better absorption and so to reduce the doses of the element, it seemed appropriate to administer it in the form of an organic matrix ' 7. The recently reported l8 and structurally documented l7. 19

bis(maltolato)oxovanadium(IV) (BMOV) has been found to be effective (at lower doses than inorganic vanadium salts) in regulating glucose levels in the plasma in diabetic rats. It lowered cholesterol and triglyceride and ameliorated the cardiac disfunction normally observed in diabetic patients. It exhibited no significant toxic effects on hepatic and kidney functions2o.

The chemistry of tungsten21 is varied and complex not only because it covers nine oxidation states ranging from -2 to +6, but also because of its ability to form complexes with different coordination numbers and geometries, because of its tendency to form clusters, polynuclear complexes with a variety of metal atoms.

Dinitrogen complexes of tungsten have recently22 been studied in great detail in relation to the function of nitrogenase. They show considerable versatility both with respect to reduction of coordinated N2 and in reactions leading to C-N bond formation. It has been shown that the coordinated nitrogen may be converted into various organonitrogen complexes such as organohydrazido23 , organodiazido and diazoalkane complexes. However, the subsequent release of the organic moieties has been limited to alkyl amines and azines. Efforts to extend this kind of chemistry continue and it has recently been found that the sequence of reactions can be carried out to produce pyrrole and N-aminopyrroIe24.

Hidai et al. 25 have recently claimed that the treatment of the tungsten dinitrogen complex cis-[W(N2h(PMe2Ph)4] with an equilibrium mixture of [Ru(CI)(dppphlX and trans-[Ru(CI)(rr H2)(dppph]X, [where X= BF4, PF6 or OS02, CF3; dppp = 1,3-bis(diphenylphosphino)-propane] under one atmosphere of H2 at 55°C for 24 h gives NH3 in moderate yield. The same reaction in the presence of acetone produced acetone azine in high yield . None of these reactions proceeded in the absence of H2.

Tungsten is the only element in the 3rd transition series known to have biological functions 26. Not only does it sometimes occur in enzymes that usually contain molybdenum, but also there are some enzymes that are known only with tungsten. Only a few reports26 are available on mealloenzyme models of tungsten.

Dioxotungsten(VI) complexes with Schiff bases are limited. They are mostly organometallics and a few studies dealing with dioxotungsten(VI) complexes of chelating molecules have been reported27 . The main reason for the lack of dioxotungsten(VI) is the non-availability of a suitable starting material. Yamanouchi et al. 28.29 have used W02Ch or W02CI4 as a starting material, while Syamal et at. have tried the reactivity of Schiff bases in aqueous medium with limjted success30 Recently, Yu and Holm31 have successfully used [W02(acach], (where acacH= acetyl acetone) to prepare dioxotungsten(Vl) complexes. Maurya et at. 32 have recently reported the synthesis and characterization of dioxotungsten(VI) complexes of the type [W02L (MeOH)] where (LH2 =Schiff base derived from salicylaldehyde or 0-vanilline and benzoyl hydrazide salicylhydrazide, furoylhydrazide or isonicotinoylhydrazide using [W02 (acac) 2] as precursor.

In view of the above, some chelating Schiff base ligands derived from 4-butyryl-3-methyl-l-phenyl-2-pyrazolin-5-one have been chosen and attempts made to synthesize and characterize their oxovanadium(VI) and dioxotungsten(VI) chelates. 5-P:/razolone and its deri vati ves are reported to possess strong antibacterial, analgesic, antihistaminic and antifungal activities33. The chelating pyrazolone based Schiff bases I-IX are shown in Structure I.

Materials and Methods Vanadyl sulphate pentahydrate (Thomas Baker

(Chemicals) Limited, Bombay), sodium tungstate dihydrate (Sisco -chem. Induslries, Bombay), ammOllIum thiocyanate (Romali Chemicals, Bombay), p-anisidine, a-phenetidine and 11'1-phenitidine (Aldrich Chemical Co., U. S. A) , p-toluidine and m-toluidine (Sarabhai M. Chemicals,' Baroda), benzidine (B.D.H. Chemicals, Bombay), 0, 111, and p-phenylenediamine (Fluka A. G., Switzerland), butyryl chloride and 3-methyl -I-phenyl -2-pyrazolin -5-one (Johnson Chemical Co., Bombay) were used as supplied . All other chemicals used were of analytical reagent grade. 4-Butyryl-3-methyl-l-phenyl-2-pyrazolin-5-one (BUMPHP) was prepared by the method reported by Jenson34 .

