Solid-state kinetics of thermal release of pyridine and morphological study of [Ni(ampy)2(NO3)2]; ampy = 2-picolylamine

Article abstract of DOI:10.1016/j.tca.2006.06.015

The re-examined X-ray crystal structure of [Ni(ampy)₂(NO₃)₂]; ampy = 2-picolylamine belongs to monoclinic P2₁/c space group having, a = 8.73510(10) ?, b = 8.73690(10) ?, c = 10.26480(10) ? and β = 101.5610(10)°. The microscopic feature calcined at 600 °C displays a thread type fiber of NiO. The thermogravimetric analysis shows that the thermal decomposition occurs in three steps where the removal of ligand occurs in an exothermic process. The activation energy was estimated with both iso-conversional and multivariate non-linear-regression methods. Friedman method agrees with a first-order kinetics having activation energy E and logarithmic pre-exponential factor A, 41 ± 1 kJ mol^-1 and 2.54, respectively. Multivariate non-linear-regression methods show expanded Prout-Tompkins Bna model is the best fit model with highest correlation coefficient 0.999998 followed by Cn which corresponds to the nth order reaction with auto catalysis through the reactants. The calculated apparent activation energies are consistent with iso-conversional methods. The corresponding function f(α), activation energy E and logarithmic pre-exponential factor A of Bna model, are (1 - α)^2.08α^1.0236E-3, 42 kJ mol^-1and 3.12, respectively, and those of Cn model are (1 - α)^2.07(1 + 0.0144α), 42 kJ mol^-1 and 3.11, respectively. The calculated rate constant and half-life time from iso-concentration plot are 2.381 × 10^-3 s^-1 and 291 s, respectively.

Full text of DOI:10.1016/j.tca.2006.06.015

Thermochimica Acta 448 (2006) 1–6
Solid-state kinetics of thermal release of pyridine and morphological
study of [Ni(ampy) (NO ) ]; ampy = 2-picolylamine
2
3 2
∗
Sumanta Kumar Padhi
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India
Received 24 April 2006; received in revised form 19 June 2006; accepted 21 June 2006
Available online 27 June 2006
Abstract
The re-examined X-ray crystal structure of [Ni(ampy)
a = 8.73510(10) A, b = 8.73690(10) A, c = 10.26480(10) A and β = 101.5610(10) . The microscopic feature calcined at 600 C displays a thread
type fiber of NiO. The thermogravimetric analysis shows that the thermal decomposition occurs in three steps where the removal of ligand occurs in
an exothermic process. The activation energy was estimated with both iso-conversional and multivariate non-linear-regression methods. Friedman
2
(NO
3
)
2
]; ampy = 2-picolylamine belongs to monoclinic P2
1
/c space group having,
◦
◦
˚
˚
˚
−
1
method agrees with a first-order kinetics having activation energy E and logarithmic pre-exponential factor A, 41 ± 1 kJ mol and 2.54, respectively.
Multivariate non-linear-regression methods show expanded Prout–Tompkins Bna model is the best fit model with highest correlation coefficient
0
.999998 followed by Cn which corresponds to the nth order reaction with auto catalysis through the reactants. The calculated apparent activation
energies are consistent with iso-conversional methods. The corresponding function f(α), activation energy E and logarithmic pre-exponential factor
2
.08 1.0236E−3
−1
2.07
−1
A of Bna model, are (1 − α)
.11, respectively. The calculated rate constant and half-life time from iso-concentration plot are 2.381 × 10
2006 Published by Elsevier B.V.
α
, 42 kJ mol and 3.12, respectively, and those of Cn model are (1 − α) (1 + 0.0144α), 42 kJ mol and
–
3
−1
s
3
©
and 291 s, respectively.
Keywords: 2-Picolylamine complex of nickel(II)nitrate; X-ray crystallography; Morphology of the complex; Kinetics of thermal decomposition; Iso-conversional
method; Multivariate non-linear-regression
1
. Introduction
beingwidelystudiedhere. Combinationofbothiso-conversional
and multivariate non-linear-regression can provide most reason-
able models than the model-fitting methods.
