Novel isatinoxime molybdenum and chromium complexes: Synthesis, spectroscopic, and thermal characterization

Article abstract of DOI:10.1016/j.molstruc.2012.05.013

Reactions of molybdenum and chromium hexacarbonyls with isatin-3-oxime (H₂L) in THF were carried out under sun light or according to the traditional thermal reflux synthetic routes. Di-μ-oxo bimolybdenum complex, [Mo(H₂L)(THF)(O)

Full text of DOI:10.1016/j.molstruc.2012.05.013

Journal of Molecular Structure 1026 (2012) 88–92
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Novel isatinoxime molybdenum and chromium complexes: Synthesis,
spectroscopic, and thermal characterization
b
b
b,
Mostafa Y. Nassar a, , Attia S. Attia , Shaymaa Adawy , M.F. El-Shahat
⇑
⇑
a Chemistry Department, Faculty of Science, Benha University, Benha 13518, Egypt
b Chemistry Department, Faculty of Science, Ain Shams University, Abbassia 11566, Cairo, Egypt
h i g h l i g h t s
"
"
"
"
"
Reactions of molybdenum or chromium hexacarbonyls with isatinoxime were studied.
The prepared isatinoxime ligand and its complexes were characterized.
Analytical, spectral, molar conductivity, magnetic and thermal measurements were used.
The prepared complexes are non-electrolytes.
The binuclear oxo complexes with formulas [Mo(H2L)(THF)(O)2]2, and [Cr(H2L)(O)2]2.
a r t i c l e i n f o
a b s t r a c t
Article history:
Reactions of molybdenum and chromium hexacarbonyls with isatin-3-oxime (H2L) in THF were carried
out under sun light or according to the traditional thermal reflux synthetic routes. Di- -oxo bimolybde-
num complex, [Mo(H2L)(THF)(O)2]2 was successfully synthesized under the reflux conditions. However,
the dichromium oxo complex, [Cr(H2L)(O)2]2 was prepared using the sun light route. The prepared com-
plexes were characterized using elemental analysis, IR, mass spectrometry, UV–Vis spectra, thermal anal-
ysis, and magnetic measurements.
Received 3 March 2012
Received in revised form 5 May 2012
Accepted 7 May 2012
l
Available online 23 May 2012
Keywords:
Chromium
Molybdenum
Isatin-3-oxime
Thermal
Ó 2012 Elsevier B.V. All rights reserved.
Spectral
1. Introduction
were synthesized and characterized [15]. However, isatin oxime,
as a special type of isatin Schiff-base ligands, has aroused a keen
Isatins and their derivatives are well known to have coordinative
properties [1–4] and biological activities like antibacterial, antimi-
crobial, antifungal, and anti-HIV activities [5–9]. It is an endoge-
nous compound that is widely distributed in mammalian tissues
and body fluids. Isatin also readily crosses the blood–brain barrier,
suggesting its possible action on the central nervous system (CNS)
[10]. Consequently, the study of metal complexes of Schiff-base
ligands derived from isatin has received much attention during
the last years [11–13]. Recently, Isatin-thiosemicarbazone Cu(II)
complexes related to the antiviral drug, methisazone, were studied
[14]. Different metal complexes such as nickel, copper, and zinc
complexes of isatin and N-methylisatin-3-picolinoyl hydrazone
interest because of its simple synthesis by condensation of isatin
with hydroxyl amine [16]. Isatin-3-oxime (H2OXI) has long been
known to form complexes, which can undergo significant changes
in biological activities on complexation as compared to their pure
ligand forms [17–19].
In earlier work we reported the reactions of some metal carbon-
yls and oxime ligands [20–23], which prompted us to further
investigate the reactions of some metal carbonyls such as Mo(CO)6,
and Cr(CO)6 with isatin-3-oxime. The aim of the present work was
to synthesize, and characterize the ligand and its novel complexes
with molybdenum, and chromium.
2. Experimental
2.1. Materials and instrumentation
⇑
Corresponding authors. Tel.: +20 1 68727555; fax: +20 1 33222578 (M.Y.
Nassar), tel.: +20 2 24196561; fax: +20 2 26842123 (M.F. El-Shahat).
E-mail addresses: m_y_nassar@yahoo.com (M.Y. Nassar), elshahatmf@yahoo.
com (M.F. El-Shahat).
