Studies on transition metal murexide complexes

Article abstract of DOI:10.1007/s10973-005-9991-3

Iron cobalt nickel copper zinc cadmium and mercury murexide complexes have been prepared and characterized. The thermal properties of these complexes are studied deeply by DTA technique where their thermal peaks are explained. The multi-stages thermal dec

Full text of DOI:10.1007/s10973-005-9991-3

Journal of Thermal Analysis and Calorimetry, Vol. 84 (2006) 3, 549–555
STUDIES ON TRANSITION METAL MUREXIDE COMPLEXES
1
M. S. Masoud , T. S. Kassem , M. A. Shaker and A. E. Ali
1
2
2*
1
Chemistry Department, Faculty of Science, Alexandria University, Alexandria, Egypt
Physics and Chemistry Department, Faculty of Education, Damanhour, Alexandria University, Egypt
2
Iron, cobalt, nickel, copper, zinc, cadmium and mercury murexide complexes have been prepared and characterized. The thermal
properties of these complexes are studied deeply by DTA technique where their thermal peaks are explained. The multi-stages ther-
mal decomposition mechanism is proposed. The thermodynamic parameters of the decomposition steps are calculated. The entropy
change values for all complexes are of the same magnitude and all transition states of the thermal reactions are more ordered than
the reactants. The thermal reactions proceed in complicated mechanisms. The fractions appeared in the calculated orders of the ther-
mal reactions confirmed that these reactions proceeded via complex mechanisms.
Keywords: DTA, murexide complexes of Fe, Co, Ni, Cu, Zn, Cd, Hg, thermal stability
Introduction
Experimental
Preparation of the complexes
Murexide, a reddish purple compound has the struc-
ture shown in Fig. 1. It has received much interest be-
cause of its application in chemical analysis and spec-
trophotometric fields [1, 2]. It is considered as the
ammonium salt of purpuric acid and named as ammo-
nium 2,6-dioxo-5-(2,4,6-trioxo-tetrahydro-pyrimi-
The metal murexide complexes were prepared by mix-
ing the molar amount of the metal (Fe, Co, Ni, Cu, Zn,
Cd and Hg) chloride or sulphate dissolved in 10 mL
water-ethanol mixture with the calculated amount of
murexide saturated with ethanol. The mixture were
refluxed for about 5 min. The complexes were precipi-
tated, filtered and then washed several times with etha-
dine-5-ylidene
amino)-1,2,3,6-tetrahydro-pyrimi-
dine-4-olate. It serves as a metal ion indicator,
commonly used in conventional EDTA titrations. It is
also used as a chromogenic reagent for conventional
spectrophotometric determination of some metals [2].
This indicator has a low potential in the literature and
few studies such as surface properties [1], stability
constants of its complexes [3, 4] and complex forma-
tion kinetics [5] were examined. No physico-chemi-
cal properties as well as proposed structures for these
complexes were carried out. So, this paper is intended
to give spotlight on the structure and thermal proper-
ties of some transition metal-murexide complexes.
Transition metal complexes are of special interest in
industry, medicine and biology and have many appli-
cations in thermochromism, antioxidation, vulcaniza-
tion acceleration, protecting paintings, catalysis and
anti-bacteriology. So far, solid-state reactions such as
thermal isomerization, conformational changes, poly-
morphic transformations, thermal phase transitions
and thermochromism have a scientific impact for co-
ordination compounds. Our research group has re-
ported a series of articles concerning with the thermal
properties of different transition metal complexes
with pyrimidine, purine, azo, nitroso, azo-nitroso and
amino alcohol derivatives [6–20]. In a continuation of
such work the subject of this article is introduced.
nol and dried in a desiccator over anhydrous CaCl
The melting points of the complexes are over 300°C.
.
2
Analysis of metal ion content
The complexes were digested and decomposed with
aquaregia. The metal ion contents were determined by
the usual complexometric procedures [21].
Carbon, hydrogen and nitrogen analyses
The carbon, hydrogen and nitrogen analyses were
done at the Micro Analytical Laboratory, Faculty of
Science, Alexandria University, Egypt.
