Chelation behaviour of nitroso-pyrazolones with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)

Article abstract of DOI:10.1023/A:1025815521606

Infrared (IR), nuclear magnetic resonance (NMR), thermogravimetric analysis (TG), derivative thermogravimetric analysis (DTG), differential thermal analysis (DTA) and molar conductivity studies have been carried out on the chelates of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) with 3-methyl- and 3-phenyl-4-nitroso-5-pyrazolones. The solid chelates were synthesized, separated, analyzed and their structures were elucidated. The data obtained show that almost all of the prepared chelates contain water molecules in their coordination sphere. The initial stage in the thermal decomposition process of these chelates shows the presence of water molecule, the second denotes to the intermediate products. The final decomposition products were found to be the respective metal oxides. The NMR spectrum of 3-methyl-4-nitroso-5-pyrazolone ligand shows the existence of the oxime rather than the nitroso form. 3-phenyl-4-nitroso-4-nitroso-5-pyrazolone acts as a neutral bidentate ligand whereas 3-methyl-4-nitroso-5-pyrazolone acts as monobasic bidentate ligand bonded to the metal ions through the two oxygen atoms of the carbonyl and nitroso groups. The solid chelates prepared behave as non-electrolytes in DMF solution. The coordination numbers of the obtained chelates using 3-methyl-4-nitroso-5-pyrazolone are four on applying the mole ratio 1:1 and six on using 1:2 mole ratio. In case of using the ligand 3-phenyl-4-nitroso-5-pyrazolone the coordination number is six in both cases.

Full text of DOI:10.1023/A:1025815521606

Journal of Thermal Analysis and Calorimetry, Vol. 73 (2003) 939–950
CHELATION BEHAVIOUR OF NITROSO-
PYRAZOLONES WITH Mn(II), Co(II), Ni(II), Cu(II) AND
Zn(II)
S. A. Abdel-Latif*, O. M. El-Roudi and M. G. K. Mohamed
Chemistry Department, Faculty of Science, Helwan University, Cairo, Egypt
(Received August 2, 2002; in revised form January 27, 2003)
Abstract
Infrared (IR), nuclear magnetic resonance (NMR), thermogravimetric analysis (TG), derivative
thermogravimetric analysis (DTG), differential thermal analysis (DTA) and molar conductivity
studies have been carried out on the chelates of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) with
3-methyl- and 3-phenyl-4-nitroso-5-pyrazolones. The solid chelates were synthesized, separated,
analyzed and their structures were elucidated. The data obtained show that almost all of the pre-
pared chelates contain water molecules in their coordination sphere. The initial stage in the thermal
decomposition process of these chelates shows the presence of water molecule, the second denotes
to the intermediate products. The final decomposition products were found to be the respective
metal oxides. The NMR spectrum of 3-methyl-4-nitroso-5-pyrazolone ligand shows the existence
of the oxime rather than the nitroso form. 3-phenyl-4-nitroso-5-pyrazolone acts as a neutral
bidentate ligand whereas 3-methyl-4-nitroso-5-pyrazolone acts as monobasic bidentate ligand
bonded to the metal ions through the two oxygen atoms of the carbonyl and nitroso groups. The
solid chelates prepared behave as non-electrolytes in DMF solution. The coordination numbers of
the obtained chelates using 3-methyl-4-nitroso-5-pyrazolone are four on applying the mole ratio
1:1 and six on using 1:2 mole ratio. In case of using the ligand 3-phenyl-4-nitroso-5-pyrazolone the
coordination number is six in both cases.
Keywords: absorption spectra, conductivity, DTA, nitrosopyrazolones, NMR, TG, transition met-
als chelates
Introduction
Nitrosopyrazolones are widely used as analytical reagents. They are capable of form-
ing chelates with a number of transition metal ions [1–3]. The formed chelates are
characterized by their high stability resulting from the formation of six-membered
rings. 3-methyl-4-carboxy-2-pyrazolin-5-one and 1-phenyl-3-methyl-4-carboxy-2-
pyrazolin-5-one were screened for antifungal activity [4]. 4-nitroso-2-pyrazolin-
5-one derivatives had significant activity against Pyricularia oryzae [5, 6].
Complexation behaviour of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (LI),
*
Author for correspondence: E-mail: salatif_1@yahoo.com
1388–6150/2003/ $ 20.00
Akadémiai Kiadó, Budapest
© 2003 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

