Synthesis and Spectral Characterization of UO2(VI), Th(IV) and ZrO(IV) Complexes with benzimidazolyl-2-hydrazones of diacetyl monoxime and benzil monoxime Ranjan Kumar Mohapatra1, Pradeep Kumar Das2

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Synthesis and Spectral Characterization of
UO2(VI), Th(IV) and ZrO(IV) Complexes with
benzimidazolyl-2-hydrazones of diacetyl
monoxime and benzil monoxime
Ranjan Kumar Mohapatra1
, Pradeep Kumar Das2
___________________________________________
Abstract
A series of metal complexes of the type [ML2.nNO3], where
L= 2-(benzimidazolyl-2'-amino) imino–1,2–dimethyl
ethanone-1-monoxime (BME), 2-(benzimidazolyl-2'-
amino) imino-1,2-diphenyl ethanone-1-monoxime
(BPE), M = UO2(VI), Th(IV) and ZrO(IV), have been
synthesized and characterized on the basis of elemental
analysis, thermal analysis, electronic, infrared and 1
H NMR
spectral studies. The results are in consistent with tridentate
chelation of the ligand.
__________________________________________________
Keywords: Benzimidazolyl-2-hydrazones, diacetyl monoxime
and benzil monoxime
______________________________________________
I. Introduction
The Schiff bases and their metal complexes are widely studied
because of increasing recognition of their role in biological
systems. The benzimidazole derivatives are found to possess
antimicrobial1
, antibacterial2
, antigungal3
, anticancer4
,
antiviral5
and anti inflammatory6
activities. Following all
these observations and as a part of the continuing research on
the coordination chemistry of multidentate ligands7-9
, I report
here the synthesis and structural studies on the complexes of
UO2(VI), Th(IV) and ZrO(IV) with some benzimidazole
derivatives such as 2-(benzimidazolyl-2'-amino) imino–
1,2–dimethyl ethanone-1-monoxime (BME), 2-
(benzimidazolyl-2'-amino) imino-1,2-diphenyl ethanone-
1-monoxime (BPE).
____________________________________________
First Author’s Name: Ranjan Kumar Mohapatra, Department of
Chemistry, Government College of Engineering, Keonjhar-758002, Odisha,
India, E-mail: ranjank_mohapatra@yahoo.com
Second Author’s Name: Pradeep Kumar Das P.G Dept. of Chemistry, G.M
(Auto)College,Sambalpur,Odisha,India,E-mail:
pradeepdas1960@gmail.com
_______________________________________________________
II. Experimental Material and Method
All the chemicals used of AR grade. The solvents were
purified before use by standard procedures. The starting
material such as 2-hydrazinobenzimidazole was synthesized
according to literature method10
.
Preparation of Ligands
The ligands used in the present investigation were
benzimidazolyl-2-hydrazones of diacetyl monoxime and
benzil monoxime have been synthesized by condensing
2-hydrazinobenzimidazole with respective monoximes in
the following manner.
Ethanolic solution of 2-hydrazinobenzimidazole
(0.01 mol in 20 mL) was added to ethanolic solution of
diacetyl monoxime and benzil monoxime (0.01 mol in
20 mL) and the resulting solution was refluxed on a
water bath for 5 to 6 hours. It was concentrated and
allowed to stand overnight when coloured precipitate
was separated out. It was filtered washed and
recrystallised from ethanol. The sample was dried in
vacuo over fused calcium chloride and then analysed.
Reaction scheme-1
(2-Hydrazino (Diacetyl (BME)
monoxime) benzimidazole)
N
N
H
N H N H 2
C H 3
C H 3
O
N
O H
+
N
N
H
N H
C H 3
C H 3
N
O H
N

