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Synthesis and Characterizationof 2,2-Biimidazole Complexesof Oxocations of Molybdenum(VI, V) and Uranium(VI)Samir S. Kandil a & Loutfy H. Madkour aa Chemistry Department, Faculty of Sciences , TantaUniversity , Tanta, EGYPTPublished online: 23 Sep 2006.

To cite this article: Samir S. Kandil & Loutfy H. Madkour (1993) Synthesis andCharacterization of 2,2-Biimidazole Complexes of Oxocations of Molybdenum(VI, V) and Uranium(VI), Spectroscopy Letters: An International Journal for RapidCommunication, 26:3, 535-550, DOI: 10.1080/00387019308011552

To link to this article: http://dx.doi.org/10.1080/00387019308011552

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SPECTROSCOPY L E T E R S , 26(3). 535-550 (1993)

Synthesis and Characterization of 2,2'-biimidazole

Complexes of Oxocations of Molybdenum (VI, V) and

Uranium(V1)

BY

Samir S. Kandil* and Loutfy H. Madkour

Chemistry Department, Faculty of Sciences, Tanta University,

Tanta, EGYPT.

ABSTRACT

t2 2,2.-Biimidazole complexes of Moo2 , Moo2+ and U02f2 have been prepared and characterized by elemental analysis,

conductance; and 'H NMR, IR and electronic spectra. Two

types of complexes have been identified. Those obtained

from slightly acidic solutions have the formulae

MOO 2 2 (H bim)C12.2H20 'l, U02(H2bim)(Ac)2 2 and U02(H2bim)C12.2H20

whereas those from alkaline solutions have the formulae

M0~0~(Hbim)~.2H~O 4, and M02(Hbim)2 ( M = Mo(V1) 5 , U(V1) 6). The infrared spectra of these complexes show characteristic

biimidazole frequencies in the 3200-2500, 1550-1000 and

1 5 0 cm-l regions as well as metal oxygen double bonds in

the 900 cm-l region.

complex has been confirmed from 'H NMR signal ratios of

The stoichiometries of the acetate

* Author to whom correspondence should be directed.

3;

535

Copyright 0 1993 by Marcel Dekker, Inc

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536 KANDIL AND MADKOUR

biimidazole to acetate protons at 7.3 and 2.3 ppm, respec-

tively. The electronic spectrum of molybdenum(V) complex

showed d-d transition band at =13,500 cm-' in accord with

that' reported for copper (d ) imidazole complexes; as well

as peaks due to charge transfer bands at 30,000-26,000 c9- l .

Peaks assignable to BIM --+ U(V1) were located at ~ 2 6 , 6 0 0

cm . The most probable structures of these complexes have

been suggested.

9

-1

INTRODUCTION

The chemistry of the transition metals in the high

oxidation states such as Mo(V1) and U(V1) is complicated

in aqueous media due to the formation of 0x0 complex and

polynuclear 0x0 complexes as well as redox reactions . Molybdenum(V1) acts as a binding site for imidazole moiety

as well as redox site in xanthine oxidase and xanthine

dehydrogenase' ) . Dioxouranium(V1) complexes containing

nitrogenuous chelating ligands such as 2,2*-bipyridine have

been known for many year^(^-^). derivatives have been involved in the model studies for

some of biologicqlly important systems(9).

ting ligand, 2,2'-biimidazole can complex as the neutral

molecule H2bim, the monoanion Hbim or the dianion bim.

Examples of all of these possibilities have been realized

( 1 )

2,2'-Biimidazole and its

As a coordina-

experimentally with many transition metals in low oxidation

states ( 1 0 - 1 5 ) .

The present study describes the synthesis and spectral

properties of some oxocation complexes of Mo(V1, V ) and

U(V1) with 2,2'-biimidazole.

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2-2' -BIIMIDAZOLE COMPLEXES

EXPERIMENTAL

537

( A ) Materials and Compound Preparations.