The following were purchased from commercial sources and
used without further purification: Mo(CO)6 (Aldrich), Cr(CO)6
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.05.013

M.Y. Nassar et al. / Journal of Molecular Structure 1026 (2012) 88–92
89
(Aldrich), and isatin (Merck). Solvents were of analytical grade and
were purified, and dried according to standard procedures [24]. Ele-
mental analyses were carried out on a Perkin-Elmer 2400 CHN
elemental analyzer. The electronic spectra were recorded with a
Jasco UV–Vis spectrophotometer (Model: V530). The IR spectra
were recorded as KBr disks with a Unicam-Mattson 1000 FT-IR
spectrometer. Molar conductance measurements were taken by
using Jenway 4010 conductivity meter. Magnetic moments were
determined on a Sherwood Scientific magnetic moment balance
(Model: MK1) at room temperature (25 °C) using with Hg[Co
(SCN)4] as a calibrant. Diamagnetic corrections were applied using
Pascal’s constants [25]. Mass spectra were performed on a JEOL
JMS-AX500 mass spectrometer. Thermogravimetric analyses
(TGA) were carried out using a Shimadzu DT-50 thermal analyzer
under nitrogen atmosphere with heating rate of 10 °C/min.
under the atmospheric pressure and gave no product. Consequently,
bipyridyl has been used in this reaction because of its labilizing
effect on the carbonyl groups [26]. In addition, reactions of metal
carbonyls with ligands under atmospheric pressure are complicated
by the sublimation metal carbonyls which either result in a small
yield or the reaction does not proceed. This problem is avoided by
starting with the amine complexes of metal carbonyls [27]. It is
worthy to report that, repeating this reaction in sunlight did not
proceed.
On the other hand, the reaction of chromium hexacarbonyl with
H2L ligand in sunlight gave the dinuclear complex Cr2O4(H2L)2 in
high yield (Scheme 2). Formation of oxomolybdenum and oxochro-
mium complexes may be attributed to the reaction with oxygen of
the atmosphere as it was expected [22]. It is noteworthy that
repeating this reaction under reflux condition did not proceed.
The complexes were initially characterized on the basis of their
mass spectra and elemental analyses. The mass spectra of the
molybdenum and chromium complexes are shown Fig. 1. For the
molybdenum complex, it revealed peaks (m/z) at 363.9, 162,
161.7, 155, 145.9, and 129.9, which may be attributed to ½
(Mo2O4(H2L)2(THF)2), H2L, MoO4, MoO2CN, MoO3, and MoO2 frag-
ments, respectively. On the other hand, the mass spectrum of the
chromium complex exhibits peaks (m/z) at 329.9, 162, and 116,
2.2. Synthesis of isatin-3-oxime (H2L) and its metal complexes
2.2.1. Synthesis of isatin-3-oxime (H2L)
A solution containing 8.5 g (57 mmol) of isatin in 20 mL of eth-
anol was added dropwise to a stirring solution of 4.0 g (28 mmol)
of hydroxylamine in 20 mL of ethanol. The reaction blend was
refluxed for 45 min. After cooling, the yellow precipitate oxime
was collected by filtration and re-crystallized from ethanol to give
a yellow crystalline product (m.p. 239–240 °C, 3.30 g yield, 75%).
Anal. Calc. for C8H6N2O2 (MW = 162.15): C, 59.62; H, 3.72; N,
17.16. Found: C, 59.20; H, 3.60; N, 17.16.
OH
N
reflux, 9 h
2.2.2. Synthesis of [Mo(H2L)(THF)(O)2]2 complex
O
+
2 Mo(CO)6
2
THF, bipyridyl
Bipyridyl (0.059 g, 0.38 mmol) was added to a solution of
Mo(CO)6 (0.10 g, 0.38 mmol) in 20 mL of THF, with stirring and
reflux for 30 min. Isatin-3-oxime (0.0614 g, 0.38 mmol) was dis-
solved in 5 mL of THF and added to the stirring molybdenum hexa-
carbonyl solution, then heated to reflux for 9 h. During this time,
the color of the reaction blend turned into deep green. The reaction
mixture was cooled to room temperature, and then the THF solvent
was evaporated by rotatory evaporator. The obtained residue was
washed several times with hot petroleum ether (40–60) and with
ethyl alcohol to give green solid. The green residue was dried under
vacuum for few hours to give a yield of 0.116 g (84%).
