Synthesis and characterization of the transition metal complexes: Their alcohol oxidation and electrochemical properties

Article abstract of DOI:10.1080/15533174.2010.538288

Five Schiff base ligands, HA¹, HA², H ₂L¹-H₂L³, and their Co(II), Mn(III) and Ru(III) complexes, have been synthesized and characterized by analytical, spectroscopic, conductance, magnetic

Full text of DOI:10.1080/15533174.2010.538288

This article was downloaded by: [Memorial University of Newfoundland]
On: 05 August 2013, At: 13:47
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer
House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthesis and Reactivity in Inorganic, Metal-Organic,
and Nano-Metal Chemistry
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/lsrt20
Synthesis and Characterization of the Transition
Metal Complexes: Their Alcohol Oxidation and
Electrochemical Properties
Mehmet Tümer a
a University of Kahramanmaraş Sütçü Imam, Faculty of Science and Arts, Department of
Chemistry, Kahramanmaraş, Turkey
Published online: 19 Feb 2011.
To cite this article: Mehmet Tmer (2011) Synthesis and Characterization of the Transition Metal Complexes: Their
Alcohol Oxidation and Electrochemical Properties, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal
Chemistry, 41:2, 211-223
To link to this article: http://dx.doi.org/10.1080/15533174.2010.538288
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of
the Content. Any opinions and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied
upon and should be independently verified with primary sources of information. Taylor and Francis shall
not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other
liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or
arising out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 41:211–223, 2011
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2010.538288
Synthesis and Characterization of the Transition Metal
Complexes: Their Alcohol Oxidation and Electrochemical
Properties
Mehmet Tu¨mer
¨
¨
University of Kahramanmaras¸ Sutc¸u Imam, Faculty of Science and Arts, Department of Chemistry,
Kahramanmaras¸, Turkey
The oxidation of alcohols into aldehydes and ketones is a
Five Schiff base ligands, HA1, HA2, H2L1-H2L3, and their
Co(II), Mn(III) and Ru(III) complexes, have been synthesized
and characterized by analytical, spectroscopic, conductance, mag-
netic moment, and electrochemical studies. The oxidation of
benzylic alcohols to the corresponding carbonyl compounds is
described. In the case of some primary benzyl alcohols, high
conversions were obtained. Secondary benzyl alcohol (2-hydroxy–
1,2-diphenylethanone derivatives) were selectively transformed to
the corresponding ketone with satisfactory conversions. The elec-
trochemical properties of all complexes have been recorded in the
different scan rates and solvents. The electrochemical properties
of the complexes change with scan rates.
ubiquitous transformation in organic chemistry, and numerous
oxidizing agents are available to affect this key reaction.[4] In
most instances, these reagents are required in stoichiometric
amounts and are usually toxic, or hazardous, or both. More-
over, purification of the reaction products is often demanding
and laborious. Despite the industrial importance of this process
and the evergrowing environmental concerns, surprisingly few
efficient catalytic oxidations of alcohols have been described.[5]
The scarcity of alcohol oxidation processes that simply use oxy-
gen or air as the ultimate stoichiometric oxidant is particularly
notable.[6]
The preparation of a new ligand was perhaps the most im-
portant step in the development of metal complexes that exhibit
unique properties and novel reactivity since the electron donor
and electron acceptor properties of the ligand, structural func-
tional groups, and the position of the ligand in the coordination
sphere, together with the reactivity of coordination compounds,
may be the factor for different studies.[7,8] Schiff bases were im-
portant class of ligands; such ligands and their metal complexes
had a variety of applications including biological, clinical, an-
alytical, and industrial, in addition to their important roles in
catalysis and organic synthesis.[9−15]
Keywords alcohol oxidation, electrochemical, Schiff base
INTRODUCTION
Schiff base ligands are able to coordinate metals through
imine nitrogen and another group, usually linked to the alde-
hyde. Modern chemists still prepare Schiff bases, and nowadays
active and well-designed Schiff base ligands are considered as
privileged ligands. The coordination chemistry of manganese
with a diverse range of ligands remains an area of considerable
interest. This is not only because of the relevance that a number
of model manganese complexes have to biological systems,[1]
but also due to the fascinating cluster compounds, which exhibit
unusual magnetic properties, and the elegant supramolecular ar-
rays that have been discovered.[2] In addition to the interest from
this inorganic standpoint, there is also considerable interest in
the application of manganese complexes in organic synthesis
due to their potent catalytic properties, particularly in the asym-
metric epoxidation of certain olefins.[3]
In this study, the author reports the synthesis, characteriza-
tion, alcohol oxidation, and electrochemical properties of the
Schiff base ligands and their Co(II), Mn(III), and Ru(III) metal
complexes.
EXPERIMENTAL
Materials
The metal salts CoCl2.6H2O, Mn(AcO)3.2H2O, RuCl3.H2O,
and other chemicals H2O2, benzoylhydroperoxide, organic sol-
vents were purchased from commercial sources and used as
received, unless noted otherwise. The organic compounds o-
vanilline, o-toluidine, p-toluidine, 1,4-di-aminobenzene, 3,5-
di-aminobenzoic acid, and 1,5-di-aminonaphtalene were pur-
chased from Fluka.
Received 21 December 2009; accepted 21 July 2010.
Address correspondence to Mehmet Tu¨mer, University of
Kahramanmaras¸ Su¨tc¸u¨ Imam, Faculty of Science and Arts, De-
partment of Chemistry, 46100, Kahramanmaras¸, Turkey. E-mail:
mtumer@ksu.edu.tr
211