2,2~-Biimidazole was synthesized according to a pub-

lished procedure(16).

reagent grade.

Na2Mo04.2H20 and U02(Ac)2.2H 2 0 were

Mo02(H2bim)C12.2H20 1: A mixture of Na2Mo04.2H20 (2.42 g,

0.01 mol) and 2,2'-biimidazole (1.34 g, 0.01 mol) in 50 ml

aqueous ethanolic solution containing 0.01 mole HC1 was

stirred in an open flask. To this solution an aqueous

sodium hydroxide was added dropwise to pH 4. After the

solution was stirred for additional 3 hours, the copious

precipitate was filtered off and digested with hot water

several times to remove unchanged ligand. The final pro-

duct was a fine yellow solid and dried over P4Ol0.

M0~0~(Hbim)~.2H~O 4: The same procedure as above, except

that the pH of the original solution was adjusted at 8.5.

After stirring for 1 hour, the blue precipitate was col-

lected by filtration; washed with hot water and dried in

vacuum over P40,0.

U0,(H,bim)(A~)~ 2: mol) was dissolved in 30 m l ethanol. To this solution,

2,2~-biimidazole (1.34 g , 0.01 mol) dissolved in 10 ml

water containing 0.01 mol HC1 was added with stirring; a

Uranyl acetate dihydrate (4.24 g , 0.01

clear yellow solution was obtained. The pH of the solution

was adjusted to 4 by adding few drops of NaOH solution.

Upon partial evaporation of the solvent, a yellow solid

was separated, which was filtered off, washed several times

with hot water, ethanol and diethyl ether and dried over

'4'1 0 '

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538 KANDIL AND MADKOUR

If an excess of NaCl was added to the original solution

at the same pH the chloro complex U02(H2bim)C12.2H20 3 was

obtained.

!400~(Hbim)~ 2: A solution of Na2Mo04.2H20 (2.42 g , 0.01

mol) and H2bim (2.68 g, 0.02 mol) in 100 ml of water was

acidified with dropwise addition of 30 m l of 1.5 N H N 0 3 at

Sac. After the solution was stirred for 1 h, the precipi-

tate was filtered, washed with water and dried in vacuum.

The orange solid was suspended in 20 ml water and the pH

was adjusted at 8.5 by adding standard solution of sodium

hydroxide. The insoluble deprotonated complexes was stir-

red for 2 h to ensure complete reaction. The yellow product

was washed with water and dried in vacuum.

U02(Hbim)2 6: in water (30 m l ) was added to a suspension of H2bim ( 2 . 6 8

g , 0 . 0 2 mol) a l s o in water (30 ml) and 0.02 M sodium hydro-

xide solution was added till pH 8.5. An immediate yellow

precipitate was formed, but the mixture was stirred for

2 h to ensure complete reaction. The product was washed

with water and dried in vacuum.

(B) Physical Measurements:

Uranyl acetate dihydrate (4.24 g , 0.01 mol)

v

The metal content of the complexes was determined by

igniting a known weight of a complex to the corresponding

stable oxide (Moo3 and U 3 0 8 ) .

N were carried out using a Perkin-Elmer 2 4 0 0 CHN elemental ana-

lyzer. The H NMR spectra were recorded in d6-dimethyl

sulphoxide on a Brutor EM390, 90 MHZ nmr spectrometer.

The electrical conductances of the complexes were measured

in DMSO at 25'C using a Hanna 8733 conductivity meter.