MAURY A el al.: STUDIES ON CHELATES OF VANADIUM & TUNGSTEN lOSS

X= - OCH, (1') (BUMPHP-PAH. I) '(= - OC, H, (0) (II. BUMPHP-OPH. Ii) X= - OC, H,(m) (Ill. BUMPHP-MPH. III) X= - CH, (/II) (I.BUMPI-IP-MTI-I. IV) X= - CI-I, (1') (III. BUMPI-IP-PTH. V)

(. )

-@ (BUMPHP-OPHDI-12·VI) /

-@ (BUMrI-IP - MPI-IDH2,VlI)

-@- (OUMPHP - PPIIDI-~·.VIII)

-@-@-I

Synthesis of Schiff bases The synthesi s of different Schiff bases was done by

usual condensation of ethanolic solution of 4-butyryl-3-methyl-I-phenyl-2-pyrazolin-5-one and ethanolic solution of aromatic amine, viz., p-anisidine, 0-, 11/-phenetidine, 11/- , p-toluidine, 0-, 111- , or p-phenylenediamine or benzidine in stoichiometric ratios, the detail s of which are given in our previous communication's .

SYllthesis of complexes

OxovonodiulI1( IV) complexes All vanadyl complexes of the BUMPHP Schiff

bases were prepared by a general method . The salt VOS04.5H20 (0 .00 I mol , 0.253 g) was dissolved in water (10 mL) and the so lution was added to a warmed, stirred solution of the corresponding Schiff base [0.02 mol , in case of BUMPHP-PAH (0.698 g) ,

BUMPHP-MPH (0.726 g) or BUMPHP-MTH (0.666 g) and 0.01 mol in case of BUMPHP-OPHDH2 (0.560 g), BUMPHP-MPHDH2 (0.560 g) BUMPHP-PPHDH2 (0.560 g) or BUMPHP-BZH2 (0.636 g.) in ethanol (15 mI.)]. The resulting solution was refluxed for 6-7 h and concentrated to half the volume. The resulting precipitate was filtered by suction and then dried ill vacuo over anhydrous calcium chloride. The analytical data of the complexes are given in Table I(a).

Dioxotungsten(VI) complexes: Na2W04. 2H20 (0.6 g) and NH4NCS (1.45 g) were

dissolved in water (IS mL) at room temperature and 3.75 mL of 11M HCl was added into it. The resulting yellow solution was mixed with ethanolic solution (10 mL) of ligand, BUMPHP-PAH (0.698 g.), BUMPHP-OPH (0.726 g), BUMPHP-PTH (0.666 g), BUMPHP-OPHDH2 (0.560g), BUMPHP-MPHDH2 (0.560g), BUMPHP-PPHDH2 (0.560g) or BUMPHP-BZH2 (0.636g). The coloured precipitate that immediately separated in each case was filtered under suction, washed several times with water containing a few drops of HCI and dried in vacuo. The analytical data of the complexes are given in Table I (b).

Microanalysis for carbon, hydrogen and nitrogen were carried out at C.D.R.I., Lucknow. Vanadium was determined36 by decomposing the complexes with conc. HN03 and then igniting to V20 S in a muffle furnace. In a few compounds, vanadium was also determined by the standard37 KMn04 method. The tungsten contents of all synthesized complexes were determined gravimetricalli8 as bi s(8-hydroxyqui nolinato )dioxotungsten(V I).

