Thermal studies on nickel(II) 4-iodopyrazole complexes

Article abstract of DOI:10.1007/s10973-006-7865-y

This work describes the synthesis, IR and UV-Vis spectroscopic characterization as well the thermal behavior of the [NiCl₂(HIPz) ₄]·C₃H₆O (1), [Ni(H₂O) ₂(HIPz)₄](NO₃)<

Full text of DOI:10.1007/s10973-006-7865-y

Journal of Thermal Analysis and Calorimetry, Vol. 87 (2007) 3, 797–800
THERMAL STUDIES ON NICKEL(II) 4-IODOPYRAZOLE COMPLEXES
1
P. M. Takahashi , Regina C. G. Frem , A. V. G. Netto , A. E. Mauro and J. R. Matos
1*
1
1
2
1
Instituto de Química de Araraquara, UNESP, C.P. 355, 14801-970 Araraquara-SP, Brazil
2
Instituto de Química, USP, SP, S±o Paulo-SP, Brazil
This work describes the synthesis, IR and UV-Vis spectroscopic characterization as well the thermal behavior of the
NiCl (HIPz) O (1), [Ni(H O) (HIPz) ](NO (2), [Ni(NCS) (HIPz) ] (3) and [Ni(N (HIPz) ] (4) (HIPz=4-iodopyrazole)
]⋅C
[
2
4
3
H
6
2
2
4
3
)
2
2
4
3
)
2
4
pyrazolyl complexes. TG experiments reveal that the compounds 1–4 undergo thermal decomposition in three or four mass loss
steps yielding NiO as final residue, which was identified by X-ray powder diffraction.
Keywords: DSC, 4-iodopyrazole, nickel(II), pseudohalides, TG
Introduction
of NiCl ⋅6H O, in 4:1 water/acetone mixture. After
2
2
stirring for 2 h a blue solution was formed, which was
slowly evaporated yielding blue crystals. The crystal-
line solid was isolated by filtration, washed with ace-
tone and dried under vacuum. The yield was 70%.
[Ni(H O) (HIPz) ](NO ) (2) complex was ob-
The versatility of coordination modes of pyrazolyl
ligands together with the potential uses of their com-
plexes as phosphorescent materials [1, 2], CVD
source reagents [3], liquid crystals [4], antimicrobial
2
2
4
3 2
[
5] and antitumoral drugs [6, 7] is the subject of in-
tained by the addition of 273 mg (1.41 mmol)
of 4-iodopyrazole to an aqueous solution of
Ni(NO ) ⋅6H O (100 mg; 0.344 mmol). After 2 h of
stirring a blue solution was formed. Blue crystals ob-
tained after the solvent evaporation were isolated by
filtration, washed with acetone and dried under vac-
uum a 50% of yield was obtained.
tense research. Particularly, Ni(II) pyrazolyl com-
plexes have attracted considerable interest mainly due
to their catalytic activities [8, 9] as well their unusual
supramolecular architectures [10].
3
2
2
As a part of our investigations on the supramo-
lecular and coordination chemistry of transition metal
complexes containing N-based ligands and
pseudohalides [11–17], we report herein the synthe-
sis, spectroscopic characterization and the thermal
The [Ni(NCS) (HIPz) ] (3) compound was syn-
2 4
thesized as follows: to a solution of NiCl ⋅6H O
2
2
(100 mg; 0.421 mmol) in 4:1 water/acetone NaSCN
(72 mg; 0.888 mmol) in 2 mL of water was dropwise
added. After 20 min, 4-iodopyrazole (335 mg,
1.73 mmol) dissolved in 5 mL of acetone was added af-
fording a purple suspension. The stirring was main-
tained for 2 h and the compound was isolated by filtra-
tion washed with acetone and dried under vacuum with
a yield of 70%.
study on the complexes [NiCl
2
(HIPz)
4
]⋅C
H O (1),
3 6
[
Ni(H O) (HIPz) ](NO ) (2), [Ni(NCS) (HIPz) ] (3)
2 2 4 3 2 4
2
and [Ni(N ) (HIPz) ] (4) (HIPz=4-iodopyrazole)
3 2 4
(
Scheme 1).
[Ni(N ) (HdmPz) ] (4) complex was prepared fol-
3 2 4
lowing the procedure: to a deep green water/acetone (4:1)
solution of NiCl ⋅6H O (100 mg; 0.421 mmol), NaN
2
2
3
(57 mg; 0.877 mmol) in 2 mL of water was added. A blue
suspension was formed after the addition of 4-iodo-
pyrazole (335 mg; 1.73 mmol) dissolved in 5 mL of ace-
tone. The stirring was maintained for 2 h and the com-
pound was isolated by filtration, washed with acetone and
dried under vacuum. Yield was 60%.
Scheme 1
Experimental
Preparation of the complexes
NiCl (HIPz) ]⋅C H O (1) was prepared by the addi-
tion of 335 mg (1.73 mmol) of 4-iodopyrazole to a
deep green solution containing 100 mg (0.421 mmol)
Instrumentation
[
2
4
3
6
Elemental analyses of carbon, nitrogen and hydrogen
were performed on a CE Instruments, model
*
Author for correspondence: rcgfrem@iq.unesp.br
1
388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
©
2007 Akadémiai Kiadó, Budapest

