Synthesis, spectral and thermal characterization of 6-hydroxymethyl pyridine-2-carboxylic acid methyl ester and its complexes

Article abstract of DOI:10.1007/s10973-005-0753-z

New pincer ligand, 6-hydroxymethylpyridine-2-carboxylic acid methyl ester, HL, and its bipositive, tripositive and uranyl metal complexes have been synthesized and characterized by elemental and thermal analyses, IR, diffuse reflectance and ¹H NMR spectra, molar conductance and magnetic moment measurements. The downfield shift of the aliphatic OH signal (from 3.87 vs. 2.96 ppm in the ligand) upon complexation indicates the coordination by protonated aliphatic OH group. Zn(II) and UO2(II) complexes are found to be diamagnetic as expected. The low molar conductance values indicate that Ni(II) and Zn(II) complexes are non electrolytes; Fe(II), Co(II), Cu(II) and UO ₂(II) complexes are 1:2 electrolytes while Fe(III) complex is a 1:3 electrolyte. The general compositions of the complexes are found to be [M(HL)X₂]?nH₂O where M=Ni(II) (X=Cl, n=1) and Zn(II) (X=Br, n=0); and [M(HL)₂]X_m?nH₂O where M=Fe(II) (X=Cl, m=2, n=0), Fe(III) (X=Cl, m=3, n=4), Co(II) (X=Cl, m=2, n=0), Cu(II) (X=Cl, m=2, n=0) and UO₂(II) (X=NO₃, m=2, n=0). The thermal behaviour of the complexes has been studied and different thermodynamic parameters are calculated using Coats-Redfern method.

Full text of DOI:10.1007/s10973-005-0753-z

Journal of Thermal Analysis and Calorimetry, Vol. 81 (2005) 111–118
SYNTHESIS, SPECTRAL AND THERMAL CHARACTERIZATION OF
6-HYDROXYMETHYL PYRIDINE-2-CARBOXYLIC ACID METHYL
ESTER AND ITS COMPLEXES
*
Nadia E. A. El-Gamel and G. G. Mohamed
Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt
New pincer ligand, 6-hydroxymethylpyridine-2-carboxylic acid methyl ester, HL, and its bipositive, tripositive and uranyl metal
1
complexes have been synthesized and characterized by elemental and thermal analyses, IR, diffuse reflectance and H NMR spec-
tra, molar conductance and magnetic moment measurements. The downfield shift of the aliphatic OH signal (from 3.87 vs.2.96 ppm
in the ligand) upon complexation indicates the coordination by protonated aliphatic OH group. Zn(II) and UO
found to be diamagnetic as expected. The low molar conductance values indicate that Ni(II) and Zn(II) complexes are non electro-
lytes; Fe(II), Co(II), Cu(II) and UO (II) complexes are 1:2 electrolytes while Fe(III) complex is a 1:3 electrolyte. The general com-
positions of the complexes are found to be [M(HL)X ]·nH O where M=Ni(II) (X=Cl, n=1) and Zn(II) (X=Br, n=0); and
M(HL) ]X ·nH O where M=Fe(II) (X=Cl, m=2, n=0), Fe(III) (X=Cl, m=3, n=4), Co(II) (X=Cl, m=2, n=0), Cu(II) (X=Cl, m=2,
n=0) and UO (II) (X=NO , m=2, n=0). The thermal behaviour of the complexes has been studied and different thermodynamic pa-
2
(II) complexes are
2
2
2
[
2
m
2
2
3
rameters are calculated using Coats–Redfern method.
