Synthesis and characterization of a novel benziloxime ligand and its iron(III) and nickel(II) complexes

Article abstract of DOI:10.1002/jccs.201000049

The synthesis of a novel benziloxime ligand, 4,4′- dibromobenzilmonoxime (DBBOH) (1) and its complexes [Fe(DBBO)₃] (2) and Na[Ni(DBBO)₃] (3) are described. The ligand (DBBOH) was prepared in MeOH from the reaction of 4,4′-dibromobenzil with hydroxylamine hydrochloride in the presence of sodium acetate. Reaction of sodium salt of 4,4′-dibromobenzilmonoxime (DBBONa) in MeOH with Fe(NO₃) ₃.9H₂O and Ni(NO₃)₂.6H₂O yielded [Fe(DBBO)₃] (2) as yellow and Na[Ni(DBBO)₃] (3) as brown precipitates respectively. The ligand, 4,4′-dibromobenzilmonoxime (DBBOH) (1) and its complexes [Fe(DBBO)₃] (2) and Na[Ni(DBBO) ₃] (3) were characterized by elemental analysis, ¹H-NMR and ¹³C-NMR, IR, and electronic spectral studies. The analysis of IR, ¹H-and ¹³C-NMR spectral data of Fe(III) and Ni(II) complexes suggest that 4,4′-dibromobenzilmonoximate is bonded to iron(III) and nickel(II) ions through the oxygen atom of the carbonyl, and the nitrogen atom of the imine groups. The electronic spectral data of the complexes in CHCl₃ are in good agreement with the octahedral coordination of Fe(III) and Ni(II) ions. The ligand field parameters for these complexes, i.e. splitting energy and Racah parameter were calculated to be 21560 cm^-1 and 707 cm^-1 for [Fe(DBBO)₃] (2), 13440 cm^-1 and 610 cm^-1 forNa[Ni(DBBO)₃] (3) respectively.

Full text of DOI:10.1002/jccs.201000049

332
Journal of the Chinese Chemical Society, 2010, 57, 332-337
Synthesis and Characterization of a Novel Benziloxime Ligand and Its
Iron(III) and Nickel(II) Complexes
Esmaiel Soleimani
Inorganic Research Laboratory, Faculty of Chemistry, Shahrood University of Technology, Shahrood, Iran
The synthesis of a novel benziloxime ligand, 4,4¢-dibromobenzilmonoxime (DBBOH) (1) and its
complexes [Fe(DBBO)3] (2) and Na[Ni(DBBO)3] (3) are described. The ligand (DBBOH) was prepared
in MeOH from the reaction of 4,4¢-dibromobenzil with hydroxylamine hydrochloride in the presence of
sodium acetate.
Reaction of sodium salt of 4,4¢-dibromobenzilmonoxime (DBBONa) in MeOH with Fe(NO3)3.9H2O
and Ni(NO3)2.6H2O yielded [Fe(DBBO)3] (2) as yellow and Na[Ni(DBBO)3] (3) as brown precipitates re-
spectively.
The ligand, 4,4¢-dibromobenzilmonoxime (DBBOH) (1) and its complexes [Fe(DBBO)3] (2) and
Na[Ni(DBBO)3] (3) were characterized by elemental analysis, 1H-NMR and 13C-NMR, IR, and electronic
spectral studies.
The analysis of IR, 1H- and 13C-NMR spectral data of Fe(III) and Ni(II) complexes suggest that 4,4¢-
dibromobenzilmonoximate is bonded to iron(III) and nickel(II) ions through the oxygen atom of the car-
bonyl, and the nitrogen atom of the imine groups. The electronic spectral data of the complexes in CHCl3
are in good agreement with the octahedral coordination of Fe(III) and Ni(II) ions. The ligand field parame-
ters for these complexes, i.e. splitting energy and Racah parameter were calculated to be 21560 cm-1 and
707 cm-1 for [Fe(DBBO)3] (2), 13440 cm-1 and 610 cm-1 for Na[Ni(DBBO)3] (3) respectively.
