Spectroscopy letters volume 26 issue 3 1993 [doi 10.1080 00387019308011552] s. s. kandil; l. h. madkour - synthesis and characterization of 2,2-biimidazole complexes of oxoca (3)

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Synthesis and Characterization
of 2,2-Biimidazole Complexes
of Oxocations of Molybdenum
(VI, V) and Uranium(VI)
Samir S. Kandil
a
& Loutfy H. Madkour
a
a
Chemistry Department, Faculty of Sciences , Tanta
University , Tanta, EGYPT
Published online: 23 Sep 2006.
To cite this article: Samir S. Kandil & Loutfy H. Madkour (1993) Synthesis and
Characterization of 2,2-Biimidazole Complexes of Oxocations of Molybdenum
(VI, V) and Uranium(VI), Spectroscopy Letters: An International Journal for Rapid
Communication, 26:3, 535-550, DOI: 10.1080/00387019308011552
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SPECTROSCOPY LETERS, 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
t22,2.-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
MOO2 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~O4, 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
150 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 01993 by Marcel Dekker, Inc

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.

2-2'-BIIMIDAZOLE COMPLEXES
EXPERIMENTAL
537
( A ) Materials and Compound Preparations.
2,2~-Biimidazolewas synthesized according to a pub-
lished procedure(16).
reagent grade.
Na2Mo04.2H20 and U02(Ac)2.2H20 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~O4: 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'

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 HN03 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 , 0.02 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

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
26 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).

vl
P0
Table(1).Analyticaldataandelectronicspectraforcomplexesof2,2-biimidazole.
Microanalysis
NoComplexColourCHNMAAbsorptionbands'lo3cm-'
-1Mo02(H2bim)C12.2H20green23.73.i17.931.92626.5;30.3;34.0;43.0;45.3
(24.1)(3.3)(18.2)(32.2)
-2U02(H2bim)(Ac)2yellow18.12.110.445.22223.2;25.5;31.9;43.2
-3U02(H2bim)C12.2H20yellow14.01.810.646.42623.8;26.7;31.8;43.3
(18.4)(2.3)(10.7)(45.6)
(14.1)(1.9)(10.9)(46.6)
-4Mo204(Hbim)2(H20)2blue25.42.119.834.0--13.5;27.7;30.3;34.0;43.0;45.3
(25.8)(2.5)(20.1)34.4)
-5Mo02(Hbim)2pale-yellow36.22.428.124.2--27.4;30.7;33.4;43.0;45.3
(36.5)(2.5)(28.4)(24.4)
-6U02(Hbim)2orange26.41.720.344.1--23.3;26.7;31.8;43.3
(26.8)(1.9)(20.8)(44.4)
x
aFound(Calcd)%.
2
Conductivities,A(Scm),areof
Nujolmullelectronicspectra,
Msolutionsindimethylsulfoxide(DMSO).

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

Table(2).Infraredspectraofn(H2bim)X2complexes.VI
PN
MoO2(H2bim)Cl2.2H2OU02(H2bim)(Ac)2U02(H2bim)C12.211,0Assignment
.-
H2bim
_------3440(s,b)antisym.andsym.Oilof1.atticewater.--3470(s,b)
3200(b)3170(b)3120(b)3170(b)N-TIstretch
1545(vs)1532(s)1530(vs)1550(vs)bimringstretch
COOstretch(v,)
1462(vs,b)COOstretch(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-11)
888(s)891(vs)......
890(vs,b)877(vs,b)v(O=U=O)
F
Ringbending
2
r
Z
z
CI
_--Antisym.Mo=O851(vs)---
L!
749(s)744(vs)745(vs)748(s)r(C-H)>
690(m)685(vs)665(vs)689(m)0
---366(m)---393VM-c1>
---266(m)265(vs)285UMNw
2s,stronp,:m,medium;w,weak;b,broad.72
764(m)772(vs)755(s)763(m)
.-

E.+
e
z
C
0
C
m
C
6
W
rY
M
C
TI
.rl
u
C
U
Lo
W
m7-4a
E
U
C
.r(
u
0
0
L4
0w
mu
mU
U
h
m
ul
CY
.rl
m
h
m
0Fi
v
n
2
u
C
I
00.r(
Lo
U
N
n
E.?I
0
XV
N
8x
ON
"i
T
N
h
E.4
e
Xv
U
R
2
N
h
E.dn
Xv
N
9
I4
a,u
m
W
U.4
uu
m3
w
0
-E
Exv1
V
c
. .
2:
m L o.rl
u e
C I
m z
cu.A
3 **
v -
a 0Q
a II
3 0
* IW W

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

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.