1
Keywords: H NMR, 6-hydroxymethylpyridine-2-carboxylic acid methyl ester, IR, magnetic moment, metal complexes, molar con-
ductance, solid reflectance, thermal analysis
Introduction
A progress on a related goal pincer ligand chem-
istry of transition metals with a secondary amine do-
nor at site E was reported [1]. Moreover, the donors E
In many catalytic reactions, coordinatively unsatu-
rated complexes appear as reactive intermediates at
some stages. Such species initiate catalytic processes
t
was made secondary amine (i.e., NH Bu) rather than
tertiary amines for the specific purpose of having a re-
active hydrogen accompanied by a bulky but 3-fold
symmetric substituent [1]. This substitution pattern
(
catalytic precursor) and, of course, are part of cata-
lytic cycles themselves. Thus, investigations of the
factors controlling and affecting the reactivity and
stability of unsaturated compounds are very important
not only for intrinsic reasons but for the understand-
ing of virtually all homogeneously catalyzed pro-
cesses. Recently, the pincer ligand class (1) has expe-
rienced a renaissance [1] from its earliest incarnations
in mono-metal coordination chemistry. Here, E is a
nitrogen or phosphorous donor and E` can be either a
(ligand abbreviation N py when E`=N) will give rise
2
to both mirror and C asymmetric isomers 3, which
2
are not anticipated to interconvert on the synthetic
time scale when the nitrogens are coordinated. it is
shown from Fig. 2 that, isomer 3 (m) clearly has a
crowded ('up') and an uncrowded ('down') sides,
–
while in 3(C ) these are equivalent. The Ru(II)/Cl ,
2
NCMe, PPh chemistry of the related (but C sym-
2ν
3
2
pyridine nitrogen or ring sp carbon as shown in
metric) ligand 4 was recently reported [2, 3].
2-tertbutylaminomethylpyridine-6-carboxylic acid
methylester ligand and its metal complexes were pre-
viously reported by the authors [4]
Fig. 1. This ligand is most often found as a meridional
ligand (i.e., E` and two E will be approximately
coplanar in the metal coordination sphere).
2
Fig. 1 Pincer ligands with E=N or P and E'=pyridine N or sp
ring carbon
2 2
Fig. 2 N Py ligand with mirror and C asymmetric isomers
*
Author for corresponding: ggenidy@hotmail.com
1
388–6150/$ 20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
©
2005 Akadémiai Kiadó, Budapest

EL-GAMEL, MOHAMED
The main idea of this article is to prepare an
asymmetric pincer ligand type with E` is a nitrogen
and E as aliphatic OH in one arm and as COOMe in
the second arm. The ligand and its complexes were
characterized using different physico-chemical tools
like elemental and thermal analyses, magnetic mo-
added NaBH (10.5 g, 55 mol), whereupon the exo-
4
thermic reaction warmed the reaction mixture to
reflux. The solution was then stirred at room tempera-
ture for 12 h. After evaporation of the solvent, the res-
idue was dissolved in saturated aqueous NaHCO so-
3
3
3
lution (200 cm ) and extracted with CHCl (300 cm )
3
1
ment, molar conductance, IR, H NMR and solid
reflectance spectral techniques.
by continuous liquid-liquid extraction for 15 h. After
evaporation of the solvent, the white product was
washed with Et O and dried in vacuo. Yield:
2
1
5.0 g (72%) IR (KBr disc): 3384 br (ν ), 1732 sh
OH
1
Experimental
(νC=O), 1590 sh (νC=N), H NMR (25°C, DMSO-d ):
6
δ (ppm)=7.75 (t, 1H, J=7.3 Hz), 7.35 (d, 2H, J=7.3
Hz), 4.65 (s, 2H), 2.96 (bs, 1H), 3.94 (5, 3H).
All reagents and solvents were obtained from com-
mercial sources and used as received. Elemental anal-
yses were carried out at the Microanalytical Center at
Cairo University. Infrared spectra were recorded on a
Perkin Elmer FT-IR type 1650 spectrophotometer in
Results and discussion
–
1
wavenumber region 4000–200 cm . The spectra were
recorded as KBr disc. The molar conductance of solid
complexes in DMF was measured using
Sybron-Barnstead conductometer. The solid reflec-
tance spectra were measured on a Shimadzu 3101 pc
spectrophotometer. The molar magnetic susceptibil-
ity was measured on powdered samples using the Far-
aday method. The thermogravimetric analysis (TG
and DTG) was carried out in dynamic nitrogen atmo-
The HL ligand used in this work is a new ligand, pre-
pared in a similar manner to 2,6-bis (hydroxymethyl)
pyridine previously published [5]. The preparation of
HL is given in Scheme 1.
3
–1
sphere (20 cm min ) with a heating rate of
1
Scheme 1 Preparation of HL ligand.
