Synthesis and characterization of new chromium, molybdenum and tungsten complexes of 2-[2-(methylaminoethyl)] pyridine

Article abstract of DOI:10.1016/j.saa.2012.03.026

A green chemistry route of synthesis using direct sunlight irradiation for the reactions of [M(CO)₆] M = Cr, Mo or W with 2-[2- (methylaminoethyl)] pyridine (maepy) in THF. The reactions resulted in the formation of the oxo complex [Cr₂(O)₄(maepy)₂] (1) and the tetracarbonyl complexes [Mo(CO)₄(maepy)] (2) and [W(CO)₄(maepy)] (3). The prepared complexes were characterized by elemental analysis, IR, NMR, mass spectrometry and magnetic measurement. The complexes (1-3) were further investigated by thermogravimetric technique (TG). The biological activity of maepy and complexes as antibacterial and antifungal reagents have been investigated.

Full text of DOI:10.1016/j.saa.2012.03.026

Spectrochimica Acta Part A 94 (2012) 164–168
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis and characterization of new chromium, molybdenum and tungsten
complexes of 2-[2-(methylaminoethyl)] pyridine
Saadia A. Alia,1, Ahmed A. Solimanb,∗,1, Amany H. Mareia, Doaa H. Nassara
a Chemistry Department, University College for Girls, Ain Shams University, Cairo, Egypt
b Chemistry Department, Faculty of Science, Cairo University, 12613 Giza, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
A green chemistry route of synthesis using direct sunlight irradiation for the reactions of [M(CO)6] M = Cr,
Mo or W with 2-[2-(methylaminoethyl)] pyridine (maepy) in THF. The reactions resulted in the formation
of the oxo complex [Cr2(O)4(maepy)2] (1) and the tetracarbonyl complexes [Mo(CO)4(maepy)] (2) and
[W(CO)4(maepy)] (3). The prepared complexes were characterized by elemental analysis, IR, NMR, mass
spectrometry and magnetic measurement. The complexes (1–3) were further investigated by thermo-
gravimetric technique (TG). The biological activity of maepy and complexes as antibacterial and antifungal
reagents have been investigated.
Received 10 February 2012
Received in revised form 3 March 2012
Accepted 9 March 2012
Keywords:
Chromium
Molybdenum
Tungsten
© 2012 Elsevier B.V. All rights reserved.
2-[2-(Methylaminoethyl)] pyridine
Spectral and biological investigation
1. Introduction
polymerization [9]. Tungsten is known as a biologically active metal
for several years. Although tungsten is not considered as one of the
Green chemistry, also called sustainable chemistry, is a philos-
ophy of chemical research and engineering that encourages the
design of products and processes that minimize the use and gen-
eration of hazardous substances and the energy requirements. One
of the principles that cover this concept is the design of energy
efficient processes. Hence, energy requirements should be recog-
nized for their environmental and economic impacts and should
be minimized. Synthetic methods should be conducted at ambient
temperature and pressure [1].
On the other hand, organometallic complexes of transition
metal carbonyls with N-containing heterocycles have been the sub-
ject of considerable interest in recent years. Their photochemical
and electronic properties and potential for industrial applications
have led to many studies for the use as photo-sensitizers, cat-
alysts and conducting coordinating polymers [2–4]. Many metal
carbonyl derivatives are used in photochemical, photochromic,
and thermochromic processes [5]. On the other hand, pyridine
derivatives have biological and pharmaceutical importance [6,7].
Oxidation–reduction of pyridine derivatives plays important roles
in biological activity [8]. These derivatives are characterized by
their antiviral, antifungal, antioxidant, antithyroid, and diuretic
action. Some pyridine complexes act as active catalysts for olefin
essential elements required by most organisms, it is a biologically
active metal and required as component for some enzyme activity.
Molybdenum or tungsten is present at the active sites of over 30
distinct enzymes [10,11].
To continue our investigation of the reactions of group 6 met-
als with various ligands, here we report the reactions of [M(CO)6]
M = Cr, Mo or W with 2-[2-(methylaminoethyl)] pyridine (maepy)
(Scheme 1), using sunlight irradiation; a sustainable source of
energy, as a route of green chemistry synthesis compared with the
traditional reflux route.