N
H
HO
N
O
H
N
O
O
O
Mo
Mo
O
O
O
N
H
N
O
Anal. Calc. for C24H28N4O10Mo2 (MW = 727.99): C, 39.79; H,
3.90; N, 7.73. Found: C, 39.90; H, 3.84; N, 7.66. Effective magnetic
moment, leff (BM): 3.31. Molar conductivity (OÀ1 molÀ1 cm2): 7.9.
OH
Scheme 1. Proposed structural formula for the dimolybdenum complex.
2.2.3. Synthesis of [Cr(H2L)(O)2]2 complex
A
mixture of Cr(CO)6 (0.2 g, 0.91 mmol) and isatinoxime
OH
N
(0.147 g, 0.895 mmol) was dissolved in 20 ml of THF. The reaction
mixture was left to expose to sunlight for 3 days. The color of the
reaction mixture turned into green. The THF solvent was evapo-
rated to give an oily residue, which was washed with hot petroleum
ether and then scratched with diethyl ether to finally produce a
brown residue. The produced residue was washed several times
with ethanol and left to dry under vacuum to give a yield of
0.174 g (78%).
sun light, 72 h
O
+
2 Cr(CO)6
2
THF, bipyridyl
N
H
HO
N
Anal. Calc. for C16H12N4O4Cr2 (MW = 419.95): C, 39.04; H, 2.46;
N, 11.38. Found: C, 38.49; H, 2.60; N, 11.30. Effective magnetic mo-
ment, leff (BM): 1.95. Molar conductivity (OÀ1 molÀ1 cm2): 8.5.
H
N
O
O
O
O
Cr
O
Cr
3. Results and discussion
N
N
H
O
The reaction of molybdenum hexacarbonyl with H2L ligand in
presence of bipyridyl produced the dinuclear complex Mo2O4
(H2L)2(THF)2 in high yield (Scheme 1). Actually, molybdenum hexa-
carbonyl did not react with the H2L ligand in absence of bipyridyl
OH
Scheme 2. Proposed structural formula for the dichromium complex.

90
M.Y. Nassar et al. / Journal of Molecular Structure 1026 (2012) 88–92
Fig. 2. The IR spectra of H2L ligand and its molybdenum and chromium complexes.
complexes, respectively. In contrast the peaks corresponding to
OAH and NAO stretching vibrations were observed at 3425 and
1038 cmÀ1 for the molybdenum complex and at 3325 and
1024 cmÀ1 for the chromium complex. Such behavior evidently
indicates that the isatin oxime ligands are coordinate to molybde-
num centers and chromium centers, in the molybdenum and chro-
mium complexes, respectively, through the nitrogen atom of the
C@NAOH group [22,30,33]. The IR spectrum the molybdenum
and chromium complexes revealed one band for each complex,
corresponding to the M@O asymmetric vibration, and observed at
904 and 871 cmÀ1, respectively. The absence of M@O symmetric
stretching vibration may suggest a symmetrical molecule in which
the two M@O moieties are located in a trans positions to one
another. These results are in good agreement with those observed
for Mo2O2(HBNO)4 and [Mo2O2(3,5-DBQ)] [22,34]. The dinuclear
structure of the molybdenum and chromium complexes may be
inferred from the IR spectra. The IR spectra of [Mo(H2L)(THF)(O)2]2
and [Cr(H2L)(O)2]2 revealed absorption bands, that are not present
in the spectrum of the free H2L ligand, at 763 and 750 cmÀ1, respec-
tively, and may be assigned to asymmetric stretching vibrations
Fig. 1. The mass spectra for [Mo(H2L)(THF)(O)2]2 and [Cr(H2L)(O)2]2 complexes.
which may be assigned to Cr2O4(H2L)2–H2L, H2L, and CrO4, respec-
tively.
associated with M2(l-O)2 structural unit. Consistence with this
It is noteworthy to report that the complexes described in this
study are soluble in DMF and DMSO. Solutions of the complexes
in DMSO with concentration of 1 Â 10À3 M have molar conductiv-
ity (km) of 7.9 and 8.5 OÀ1 molÀ1 cm2 for the molybdenum and
chromium complexes, respectively, and these values indicate the
non-electrolytic nature of the prepared complexes [28,29].