Solid state infrared spectra were recorded in KBr pellets on a Perkin-Elmer model 1620 Ff-IR spectrophotometer. Electronic spectra were recorded on an ATI Unicorn UV-2-100 UVlYi sible spectrophotometer having matched 1.0 cm silica cells. Conductance measurements were made in DMF solution using a Toshniwal conductivity bridge and dip-type cell with a smooth platinum electrode of cell constant 1.02. Magnetic measurements were performed by Gouy's method using mercury(ll ) tetrathiocyanatocobaltate(lI) as cali brant at C S & M C R I, Bhavnaagar. The decomposition temperatures of the complexes were recorded using an electrically operated melting point apparatus( Kumar Industri es , Bombay). The X-band EPR spectra of the complexes were recorded on a Bruker ESP spectrometer using powdered samples at the microwave frequency of

0 VI 0-----

Table I a-Elemental analysis and some physical properties of the synthesized oxovanadium(IV) complexes

S. No. Complex Found (Caled). % Colour Yield ~ff Decomp. AM (Empirical formula) (M .W.) C H N V (%) (BM) Temp (Ohm-' cm2mole- ')

(oq (DMF) I. [VO(BUMPHP-PAh )·HzO 64 .70 5.64 10.78 6.33 Duck egg 55 1.54 255 40

(VC42~t;N6 0 6) (780.94) (64.53) (5.89) (10.75) (6.53)

2. [VO(BUMPHP-MPh).H2O 65.43 5.94 10.60 6.51 Dark bottle 50 1.58 171 30 (VC44H~oN6 0 6) (808.94) (65 .27) (6.18) (10.38) (6.29) green

3. [VO(BUMPHP-MT)21·HzO 67.47 5.89 11.54 6.52 Cream 55 1.56 221 25 (VC42~6N6 0 41 (748.94) (67.29) (6.14) (11.21) (6.80) yellow

4. rVO(BUMPHP-OPHD») .HzO 63.75 5.35 13.47 7.43 Daffodil 45 1.62 187 30 (VC34H36N604) (642.94) (63.45) (5 .59) (13 .06) (7.92)

5. [VO(BUMPHP-MPHD)(HzO») 63.28 5.44 13.44 8.15 Pale yellow 50 1.60 179 35 z (VC34H3~604) (642.94) (63.45) (5.59) (13.06) (7.92) Q

» 6. [{ VO(HzO)(OH) !z(BUMPHP-PPHD») 53.89 4.18 11.35 13.54 Pale yellow 55 1.28 220 40 z

(V2C34~608) (761.88) (53.55) (4.46) ( 11.02) (13.37) '-n 7. [{ VO(H20)(OH) !z(BUMPHP-BZ») 56.82 5.40 10.32 12.56 Cream 55 1.30

:r: >300 35 tTl

(V 2C4QH44N6 Os) (837.88) (57.28) (5.25) (10.02) (12.15) yellow 3::: (/)

tTl Table-l(b)-Analytical data and some physical properties or the synthesized dioxotungsten(VI) complexes n

» Sr. Complex Found (Caled. %) Colour Yield Decomp AM

. 0 No. (Empirical formula. Mol. Wt.) C H N W % Temp (Ohm·'cm

2mole·') n °C -l 0

8. [WOiSCN)(C2HsOH)z(BUMPHP-PA)] 43.38 4.18 7.72 25.82 Green gold 55 182 35 o:l tTl (WC26H34N406S) (713.85) (43.70) (4.76) (7.84) (25.75) ;:0

tV

9. [W02(SCN)(CzHsOHh(BUMPHP-OP)] 44.59 5.02 7.77 25.37 Yellow gold 50 191 40 8 (WC27H36N406S) (727.85) (44.51) (4.94) (7.69) (25.25)

10. [W02(SCN)(C2HsOH)z(BUMPHP-PT») 44.81 4.92 7.92 26.43 Olive green 60 180 40 (WCz~34N40SS) (697 .85) (44.70) (4.87) (8.02) (26.34)

11. [W02(SCN) (BUMPHP-OPHDH)] 50.54 4.34 11.82 22.18 Silver grey 55 195 60 (WC3sH3SN704S) (832 .85) (50.42) (4.20) (11.76) (22.07)

12. [W02(SCN) (BUMPHP-MPHDHJ 50.53 4.31 11.87 22.14 Nut brown 50 201 45 (WC3sH3SN704S) (832.85) (50.42) (4.20) (11.76) (22.07)

13. l {WOz(SCN)(H20h lzE UMPH-PPHD] .2HzO 34.16 3.38 9.32 30.37 Olive green 55 20, 30 (W2C36~80'ZS2) (1213.7) (35.59) (3 .79) (9.22) (30.29)

14. [{WOz(SCN)(H20h!zBUMPHP-BZ) .2HzO 39.19 3.99 8.79 28.60 Yellow 60 331 30 (W2C4ZHsoNsO'ZS2) 1289.7) (39.07) (3.87) (8.68) (28.51 )

MAURY A el at. : STUDIES ON CHELATES OF VANADIUM & TUNGSTEN 1057

9.46-9.47 GHz and IH NMR spectrum of a representative compound was recorded in DMSO-(h at Indian Institute of Technology, Madras.

