Spectral and thermal studies of some chromium and molybdenum complexes with ONO donor Schiff bases

Article abstract of DOI:10.1016/j.saa.2006.01.016

Reactions of M(CO)₆, where M = Cr and Mo with Schiff bases prepared by the condensation of ethanolamine with either acetylacetone or benzoylacetone were investigated. The reactions of Cr(CO)₆ in benzene resulted in the formation of the tricarbonyl drivatives [Cr(CO)₃(HL)], HL = acaceaH or baceaH. The HL proved to act as a tridentate ligand. The corresponding reactions with Mo(CO)₆ in dioxane gave the oxo complexes [Mo₂O₆(HL)₂] with HL was a bidentate. All prepared complexes were investigated using elemental analysis, IR, mass spectrometry, UV-vis absorption spectra and magnetic measurement. Thermal behaviors of the complexes were studied using by thermogravimetry (TG). Schemes for the thermal decomposition were proposed along with their mass fragmentation patterns.

Full text of DOI:10.1016/j.saa.2006.01.016

Spectrochimica Acta Part A 65 (2006) 841–845
Spectral and thermal studies of some chromium and molybdenum
complexes with ONO donor Schiff bases
Ahmed A. Solimana,∗, Saadia A. Alib, Adel Orabic
a Department of Chemistry, Faculty of Science, UAEU, P.O. Box 17551, Al-Ain, UAE
b Chemistry Department, University College for Girls, Ain Shams University, Cairo, Egypt
c Chemistry Department, Faculty of Science, Suez Canal University, Ismallia, Egypt
Received 5 October 2005; received in revised form 30 November 2005; accepted 16 January 2006
Abstract
Reactions of M(CO)6, where M = Cr and Mo with Schiff bases prepared by the condensation of ethanolamine with either acetylacetone or
benzoylacetone were investigated. The reactions of Cr(CO)6 in benzene resulted in the formation of the tricarbonyl drivatives [Cr(CO)3(HL)],
HL = acaceaH or baceaH. The HL proved to act as a tridentate ligand. The corresponding reactions with Mo(CO)6 in dioxane gave the oxo
complexes [Mo2O6(HL)2] with HL was a bidentate. All prepared complexes were investigated using elemental analysis, IR, mass spectrometry,
UV–vis absorption spectra and magnetic measurement. Thermal behaviors of the complexes were studied using by thermogravimetry (TG).
Schemes for the thermal decomposition were proposed along with their mass fragmentation patterns.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Chromium; Molybdenum; Metal carbonyls; Schiff bases; IR Spectra; Thermogravimetry
1. Introduction
happramH [9] have been reported. Several complexes with inter-
esting structural features were isolated. The aim of this investi-
gation is to study the reactions of chromium and molybdenum
hexacarbonyls with two Schiff bases of ONO donor system
derived from ethanolamine with either acetylacetone (HL1) or
benzoylacetone (HL2), Scheme 1.
Metal carbonyls have been proved as reactive species in
homogeneous catalytic reactions such as hydrogenation, hydro-
formylation and carbonylation. Carbon monoxide serves simply
as a ligand providing the complex with the necessary reactivity
and/or stability to allow reaction to ensue [1]. On the other hand,
a large number of Schiff bases and their complexes have been
studied for their interesting and important properties, such as
their ability to reversibly bind oxygen [2], catalytic activity in the
hydrogenation of olefins [3], transfer of amino groups [4], pho-
tochromic properties [5] and complexing ability towards some
toxic metals [6]. In addition, the metal complexes of Schiff bases
simulate the interaction between metal ions and amino acids for
metal–protein systems as well as they have been considered as
interesting models in a variety of biological systems [7].
2. Experimental
Cr(CO)6 and Mo(CO)6 were supplied by Aldrich. Acety-
lacetoneethanolimine (HL1) and benzoylacetoneethanolimine
(HL2) were prepared as described in literature [10]. All solvents
were of analytical grade.
IRmeasurements(KBrpellets)werecarriedoutonaUnicam-
Mattson 1000 FT-IR. Electronic absorption spectra were mea-
sured on a Unicam UV2-300 UV–vis spectrophotometer with
10.0 mm quartz cells. Thermogravimetric analysis (TG) was
carried out using a Shimadzu DT-50 thermal analyzer under
nitrogen atmosphere with a heating rate of 10 ◦C/min. Elemental
analyses were carried out on a Perkin-Elmer 2400 CHN elemen-
talanalyzer. Massspectraofthesolidcomplexeswereperformed
on a Finnegan MAT SSQ 7000 spectrometer. Table 1 gives the
elemental analysis, UV–vis, mass spectrometry and magnetic
moments data for the complexes.
The reactions of chromium and molybdenum hexacarbon-
yls with the Schiff bases bis-(2-hydroxyacetophenone)ethylene-
diimine, hapenH2 [8] and 2-hydroxylacetophenonepropylimine,
∗
Corresponding author at: Department of Chemistry, Faculty of Science,
Cairo University, Giza, Egypt. Tel.: +20 25187785; fax: +20 25727556.
E-mail addresses: ahmed.soliman@uaeu.ac.ae,
ahmedsoliman2@hotmail.com (A.A. Soliman).
1386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2006.01.016