Fig. 1 Structure of murexide
*
Author for correspondence: dralaaeldeen@yahoo.com
1
388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
©
2006 Akadémiai Kiadó, Budapest

MASOUD et al.
–
1
Halogen and sulphate analyses
ing range of 190–900 cm . The spectra were mea-
sured in nujol mull following the method described
by Lee et al. [23].
The halogen content was determined by titration with
standard Hg(NO ) solution using diphenyl carbazone
indicator [21]. The sulphate content was determined
3
2
Magnetic susceptibility measurements
gravimetrically as BaSO [21]. The analytical data
4
and colors of the prepared complexes are collected in
Table 1.
Room temperature molar magnetic susceptibilities of
the complexes were measured by using an Evan bal-
ance. The measurements were calibrated against a
IR spectra
Hg[Co(SCN) ] standard [24].
4
Infrared spectra were recorded as KBr disc using
Perkin Elmer Spectrophotometer model 1430 cover-
ing range of 200–4000 cm . Calibration of the fre-
quency readings was made with polystyrene film.
Thermal analysis
–
1
Thermogravimetric measurements and differential
thermal analysis were performed on a Du Pont 9900
computerized thermal analyzer. The heating rate was
–
1
ESR spectra
10°C min . A 60 mg sample was placed in a platinum
crucible. Dry nitrogen was flowed over the sample at
ESR spectra were recorded at 100 kHz modulation and
10 G modulation amplitude on Varian E-9 Spectro-
–1
a rate 10 mL min and a chamber cooling water flow
–1 –1
rate was 10 L h . The speed was 5 mm min .
photometer. Incident power of 10 mV was used and
resonance conditions were at ca. 9.75 GHz (X-band) at
room temperature. Spectra were obtained with an air
products LTD-3-110 Heli-Trans liquid helium transfer
refrigerator. The field was calibrated with a powder
sample of 2,2-diphenyl pyridylhydrazone (DPPH)
g=2.0037 [22].
Results and discussion
Spectral and magnetic identification of murexide
complexes
The structure of murexide was determined and re-
ported [25]. In this work, the molecular structure of
the murexide ligand, Fig. 2 is examined by Chem. 3D
Program, and interesting data are observed. Table 2
UV-Vis spectra
The electronic absorption spectra data were recorded
by Perkin Elmer Spectrophotometer model 48 cover-
Table 1 Analytical data and color of metal murexide complexes
Calculated (found)/%
Complex
Abbreviation Color
M
C
H
N
Cl
S
–
1
3.59
23.36
(23.29)
1.46
(1.48)
17.03
(17.00)
17.27
(17.26)
FeLCl
Fe LCl
CoLCl·2H
Co LCl ·3H
NiLCl·2H
Ni LCl ·3H
CuLCl·2H
Cu LCl ·3H
Zn SO ·4H
CdLCl·2H
2
·H
2
O
I
II
orange
brown
yellow
brown
yellow
olive-green
orange
brown
white
(
(
(
(
(
(
(
(
(
(
(
13.58)
0.09
20.08)
4.83
14.80)
1.64
21.70)
4.81
14.80)
1.58
21.56)
5.84
15.86)
2.95
22.96)
5.73
15.70)
4.97
24.97)
7.26
37.19)
2
17.27
(17.28)
1.44
(1.50)
12.59
(12.59)
25.54
(25.58)
–
–
–
–
–
–
–
2
4
·2H
2
O
1
17.27
(17.29)
2.02
(2.08)
17.65
(17.60)
8.95
(8.98)
2
O
III
IV
V
2