Analyzing the IR spectra of the synthesized complexes was use-
ful in assigning the ligand coordination modes to the molybdenum
and chromium centers. The IR spectra of the H2L ligand and its
molybdenum and chromium complexes as well are shown in
Fig. 2. The IR spectrum of the free ligand displayed some character-
assignment, the IR spectrum of the structurally characterized dinu-
clear, doubly-bridged [Mo2O4(Sabp)2] complex showed an absorp-
tion peak at 760 cmÀ1 due to the stretching frequency of the
bridging MAO [35]. Also, [Au2 (bipy)2(
l
-O)2]2+ and [(Cu2(Sp)2
(M2O2) at 682
(l
-O)2]2+ complexes were found to exhibit the
l
and 619 cmÀ1, respectively [36]. Additional characteristic vibra-
tions of coordinated THF are observed for the molybdenum com-
plex at 2922 and 2866 cmÀ1 (CAH stretching vibrations) and
1116 cmÀ1 (vibration associated with CAOAC moiety). This assign-
ment is in good agreement with that reported for coordinated THF
[30,37,38]. Finally, stretching vibrations which can be assigned to
MAO and MAN were found respectively, at 659 and 513 cmÀ1 for
the molybdenum complex and at 630 and 463 cmÀ1 for the chro-
mium complex [36].
istic absorption peaks at 3228, 3189, 3090, 1714, 1661, 946 cmÀ1
,
which may be due to OH, NH, CAH aromatic, C@O, C@N and NAO
stretching vibrations, respectively [30,31]. Generally, the IR absorp-
tion bands of OAH, C@N and NAO stretching vibrations are used to
assign the coordination modes of the CANAOH group to the metal
center. Upon coordination through the N atom of the oxime group,
the stretching vibration corresponding to C@N shifts to lower fre-
quency. In contrast, the bands corresponding to OAH and NAO
stretching vibrations shift to higher frequencies [30,32]. The molyb-
denum and chromium complexes displayed the peaks correspond-
ing to C@N stretching vibrations of the oxime group at 1602 and
1624 cmÀ1, respectively. These bands have shifted to lower fre-
quencies of 59 and 37 cmÀ1 for the molybdenum and chromium
The magnetic susceptibility measurements of the synthesized
complexes were carried out on the solid samples at 298 K. The
effective magnetic moment (leff) was found to be 3.31 and
1.95 B.M. for the dimolybdenum and dichromium complexes,
respectively. For a dimolybdenum(IV) complex, an intramolecular
magnetic exchange can produce S = 0, S = 1 and S = 2 magnetic
state[22]. When the magnetic exchange was antiferromagnetic,
the S = 0 would be the ground state. It was reported that the dimo-
lybdenum(IV) complexes containing MoAMo bond are diamagnetic

M.Y. Nassar et al. / Journal of Molecular Structure 1026 (2012) 88–92
91
Table 1
The electronic absorption data for H2L ligand and its complexes in recorded DMSO.
Compound
k (nm; logea
)
H2L
300 (3.88), 400b (2.10)
350 (4.16), 600b (2.80)
310 (4.22), 350b (3.67)
[Cr(H2L)(O)2]2
[Mo(H2L)(THF)(O)2]2
a
e
MÀ1 cmÀ1
Broad.
.
b
The thermal studies of the dimolybdenum and dichromium
complexes shown in Fig. 3 provided further insight into the pro-
posed structures and the thermal stability of the complexes inves-
tigated. The reported complexes were found to be air stable. The
thermogravimetric studies were carried out within the tempera-
ture range 20–1000 °C at a heating rate of 10 °C/min under nitro-
gen atmosphere. The TGA curve of the dichromium complex
revealed one decomposition step (Scheme 3). This step occured
at 101–472 °C and attributed to the decomposition of the organic
part of the dichromium complex leaving Cr2O3 residue (found
30.88%, calcd. 30.8%). On the other hand, the thermal decomposi-
tion of dimolybdenum complex took place in three steps as
showed by the TGA analysis (Scheme 3). The first step, within
the temperature range of 82–333 °C, was related to the evolution
of two THF molecules due to a mass loss of 19.7% (calcd. 18.7).