¨
212
M. TUMER
O
OH
H2O
Co
H3C
H3CO
O
N
N
nX
O
N
N
nX
Cl
Cl
O
H3CO
Ru
Cl
OH2
Co
O
OCH3
H2O
OCH3
CH3
FIG. 1. Proposed structures of some synthesized metal complexes.
Physical Measurements
Elemental analyses (C, H, N) were performed using a LECO
Preperation of the Ligands
All ligands were prepared by a similar method. Solutions of
CHNS 932 elemental analyzer. FT-IR spectra were obtained us- o-vanilline (1 mmol for o-toluidine and p-toluidine; 2 mmol
ing KBr discs (4000–400 cm−1) on a Shimadzu 8300 FT-IR for 1,4-di-aminobenzene, 3,5-di-aminobenzoicacid, and 1,5-
spectrophotometer. The electronic spectra in the 200–1100 nm di-aminonaphtalene in 20 cm3 EtOH) and amine derivatives
range were obtained on a Shimadzu UV-160 A spectropho- (1 mmol, in 20 cm3 EtOH) were mixed together and refluxed
tometer. Magnetic measurements were carried out by the Gouy for about one hour in a water bath. The precipitated product
method using Hg[Co(SCN)4] as calibrant. Mass spectra of the was filtered and washed with cold EtOH (Figure 1). The ligands
ligands were recorded on a LC/MS APCI AGILENT 1100 MSD were recrystallized from hexane/EtOH (1:3 by vol) and dried in
spectrophotometer. 1H-NMR spectra were recorded on a Varian the vacuum dessiccator over P2O5. The purity was checked by
XL-300 instrument. TMS was used as internal standard and deu- elemental analyses and t.l.c. studies.
teriated DMSO-d6 as solvent. The metal and chloride contents
HA1: 1H-nmr: (DMSO-d6 as solvent, δ in ppm): 11.05(s, OH,
of the complexes were determined as gravimetrically according H), 8.70 (s, CH N), 6.45–7.50 (m, Ar-H, 7H), 3.75 (s, OCH3,
to the known procedure.[16] The thermal analyses studies of the 3H), 2.10 (s, CH3, 3H). Mass spectrum (LC/MS APCI): m/z 242
complexes were performed on a Perkin Elmer Pyris Diamond [M+1]+ (100%), 243 [M+2]+2 (16.9%), 227 [C14H13NO2]+.
DTA/TG Thermal System under nitrogen atmosphere at a heat- (4.2%), 167 [C8H7O4]+. (2.4%), 108 [C7H10N]+ (6.3%).
ing rate of 10◦C/min. Thermal analyses studies have been done
in the range 298–1273 K.
HA2: 1H-nmr: (DMSO-d6 as solvent, δ in ppm): 11.04(s, OH,
H), 8.65 (s, CH N), 6.43–7.50 (m, Ar-H, 7H), 3.78 (s, OCH3,
Cyclic voltammograms were recorded on an Iviumstat Elec- 3H), 2.06 (s, CH3, 3H). Mass spectrum (LC/MS APCI): m/z 242
trochemical workstation equipped with a low current module [M+1]+ (100%), 243 [M+2]+2 (16.9%), 227 [C14H13NO2]+.
(BAS PA–1) recorder. The electrochemical cell was equipped (4.2%), 167 [C8H7O4]+. (2.4%), 108 [C7H10N]+ (6.3%).
with a BAS glassy carbon working electrode (area 4,6 mm2),
H2L1: 1H-nmr: (DMSO-d6 as solvent, δ in ppm): 13.09
a platinum coil auxiliary electrode, and a Ag/Ag+ (0.03 M (s, OH, 2H), 9.06 (s, CH N, 2H), 6.95–8.15 (m, Ar-H,
AgNO3) reference electrode filled with tetrabutylammonium 10H), 3.87 (s, OCH3, 6H). Mass spectrum (LC/MS APCI):
tetrafluoroborat (0.1 M) in DMF solvent and adjusted to 0.00 V m/z 391 [M+1]+ (10%), 301 [C21H20N2+ 1]+2 (21%), 201
vs SCE. Cyclic voltammetric measurements were made at room [C13H18N2]+1 (19.6%), 167 [C11H7N2]+3 (100%).
temperature in an undivided cell (BAS model C–3 cell stand)
H2L2: 1H-nmr: (DMSO-d6 as solvent, δ in ppm): 13.21
with a platinum counter electrode and an Ag/Ag+ (0.03 M (s, OH, 2H), 9.03 (s, CH N, 2H), 6.68v7.55 (m, Ar-H,
AgNO3) reference electrode (BAS). All potentials are reported 12H), 3.85 (s, OCH3, 6H). Mass spectrum (LC/MS APCI):
with respect to Ag/Ag+ (0.03 M AgNO3). The solutions were m/z 427 [M+1]+ (57.1%), 293 [C18H17N2O2]+ (100%), 276
deoxygenated by passing dry nitrogen through the solution for [C18H14NO2]+. (5.2%), 79 [C5H3O]+ (38.1
1
30 min prior to the experiments, and during the experiments, the
H2L3: H-nmr: (DMSO-d6 as solvent, δ in ppm): 11.17 (s,
flow was maintained over the solution. Digital simulations were COOH, 1H), 10.27 (s, OH, 2H), 9.12 (s, CH N, 2H), 6.76–7.87
performed using DigiSim 3.0 for windows (BAS, Inc.). Exper- (m, Ar-H, 6H), 3.80 (s, OCH3, 6H). Mass spectrum (LC/MS
imental cyclic voltammograms used for the fitting process had APCI): m/z 421 [M+1]+ (10%), 311 [C17H15N2O4]+. (34.1%),
the background subtracted and were corrected electronically for 312 [C17H16N2O4]+2. (6.6%), 287 [C15H15N2O4]+ (100%), 288
ohmic drop.
[C15H16N2O4]+2 (17.0%), 289 [C15H17N2O4]+3 (3.0%).