–
0°C min using Shimadzu TGA-50H thermal ana-
1
1
lyzer. The H NMR spectra were recorded using a
Bruker ARX-300 instrument. Chemical shifts are re-
ported in parts per million downfield from
tetramethylsilane. Deuterated chloroform and DMSO
were used as a solvent in a concentric tube containing
1
The H NMR spectrum of HL is given in Fig. 3
with indexing of various types of protons. The forma-
tion of this ligand is revealed by the appearance of
pyridyl protons at 7.75 and 7.35 ppm, –COOCH
ton at 3.94 ppm, –CH protons at 4.65 ppm and OH
pro-
3
d
6
-acetone.
2
proton at 2.96 ppm. This is further supported by the
appearance of bands due to (C=O), δ(C=N) and
2
,6-pyridinedicarboxylic acid dimethyl ester
–
C–O) at 1732, 1590 and 1231 cm respectively. All
1
(
the new complexes have the [M(HL)X ]·nH O
(
C H NO )
9 9 4
2
2
2
and H SO concentrated (0.2 cm ) in methanol
,6-pyridinedicarboxylic acid (26.0 g, 155.7 mmol)
3
(M=Ni(II) and Zn(II), X=Cl or Br and n=0–1) and
[M(HL) ]X ·nH O (M=Fe(II) (X=Cl, m=2, n=0),
2
4
2
m
2
3
200 cm ) were heated to reflux for 100 h. After evap-
(
oration of the solvent, the residue was redissolved in
Fe(III) (X=Cl, m=3, n=4), Co(II) (X=Cl, m=2, n=0),
Cu(II) (X=Cl, m=2, n=0) and UO (II) (X=NO , m=2,
2
3
3
CH Cl (200 cm ), extracted twice with saturated
n=0) stoichiometry and were prepared by reaction of
HL with metal salts in ethanol according to the reac-
tion given below:
2
2
3
aqueous solutions of NaHCO (100 cm ) followed by
3
3
H O (100 cm ). The organic layer was dried over
2
Na SO , filtered and the solvent removed. The white
2
4
MX
2
+HL+nH
M=Ni(II), Zn(II))
MX +2HL+nH O→[M(HL) ]X ·nH O (M=Fe(II),
2
O→[M(HL)X
2 2
]·nH O
product was dried in vacuo. Yield: 26.0 g (85%) IR
1
(
(
(
KBr disc): 1730 sh (νC=O), 1595 sh (νC=N), H NMR
(
25°C, CDCl ): δ(ppm)=8.33 (d, 2H, J=7.8 Hz), 8.02
3
m
2
2
m
2
t, 1H, J=7.8 Hz), 4.02 (s, 6H).
Fe(III), Co(II), Cu(II), UO (II))
2
2-hydroxymethylpyridine-6-carboxylic acid methyl
ester (C H NO ) (HL)
The complexes are insoluble in ethanol, acetone,
chloroform, ether, methanol, methylenechloride but
have a good solubility in DMF and DMSO. Analyti-
cal data, decomposition points and colours of the
8
9
3
To 2,6-pyridinedicarboxylic acid dimethylester
(
3
20.9 g, 107.1 mmol) in MeOH (200 cm ) was slowly
112
J. Therm. Anal. Cal., 81, 2005

6
-HYDROXYMETHYL PYRIDINE-2-CARBOXYLIC ACID METHYL ESTER COMPLEXES
Table 1 Analytical and physical data of HL and its complexes
Found (Calcd)/%
Colour
(yield/%)
µ
eff.
m
Λ /
Compound
HL
M.p./°C
–1
2
–1
(B.M.)
Ω cm mol
C
H
N
M
–
57.32
(57.49)
5.65
(5.39)
8.49
(8.38)
white (90)
yellow (73)
brown (82)
rose (80)
75
–
–
C
8
H
9
NO
3
[
C
Fe(HL)
2
]Cl
FeN
2
41.90
(41.65)
4.15
(3.90)
5.89
(6.07)
12.40
(12.15)
Dec.
