Indian Journal of Chemistry Vol. 43A, March 2004, pp. 516-526

A study on heterobimetallic chemistry of polyfunctional bis(2-hydroxy-l­naphthaldehyde)malonoyldihydrazone: Dioxouranium(VI),

dioxomolybdenum(VI), zinc(II), copper(II), nickel(II) and cobalt(II) complexes a• . b c

R A Lal , J Chakraborty, A Kumar , S Bhaumik, R K Nath & D Ghosh

Department of Chemistry, T1ipura University, Suryamaninagar, 799 130. Tripura, India Emai I : ramashrayl al @rediffmai l.com; ramashraylal@ nehu.ac. in

Received 7 May 2002: revised 10 December 2003

The monometallic uranium (V l) complex [UO/CH~LH)(H,O) l has been synthesized from bis(2-hydroxy-l­naphthaldehyde)malonolydihydrazone (CH

2LH ,) in ethanol. The reaction of this complex with bis (acety lacetonato)

dioxomolybdenum(Vl) and metal acetates (M = Zn, Cu, Ni , Co and Mn) in I: I molar ratio in ethanol (methanol in the case of copper) under reflux yields hetcrobimetallic complexes [MUO,(CH, L)(H,O),] (M = Zn and Cu) and [MUO,(CH,L)(H,O),] (M = Mo0

2, Ni, Co and Mn), respecti ve ly. The complexes have bee~ characterized by analytical , molecu la~· weight, molar

conductance, magnetic moment data and spectral studi es. In all the complexes. the dihydrazone coordinates to the metal centers in an anti-cis-configuration.

The molecular complexes containing two or more

different metal ions are of interest in several areas like

multi metallic enzymes', homogeneous catalysis2

,

heterogeneous catalysis3

and synthesis of solid state phases of industrial and technological importance. The heterobimetallic complexes of uranium (VI) and first row transition metal ions exhibit well defined four electron transfer process

4, a process which occurs in

the reduction of dioxygen. Heterobimetall ic complexes are also important in preparation of ceramic materials favouring an intimate mixing of elements which can

enable reactions at lower temperatures5

.

The synthesis of pure samples of heterobimetallic complexes is a difficult task. It is important to ensure that the metals are not scrambled giv ing rise to considerable quantities of other undesired binuclear products. Hetero-bime tallic compounds may be synthesized using accessible monometallic precusors

6"7

and polyfunctional ligands v ia tran s metallation beginning with a complex of discrete molecularity as

"Present address: Departmen t of ChemisJry, North-Eastern Hill Universi ty, Shillong 793022, Mcghalaya, India

" Present address: Department of Chemistry, MS 60, Rice University, 6100 Main Street, Houston, Texas, USA

c Department o f Life Science, Tripu ra Univers it y, Suryamaninagar, 799130, Tripura, Indi a

target and another metal complex as transmetallator.

The dihydrazones derived from condensation of o­hydroxyaromatic aldehydes and ketones with acyl- ,

aroyl- and pyridoyldihydrazines are a homologous series capable offor-ming a homologous series of heterometal complexes. Dihydrazones are potential polyfunctional ligands containing amide, azomethine and phenol functions in duplicate which have the potential to yield

mononuclear and polynuclear complexes. A survey of literature reveal s that although metal

complexes of monoacylhydrazones, aroylhydrazones and pyridoylhydrazones have been studied in details

8,

those of acyl-, aroyl- and pyridoyldihydrazones have received attention in recent years onl/.'

2• Further, the

reported existence of heterobimetallic complexes of dihydrazones is quite meagre 13

• '

The present paper aims at syn thesis and characterization of heterobimetallic complexes of the dioxouranium(VI) with late first row transition metals ions and oxometal species like Mo02 derived from bis(2-hydroxy-l-naphthaldehyde) malonoy I dihydrazone (CH2LH) (1).

Materials and Methods

Metai(II) salts, uranyl nitrate hexahydrate, diethyl

LAL et al.: HETEROBIMETALLIC COMPLEXES OF SOME METALS 517

malonate, hydrazine hydrate , 2-hydroxy-1-

naphthaldehyde, acetylacetone and ammonium molybdate were E-Merck products. Mo0/acac)2 was prepared by the literature method 14

•

Malonoyldihydrazine was prepared by reacting diethylmalonate with hydrazine hydrate (2 mol). Bis(2-

hydroxy-1-naphthaldehyde )malonoy ldihydrazone (CH2LH4)(1) was prepared by reacting a warm ethanol solution of malonoyldihydrazine (1 mol) with 2-hydroxy-1-naphthaldehyde (2 mol) and was suction filtered, washed with ethanol and dried in vacuo (m.p. 265 oq [Found: C, 68.45; H, 4 .62; N, 13.00. Reqd.

