Indian Journal of ChemistryVol. 35A, July 1996, pp. 580-585

Synthesis and characterization of cobalt complexes of diacetylbis(4-methoxybenzoyl hydrazone)

Kamalendu Dey", P K Bhattacharya, D Bandyopadhyay & KChakraborty

Department of Chemistry, University of Kalyani, Kalyani 741 235

Received 23 April 1995; revised 29 December 1995

The preparation and characterisation of some new Co(II and In) complexes derived from diacetylbis(4-methoxybenzoyl hydrazone), (Hjdambhon) and cobalt salts under varied reaction conditions arereported. Reduction of [Co'{darnbhonj], isolated in this study, with Na(Hg) in THF under N2 affordedNa[Co'(dambhon)], subsequent reaction of which with RX and normal work up gave many new orga-nocoba\t(JIl) complexes of the type [RCo1JI(dambhon)H20], which on treatment with L (L= NH3, Py orPh,P) afforded [RCollI(dambhon)L]. The stereochemistry of the isolated solid complexes have been dis-cussed by elemental analyses, molar conductance values, magnetic susceptibilities and spectroscopic (lRand electronic) data. Depending on the reaction condition, the ligand can function either as a monoba-<icquadridcntatc or dihasic quadridentate ONNO donor ligand.

Despite extensive research on the complexes ofcobalt(II) and cobalt(III) with different types ofaroyl hydrazone ligands J -7, no work is availableon cobalt complexes of diacetyl bis(4-methoxy-benzoyl hydrazone), Hjdambhon.

In continuation of our work on metal com-plexes of Hydambhon with transition and non-transition elements'"!", we have synthesised sever-al cobalt (II and III) complexes of this ligand in-cluding some organo-derivatives. This paper de-scribes the results of this investigation.

Materials and MethodsThe solvents were dried before use. Physico-

chemical data were collected as described in ourearlier publication J 5. The elemental analysis wasperformed at RSIC, CDRl, Lucknow and lITMadras.

Preparation of the ligandThe ligand was synthesized by our previously

published method",

Preparation of complexes [Cd"(dambhon) (NH3)-(H20)], NO~ (1)

To a methanolic (20 mI) suspension ofHvdambhon (1.91 g, 0.005 mol), solidCo(N01h6H20 (1.45 g, 0.005 mol) and NH4NOJ

(1 g) were added, followed by the addition ofNH.jOH solution (15%) to raise the pH to -4).

Then air was bubbled through the mixture for 32

h (pH - 9 was maintained during this period). Thereaction mixture was filtered and clear dark filtr-ate yielded deep brown powder on cooling in arefrigerator (- 5°C) for overnight. It was filteredoff, washed with small amount of methanol anddried in vacuo, yield 60%.

[Cd'(Hdambhon)(NOJ)(H20)1, (2)Similarly, a methanolic (15 mI) suspension of

Hjdambhon (1.91 g, 0.005 mol) was treated witha methanolic solution (10 mI) of CO(NOJ)2.6H20(1.45 g, 0.005 mol) under nitrogen atmosphereand allowed to reflux for 3 h and filtered. Thebrownish filtrate (pH - 4) on concentration, cool-ing ( - 5°C) and thorough stirring with few ml ofdiethyl ether afforded a brown crystalline com-pound. It was collected by filtration, washed withEtOH-Et20 mixture (50:50, v/v) and dried invacuo, yield 60%.

[ColII(dambhon)(NH3lz1 N03, (3)Air was bubbled through a methanolic (15 mI)

solution of [CoJJ(Hdambhon)(N01)(H20)], (2)(2.60 g, 0.005 mol) containing solid NH.jN01 (0.4g, 0.005 mol) at pH - 9 (15% NH.jOH solution)for - 12 h to get a clear solution. The clear filtr-ate on concentration and cooling ( - 5°C) affordeda violet-brown crystalline compound, which wascollected by filtration, washed with cold ethanoland then dried in vacuo, yield 75%.