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Reaction scheme-2
(2-Hydrazino benzimidazole) (Benzil monoxime)
(BPE)
Preparation of the complexes
The complexes were synthesized by refluxing
ethanolic solution of the ligand BME / BPE (0.02 mol in
20 mL) with a hot ethanolic solution of corresponding
UO2(VI), Th(IV) and ZrO(IV) nitrates (0.01 mol in 20 mL)
for about 6 hours when coloured complexes precipitated
out in each case. The complexes were filtered, washed
with ethanol followed by ether and finally dried in vacuo
over fused CaCl2.
Analysis and Physical measurements
The metal contents in the complexes were determined
gravimetrically following standard procedure11
. Carbon,
hydrogen and nitrogen contents of the complexes were
determined by using a MLW-CHN micro analyser. FTIR
spectra in KBr pallets were recorded on a Varian FTIR
spectrophotometer, Australia. The electronic spectra of the
complexes in DMSO were recorded on a Perkin-Elmer
spectrophotometer. Thermo gravimetric analysis was done by
Netzch-429 thermo analyzer.
III.Results and Discussion
The complexes were formulated from the analytical
data support the suggested formulae (Table-1). The complexes
are highly coloured and insoluble in water and common
organic solvents but soluble in highly coordinating solvents
such as DMF and DMSO. They are non hygroscopic, highly
stable under normal conditions and all of them decompose
above 2500
C.
Table-1: Analytical and physical data of the compounds
S
l
n
o
Compounds C
Found
(Calcd
)
H
Found
(Calcd
)
N
Foun
d
(Calc
d)
M
Found
(Calcd
)
1 BME 57.09
(57.14)
5.58
(5.63)
30.25
(30.30)
-
2 BPE 70.95
(70.98)
4.77
(4.79)
19.68
(19.72)
-
3 [UO2(BME)2].2NO3 30.78
(30.84)
3.01
(3.04)
19.58
(19.62)
27.75
(27.80)
4 [Th(BME)2.4NO3] 27.97
(28.02)
2.72
(2.76)
20.75
(20.81)
24.59
(24.63)
5 [ZrO(BME)2].2NO3 38.04
(38.09)
3.71
(3.75)
24.20
(24.24)
13.09
(13.13)
6 [UO2(BPE)2].2NO3 45.61
(45.65)
3.04
(3.08)
15.18
(15.22)
21.53
(21.56)
7 [Th(BPE)2 4NO3] 42.30
(42.35)
2.83
(2.86)
16.43
(16.47)
19.45
(19.49)
8 [ZrO(BPE)2].2NO3 53.52
(53.56)
3.58
(3.61)
17.80
(17.85)
9.43
(9.47)
a
Ohm-1
cm2
mole-1
IR spectra
In the high frequency region, 2-hydrazinobenzimidazole
exhibits a pair of strong bands precisely located at ~3320 and
~3265 cm-l
which may be assigned to asymmetric and
symmetric stretching modes of vibrations of the -NH2 group.
Apart from these bands a multiple band system of medium
intensity is observed at ~3150 and ~3100 cm-1
which may be
attributed to v (N-H) benzimidazolyl group and v(N-H)
exocyclic respectively. Apart from these bands, a multiple
band system of medium intensity is observed at ~1540 v
(C=N) cyclic and ~1340 v (C-N) cyclic which may be due to
ring stretching vibrations mode of benzimidazole moiety.
Reaction of 2-hydrazinobenzimidazole with diacetyl
monoxime and benzil monoxime brings about significant
changes in the IR spectra of the product, which has been used
as ligand in the present investigation. The position of bands
due to v (C=N) cyclic, and v (C-N) cyclic remains practically
unaltered in the present complexes indicating non-
coordination of ring nitrogen atom to the metal ions. Whereas,
the Position of benzimidazole v(N-H) band occurring at 3150
cm-l is shifted by 20-25 cm-l to lower frequency region
indicating involvement of -NH group of benzimidazole in
coordination to the metal ions.
Thermal analysis
These complexes follow the same pattern of thermal
decomposition. The complexes remain almost unaffected up
to ~300 o
C and thereafter the complexes show rapid
degradation presumably due to decomposition of organic
N
N
H
N H N H 2
O
N
O H
+
C 6
H 5
C 6
H 5
N
N
H
N H
N
O H
N
C 6
H 5
C 6
H 5

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constituents of the complex molecules as indicated by the
steep fall in the percentage weight loss. The decomposition
continues up to ~550 °C and reaches to a stable product in
each complex as indicated by the consistency in weight in the
plateau of the thermogram. This corresponds to the
composition of their stable oxides. The decomposition
temperature varies for different complexes.
Electronic spectra and Magnetic moment
The electronic spectra of the UO2(VI) complexes are quite
similar. The complexes display mainly one weak band at ~470
nm and a highly intense band at ~270-290
nm, which may be due to 1
Σg
+
→ 3
Πu transitions and charge
transfer transitions respectively. The electronic spectra of
Th(IV) and ZrO(IV) exhibit only one extra highly intensive
band in the region 350-385 nm which may be due to charge
transfer band besides the ligand bands. However the electronic
spectra could not provide structural details of these
complexes. All the complexes are diamagnetic in consistent
with their d0
and f0
electronic configuration.
IV. Conclusion
Based on the above foregoing observations the tentative
structure of the UO2 complex is shown in the following Fig. 1.
Fig. 1: Proposed structure of [UO2 (BPE)2].2NO3
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N
H N H
O HHH N
H O
N
C 6
H 5
C 6
H 5
C 6
H 5
C 6
H 5
N
N
N
N
U O 2
N
N
N O 3
2