Dec
4.98
5.30
193
280
16
H18Cl
2
2
O
6
Fe(HL)
2
]Cl
3
⋅4H
2
O
33.94
(33.78)
4.22
(4.57)
5.05
(4.93)
10.23
(9.85)
C
16
H26Cl
3
FeN
2
O
7
[
C
Co(HL)
2
]Cl
CoN
2
41.58
(41.38)
4.00
(3.88)
6.32
(6.03)
12.51
(12.72)
Dec.
Dec.
Dec.
Dec.
Dec.
5.15
185
16
H18Cl
2
2
O
6
Ni(HL)Cl
2
]⋅H
2
O
30.80
(30.38)
3.69
(3.48)
4.82
(4.43)
18.73
(18.99)
green (62)
yellow (69)
white (80)
3.32
13.75
188
C
8
H11Cl
2
NNiO
4
Cu(HL)
2
]Cl
2
40.58
(40.98)
3.79
(3.84)
5.63
(5.98)
13.90
(13.55)
1.95
C
16
H18Cl
2
CuN
2
O
6
[Zn(HL)Br
2
]
24.25
(24.49)
2.44
(2.30)
3.42
(3.57)
16.32
(16.58)
diam.
diam.
21.42
202
C
8
H
9
Br NO
2
3
Zn
[
C
UO
H
18
2
(HL) ](NO
2
3
)
2
26.79
2.71
8.09
yellow (76)
–
16
N
4
O
14
U
(26.52)
(2.49)
(7.37)
complexes are shown in Table 1. They are character-
ized by the following physicochemical studies.
IR spectra and mode of bonding
The effective IR spectral bands of the ligand and its
metal complexes with Fe(III), Co(II), Ni(II), Cu(II)
and Zn(II) and UO (II) are listed in Table 2 together
2
with assignments for most of the major peaks. The
ligand used in the present investigation contains three
possible donor sites: (i) aliphatic OH, (ii) pyridyl ni-
trogen and (iii) carboxylate oxygen.
–
1
The ν(C=N) band occurs at 1590 cm in the free
ligand. This band shifts to higher frequency by
–
–49 cm after complexation, indicating the coordi-
1
9
nation of pyridyl nitrogen to metal ions [6]. The par-
ticipation of the pyridyl nitrogen; as its band over-
lapped with those of the carboxylate group, is con-
firmed from the band due to in-plane deformation
–
1
ρ(py) located at 667 cm in the free ligand. The coor-
dination of the pyridyl nitrogen to the metal ions is
–
confirmed by the blue shift (47 cm ) or red shift
1
–
1
(
2–23 cm ) of the ρ(py) [7–9]. In the wavenumber re-
–1
gion 1732 cm range, some of the most characteristic
bands of these systems are found. The so-called am-
ide I band, which represents mainly the ν(C=O)
stretching mode, in the chelates. This band is shifted
–
1
to higher frequency (6–48 cm ), supporting the par-
ticipation of the carbonyl group of this ligand in the
metal coordination [10]. The bands at the
–
1
wavenumber 1573 and 1304 cm regions in the free
ligand are assigned to the asymmetric and symmetric
stretching vibrations of the carboxylate group, respec-
tively. The νasym(COO) band is shifted to higher
1
Fig. 3 H NMR spectra of HL and its Zn(II) complex
J. Therm. Anal. Cal., 81, 2005
113

EL-GAMEL, MOHAMED
–
Table 2 IR assignment (4000–200 cm ) of HL and its complexes
1
ν
asym
ν
sym
COO) (COO)
ν(Μ Ο)
aliphatic OH)
ν(M–O)
(ester)
Compound
HL
ν(C=N) ρ(py) ν(C-O) δ(OH) ν(C=O)
ν(M–N)
(
1590 sh 667 m 1231 m 1445 m 1732 sh 1573 sh 1304 sh
1607 sh 669 sh 1250 m 1465 m 1773 m 1576 m 1330 m
–
–
–
[
Fe(HL)
Fe(HL)
2
]Cl
2
3
550 s
521 s
444 s
[
2
]Cl
1
639 m 685 m 1272 m 1400 sh 1756 s 1595 m 1300 m
561 m
489 m
476 s
·
4H
Co(HL)
Ni(HL)Cl
Cu(HL)
Zn(HL)Br
UO (HL) ](NO
2
O
[
[
[
[
2
]Cl