DEY et af.: COBALT COMPLEXES OF D1ACETYL BIS(4-METHOXYBENZOYL HYDRAZONE) 581

[Coll(dambhon)], (4)Hydambhon (0.76 g, 0.002 mol) was taker. in

THF (100 ml) and NaH (0.53 g, - 10% excessover 0.002 mol) was added to it and heated to -50°C for 2 h. To the mixture was then added an-hydrous CoCl2 (0.26 g, 0.002 mol) and heatedunder reflux for 2 h to yield a yellow brown solu-tion. It was filtered and the filtrate on concentra-tion and cooling afforded a light brown com-pound. It was filtered, washed with methanol(containing a few drops of .THF) and dried invdcuo, yield 65%.

[RColll(dambhon)H20] (R= Me, (5); Ph, (6);Ph - CH2, (7); CH2 - CH= CH2, (S)

A suspension of Co'{dambhon), (4) (4.39 g,0.01 mol) in anhydrous THF was reduced with1% Na(Hg) under nitrogen. The green solutionwas separated from the amalgam and treated withR1 (alkyl and aryl iodide) at - 20°e. This mixturegave red/red-orange crystalline/powdery producton treatment with ice-water and removing THF invacuum:',

[RColll(dambhon)H20], on treatment with L,yielded[RColll(dambhon)L] in good yield",[R=CHJ, L=NH3' (9); R=Ph, L=NHJ' (10);R=PhCH2, L=NH3, (11); R=CH2CH=CH2,

L=NH1, (12); R=Me, L=Py, (13); R=Ph,L= Py (14); R= PhCH2, L=Py, (15); R= CH2CH= CH2, L= Py, (16); R= Me, L= PH3P, (17);R= Ph, L= Ph,P (IS)]. [CdlI(dambhon)(L)](L= anion of salicylaldehyde, (19); anion of acetyl-acetone, (20); anion of glycine, '21) .

These cobalt(ITI) heterochelates were synthes-ized by two different routes following our previ-ously published methods 15: (i) the dir.ect reactionof Hjdambhon, Co(N03h.6H20 and HL (equi-molar ratio) in methanol and in the presence ofair; or (ii) by the reaction of preformed[Coll(Lh].2H20 with Hjdambhon in the presence,of air. The analytical and other physicochemicaldata of the cobalt (II and III) complexes are pre-sented in Table 1.

Results and DiscussionThe reaction of diacetyl bis(4-methoxybenzoyl

hydrazone), Hjdambhon with Co(N03h·6H20,CoCl2, Co(acach·2H20 and Co(salk2H20 underdifferent reaction conditions yielded colouredcomplexes of cobalt (II and III), (1-21), (Table 1).Reactions of cobalt(II) salts/compounds in thepresence of air invariably afforded complexes ofcobalt(III) ion, while reactions under nitrogen at-mosphere yielded complexes of coba\t(II) ion.

Direct reaction of Co(N03h"6H20 withHvdambhon in methanol at pH - 5.0 yielded theco-mplex, [CoIl(Hdambhon)(N03)(H20)], (2) wherethe ligand functions in a monobasic quadridentatefashion (see later discussion). On the other hand,di-sodium salt, (Na.dambhon), prepared by treat-ing Hjdambhon with NaH in THF, reacted withCoCl. (anhydrous) in THF to afford a cobaltrll)complex, [Co'{dambhonj], (4) where the ligandfunctions as a dibasic quadridentate chelate (seelater discussion). Aerial oxidation of the complex[Coll(Hdambhon)(N01)(H20)], (2) in the presenceof NH4NOJ and NH40H yielded cobalt(ITI) com-plex [Co'l'(dambhon) (NH3h]N03, (3) where boththe keto groups are enolised and deprotonatedprior to hond formation with cobalt(III) ion. Re-duction of Co'{dambhon) with Na(Hg) in THFunder nitrogen yielded a cobaltil) species (not iso-lated) Na[Co'(dambhon)] as found with severalother square planar cobalt(II) complexes withNcO] donor ligand!", the subsequent reaction ofwhich with RX (alkyl or aryl iodide) providedseveral new organo-cobalttlll) complexes of thetype [RCo11l(dambhon)L] (Scheme 1; Table 1). Inthese organo derivatives, the ligand functions as adibasic quadridentate N202 donor chelate. Theheterochelates [Col'{dambhonjtl.j], [(19), whereLe=sal': '; (20) where L=acac-'; (21) whereL= gly-'] can be synthesised by two differentroutes. The direct reaction of Hjdambhon withCo(N03h. 6H20 and HL in methanol in the pres-ence of air resulted the heterochelates (19 )-(21).The same heterochelates can also be synthesizedby the reaction of preformed [ColI(Lh]·2H20 withHjdambhon in the presence of air.