Keywords: 4,4¢-Dibromobenzilmonoxime; Octahedral complexes; Iron(III) ion; Nickel(II) ion;
Ligand field parameters; Monooximes; IR; Electronic spectra; 1H- and 13C-NMR
studies.
1. INTRODUCTION
plexes with Fe(III) and Ni(II) salts. The properties of the
complexes were investigated by spectroscopic methods.
Oximes play an important role in the development of
transition metal coordination chemistry due to their versa-
tile bonding modes.1 Benzilmonoximes are known as che-
lating agents and are frequently used in extractive and ana-
lytical chemistry. For example, the concentration of copper
in a solution has been determined its benzilmonoxime com-
plex by atomic absorption spectroscopy.2 It is a well known
extracting agent for molybdenum, tungsten, vanadium,3
and also for the determination of cobalt at microgram
amount.4 A number of benzilmonoximates which have
been reported show interesting stereochemistry.5 Benzil-
monoximes are of special interest owing to their biological
activities, and semi-conducting properties.6 In view of this,
and our continuing interest on the synthesis of new benzil-
monoximes,7,8 we wish to report the synthesis and charac-
terization of 4,4¢-dibromobenzilmonoxime and its com-
2. RESULTS AND DISCUSSION
The reaction of sodium 4,4¢-dibromobenzilmono-
ximate (DBBONa) with Fe(NO3)3.9H2O and Ni(NO3)2.
6H2O in methanol gave [Fe(DBBO)3] (2) as yellow and
Na[Ni(DBBO)3] (3) as brown complexes, respectively
(Scheme I).
The ligand, 4,4¢-dibromobenzilmonoxime (DBBOH)
(1) and its complexes [Fe(DBBO)3] (2) and Na[Ni(DBBO)3]
(3) were characterized on the basis of elemental analysis,
1
and H-NMR, 13C-NMR, IR, and electronic spectra data.
The molar conductance of complexes 2 and 3 were 25 and
123 W-1.cm2.mol-1, respectively, indicating that the iron(III)
complex 2 to be non-electrolyte, but the nickel(II) complex
3 showed a 1:1 electrolyte behavior.9
* Corresponding author. Tel/Fax: 00982733395441; E-mail: essoleimani@shahroodut.ac.ir; es_soleimani@yahoo.com

Synthesis of Two Complexes of Dibromobenziloxime
J. Chin. Chem. Soc., Vol. 57, No. 3A, 2010 333
Scheme I Reactions for preparation of the iron(III) and nickel(II) complexes with 4,4¢-dibromobenzilmonoximate
2.1. IR spectra
the iron(III) and Ni(II) complexes, which were assigned to
the n(Fe-O), n(Ni-O) and n(Fe-N), n(Ni-N) stretching vi-
brations respectively.13
The 4,4¢-dibromobenzilmonoxime ligand, showed
characteristic IR bands at 3455, 1645, 1220 cm-1 due to the
OH, C=N, and N–O stretching vibrations of the oxime
group (C=N-OH), and a sharp band at 1715 cm-1 due to
n(C=O) of the carbonyl group (Table 1). A strong and
broad band is observed at 3455 cm-1 for the free ligand due
to n(N–OH) which is absent in both complexes, suggesting
the deprotonation of the hydroxyl group of the oxime in the
process of formation of the complexes.10
The band at 1715 cm-1, which was assigned to n(C=O)
of ligand was shifted to a lower energy at 1685 cm-1 in
iron(III) and 1690 cm-1 in nickel(II) complexes, indicating
the participation of the carbonyl group of 4,4¢-dibromo-
benziloxime in coordination.11 Also the band at 1645 cm-1
due to n(C=N) of the oxime group in ligand was shifted to
lower frequencies at 1625 cm-1 and 1618 cm-1 in its iron(III)
and nickel(II) complexes, suggests the coordination of
azomethine group (C=N) with the metal ions.12
The absorption band due to C-Br (710 cm-1) of the
ligand does not show any shift in the spectra of the com-
plexes (705, 707 cm-1) which means it dos not take parting
coordination. The band at 1220 cm-1 due to n(N-O) of the
ligand appeared at 1225 and 1228 cm-1 in the complexes.