546 KANDlL AND MADKOUR
x
L.
mL.Y
v1
4
e
200 3 50 550 750 nm
Figure ( 3 ) . Solid state 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
393 cm-’.

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 ~24,000cm-' 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)

OH2 F
I, y-M
N
1 AO N
4-
M = M o 5
M = U 6
REFERENCES
1. F.A. Cotton and G. Wilkinson "Advanced Inorganic Che-
mistry" , 3rd ed. , Interscience ( 1972).
2 .
3.
4 .
5.
6 .
7.
a.
9.
E. Ochiai, "Bioinorqanic Chemistry An Introduction", Ch. 1 1 ,
Allyn and Bacon, Inc., Boston (1977).
L. Cattalini, P . A . Vigato, M. Vidali, S. Degetto and
U. Casellato, J. Inorg. Nucl. Chem., 37, 1721 (1975).
R.H. Holm, G.W. Everett and A. Charkravorty, Progress in
Inorganic Chemistry, 7, 23 (1966).
L. Cattalini, S. Deqetto, M. Vidali and P.A. Viqato,
Inorg. Chim. Acta, 6, 173 (1972).
G. Bandoli, D.A. Clemente, U. Croatto, M. Vidali and
P.A. Vigato, J. Chem. SOC. Dalton Trans. 1330, 1973.
V . P . Markov and V.V. Tsapkin, Russ. J. Inorg. Chem.,
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N.W. Alcock and D.J. Flanders, J. Chem. SOC. Dalton
Trans., 1001 (1985).
E.E. Bernarducci, P.K. Bharadwaj, R.A. Lalancette, K.K.
Jespersen, J.A. Pontenza and H.J. Schugar, Inorg. Chem.,
22, 3911 (1983).
Y

2-2’ -BIIMIDAZOLE COMPLEXES 549
10. R. Usan, L.A. O r o , J. Gimeno, M.A. Ciriano and J.A.
Cabeza, J. Chem. SOC. Dalton Trans., 323 ( 1 9 8 3 ) .
1 1 . R. Usan, L.A. O r o , J. Gimeno, L . A . Oro, M. de Llarduya
and J. Cabenza, Ibid, 1729 ( 1 9 8 3 ) .
12. S.W. Kaiser, R.B. Saillant, W.M. Bulter and P.G. Rasmussen,
Inorg. Chem., 1 5 , 2681 ( 1 9 7 6 ) .
13. R. Us&n, J. Gimeno, L.A. Oro, M. Valderrama, R. Sariego
and E. Martinez, Transition Met. Chem., 6, 103 (1 981).
14. L . A . Oro, D. Carmona and M.P. tamata, J. Chem. SOC.
Dalton Trans., 1 5 (‘1986).
15. A.S. Abushamleh and H . A . Goodwin, Aust. J. Chem., 34,
513 ( 1 9 7 9 ) .
16. B.F. Fieselmann, D.N. Hendrickson and G.D. Stuky,
Inorg. Chem., 17, 2078 ( 19 78 ) .
17. F. Holmes, K.M. Jones and E.G. Torrible, J. Chem. Soc.
4790 ( 1 9 6 1 ) .
18. J.L. Lippert, J.A. Robertson, J.R. Havens and J.S. Tan,
Macromolecules, 18, 67 ( 1985 ) .
19. G.C. Eastmond, M. Jiang and M. Malinconico, Polymer,
24, 1162 ( 1 98 3) .
20. F.W. Moore and R.E. Rice, Inorg. Chem. 7, 2510 (1968).
21. N.B. Biradar, M.D. Patil and T.R. Goudar, J. Inorg.
Nucl. Chem., 37, 1437 ( 19 75 ) .
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2319 (19691.

23. K. Nakarnoto “Infrared and Raman Spectra of Inorganic
and Coordination Compounds”, 4 t h ed., Wiely-Interscience,
New York (1986
24. M. Vidali, P.A
0. Traverso. J
Vigato, U. Casellato, E. Tondello and
Inorg. Nucl. Chem. 37, 1715 ( 1 9 7 5 ) .
Date Recei;’ed: September 10, 1992
Date Accepted: November 2, 1992

Spectroscopy letters volume 26 issue 3 1993 [doi 10.1080 00387019308011552] s. s. kandil; l. h. madkour - synthesis and characterization of 2,2-biimidazole complexes of oxoca (3)

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Spectroscopy letters volume 26 issue 3 1993 [doi 10.1080 00387019308011552] s. s. kandil; l. h. madkour - synthesis and characterization of 2,2-biimidazole complexes of oxoca (3)