940
ABDEL-LATIF et al.: NITROSOPYRAZOLONES
oximidobenzotetronic acid (LII) and 4-nitroso-3-methyl-1-phenyl-2-pyrazolin-5-one
(LIII) each containing the same NO coordination group is reported [7] with some tran-
sition metal ions. Thermogravimetric data were used to evaluate the kinetic parame-
ters of the solid state reactions. LII and LIII complexes have a chelate ring and are
more stable. New complexes of CuL2 2H2O, CoL2 3H2O, MnL2 2H2O and
FeL3 2H2O, L=γ-L-glutamyl-5-(p-nitroanilide) were synthesized [8] and character-
ized by their spectral, magnetic and thermal properties. The thermal stabilities of the
synthesized complexes were examined in the temperature range 20–500°C. New
complexes of non-natural amino acid (p-iodo-phenylalanine) with divalent cobalt
and nickel ions have been synthesized [9]. The crystal structure belongs to
orthorhombic system. The first stage in the thermal decomposition process of the
complex shows the presence of water of crystallization. The mixed
2,4-bipyridine-oxalato complexes of Mn(II), Co(II), Ni(II) and Cu(II) have been pre-
pared and characterized [10]. Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) com-
plexes with 3-methylglutarates were prepared [11]. The complexes of 4,4’-bipyridine
adducts of Mn(II), Co(II), Ni(II) and Cu(II) monochloroacetate were prepared [12]
and characterized via the IR, electronic spectra, conductivity measurements and ther-
mal analyses. The thermal behaviour of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II),
Cd(II) and Pb(II) complexes of uracil were studied by TG, DTG and DTA in a dy-
namic nitrogen atmosphere [13]. The thermal decomposition of Co(II), Ni(II) and
Cu(II) complexes of 4-(3’-sulfonylazido-6’-methoxyphenylazo)-3-phenyl-3-methyl-
-2-pyrazolin-5-one were studied by thermogravimetry [14].
The present study deals with the preparation of Mn(II), Co(II), Ni(II), Cu(II) and
Zn(II) chelates with 3-methyl- and 3-phenyl-4-nitroso-5-pyrazolones. The chelates
obtained were characterized by elemental analysis, IR, proton NMR, TG, DTG, DTA
molar conductance and electronic spectra to throw some light on the bonds formed
and on their structures.
Experimental
All chemicals used in the present work were chemically pure, obtained from BDH chem-
icals. These include MnCl2 4H2O, CoCl2 6H2O, NiCl2 6H2O, CuCl2 2H2O and ZnCl2,
NH4OH, sodium nitrite; also the solvents used were ethanol, deuterated dimethyl
sulfoxide (d6-DMSO) and dimethyl formamide (DMF); ethylacetoacetate, ethyl-
benzoylacetate, hydrazine hydrate and sodium methoxide. 3-methyl-5-pyrazolone was
prepared as reported [15]; m.p. 222°C. 3-phenyl-5-pyrazolone was described by Fitton
[16]; m.p. 250°C.
3-methyl-4-nitroso-5-pyrazolone; m.p. 205°C and 3-phenyl-4-nitroso-5-pyrazo-
lone; m.p. 190°C ligands were prepared [17] as follows, the nitrosation reaction were
carried out by acidifying the cooled aqueous solution of 3-methyl- and
3-phenyl-5-pyrazolones (0.2 mol) at 0°C in sodium hydroxide solution containing
equivalent amount of sodium nitrite (0.2 mol) with hydrochloric acid. The precipi-
tated compounds were filtered off, washed several times with water and re-
crystallized from ethanol. The purity of these ligands were determined from the re-
J. Therm. Anal. Cal., 73, 2003