ALCOHOL OXIDATION AND ELECTROCHEMICAL PROPERTIES
213
Co(II), Mn(III), and Ru(III) complexes from these ligands, then
synthesized the Ru(III) complexes according to the Co(II) and
Mn(III) complexes as the low solubility of the RuCl3.H2O in the
EtOH. The ligands HA1 and HA2 occur the mononuclear metal
complexes, whereas the complexes of the ligands H2L1-H2L3
have binuclear nature. For all complexes of the ligands, the
Co(II) complexes are the most soluble while the Ru(III) are the
least. The proposed structures of the some of the synthesized
metal complexes are given in Figure 1.
Preparation of the Complexes
The complexes were prepared by similar methods. A solution
of the metal salt (1 mmol for HA1, HA2; 2 mmol for H2L1-H2L3)
in absolute EtOH (25 cm3) was added to a solution of the ligands
(2 mmol for HA1, HA2; 1 mmol for H2L1, H2L2 and H2L3) in
absolute EtOH (20 cm3) and the mixture was boiled under reflux
for 6–7 h. At the end of the reaction, determined by t.l.c., the
precipitate was filtered off, washed with distilled water, and then
EtOH, and dried in vacuo.
The infrared spectral data of all compounds are given in
Table 2. In the spectra of the ligands, the broad bands in the
range 3420–3336 cm can be attributed to the ν(OH) vibra-
Catalytic Oxidation
–1
Catalytic oxidation of primary alcohols to corresponding
aldehyde and secondary alcohol to ketone by Co(II), Mn(III)
and Ru(III) complexes were studied in the presence of H2O2
and benzoylperoxide as cooxidant. A typical reaction using the
complex as a catalyst and four benzyl alcohol derivatives, three
2-hydroxy-1,2-diphenylethanone derivatives, cyclooctanol and
cyclohexanol as substrates at 1:100 molar ratio is described
as follows. A solution of the complexes (0.01 mmol) in the
CH2Cl2 (20 cm3) was added to the solution of substrate (1 mmol)
and H2O2 or benzoylperoxide (3 mmol). The solution mix-
ture was refluxed for 3 h and the solvent was then evap-
orated from the mother liquor under reduced pressure. The
solid residue was then extracted with pethroleum ether (at
the room temperature or in the 60–80◦C temperature range)
(20 cm3), and the ether extracts were evaporated to give cor-
responding aldehydes/ketones which were then quantified as
2,4-dinitrophenylhydrazone derivative.[16]
tions. In the complexes, this band disappear and this situation
confirm that the oxygen atom of the (OH) group coordinates
to the metal ions. In the spectra of the ligands, the ν(CH N)
vibrations of the azomethine groups are shown in the range
1635–1602 cm−1. In the complexes, these vibrations shifted to
the lower or higher regions and can be attributed to the com-
plexation of the metal ions and nitrogen atom of the azomethine
group. In the IR spectra of the complexes of the ligand H2L3,
the COOH groups remained free as evidenced by the appear-
ance of infrared bands in the region 1710–1725 cm−1. The very
slight blue-shifting from the free ligand value may be due to the
combined effect of the rearrangement of the ligand structure,
stereospecific interaction with the coordinated metal ion, and
the presence of coordinated water in some cases. The presence
of coordinated acetate group in the [Mn(L3)AcO(H2O)]H2O
complex is confirmed by the appearance of bands at 1650 and
1360 cm .
−1 [17] Furthermore, the presence of broad bands around
3540–3330 cm−1 in some of the complexes due to ν(OH) in-
RESULTS AND DISCUSSION
dicates presence of water molecules. Complexes show broad
In this study, I synthesized the five Schiff base lig- bands in the region 3340–3330 cm−1 along with the appearance
ands from the reactions between the o-vanilline and of bands at 985–940 cm−1 (wagging modes of water) indicating
various amine derivatives in the ethanolic media. Analyt- coordinated water molecules.[17]
ical data are given in Table 1. The synthesized ligands
The electronic spectra of the ligands and their complexes
are
2-methoxy-6-{(E)-[(4-methylphenyl)imino]methyl} were recorded in EtOH solvent in the region of 200–1100 nm.
phenol (HA1), 2-methoxy-6-{(E)-[(2-methylphenyl)imino] The spectral data are listed in Table 2. The uv spectra of the
methyl}phenol
(HA2),
2-{(E)-[(4-{[(1E)-(2-hydroxy-3- complexes [Co(A1)].2H2O, [Mn2(L3)(AcO)4(H2O)4].2H2O,
methoxyphenyl ) methylene ] amino } phenyl)imino]methyl}-6- [Ru(L1)2Cl(H2O)].2H2O are shown in Figure 2. In the spec-
methoxyphenol (H2L1), 2-{(E)-[(4-{[(1E)-(2-hydroxy-3- tra of the ligands, the bands in the range 460–346 nm may be
methoxyphenyl)methylene]amino}-1-naphthyl)im-ino]methyl}}- assigned to the n-π* transitions. The observed bands in the
6-methox-yphenol (H2L2), 3-{[(1E)-(2-hydroxy-3-methoxyph- ranges 343–321 and 317–275 nm can be attributed to the π -π*
enyl)methy-lene]amino}-5-{[(1E)-(2-hydroxy-3-methylphenyl)met- and π -δ* transitions, respectively. The complexes exhibiting
hylene]amino}benzoic acid (H2L3). If the Schiff bases are multiple absorptions in the UV–visible region. In the visible re-
insoluble in hexane or cyclohexane, they can be purified by gion, the Co(II) complexes show the d-d transitions in the range
stirring the crude reaction mixture in these solvents, sometimes 731–617 nm. Moreover, the bands in the range 457–377 nm can
adding a small portion of a more polar solvent (Et2O, CH2Cl2), be assigned to the dπ (Co)→ π*(ligand) metal to ligand charge
in order to eliminate impurities. In general, Schiff bases are transfer transitions. In Figure 2, the d-d and MLCT transitions
stable solids and can be stored without precautions. The of the complex [Co(A1)]. 2H2O are shown. The electronic spec-
ligands are more soluble in polar organic solvents as EtOH, trum of the complex [Mn2(L3)(AcO)4(H2O)4].2H2O in EtOH
MeOH, CHCl3, DMSO, but they are partially soluble in apolar is shown in Figure 2. The absorption bands appearing in the
organic solvents, such as, hexane, heptane, toluene, etc. As energy region higher than ∼400 nm are thought to be associated
the ligand H2L3 contains the COOH group on the phenylene mainly with the ligand transition. In the visible and near-IR re-
ring, its solution is slightly acidic. The author prepared the gion, the spectra of the complexes exhibit one absorption bands