for C25FI.z0NP4: C, 68.18: H, 4.55; N, 12.73 (%)]. Metals in the complexes were determined by

standard literature method15

• Carbon, hydrogen and nitrogen were determined microanalytically on Microanalyzer Heraeus Carbo Erba 1108. Water molecules were determined by heating the samples in an oven at 110°C and 180°C and passing the vapours

through a trap containing anhydrous copper sulphate and a test-tube containing a solution of 12 and sodium hydroxide. Water was also estimated by the weight loss of the complexes. The molecular weights of the

complexes were determined in DMSO solution by freezing point depression method. The molar conductance of the complexes at l0.3 M dilution in

DMSO was measured on a direct reading conductivity meter with dip-type conductivity cell. IR spectra were recorded on a Paragon-500 spectrophotometer in the range 4000-350 em·' in KBr discs. The

1H NMR spectra

were recorded on EM-390, 90 MHz spectrometer, whi le the "c NMR spectra were recorded on a Ff­NMR spectrometer (Model Bruker ACF-300) at a frequency 75.47 MHz in DMSO-d6 solution using

TMS as an internal standard. The electronic spectra of the complexes in DMSO solution were recorded on a Milton Roy Spectronic-21 spectrophotometer and DMR-21 spectro-photometer. The ESR spectra of the compound in powdered form at room temperature and liquid nitrogen temperature were recorded at X-band frequency on a Varian E-12 X/Q-band spectrometer using DPPH as an internal field marker.

Preparation of [UOiCH2LII2)(ll20)](1)

Uranyl nitrate hexahydrate (3.1 g, 6.0 mmol) in ethanol (30 mL) was added to dihydrazone CH2LH4

(0.9 g, 2.0 mmol) in hot ethanol (20 mL) accompanied by gentle stirring. The resulting reaction mixture was

refluxed for 2 h, during which a brown coloured compound precipitated. The compound so obtained was filtered hot, washed three times with ethanol using 5 ml each time and finally one time with 5 mL ether

and dried over anhydrous CaCI2.

[Yield : 0.94 g (65% )].

Preparation of [Mo02(U02)(CH2L)(ll20).1](2)

To the solution of bis(acetylacetonato) dioxo­molybdenum(VI) (0.4g, 1.1 mmol) in hot ethanol (50 mL), the suspension of the precursor complex [(U02)

(CH2LH2)(Hz0)](1), (0.7 g, 1.0 mmol) in ethanol (30 mL) was added drop by drop with constant stirring

Bis(2-hydroxy- l-naphthaldehyde )malonoy ldihydrazone (CH~LH4)

I within a period of 10 min. The reaction mixture thus obtained was stirred for another 30 min at 60-70°C followed by reflux for 3 h. The brown coloured compound thus obtained was purified by washing three times with ethanol using 5mL each time and finally

with 5 mL ether and dried over anhydrous CaCI2. Yield :0.60g, (68%).

Preparation of [M(U02)(CH2L)(H20)2] (where M = Zn(3) and Cu(4) and [M(UO~)(CH2L)(II20).1].xH20 ( where M = Ni(S), Co(6) and Mn(7); x = 0, 1)

In order to prepare the complex [Zn(U02)(CH2L) (H 20) 2](3), a suspension of the precurso r [UOiCHzl,H2) (HzO)](l) (0.7 g 1.0 mmol) in ethanol (30 mL) was added to a solution of Zn(0Ac)2.2Hz0 (0.2 g, 1.1 mmol) in ethanol (50 mL) containing a trace of acetic acid over a time period of 10 min followed by reflux for 1.5 h. This yielded a yellow coloured

compound which was filtered, washed three times with ethanol using 5 mL each time and finally with 5 mL ether and dried over anhydrous CaCI 2[Yield :0.58g (70%)].

518 INDIAN J CHEM, SEC A. MARCH 2004

Enol form(IV)

Staggared-configuration(V)

Anti-cis-configuration(Vl)

Syn-cis-configuration(VII)

LAL et al.: HETEROBIMETALLIC COMPLEXES OF SOME METALS 519

The heterobimetallic copper-uranium complex (4) was prepared in a similar manner as above by reacting a suspension of [U02(CH2LH2)(Hp)] in methanol with Cu(0Ac)2.Hp in methanol instead of zinc acetate in ethanol. The complexes (5)- (7) were also synthesized by essentiall y the above procedure by using respective metal acetates instead of zinc acetate[Yield : 4, 0.60 g (69%); 5, 0.57g (65%), 6, 0.55g (66%); 7 , 0.55 g (67%)].