842
A.A. Soliman et al. / Spectrochimica Acta Part A 65 (2006) 841–845
2.4. Synthesis of [Mo2O6(HL2)2] complex
Similar procedure was used as for [Mo2O6(HL1)2] with a
reaction period of 7 h. Brown crystals with a yield of 58% were
obtained.
3. Results and discussion
The results of elemental analyses of the isolated complexes
are given in Table 1. A good agreement between the calculated
and experimental values was observed. The parent molecular
ion peaks are in good agreement with the molecular masses of
the complexes.
Scheme 1.
3.1. Spectral study
2.1. Synthesis of [Cr(CO)3(HL1)] complex
The IR spectra of HL1 and HL2 showed a strong and
broad νOH at 3350–3850 cm−1 and strong νCH N stretch-
ing frequencies at 1620–1600 cm−1, Table 2. Reactions of
chromium hexacarbonyl with acaceaH (HL1) and baceaH (HL2)
in benzene under reduced pressure resulted in the formation of
[Cr(CO)3(HL1)] and [Cr(CO)3(HL2)], respectively. Upon com-
plexation, the νOH bands of the ligands moities were shifted to
lower wave numbers indicating that the OH group has partici-
pated in the coordination without proton displacement. Partic-
ipation of the OH in coordination is also further confirmed by
the shift of the νC O to lower frequencies [11–13], Table 2. The
νCH N stretching band was also found to be shifted in the spec-
tra of the complexes indicating the participation of the azome-
thine group in coordination. Therefore, the ligand coordinates as
a tridentate with a facial structure. In addition, the IR spectrum of
the [Cr(CO)3(HL1)] complex showed two strong ν(CO) bands
in the terminal metal carbonyl region at 1962 and 1878 cm−1
with a shoulder at 1841 cm−1, while the IR spectrum of
[Cr(CO)3(HL2)] complex exhibited two strong ν(CO) bands at
1962 and 1882 cm−1 and a weak ν(CO) band at 2003 cm−1. The
number and pattern of the CO bands indicated the coordination
ofthreecarbonylgroupstochromiuminbothcomplexes [14,15].
From the spectroscopic and elemental analyses data, it can
be concluded that zero valent chromium exists in an octahe-
dral environment with the HL ligand coordinated as a tridentate
(Scheme 2) [16].
Cr(CO)6 (0.10 g, 0.45 mmol) and acetylacetoneethanolimine
(HL1) (0.07 g, 0.45 mmol) were mixed together in a sealed tube
containing 20 ml benzene. The mixture was degassed and heated
for10 h at 60 ◦C. The colorofthesolution waschangedto brown.
The reaction mixture was cooled and the solvent was evaporated
on a vacuum line. The brown residue was washed several times
with hot petroleum ether and recrystallized from hot ethanol.
The brown crystals were dried under vacuum for few hours to
give a yield of 45%.
2.2. Synthesis of [Cr(CO)3(HL2)] complex
Similar procedure was used as employed for [Cr(CO)3(HL2)]
with a reaction period of 48 h. Brown crystals with a yield of 54%
were obtained.
2.3. Synthesis of [Mo2O6(HL1)2] complex
A mixture of Mo(CO)6 (0.10 g, 0.38 mol) and HL1 (0.05 g,
0.38 mmol)in30 mldioxanewasrefluxedinairfor7 h. Thecolor
of the reaction mixture was changed from yellow to brown. The
reaction mixture was cooled and the brown solid was isolated by
filtration. The isolated brown complex was washed several times
with dioxane and then recrystallized from DMSO and redried in
vacuum for several hours (yield 53%).
Interaction of molybdenum hexacarbonyl with HL1 and HL2
in dioxane resulted in the formation of dinuclear complexes
Table 1
Elemental, UV–vis and mass spectral data of the chromium and molybdenum complexes
Complex
Mol.
Elemental analysis found (calc.)
UV–visa λmax
Mass spectral
weight
(nm) (DMSO)
data m/z (p+)
%C
%H
%N
%M
[Cr(CO)3(HL1)] C10H13NO5Cr
[Cr(CO)3(HL2)] C15H15NO5Cr
[Mo2(O)6(HL1)2] C14H26N2O10Mo2
[Mo2(O)6(HL2)2] C24H30N2O10Mo2
279.21
341.28
574.24
698.38
44.23 (43.02)
51.80 (52.79)
28.84 (29.28)
41.90 (41.27)
5.5 (4.69)
5.80 (4.43)
4.26 (4.56)
4.19 (4.33)
2.86 (2.54)
2.73 (2.80)
4.80 (4.88)
4.00 (4.01)
18.45 (18.62)
15.31 (15.24)
33.78 (33.41)
27.04 (27.47)
317, 352
308, 372
320
278.0
341.0
576.1
698.5
320
a
(HL1): 255 and 350 nm; (HL2): 250 and 350 nm.