The design and synthesis of nickel(II)ampy complexes, has
been extensively studied over past few decades [1–3]. The util-
ity of such complexes as molecule-based magnets and photo-
magnetic properties are widely reported. The presence of fer-
romagnetic and antiferromagnetic interactions in 1D, 2D and
2
. Experimental
2.1. Materials
3
D bimetallic complexes obtained through self-assembly pro-
2+/3+
2+
cesses having M
–Ni pairs are the exciting one in modern
[Ni(ampy)2(NO3)2]; (ampy = 2-picolylamine) was synthe-
chemistry [1]. Magnetic phase transitions at lower temperatures
in different molecular architecture of such molecules are most
impulsive.
This application oriented field stems our interest through a
close look towards the thermal decomposition of [Ni(ampy)2
sized by the reported procedure [1]. An ORTEP (30% probabil-
ity) diagram is shown in Fig. 1 [4]. Nickel(II)nitrate hexahydrate
was purchased from Merck India Ltd. 2-Picolylamine was pur-
chased from M/S Aldrich, USA. All the chemicals and solvents
(reagent grade) were used as received without further purifica-
(
NO3)2] at static nitrogen atmosphere. In this article we report
tions.
the thermal and morphological study of [Ni(ampy)2(NO3)2].
Iso-conversional, Non-isothermal and iso-thermal methods are
2.2. Instrumentation and methods
FT-IR spectra of range 4000–400 cm 1 were recorded using
−
∗
Tel.: +91 361 2582345; fax: +91 361 2690762.
E-mail address: sumanta@iitg.ernet.in.
Perkin-Elmer Spectrum One in KBr disc. SEM studies were
0
040-6031/$ – see front matter © 2006 Published by Elsevier B.V.
doi:10.1016/j.tca.2006.06.015

2
S.K. Padhi / Thermochimica Acta 448 (2006) 1–6
2
.2.2. Thermogravimetry (TG) measurements
The thermal behaviors including thermal decomposition tem-
perature were determined by a computer controlled METTLER
e
e
TOLEDO STAR system of module TGA/SDTA851 under
static nitrogen atmosphere. Prior to record the data the instru-
ment was properly calibrated and sensor used here is RTypS-
DTA. Decompositions were recorded for the sample upon plat-
inum pan. Onset temperature of DTG curve used to evaluate the
onset decomposition temperature, which estimates the thermal
stability of the sample. TG data were recorded at a heating rate
◦
−1
◦
of 10 C min from 25 to 700 C under static nitrogen atmo-
sphere.
2
.2.3. Differential scanning calorimetry (DSC)
Fig. 1. ORTEP (30% probability) of [Ni(ampy)2(NO3)2].
measurements
The thermal behaviors were studied by a computer controlled
e
e
METTLERTOLEDOSTAR systemofmoduleDSC821 under
static nitrogen atmosphere. Prior to recording the data, the tem-
perature and energy of the instrument were calibrated with
standard indium and ceramic sensor FRS5. A 70 ␮L aluminum
reference pan was used and the data were recorded from 25 to
done by Variable Pressure Digital Scanning Electron Micro-
scope (model LEO 1430 VP) with EDS for X-ray Microanalysis.
2
.2.1. X-ray crystallography
Single crystals X-ray crystallographic data were collected
◦
◦
−1
6
00 C at heating rates of 5, 10, 15, 20 and 25 C min .
using Bruker SMART APEX-CCD diffractometer with Mo
˚
K␣ radiation (λ = 0.71073 A). The intensity data were cor-
2.2.4. Methods
rected for Lorentz and polarization effects and empirical absorp-
tion corrections was applied using SAINT program [5]. The
structure was solved by direct methods using SHELXS-97
and non-hydrogen atoms located from the difference Fourier
maps were refined anisotropically by full-matrix least-squares
Iso-conversional methods and Multivariate non-linear-
regression methods were performed by Netzsch TA4 thermoki-
netics software.
2
3
3
3
. Results and discussion
on F using SHELXL-97 [6]. The hydrogen atoms were
included in the calculated positions and refined isotropically
using a riding model. Table 1 shows the crystal data and
parameters.