¨
214
M. TUMER
TABLE 1
Analytical and physical data for the Schiff base ligands and their metal complexes
Yield
(%)
M.p.
(◦C)
Found
(calc.)% C
Compound
Color
H
N
M
HA1
orange
brown
brown
brown
orange
green
87
70
64
68
85
71
70
65
80
65
66
72
90
67
63
60
85
65
62
60
90
>250
>250
157
59
228
74.71 (74.67)
62.58 (62.55)
60.94 (60.90)
53.67 (53.64)
74.70 (74.67)
62.60 (62.55)
59.25 (59.21)
56.64 (56.68)
70.25 (70.20)
42.74 (42.77)
44.46 (44.43)
33.10 (33.06)
73.25 (73.22)
45.43 (45.39)
45.39 (45.42)
34.69 (34.72)
68.34 (68.31)
41.70 (41.66)
43.40 (43.44)
32.27 (32.30)
6.30 (6.27)
5.60 (5.56)
5.60 (5.55)
5.10 (5.07)
6.23 (6.27)
5.17 (5.21)
5.28 (5.24)
4.75 (4.72)
5.41 (5.36)
3.94 (3.89)
4.98 (4.93)
3.47 (3.51)
5.24 (5.20)
4.40 (4.36)
5.30 (4.34)
3.75 (3.78)
5.02 (4.98)
3.89 (3.92)
4.76 (4.90)
3.48 (3.51)
5.84 (5.81)
4.90 (4.87)
4.49 (4.44)
4.21 (4.17)
5.77 (5.81)
4.90 (4.86)
4.35 (4.32)
4.45 (4.41)
7.40 (7.44)
4.58 (4.54)
3.49 (3.46)
3.54 (3.51)
6.61 (6.57)
4.10 (4.07)
3.16 (3.12)
3.14 (3.12)
6.97 (6.93)
4.26 (4.22)
3.30 (3.27)
3.24 (3.28)
–
[Co(A1)2].2H2O
10.32 (10.24)
8.78 (8.71)
15.10 (15.06)
[Mn(A1)2(AcO)(H2O)].H2O
[Ru(A1)2Cl(H2O)].2H2O
HA2
[Co(A2)2].H2O
10.31 (10.24)
8.54 (8.47)
15.97 (15.91)
[Mn(A2)2(AcO)(H2O)].2H2O
[Ru(A2)2(Cl)(H2O)]
H2L1
black
153
142
124
brown
orange
brown
brown
brown
orange
brown
black
[Co2(L1)(Cl)2(H2O)2].H2O
[Mn2(L1)(AcO)4(H2O)4].H2O
[Ru2(L1)(Cl)4(H2O)4].H2O
H2L2
240∗
>250
>250
205
19.16 (19.09)
12.64 (12.57)
25.36 (25.31)
[Co2(L2)(Cl)2(H2O)2].2H2O
[Mn2(L2)(AcO)4(H2O)4].3H2O
[Ru2(L2)(Cl)4(H2O)4].2H2O
H2L3
245
244
17.22 (17.15)
12.28 (12.23)
22.55 (22.49)
black
>250
228
>250
>250
>250
brown
brown
black
[Co2(L3)(H2O)2(Cl)2].2H2O
[Mn2(L3)(AcO)4(H2O)4].2H2O
[Ru2(L3)(Cl)4(H2O)4].2H2O
17.80 (17.77)
12.89 (12.83)
23.72 (23.65)
brown
∗ꢀ−1 cm2 mol−1
.
in the range 576–510 nm Based on the intensities and positions, M to L) transitions. The electronic spectrum of the com-
these bands can be assigned to the d-d transitions. However, plex [Ru(L1)2Cl(H2O)].2H2O in EtOH is shown in Figure 2.
the spectrum of the complex [Mn2(L3)(AcO)4(H2O)4].2H2O In the spectra of the complexes [Ru(L1)2Cl(H2O)].2H2O and
also exhibits the absorption band around 525 nm. In the [Ru2(L3)(Cl)4(H2O)4].2H2O, the bands at 581 and 550 nm may
lower wavenumbers, there are charge transfer (L to M or be assigned to the d-d transitions, respectively. In the other
FIG. 2. Electronic spectra of the complexes (a) [Mn2(L3)(AcO)4(H2O)4].2H2O, (b) [Co(A1)].2H2O, and (c) [Ru(L1)2Cl(H2O)].2H2O using the EtOH solutions
(1 × 10−4 M).

215

¨
M. TUMER
216
Ru(III) complexes, the d-d bands have not been observed. The
lowest energy band is associated with a shoulder near 600 nm.
The bands in the range 480–415 nm can be assigned to the
the dπ (Ru) → π*(L) (symmetric) and dπ (RuIII) → π*(L) (an-
tisymmetric) MLCT (metal-to-ligand charge-transfer) transi-
tions. The next highest energy band near 350 nm may be due to
the dπ (Ru ) → L (MLCT) transition. The higher energy bands
in the UV region are of intra-ligand p–p* type or charge-transfer
transitions involving energy levels that are higher in energy than
the ligand lowest unoccupied molecular orbital (LUMO).
The magnetic moment measurements of the complexes have
been measured at room temperasture (298 K), and data of the
complexes are given in Table 2. The magnetic moments per
one manganese ion of the complexes measured at room tem-
perature are in the range 4.71–4.82 µB. These values are close
to the spin only value of 4.9 µB expected for a magnetically
diluted high spin d4 manganese(III) ion. These results indi-
cate that there is little or no intramolecular anti-ferromagnetic
coupling between the metal centers of the complexes. In the
[Mn2(Lm)(AcO)4(H2O)4].xH2O complexes (m: 1, 2 and 3), the
two manganese ions are thus separated by the phenylene back-
bone of the Schiff base ligands making them essentially mag-
netically isolated.
FIG. 3. 1H-NMR spectrum of the ligand H2L3.
multiplet, the aromatic ring protons are shown in the range 6.43–
8.15 ppm. The very strong singlets in the range 3.75–3.87 ppm
are attributed to the protons of the -OCH3 group. The resonance
peak for the COOH proton in the ligand H2L3 could be detected
around δ 11,17 ppm (broad signal).[18]
Mass spectra of the ligands have been obtained using the
LC/MS method. The mass spectra of the ligands HA1, H2L1
and H2L3 are shown in Figures 6–8. Spectral data of the ligands
are given in the Experimental Section. The mass spectra of the
Schiff base ligands indicate high thermal stability. Signals due
to the parent ions were observed in all cases. The major peaks
in the mass spectrum of the ligands provide an example of the
fragmentation patterns observed. The isotopic patterns of the
individual signals are in good agreement with those predicted
from the isotopic distribution of ligand atoms. In all ligands, the
molecular ion peaks are observed as [M+1]+. We investigated
all fragmentation products. Among the ligands, we suggest
Tetrahedral and high spin octahedral cobalt(II) complexes
each possess three unpaired electrons, but may be distinguished
by the magnitude of the deviation of effective magnetic moment
value (µeff value) from the spin-only value. Magnetic moments
of tetrahedral cobalt(II) complexes with an orbitally degener-
ate ground term are increased above the spin-only value via
contribution from higher orbitally degenerate terms and occur
in the range of 4.2–4.7 BM. This is supported by the visible spec-
4
tra in the range of 675–640 nm assignable to the 4A2 → T1(P)
transition in a pseudotetrahedral geometry.
The magnetic moment data for the RuIII complexes are in the
1.70–1.85 µB range. The magnetic moment values of the RuIII
correspond to one unpaired electron suggesting a low spin t25g
configuration for the RuIII ion in an octahedral environment.
The H NMR spectra of the ligands were recorded in
(CD3)2SO solvent using a 300 MHz instrument. The spectra
of the ligands H2L1-H2L3 are shown in Figures 3–5. Spectral
data of the ligands are given in Experimental Section. The asym-
metric ligands HA1, HA2, and H2L3 make all the aromatic rings
inequivalent. The ligands HA1, HA2, and H2L3 thus possess 5,
7, and 9 non-equivalent aromatic protons, respectively. Since the
electronic environment of many aromatic hydrogen atoms are
similar, their signals appear in a narrow chemical shift range. In
fact, the aromatic regions of the spectra are complicated due to
the overlapping of several signals that have precluded the iden-
tification of individual resonances. However, the ligands H2L1
and H2L2 are symmetric, therefore they possess similar chemi-
cal environments. In the spectra of the ligands, the broad bands
in the range 10.27–13.21 ppm can be assigned to the hydroxyl
proton resonance. The singlet due to the azomethine (–CH N–)
proton in the ligands are in the range δ 8.65–9.12 ppm. As
FIG. 4. 1H-NMR spectrum of the ligand H2L2.