The second step occurred in the temperature range of 333–
517 °C, and was accompanied by a weight loss of 22.5% (calcd.
22.3%), corresponding to the loss of one isatin-oxime ligand mole-
cule. The third stage involved a significant mass loss (47.6%)
extending from 648 °C to 1000 °C, corresponding to the removal
of one molecule ligand to give a molybdenum dioxide residue
(x MoO2; 10%, where x = 0.57) and sublimed (1 À x)MoO3 molecule.
The electronic absorption spectra recorded for the two com-
plexes and the free ligand in DMSO are summarized in Table 1.
The free ligand revealed two absorptions at 300 and 400 nm attrib-
Fig. 3. TGA and DTGA plots for Chromium and Molybdenum complxes.
due to molybdenum–molybdenum bonding interaction. Moreover,
oxo-bridged metal ion dimers also exhibit magnetic exchange
interactions [22,39]. Consequently, the obtained magnetic for
Mo2O4(H2L)2(THF)2 and Cr2O4(H2L)2 complexes can fit with the pro-
posed dimeric structures containing two M(IV) centers and bonded
through two MAOAM bridges. Additionally, as expected, the de-
crease in the effective magnetic moments for both dimetallic com-
plexes than the spin-only value (4.9 BM) was theoretically
calculated for four unpaired electrons and may be due to the intera-
molecular magnetic interaction between the two M(IV) centers
through the two MAOAM bridges. Also, the magnetic moment va-
lue for the dichromium complex was lower than that of the dimo-
lybdenum complex, which mean that the unpaired electrons on
the two chromium centers can interact more than those of the
two molybdenum centers due to the fact that the atomic orbitals
of molybdenum atom are larger than those of chromium atom so
that the probability that the electrons can see each other is more
for the dichromium atoms than that for the dimolybdenum atoms
[40].
uting to
p–
pà and n–pà transitions, respectively. However, the
UV–Vis region is characterized by two absorptions displayed by
the two prepared complexes. For the dichromium complex, the in-
tense absorption at shorter wave length (350 nm) can be assigned
to a
p
–
pà transition, while the absorption at the longer wave length
3
(600 nm) may be attributed to a chromium(IV) T1g–3T2g transi-
tion[41], and /or n–pà transition, which commonly displays a
bathochromic shift upon complexation. The higher energy d–d
transitions characteristic for Cr(IV) centers are obscured by the
intense
p–
pà transition. On the other hand, the dimolybdenum
complex showed the absorption corresponding to the intraligand
p–
pà transition at 310 nm. In addition, an intense absorption was
100 - 400 oC
[Cr2(C8H6N2O2)2(O)4]
(100 %)
Cr2O3
- C16H12N4O5, (69.2 %)
(30.8 %)
82 - 333 oC
[Mo2(C8H6N2O2)2(O)4(C4H8O)2]
(100 %)
[Mo2(C8H6N2O2)2(O)4]
(81.3 %)
- 2(C4H8O), (18.7 %)
333 - 517 oC
-(C8H6N2O2)
(22.6 %)
648-1000 oC
[Mo2(C8H6N2O2)(O)4]
(58.7 %)
x MoO2
-[(MoO3)1-x, C8H6N2O3y] (47.6 %), y=1-x
(x= 0.57, 11.1 %)
Scheme 3. Proposed thermal decomposition mechanisms of chromium and molybdenum complexes.

92
M.Y. Nassar et al. / Journal of Molecular Structure 1026 (2012) 88–92
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is in good agreement with that observed for the analogous
benzoin oxime complex, Mo2O4(HBNO)2 [22]. Also, the electronic
absorption spectrum of the doubly-bridged [Mo2O4(Sabp)2]
showed the absorption band at 428 nm (log = 4.63) due to the
charge transfer transition from oxygen orbital to a metal d-orbital
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4. Conclusions
Two novel bimetallic complexes; [Mo(H2L)(THF)(O)2]2, and
[Cr(H2L)(O)2]2 were prepared using their corresponding metal hexa-
carbonyls in THF under reflux and sun light routes, respectively.
These two complexes were characterized using IR, mass spectros-
copy, UV–vis spectra, thermal analysis and magnetism. Additionally,
for both complexes, the lowering in leff values may be due to strong
antiferromagnetic coupling between the two metal centers through
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