Microanalysis of C, H and

l

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2-2' -BIIMIDAZOLE COMPLEXES 539

The infrared spectra (KBr discs) were recorded on a Perkin-

Elmer 7430 Ratio Recording spectrophotometer and a Perkin-

Elmer 6 8 3 spectrophotometer. The electronic spectra in

Nujol mull were recorded on a Shimadzu 2 4 0 UV spectrophoto-

meter. All the complexes are insoluble in the common

solvents such as ethanol, nitrobenzene and CHCl 3 '

RESULTS AND DISCUSSION

Treatment of Mo02C12 (prepared in situ by reduction

of Na2Mo04 in 2N HC1) and U02(Ac)2.2H20 with H2bim, results

in the separation of two types of complexes. The analy-

tical data, Table ( l ) , indicates that those obtained from

slightly acidic solutions are formulated as MOO (H bim)C12.2H20

1, U02(H2biml(Ac)2 2 and UO (H bim)C12.2H20 2; whereas those

from slightly alkaline solutions are formulated as

Mo204(Hbim12.2H20 4, and M(Hbirnl2 where M = Mo(V1) 5, U(V1)

- 6 . The conductivity measurements on the complexes in the

DMSO solutions at concentration M are too small ( 2 2 -

2 2

2 2

2 6 S cm') to account for any dissociation. Hence these

complexes can be regarded as nonelectrolytes. The ' Hnmr spectra of 2, Figure ( 1 1 , obtained in DMSO solutions con-

tains a sharp singlet resonance at 2 . 3 ppm assigned to

acetato protons and broad multiplet centered at 7 . 2 ppm

assigned to biimidazole hydrogens. Total integration of

peak ratios revealed 3 : 2 acetato to ring biimidazole

protons ratio consistent with U02(H2bim) (Ac)* stoichiometry.

No imino hydrogen resonances could be detected since they

rapidly exchange with the solvent" 6).

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vl

P 0

Table

(1).

Analytical data and electronic spectra for complexes of 2,2 -biimidazole.

Microanalysis

No

Complex

Colour

C H

N M

A Absorption bands'

lo3 cm-'

- 1 Mo02(H2bim)C12.2H20

green

23.7

3.i

17.9

31.9

26

26.5; 30.3;

34.0; 43.0; 45.3

(24.1)

(3.3

) (18.2)

(32.2)

- 2 U02(H2bim)(Ac)2

yellow

18.1

2.1

10.4

45.2

22

23.2; 25.5;

31.9; 43.2

- 3 U02(H2bim)C12.2H20

yellow

14.0

1.8

10.6

46.4

26

23.8; 26.7; 31.8; 43.3

(18.4)

(2.3)

(10.7)

(45.6)

(14.1)

(1.9)

(10.9)

(46.6)

- 4 Mo204(Hbim)2(H20)2

blue

25.4

2.1

19.8

34.0

--

13.5; 27.7;

30.3; 34.0; 43.0; 45.3

(25.8)

(2.5)

(20.1)

34.4)

- 5 Mo02(Hbim)2

pale-yellow

36.2

2.4

28.1

24.2

--

27.4; 30.7;

33.4; 43.0;

45.3

(36.5)

(2.5)

(28.4)

(24.4)

- 6 U02(Hbim)2

orange

26.4

1.7

20.3

44.1

--

23.3; 26.7;

31.8; 43.3

(26.8)

(1.9)

(20.8)

(44.4)

x

a Found (Calcd)

%.

2 Conductivities,

A (S

cm

),

are of

Nujol

mul

l electronic spectra,

M solutions in dimethylsulfoxide (DMSO).

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2-2' -BIIMIDAZOLE COMPLEXES 541

t I I I I I I I 1 1 8 7 6 5 4 7 2 I 0 ppm

pigure (1). 'HNMR spectrum of U02(H2bim)(Ac)2 in DMSO. calibrated in ppm downfield from TMS. ( d l DMSO peaks.

Chemical shifts are

Infrared Spectra

The IR frequencies of the prepared complexes along

with their assignments are given in Tables 2 and 3. The

IR spectra of complexes 1_ - 3 display many characteristic

group frequencies for biimidazole (e.g. v(N-H) = 3200 ern-'; -1 va (C=N-C=C) = 1530-1580 cm-'; v(C=N-C=C) = 1450-1460 cm ,

6 (C-H) = 1100-1130 cm-l and 6 (bim) = 755-735 cm-') as in

the case of [Rh(COD) [H2bim) ]C104"3) and C~(H~bim)~Cl~.H~o('~);

whereas the i.r. of complexes 3 - 5 are found to be closely

similar to those of some transition metal complexes reported

to contain Hbim(17).