Since no considerable change was observed for n(N-O) of
the free ligand and the complexes, indicates no participa-
tion of oxygen atom of the N-O group in the coordination.
1
2.2. H- and 13C-NMR spectra
1
The H-NMR spectra of 4,4¢-dibromobenzilmono-
xime and its iron(III) and nickel(II) complexes show a
multiplet in the aromatic region 6.7-7.80 ppm due to the
phenyl groups. The singlet peak due to the N–OH proton at
10.20 ppm in 4,4¢-dibromobenzilmonoxime is absent in its
iron(III) and nickel(II) complexes, suggesting the deproto-
nation of the hydroxyl group of the oxime in the ligand.14
The 13C-NMR spectra for 4,4¢-dibromobenzilmono-
These facts are further supported by the appearance
of new bands in the regions 492, 490, 448, and 452 cm-1 in
Table 1. Important IR bands (cm-1) and their assignments for 4,4¢-dibromobenzilmonoxime and its Fe(III)
and Ni(II) complexes
Vibration modes
n(O-H) n(C=O) n(C=N) n(N-O) n(C-Br) n(M-O) n(M-N)
4,4¢-dibromobenzil-monoxime (1)
[Fe(DBBO)3] (2)
3455
1715
1685
1690
1645
1625
1618
1220
1222
1228
710
705
707
492
490
448
452
Na[Ni(DBBO)3] (3)

334 J. Chin. Chem. Soc., Vol. 57, No. 3A, 2010
Soleimani
xime show peaks at the regions 129, 131, 135, 139, 168,
198.5, and 201 ppm (Table 2). The signals at 201 and 198.5
ppm were assigned to the carbon of the carbonyl group and
the carbon of the oxime group in 4,4¢-dibromobenzilmono-
xime ligand, respectively.15 These bands shifted upfield to
191, 193 ppm and 183.5, 185 ppm, in its iron(III) and
nickel(II) complexes, respectively, due to shielding effects
in its complexes, which suggest coordination of the oxygen
atom of the carbonyl group and the nitrogen atom of the
oxime group to metal ions.16
exhibit absorption bands at 260-264 and 365-366 nm with
high molar extinction coefficient (Table 3) that can be as-
signed to p ® p* and n ® p* intra-ligand charge transfer,
respectively.11 These absorption bands have high intensity
since they obey the Lapport selection rule. In addition to
the above bands, same other bands were also observed at
384, 451, and 542 nm for its iron(III) and at 535 and 744
nm for nickel(II) complexes.
Since there are no spin-allowed d®d transitions for
iron(III) with high spin d5 configuration, therefore, the
bands at the regions 451 and 542 nm with molar extinction
coefficients lower than 100 M-1.cm-1 can be assigned to the
ligand field transitions for iron(III) with low spin (t2g)5 con-
figuration.18
The resonance at 168 ppm belongs to the C4, C4¢ car-
bons carrying bromine atoms. The other two resonances
which appear at 131 and 129 ppm are assigned to C2, C2¢,
C6, C6¢ and 3, 3¢, 5, 5¢ carbon atoms of the phenyl rings.
The resonances at 139 and 135 ppm were assigned, respec-
tively, to the C1 carbon atom of the phenyl ring bonded to
the carbonyl group and to the C1¢ carbon atom of the
phenyl ring bonded to the oxime group.17 These bands are
also present in the spectra of the iron(III) and nickel(II)
complexes at almost the same positions, indicating no par-
ticipation of them in coordination.
The low spin configuration of the Fe(III) complex is
further confirmed by magnetic susceptibility measurement.