Results and Discussion The oxovanadium(IV) complexes were prepared

according to the reactions, (I )-(3), while dioxotungsten(VI) complexes were prepared as per reactions (4)-(6) given below:

> Reflux

where LIH = BUMPHP-PAH, BUMPHP-MPH or BUMPHP-MTH

H20 , C2HsOH VOS04. 5H20 + L2H2 >

Reflux

x=O, when L2H2 = BUMPHP-OPHDH2 or x=l, when L2H2=BMPHP-MPHDHD2

H20, C2HsOH 2VOS04. 5H20 + LJ H2 >

Reflux [{ VO (H 20)(OH) hL) ] +H 2S04 ... (3)

where L,H2 =BUMPHP-PPHDH2 or BZH2

H20 >

C2HsOH

[W02 (SCN)(C2HsOH) 2 (L I)] + 3SCN- .. . (4)

where LIH = BUMPHP-PAH, BUMPHP-OPH or BUMPHP-PTH

H20 [W02(NCS)4f -+ L2H2 >

C2HsOH

[W02 (SCN)(L2 H)1 + 3SCN- .. . (5)

where L2Hc = BUMPHP-OPHDH2 or BUMPHP-MPHDH 2

H20 2[W02(NCS)4J"-+ L)H2 >

C2HsOH

[! W02(SCN)(H20) HL) ].2H20 + 6SCN ... (6)

where L)H2 = BUMPHP-PPHDH2 or BUMPHP-BZH2

These complexes are found to be air stable. They are thermally stable and their decomposition temperatures are given in Table I (a and b). These are insoluble in most of the common organic solvents but are fairly soluble in DMF and DMSO. The formulations of these complexes are based on their elemental analyses, infrared spectra, magnetic measurements, ESR/ NMR and electronic spectral studies.

Infrared spectral studies The infrared spectra of all the Schiff bases (except

the ligands VI and IX, which exhibit two bands at 3480-3490 and 3200-3300 cm- I.) exhibit a medium broad band with fine structure in the region 3500-3150 cm- I. This indicates the involvement of 5-0H group of the pyrazolone moiety (enol form) in the intramolecular or intermolecular hydrogen bonding with the lone pair of nitrogen3,). This suggests that the ligand exists in the enol form in the solid state. Hence, the ligands BUMPHP-PAH, BUMPHP-OPH, BUMPHP-MPH, BUMPHP-MTH and BUMPHP-PTH contain four potential donor sites: (i) the ring nitrogen N \, (ii) the ring nitrogen N2, (iii) the enolic oxygen (-OH) and (iv) the azomethine nitrogen (>C=N). However, considering the planarity of the ligands, it is unlikely that these five ligands could act as tetradentate towards a single metal. Hence, these ligands are potentially bidentate and the three favourable possibilities of donor sites are: (i) the azomethine nitrogen and (ii) the enolic oxygen or (i) the enolic oxygen and (ii) the ring nitrogen N I or (i) the ring nitrogen N I and (ii) the ring nitrogen N2. The rest of the four Schiff bases, such as BUMPHP-OPHDH2, BUMPHP-MPHDH2, BUMPHP -PPHDH2, and BUMPHP-BZH2 possess eight potential donor site: (i) and (ii) ring nitrogen NI, (iii) and (iv) ring nitrogen N2, (v) and (vi) the azomethine nitrogen and (vii) and (viii) the enolic oxygen. However, considering the planarity of the ligands, it is unlikely that these two ligands could act as octadentate towards a single metal. Hence, these two ligands are potentially tetradentate. By the reasoning given above the most probable donor sites in these ligands are viz., (i) two enolic oxygen and (ii) two azomethine nitrogens. For the sake of convenience, the remaining interpretation of the infrared spectra is divided into two parts:

1058 INDIAN J CHEM, SEC A, OCTOBER 2001

(A) Oxovanadium(1V) complexes

(i) Complexes with BUMPHP-PAH. BUMPHP-MPH or BUMPHP-MTH .