.1. Proposed mechanism of thermal decomposition
.1.1. FT-IR and morphological study
The FT-IR spectra (Fig. 2), shows both ν(NH2)as and ν(NH2)s
which is present at 3341 and 3288 cm vanishes with the
Table 1
Crystal data and refinement
−1
−
1
increase of temperature [7,8]. The aromatic region at 1610 cm
Formula
Mr
Crystal color, habit
T (K)
Wave length ( A˚ )
Crystal system
Space group
a ( A˚ )
C12H16N6O6Ni
394.99
Blue, blocks
296 (2)
0.71073
Monoclinic
P21/c
8.73510 (10)
8.73690 (10)
10.26480 (10)
101.5610 (10)
767.492 (15)
2
◦
gradually becomes absentfrom the original peakafter280 C. At
40 C, the removal of pyridine is not completed as it shows the
presence of aromatic peak at 1596 cm . At 600 C ν(Ni–O)str
◦
3
−
1
◦
−
1
appears at 531 cm
.
b ( A˚ )
c ( A˚ )
◦
β ( )
V ( A˚ )
3
Z
F(0 0 0)
404
1.709
1.310
1.068
2.03
5.88
ρcalc (g cm 3)
−
−
1
µ (mm
)
2
a
GOF on F
b
R1 (%)
wR2c (%)
ꢀ
1/2
2
a
GOF = [ [w(F 02 − F ) ]/M − N]
2
(M = number of reflections, N =
c
number of parameters refined).
ꢀ
ꢀ
b
R1 =
||F0| − |Fc||/
|F0|.
ꢀ
ꢀ
2
2
2
0
c
2
2
wR2 = [ [w(F − F ) ]/ [w(F ) ]].
2 3 2
Fig. 2. FT-IR spectra observed at different temperatures for [Ni(ampy) (NO ) ].
0
c

S.K. Padhi / Thermochimica Acta 448 (2006) 1–6
3
The morphological evolution of powdered [Ni(ampy)2
(
2
NO3)2] was examined by SEM (Fig. 3) after calcinations. At
80 C (Fig. 3A) the microscopic feature shows a porous metal-
◦
lic surface resulting from the elimination of NO(g). A jelly type
◦
fiber started to form (Fig. 3B) at 340 C where pyridine gets sub-
limed, contains2.16%(byweight)N-contentinthecomposition.
◦
Complete removal of pyridine at 430 C shows a layered fiber
(Fig. 3C). In (Fig. 3D) the morphological view shows thread
type fibers of NiO.
3
.1.2. Thermal decomposition
The TG, DTG curves in Fig. 4 displays the weight loss in
three distinct steps. Removal of two moles of NO(g) (15.09%,
◦
ca. 15.18%) occurs in step I at DTG midpoint 217 C within
◦
the temperature range 154–285 C. In step II two moles of
pyridine (40.63%, ca. 40.05%) gets removed at DTG mid-
◦
◦
point 309 C within the temperature range 285–345 C. Step III
shows the formation of volatile components leaving behind one
◦
mole of NiO (19.11%, ca. 18.91%) as residual part at 588 C.
The thermal decompositions are provided in the following
equations:
ꢀ
•
•
•
Step I [Ni(ampy) (NO3) ]−→ 2NO ↑ +Residue (R)
2
2
ꢀ
Step II R−→ 2Py + Residue (R1)
ꢀ
Step III R1−→ Product
+ NiO(s)
(
volatile)
The DSC curve (Fig. 5) indicates that the removal of both
NO(g) and 2-picolylamine occurs through exothermic processes
◦
in the range of 180–375 C. The fractional DSC profile begins
◦
with an endothermic up to 150 C and irreversible exothermic
ending.
3
3
.2. Kinetics of thermal decomposition
.2.1. Iso-conversional methods
In iso-conversional method it is assumed that a degree of con-
version α can be explicitly assigned to each point of the reaction
curve. The kinetic analysis was considered for the elimination of
pyridine in Step II, taking into account the DSC curves within
◦
temperature span 285–345 C, utilizing Friedman and ASTM
E698 methods [9–16].