ALCOHOL OXIDATION AND ELECTROCHEMICAL PROPERTIES
217
FIG. 5. 1H-NMR spectrum of the ligand H2L1.
FIG. 7. Mass spectrum of the ligand HA1.
complexes of the ligands H2L1-H2L3 contain both adsorbed and
coordinated water (or Cl− ion) molecules. After the adsorbed
water molecules loss, in the temperature range 383–553 K, the
coordinated water molecules AcO− and Cl− ions loss from the
complexes. When they are heated to higher temperatures, they
are decompose directly to the oxides of the corresponding met-
als (Mn2O3, CoO, Ru2O3). The dehydration processes are con-
nected with an endothermic effect seen on the DTA curves. The
results indicate the following routes thermal decompositions of
the complexes:
the fragmentation patterns for the ligands HA1 and H2L3 as in
Figure 9.
The thermal stability of the Schiff base complexes Co(II),
Mn(III) and Ru(III) have been studied in the range of 298–
1273 K. Their thermal decompositions reveal that they contain
the adsorbed or coordinated water (chloride or acetate ions)
molecules, which are consistent with the elemental and IR spec-
tral analyses (Tables 1 and 2, respectively). The complexes were
stable in air at room temperature. They decompose in various
ways when heated in air. Considering the temperature (the tem-
perature range 323–373 K) at which the dehydration process
of the complexes occur and the way in which it proceeds, it is
assumed that the water molecule is in the outer sphere of the
complex. For the Co(II) complexes of the ligands HA1 and HA2,
the anhydrous complex forms CoO in the range of 573–917 K,
which is oxidized to Co3O4 (919–965 K), the final product of
the complex decomposition. The Co(II), Mn(III), and Ru(III)
[Mn(Lm)n(AcO)(H2O)].xH2O
→ [Mn(Lm)n(AcO)(H2O)] → [Mn(Lm)n] → Mn2O3
[Co(Lm)n].xH2O → [Co(Lm)n] → CoO → Co3O4
[Ru(Lm)n(Cl)(H2O)].xH2O
→ [Ru(Lm)n(Cl)(H2O)] → [Ru(Lm)n] → Ru2O3
FIG. 6. Mass spectrum of the ligand H2L2.
FIG. 8. Mass spectrum of the ligand H2L3.

¨
M. TUMER
218
H3CO
OH N+
H
[M + 1]+ : 242 (m/e)
H3CO
+
+
H3CO
OH
N
.
+
H
N
2
+
m/e: 108
m/e: 93
+
[M-CH3]+ : 227 (m/e)
HO
O
HO
N
O
H
N+
NH2
N+
N+
N
OH
OH
HO
OCH3
OCH3
OCH3
m/e : 287
[M+1]+ ( m/e : 421)
m/e : 167
FIG. 9. Fragmentation patterns for the ligands HA1 and H2L3.
In the series of hydrated Mn(III), Co(II), and Ru(III) com- found. In the case of some primary benzyl alcohols (Table 3),
plexes, the most stable are the complexes of Mn(III) and Co(II), high conversion were obtained. Secondary benzyl alcohols
while the least thermally stable is Ru(III) complexes. The ther- (Table 3) were selectively transformed to the corresponding
mal stabilities of the anhydrous Co(II), Mn(III), and Ru(III) ketones with satisfactory conversions. In our synthesized
complexes do not change regularly with increasing atomic num- ligands, there are several electron-donating substituents. These
ber of the element.
are OH, OCH3, and CH3 groups. These groups are electron-
All benzylic alcohols used as substrates were known withdrawing with inductive effect, but electron-donating with
compounds; some of them were of commercial quality mesomeric effect. The mesomeric effect had more strength
(Fluka), while the others were synthesized as described in than the inductive effect. However, the ligand H2L3 possess
the literature.[4] Diethyl ether was purified using standard the COOH group on the p-position. The COOH group is
techniques. Bidistilled water was used for preparing the electron-withdrawing from the molecule. The introduction
alkaline reagent solutions. The ratio of the substrate and reagent of electron-withdrawing substituents into the aromatic rings
was 1:1. The reactions were performed in alkaline solution at increase the yield compared to alcohols with electron-donating
room temperature or at boiling point of the solvent, depending substituents. Moreover, substrates with electron-donating
on the substrate used. The reaction was monitored through the substituents, such as 4-(dimethylamino)benzylalcohol, 2-, 3-,
change in the color of the reaction mixture from one color 4-methoxybenzylalcohol, 1,2-bis[4-(dimethylamino)phenyl]-
to another color. Satisfactory spectroscopic data (IR) were 2-hydroxyethanone
and
2-hydroxy-1,2-bis(4-
obtained for all products, which were characterized by direct methoxyphenyl)ethanone (Table 3) reacted less effeciently
comparison with authentic samples. In a control experiment in when compared to substrates containing electron-wirthdrawing
which the ligand was omitted, strong peroxide decomposition groups, such as 2-hydroxy-1,2-diphenylethanone (Table 3).
and no oxidation products were found. In the absence of the The secondary benzyl alcohols 1,2-bis[4-(dimethylam-
manganese salt only substrate and no oxidation products were ino)phenyl]-2-hydroxyethanone and 2-hydroxy-1,2-bis(4-