The ligands under discussion show a sharp and

strong band due to v(C=N) of the azomethine group at 1624-1633 cm-I . The observed low energy shift of this band in the complexes (Table 2a) suggests the coordination of the azomethine nitrogen4o. The significant absorption band due to coordinated enolic oxygen in these complexes is v(C-O) 41 . This band is

observed at 1240-1257 cm- I in these complexes. The coordination of ring nitrogen N I is unfavourable because of the presence of a bulky phenyl group attached to it. These ligands show a band at -1585 cm- I due to v(C=N2) in a cyclic environment

42 , which is observed at the same frequency in the chelates, indicating nonparticipation of the cycl ic nitrogen in coordination.

Most of the oxovanadium(IV) complexes exhibit a strong band near 1000 cm - I, which has been assigned

to the V(V=O)43. In contrast , several oxovana-dium(IV) complexes have been reported in which this

h· d . I 4445 stretc 1I1g mo e appears at qUIte ower' wave numbers around 900 cm - I, In this work, the v(V=O) is found at 903-910 cm- I. This shift of v(V=O) to lower wave numbers suggests the presence of a ------V=O-----V=O------ chain structure, which is formed by the interaction of the vanadyl oxygen of one molecule with a vanadi um metal in another molecule46. The metal complexes also show two medium bands at

3430-3450 and 3358-3370 cm- I attributed to vas(OH)

and vs(OH), respectively, due to lattice water.

Table 2a- lmportant IR spectral bands (cm ') of the oxovanadium (IV) complexes

S. No. Complex v(V=O) v(C-O) v(C=N) (Enolic) (Azomethine)

I. rVO(B UMPHP-PA)2]·H2O 903 1257 1605

2. rVO(BUMPHP-MP)21·H2O 910 1250 1608

3. [VO(B UM PHP-MTMH2O 908 1240 1610

4. [VO(BUMPHP-OPHD)] .H2O 908 1392 1625

5. [VO(BUMPHP-MPHD)(H2O)] 904 1380 1610 1626

6. [( VO(H20)(OH) 12(BUMPHP-PPHD)] 906 1385 1605

7. [( VO(H20)(OH) h (BUMPHP-BZ)] 903 1387 1605

vt I-:l20)/ v(O-H)

3430 3370

3340 3350

3450 3360

3418 3344

3500 3300

3420 3370

3417 3373

MAURYA et af.: STUDIES ON CHELATES OF VANADIUM & TUNGSTEN 1059

(ii) Complexes with BUMPHP-OPHDH2 or BUMPHP-MPHH2

VOS04 reacts with BUMPHP-OPHDH2 or BUMPHP-MPHDH2 in H20/ethanol medium to form stable mononuclear complexes. The analytical data of these complexes indicate that they are of the compositions, [VO(BUMPHP-OPHD)].H20 and [VO(BUMPHP-MPHD)(H20)] . The IR spectra of these two Schiff bases show a strong band at 1624-1635 cm- I that is assigned to v(C=N) (azomethine group). In the spectra of the corresponding complexes, this band is shifted to the lower frequency site and is observed at 1610-1625 cm- I, indicating coordination of the azomethine nitrogen to the V02+ moiety. The coordination of the enolic oxygen to vanady l centre in these complexes is indicated by the appearance of a new band at 1380-1392 cm -I due to v(C-O) (enol)47. In case of compound, [VO(BUMPHP-MPHD)], the ligand BUMPHP-MPHDH 2 behaves as tridentate, one of the azomethine nitrogens being unable to coordinate to the metal due to its meta position . This is shown by the presence of an additional band at 1626 cm- I [as in the li gand for v(C=N) azomethine]. Such a result is expected because of the rigidity of aromatic ring and the presence of two-azomethine group far apart in the ligand. The appearance of two bands at 3418 and 3344 cm- I in the complex 4, and a broad band at 3500-3800 cm- I in the complex 5 due to v(OH) indicates the presence of water molecule in these complexes. The presence of a strong band at -904 cm- I is indicative of the V=O grouping in these two complexes with a chain of the type ---V=O---V=O---(vide supra).