ABDEL-LATIF et al.: NITROSOPYRAZOLONES
941
sults of elemental analysis (Table 1), IR, 1H NMR. The resulting nitroso compounds
have the following general structure:
Scheme 1
The 1:1 and 1:2 chelates were prepared by mixing a hot alcoholic solution of the
ligands under investigation (1 or 2 mol) with the calculated (1 mol) of metal salt so-
lution. The reaction mixture was refluxed for 4 h. The pH of the solution was main-
tained at a value of 5.0–6.0 by the addition of dilute ammonia solution (1:10). The
solid product was dried on a steam bath with stirring, then filtered and washed several
times with ethanol till a colourless filtrate was obtained. The solid was dried by suc-
tion and finally kept in a vacuum desiccator.
The IR spectra were recorded on a Jasco FTIR spectrophotometer applying the
1
KBr disc technique. The H NMR spectra were measured using Varian Gemini
200–200 MHz NMR spectrometer and the spectra were recorded from 0–15 ppm us-
ing TMS as internal standard and dimethylsulfoxide (d6-DMSO) as the solvent. Ther-
mal analyses (TG, DTG and DTA) were obtained in a nitrogen atmosphere using a
type TGA 50 Shimadzu derivatograph thermal analyzer. The molar conductivities
were carried out using a Jenway conductivity meter 4310. The electronic spectra
were recorded using Jasco V-530 UV-Vis spectrophotometer.
Results and discussion
The results of elemental analysis (Table 1) are in good agreement with those calcu-
lated by the proposed formulae for 1:1 and 1:2 (M:L) solid chelates.
Infrared spectra
The IR spectral bands of all chelates display interesting changes that may give a rea-
sonable idea about the functional groups of these chelates. These changes are inter-
preted in relation to elemental analysis (Table 1), the results of thermogravimetric
analyses, 1H NMR, molar conductance and electronic spectra, in order to deduce the
structure of the solid chelates obtained. In the IR spectra of the chelates, the band ob-
served within the range 1338–1476 cm–1 [17] assigned to ν(N=O) in the free ligands
were shifted to lower wavenumber (1275–1383 cm–1) indicating coordination of the
NO group through its oxygen atom to the central metal ion. Also the band observed
within the range 1707–1713 cm–1 assigned to ν(C=O) in the free ligands were also
J. Therm. Anal. Cal., 73, 2003

Table 1 Analytical data of the ligands and their Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) chelates
C/%
found
H/%
found
N/%
found
M/%
found
Ligands and
complexes
m.p./
°C
Λm
M:L Colour
calcd.
35.29
48.00
22.23
27.99
21.82
27.67
21.84
27.68
19.75
27.31
21.21
27.17
calcd.
4.41
4.80
3.24
3.49
3.18
3.45
3.18
3.46
2.46
3.41
3.09
3.39
calcd.
30.00
18.60
19.45
24.49
19.09
24.21
19.11
24.22
17.28
23.89
18.55
23.77
calcd.
–
C4H5N3O2 1/2H2O (Ia)
C9H7N3O2 2H2O (Ib)
[Mn(Ia)(OH) H2O]
[Mn(Ia)2 2H2O]
–
–
yellow
yellow
205
190
320
325
347
343
35.0
47.4
22.3
28.2
22.1
28.5
21.9
27.8
19.9
27.5
21.6
27.7
4.2
4.8
3.7
3.8
3.5
4.1
3.1
3.5
2.5
3.6
3.0
3.7
30.2
18.5
19.1
24.6
19.1
24.6
19.2
24.3
17.4
23.9
18.4
23.8
–
–
–
–
–
1:1 pale brown
1:2 dark brown
1:1 brown
25.2
16.1
26.5
17.1
26.4
17.1
26.3
18.7
29.1
18.6
25.42
16.01
26.78
16.97
26.71
16.93
26.13
18.65
28.85
18.48
32.40
9.38
–
[Co(Ia)(OH) H2O]
[Co(Ia)2 2H2O]
1:2 brown
8.60
–
[Ni(Ia)(OH) H2O]
[Ni(Ia)2 2H2O]
1:1 greenish yellow 341
1:2 dark green
1:1 black
330
286
301
336
350
35.50
9.58
–
[Cu(Ia)(Cl) H2O]
[Cu(Ia)2 2H2O]
1:2 black
[Zn(Ia)(OH) H2O]
[Zn(Ia)2 2H2O]
1:1 yellow
1:2 yellow
8.76
9.59