At ambient temperature, the Fe(III) complex exhibit effec-
tive magnetic moment of 1.98 B.M. This magnetic moment
value confirm that Fe(III) complex remain low spin (S =
1/2) with (t2g)5 configuration. Mononuclear Fe(III) com-
plexes [CpFe(dppe)-SR]PF6 and [Fe(pyAS)2]Bph4 with a
low spin d5 configuration have been reported to exhibit
magnetic moment at 1.93 and 1.97 B.M. respectively.19,20
According to the Tanabe-Sugano diagram for low
spin d5 configuration, the bands at the regions 542 nm
2.3. Electronic spectra
The electronic spectra of 4,4¢-dibromobenzilmono-
xime and its iron(III) and nickel(II) complexes in CHCl3
Table 2. The observed chemical shift values (ppm) for the 13C-NMR spectra of 4,4¢-dibromobenzilmono-
xime, and its Fe(III) and Ni(II) complexes
C3, C3¢
C5, C5¢
C2, C2¢
C6, C6¢
Carbon type
C1¢
C1
C4, C4¢ C=N-OH C=O
4,4¢-dibromobenzil-monoxime (1)
[Fe(DBBO)3] (2)
129
129
129
131
131
132
135
139
138
168
169
168
198.5
183.5
185
201
191
193
135.5
134.5
Na[Ni(DBBO)3] (3)
138.5
Table 3. The electronic absorption data (nm) 4,4¢-dibromobenzilmonoxime, and its Fe(III) and Ni(II) complexes
recorded in CHCl3. Log e of absorption bands are in parentheses
Intra ligand charge
transfer
Transition type
Ligand to metal
charge transfer
Splitting
energy/cm-1
p ® p*
n ® p*
Ligand field transfer
4,4¢-dibromobenzil-
monoxime (1)
260 (4.2) 365 (2.8)
262 (3.8) 365 (2.4)
264 (3.9) 366 (2.5)
pp(O) ® eg*(Fe) 2T2g ® (2A2g or 2T1g) 2T2g ® 2Eg
[Fe(DBBO)3] (2)
21560
13440
384 (3.7)
542 (1.85)
3A2g ® 3T2g
451 (1.8)
3A2g ® 3T1g
Na[Ni(DBBO)3] (3)
744 (1.95)
535 (1.84)

Synthesis of Two Complexes of Dibromobenziloxime
J. Chin. Chem. Soc., Vol. 57, No. 3A, 2010 335
(18450 cm-1) and 451 nm (22170 cm-1) were assigned to the
solvents used were purified, and dried according to the
standard procedures.23 The reaction progress, and the pu-
rity of the products were checked using silica gel TLC
plates (CHCl3:CH3OH, 5:1).
2
2
2
2T2g ® (2A2g or T1g) and T2g ® Eg transitions, respec-
tively.21
When working with electronic spectra, it is often use-
ful to determine the ratio of the energy of the second transi-
3.1. Physical and spectral measurements
n2
The elemental analysis was performed on a Heraeus
Carlo Erba1108 elemental analyzer. The 1H- and 13C-NMR
spectra were recorded on a Brucker AV300 NMR spec-
trometer with the TMS as internal reference. The IR spectra
were recorded on a Perkin-Elmer model 377 spectrometer
using KBr pellets. The electronic spectra were obtained in
CHCl3 with a Shimadzu UV-160 spectrophotometer. Mag-
netic susceptibility measurements were done with a 155
Allied Research vibrating sample magnetometer at room
temperature. Melting points were measured using an elec-
trothermal Buchi 512 melting point apparatus. Molecular
weights were measured on a Knauer Vapour Pressure
Osmometer in CHCl3 solution at room temperature. Molar
conductivities (10-3 M in DMSO) were measured with
CMD 8500 Laboratory Conductivity Meter. Iron and nickel
were determined by spectrophotometeric method using an
AA-670 Shimadzu atomic absorption-flame emission spec-
trophotometer.
tion to the first one. In the iron(III) complex,
=
n1
22170 cm-1
18450 cm-1
DO
= 1.2, and this ratio corresponds to
being
B
equal to 30.5 on the Tanabe-Sugano diagram. By using this
value in the calculation of the Racah parameter, splitting
energy, unobserved third transition, and nephelauxetic pa-
rameter for the iron(III) complex, the following results
were obtained B = 707 cm-1, DO = 21560 cm-1, n3 = 30400
cm-1, and b = 0.642.