The cobalt(II) complexes, when dried, are suffi-ciently stable against aerial oxidation, althoughthey slowly oxidise in solution of donor solvents.Elemental analyses (Table 1) of all the newly syn-thesised complexes support their formulations.The complexes (1) to (7) are soluble in water andcoordinating solvents whereas' all other com-pounds are soluble only in coordinating solventssuch as DMSO, DMF and pyridine.

The compounds (4 )-(21) behave as non-electro-lytes in DMSO (AM of 10-3 M solution at roomtemperature varies between 10-14 em? ohm - 1

mol- 1)17 (Table 1). The conductance value of30.93 for the complex (2) in DMSO at room tem-perature indicates partial solvolysis. Both waterand DMSO solutions of the complexes (1) and (3)behave as 1:1 electrolytes.

The magnetic moment values of cobaJt(II) com-plexes are generally diagnostic of the coordinationgeometry about the metal ion lR-24. The observed

582 INDIAN J CHEM, SEC. A, JULY 1996

Table I-Characterization data of the complexes

Complex M.Pt. Found (Calcd.), % A'M(0C) 'ohm-'cmzmol-'

C H N Co

[Co11I(dambhon)(NH,)(HP)]NO-" (1) 208 43.02 4.71 17.84 10.70 58.34(dec.] (43.41 ) (5.06) (17.72) (10.65) 92.8b

[ColI(Hdambhon)(NOJ)(HzO)],(2) 105-110 46.30 4.50 13.74 11.05 30.93(dec.) (46.16) (4.42) (13.46 ) ( 11.33)

[ColII(dambhon)(NHJh]NOJ, (3) 195 45.08 5.00 17.95 1l.l5 52.60(44.86) (4.86) ( 18.32) (11.01 ) 98.20"

[Co'(dambhonl], (4) 138-140 54.26 4.58 J 2.70 13.84 IOA5

(dec.) (54.66) (4.55) ( 12.75) ( 13.43)[MeCo'lI(dambhon)HzO], (5) 150-152 53.80 5.02 12.00 12.32 7.65

(dec.) (53.38) (5.29) ( 11.86) ( 12.5)[Ph Co't'(dambhonjl-l.O], (6) 179-183 59.00 5.00 10.92 10.96 10.20

(dec.) (58.42) (5.05) ( IOAl{) ( 1\.04)[Ph Cl-l.Co'I'(dambhonjl-l.O], (7) 185-187 60.10 5.33 1O.!i2 10.94 6.65

(dec.) (59.12) (5.29) (10.21 ) ( 10.76)[CHzCH = CHzCoII1(dambhon)Hp], (8) 55.21 5.50 11.!i0 IIAY 9.85

(55.42) (5.42) ( 11.24) ( 11.!i4)[CH3Co'lI(dambhon)NH,], (9) 148-150 53.62 5.82 15.02 12.76 8.95

(dec.) (53.50) (5.52) (14.86) ( 12.52)[C6H5ColIl(dambhon)NHJ]' (10) 59.00 5.60 13.88 10.89 6.30

(58.53) (5.52) (13.13) ( 11.06)[PhCHzCo'lI(dambhon)NHJ], (II) 60.00 5.50 13.00 11.02 7.35