(iii) Complexes with (BUMPHP-PPHDH2) alld (BUMPHP-BZH2)

The C, H, N, analyses of these two complexes indicate that they are binuclear involving ligand bridging. The formation of binuclear complexes is most probably due to I, 4 and I , 6 positions of the

azomethine nitrogens in the ligands, BUMPHP-PPI-IDH2 and BUMPHP-BZH2, respectively, wherein coordination of both azomethine nitrogens with the same V02+ moiety is difficult. The IR spectra of these complexes exhibit a strong band at 1605 cm- I (as compared to that of the free ligands at 1616-1620 cm- I), indicating the coordination of azomethine nitrogens. A medium strong band appearing at -1 285 cm- I in the complexes corresponds to the coordinated enolic oxygen48 in these complexes.

The appearance of two bands due to v(OH) in the regions 3417-3420 and 3373-3370 cm- I suggests the presence of coordinated water as well as 01-1 grouping in these complexes. There two complexes exhibit a strong band at 903-906 cm- I, a lower wave number than the usual range of -1000 cm -I . This corroborates again the presence of a ---V=O---V=O--- chain

46· h 1 structure In t ese comp exes.

(B) Dioxotungsten(VI) complexes The infrared spectra (Table 2b) of all the

complexes show bands in the region 860-880 cm- I

and 935-958 cm-I assignable to Vas (O=W=O) and VS (O=W=O) modes, respectively. This observation indicates the presence of cis-W02 structure in these complexes. The trans-W02 moiety will exhibit only the Vas (O=W=O) due to asymmetric stretch. The thiocyanato group may coordinate to the metal through either the nitrogen or the sulphur atom or both. Tungsten, being in the first half of the third transitional series, is a class 'A' metal and it is expected that thiocyanate will coordinate through nitrogen. The v(C == N) mode observed in the spectra of compounds, 8-14 indicates bonding of thiocyanate group through nitrogen49 . For the sake of convenience the remaining interpretation of the infrared spectra is divided into three parts.

(i) Complexes with BUMPHP-PAH, BUMPHP -OPH and BUMPHP -PTH

The coordination of the ring nitrogen N I is unfavourable because of the presence of a bulky phenyl group attached to it .The reluctance of the ring nitrogen N2 towards coordination is ascertained by the presence of y(C=N 2) cyclic in the complexes 8-10 at almost the same position as in the respective ligands.

The IR spectra of these three ligands show a medium band at 1624-1633 em- I, which is assigned to v(C=N) (azomethine group). In spectra of complexes, 8-10, this band is lowered to 1590-1594 cm- I, indicating coordination of the azomethine nitrogen to

1060 INDIAN J CHEM, SEC A, OCTOBER 200 1

the WO/+ moiet/ o. The IR spectra of these complexes exhibit a medium band at 1238-1261 cm- I

due to v(C-O) (enol) indicating the coordination of enolic oxygen after deprotonation41 • Further, in the IR

spectra of complexes, 8-10, a new band is observed at 872-878 cm- I due to coordination of ethanolic oxygen50 to tungsten.

(ii) Complexes with (BUMPHP-OPHDH2) and (BUMPHP-MPHDH2) The analytical data of these complexes indicate that their compositions correspond to [W02(SCN)(BUMPHP-OPHDH)] and [W02(SCN)(BUMPHP-MPHDH)]. The appearance of v(C-O) (enolic)47 at 1360-1378 cm- 1 in these two complexes suggests the coordination of at least one of the enolic oxygens (after deprotonation) . Further, the appearance of another new band at 1565-1575 cm- I in these complexes shows coordi nation of cyclic carbonyl 50 oxygen to WO/+ moiety. These two Schiff bases display a strong band due to v(C=N) of the azomethine group at 1626- 1635 em- I , which undergoes a low energy shi ft and appears at 16 14-1620 cm- I. Thi s indicates the coordinat ion of both the azomethine nitrogens in these two Schiff bases.