ALCOHOL OXIDATION AND ELECTROCHEMICAL PROPERTIES
219
TABLE 3
Catalytic oxidation data of alcohols by the metal complexes
Substrate
Complex
Product
Temp. (◦C)
Reaction time (h)
Yield (%)
A
B
C
D
E
F
G
H
I
1–3
4–6
7–9
10–12
13–15
1–3
4–6
7–9
10–12
13–15
1–3
Aldehyde
Aldehyde
Aldehyde
Keton
Keton
Keton
Keton
Keton
Keton
Keton
b.p.
b.p.
b.p.
r.t.
b.p.
b.p.
r.t.
b.p.
b.p.
r.t.
4–5
4
3
0.5
0.5
1
1
0.5
1
0.5
0.5
30
58
77
90
95
100
100
96
100
100
80
J
K
Aldehyde
b.p.
1: [Co(A1)].2H2O; 2: [Mn(A1)2(AcO)(H2O)].H2O; 3: [Ru(A1)2Cl(H2O)].2H2O;
4: [Co(A2)]H2O; 5: [Mn(A2)2(AcO)(H2O)].2H2O; 6: [Ru(A2)2(Cl)(H2O)];
7: [Co2(L1)(Cl)2(H2O)2]H2O; 8: [Mn2(L1)(AcO)4(H2O)4].H2O; 9: [Ru2(L1)(Cl)4(H2O)4].H2O; 10: [Co2(L2)(Cl)2(H2O)2].2H2O;
11: [Mn2(L2)(AcO)4(H2O)4].3H2O;
12: [Ru2(L2)(Cl)4(H2O)4].2H2O; 13: [Co2(L3)(Cl)2(H2O)2].2H2O;
14: [Mn2(L3)(AcO)4(H2O)4].2H2O; 15: [Ru2(L3)(Cl)4(H2O)4].2H2O.
r.t.: room temperature, b.p.: boiling point of solvent used. All yields are for pure, isolated products.
A: 2-Methoxy benzyl alcohol, B: 3-Methoxy benzyl alcohol, C: 4-Methoxy benzyl alcohol; D: 2-hydroxy-1,2-diphenylethanone,
E: 1,2-bis[4-(dimethylamino)phenyl]-2-hydroxyethan-one, F: 2-hydroxy-1,2-bis(4-methoxyphenyl)ethanone, G: 1,2-bis[4-
(dimethylamino)phenyl]-2-hydroxyethanone, H: 2-hydroxy-1,2-diphenylethanone, I: cyclohexanol, J: cyclooctanol,K: Cin-
namyl alcohol.
methoxyphenyl)ethanone and some primary benzyl al- on the amine ring. The striking influence of the additional
cohols 4-methoxy benzyl-alcohol and [4-(dimethylam- methyl groups on the reactivity could be a result of either
ino)]benzylalcohol have p-substitutents with electron-donating electronic or steric properties of the ligand. In the oxidation
properties with the mesomeric effect, proceed to only low reaction, the order of the activity of the metal complexes is
conversions. As the ligand H2L3 has the COOH group that Co > Mn > Ru. Moreover, the binuclear complexes have
electron-withdrawing, according to the other Schiff base higher activity than the mononuclear complexes.
complexes, its metal complexes reacted very quickly at room
temperature and the reaction went to completion within a
Electrochemistry
few minutes. Other oxidation reactions required a longer
reaction time (from half an hour to several hours, Table 3).
It appeared that substituents on the aromatic ring affected the
yield of benzylic carbonyl product as well as the rate of the
reaction. However, a distinct steric effect was observed as
ortho substituted substrates react more sluggishly, and in fact
2-methoxybenzyl alcohol was found to be virtually unreactive.
High conversions were also obtained when secondary alcohols
were oxidized. For example, the oxidation of cyclohexanol and
cyclooctanol were found with selectivities up to 99% to the
corresponding ketones. For 4-methoxy benzylalcohol, lower se-
lectivities were observed. Perhaps over oxidation to benzoic acid
takes place (Figure 10); however, this was not quantified. Other
secondary alcohols like 2-hydroxy–1,2-diphenylethanone,
1,2-bis[4-(di-methylamino)phenyl]-2-hydroxyethanone and 2-
hydroxy–1,2-bis(4-methoxyphenyl) ethan-one were selectively
transformed to the corresponding ketones with high conver-
sions. The ligand HA2 has the methyl group on the 2-position
The redox properties of the ligands were investigated in
DMF and DMSO solutions (in nitrogen atmosphere) by cyclic
voltammetry and the redox processes are ligand centered only
(Table 3). The cyclic voltammograms of the ligands HA2 and
H2L3 are seen in Figure 11. For all Schiff-base ligands stud-
ied, cyclic voltammograms at a wide range of scan rates from
50 to 500 mVs−1 consist of a single cathodic peak at poten-
tials ranging from −0.620 to 1.390 V; no anodic wave, ex-
cept for the ligand H2L3, occurs in the reverse scan. Hence,
such a reduction process should correspond to a totally ir-
reversible electron transfer. The ligand H2L3 shows two an-
odic peaks at −1.430 and −0.720 V. These peaks can be at-
tributed to the reduction of the COOH group. This situation
indicates that the anodic wave observed corresponds to a two-
electron transfer. In fact, the shapes of the anodic waves sug-
gest that they would consist of two overlapped one-electron
processes. Such a requirement would arise from the fact that