2. Experimental
2.1. Materials and reagents
Cr(CO)6, Mo(CO)6 and W(CO)6 were purchased from Fluka. 2-[2-
(methylaminoethyl)] pyridine was supplied by Aldrich. All solvents
were of analytical grade.
2.2. Measurements
Infrared measurements using KBr pellets were carried out on
a Unicam-Mattson 1000 FT-IR spectrometer. Magnetic measure-
ments of the complexes in the solid state (Gouy method) were
carried out using a Sherwood magnetic susceptibility balance.
1H NMR measurements were performed on a Varian-Mercury
300 MHz spectrometer. Elemental analyses for carbon, hydrogen,
∗
Corresponding author. Tel.: +20 1110121379; fax: +20 2 35727556.
E-mail address: ahmedsoliman61@gmail.com (A.A. Soliman).
These authors contributed equally to this work.
1
1386-1425/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2012.03.026

S.A. Ali et al. / Spectrochimica Acta Part A 94 (2012) 164–168
165
3. Results and discussion
CH3
NH
Interaction of [M(CO)6] M = Cr, Mo and
2-[2-(methylaminoethyl)] pyridine (maepy)
W
in
with
THF
gave [Cr2(O)4(maepy)2] (1), [Mo(CO)4(maepy)] (2) and
[W(CO)4(maepy)] (3) complexes. Table 1 summarizes the reaction
conditions for the two routes of synthesis. The sunlight irradiation
route resulted in lower yield compared with the reflux method but
the former has the advantages of using a cheaper and sustainable
source of energy. Although the sunlight irradiation is used in this
work only as a synthesis route, this may give some attention for
further research on the role of light in the reaction, the nature of
interaction (photochemical or photothermal) and which part of
the light efficiently induces such reactions.
N
Scheme 1. 2-[2-(Methylaminoethyl)] pyridine (maepy).
and nitrogen (CHN) were performed on a Perkin-Elmer 2400 CHN
elemental analyzer. Mass spectrometry measurements of the solid
complex were carried out on a JEOL JMS-AX 500 spectrometer.
Thermogravimetric (TG) analyses were carried out under nitrogen
atmosphere with a heating rate of 10 ◦C min−1 using a Shimadzu
DT-50 thermal analyzer.
3.1. Elemental analysis
Elemental analyses of the complexes resulted from the two
routes of syntheses were found to be very similar and in good agree-
ment with that calculated for the proposed formulae. The results of
the elemental analysis of the complexes resulted from the sunlight
irradiation are given in Table 1.
2.3. Sun irradiation synthesis of [Cr2(O)4(maepy)2] complex (1)
A mixture of Cr(CO)6 (0.2 g, 0.90 mmol) and maepy (0.12 g,
0.89 mmol) in 30 ml THF, in sealed 50-ml tubes, was exposed
to unaided sunlight irradiation for 10 h; The tubes were hanged
horizontally from both sides in a way to not obstruct sunlight
to go through the tubes. The reaction resulted in the formation
of a brown precipitate. Comparatively, a mixture of [Cr(CO)6]
(0.2 g, 0.90 mmol) and maepy (0.12 g, 0.89 mmol) in 30 ml THF was
refluxed for 11 h where a brown precipitate was also separated.
The isolated green precipitates from both routes of synthesis were
washed several times by hot THF, left to dry and kept at vacuum
desiccators.