(59.23) (5.48) (12.79) ( 10.78)[CHz·CH = CHzCo11I(dambhon)NH)], (12) 55.98 5.60 14.92 12.20 7.95

(55.53) (5.63) (14.08) (11.87)[CHFolII(dambhon)Py], (13) 150-152 58.99 5.67 13.02 10.98 8.40

(dec.) (58.53") (5.25) ( 13.13) (11.06)PhCo't'(dambhonll'y], (14) 62.11 5.91 11.99 10.00 9.30

(62.52) (5.04) ( 11.76) (9.91)[PhCH2Co11I(dambhon)Py], (15) 63.58 5.00 11.69 9.93 10.15

(63.05) (5.25) (11.49) (9.68)[CH2CH= CH2ColII(dambhon)Py], (16) 60.79 5.68 12.79 10.72 6.95

(60.10) (5.36) (12.52) (10.55)[CH3ColII(dambhon)PhJP], (17) 190-192 65.00 5.54 8.02 8.41 8.25

(dec.) (65.36) (5.30) (7.82) (8.24)[PlrCo'I'(dambhonlf'hP], (18) 68.11 5.71 7.90 7.40 9.90

(67.86) (5.14) (7.19) (7.58)[Co'l'(dambhonusalj], (19) 2W 57.92 4.82 10.07 10.7 11.75

(57.86) (4.46) (10.00) ( 10.52)[Co'I'(dambhonuacacl], (20) 165-170 55.29 4.98 10.59 10.90 13.25

(dec.) (55.77) (5.02) (10.41 ) (10.95)[Co'I'(darnbhon'{glyl], (21) 280 51.98 4.15 13.60 IJ.20 12.40

(51.47) (4.68) (13.65) ( 11.48)

"10-3 Msolution in DMSO at room temperature; "10-3 A/solution in H20 at room temperature

DEY et al: COBALT COMPLEXES OF DIACETYL BIS(4-METHOXYBENZOYL HYDRAZONE) 583

magnetic moment value of 4.95 B.M. for (2) iswithin the range of octahedral/ or tetrahedral co-baJt(II) complexes 18. High spin five-coordinate co-balt(II) complexes also show magnetic momentvalue in this range 18. Therefore, no definite con-clusion regarding the structure can be drawn onthe basis of the magnetic moment value alone.The magnetic moment value of 2.28 B.M. for (4)indicates its square planar geometry which is alsosupported by the electronic spectral data. The di-amagnetic nature of all other complexes (1), (3),(5 )-(21) may be taken as suggestive of the forma-tion of octahedral cobalt(lII) complexes.

The electronic spectral data (in DMSO) of thecobalt (II and ill) complexes were recorded. Nujolmull spectra for the cobalt(II) complexes havealso been measured and compared. The electron-ic spectra of the cobaltflll) complexes (1), (3), (5)-(21) in the near UV and visible region show threebands in the range 525-590; 455-500 and 370-400 nm. The two bands at - 525 and 500 nmmay be tentatively assigned as the split compo-nents of the lAlg_l~g transitions 19. The higherenergy band at - 370 nm is probably due to the1Alg - '12g transition mixed up with metal to li-gand (t2g - n*) transitions".

The spectral band positions and their tentativeassignments suggest pseudo-octahedral geometry'?for the chelate [CoIl(Hdambhon)(N03)(H20)], (2).We could not measure the spectral bands beyond1000 nm, and thus we are unable to locate the VI

band (4~g-412g). However, the position of VI

band has been calculated quantitatively with thehelp of V2 and V3

19, and the calculated value is320-305 nm. However, as in the present case, theV3 band is commonly split into many components,which makes the assignments difficult. Thesecomponents may be due to lifting of the degener-acy of the 4 ~g level either by spin orbit couplingor by the presence of a low-symmetry componentin the ligand field. Alternatively, the componentsmay be due to the presence of a spin-forbiddenband or the appearance of the V2 transition". Weare not sure whether the band near 550 nm (sh)is due to v2 transitions. IT it is so, then the shoul-der observed - 670 nm in the chelate (2) may bedue to the spin-forbidden transitions 4 ~g _ 2 ~g,

212g(2G)19.