24.20
(24.20)
1.84
(1.80)
12.85
(12.79)
19.56
(14.54)
2
3
2
O
1
17.63
(17.65)
2.02
(2.03)
17.66
(17.68)
8.96
(8.85)
2
O
2
17.64
(17.64)
1.84
(1.80)
12.87
(12.84)
19.57
(19.57)
2
3
2
O
VI
VII
VIII
IX
X
1
23.93
(23.96)
1.99
(1.99)
17.45
(17.45)
8.85
(8.84)
2
O
2
17.34
(17.33)
1.81
(1.80)
12.64
(12.63)
19.23
(19.22)
2
3
2
O
1
11.55
(11.56)
1.44
(1.41)
8.42
(8.39)
–
3.85
(3.81)
2
L
2
4
2
O
2
21.33
(21.30)
1.78
(1.75)
15.55
(15.50)
7.89
(7.86)
–
–
2
O
white
3
17.84
(17.87)
1.49
(1.45)
13.00
(12.99)
6.60
(6.59)
HgLCl·2H
2
O
XI
white
550
J. Therm. Anal. Cal., 84, 2006

STUDIES ON TRANSITION METAL MUREXIDE COMPLEXES
shows some of the obtained bond lengths () and
characteristics of stretching, rocking and waging
modes of coordinated H O molecules. Murexide ex-
bond angles (°). From Table 2, the C(23)-O(4) bond
has the highest bond length value, 1.259 , among
the other C–O bonds as this bond is more single than
the others. Also, the bond angles in most cases shifted
from those of tetrahedral (109.5) or trigonal planar
2
–1
hibits bands at 3264, 3244 cm which are due to N–H
vibration modes. The ligand gave strong splitted car-
–1
bonyl bands at 1695 and 1670 cm corresponding to
–1
the nC=O of the amide and the band at 1653 cm is due
to the C=N vibration. The N–H and C=O bands are
shifted on complexation. Murexide presumably coor-
dinates through ring nitrogen with appreciable shifts.
However, the observed shifts for the C=O band of the
ligand on complexation indicate that it is involved in
the structural configuration of the complexes. The
band corresponding to nC–N (amide) in the free ligand,
(120) angles due to the interaction between the lone
pair electrons of the heteroatoms.
The IR spectral data of the murexide ligand and
its complexes are collected in Table 3. Murexide com-
pound has various potential donor sites. All complexes
–1
show bands at 3500–3400, 750–730 and 600 cm
–1
at 1462 cm is shifted due to its involvement in the
complexation. This indicates the donating nature of the
N atom because of its resonance stabilization. The
presence of both nNH and nC=O bands in the spectra of
the murexide complexes and the disappearance of new
bands assigned for nOH are strong evidences that no
tautomerization of the NH groups with the adjacent
carbonyls takes place before complexation. The com-
plexes gave new IR bands in the ranges of
–
1
–1
407–590 cm corresponding to n , 231–390 cm
corresponding to n , 340–431 cm corresponding to
M–O
–1
M–N
–1
nM–Cl and at 369 cm corresponding to nM–S.
The Nujol mull electronic absorption spectra of
the separated solid murexide complexes gathered
with that of effective magnetic moment values
(Table 4) indicated the octahedral geometry of all
complexes [26]. The magnetic moment of the iron
complexes (I, II) at room temperature, 2.03 BM, is
comparable to the low spin iron (III) systems with a
2
characteristic configuration ( T
g ground state) [27].