Table 1 Continued
C/%
found
H/%
found
N/%
found
M/%
found
Ligands and
complexes
m.p./
°C
Λm
M:L Colour
calcd.
34.40
46.26
33.97
45.86
33.99
45.88
33.48
45.42
33.30
45.25
calcd.
4.14
3.42
4.08
3.39
4.09
3.39
4.03
3.36
4.00
3.37
calcd.
13.38
20.56
13.21
17.83
13.22
17.84
13.02
17.66
12.95
17.59
calcd.
17.48
11.75
18.52
12.50
18.47
12.47
19.68
13.35
20.13
13.68
[Mn(Ib)(OH)2 2H2O]
[Mn(Ib)2(OH)2]
1:1 greenish brown
1:2 greenish brown
1:1 brown
340
315
325
330
347
338
279
286
350
335
34.5
47.6
34.1
44.4
33.6
45.7
33.6
45.6
33.2
45.5
3.9
3.8
4.0
3.8
4.3
3.9
4.0
3.7
3.7
3.7
13.6
20.4
13.2
17.6
13.3
17.8
13.4
17.8
12.8
17.4
17.6
11.9
18.4
12.3
18.5
12.5
19.5
13.5
20.4
13.8
6.10
11.52
–
[Co(Ib)(OH)2 2H2O]
[Co(Ib)2(OH)2]
1:2 brown
13.00
–
[Ni(Ib)(OH)2 2H2O]
[Ni(Ib)2(OH)2]
1:1 pale brown
1:2 brown
10.52
–
[Cu(Ib)(OH)2 2H2O]
[Cu(Ib)2(OH)2]
1:1 dark brown
1:2 dark brown
1:1 yellow
21.9
8.50
17.83
[Zn(Ib)(OH)2 2H2O]
[Zn(Ib)2(OH)2]
1:2 yellow

944
ABDEL-LATIF et al.: NITROSOPYRAZOLONES
shifted to lower wavenumber (1620–1652 cm–1) indicating the involvement of the
(C=O) group in chelation. The strong band at 3524 cm–1 for Ia is assigned to ν(OH) of
the oxime, whereas that observed at 3550 cm–1 is assigned to water of crystallization
and the strong band observed at 1090 cm–1 is assigned to ν(N–O) [18]. For all investi-
gated chelates, the broad bands observed within the range (3232–3450 cm–1) were as-
signed to ν(OH) of coordination of water and OH– group which is present to neutral-
ize the charge on the metal ion [19]. The spectra of the metal chelates exhibit bands in
the range 453–545 cm–1 that may be assigned to ν(M–O) stretching frequency [20].
These bands are not observed in the spectra of the free ligands and are possibly due to
the formation of coordinate bond (M←O) or (M–O) [21].
Nuclear magnetic resonance spectra
Further support for the results obtained from the IR spectra is gained by considering
the changes in the 1H NMR spectra of the investigated chelates. The spectrum of the
Ia exhibits a singlet at 14.05 ppm which is assigned to the oxime H-atom =N–OH
which means that this ligand is involved in nitroso–oxime tautomer, such kind of
equilibrium may be represented as:
Scheme 2
A singlet observed at 2.22 ppm is assigned to the CH3 proton (integration curve
shows three H-atoms). The presence of this CH3 group which is an electron donating
group assists the formation of oxime tautomer by increasing the electron density on
the NO group, increasing its polarity. This facilitates the formation of =N–OH oxime
group since the oxygen atom is more electronegative than the nitrogen atom. A sin-
glet observed at 3.45 ppm is assigned to H-atoms of the water of crystallization (inte-
gration curve shows one H-atom, half water molecule). A singlet observed at
11.35 ppm is assigned to –NH H-atom (integration curve shows one H-atom) [19].
For Ib ligand a singlet observed at 3.47 ppm is assigned to water of crystallization (in-
tegration curve shows four H-atoms corresponding to two water molecules). The sig-
nals observed at 7.40–7.95 ppm are assigned to the aromatic H-atoms (integration
curve shows five H-atoms). A singlet observed at 11.91 ppm is assigned to –NH
H-atom (integration curve shows one H-atom) [19].
For Zn–Ia (1:2) chelate, a singlet observed at 2.23 ppm is assigned to CH3
H-atoms (integration curve shows six H-atoms). A singlet observed at 3.39 ppm is as-
signed to H-atoms of water of coordination (integration curve shows four H-atoms
corresponding to two water molecules). A singlet observed at 11.49 ppm is assigned
to –NH H-atom (integration curve shows two H-atoms). A singlet observed at
14.05 ppm corresponding to =N–OH in the spectra of the free ligand disappeared or
J. Therm. Anal. Cal., 73, 2003