Results and Discussion

Synthesis of monomel.allic and heterobimetallic complexes

The mononuclear U02(VI) complex is conveniently prepared by direct reaction of uranium nitrate hexahydrate with preformed dihydrazone in 3:1 molar ratio in ethanol as shown below

ethanol (90%) (3 : l) U02(N03) 2.6Hp + CH2LH4 ------+

reflux, 2h

.. . (1)

When the monometallic complex lU02(CH2LH2)

(Hp)] was treated with Mo02(acac)2 or second metal acetates, the heterobimetallic complexes [MUOiCH2L)(Hp)2] (M = Mo0z(2), Zn(3), Cu(4)] and lM(U02)(GHiL)(Hp)3].xHp (M = Ni(5), Co(6) and Mn(7) ; x = 0,1) were obtained, according to Eqs (2) - (4).

ethanol (90% ),(!: l .l)

[UOz(CH2LH2)(Hp)]+Mo02(acac)1 --------+ reflux, 3h

ethano l(90% ),(I: 1.1)

[U01(CH2LH2)(Hp)] + M(OAc)2.nHp ---~

reflux , 3h

[M(U02)(CH2L)(Hp)3] + 2AcOH + xHp

M = Zn11,Cu

11

... (3)

Table 1- Characterization and analytical data of the complexes

SI.No. Complex Colour(decomp .. "C)

[U01(CH, LH 2)Hp] Brown ( >280)

2 [Mo0/ UO) CH, L)( H20)3]

Brown(>300)

3 [Zn(UO,(CH, L)(Hp)j Yel low (>300)

4 [Cu(UO),(CH 2L)(H 20)2

]

Brown (>300)

5 [Ni(UOJ(CH1L)(Hp),] Orange (>300)

6 [Cu(UO)(CH 2L)(Hp),l Brown (>300)

7 [Mn(UO,) (CH, L)(H,O),] Yellow (>300)

Mol. Wt.

Ex pl. (Calcd) U

780±32 32.29 (726) (32.78)

1030±40 26.75 (888) (26.80)

1850±70 30.09 ( 1614.75 ) (29.78)

1850±70 30.10 ( 16 11.08) (29.55)

1950±80 29.56 ( 1637.42) (29.07)

1950±42 28.92 ( 1673.86) (28.44)

1940±75 28.94 ( 1665.88) (28.57)

Found C Calcd)% Molar Electronic spectra Cond. (A.,,"') nm

M C H N A., £.,,., (dm3mor'

(S cm2mor ') em·')

41 .73 2.70 7.02 1.8 350 (8970). ... ( 41.32) (2.75) (7.71) 420( 12750).

540(56)

11 .20 34.25 2.43 6.50 1.5 380( 12780), ( 10.81 ) (33 .78) (2.48) (6.30) 41 0( I 0750),

530(48)

8. 15 37.62 2.45 6.65 2.3 350(9870), (8. 10) (37. 16) (2.48) (6.94) 410(11125),

530(65)

8. 15 37.98 2.46 6.55 1.9 360( I 0260), (7 .90) (37.24) (2.48 ) (6.95 ) 420(9850),

560(250)

7.20 36.95 2.65 6.41 2.8 340( 12780) (7. 17) (36.64) (2.69) (6.85) 415(13720)

700(45)

7.54 36.36 3.51 6.78 1.6 350( 12540) 7.04 (35.85) (2.81) (6.69) 420(10750)

540(48)

6.95 36. 10 2.82 6.82 1.8 360( 13540) (6.60) (36.02) (2.88) (6.72) 430(10780)

5 1 5(56)

520 INDIAN J CHEM, SEC A. MARCH 2004

ethanol(90% )( l: 1.1) [U02(CH2LH2(Hz0)] + M(OAc)2.nHz0---------+

reflux, l.Sh

fM(U02)(CH2L)(Hp)3] + 2AcOH + xHp ... (4)

The mononuclear dioxouranium(VI) complex does

not undergo any transmetallation reaction when treated

with Mo0z(acac)2 or meta l acetates (M = Zn, Cu, Ni,

Co and Mn) and hence gives rise to true

hetcrobimetallic complexes. It must be noted that for heteronuclearcomplexes, prolonged reflux did not lead

to transmetallation reaction . The homogeneity and

metal ion ratio in the heteronuclear complexes have

been established. It was observed that the complexes

are homogeneous with 1:1 metal ratio within

experimental etTor.