3.2. Mass spectra of complexes
The mass spectral data of the complexes showed the major
mass fragmentation peaks. The parent ion peak at m/z = 424 for
chromium complex (1) which is coincident with the parent-O
species. On the other hand, for molybdenum complex (2) the par-
ent ion peak at m/z = 340 correspond to [P–4H]+ and the tungsten
complex (2) showed the parent ion peak at m/z = 432 due to the
molecular weight (Table 1). It is interesting to highlight the con-
tribution of the different isotopes of chromium, molybdenum and
tungsten to the molecular mass of their complexes. This is clear in
the mass fragmentation peaks due to the elements. For chromium,
a close two fragmentation peaks were observed at m/z = 51 (74.28%)
and 52 (17.58%), this is in addition to the Cr2 species observed at
m/z = 104 (7.88%) and 106 (15.17%). Tungsten showed also close
mass fragmentation peaks with m/z = 182 (6.96%), 183 (5.37%), 184
(11.15%) and 186 (14.02%) corresponding to the known stable W
isotopes. It is worthy to mention that the resolution of mass frag-
mentation patterns of [Mo(CO)4(maepy)] (2) did not enable us to
trace the Mo isotopes.
2.4. Synthesis of [Mo(CO)4(maepy)] complex (2) and
[W(CO)4(maepy)] complex (3)
Similar procedure to that used for the preparation of
[Cr2(O)4(maepy)2] (1) was employed for the preparation of
[Cr2(O)3(maepy)2] (2) and [W(CO)4(maepy)] (3) complexes (the
reaction time and yield were reported in Table 1).
2.5. Biological activity
Antibacterial activity of 2-[2-(methylaminoethyl)] pyri-
dine (maepy) and its complexes [Cr2(O)4(maepy)2] (1)
[Mo(CO)4(maepy)] (2) and [W(CO)4(maepy)] (3) were deter-
mined using a modified Kirby–Bauer disk diffusion method [12].
Plates incubated with filamentous fungi as Aspergillus flavus at
25 ◦C for 48 h. Gram-positive bacteria as Staphylococcus aureus and
gram-negative bacteria as Escherichia coli were incubated at 30 ◦C
for 24–48 h. The diameters of the inhibition zones were measured
in millimeters. The samples were repeated three times from which
the inhibition was averaged.
3.3. IR spectra
The IR spectra of the complexes were compared with the free
ligand (maepy) in order to determine the coordination sites that
may be involved in chelation. The characteristic peaks of maepy
ligand and its complexes are listed in Table 2.
The IR spectrum of the 2-[2-(methylaminoethyl)] pyridine lig-
and (maepy) showed a broad band at 3305 cm−1 which assigned
to the stretching vibration of NH group. This band has been
found to be shifted to higher wave numbers in the spectra of
Table 1
Analytical data of the complexes (1–3).
% yield
Reaction time (h)
M.wt.
Mass spectra m/z
% C
% H
% N
Calc. (found)
Calc. (found)
Calc. (found)
Reflux
Sunlighta
Reflux
Sunlighta
[Cr2(O)4(dap)2]
[Mo(CO)4(maepy)] (2)
[W(CO)4(maepy)] (3)
75.00
77.50
76.00
65.00
46.00
63.50
11.00
7.00
5.50
10.00
7.00
5.00
440.38
344.20
432.09
424 (P-O)
340 (P–4H)
432 (P+)
43.64 (43.75)
41.87 (42.00)
33.33 (33.91)
5.49 (4.90)
3.51 (3.98)
3.51 (3.00)
12.72 (12.50)
8.14 (8.21)
6.48 (6.31)
a
The reactions had been carried out in Cairo, April 2008; average temperature = 31 ◦C and the weather at the time of reactions was sunny.

166
S.A. Ali et al. / Spectrochimica Acta Part A 94 (2012) 164–168
Table 2
Important IR data of molybdenum and tungsten of complexes with (maepy).
Compound
IR (cm−1
)
ꢀ(NH)
ꢀ(CO)
ꢀ(C N)
ꢀ(M O)
ꢀ(M O)
␦(py)
ꢀ(M N)
maepy
3305(b)
3401(b)
3427(s)
3414(b)
–
–
1569(s)
1605(m)
1594(w)
1594(s)
–
–
605(w)
693(w)
731(m)
683(m)
–
[Cr2(O)4(maepy)2] (1)
[Mo(CO)4(maepy)] (2)
[W(CO)4(maepy)] (3)
995(w), 914(w)
–
–
837(w)
–
–
515(w)
470(w)
612(m)
2007(m), 1888(m) 1855(m), 1799(m)
2004(m), 1877(w) 1811(s), 1730(m)
b, broad; m, medium; s, strong; w, weak.