ABDEL-LATIF et al.: NITROSOPYRAZOLONES
945
was not observed in the spectra of the chelate which means that the nitroso–oxime
tautomer is a center of chelation. For Zn–Ib (1:2) chelate, a singlet observed at
3.37 ppm is assigned to water of coordination (integration curve shows eight H-atoms
corresponding to four water molecules) two of these molecules being inside the coor-
dination sphere and the other two outside this sphere. The signals observed at
7.30–8.11 ppm are assigned to the aromatic H-atoms (integration curve shows
10 protons). A singlet observed at 11.97 ppm is assigned to –NH H-atom (integration
curve shows two H-atoms).
Thermogravimetric, derivative and differential thermal analysis
The aim of the thermal analysis is to obtain information concerning the thermal sta-
bility of the investigated chelates (Table 2), to decide whether the water molecules
are inside or outside the coordination sphere, and to suggest a general scheme for the
thermal decomposition of these chelates.
TG curves of Cu(II) chelates with the investigated ligands (1:1 and 1:2) were
carried out (Figs 1 and 2). The mass loss, measured from ambient temperature to
800°C at a rate of 10°C min–1, was used to calculate the number of coordinated water
molecules. The investigated chelates show no hygroscopic water or moisture within
the temperature range 25–100°C.
For the Cu–Ia (1:1) chelate, one water molecule is coordinated to the metal ion
and expelled within the temperature range 230–323°C [22] in addition to the loss of
C–CH3, N–NH and CO groups corresponding to the loss of 41.61% (calcd. 41.97%).
In the temperature range 388–673°C a mass loss of 25.49% is observed correspond-
ing to the formation of intermediate species through the decomposition of the organic
part with the loss of CN and Cl atom (calcd. 25.30%). At a temperature higher than
673°C and at the end of the process CuO was formed; the remainder is 30.89% (calcd.
31.70%). The data obtained are in good agreement with the calculated metal content
obtained by determination of the metal ions applying the method described by Mac-
donald [23] and the results of elemental analysis (Table 1).
For Cu–Ib (1:1) chelate, a mass loss occurred within the temperature range
214–324°C corresponding to the loss of 81.15% (calcd. 82.28%) for two coordinated
water molecules, two OH groups, one phenyl group, NO group, CO group, N–NH
and two carbon atoms which were oxidized by the atmospheric oxygen to CO2 [19].
After this temperature and in the range 324–800°C, the CuO residue was obtained
18.74% (calcd. 17.71%).
For Ni–Ia (1:2) chelate, a mass loss occurred within the temperature range
100–150°C corresponding to the loss of 10.12% (calcd. 10.38%) for two water mole-
cules and at the temperature range 150–254°C corresponding to a loss of 9.99%
(calcd. 9.65%) for two methyl groups. At a temperature range 254–350°C a loss of
73.62% (calcd. 73.38) corresponding to a loss of the organic part as intermediate spe-
cies. At high temperature more than 350°C and at the end of the process NiO is
formed, the remainder is 21.79 (calcd. 21.54).
J. Therm. Anal. Cal., 73, 2003

Table 2 Thermogravimetric analysis results of some metal(II)–nitrosopyrazolone chelates
Temperature/°C Mass loss/%
Chelate
Assignment
TG range of
thermal steps
DTA
DTG
275
found
calculated
[Cu(Ia)(Cl) H2O]
230–323
388–673
673–800
214–324
324–800
100–150
150–254
254–350
350–800
100–250
250–462
462–550
550–800
258, 410
41.61
25.49
30.89
81.15
18.74
10.12
9.99
41.97
25.30
31.70
82.28
17.71
10.38
9.65
C–CH3, N–NH, CO, H2O
CN, Cl
CuO
[Cu(Ib)(OH)2 2H2O]
[Ni(Ia)2 2H2O]
296, 446
297, 387
273
290
2H2O, 2C, 2OH, N–NH, C6H5, NO, CO
CuO
2H2O
2CH3
73.62
21.79
7.14
73.38
21.54
7.12
2CO, 2NO, 2N–NH, 4C
NiO
[Zn(Ib)2 (OH)2]
412, 501
420
2OH
51.41
14.99
17.03
51.88
14.75
17.40
2C6H5, 2N2, CO
NO
ZnO