The complexes are brown, yellow and orange in

colour. The complexes are insoluble in water and most

common organic solvents. However, the freshly prepared complexes are slightly soluble in aceton itrile

and completely soluble in highly coordinating solvents

like DMF and DMSO.

Detailed decomposition studies of a ll the

complexes were carried out in the temperature range

80-250°C and the evolved vapours identified by

passing the vapours through a trap containing

anhydrous copper sulphate and a test tube containing

a solution of 12 and sodium hydroxide. None of the

complexes showed weight loss below 120°C ruling

out the possibility of the presence of solvent mo lecules in the lattice structure of the complexes. However, al l

of the complexes showed we ight lo ss in the

temperature range 160-180° C. In this temperature

range the vapours evolved from all of the complexes

turned anhydrous copper sulphate blue confirming that they originate from water molecules. Also, the vapours

evolved from none of the complexes gave yellow

precip itate with a solution of iodine and sodium

hydroxide ruling out the possibility of presence of

ethanol. The weight loss in the temperature range 160-1800 C corresponds to loss of one water molecu le in

the case of complex (1), while in complexes (3) and

(4) it corresponds to the loss of two water molecules each. On the other hand, in the remaining complexes,

the weight loss corresponded with three molecules of

water in each. The loss of these water molecules in

the temperature range 160-180° C indicates that they

are coordinated to the mu&l centre.

All the complexes decompose above 300°C except

the complex (1) which melted with decomposition at

> 280°C. The high decomposition temperature of the

complexes also indicates good thermal stability . The molecular weights of the complexes (Table 1) in

DMSO solution show that the monometallic complex (1) and heterobimetallic complex (2) are monomeric

while the remaining complexes are dimeric. 1H NMR spectra

The complexes (1), (2) and (3) were characterized

by 1H NMR recorded in DMSO-d6 solution. The

1H

NMR spectral data for the free dihydrazone and the

metal complexes have been set out in Table 2.

The dihydrazone can coordinate to the metal centres in keto(II), keto-enoi(III) and enol (IV) fotms

and can adopt staggered configuration(V) or anti-cis

configuration (VI) or syn-cis-configuration(VII) 16

• The

present ligand can prov ide two types of coordination

chambers if it coordinates to the different metal centres

Table 2- 'H NMR Spectral data of the complexes

Sl. Ligand/Complex No. 8CH ~

3.90 3.60

a

8 (naphthyl)

7 .03-8.30(m)

7.07-8.54

7.10-8.45(m)

'H NMR (ppm) 8>CH=N- (J , Hz)

9.30 (d, 32.9) 8.60 (d, 32.0)

9.84(d, 35.6) 9.00(d,35.6)

9.70(d, 19. 8)

4 [Zn(U02)(CH2L)(Hp)2] a 7.00-8.65(m) 9.53(d.41.9) 8.85(d,41.9)

80H + dNH (J. Hz)

12.65 (d,63 00) I I .SO(d, 63.00)

12.29(d, 61.7) 11.18(d, 61.7)

a. 8CH 2 signal from dihydrazone and 8CH 3 signal from coordinated CH,COO group masked by signal arising from water absorbed by DMSO-d6

LAL et at.: HETEROBIMETALLIC COMPLEXES OF SOME METALS 521

in the anti-cis-configuration while it can provide only

one type of coordination chamber if it coordinates to the different metal centres in either staggered

configuration or syn-cis configuration. The N20 2 donor atoms originating from azomethine nitrogen atoms and naphtholqte oxygen atoms belonging to the naphthaldimine fraction of dihydrazone constitute one type of coordination chamber while another coordination chamber is constituted by the 0 20 2 donor atoms which originate from carbonyl group and naphthol ate group provided the latter acts as a bridging group. On the other hand, when the dihydrazone coordinates to the metal centres in either the syn-cis­

configuration or staggered configuration, the different metal centres bond through naphtholate oxygen atoms, carbonyl oxygen atoms and azomethine nitrogen atoms making up N02 donor sets. Such a difference in the bonding mode of dihydrazones could be reflected in their spectral properties.