The magnetic moment value of the complex[CoIJ(dambhon)], (4) is found to be 2.29 B.M. sug-gesting square planar geometry, which is furthercorroborated by the appearance of electronic ab-sorption bands (nujol] in the regions - 550 and- 470 nm assignable (tentatively) to 2B2g-4Eg(P)and 2 E28 - 4A2g transitions":".

The free ligand shows absorption bands in theregion 230-240, 290 and 335 nm. The complexesalso show some of the bands with slight shifting,which suggests the coordination of the ligands tothe metal.

The infrared spectra of the ligand and its cobalt(II and III) complexes have been measured in KBrphase. The free ligand shows band for vNH at -3280-3310 em-I, which disappeared in the com-plexes (1), and (3 )-(7) suggesting the enolizationof the ligand and subsequent coordination withcobalt ions after deprotonation as a dianionic li-gand. However, the presence of HiO and NH3 inthe complex (1) and NH3 in the complex (7) re-spectively complicates this interpretation.

The free ligand exhibit amide-I, "c = N, amide-II and amide-III band at -1650, 1605, 1575,1495 and 1255 em -I respectively. Negative shiftsof the amide-I (~v= 10 em-I), "c=N (~v= 15

.cm=") amide-Il (~v=20 em-I) bands and a posi-tive shift of the amide-ill (~v= 15-20 em-I) bandin the spectra of the complex (2) indicate mono-basic quadridentate nature of the ligand in thecomplex (2). These bands disappeared in the de-protonated complexes (1) and (3)-(7). The fea-tures discussed above are parallel to the observa-tion of Iskandet et al. on the similar type of com-plexes2,22-24. However, the presence of strong andsharp band(s) at - 1600-1615 em - I is diagnosticof the azine chromophore (> C = N - N = C ~ )25.Further, in the monodeprotonated compound (2),an increase in the intensity of the band centered at1600-1610 em-I, due to the C =N - N= C (refs22-24) residue can be observed together with theappearance of a strong band at 1050 em -I due tovC - 026-28 in addition to vNH band at 3185em -I. However, the presence of H20 complicatesthe interpretation. On the other hand, all othercomplexes with deprotonated ligand showedneither absorption band due to vNH nor theamide-I band vC = 0 (see above discussion) butinstead showed the same strong absorption at -1610 and 1035 em-I. The vibration observedaround 1550-1510 and 1380-1330 em-I arecharacteristic of vNCO (ref. 29). In the free li-gand, vC = N appears - 1605 em -I, while thisband gets shifted to - 1585-1600 em - I suggest-ing coordination of azomethine nitrogen". Thepresence of NH3, however, complicates this infer-ence. Coordination of NH3 in the complexes (1)and (3) are indicated by the appearance of bandsat 1585-1595 (sh), 1300-1305 and - 850 em-Iassignable respectively to the 0d NH 3, 0~ NH 3

and p, NH3 vibrations, while the assignments ofvNH, is complicated by the presence of bands for

584 INDIAN] CHEM, SEe 1\,JULY 1996

H20 in the complex (1) (ref. 30). However, ap-pearance of a band at - 3180-3300 cm-I suggestthe presence of NH3 in the complex (7) (ref. 31).The bands observed in the range 840, 1390 and750 cm-I in the nitrate salts (1) and (7) can beassigned to VI' v2 and V3 mode of vibrations (inD3h symmetry)": On the other hand, unidentatenature of N03( C2J in the complex (2) is demon-strated by the appearance of infrared bands at -1480, 1260, 1020, 850 and 760 em - I (refs 32,33) ..