3
.2.1.1. Friedman method. The convergence of the activation
energy values obtained by means of a differential method like
the Friedman method with those resulting from using integral
methods with integration over small ranges of reaction progress
α, comes from the fundamentals of the differential and integral
calculus [9–14]. Friedman analysis follows the mathematical
equation:
E
ln(dα/dt)|α−α = ln A −
+ ln f(αj)
j
RTkj
Fig. 3. SEM morphological aspects for [Ni(ampy)2(NO3)2] calcined at: (A)
2
where E is the activation energy, A the pre-exponential factor;
R corresponds to universal gas constant. The kinetic parameters
wereextractedfromtheexperimentalenthalpychangedatausing
◦ ◦ ◦ ◦
80 C, (B) 340 C, (C) 430 C and (D) 600 C.

4
S.K. Padhi / Thermochimica Acta 448 (2006) 1–6
Fig. 6. Logarithmic rate as function of reciprocal of temperature by Friedman
method.
where α is the general variable reactiondegree, ꢀHpart the partial
−
1
−1
area (J g ), and ꢀHtot is the total peak area (J g ). Fig. 6
shows the logarithmic conversion rate as function of reciprocal
of temperature by this method. In Fig. 6 the steeper slope of
the experimental curves versus the iso-conversion lines in the
range of 1000/T > 2.70 is a finite indication of the presence of an
auto-catalytically activated initial reaction. The analysis curve
in Fig. 7 almost remains constant from the fractional reaction
progress 0.1 to 0.9 which indicating a single step reaction.
Here the plot simulates to first-order kinetics. The analysis
plot (Fig. 7) extrapolates E and A as function of α. Friedman
analysisrevealsthattheaverageactivationenergyofthecomplex
◦
−1
.
Fig. 4. TG/DTG plot of [Ni(ampy)2(NO3)2] at a heating rate 10 C min
−
1
[
Ni(ampy)2(NO3)2] is 41 ± 1 kJ mol and the corresponding
−1
average logarithmic pre-exponential factor (log A (s )) is 2.54.
3.2.1.2. ASTM method. Kissinger introduced the equation
where pre-exponential factor is evaluated on assumption of a
first-order reaction [15,16]:
◦
−1
.
Fig. 5. DSC curves at heating rates 5–25 C min
β
E
ln
= −
Tj,m
RTj,m
following transformation (Table 2):
ASTM E698 method utilizes Kissinger’s plot where a reac-
ꢀ
Hpart
α =
tion of first-order results from the displacement of the max-
imum temperatures of DSC curves. Kissinger’s plot shows a
straight line with slope (−E/R) and Tj,m is the maximum tem-
ꢀ
Htot
Table 2
Arrhenius parameters in Friedman analysis
α
Friedman analysis
E (kJ mol 1)
−
−1
log A (s )
0
0
0
0
0
0
0
0
0
0
0
0
0
.02
43.13 ± 0.04
42.20 ± 0.09
42.37 ± 0.07
42.37 ± 0.10
42.38 ± 0.08
42.40 ± 0.01
42.43 ± 0.10
42.46 ± 0.07
42.52 ± 0.08
42.67 ± 0.10
43.37 ± 0.28
45.20 ± 0.13
24.82 ± 0.68
3.27
3.08
3.09
3.03
2.97
2.90
2.82
2.71
2.59
2.41
2.16
2.00
0.00
.05
.10
.20
.30
.40
.50
.60
.70
.80
.90
.95
.98
Fig. 7. E and A in Friedman method. Symbols are experimental along with
simulated lines.
Average
41.41 ± 0.14
2.54

S.K. Padhi / Thermochimica Acta 448 (2006) 1–6
5
sponds to the nth order reaction with auto catalysis [f(α) in Cn
n
is (1 − α) (1 + Kcatα)] through the reactants having Fexp, F
crit
1
.00 and 1.10, respectively. The function f(α) in Bna and Cn are
2
.08 1.0236E−3
2.07
(1 − α)
α
and (1 − α) (1 + 0.0144α), respectively.
Three-dimensional Jander’s diffusion model (D3), the activa-
tion energy slightly deviates than the other mentioned models
in Table 3, which is very difficult to predict with the similar
changes of α with respect to both time and temperature.