The doublets and two proton signals observed in the 811.11-12.96 ppm and 8.40-9.48 ppm regions downfield of TMS may be assigned to 80H + 8NH and 8-CH=N-protons, respectively. Further, two

signals observed at 83.60 and 3.90 ppm are assigned to methylene protons

17. The multiplet due to aromatic

protons appear in the 87.03-8.30 ppm reg ion . The appearance of two doublets in the region 811 .11 -12.96

Table 3- 75.47 MHz Proton noi se decoupled spectral malonoy ldihydrazone (CH2LH4) and

Sl. CH2LH 4

No. Carbon atom 8'

C(2a).C(2b) 168.3. 167.3 2 C(2a), C(2b) 162.6. 162.2

3 C(l3a) C(l3b) 157.8.156.7 4 C(3a),C(3b) 146.0, 145 .6 5 C(IOa),C(IOb) 142.9, 142.5

6 C(5a).C(5b) 132.8, 132.4 7 C(9a),C(9b) 13 1.4. I 3 I. I 8 C(6a),C(6b) 128.9, 128.6

9 C(4a),C(4b) 127.8, 127.6 10 C( 13a).C( 13b) 123.5, 123.3 II C( 12a),C( 12b) 121.0. 120.8 12 C( 13a),C( 13b) 11 8.1 , 11 8.0q 13 C( lla),C( IIb) 108.4.108.3 14 C(lh) 110. 1 15 C(la) 41.5

t>S = 8'(CH2LH,) - 8' (complex)

ppm coupled with signals at 83.60 and 3.90 ppm suggests enolization of dihydrazone involving active

methylene group with keto-enol equilibrium in the solution. Thus, the signal at 83.60 ppm may be

attributed to methylene ( -CH2-) and that at 83.90 ppm to methine proton ( =CH-).

I ?+ The H NMR spectrum of U02- (VI) complex (1)

indicates that the conformation of the dihydrazone remains unaltered on coordination .The signals in the

H

7a

2b

C-N­H

8a

data ( DMSO-d6) for bis (2-hydroxy-1-naphthaldehyde)-its [U02(CH2LH,)(Hp)] complex(l)

[UOCH,LH)(Hp)]

8' 68'

162.5 +4.80 160.2 +2. 10 171.6, 171.2 163 .0.161.1 '1 59.5, 158.8, 157.3 -14.14 145.4. 143.0 - 1.50 135.2, 134.7 -2 .35 I 32.2, 13 1.4 -0.38 128.8. 128.6 +0.05 128.0. 127.8 -0.20 125.0. 123.3 -.40 120.9, 120.7 +0.10 118.1 ,11 8.0 0.00 108.5, 104.8 + 1.65 95.3 +14.8 19.0 +22.5

'a' refers to axial carbon atom and 'h' refers to equatori al carbon atom

522 INDIAN J CHEM, SEC A. MARCH 2004

8a

8b

[U02(CH2LH2)(H20)]

(IX)

811-13 ppm region are weak, broad and shifted upfield

by about 0.34 ppm in the complex as compared to that in the free dihydrazone in which they are relatively

intense indicating that they arise due to secondary

-NH protons17

. This suggests coordination of the

naphtholic -OH groups to the metal centre via

deprotonation ruling out the possibility of involvement

of secondary NH group in bonding. Similar to 80H + 8NH resonance, the 8CH=N- signals also appear in

the form of two doublets in the complex. The average

position of 8-CH=N- signal shifts downfie ld by 0.48

ppm suggesting coordination of <lzomethine nitrogen 17 I

atoms to the metal centre . These H NMR spectral

features suggest that the metal centre occupies the N20 2

coordi nation chamber of the ligand. This is possible

only if the dihydrazone coordinates to the metal centre

in the anti-cis -configuration . This is also supp011ed

by the fact that the 8NH and 8CH=N-signals appear as two doublets .

On the other hand, the 1H NMR spectra of the

heterobimetallic complexes (2) and (3) show different

features as compared to that of the precursor complex.

In the spectra of the complexs no signal is observed in the 811.00-20.00 ppm region . This indicates loss of

secondary -NH proton in these complexes as a result

of enolization of ligand on heterobimetallic complex

formation. The 8CH=N- signals are shifted upfield by 0.17 and 0.23 ppm as compared to that in the precursor complex. However, these signals are still downfie ld by 0.31 and 0.25 ppm as compared to that in the free

dihydrazone. Such a feature associated with the shift

of 8CH=N- proton signals may be related to the flow

of electron density to the second metal centre through

enolate oxygen atoms suggesting bonding th rough

enolate oxygen atoms to the second metal centre. This

in turn, may reduce the amount of charge flowing to

the original metal through azomethine nitrogen atom

indicating that the metal-nitrogen bond in these complexes is weaker than in the precursor monometallic complex.