The bands at the regions 744 nm (13440 cm-1) and
535 nm (18690 cm-1) for nickel(II) complex were assigned
to the first and second ligand field transitions 3A2g ® 3T2g
3
and A2g ® T1g, respectively. The ratio of the second to
3
18690 cm-1
13440 cm-1
n2
first transition
=
= 1.4, which corresponds
n1
DO
to
being equal to 22 on the Tanabe-Sugano diagram. By
3.2. Preparation of the ligand and its complexes
4,4¢-dibromobenzilmonoxime was prepared accord-
ing to a modified procedure described for the preparation
of benzilmonoxime in two steps.24 First, 4,4¢-dibromoben-
zil was obtained from the reaction of 4-bromobenzalde-
hyde with sodium cyanide in the presence of nitric acid in
methanol. Then in the second stage, the solution of the
product in the same solvent was treated with hydroxyl-
amine hydrochloride in the presence of sodium acetate to
yield 4,4¢-dibromobenzilmonoxime (Scheme II).
B
using this value in the calculation of the Racah parameter,
splitting energy, unobserved third transition, and neph-
elauxetic parameter for the nickel(II) complex, the follow-
ing results were obtained B = 610 cm-1, DO = 13440 cm-1, n3
= 29280 cm-1, and b = 0.608.
The absorption bond at 384 nm (26040 cm-1) with log
e equal to 3.3 for iron(III) complex could be assigned to the
charge transfer from the filled p-orbital of 4,4¢-dibromo-
benzilmonoximate to the empty eg* orbital of iron(III) in
the complex,22 which has a high intensity (Lapport selec-
tion rule).
3.2.1. Preparation of 4,4¢-dibromobenzil
A solution of 4-bromobenzaldehyde (925 mg, 5
mmol) in methanol (25 mL) was added dropwise to sodium
cyanide (245 mg, 5 mmol) in methanol (30 mL) with stir-
ring at room temperature. The mixture was then heated at
80 °C for 8 hours. When concentrated nitric acid (10 mL)
was added to the solution a yellow residue was formed
which was filtered off, and washed with cold methanol and
recrystalized from ethanol to give (1.65 g, 90%) of pure
C14H8Br2O2. Anal. Calcd: C, 45.68; H, 2.17; Br, 43.44.
Found: C, 45.83; H, 1.98; Br, 43.61%. IR (KBr, cm-1): 3052
(m), 3025 (m), 1675 (s), 1591 (w), 1441 (m), 1405 (m),
1293 (w), 704 (m). 1H-NMR (CDCl3, d ppm): 6.8-7.5 (m,
The molar extinction coefficient of d®d transitions
for trigonal prismatic complexes is more than 250 M-1cm-1
due to the lack of a center of symmetry. However, the molar
extinction coefficient of d®d transitions for the iron(III)
complex was lower than 100 M-1 cm-1, indicating that
[Fe(DBBO)3] and Na[Ni(DBBO)3] complexes have octa-
hedral geometry.
3. EXPERIMENTAL SECTION
All the chemicals used were of analytical grade. All
synthetic works were carried out open to atmosphere. The

336 J. Chin. Chem. Soc., Vol. 57, No. 3A, 2010
Soleimani
Scheme II Two steps for preparation of the 4,4¢-dibromobenzilmonoxime ligand
8H).
Found: C, 42.12; H, 1.92; N, 3.43; Br, 40.27; Fe, 4.50%. IR
(KBr, cm-1): 3058 (m), 3025 (m), 1685 (s), 1625 (m), 1435
3.2.2. Preparation of 4,4¢-dibromobenzilmonoxime
To a solution of 4,4¢-dibromobenzil (1.839 g, 5 mmol)
in warm methanol (30 mL) was added a solution of sodium
acetate (410 mg, 5 mmol) and hydroxylamine hydrochlo-
ride (342 mg, 5 mmol) in 50% aqueous methanol (25 mL).