2
1599 sh 679 m 1245 sh 1396 m 1678 sh 1570s 1301 sh
530 m
520 s
530 s
545 s
530 s
490 s
490 s
480 s
490 s
475 s
461 m
469 w
456 w
460 w
462 w
2
] ·H
2
O 1603 sh 620 m 1277 m 1398 m 1672 sh 1585 m 1306 m
1607 sh 690 m 1250 sh 1431 m 1738 sh 1580 m 1292 sh
1607 sh 690 m 1248 m 1433 m 1740 h 1580 m 1323 sh
2
]Cl
2
2
]
[
2
2
3
)
2
1599 sh 679 m 1246 m 1423 m 1680 sh 1570 s 1331 sh
s = small; w = weak; m = medium; br = broad, sh = sharp
–
1
wavelengths (1576–1595 cm )
or lower wave-
1
Table 3 H NMR data of HL and its Zn complex
–
1
lengths (1570 cm ), while ν (COO) band is shifted
sym
–
1
to higher wavelengths (1306–1331 cm ) or lower
Chemical shift
(δ) ppm
Compound
Assignment
–
1
wavelengths (1301–1300 cm ). The shift of these
two bands to higher or lower frequencies suggest the
participation of –COOMe group in complex forma-
tion [11, 12]. Coordination of aliphatic OH group can
be confirmed by the blue or red shift of ν(C–O)
aliphatic and in-plane OH bending δ(OH). The band
7.75
(t, 1H, py, J = 7.3 Hz)
(d, 2H, py, J = 7.3 Hz)
7
.35
4.65
.94
2.96
.99
HL
(s, 2H, –CH
(s, 3H, –COOH
(bs, 1H, –OH)
2
)
3
3
)
–
1
at 1231 cm which is attributed to ν(C–O) in free
7
(t, 1H, py, J = 7.3 Hz)
(d, 2H, py, J = 7.3 Hz)
(s, 2H, –CH2)
ligand is shifted to higher frequency
(
–
14–46 cm ), while the band at 1445 cm which is
1
–1
7.39
4.61
attributed to δ(ΟΗ) in free ligand is shifted to higher
frequencies (20 cm ) or to lower frequencies
12–49 cm ) by the effect of the metal complexation.
New bands observed in the complexes at 561–520,
1
21–475 and 476–444 cm are tentatively assigned
[
2
Zn(H L)Br ]
–
1
4
3
.35
.87
(s, 3H, –CH
3
)
–
1
(
(bs, H, –OH)
–
5
to the ν(M–O) of aliphatic OH, ν(M–O) of ester and
ν(M–N) of the pyridine [6, 9].
fection by the coordination of the pyridyl-N, carbonyl
ester and aliphatic-OH to the metal ions.
In the UO (II) complex, two additional bands at
–
2
1
9
50 and 862 cm , which are assigned to νasym(UO2)
Molar conductance data
and νsym(UO ) modes, respectively. This observation
2
indicates that the O=U=O moiety is virtually in this
complex.
The observed molar conductance ∆
m
=13.75 and
–1
2
–1
31.42 Ω cm mol of the Ni(II) and Zn(II) complexes,
–3
Therefore from the IR spectra, it is obvious that
HL ligand behaves as a neutral terdentate ligand coor-
dinated to the metal ions via pyridyl-N, carbonyl ester
and protonated aliphatic OH groups.
respectively, in 10 M DMF solutions are given in Ta-
ble 1 which suggest the non-electrloytic nature of these
complexes [13]. While the molar conductance values
–1
2
–1
(∆ =185–202 Ω cm mol ) of the Fe(II), Co(II),
m
Cu(II) and UO (II) complexes indicate the electrolytic
nature of these complexes and that they are of the type
2
1
H NMR spectra
1
:2 electrolytes [13]. The Fe(III) complex has a molar
–1
1
The H NMR spectra of HL and its diamagnetic Zn(II)
2
–1
conductance value of 280 Ω cm mol which indicates
that it is a 1:3 electrolyte [13].