°C NMR spectra

Only the coordinated ligand and the complex (1) were characterized by

13C NMR spectroscopy in order

to derive information reg;.:rding the coordination mode

of the ligand to the metal centre (Ta ble 3). The

chemical shift 8 ( ppm from SiMe4) and the chemical

shift changes .6.8 (ppm) accompanying the coordination of the ligand have been deduced taking into account

the shift in the resonances of naphthy l ring carbon

atoms caused by the substituents azomethine group and naphtholic -OH group

18• The numbering scheme

for the carbon atoms in both ligand and complex is the

same as shown in structures (VIII) and (IX). The

carbon atoms in the axial and equatorial positions have

been designated by the letters 'a' and 'b' respectively.

As a result of coordination, some s igna ls split resulting in a higher number of signals than those in the free ligand . The effect of metal ions on carbon

resonances of naphthyl ring thus shifts the signals for C(6), C(8) and C(9) downfield by at least 0.40-0.20

ppm. On the other hand, the signals due to C(7) and

C(11) show an upfield shift of+ 0.05 to +1.65 ppm,

respectivley. Further, the signals due to C(2), C(4) and

C( 12) either remain almost unshifted or shift upfield

by 0.10-5.85 ppm. The shift to higher field of the s ignals due to C(2) rules out the poss ibility of

coordination of >C = 0 group to the metal ion. It is therefore, reasonable to expect that the C(l3) and C(3)

resonances are shifted downfield even more since they are closer to the coordinated oxygen and nitrogen

atoms. As a consequence, the signals for C(l3), which

in the free ligand, were at 8 157.8, 156.7 ppm,

respectively, can be either in the region 8 156.3 - 163.0

ppm or in the region 171.2-171.6 ppm. The latter

assignment is much more likely since, it gives a

deshielding of 8 14.15 ppm, whereas the former

a~signment gives only small shielding of 2.69 ppm.

LAL et al.: HETEROB IMETALLIC COMPLEXES OF SOME METALS 523

On this basis, the signals in the region 157.3 -163.0 ppm may be assigned to the azomethine carbon atoms C(3) alone which in free ligand were at 8 145.6 and

146.0 ppm giving a change in chemical shift in the

region 8 14.14 ppm. The signals at 143.0-145.4 ppm may be assigned to C(lO) while those in the region 8 134.7- 135.2 ppm to C(5) carbon atoms. These carbon atoms absorb at 8 142.5, 142.9, and 132.3, 132.4 ppm respectively in free dihydrazone giving chemical shift changes of 1.5 and 2.35 ppm respectively. The signal at 8120.7, 120.9 ppm is assigned to C(4a) and C(4b) carbon atoms which in free ligand appeared at 8 120.8 and 121.0 ppm giving an upfield shift of about 0.10 ppm. Such a feature associated with C(4a) and C(4b) resonances may be attributed to the combined effect of drainage of electron density from azomethine nitrogen atom in opposite direction.

In view of the above spectral feature and discussion of the

13C NMR spectra of both the ligand and the

complex it is resonable to suggest that the ligand and metal complexes have the same symmetry and that

the dihydrazone is coordinated to the metal centre in

anti-cis-configuration. It is worth noting that all signals appear as pairs in

free dihydrazone except the signal due to methylene carbon atoms which appear at 8 41.5 and 110.1 ppm due to keto and enol forms giving rise to a total of 28 resonances . These signals are shifted upfield in the 13

C NMR spectrum of complex. The appearance of both the signals in the NMR spectrum of the complex indicates that the complex exists in keto-enol form involving methylene protons in the solution . Each

reasonance from a pair cotTesponds to the axial and equatorial carbon atoms. On the other hand ,

13C NMR

spectrum of the complex shows more number of signals than those in free dihydrazone. The additional signals may be attributed to the effect of coordination of metal centre to the ligand molecule.

Table 4- IR spectral data of the dihydrazone and the complexes

Complex

[1]

[2]

[3]

[4]

[5]

[6]

[7]

v(OH)

+v(NH )

3450 sbr 3200s 3047s

3450sbr 3190s 3080s

3500-3000sbr 3500-3000sbr

3550-3300sbr

3550-3000sbr

3500-3000sbr

3500-3000sbr

• bands due to vMoO,'•

v(C=O) v(C=N) Amide II+ v(NCO·) f)(C-0)

v(C-0)

(naphLholi c)

1699vs 1617vs 1532vs em' 1278s 1661 vs 1596vs

1679vs 1622vs 1542vs em' I 281m 1662vs 1602vs

1623s 1540vs 1507s I 283m 890vs 1604s

1622s 1550sh 1510s 1283s 1604s

1620vs 1530vs 1505sh I 283m 1600vs

1620vs 1532vs !305m 1602vs

1618vs 1532vs 1302s 1602vs

1619vs 1531 vs !300m 1604vs

v(Uo,~· ) o v(MO) v(M-0) - /'-....