complexes (3401–3427 cm−1). The shift in band position is an indi-
cation of the participation of NH in coordination to the metal ions
under investigation without proton displacement [13]. Further-
more, the spectrum of (maepy) exhibited a band due to ꢀ(C N)
pyridyl ring [14,15] which was found to be shifted to higher
wave number in the spectra of complexes [16–19]. Also, the
IR spectra of [Cr2(O)4(maepy)2] (1), [Mo(CO)4(maepy)] (2) and
[W(CO)4(maepy)] (3) complexes displayed shifted bands due to the
in-plane ring deformation (␦(py)) in the range of 683–731 cm−1
indicating the participation of the pyridyl ring in coordination.
Thus, the maepy behaves as bidentate ligand in complex forma-
tion. In addition, [Cr2(O)4(maepy)2] (1) complex showed band at
995 cm−1 due to Cr O stretching vibration [20]. The infrared spec-
trum of the chromium complex exhibited also band at 837 cm−1
Table 3
Important 1H NMR data for the maepy ligand and their complexes.
Compound
maepy
1H NMR (ppm)
8.47s (1H, NH), 7.66–7.12m (4H, pyridine),
3.00–2.74m (4H, CH2), 2.27s (3H, CH3).
7.42s (1H, NH), 5.94–5.71m (4H, pyridine),
3.44–3.42m (4H, CH2), 2.56s (3H, CH3).
8.50s (1H, NH), 5.87–4.44m (4H, pyridine),
3.30–2.97m (4H, CH2), 2.49s (3H, CH3).
[Mo(CO)4(maepy)] (1)
[W(CO)4(maepy)] (3)
m, multiple; s, singlet.
ligand with appropriate shift as a result of complexation. The 1H
NMR of the [Mo(CO)4(maepy)] (2) showed singlet at 7.42 ppm due
to NH proton and multiplets in the range of 5.71–4.44 ppm for aro-
matic protons of the pyridine ring. Similarly, the 1H NMR of the
[W(CO)4(maepy)] (3) exhibited singlet at 8.50 ppm for NH proton
and showed multiplets at 5.87–4.44 ppm for aromatic protons of
the pyridine ring (Table 3). These findings indicate that both NH
and pyridine nitrogen participated in the coordination to metals.
The shifts of the other signals may be due to the change in the
electronic system of the ligand upon complex formation [13].
which characteristic to Cr
complex displayed band at 515 cm−1 which is assigned to Cr
bond [19]. The infrared spectra of the molybdenum and tungsten
complexes exhibited four bands in the range of 1730–2007 cm−1
O Cr stretching vibration [20]. Also, the
N
,
due to the presence of four CO in the terminal metal carbonyl region
[13,21–23]. In addition, the IR spectrum of the molybdenum and
tungsten complexes showed bands at 470 cm−1, 612 cm−1 due to
M
N bonds [19].
3.4. Magnetic measurements
The magnetic susceptibility
[Cr2(O)4(maepy)2] (1) complex in the solid state at 298 K showed a
value of 2.79 × 10−5 e.m.u. g−1 with an effective magnetic moment
of 5.43 BM. However, the corresponding value for each chromium
(2.72 BM) is less than the spin-only moment of two unpaired elec-
trons (2.83 BM). The observed ꢁeff may indicate the existence of
the complex as a binuclear species with strong antiferromagnetic
coupling between the two metal centers. The dimeric structures
of the chromium complex was further confirmed from the ther-
mogravimetric analysis and mass spectra (m/z = 424; P+–O) (vide
supra).
3.6. Thermal analyses
The reported chromium, molybdenum and ruthenium com-
plexes (1–3) were found to be air stable and have higher thermal
stability. These properties along with their possibility to use as cat-
alysts in epoxidation reactions have prompted us to investigate
their thermal decomposition [24]. In addition, a deeper insight on
the structures of the investigated complexes was undertaken using
thermogravimetry (t.g.) and derivative thermogravimetry (d.t.g.)
techniques (Figs. 1 and 2). The detailed thermal decomposition data
for chromium (1) and tungsten (3) were given in Table 4.