complex are shown in Fig. 3 and the data are listed in
Table 3. It is apparent from the spectra that the
aliphatic OH proton signal shifts downfield (3.87
ppm vs. 2.96 ppm in the ligand) upon complexation,
which confirms the coordination by aliphatic oxygen
to the metal ions without deprotonation. This is sup-
ported by the IR and molar conductance data. The up-
field shifts in the other signals may be due to their af-
Electronic spectra and magnetic moment data
As the result of failer to obtain a single crystal for
X-ray analyses to confirm the octahedral and trigonal
bipyramidal structures for these complexes, solid
114
J. Therm. Anal. Cal., 81, 2005

6
-HYDROXYMETHYL PYRIDINE-2-CARBOXYLIC ACID METHYL ESTER COMPLEXES
Table 4 Thermal analysis data of the metal chelates
Total mass
loss
Mass loss
Temp.
range /°C
*
Metallic
residue
Complex
DTGmax/°C
n
Assignment
2
Loss of 4H O (hydrated).
-Loss of 3HCl.
-Loss of two ligand
molecules.
%
Found (Calcd)
-
3
0–130
130–270
70–600
85
240
465
1.0
1.0
1.0
12.00 (12.66)
20.00 (19.26)
53.00 (53.47)
85.00
85.39)
[Fe(HL)
2
]Cl
3
⋅4H
2
O
2 3
½Fe O
(
2
5
0
30–110
110–250
1.0
2.0
3.0
6.00 (5.71)
23.00 (23.18)
48.00 (47.30)
2
-Loss of H O (hydrated).
-Loss of 2HCl.
-Loss of ligand molecule.
1
3
65, 210
10, 405,
75
77.00
(76.19)
[Ni(HL)Cl
2
]⋅H
2
O
NiO
2
50–650
5
Loss of 2HCl.
-Loss of two ligand
molecules.
1
2
70–220
20–650
205
265, 500
1.0
2.0
15.00 (15.58)
68.00 (67.02)
83.00
(82.60
[
Cu(HL)
2
]Cl
2
CuO
ZnO
1
4
90–450
50–700
220, 320
550
2.0
1.0
41.00 (41.33)
39.00 (38.01)
80.00
(79.34)
-Loss of 2HBr.
-Loss of ligand molecule.
[
2
Zn(HL)Br ]
3
20
410, 470,
10
7
3
0–350
50–800
1.0 18.00 (17.13)
1.0 46.00 (46.13)
64.00
(63.26)
2 2
-Loss of 2NO and O .
-Loss of C16H N O
18 2 6.
[
UO (HL)
2
](NO )
2 3 2
UO
2
5
*
n = number of decomposition steps
Table 5 Thermodynamic data of the thermal decomposition of HL chelates
Decomp.
range/°C
E*/
kJ mol
A/
–1
s
∆S*/
J K mol
∆H*/–1
kJ mol
∆G*/–1
kJ mol
2
Complex
–1
–1
–1
r
4
5
3
3
0–130
130–270
70–600
35.12
37.17
66.29
1.01·10
4.27·10
3.99·10
–18.99
–16.29
–21.47
34.42
35.18
62.97
36.03
39.08
71.56
0.977
0.979
0.947
[
[
Fe(HL)
2
]Cl
3
⋅4H
2
O
2
30–110
110–250
13.03
45.10
29.69
9.22
1.64·10
2.94
–25.46
–12.39
–28.76
12.61
43.54
26.12
13.89
45.87
38.49
0.897
0.952
0.956
7
Ni(HL)Cl
2
2
]⋅H O
2
50–650
15
1
2
70–220
20–650
144.5
26.27
1.35·10
1.14
–5.75
–29.58
142.8
23.09
141.6
34.39
0.959
0.931
[Cu(HL)
2 2
]Cl
1
2
1
4
90–450
50–700
132.2
79.90
3.99·10
4.39·10
–0.35
–21.70
129.9
75.32
130.0
87.26
0.931
0.942
[Zn(HL)Br
2
]
2
-
1
7
0–350
2.15
7.55
4.69·10
–30.29
–27.34
0.52
3.89
9.18
0.947
0.955
2 2 3 2
[UO (HL) ](NO )
1
3
50–800
1.24·10
15.92
6
the ground state S. Reflectance spectrum shows three
reflectance spectra and magnetic moment measure-
ments are used for this purpose.