3200-2500 cm-l in the spectra of 4 I f; is similar to that of free biimidazole, suggesting the presence of an N-H bond

The broad structure in the region

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Tab

le (2).

Infr

ared

sp

ectr

a of

n(H

2bim

)X2

com

plex

es.

VI

P

N

MoO2(H2bim)Cl2.2H2O

U02(H2bim)(Ac)2

U02(H2bim)C12.211,0

Ass

ignm

ent

.-

H2bim

_---

---

3440 (

s,b

) an

tisy

m.

and

sym

. O

il of

1

.att

ice

wat

er.

--

3470 (

s,

b)

3200

(b

) 3170 (

b)

3120 (

b)

3170 (

b)

N-TI

stre

tch

1545 (

vs)

1532 (

s)

1530 (

vs)

1550 (

vs

) bi

m r

ing

str

etc

h

COO

stre

tch

(v,

)

1462 (

vs,

b)

COO

stre

tch

(us)

-. 1517 (

s)

1460 (

vw)

1468 (

vw)

....

1460 (w)

1437 (

s)

1421 (

s)

1425 (m)

u(C-C)

1334 (

s)

1320 (w)

1315 (

m)

1333 (

vs)

--

1128 (

s)

1120 (

s)

1125 (

s)

6(C-H)

1105 (

s)

1100 (

s)

1100 (

s)

1100 (

s)

--

996

(m)

--

944

(s

)

sym

. Mo=O

939

(vs)

923 (vs)

920

(vs)

939

(s

)

(C-1

1)

888

(s)

891

(vs)

...

...

890

(vs,

b)

877

(vs,

b)

v( O

=U=O

)

F R

ing

bend

ing

2

r

Z z CI

_--

A

ntis

ym.

Mo=

O 85

1 (v

s)

---

L! 749

(s)

744

(vs)

745

(vs)

748

(s)

r(C-H)

>

690 (m)

685 (vs)

665 (vs)

689 (m)

0

---

366

(m)

---

393

VM-c1

>

---

266

(m)

265 (vs)

285

UM

N

w 2 s

, st

ronp

,: m,

med

ium

; w

, we

ak;

b, b

road

. 72

764

(m)

772

(vs)

755

(s)

763

(m)

.-

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2-2' -BIIMIDAZOLE COMPLEXES 543

E .+ e z C 0

C m C 6 W r Y

M C TI

.rl

u C U

Lo W

m 7-4 a E

U

C

.r( u

0 0

L4 0 w

m u m U

U

h m ul C Y

.rl

m

h

m

0 Fi

v

n 2

u C

I 00 .r(

Lo

U

N n

E .?I 0 X V

N

8 x

ON

"i T

N h

E .4

e X v U

R 2

N h

E .d n X v

N

9

I4 a, u m

W U .4

u u m 3

w 0 - E

E x v1

V c

. . 2: m L o .rl u e C I m z

c u .A

3 * * v - a 0 Q a II

3 0 * I W W

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544 KANDIL AND MADKOUR

remaining in the monoanion Hbim. This structure is now

being assigned as due to Fermi resonance between N-H stret-

ching Sands and combinations of bands in the 1600-1000 cm-'

regions (18,191

Complete tabulation of the i.r. frequencies of the

prepared complexes and biimidazole reveals drastic changes in

the 1100 and 900 an-' regions (Fig. 2). The in-plane C-H defor-

mation of biimidazole has been replaced by two strong bands

at 1100-1130 cm-l in the complexes as consequences of

lowering symmetry of biimidazole on complexation. In

molybdenyl complex 1, two strong bands appear at 944 and 851 cm-', which do not correspond to any bands in the free