The electronic absorption spectra gave the spec-
2
tra of the low spin O iron (III) complexes where two
h
spectral bands are observed at 352 and 550 nm, due to
L®M charge transfer transitions. Based on the ele-
Fig. 2 The postulated structure of murexide
Table 2 The calculated lengths and angles for some murexide bonds
O(1)–C(18)
O(2)–C(15)
O(3)–C(12)
O(4)–C(23)
O(10)–C(25)
O(11)–C(28)
C(12)–N(13)
C(12)–C(19)
N(13)–C(15)
N(13)–H(14)
C(15)–N(16)
N(16)–C(18)
N(16)–H(17)
C(18)–C(19)
1.237
1.249
1.254
1.259
1.239
1.252
2.822
1.483
1.410
0.996
1.397
1.408
0.997
1.500
C(19)–N(20)
N(20)–C(24)
N(21)–C(23)
N(21)–C(28)
N(21)–H(22)
C(23)–C(24)
C(24)–C(25)
C(25)–N(26)
N(26)–C(28)
N(26)–H(27)
N(5)–H(6)
1.309
1.345
1.411
1.413
0.998
1.451
1.483
1.415
1.390
0.998
1.016
1.042
1.017
1.033
O(3)–C(12)–N(13)
O(3)–C(12)–C(19)
C(12)–N(13)–C(15) 122.560
117.193 H(22)–N(21)–C(23) 118.344
124.348
O(4)–C(23)–N(21)
O(4)–C(23)–C(24)
114.796
125.786
C(12)–N(13)–H(14) 120.232 N(20)–C(24)–C(23) 126.130
H(14)–N(13)–C(15) 117.052 C(23)–C(24)–C(25) 118.274
C(15)–N(16)–C(18) 123.546 O(10)–C(25)–C(24) 126.602
O(2)–C(15)–N(13) 120.119 O(10)–C(25)–N(26) 115.859
N(13)–C(15)–N(16) 118.089 C(25)–N(26)–C(28) 123.899
C(15)–N(16)–H(17) 117.267 H(27)–N(26)–C(28) 117.356
O(1)–C(18)–N(16)
117.814 O(11)–C(28)–N(26) 122.259
N(16)–C(18)–C(19) 116.235
C(12)–C(19)–C(18) 115.071
C(12)–C(19)–N(20) 129.118
C(19)–N(20)–C(24) 131.257
H(6)–N(5)–H(8)
H(6)–N(5)–H(9)
H(7)–N(5)–H(8)
H(8)–N(5)–H(9)
111.273
109.613
110.544
110.476
N(5)–H(7)
N(5)–H(8)
N(5)–H(9)
J. Therm. Anal. Cal., 84, 2006
551

MASOUD et al.
–
Table 3 Fundamental infrared bands (cm ) of murexide and its complexes
1
Compound
Murexide
n
N–H
n
C=O
n
C=N
n
C–N
n
M–O
n
M–N
n
M–Cl
n
M–S
3
3
264
244
1729
1690
1653
1462
I
3295
3197
3197
3195
3200
3282
3215
3166
3199
3189
2990
1680
1659
1685
1700
1705
1699
1688
1711
1687
1645
1703
1653
1653
1653
1653
1653
1653
1653
1653
1653
1653
1653
1415
1400
1390
1399
1401
1425
1423
1399
1403
1425
1433
564
536
590
547
522
515
437
408
407
409
550
232
234
268
266
231
299
390
369
313
299
287
340
344
400
415
431
411
399
366
II
III
IV
V
VI
VII
VIII
IX
X
369
423
409
XI
Table 4 Electronic spectral and effective magnetic moment values at 298 K for the complexes
eff
m /BM
Complex
l
max/nm
I
352, 550
2.03
2.03
5.21
5.21
2.15
2.15
2.50
2.54
II
352, 550
III
IV
V
696(sh), 587(sh), 413(s), 312(s)
696(sh), 587(sh), 413(s), 312(s)
853(sh), 743(w.b), 416(s), 286(s), 262(sh)
853(sh), 743(w.b), 416(s), 286(s), 262(sh)
683(v.b), 423(sh), 409(s), 355(w), 313(s)
683(v.b), 423(sh), 409(s), 355(w), 313(s)
VI
VII
VIII
mental analyses, spectral and magnetic measurements
the structure of the murexide complexes can be pro-
posed to be as shown in Fig. 3 where murexide acts as
a tridentate monobasic ligand and the chloride ion be-
haves as a strong nucleophile during complexation.