–1
bands at 21.321, 17.452 and 12.820 cm which may be
6
The solid reflectance spectra of the complexes
show three bands in the range 46.269–43.478,
assigned to A →T (G) transition in octahedral ge-
1g
2g
ometry [16]. Also the spectrum shows a band at
–
1.666–39.682 and 33.333–32.362 cm which may
1
–1
23.255 cm which can be attributed to charge transfer.
The electronic spectra of Co(II) complex give three
4
attribute to interligand transitions.
–1
The diffused reflectance spectrum of Fe(II) com-
plex displays two absorption bands at 12.820 and
bands at 12.738, 15.082 and 17.482 cm . The fourth
–1
band at 22.624 cm refers to the charge transfer band.
4
The bands observed are assigned to the transitions T1g
–
1
5
5
2
0.000 cm which are assigned to T2g→ E
g
transi-
4
4
4
4
tion and charge transfer, respectively [14, 15]. It ex-
hibits magnetic moment values of 4.98 B.M., which
are consistent with a high spin octahedral geometry.
In the high spin octahedral Fe(III) complex, the
magnetic moment is always very close to spin-only
value of 5.9 B.M. because the ground state has no
orbital angular momentum. The complex under study
has a magnetic moment of 5.30 B.M.; where Fe(III) has
(F) → T (F) (ν ), T (F)→ A (F) (ν ) and T
2g
1
1g
2g
2
1g
4
(F)→ T (P) (ν ), respectively, suggesting that there is
2
g
3
an octahedral geometry around Co(II) ion [17–19].
For calculating the Racah parameters, the fol-
lowing two equations are used [18].
1
0Dq= 2ν –ν + 15B
1
3
2
2
1/2
B=1/30 [–(ν –ν )±(–ν + ν +ν ν ) ]
1
3
1
3
1 3
J. Therm. Anal. Cal., 81, 2005
115

EL-GAMEL, MOHAMED
1
0Dq=1/3 (2ν –ν )+ 5B
2
3
2
1/2
B=1/510 {7 (ν -2ν )±3 [81ν –16ν (ν – ν ) ]}
3
2
3
2
2
3
From the position of the bands and the calculated
Racah parameters, the chelates are octahedral with
largely covalent bonds between the organic ligands
and the metal ion [18]. The magnetic susceptibility
measurement lie at 5.15 B.M. range (normal range for
octahedral Co(II)–complexes is 4.3–5.2 B.M.), is an
indicative of octahedral geometry [20].
The reflectance spectrum of Cu(II) chelate
–
shows broad band at 22.935 cm that forms part of
1
2
the charge transfer band. The E and T states of the
2
g
2g
9
octahedral copper(II) ion (d ) split under the influence
of the tetragonal distortion and the distortion can be
2
2
such as to cause the three transitions B → B
;
2g
1
g
2
2
2
2
B → E and B → A to remain unresolved in the
1
g
g
1g
1g
spectra [21]. It is concluded that, all three transitions
lie within the single broad envelope centered at
–
7.421 cm . This assignment is in agreement with the
1
1
general observation that copper(II) d–d transitions are
normally close in energy [22]. The magnetic moment
value of 1.95 B.M. falls within the range normally ob-
served for octahedral Cu(II) complexes [23].
The reflectance spectrum of the Ni(II) complex
shows recognizable spectral bands at 13.157, 17.361
–
1
and 21.691 cm . The positions of these spectral bands
are quite consistent with those predicted for five coordi-
nate Ni(II) complex whose structure has been estab-
lished by X-ray crystallographic measurements [24].
The bands can be assigned respectively [24] to
3
3
3
3
3
3
B → E, B → A and B → E transitions assuming
1
1
2
1
the effective symmetry to be C . The band at
2
4
V
–
1
9.069 cm may assign to L- M CT band.
The Zn(II) and UO (II) complexes are diamag-
2
2
Fig. 4 TG and DTG plots of UO (II), Fe(III) and Zn(II)
complexes
netic and assumed respectively to be trigonal bipyra-
midal and octahedral structures.