TAKAHASHI et al.
–1
EA 1110 – CHNS-O microanalyser. Infrared spectra
were recorded on a Nicolet FTIR-Impact 400 spectro-
modes to lower wavenumbers (1520–1506 cm ) when
–1
compared to the free ligand (1533 cm ) [11–13]. IR
–
1
photometer in the spectral range of 4000–400 cm
using KBr pellets. UV-Vis spectra were obtained on a
PerkinElmer Lambda 14P spectrophotometer, in
experiments also revealed the presence of acetone lat-
tice in 1 by the appearance of the typical ν band
CO
–1
at 1736 cm . The presence of coordinated water mole-
–
3
–1
the 190–1100 nm range using 5⋅10 mol L ethanol
solutions. Conductivity measurements were perfomed
cules in 2 was detected by their characteristic absorp-
–1
tions at 3400 (νOH), 1637 (δHOH) and 814 (ρ
) cm .
r(H2 O)
–
3
–1
–1
at room temperature in 10 mol L methanol solu-
tions employing a Digimed DM-31 conductometer.
TG and DSC experiments were carried out using a
Shimadzu system model TGA-50 and DSC-50, respec-
tively. The TG curves were recorded in flowing dry syn-
An intense band centered at 1382 cm (νas(ONO)) in the
IR spectrum of 2 strongly suggests the presence of
ionic nitrate [19]. In fact, conductivity value of
–1
227 μS cm in methanol for 2 is in agreement
with 1:2 electrolytes [20]. In the spectra of 3 and 4 the
terminal coordination of the pseudohalides was evi-
denced by the appearance of intense and sharp bands
–1
thetic air (100 mL min ) up to 900°C at heating rate of
–1
20°C min in platinum sample holders. With the same
–1
–1
heating rate was applied in the DSC experiments up
to 500°C using aluminum sample holders. X-ray pow-
der diffractograms of the residues were obtained using a
Siemens D-5000 diffractometer equipped with a propor-
tional counter and pulse height discriminator. The
at 2082–2067 cm (νas(NCS)) and 2063 cm (νas(NNN)),
respectively [19].
UV-Vis studies
Bragg–Bretano arrangement was adopted using CuK
α
The electron absorption data of 1–4 as well their attri-
radiation (λ=1.541 ) and setting of 34 kV and 20 mA.
The peaks were identified using PDF base [18].
butions are listed in Table 2. In the spectra bands at
3
3
ca. 384–400 nm { A → T (P)}, 618–730 nm
2
3 3 3 3
g
1g
{
A → T (F)} and 1001–1075 nm { A → T (F)}
2
g
1g
2g
2g
association to spin-allowed ligand field transitions
were observed, which is typical for Ni(II) octahedral
Results and discussion
8
d electron systems [21].
The reactions involving nickel(II) salts as precursors
carried out under mild conditions afforded new and
air-stable coordination compounds whose analytical
data (Table 1) agree well with the proposed formulae.
Thermoanalytical studies
TG and DSC curves for 1–4 complexes are illustrated
in Fig. 1. Table 3 lists the results of the thermal inves-
tigations of these compounds together with the as-
signments of each decomposition stage based on mass
calculation. It is worth mentioning that the groups in-
dicated at the right column of the Table 3 do not cor-
respond necessarily to the gaseous final products of
decomposition. The TG curves showed that the ther-
Infrared spectra
The neutral monodentate coordination of the pyrazolyl
ligand in 1–4 was evidenced by the presence of intense
–1
ν
the bands associated to ring breathing vibrational
NH bands at ca. 3400–3270 cm as well by the shift of
Table 1 Melting points (°C) and analytical data of the nickel(II) compounds
Carbon/% Nitrogen/%
Hydrogen/%
Complex
m.p./°C
found
calc.
found
calc.
found
calc.
1
2
3
4
210 dec.
102–103
170 dec.
134 dec.
18.83
14.80
17.55
15.35
18.70
14.49
17.69
15.69
11.57
13.48
14.33
21.18
11.63
14.08
14.73
21.35
1.99
1.56
1.29
1.24
1.88
1.62
1.27
1.32
Table 2 Ligand field transitions in nickel(II) complexes
λ/nm
Complex
3
3
–1
–1
3
3
–1
–1
3
3
–1
–1
A2g→ T1g(P)
ε/M cm
A2g→ T1g(F)
ε/M cm
A2g→ T2g(F)
ε/M cm
1
2
3
4
400
396
393
384
11.3
31.2
15.4
51.2
671–730
665–728
653–729
618
4.3
14.2
6.8
1075
–
2.9
–
1037
1001
6.8
10.7
22.4
798
J. Therm. Anal. Cal., 87, 2007