ESR spectra of copper complexes
It is possible to measure the covalent bond character
2
a , where a is the coefficient of the ground state of
dx2–y2 orbital, from the expression [28–33]:
2
a =
A
11
3
Fig. 3 The structures of all murexide complexes except IX
where Complex I when there is no M and M =Fe,
X=Cl. Complexes III, V, VII, X and XI when there is
no M , X=H O and M =Co, Ni, Cu and Cd , respec-
tively. Complex II M = M =Fe and X=Y=Z=Cl. Com-
plexes IV, VI and VIII when, X=H O, Y=Z=Cl and
=M =Co, Ni and Cu, respectively
+(g –2.0023)+ (g –2.0023)+0.04
11 ^
2
1
0.036
7
–1
2
A11 is the parallel coupling constant (cm ). The a
2
2
1
value for Cu(II) complexes with tetragonal distortion
lies in the range of 0.63–0.84 for nitrogen donor lig-
ands [34] and 0.84–0.94 for oxygen donor ligands
1
2
2
M
1
2
[35]. Axial ligands cause changes in equatorial bond
length and hence g and A values [36]. Bonding be-
tween ligands and Cu(II) ion occurs through the 4s and
4p orbitals of the Cu(II) ion with the ligand orbitals.
The presence of apical ligands introduces 4s character
in the ground state which decreases the contact
hyperfine interaction. Therefore, if the 4s character in
the ground state is known, it is possible to know the ax-
ial field strength in the presence of small percentage of
4s character in the ground state, the fraction of the 3d
character in the Cu(II) 3d–4s ground state, f , can be
determined from the following equation [33]:
2
552
J. Therm. Anal. Cal., 84, 2006

STUDIES ON TRANSITION METAL MUREXIDE COMPLEXES
Table 5 ESR parameters for copper murexide
2
2
Complex
g
11
g
^
<g>
G
A
11
A
^
a
f
VII
2.23
2.11
2.05
2.03
2.11
2.06
3.60
3.66
188
185
38
0.52
0.67
0.80
0.98
VIII
18.5
#
The entropies of activation DS were obtained
from the following equation:
2 2
a f =
7 ⎡ A11
A
2
5
6⎤
–
0.036 0.36
+ g
–
1
g⊥ –
1
⎢
⎥
4
3
21
7
⎣
⎦
KTm
h
≠
The room temperature polycrystalline X-band ESR
spectral pattern of the Cu-murexide complexes
Z =
exp(ΔS / R)
(
VII, VIII) gave similar pattern (Table 5). Both are of
anisotropic nature. The spectral analysis of these com-
plexes gave two values of g11 (2.11, 2.23) and of g
2.03, 2.05) for both complexes, respectively. The cal-
culated <g> values=(g +2g )/3 are 2.06 and 2.11, re-
where R is the molar gas constant b is the rate of heating
–1
(K s ), K is the Boltzman constant and h is Planck’s
constant. The activation energy, DE , of the thermal de-
^
a
(
composition step is determined from the slope of the
straight line of the ln DT vs. 1/T relationship. The slope
11
^
spectively. The lowest g value was found to be more
than 2.00, consequently, the tetragonal distorted sym-
is of Arrhenius type and equals to –DE /R. The change
a
#
of entropy, DS , values for all complexes are given in
2
metry associated with dx2–y2 ground state rather than dz
Table 6. The negative values indicated that the activated
complexes have more ordered structures than the reac-
tants [40]. The lower values of the collision factor, Z, in
most of the complexes indicated the slow nature of the
11
ground state is suggested [37]. The A values for the
two complexes were 185 and 188, indicating the proba-
bility of the pseudo O structure around Cu ion in the
h
two complexes; where the value of A >100. The calcu-
1
1
reactions [41]. The degree of decomposition, a , was
m
2
lated a and f values (Table 5) indicated the stronger
2
#
calculated and given in Table 6. Also, it seems that DS
2
axial field in the two complexes. From the values of a
one can say that the metal–ligand bond in complex VII
is less covalent than that of complex VIII.