The TG curves of the Cu(II), Zn(II) and UO (II)
2
complexes consist of two or three stages of mass loss.
The first and first and second mass loss occur in the
range 70–450°C can be attributed to a loss of HBr,
Thermal analysis data
HCl, 2NO
temperature range 220–800°C corresponds to the de-
composition of the ligand molecules as CO , NO ,
2 2
and O gases. The final step within the
The thermal decomposition curves are given for
Fe(III), Zn(II) and UO (II) complexes, as examples,
2
are represented graphically in Fig. 4. The thermo-
gravimetric analysis of the complexes was recorded
in the 30–800°C range. The Fe(III) and Ni(II) com-
plexes show the same decomposition pattern. The
Fe(III) complex decompose in three steps while the
Ni(II) complex decompose in five steps. The first step
is related to the evolution of hydrated water mole-
2
2
NO, CO, O ,…etc gases with an estimated mass loss
2
of 68.00 (calcd. 67.02%), 39.00% (calcd. 38.01%) and
46.00% (calcd. 46.13%) for the Cu(II), Zn(II) and
UO (II) complexes, respectively. The final products for
2
these decomposition are CuO, ZnO and UO residues.
2
cules (4H O:13.00, calcd. 12.66% for Fe(III) com-
2
Kinetic parameters of the complexes
plex; H O:found 6.00%, calcd. 5.71% for Ni(II) com-
2
plex) leaving anhydrous complexes. The anhydrous
complexes decompose in the subsequent steps within
the temperature range 110–650°C leaving ½Fe O3
The kinetic parameters namely activation energy
(E*), enthalpy (∆H*), entropy (∆S*) and free energy
change of decomposition (∆G*) were evaluated graph-
ically by employing the Coats–Redfern relation [25]:
2
and NiO residues.
116
J. Therm. Anal. Cal., 81, 2005

6
-HYDROXYMETHYL PYRIDINE-2-CARBOXYLIC ACID METHYL ESTER COMPLEXES
2
log[log[W / (W − W)] / T ] =
Conclusions
f
f
(
1)
*
*
*
log[AR / E (1− 2RT / E )] − E / 2.303RT
From the satisfactory microanalytical, magnetic, mo-
lar conductance and various spectral data, it is con-
cluded that HL acts as a neutral terdentate ligand and
coordinate through its aliphatic OH (protonated),
pyridyl-N and carbonyl ester atoms to yield five- and
six-coordinate metal complexes. The thermoanaly-
tical results of the complexes conclusively prove that
the hydrated water and anions are removed in the first
steps followed immediately by decomposition of the
where W is the mass loss at the completion of the re-
f
action, W is the mass loss up to the temperature T, R is
the gas constant, E* is the activation energy in
–
1
kJ mol , θ is the heating rate and (1–(2RT)E*))≅1. A
plot of the left-hand side of Eq.(1) vs. 1/T gives a
slope from which E* was calculated and A (Arrhenius
constant) was determined from the intercept. The en-
tropy of activation (∆S*), enthalpy of activation
(
∆H*) and free energy change of activation (∆G*)
ligand molecules. Also, the metal oxides; ½Fe O ,
2 3
were calculated using the following equations:
NiO, CuO, ZnO and UO are the final products.
2
∆
S*=2.303[log(Ah/kT)]R
H*=E*–RT
G*=∆H*–T∆S*
(2)
(3)
(4)
References
∆
∆
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2
where k and h are the Boltzman and Plank constants,
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2
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–
1
5 C. Gemel, K. Foltin and G. K. Caulton, Inorg. Chem.,
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–
1
7
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9
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1
1
0 T. Miyazawa, T. Shimanouchi and S. Mizushima,
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1
1
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1
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1
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1
2
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J. Therm. Anal. Cal., 81, 2005
117

EL-GAMEL, MOHAMED
2
1 J. Kohout, M. Hvastijova, J. Kozisek, J. G. Diaz,
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2
2
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Received: September 7, 2004
In revised form: December 6, 2004
10 (1991) 365.
DOI: 10.1007/s10973-005-6428-y
118
J. Therm. Anal. Cal., 81, 2005