The reaction mixture was refluxed for 6 hours. When the
solution was cooled in a beaker containing ice-water a
white precipitate was formed which was filtered off, and
washed with cold water. The crude material was then re-
crystallized from ethanol to give (1.75 g, 92%) of pure
C14H9Br2NO2. Anal. Calcd.: C, 43.88; H, 2.35; N, 3.66; Br,
41.74. Found: C, 44.02; H, 2.24; N, 3.53; Br, 41.97%. IR
(KBr, cm-1): 3455 (s), 3063 (m), 3022 (m), 1715 (s), 1645
1
(m), 1405 (m), 1225 (s), 705 (m), 492 (m), 448 (m). H-
NMR (CDCl3, d ppm): 6.6-7.6 (m, 8H). 13C-NMR (CDCl3,
d ppm): 191, 182.5, 169, 138, 135.5, 131, 129; UV-Vis
(CHCl3, lmax/nm, (log e)): 262 (3.8), 365 (2.4), 384 (3.7),
451 (1.8), 542 (1.85).
3.2.4. Preparation of the complex sodium tris(4,4¢-
dibromobenzilmonoximato)nickelate(II)
A fresh solution of sodium methoxide was prepated
by dissolving metallic sodium (0.138 g, 6 mmol) in metha-
nol (5 mL) which was added to a stirred hot solution of
4,4¢-dibromobenzilmonoxime (2.290 g, 6 mmol) in metha-
nol (30 mL). The resulting solution was refluxed for 4
hours until a yellow solution was obtained. A solution of
Ni(NO3)2.6H2O (0.580 g, 2 mmol) in methanol (25 mL)
was then added to this solution. The reaction mixture was
refluxed for 8 hours to ensure the completion of the reac-
tion. The resulting solution was placed in a ice-water con-
tainer until a brown precipitate was formed which was fil-
tered off, and washed with cold water and methanol, and
recrystallized from ethanol to give (2.21 g, 90%) of pure
product (C42H24Br6N3NaNiO6). Anal. Calcd.: C, 41.07; H,
1.96; N, 3.42; Br, 39.07; Ni, 4.78. Found: C, 41.35; H, 1.88;
N, 3.35; Br, 39.35; Ni, 4.52%. IR (KBr, cm-1): 3058 (m),
3030 (m), 1690 (s), 1618 (m), 1433 (m), 1409 (m), 1228
(s), 707 (m), 490 (m), 452 (m). 1H-NMR (CDCl3, d ppm):
6.6-7.6 (m, 8H). 13C-NMR (CDCl3, d ppm): 193, 185, 168,
138.5, 134.5, 132, 129; UV-Vis (CHCl3, lmax/nm, (log e)):
264 (3.9), 366 (2.5), 535 (1.84), 744 (1.95).
1
(m), 1438 (m), 1402 (m), 1220 (s), 710 (m). H-NMR
(CDCl3, d ppm): 6.7-7.5 (m, 8H); 10.20 (s, 1H). 13C-NMR
(CDCl3, d ppm): 201, 198.5, 168, 139, 135, 131, 129; UV-
Vis (CHCl3, lmax/nm, (log e)): 260 (4.2), 365 (2.8).
3.2.3. Preparation of the complex tris(4,4¢-dibromo-
benzilmonoximato)iron(III)
A fresh solution of sodium methoxide was prepated
by dissolving metallic sodium (0.138 g, 6 mmol) in metha-
nol (5 mL) which was added to a hot solution of 4,4¢-di-
bromo-benzilmonoxime (2.290 g, 6 mmol) in methanol (30
mL). The resulting solution was refluxed for 4 hours until a
yellow solution was obtained. Then Fe(NO3)3.9H2O (0.808
g, 2 mmol) was dissolved in a minimum quantity of metha-
nol, and was added to this solution, the mixture was re-
fluxed for 5 hours to ensure the completion of the reaction.
After cooling the solution in a ice-water container a yellow
precipitate was formed which was filtered off, and washed
with methanol, and recrystallized from ethanol to give
(2.11 g, 88%) of pure product (C42H24Br6FeN3O6). Anal.
Calcd.: C, 41.96; H, 2.00; N, 3.50; Br, 39.91; Fe, 4.65.
ACKNOWLEDGEMENT
The author would like to thank the Research Council
of Shahrood University of Technology for the financial

Synthesis of Two Complexes of Dibromobenziloxime
J. Chin. Chem. Soc., Vol. 57, No. 3A, 2010 337
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