¨
M. TUMER
220
FIG. 10. IR spectra of the (A) 4-methoxy benzaldehyde and (B) 4-methoxy benzoic acid that forms in alcohol oxidation reaction. (Figure is provided in color
online.)
both the dielectric constant and the dipole moment of DMF where Epa, Epc, and n are anodic potential, cathodic potential
are smaller than those of DMSO. For all Schiff bases under and the number of electrons transferred, respectively. Thus, a
study, this irreversible reduction peak would be ascribed to one electron process exhibits a ꢁEp approximately 0.059V. At
an intramolecular reductive coupling of the two imine groups slower scan rate, the peak separation for the cathodic and anodic
to yield a piperazine.[19] Such a process would involve self- cyclic voltammetric peak potentials is very close to 60–70 mV,
protonation reactions where the phenolic hydroxyl groups act indicating that the number of electrons transferred should be
as proton donors. On the other hand, in each series of lig- 1.0. Cyclic voltammograms of all the complexes (1 × 10−3 M)
ands, the cathodic peak potential (Epc) corresponding to the exhibit a reversible oxidation and reversible reduction peaks
intramolecular reductive coupling of the imine groups varies as at the scan rates 50, 100, and 500 mVs−1. A representative
can be expected from the electronic effects of the substituents cyclic votammograms of [Ru2(L1)(Cl)4(H2O)4].H2O (C) and
at positions 2,2ꢀ and 3,3ꢀ. Thus, in the ligands HA1, HA2 and [Ru(A1)2Cl(H2O)].2H2O (D) are shown in Figure 12. In the scan
H2L3, Epc becomes more negative according to the sequence rate 50 mvs−1, all the Ru(III) complexes showed well-defined
OCH3, CH3 and COOH, i.e., in order of an increase in both waves in the range (E1/2)+1.235 to +0.130 V (RuIV/RuIII)
electron-withdrawing and -acceptor qualities of the substituents. and −1.650 to −0.015 V (RuIII/RuII) versus Ag/AgCl, ut this
This fact agrees with a mechanism involving self-protonation property changes in the scan rate 500 mVs–1. For scan rate
reactions for the electrochemical reduction of the imine groups 500 mVs–1, the ratio ip/SR (ip = peak current; sr = scan rate)
in the Schiff base ligands in the study.
was approximately one, the peak separation being independent
The redox properties of all the RuIII complexes were in- of the scan rate. This indicates that the electron transfer is re-
vestigated in DMF solution (in nitrogen atmosphere) by cyclic versibleandthemass transferislimited. Ithasbeenobservedthat
voltammetry and the redox processes are metal centered only the complexes show quasi-reversible redox processes, which
(Table 3). The number of electrons transferred in the electrode did change with change in scan rates. The electron donating
reaction for a reversible couple can be determined from the group (-OH) as the mesomeric effect ability of the substituent
separation between the peak potential.
on the phenyl ring of the Schiff base favors oxidation of RuIII to
RuIV.[20] The electrochemistry of these complexes in DMF con-
sists of a well-defined Ru(III/II) oxidation couple, the position
of which is highly dependent upon the substituent (see Table 4).
0.0591
ꢁEp = Epa − Epc =
n

ALCOHOL OXIDATION AND ELECTROCHEMICAL PROPERTIES
221
FIG. 12. Cyclic voltammetry of (C) [Ru2(L1)(Cl)4(H2O)4].H2O and (D)
[Ru(A1)2Cl(H2O)].2H2O in DMF in the presence of tetrabutylammonium
tetrafluoroborat (0.1 M) (scan rate: 100 mv/s).
FIG. 11. Cyclic voltammetry curves of the ligands (A) H2L3 and (B) HA2
in DMF in the presence of tetrabutylammonium tetrafluoroborat (0.1 M) (scan
rate: 500 mv/s).
the scan rate 100 mVs−1. A representative cyclic votammograms
of [Co2(L3)(Cl)2(H2O)2].2H2O (E) and [Co(L1)].2H2O (F) are
shown in Figure 13. In the mononuclear Co(II) complexes, it
is shown that a reversible oxidation (1.510 and 1.730 V) and
reversible reduction (−1.880 and 0.370 V) peaks at the scan
rate 50 mVs−1. These peaks change to 0.420 and 0.190 V for
oxidation, and −1.840 and −0.640 V for reduction processes,
respectively. One quasi-reversible redox couple is a common
feature of the cyclic voltammograms of the Co(II) complexes.
The values of ꢁEp and peak current ratios of the waves are
consistent with one-electron transfer processes. The reduction
wave approximately at 0.8 V is assigned to the CoII/I couple.
In DMF, the E1/2 data are the 570, 535, 1235, 80, and −1650 mV
for the CH3 and OCH3 (for HA1 and HA2), dimethoxy (for H2L1
and H2L2), and dimethoxy and carboxy (for H2L3) groups, re-
spectively. The shifts in oxidation potential are a reflection of
the donor-acceptor ability of the substituents, with the electron-
donating methoxy substituent shifting the Ru(III/II) oxidation
to more positive potentials, and the electron-withdrawing car-
boxy substituent shifting the Ru(III/II) couple to less positive
potentials.
[RuIII(X)Cl(H2O)] ↔ [RuIVCl(H2O)(X)]+ + e−
[CoII(A1−2)] · H2O + e− → [CoI(A1−2)]H2O
The redox properties of the CoII complexes were investigated
in DMF solution by cyclic voltammetry, and the redox processes
are metal centered only (Table 3). Cyclic voltammogram of all
the complexes (1×10−3 M) exhibit a reversible oxidation and
reversible reduction peaks at the scan rate 100 mVs−1. In the
mononuclear Co(II) complexes, it is shown that a reversible
oxidation (1.510 and 1.730 V) and reversible reduction peaks at
In the binuclear Co(II) complexes, there are two reduction
and oxidation peaks. These peaks are revesible. For the scan
rate 50 mVs–1, the anodic and cathodic peaks are in the range
−1.30 to 0.36 V and −1.00 to 1.91 V. When the scan rate is
increased, these peaks change. An unsaturated nitrogen as the