(iii) Complexes with ligands (BUMPHP-PPHDH2) and (BUMPHP-BZH2)

The analytical data suggest that these complexes are binuclear involving li gand bridging . The low energy shift of the v(C=N) mode due to azomethine group at 1600- 1606 cm- I in the complexes (as compared to that o f the free ligands at 1616-1620 cm- I) suggests the coordinati on of azomethine nitrogen to W02

2+ moiety . The signi ficant absorpt ion band due to coordinated enolic oxygen in these complexes is v(C-O). This band is observed47 at 1340-1378 cm- I in these co mplexes. The appearance of a broad band in the region 3433-3350 cm- I indicates the presence of lattice-held as well as coordinated water

Table-2b-IR band (cm- I ) of the dioxolullgstell (VI) complexes

S. Complex v as Vs v(C=N) v(C=N) v(C-O) v(C=N) No (O=W=O) (O=W=O) (Cycl ic) (Th iocyanate) (Ellolic) (Azoillethine)

8. IW02(SCN)(C2H\OHh(BUMPHP-PA)] 860 940 1590 2060 1250 10 10

9. I W02(SCN)(C2H,OHh(B UM PHP-OP)] 878 935 1594 2056 126 1 1618

10. I W02(SCN)(C2H"OHh(B UMPHP-PT)] 870 935 1592 2031 1238 1616

II. IW02(SCN ) (BUMPHP-OPHDH)] 880 958 1596 2031 1378 1620

1575*

12. IWOiSCN) (BU MPHP-MPHDHj 875 950 1592 2050 1360 1614

1565*

13. I {W02(SCN)( 1I20h }2BUMPH-PPHDI.2Hl 0 865 945 1590 2035 1340 1606 I·t I {W02(SCN)(H10 h } l BUMPHP-BZj .2H1O 878 935 1590 2042 1378 1000

*v(CO)(cyclic)

MAURYA e' al.: STUDIES ON CHELATES OF VANADIUM & TUNGSTEN 1061

in these complexes. The nonparticipation in coordination of the two ring nitrogens N I and the two ring nitrogens N2 in all the four ligands under discuss ion is due to the same reasoning as given in the case of potenti ally tetradentate ligand (vide supra). Conductance measurements

The observed molar conductances of these complexes measured in dimethylformamide solutions are in the range 25-40 ohm- 'cm

2 mol- I and thereby indicate their non-electrolytic51 nature.

Magnetic measurements The observed magnetic moments (1.28-1.62 B.M .)

of vanadi um complexes are given in Table I. These resu lts suggest that a chain52 of the type ---V=O---V=O--- is present in these complexes . The magnetic measurements of tungsten complexes indicate that they are diamagnetic , as expected for dioxotungsten(V I) complexes.

Electronic spectral studies The electronic spectra (Fig. 1 a, I b) of four

oxovanadium(lV) compounds, namely, compounds I , 2, 4, and 5 were recorded 111 10-3 molar dimethylformamide solutions. The Amax of electronic spectral peaks, their molar extinction coefficients and tentative assignments are given in Table 3. The compounds 1 and 2 exhibited only high intensities change transfer transit ions. On the other hand, the compounds 4 and 5 di splayed few change transfer transitions and 2-3 d-d transitions . Thi s is in agreement with previous observations and suggests square-pyramidal geometry for these complexes53.

Electronic spectra (Fig. I c) of four representative dioxotungsten(VI) complexes 8, 9, 11 and 14 were

6.0 .---- --- ------------,

3 I

4.0

;,/1 ;v\ I \

i I \ \ I' 2 I \ III I I , I" 'I I', ) \

I,) \ nf \ V

u ~

2.0

0.0 +----,----.-----~=;===~.,---__1 200 300 400 500 600 700

Wavelenoth(nm )

Fig. la-Electronic speclrum of [(VO(BUMPHP·PA)2).HPl ( I)

recorded in 10-3 molar solutions In dimethylformamide, These complexes exhibit two significant spectral peaks in the region 303 -362 and 350 - 408 nm, which may due to ligand to metal charge transfer transitions54,