[Cr2(O)4(maepy)2] (1) complex (m/e = 424; 5%) decomposed in
three thermal steps (Fig. 1) covering the temperature 474–845 K.
The first decomposition step occurred at 474–520 K with a weight
loss of 7.22% (7.27% calc.). The percentage loss was consistent
with the elimination of one O2 molecule assigned as the removal
of the di-oxo bridges. The second decomposition peak occurred
at 641–674 K with a weight loss of 34.30% (34.50% calc.) could
measurements
of
the
The
magnetic
susceptibility
measurements
for
[Mo(CO)4(maepy)] (2) and [W(CO)4(maepy)] (3) indicated
their diamagnetic nature. This is confirmed also from the 1H
NMR spectra of complexes (vide infra). In the low spin octahedral
molybdenum and tungsten complexes with t2g6eg0 configuration
is expected to be diamagnetic [13].
2.5
2
0.00010
0.00000
‐0.00010
‐0.00020
‐0.00030
‐0.00040
‐0.00050
‐0.00060
‐0.00070
3.5. 1H NMR spectra
TG
DrTG
The 1H NMR of (maepy) in deuterated DMSO ligand showed a
singlet at 8.47 ppm, which has been assigned to NH proton and
multiplets at 7.66–7.12 ppm, which has been assigned to the aro-
matic protons of the pyridine ring. In addition, the ligand showed
two doublets at 3.00 ppm and 2.85 ppm with an integration of 4
protons, which has been assigned to the protons of the two CH2
groups. It also displayed a singlet at 2.27 ppm which is assigned to
the protons of CH3 group.
1.5
1
0.5
0
Temperature, ºC
Fig. 1. TG and DrTG plot of [Cr2(O)4(maepy)2] complex.
The 1H NMR spectrum of the isolated [Mo(CO)4(maepy)] (2) and
[W(CO)4(maepy)] (3) complexes showed similar signals to maepy

S.A. Ali et al. / Spectrochimica Acta Part A 94 (2012) 164–168
167
Table 4
Thermal data for the complexes of chromium and tungsten with (maepy) ligand.
Molecular formula
M.wt.
DTGmax (K)
Decomposition
temperature (K)
Weight loss %
Mass loss
Calc.
Eliminated species
Metallic residue %
Found
440.38
432.09
495
657
824
474–520
641–674
795–845
7.22
34.30
35.00
32.00
151.80
154.60
31.80
151.00
154.00
O2
[Cr2(O)4(C8H12N2)2]
[W(CO)4(C8H12N2)]
C9H15N2
2O, C7H9N2
2Cr (23.6%)
W (42.8%)
412
464
392–492
523–773
12.80
44.30
55.40
191.0
56.00
192.00
2CO
2CO, C8H12N2
2.5
2
0.0005
0.0000
‐0.0005
‐0.0010
‐0.0015
‐0.0020
CH3
DrTG
O
O
NH
N
Cr
1.5
1
Cr
O
N
NH
O
TG
0.5
H3C
0
‐0.0025
Scheme 2. The proposed structure of [Cr2(O)4(maepy)2].
36
129
230
331
430
530
630
731
831
931
Temperature, ºC
Fig. 2. TG and DrTG plot of [W(CO)4(maepy)]complex.
CH3
CO
NH
be attributed to the loss of C9H15N2 species (mass loss = 151;
m/e = 150; 13.69%). The third decomposition peak observed in the
temperature range of 795–845 K with a weight loss of 35.00%
(35.10% calc.) which may be assigned for the removal of the rest
of the ligand molecule (mass loss = 154; m/e = 154; 8.74%) leaving
2Cr (23.6%) as the metallic residue (mass loss = 103.93; m/e = 52;
17.58% and m/e = 102; 21.56%).
CO
CO
M
N
CO
Scheme 3. The proposed structure for [M(CO)4(maepy)] where M = Mo or W.