values are nearly of the same magnitude suggesting a
uniform decomposition pattern. The thermal decompo-
sition of the murexide complex I showed three peaks at
134, 298 and 403°C with activation energies 28.00,
33.00 and 50.00 kcal mol
–1
, respectively, and an order
Thermal analysis
of reactions 1.95, 1.35 and 0.65, respectively. The latter
peak is assigned to the Fe O . The first peak is due to
The compositions of the complexes were confirmed by
DTA and TG. The thermal pattern of the decomposi-
tion steps of the investigated complexes showed that
M–ligand bonds dissociated after removal of small
molecules. At the beginning of the DTA-curves of the
complexes there is a clearly manifested endothermic
effect (above 100°C), which is due to the hygroscopic
moisture released. The amount of this mass loss, deter-
mined also by Karl Fisher analysis, is correlated with
the intensity of these endothermic effects and with the
respective decreases in the mass. On heating the com-
plexes the decomposition step in all cases corresponds
to the loss of molecules of the ligands, which is in
agreement with the compositions in Table 6. The
exothermal effect (300–500°C) dominates in the
curves of all the complexes, resulting from the decom-
position of the organic matter. A further mass loss re-
corded up to higher temperatures indicates the forma-
tion of thermally stable oxide. The reaction order of the
thermal reactions was calculated using Kissinger ap-
proach [38]. The values of the collision factor, Z were
obtained, Table 6, based on Horowitz–Metzger equa-
tion [39] by making use of the following equation:
2
3
the dehydration reaction of probably adsorbed water. Its
decomposition begins at 134°C and proceeds in three
stages involving a loss in mass. The stages probably
consist of a number of unidentifiable processes. The de-
hydration of the iron complex is suggested in stage 1.
The processes occurring in the endothermic first stage of
the decomposition partly coincide with those of the sec-
ond stage, so it is difficult to determine precisely the
corresponding temperature ranges. The total thermal ef-
fect of the second stage is endothermic (an intense endo
peak). Above 403°C the next stage of the decomposition
(stage 3) of the sample proceeds involving a stepwise
loss of its mass. The thermal decomposition of complex
II is similar to that observed for the complex I, but the
processes are preceded by dehydration at 105°C
(stage 1). It showed also three peaks at 105, 300 and
4
7
0
30°C with activation energies 79.23, 38.20 and
–1
9.20 kcal mol , respectively, and an order of reactions
.73, 0.87 and 0.87, respectively. The analysis of the
mass spectra of the gaseous products of complex II de-
composition confirmed that water molecules are re-
leased in the first stage of decomposition. In the temper-
ature range 200–380°C, the anhydrous salt from stage 1
decomposes rapidly (the second stage), and then more
ΔE
RTm
2
Z =
βexp(ΔE / RT )
m
J. Therm. Anal. Cal., 84, 2006
553

MASOUD et al.
Table 6 Thermodynamic parameters of murexide complexes
–1
#
DS /cal mol
–1 –1
K
#
DH /kcal mol
–1
Complex Type
endo
T
m
/°C
n
S
DE/kcal mol
a
m
b
Z
134
298
403
1.95
1.35
0.65
3.50
0.98
0.10
28.00
33.00
50.00
1.84
2.15
3.35
2.14
2.34
1.06
59.68
79.43
86.26
–51.61
–50.53
–51.15
29.21
28.55
–27.98
I
endo
exo
endo
endo
exo
105
300
430
0.73
0.87
0.87
0.63
0.48
0.47
79.23
38.20
79.20
3.17
2.55
2.60
1.69
1.59
1.59
30.04
40.18
31.08
–49.87
–53.04
–49.93
31.33
32.72
–31.89
II
endo
exo
202
428
1.14
1.14
0.82
0.82
87.44
41.81
2.15
2.19
2.25
2.25
179.18
78.63
–50.09
–51.68
31.51
–32.52
III
IV
endo
exo
149
453
0.84
0.84
0.44
0.44
20.34
62.50
2.47
2.43
1.60
1.60
33.63
112.27
–52.94
–50.53
26.71
–25.50
endo
endo
exo
150
368
403
2.35
1.24
0.39
3.50
0.98
0.10
18.00
35.00
80.00
1.83
2.11
3.33
3.14
2.34
1.06
62.68
89.43
90.26