ESR spectral' H NMR spectraL studies The room temperaturelLNT ESR spectra of two

representative compounds [VO(BUMPHP-MP)2]. H20 (2) and [VO(BUMPHP-MPHD)(H20)] (5) were recorded on powdered sample without DPPH using the microwave frequency 9.44/9.14 and 9.46 / 9.15 GHz respectively, ESR spectrum of compound, [(VO(BUMPHP-MP)2].H20 at RT / LNT shows slight

6~~----------------,

4

~ JI5 6

4.0 1'1 II ~ \ I ~" 'I '11\

, I oJ \ 11 ___ 3 II

\ 1 \

'I ,(! I I "/ , 2.0 I. 1\ 2 I \I i

'I \ I /',1 J \ 1 i I !III : , I U IJ It ~

0.0 I I 200 300 400 500 600

Wavelenglh(nm.)

Fig. I b-Electronic spectrum of [VO(BUMPHP·OPHDH )].H20 (4)

6.0-r---;----------- --- ---- --,

4.0

2.0

0.0.J----.---.----=::;::::===:;:::::::==r====----j 200 300 400 500

Wave1englh(nm.)

600

Fig. Ie-Electronic spectrum of [W02(SCN)(B UMPHP-OPHDH)] (II )

700 800

1062 INDIAN J CHEM, SEC A, OCTOBER 2001

Table 3-Electronic spectral peaks of the some oxovanadium(IV) complexes.

S. No. Complex Amax (nm) Peak assignment (€, litre morlcm·l)

I. [VO(BUMPHP-PAhj.H20 316 (4260) Charge transfer transition

2. [VO(BUMPHP-MPh ].H20

3. [VO(BUMPHP-MThj.H20

326 (4650) Charge transfer transition

337 (5000) Charge transfer transition

314 (4315)

333 (4130)

Charge transfer transi tion

Charge transfer transition

4. [VO(BUMPHP-OPHD)] .H20 316 (4730)

332 (3940)

349 (3890)

564 (130)

Charge transfer transition

Charge transfer transition b2 ........... > al' b2 .... > e'

5. [VO(BUMPHP-MPHD)(H20)] 311 (3890)

325 (4100)

340 (4520)

451 (60)

573 (20)

Charge transfer transition

Charge transfer transition

b2 .. > al' b2 ...... > bl' b2 .. ....•. > e'

g·o 60 5·0 4·0 3·0 2·0 10 00 ppm

Fig. 2_I H NMR spectrum of [W02(SCN)(C2H50HMBUMPHP-OP)]

nucl ear hyper fin e coupling, a characteri stic of an unpaired electron being coupled with a vanadium nuclear spin (! = 7/2). The observed g values are as follow s: [VO(BUMPHP-MPh lH 20, (RT) gay : 1.972; (LNT) gav 1.966, and [VO(BUMPHP-MPHD)(H20)] , (RT ) gav : 1.976, (LNT) gav : 1.969. The g values so obtained are comparable with the g value already reported55 for oxovanad ium(l V) complexes.

The IH NMR spectrum (Fig.3) of a representative compound [W02(SCN)(C2HsOHh(B UM PH P-OP)] (8) was recorded in DMSO-d6 . The proton signals due

to aromatic protons of the phenyl group of thi s compound appeared at 7-8 ppm. The butyryl group [CH2(b) CH2(a) CH) ] shows protons signals at 0.82 ppm for -CH) , 2.8 ppm for-CH 2 (a) and 4.3 ppm for -CH2 (b) . Likewise coordinated OH CH2CH) exhibits proton signals at 0.9\ for -CH), 3.4 for -CH2 and 2.29 for -OH. These proton signals are consistent with the composition of the complex .

Acknowledgement We are thankful to Shri A. Gurtoo, Vice-chancellor

of thi s University, for encouragement, and Professor

MAURY A et al.: STUDIES ON CHELATES OF VANADIUM & TUNGSTEN 1063

K K Mishra, Head, Department of Chemistry, for laboratory facilities. We are grateful to UGC, New Delhi (Project No. F. l2-S7/97 (SR-I), and CSIR, New Delhi (Project No.Ol (l609)199/EMR-II), for financial assistance. Analytical facilities provided by CDRI, Lucknow and RSIC, I1T, Madras are gratefully acknowledged.

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