NICKEL(II) 4-IODOPYRAZOLE COMPLEXES
Table 3 Thermal analysis data for nickel(II) compounds
Δm/%
DSC peaks/°C
Complex
Step
ΔT/°C
Assignment
obt.
calc.
endo
84
exo
1
40–121
121–277
277–312
312–636
–7.39
–43.13
–23.13
–18.46
7.89
–6.03
–42.27
–24.16
–19.79
7.75
–
–C
–2.10HIPz
–1.20HIPz
–0.70HIPz, –2Cl , +0.5O
NiO
–2H
–1.25HIPz
3 6
H O
2
139, 236
–
–
–
1
3
4
280
–
–
2
residue
1
85–280
280–452
452–601
–49.64
–24.93
–18.27
7.16
–50.43
–24.38
–17.68
7.51
94
–
177, 195
2
O, –2.40HIPz
2
3
–
–
2
3
4
–
–0.35HIPz, –2NO , +0.5O
–
2
3
residue
NiO
1
136–254
254–484
484–607
607–705
–48.24
–26.63
–14.97
–2.64
7.52
–48.96
–26.52
–14.97
–1.69
7.86
215
268
–
–
–
–
–
–2.40HIPz
–1.30HIPz
–
–0.30HIPz, –NCS , –CN
2
–
3
4
2–
–
–S , +0.5O
2
residue
NiO
1
92–302
302–423
423–497
–38.52
–41.00
–11.91
8.57
–38.00
–42.23
–11.64
8.13
177
–
–
386
–
–1.80HIPz
–2HIPz
–
–0.2HIPz, –2N , +0.5O
2
3
–
2
3
residue
NiO
Fig. 1 — – TG and ⋅⋅⋅ – DSC curves for the complexes 1–4
mal degradation pattern of 1–4 consists of the gradual
elimination of the 4-iodopyrazolyl ligands during the
initial decomposition steps. For 1, 2 and 4 complexes
the degradation of the anionic groups of the remain-
Conclusions
This work describes the synthesis, spectroscopic char-
acterization and thermal studies of the new nickel(II)
pyrazolyl complexes [NiCl (HIPz) (1),
]⋅C
[Ni(H O) (HIPz) ](NO (2), [Ni(NCS) (HIPz) ] (3)
and [Ni(N (HIPz) ] (4). From the inspection of TG
curves of the neutral [NiX (HIPz) ] complexes
{X=Cl (1); NCS (3); NNN (4)}, it is noticed that the
stability varies according to the anionic groups follow-
ing HIPz ligands and the uptake of O occur in the last
2
2
4
H O
3 6
mass loss affording NiO as a final residue
2
2
4
3
)
2
2
4
(
ASTM 78-0643) [10]. With regard to the thermal be-
3
)
2
4
havior of 3, NiS (ASTM 77-1624) [18] is formed after
the decomposition of the ligands. A further increase
of temperature up to 705°C results in the last mass
loss characterized by the conversion of NiS to NiO
2
4
–
–
–
–
–
–
ing the NCS >Cl >NNN order. The lowest thermal
stability of 4 is probably ascribed to the known explo-
sive nature of inorganic azides [22].
(
ASTM 78-0643) [18]. The DSC curves of 1–4 show
a series of signals associated to endothermic and exo-
thermic decomposition processes. According to the
DSC curve of 1 (Fig. 1), the lattice acetone is lost
at 84°C, yielding [NiCl (HIPz) ] in its anhydrous
2 4
form, which is thermally stable up to 121°C.
J. Therm. Anal. Cal., 87, 2007
799

TAKAHASHI et al.
Acknowledgements
11 A. V. G. Netto, A. M. Santana, A. E. Mauro,
R. C. G. Frem, E. T. de Almeida, M. S. Crespi and
H. E. Zorel Jr., J. Therm. Anal. Cal., 79 (2005) 339.
2 P. M. Takahashi, A. V. G. Netto, A. E. Mauro and
R. C. G. Frem, J. Therm. Anal. Cal., 79 (2005) 335.
3 A. V. G. Netto, P. M. Takahashi, R. C. G. Frem,
A. E. Mauro and H. E. Zorel Jr., J. Anal. Appl. Pyrolysis,
We thank the CNPq, CAPES, FAPESP and FINEP for finan-
cial support.
1
1
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DOI: 10.1007/s10973-006-7865-y
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J. Therm. Anal. Cal., 87, 2007