The complexes (1) and (2) show broad mediumbands in the region 3500-3200 cm - 1, which areassignable to OH stretching vibrations due to thepresence of water. However, exclusive identifica-tion of these bands in the region mentioned is notpossible due to the presence of NH 3 in the com-plex (1) and NH chromophore in the complex (2)respectively. Nevertheless, additional bands -1630, 940 and 755 em - I observed in these com-plexes indicate the presence of coordinated " wa-ter molecule in the chelate under discussion.

For the complex (20), the oxygen bonded che-lating acetylacetonate anion has been inferredfrom the vibrational spectral data34,35 which in thepresent complex show vC~O at - 1570(s)em - I, while vC = 0 is observed generally in theregion 1520-1540 cm-I. It may be mentionedhere that the vC = 6 for C-bonded acetylacetoneoccurs above 1650 em - I. The spectral data clear-ly suggest the presence of oxygen bonded chelat-ing acetylacetonate anion in these mixed chelatesof cobalt(III).

The non-appearance of an infrared band at -1740 em - I (vCOOH) in the complex (21) sug-gests the involvement of glycinate anion in chelateformation. Despite the difficulties in interpretingthe V, COO and va, COO of glycinate anion inthe complex (21) due to the presence of the dian-ion of the ligand, dambhon? -, the infrared bandsat 1395 (s) and 1385 em - I (sh) can be assignedto VS COO and vas COO respectively" of glycin-ate anion. All the above assignments of infrareddata are tentative.

The 'H NMR spectra of the ligand Hjdambhonand some of the cobalt(III) complexes have beenrecorded. It was observed that the free ligandHjdambhon shows signals at 0 11.8 ppm which isassignable to NH proton. This signal is absent inthe complexes (13), (14) and (18) indicating there-by the enolization followed by deprotonation dur-ing complex formation with cobalt(III) ion. Thephenolic proton (OH group) in the ligand shows asignal at 0 12.7 ppm which disappears on com-plexation with cobalt(III) ion. These observations

CH3 CH,I IC--c" ,

N-N N- NII ..•..co·,.. IIc-o/ "'--O-C

$ $OCH, OCH,

(~..> COD (dombhon)

R

(-:::1::»0/1""-...0

l

NO(Hgl. THF.

N,No [Co' (dombhonl)

not isolotod

Rx l<iC. \Motor)

~ NH4CI

CHI CH,I IC--CI R IrN<,~om,..N-1i

C-O./'t "-O-C

~ OH, $OCHJ HJCO

'<9)l,NH"R'M.;(10)l'Mi"R'Ph (S)R'M.,(6) R,Ph.(U) l' NH" R,PhC",'(l1.)l;NH,.R,C",CH'CH" (L) R. PhCH" (~) R, CH,CH, CH,.(!1)l'Py ,R, M. ;(~) Le Py, R, Ph,(~) l' Py ,R.PhCH,.(~)l= Py. R.Cfl,CH.CH,(.!Z) l' Ph,P . R. M. ,(~) l.Ph,P. R= Ph

Scheme - 1

support deprotonation of phenolic OH group andenolization of keto group followed by its depro-tonation during complexation. The aromatic pro-ton (Ph - H) absorbs - 0 6.5-6.9 ppm in the freeligand, which absorbs - 0 6.3-6.6 ppm in thecomplexes. The singlet due to CH, ofCH3C'C = N - group experience a deshielding ofabout 0 0.5 ppm due to coordination of imine ni-trogen with the metal ion. Signals due to OCH,protons in all the complexes and ligand occur .,3.8 ppm. These results are also consistent withthe tentatively suggested structures for the presentcomplexes.

The physicochemical data discussed above lendsupport for the structural formulations of thecompounds as tentatively proposed above andshown in Scheme 1. However, ESR spectroscopicdata of complexes (2) and (4) along with theX-ray crystal structure analysis might throw morelight on the structural features of the complexesisolated in this investigation.

AcknowledgementThe authors (PKB and DB) thank DST and

CSIR, for senior research fellowship and researchassociates hip and KC thanks Kalyani Universityfor a senior research fellowship. We are alsothankful to the RSIC, CDRI, Lucknow, for ele-mental analyses and spectral data.

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