v(M V M) (naphlholic)(carhonyl)

0

em' em' em'

913s em' 526w em '

em' em ' 535vs 420m

913s 800s 554w 476w

943s 860w 527w 4llw

922s 867w 528w 420w

919s 867s 524s 420s

922s 860w 558w

524 INDIAN 1 CHEM, SEC A. MARCH 2004

Infrared spectra

[UO/CH 2LH 2)(Hc0)]

(X)

[Mo02(CH2LH2)(1-1 20)3]

(XI)

Structurally significant IR bands for the free

dihydrazone, and complexes have been set out in Table

4. The spectrum of the mononuclear complex [U02

(CH2LH2) (HzO)] resembles that of the dihydrazone.

It is characterized by the presence of a very strong vC =0 band at 1679 and 1662 cm-

1• The uranyl centre,

most probably, lies in the Nz02 coordination chamber,

since the vC = 0 band lies at almost the same position

as in other monomer complexes with the similar

dihydrazone ligand where Nz02 occupancy does not 19

affect the vC =0 band .

The vC = N band appears as two bands at 1622 and 1602 cm-

1 in the complex (1 ). The shift of v(C-0)

band at 1281 cm·1

to higher frequency by about 3 cm·

1 in combination with the appearance of a new band

at 526 cm-1

in complex(!) ind icates coordination

through naphtholic -OH group via deprotonation20

•

TheIR spectra of the heterobimetallic complexes (2) to (7) are clean in the region 1630-1700 cm·

1

indicating destruction of amide structure of the ligand as a resu lt of enolization of the dihydrazone

12• The

v(C -0) band appears in the region 1280-1305 cm-1

similar to that in complex (1). The vC =N band appears

[MU02(CH2L)(H20)2) ( M = Zn(3), Cu(4))

(XII)

[M U02(CH2L)(H20)3](M =Ni(5), Co(6). Mn(7))

(XIII)

in the region 1600-1623 cm-1

as a couple of bands.

The complexes (3)- (7) show a new, weak to strong,

intensity band in the 800-876 cm-1

region. This band

0

is characteristic of the tetraatomic species M () M

0 resulting from involvement of naphthoxide oxygen in bridge formation

12• Its position is dependent on the

nature of the metal atoms.

A new strong band appearing in the region 943-913 cm-

1 in the complexes (3) - (7) is attributed to

viU02

2+) stretching vibration. The com~lex (2) shows

three new bands at 970,930 and 890 em- . Out of these

three bands, the bands at 970 and 930 em 1 are assigned

2+ 0 - 1 • to cis-Mo02 group, while the band at 89 em IS

attributed to linear uranyl group.

LAL et al.: HETEROBIMETALLIC COMPLEXES OF SOME METALS 525

The non - ligand bands appearing in the region 524-558 cm-

1 and the new weak to medium intensity

band in the 420-476 cm·1

region in complexes (2) -

(7) are attributed to v(M-O)(naphtholic ) and v(M­O)(carbonyl ) resulting from coordination of naphtholate and enolate oxygen atoms.

Magnetic moment

The complexes (1), (2) and (3) are diamagnetic

consistent with the f 0, d 0 and d 10 configuration of

U(Vl), Mo(VJ) and Zn(Il).

The heterobimetallic copper complex (4) has magnetic moment value 1.75 B.M. which is very close to the spin-only value for one unpaired electron (1.73 B.M). This suggests either no interaction or very weak interaction in the structural unit of the complex. The magnetic moment value of 2.80 B.M. for the heterobimetallic nickel complex (5) indicates the

presence of nickel atom in the high-spin state having octahedral stereochemistry.

The f.lB value of 4.0 B.M. for the complex (6) is in the range reported for cobalt(II) complexes having weak interaction between metal atoms in the structural unit of the complex. The heterobimetallic manganese complex (7) has f.lB value equal to 5.57 B.M. indicating the presence of Mn(Il) with weak M-M interaction in the structural unit of the complex.

Electronic spectra

The important electronic spectral bands along with molar extinction coefficients are summarised in Table 1. The free ligand, CH2LH4 shows two bands at

320 nm (E111

ax' 9500 dm3mor

1cm.

1) and 390 nm (E,mx.

15700 dm3mor

1cm-

1) in the region 300-400 nm. The

band at 320 nm is assigned to intraligand n-n· transition while the band at 390 nm is assigned to n-n· transition.

The electronic spectra for the complexes show two to three bands in the 330-550 nm region.