A.A. Soliman et al. / Spectrochimica Acta Part A 65 (2006) 841–845
843
Table 2
Important IR data of chromium and molybdenum complexes
Compound
IR data (cm−1
)
νOH
νC
N
νC
O
νC
O
νas Mo
O
Mo
νs Mo
O
ν␣s Mo O
HL1
HL2
3415(s,b)
3355(s,b)
3388(s,b)
3386(s,b)
3411(s,b)
3412(s,b)
1620(s)
1610(s)
1589(s)
1600(s)
1612(s)
1600(s)
1266(s)
1279(s)
1249(m)
1256(m)
1266(m)
1278(m)
[Cr(CO)3(HL1)]
[Cr(CO)3(HL2)]
[MoO2(O)6(HL1)]
[MoO2(O)6(HL2)]
1962(s), 1882(s), 2003(w)
1962(s), 1841(sh), 1878(s)
724(m)
716(m)
900(s)
904(s)
942(m)
940(m)
s, strong; m, medium; w, weak; sh, shoulder; b, broad.
[Mo2(O)6(HL1)2] and [Mo2(O)6(HL2)2], respectively. The IR
spectra of complexes showed that the νOH bands were not
shifted with respect to those of free ligands indicating that the
ligands acted as bidentate with non-facial structure in which the
OH is oriented away from the coordination center (Scheme 3).
The IR spectra of complexes also displayed two strong to
medium bands at 942 and 904–900 cm−1 assigned for the
asymmetric and symmetric stretching frequencies of the Mo O
bonds, respectively. This has been found to be common for
Mo O bonds reported for a cis MoO2 fragments of a dimeric
structures having the Mo2O6 core [17–19]. In addition, the IR
spectra of the molybdenum complexes showed two stretches
νas(Mo2O) and νs(Mo2O) of the oxo-bridging groups at 724
and 716 cm−1, respectively [15,17]. Several complexes having
the Mo2O6 or Mo2O5 cores have been recently reported,
where molybdenum atoms bonded to a cis dioxo group and
the two Mo atoms were bridged by one or two oxygen atoms
[14,17]. The dimeric structures of the two complexes were
further confirmed from the mass spectral data in which the
molecular ion peaks were found to be 576.1 (38.0%) and
698.50 (5.57%) for [Mo2(O)6(HL1)2] and [Mo2(O)6(HL2)2],
respectively. These structures were also found to be consistent
with the TG data and the proposed decomposition scheme
(vide infra). Scheme 3 gives the proposed structures of the
complexes.
which may be attributed to metal-to-ligand charge transfer
(MLCT) [14,20,21].
3.2. Thermal analysis and mass spectrometry
A deeper insight on the structures of the investigated com-
plexes was undertaken using thermogravimetry (TG) and deriva-
tive thermogravimetry (DTG) techniques. Fig. 1 shows the TG
and DTG curves of the complexes. The [Cr(CO)3(C7H13NO2)]
complex (m/e: 278; 24.5%) decomposed in three decomposition
steps covering the temperature range 98–426 ◦C (Scheme 4).
Two carbon monoxide molecules were eliminated in the first
two steps while the third carbonyl was eliminated along with
The electronic absorption spectra of both HL1 and HL2 dis-
played two bands at 250, 350 and 255, 355 nm, which are
assigned for the ␲–␲* and n–␲* transitions, respectively. Upon
complexation with chromium and molybdenum the two bands
were red shifted. In addition, the monomeric chromium com-
plexes displayed additional bands in the range 252–372 nm,
Scheme 2.
Scheme 3.