ABDEL-LATIF et al.: NITROSOPYRAZOLONES
947
Fig. 1 Thermogravimetric, derivative and differential thermal analyses curves of
Cu(II)–Ia (1:1) and Cu(II)–Ib (1:1) chelates
Fig. 2 Thermogravimetric, derivative and differential thermal analyses curves of
Ni(II)–Ia (1:2) and Zn(II)–Ib (1:2) chelates
For Zn–Ib 1:2 chelate, a mass loss observed within the temperature range
100–250°C corresponding to a loss of 7.17% (calcd. 7.12) for two OH groups, at
higher temperature range 250–462°C a loss occurred are corresponding to a loss of
J. Therm. Anal. Cal., 73, 2003

948
ABDEL-LATIF et al.: NITROSOPYRAZOLONES
51.41% (calcd. 51.88) for two phenyl, two nitrogen molecules and one CO group. At
a temperature range 462–550°C a loss occurred corresponding to a loss of 14.99%
(calcd. 14.75) for NO group. At a temperature more than 550°C and at the end of the
process ZnO residue obtained is 17.40% (calcd. 17.03%).
The derivative thermogravimetric analyses curves show that peaks lie at tem-
peratures of 273 and 420 for the investigated Ni, Cu, Zn–Ia or Ib 1:1 and 1:2 chelates
indicating decomposition of the organic part at these temperatures.
From the DTA curves of the investigated Cu–Ia and Cu–Ib 1:1 chelates, two exo-
thermic peaks were observed within the range 258 and 446°C, whereas for Ni–Ia and
Zn–Ib 1:2 chelates, two exothermic peaks were observed within the temperature
range 297 and 501°C. At these temperatures the chelates are no longer stable and a
phase change in the crystal structure of the chelates are liable to occur i.e. crystallo-
Scheme 3
J. Therm. Anal. Cal., 73, 2003

ABDEL-LATIF et al.: NITROSOPYRAZOLONES
949
graphic phase transition. Above this temperature decomposition and combustion be-
gins leaving a final residue of the metal oxide.
Molar conductivity measurements
The molar conductivity values of 1 mM in DMF of the given chelates show that the
investigated chelates are neutral in nature since the values obtained are
6.10–35.5 ohm–1 cm2 mol–1. These values were small to account for ionic chelates of
the investigated divalent metal ions. These low conductivity values may be attributed
to the coordination of chloride ions, if present, rather than the ionic association to the
metal ions during chelate formation. This directly supports the fact that all of the in-
vestigated chelates are non-ionic in nature.
Electronic absorption spectra
The electronic spectra of the free ligands and some of their chelates were recorded in
DMF. In the free ligands the C.T. band appears at 352 and 371 nm for Ia and Ib, re-
spectively. A shift to higher wavelength is observed on complex formation. This is at-
tributed to the (M→L) charge transfer spectra (C.T.). In all of the spectra of the pre-
pared chelates a band of low intensity is observed at 460 and 458 nm for Mn and Co
chelates with Ia (1:2); at 458 nm for Mn:Ib (1:1); 460, 458 and 458 nm for Co, Ni and
Zn with Ib, respectively. This may be ascribed to d–d transition within the metal ion
indicating the presence of the metal ions in chelate formation.
Based on the above results the structure of the 1:1 and 1:2 (M:L) chelates formed
between the metal ion and the ligands can be represented as follows in Scheme 3.
Conclusions
Based on the data obtained from elemental analysis, IR, 1H NMR electronic absorp-
tion spectra, thermal analyses and molar conductivities measurements, the chelates of
Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) with Ia and Ib ligands may be formulated,
where bonding in the case 1:1 and 1:2 chelates are formed through coordination with
the oxygen of the carbonyl group and the oxygen of the nitroso–oxime tautomer. The
chelates prepared contain water of coordination in their coordination sphere. Ib acts
as neutral bidentate ligand whereas Ia acts as monobasic bidentate. The solid chelates
prepared behave as non-electrolytes in DMF solution. The electronic spectra of the
free ligands exhibit a C.T. band at 352 and 371 nm for Ia and Ib, respectively. A shift
to higher wavelength is observed on complex formation may be attributed to M→L
charge transfer spectra. The bands observed at higher wavelengths which are not ob-
served in the spectra of the free ligands may be ascribed to d–d electronic transition
within the metal ions. The coordination numbers of the obtained chelates using Ia are
four on applying the mole ratio 1:1 and six on using 1:2 mole ratio. In case of using
the ligand Ib the coordination number is six in both cases.
J. Therm. Anal. Cal., 73, 2003

950
ABDEL-LATIF et al.: NITROSOPYRAZOLONES
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