The ligand bands at 320 nm and 390 nm show red shift on complexation. The bands appearing in the region 330-370 nm are attributed to the ligand band at 390 nm. The red shift of the ligand bands gives good evidence of chelation of dihydrazone to the metal centre.

The uranyl complex (1) shows a weak band at 540 nm (E ma x = 56 dm

3mor

1 cm-

1). This band is

characteristic of the triatomic entit/1 uo/+ .

The heterobimetallic complexes (2) to (7) show two bands in the region 330-430 nm similar to that of precursor complex. These bands are attributed to arise

due to ligand bands. No additional band is observed in

these complexes which may be assigned to charge­transfer transition. It appears that charge-transfer band, if any is masked by strong ligand band appearing in the region 410-430 nm.

The heterobimetallic complexes (2) and (3) show a weak band at- 525 nm. This band is similar in nature

to the band observed for the precursor uranyl complex

(1). Hence, it is attributed to the uot group13

. The heterobimetallic Cu-U02 complex (4) shows a band at 560 nm, which may be assigned to the uranyl ion . However, molar extinction coefficient of the band is 250 dm

3mor

1cm·

1 which is higher than that of the band

' which appears at 525 nm in the complexes (2) and (3). Futther, this band appears at lower energy than the band at 525 nm in the complexes (2) and (3). In view

of this , it is suggested that this band has contribution due to d-d band arising from Cu(II) as well. High

molar extinction coefficient of this band suggests a square pyramidal stereochemistry for Cu(II) centre in

22 the complex .

The heterobimetallic Ni-U02 complex (4) shows a band at 700 nm. The position of this band is typical that of an octahedrally coordinated nickei(II) and rules out the square planar or tetrahedral structure .

Comparison of the absorption bands of this complex at 700 nm with the corresponding bands in the spectra of [Ni(Hp)6t at 740 and 395 and [Ni(NH3) 6]

2+ at 570

and 355 nm suggests that the band at 700 nm in the complex bears similarity to that of the oxygen donor ligands

23• This suggests that the Ni atom in the complex

is surrounded by oxygen donor ligands only. This is possible only if nickel is bonded to carbonyl oxygen atoms·. The band around 415 nm does not show similarity either with oxygen donor ligands or with

nitrogen donor ligand obviously due to its different character.

The heterobimetallic cobalt(Il) complex shows a new band at 540 nm in the visible region . The position of this band together with the molar extinction coefficient suggests that cobalt is present in distorted octahedral environment in this comple/

3.

Electron spin resonance spectra

The heterobimetallic Cu-U02 complex (4) shows completely anisotropic spectra. The ESR spectral features for this complex indicate it to be five coordinated. Analysis of the spectra according to

526 INDIAN J CHEM, SEC A, MARCH 2004

Kneubuhl's method24

gave three g-values. At LNT, the

values of g"', g '· g2 and g3 were found to be 2.19, 2.338, 2.172 and 2.085 respectively . In CH3CN-DMSO at LNT, the cotTesponding va lues were 2.18, 2.320, 2.149 and 2.087.

The value of R for this complex is 0.524 which is

less than 1, indicating that d rl-yl is the ground state in thi s complex. The relatively high value of g parameters are most probably indicative of binuclear nature of the comple/

5•

The present study shows that the monometallic compl ex [U0 2(CH 2L H 2)(H20)] allows for the incorporation of the different metal ions under very mild conditions leading to the formation oftetranuclear

heterobimetallic complexes in all cases except in the case of Mo02-U02 complex (2) which is binuclear. The monometallic dioxouranium(VI) complex (1) does not suffer any transmetallation. The dihydrazone functi ons as a dibasic tetradentate li gand in the

mon o meta llic complex (1) which is tetrabasic hexadentate in the heterobimetallic complexes . The dihydrazone coordinates through naphthol ate function to one metal center and through enolate oxygen atoms to the second meta l center. The dihydrazo ne coordinates to the metal center in anti-cis-configuration

in monometallic as well as heterobimetallic complexes and functions as a bridgin g ligand in the heterobimetallic complexes. Based on the above, the tentative Structures X-XIII have been suggested for

the complexes.

Acknowledgement The authors are thankful to Head, Regional

Sophisticated Instrumentation Centre, Shillong, for

providing 1H NMR specra and

13C NMR spectra, the

Head, Regional Shophisticated Instrumentation Centre, Indian In stitute of Technology, Madras, for ESR spectral data and the Head, Reg ional Sophisticated Instrumentation Centre, Central Drug Research Institute, Lucknow fo r C, H and N analysis.

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