222

ALCOHOL OXIDATION AND ELECTROCHEMICAL PROPERTIES
223
REFERENCES
1. Pecoraro, V.L. In: Manganese Redox Enzymes, Pecoraro V.L.(ED.), VCH:
New York, 1992, 197–232.
2. Doble, D.M.J.; Benison, C.H.; Blake, A.J.; Fenske, D.; Jackson, M.S.;
Kay, R.D.; Li, W.S. Template assembly of metal aggregates by imino-
carboxylate ligands. Angew Chem. Schro. der, Int. Ed. Engl. 1999, 38, 1915–
1918
3. (a) DuBois, J.; Hong, J., Carreira, E.M.; Day, M.W. Nitrogen transfer from
a nitridomanganese(V) complex: Amination of silyl enol ethers. J. Am.
Chem. Soc. 1996, 118, 915–916. (b) Finney, N.S.; Pospisil, P.J.; Jacobsen,
E.N. On the viability of oxametallacyclic intermediates in the (salen)Mn-
catalyzed asymmetric epoxidation. Angew. Chem. Int. Ed. Engl. 1997, 36,
1720–1723.
4. Larock, R.C. Comprehensive Organic Transformations; VCH Publishers:
New York, 1989, pp. 604–615.
5. Krohn, K.; Vinke, I.; Adam, H. Transition-metal catalyzed oxidations.
Zirconium-catalyzed oxidation of primary and secondary alcohols with
hydroperoxides. J. Org. Chem. 1996, 61, 1467–1472.
6. Inokuchi, T., Nakagawa, K., Torii, S. One-pot conversion of primary al-
cohols to alpha-oxygenated alkanals with tempo in combination with
molecular-oxygen and ruthenium complex. Tetrahedron Lett. 1995, 36,
3223–3226.
7. Balsells, J., Mejorado, L., Phillips, M., Ortega, F., Aguirre, G., Somanathan,
R., Walsh, P.J. Synthesis of chiral sulfonamide/Schiff base ligands. Tetra-
hedron Asymm. 1998, 9, 4135–4142.
8. Sima, J. Mechanism of photoredox reactions of iron(III) complexes con-
taining salen-type ligands. Crao. Chem. Acta 2001, 74, 593–600.
9. Ouyang, X.M.; Fei, B.L.; Okamuro, T.A.; Sun, W.Y.; Tang, W.X.; Ueyama,
N. Synthesis, crystal structure and superoxide dismutase (SOD) activity
of novel seven-coordinated manganese(II) complex with multidentate di-
Schiff base ligands. Chem. Lett. 2002, 3, 362–363.
10. Raman, N.; Raja, Y.P.; Kulandaismy, A. Synthesis and characterisation
of Cu(II), Ni(II), Mn(II), Zn(II) and VO(II) Schiff base complexes de-
rived from o-phenylenediamine and acetoacetanilide. Proc. Ind. Acad. Sci.
(Chem. Sc.) 2001, 113, 183–189.
FIG. 13. Cyclic voltammetry curves of [Co2(L3)(Cl)2(H2O)2].2H2O (E) and
[Co(L1)].2H2O (F) in DMF in the presence of tetrabutylammonium tetrafluo-
roborat (0.1 M) (scan rate: 500 mv/s).
11. Datta, A.; Karan, N.K.; Mitra, S.; Rosair, G. Synthesis and structural charac-
terization of [Cu(NH2CH2C6H4N=CHC5H5N)Cl-2]. Z. Naturf. 2002, 57,
999–1002.
12. Gao, W.T.; Zheng, Z. Synthetic studies on optically active Schiff-base lig-
ands derived from condensation of 2-hydroxyacetophenone and chiral di-
amines. Molecules 2002, 7, 511–516.
13. El-Sonbati, A.Z.; El-Bindary, A.A. Stereochemistry of new nitrogen
containing aldehydes. V. Novel synthesis and spectroscopic studies of
some quinoline Schiff bases complexes. Polish J. Chem. 2000, 74, 621–
630.
donor atom in the ligand stabilizes a more low oxidation state,
such as CoI, than a saturated one, by π-back bonding between
the metal and the nitrogen atoms.
Cyclic voltammograms of the M(III) complexes were mea-
sured in DMF and DMSO over the potential range from + 2.0
to −2.0 V (Ag/AgCl). Quasi reversible redox waves were ob-
served in the range 1.30 to −0.11 V and 1.215 to −1.520 V
for the Mn(III) complexes in the different scanning rates (Table
4). By the introduction of an electron-withdrawing substituent,
COOH group, the redox potentials of of the complexes of the
ligands H2L3 are shifted to more positive values than those of
other complexes. These shifts can be explained in terms of a de-
crease in the electron density on the central manganese ion in the
complexes. Both of the reduction and oxidation at these poten-
tials are found to be two electron processes. This means that the
reduction and oxidation processes of these mono and binuclear
complexes may undergo two electron transfer processes.
14. Vogel, A.I. Test Book of Practical Organic Chemistry, 5th ed.; Longman:
London, 1989.
15. Nakamoto, K. Infrared Spectra of Inorganic and Coordination Compounds,
2nd Edn; Wiley Inter-Science: New York, 1963, pp. 108253.
16. Dey, K.; Bhowmik, R.; Sarkar, S. Coordination behaviour of 2-(1-carboxyl-
2-hydroxyphenyl)benzothiazoline. Synth. React. Inorg. Met-Org. Chem.
2002, 32, 1393–1408.
17. Isse, A.A.; Gennaro, A.; Vianello, E. Electrochemical reduction of Schiff
base ligands H(2)salen and H(2)salophen. Electrochim. Acta 1997, 42,
2065–2071.
18. El-Shahawi, M.S.; Shoair, A.F. Synthesis, spectroscopic character-
ization, redox properties and catalytic activity of some ruthe-
nium(II) complexes containing aromatic aldehyde and triphenylphos-
phine or triphenylarsine. Spectrochim. Acta Part:A 2004, 60, 121–
127.