!4 bim, assignable to symmetric and antisymmetric vibrations

of bent Moo2 group(20).

bands due to Mo=O appear to be partially overlapped with

biimidazole ring modes, giving rise to a shoulder at 948

and a stronger band at 896 cm-l in complex 5 and medium

and broad bands at 9 2 0 and 856 cm-l in complex 5.

uranyl complexes, an unusual intense broad bands appear

in the region 890-870 cm-l, ascribed to v 3 anti symmetric

stretch of linear" O=U=O(21

vibrations of biimidazole. The observed low frequency for

2

In molybdenum complexes 4 and 2,

In

overlapped with ring mode

( 2 2 ) as compared to that of uranyl acetato complexes "0=U=O'

may be due to the greater perturbation caused by the stronger

chelation of biimidazole group. The occurrence of the asym-

metric and symmetric vibrations of 0-C-0 at 1517 and 1462 cm-'

in complex 2. is consistent with the bidentate nature of

acetato group ( 2 3 ) presumbly through chelation to the same

uranium atom. This type of bonding of acetato group has

been well established in closely related systems such as

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2-2‘ -BIIMIDAZOLE COMPLEXES

X T

545

-1 cm

Figure ( 2 ) . Infrared spectra of; ( A ) H2bim,

( B ) MoOZ(HZbim)Cl2.2H20 1, ( C ) Mo2O4(Hbim).2H20 4, (D) Mo02(Hbim)2 5, (E) U02(H2bim)CL2.H20 2.

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546 KANDlL AND MADKOUR

x L. m L. Y

v1

4 e

200 3 50 550 750 nm

Figure ( 3 ) . Solid s ta te electronic spectra o f ; (- ) M0~0~(Hbim)~.2H~O ( - - - -) U02 (Hbim) ( - . . . . . . . . . . ) U02(H2bim)(Ac)2.

U02(bpy\ ( A C ) ~ (’).

due to the water molecules are observed at 3500 and 1600

In the hydrated complexes, absorptions

cm-’ . In the f a r - I R region, strong to medium bands are ob-

served at 265-240 cm-’ in the complexes, corresponding to

a very weak band at 270 cm-‘ in the free biimidazole, due

to metal-nitrogen stretching vibrations(23).

metal-chlorine are located in 1 at 366 cm-’ and in 2. at

Bands due to

3 9 3 cm-’.

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2-2' -9IIMIDAZOLE COMPLEXES 547

Electronic Spectra

The electronic spectra of the molybdenum complexes 1, - 4 and 5 show bands at assigned as due to ( n ,

BIM -+ Mo overlapped with TI - n* transition of biimida-

zole").

complex at -13,500 cm-' , which is absent in either Mo02(Hbim)C12.2H20 or M00~(Hbim)~, is assigned as the

expected d-d transition of Mo(V).

26,000 and 3 0 , 0 0 0 cm-l, Figure 3,

- n2) BIM -+ Mo and (nl + n 2 )

The broad absorption exhibited by Mo204(Hbim)2(H20)2

The electronic spectra of the uranyl complexes are

completely different from that of U02(Ac)2.2H20 and show

intense band at 26,600 cm-l due to BIM -+ U02 transition(24).

Additionally, bands at ~24,000 cm-' may be assigned to U02

moiety.

Absorption bands below 39,000 cm-l in the spectra of

the prepared complexes have to be assigned as due to the

biimidazole because they are present irrespective of cations.

From the above discussions the most probable structures

of these complexes can be as:

c1 O

II \ "

M

0

I \

H-N u M = M o L M = U 3-

2 -

(continued)

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548 KANDIL AND MADKOUR

OH2 F\ I, y- M

N 1\ A\ O N

4 - M = M o 5 M = U 6

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Date Recei;’ed: September 10, 1992

Date Accepted: November 2, 1992

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