–51.55
–50.97
51.10
24.21
25.55
–27.60
V
endo
endo
endo
exo
100
305
379
396
0.83
0.83
0.77
0.77
0.53
0.53
0.38
0.37
13.84
179.23
35.20
2.52
2.92
2.54
2.50
1.60
1.60
1.39
1.39
18.79
306.04
40.17
–54.45
–48.87
–53.04
–48.93
32.68
29.33
33.72
VI
219.20
314.08
–31.11
exo
endo
exo
100
138
280
1.05
1.05
0.33
0.69
0.69
0.07
17.69
2.00
12.50
2.28
2.85
3.52
2.09
2.09
2.06
46.19
5.25
23.02
–51.93
–56.28
–53.94
–21.82
28.49
–30.78
VII
exo
endo
endo
118
149
368
0.75
0.93
0.95
0.75
0.93
0.95
9.80
38.50
21.20
2.60
2.34
2.36
1.34
1.85
1.90
16.35
83.29
38.91
–53.98
–50.96
–52.77
–22.29
23.79
28.32
VIII
endo
exo
endo
115
386
421
1.32
1.32
0.57
1.10
1.10
0.20
41.00
164.44
16.00
2.10
2.03
2.84
2.485
2.485 288.59
0.490 5.61
88.24
–51.92
–49.56
–57.70
41.44
–39.84
40.61
IX
X
endo
exo
162
421
1.21
1.21
0.92
0.92
59.00
129.00
2.12
2.04
2.347 136.41
2.347 330.62
–50.34
–48.57
28.08
–27.09
slowly between 380 and 450°C (the third stage). The
processes which take place in the second and third
stages are endothermic and exothermic, respectively.
The final product of decomposition is also ferric oxide.
At temperatures exceeding 350°C the decomposition of
the sample is firstly slow and then at over 800°C, its rate
increases, resulting in the formation and stepwise evap-
oration of iron oxide. In the thermal curves of the octa-
hedral murexide complex III two main stages of decom-
position can be distinguished, connected with
continuous mass loss and strong exothermic effects. Its
DTA curve exhibits two peaks one is endothermic and
the other is exothermic in the temperature range
blue was also observed during decomposition. The or-
der of the decomposition reaction was 0.84 and the DE
a
–1
value was calculated as 20.34 kcal mol . The interme-
diate formed is stable up to 220°C and decomposes in
one step to give CoO as the end product at 453°C in an
exothermic step. Complex V decomposes in three
stages. The first stage corresponds to dehydration in the
temperature range 100–150°C. Thermal dehydration is
–1
first order with energy of activation of 18.0 kcal mol .
In the second stage, the anhydrous complex undergoes a
strong endothermic decomposition between 150 and
368°C to produce a stable solid moiety. A large mass
loss was observed in this decomposition stage with a
sharp color change from pale-blue to dark blue. This
202–428°C, Table 6. The presence of CoO and CoCl
–1
was confirmed in the sinter obtained at about 300°C.
Above 500°C the mass of the sample does not change.
The main gaseous products of the decomposition of the
step is endothermic with a DE value of 35.0 kcal mol .
a
The third stage corresponds to the decomposition of the
intermediate to yield NiO as the final decomposition
product. Complex VI begins to lose mass around 100°C
and up to 300°C. This is the dehydration stage in which
two water molecules are eliminated. No stable interme-
diate is formed between the first and second stages as
the second stage starts at 305°C. Around 300°C, a sharp
decrease in mass is noted and the subsequent slow mass
loss occurs until 379°C. The last stage, that starts around
396°C suggests the formation of NiO residue, which is
complexes under study are CO , small amounts of H O
2 2
and trace amounts of HCl. A careful examination of the
thermal decomposition curves of murexide complex IV
reveals that decomposition proceeds via two steps. The
complex is stable up to 115°C and undergoes a violent
endothermic decomposition in the temperature range
115–150°C. Mass loss calculations suggest the loss of a
water molecule. A color change from brown to deep
554
J. Therm. Anal. Cal., 84, 2006

STUDIES ON TRANSITION METAL MUREXIDE COMPLEXES
1
1
1
1
1
2 M. S. Masoud, S. A. Abou El-Enein and O. F. Hafez,
J. Thermal Anal., 38 (1992) 1365.
3 M. S. Masoud, O. H. Abd El-Hamid and Z. M. Zaki,
Transition Met. Chem., 19 (1994) 21.