The thermogram of [W(CO)4(maepy)] displayed three succes-
sive decomposition steps (Fig. 2). The first decomposition peak
occurred at 372–492 K with weight loss of 12.8% (12.9% calc.) (mass
loss = 56; m/e = 55; 17.9%) was assumed to the loss of two CO groups.
The second and third peaks were existed over a wide temperature
range of 523–773 K, with a net mass loss of 44.3% (44.4% calc.) (mass
loss = 192; m/e = 192; 5.85%) which may be due to the elimination of
other two CO groups along with C8H12N2 species to yield finally the
metallic tungsten as residue (42.8%) (mass loss = 184.93; m/e = 184;
11.15%).
tion of the final product (III) Cr(IV) (Scheme 4). This mechanism is
proposed for many of group 6 complexes [13,25,26].
3.8. Antimicrobial activity
Antimicrobial activities of (maepy) and its [Cr2(O)4(maepy)2]
(1), [Mo(CO)4(maepy)] (2) and [W(CO)4(maepy)] (3) complexes
have been carried out against S. aureus as gram-positive bacteria,
E. coli as gram-negative bacteria and both A. flavus and Candida albi-
cans as fungi, using a modified Kirby–Bauer disk diffusion method
[12]. The tetracycline as antibacterial agent and amphotericin B
as antifungal agent were used as standards. The mean inhibition
values as well as the error limits are given in Table 5.
The (maepy) ligand has been found to be the most active against
fungi (C. albicans and A. flavus) as compared with the metal com-
plexes and standard. Moreover, [Mo(CO)4(maepy)] complex show
considerable activity against C. albicans fungi in contrast with
3.7. Structural interpretation
On the basis of the above observations, the structures of the
complexes are shown in Schemes 2 and 3.
It is interesting to explain that the oxocomplexes of chromium
complex were passed through the intermediate Cr(CO)3(maepy)
(I) which upon reaction with oxygen would result in the forma-
Table 5
Antimicrobial activity of (maepy) ligand and its complexes.
Compound
Zone of inhibition (mm/mg sample) (error limit)a
Escherichia coli
Staphylococcus aureus
Aspergillus
Candida albicans
(Gram-negative)
(Gram-positive)
flavus (Fungus)
(Fungus)
maepy
21(2.3)
11(1.12)
13(2.4)
11(2.3)
32(2.1)
–
23(1.45)
11(1.67)
16(3.1)
12(1.2)
30(2.4)
–
23(2.1)
0
0
0
25(1.94)
0
18(1.2)
0
[Cr2(O)4(maepy)2] (1)
[Mo(CO)4(maepy)] (2)
[W(CO)4(maepy)] (3)
Tetracycline Antibacterial agent
Amphotericin BAntifungal agent
–
–
16(1.1)
17(1.7)
a
Error limit = (maximum value − minimum value).

168
S.A. Ali et al. / Spectrochimica Acta Part A 94 (2012) 164–168
CO
Cr
CO
Cr
N
N
N
N
CO
CO
OC
OC
CO
CO
+
CO
CO
-CO
CO
O
CO
Cr
N
N
N
N
N
N
O
+O2
Cr
Cr
CO
CO
-4CO
O
O
CO
II, Cr(IV)
I, Cr(0)
-2CO
O
N
N
N
O
Cr
O
Cr
N
O
III,Cr(IV)
Scheme 4. Proposed mechanism for the formation of Cr oxocomplex.
chromium and tungsten complexes which have no activity against
fungi. The maepy ligand has higher activity than its complexes(1–3)
towards both gram-positive and gram-negative bacteria. The com-
plexes have activities very close to each other and far from both
ligand and standard which may be due to their limited solubility in
most of the solvents.
[8] L.K. Ravindranath, S.R. Ramadas, S.B. Rao, Electrochim. Acta 28 (1983)
601–608.
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4. Conclusion
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The direct sunlight irradiation synthesis for the reactions of
[M(CO)6] M = Cr, Mo or W with 2-[2-(methylaminoethyl)] pyridine
(maepy) in THF may stand as a feasible and sustainable method of
synthesis of metal carbonyl-organic systems.
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