844
A.A. Soliman et al. / Spectrochimica Acta Part A 65 (2006) 841–845
Table 3
Selected mass spectral data of the complexes
Complex
Molar mass
279.21
m/z values
[Cr(CO)3(HL1)] C10H13NO5Cr
278.0, 252.0, 244.9, 224.21, 213.9, 190.9, 157.9, 154.6, 129.9, 125.0,
110.0, 84.2, 78.0, 52.0
[Cr(CO)3(HL2)] C15H15NO5Cr
341.28
574.24
698.38
341.0, 313.0, 299.4, 269.4, 257.5, 210.1, 196.0, 187.1, 173.1, 169.1,
158.1, 143.3, 115.1, 91.2, 84.2, 77.1
576.1, 500.1, 485.8, 424.1, 420.0, 393.8, 362.9, 344.0, 321.9, 278.8,
220.3, 176.4, 149.2, 128.0, 112.2, 91.0, 65.1
698.5, 664.1, 632.9, 548.7, 526.9, 474.6, 424.3, 409.2, 374.1, 356.9,
348.2, 310.7, 289.1, 257.4, 218.1, 194.1, 183.2, 146.7, 128.2, 112.6,
105.2, 77.3
[Mo2(O)6(HL1)2] C14H26N2O10Mo2
[Mo2(O)6(HL2)2] C24H30N2O10Mo2
Scheme 4.
Scheme 5.
the decomposition of the organic part in the third step leaving
CrO2 (m/e: 84.2; 8.0%) as a metallic residue. The decomposition
patterns were further confirmed from the mass spectral peaks,
Table 3.
The [Cr(CO)3(C12H15NO2)] complex (m/e: 341.0; 1.9%)
was also shown to decompose in three steps within the tempera-
ture range 125–462 ◦C. Three carbonyl groups were eliminated
in the first two steps. The organic part was decomposed in the last
step with the formation of CrO2 as a metallic residue, Scheme 5.
The dimeric structures of the two molybdenum complexes
were further confirmed from their thermal decomposition
schemes and mass spectra. Weight losses of the different
species either eliminated or remained in each decomposition
steps with the mass fragments in their mass spectra. The
Scheme 6.

A.A. Soliman et al. / Spectrochimica Acta Part A 65 (2006) 841–845
845
ture range 438–928 ◦C starting with the dimeric structure (m/e:
698.50; 5.57%) and ended with molybdenum oxide MoO2 (m/e:
128.2; 22.67) (Scheme 7).
4. Conclusion
From the spectroscopic, elemental and thermal analyses data,
it can be concluded that zero valent chromium exists in an octa-
hedral environment with the HL ligand coordinated as a triden-
tate with a facial (O,N,O)donor. On the other hand molybdenum
atoms bonded to a cis dioxo group and the two Mo atoms were
bridged by one or two oxygen atoms in dimeric structures which
were further confirmed from the mass spectral data in which the
molecular ion peaks were found to be 576.1 (38.0%) and 698.50
(5.57%) for [Mo2(O)6(HL1)2] and [Mo2(O)6(HL2)2], respec-
tively. These molybdenum dimeric structures were also found
to be consistent with the TG data and the proposed decomposi-
tion scheme.
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[Mo2(O)6(C7H13NO2)2] complex showed thermal decomposi-
tion patterns in four steps in the temperature range 110–996 ◦C
with molybdenum oxide MoO2 as the metallic residue (m/e:
128.0; 38.0%) (Scheme 6).
The [Mo2(O)6(C12H15NO2)2] complex showed a relatively
better thermal stability, Fig. 1, from the room temperature up to
438 ◦C before it decomposed in three steps within the tempera-