4 M. S. Masoud, A. A. Hasanein, A. K. Ghonaim, E. A. Khalil
and A. A. Mahmoud, Z. Phys. Chem., 209 (1999) 223.
5 M. S. Masoud, E. A. Khalil, A. A. Ibrahim and
A. A. Marghany, Z. Phys. Chem., 211 (1999) 13.
6 M. S. Masoud, A. K. Ghonaim, R. H. Ahmed,
A. A. Mahmoud and A. E. Ali, Z. Phys. Chem.,
stable even above 800°C. The thermal mode of decom-
position of the murexide complex VII indicates that it is
thermally stable up to 100°C. The thermal decomposi-
tion appears to take place in two stages, one is endother-
mic and the other is exothermic at 138 and 280°C, re-
spectively. The final decomposition product was
estimated as CuO. TG of the complex VIII starts to de-
compose around 118°C. This stage continues until
149°C and one water molecule is eliminated. The main
degradation step starts around 368°C in the last step.
2
15 (2001) 53.
17 M. S. Masoud, A. K. Ghonaim, S. A. Abou El-Enein and
A. A. Mahmoud, J. Coord. Chem., 55 (2003) 79.
8 M. S. Masoud, A. A. Soayed, A. E. Ali and O. K. Sharsherh,
J. Coord. Chem., 56 (2003) 725.
9 M. S. Masoud, S. A. Abou El-Enein and N. A. Obeid,
Z. Phys. Chem., 215 (2001) 867.
Residue, in this case, is again CuCl . Thermal dehydra-
2
1
tion of complex IX apparently occurs in three steps. The
DE and n values were found to be 41.00, 164.40 and
a
1
–1
16.00 kcal mol and 1.32, 1.32 and 0.57, respectively.
The mass loss at 115°C accounts for the endothermic
elimination of a water molecule and the formation of a
stable solid intermediate. The decomposition process is
20 M. S. Masoud, S. A. Abou El-Enein, H. A. Motaweh and
A. E. Ali, J. Therm. Anal. Cal., 74 (2003) 1.
21 A. I. Vogel, A Text Book of Quantitative Inorganic Analysis,
Fourth Ed., Longmann, London, 452 (1978) 116.
–1
about first order with a DE value of 41.00 kcal mol .
a
22 P. H. Lee, E. Griswold and J. Kleinberg, Inorg. Chem.,
The major decomposition is observed in the temperature
range 386–421°C with a mass loss to yield ZnO. The or-
der of dehydration of the complex was found to be 1.32
while the order of decomposition was 0.57. The ener-
gies of activation of dehydration were somewhat lower
than that of the second stage of decomposition. The
DTA curve of the complex X shows two peaks, endo-
thermic and exothermic corresponding to the first and
last step of the TG curves. First step in the decomposi-
tion of the complex at 162°C is accompanied by endo-
thermic effect in the DTA curves with the evolution of
one molecule of HCl moiety from the complex. Last
step in the thermal decomposition involves the decom-
position of intermediates and oxidation of metal by at-
mospheric oxygen.
3
23 D. Reinen and G. Friebel, Inorg. Chem., 23 (1984) 791.
(1964) 1278.
2
2
2
4 N. B. Figgs and J. Lewis, Modern Coordination Chemistry,
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7 B. F. Little and G. J. Long, Inorg. Chem., 17 (1978) 3401.
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D. J. Hodgson and W. E. Halfield, Inorg. Chem.,
2
2
16 (1977) 2675.
2
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3
9 W. Levason and C. M. MacAulife, Inorg. Chim. Acta,
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2 R. K. Parasher, R. C. Sharma, A. Kumar and G. Hohan,
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Accepted: May 26, 2005
OnlineFirst: January 11, 2006
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DOI: 10.1007/s10973-005-9991-3
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555