3.2.3. Determination of half-life period and rate constant
Based on the predictions of Fn model, reaction was consid-
◦
ered for 25–600 C. DSC curves calculated within the range of
temperature for the decomposition process, this generates the
change in concentration of reaction progress. These curves with
degree of conversion as a parameter indicates an exponential
progress in percentage of conversion with time and tempera-
ture. For clarification, thermoanalytical isothermal predictions
Fig. 8. ASTM plot of [Ni(ampy)2(NO3)2].
perature. The logarithms of heating rates were plotted over the
maximum reciprocal temperatures of DSC curves, where the
obtained slope gives the activation energy. The pre-exponential
factor was obtained on the assumption of a first-order reaction
◦
are investigated in a narrow temperature range 271–320 C. The
◦
conversion shows a maximum at 320 C. Both the results were
taken into account where, the 50% of concentrations changes
2
A = βE/RT exp (E/RTj,m). Tj,m was determined utilizing
◦
j,m
the smoothed numerical derivatives of dα/dT. The ASTM anal-
at 4.85 min, at about 315 C. Iso-concentration plot dynamic
reactants reveal a sigmoidal increase in product concentration
to attain a saturation limit at 18.6 min. Rate constant was cal-
culated from the first-order kinetic equation, k = 0.693/t1/2. The
ysis plot (Fig. 8) of [Ni(ampy)2(NO3)2] shows the activation
−
1
energy of the complex is 46 ± 2 kJ mol and the correspond-
−
1
ing average logarithmic pre-exponential factor (log A (s )) is
calculatedrateconstantandhalf-lifetimefromiso-concentration
3
.44.
−3 −1
and 291 s, respectively.
plot are 2.381 × 10
s
3
.2.2. Determination of kinetic model of thermal
4. Conclusion
decomposition
Multivariate non-linear-regression (Netzsch TA4 thermoki-
netics) was applied to determine the most probable kinetic
model. The software module Netzsch TA4 thermokinetics
numerically solves the relevant differential equations and the
parametersofthedifferentialequationsareiterativelyoptimized.
Here all the commonly used models were utilized for the deter-
mination of activation energy [17–19]. Combination of both
iso-conversional and multivariate non-linear-regression can pro-
vide most reasonable models than the model-fitting methods.
The mentioned models listed in Table 3 are based on correlation
coefficient and the “goodness of fit” from a statistical point of
view, simulates to a first-order reaction path A → B. The best
model imaged from the correlation coefficient is Bna which
Solid-state kinetics of monoclinic [Ni(ampy)2(NO3)2] com-
plex for thermal release of pyridine, was investigated through
both iso-conversional and multivariate non-linear-regression
methods. The thermal behavior of [Ni(ampy)2(NO3)2] shows
thermal decomposition in three steps with the removal of ligand
in an exothermic process. The microscopic surface morphology
◦
shows a thread like fiber of NiO calcined at 600 C. Thermoki-
netics plays an important role in this magnetically impulsive
compound providing the scheme of kinetic process with itera-
tions. The kinetics of elimination of pyridine can be described
with a generalized expanded Prout–Tompkins equation. The
considerable improvement of the fit quality of DSC data was
achieved by single step kinetic model. At the best of our knowl-
edge, the novelty of this work provides the determination of
half-life period based on first-order kinetics. The multifarious-
ness application of thermokinetics can be used as a device to
n
corresponds to expanded Prout–Tompkins equation (1 − α)
a
α having Fexp, F 1.00 and 1.09, respectively. Next to this
crit
model the others like Fn, Cn and F2 fit better. Cn, which corre-
Table 3
Arrhenius parameters in multivariate non-linear-regression methods
E (kJ mol 1)
−
log A (s
−1
)
Correlation coefficient
n or a or log Kcat
Fexp
Fcrit (0.95)
Model
Bna
An
Cn
D2
D3
D4
F2
42.23 ± 0.03
41.71 ± 0.96
42.17 ± 0.03
41.82 ± 0.73
47.69 ± 0.68
43.69 ± 0.73
41.12 ± 0.04
42.43 ± 0.03
3.12 ± 0.003
2.73 ± 0.12
3.11 ± 0.01
2.12 ± 0.09
2.36 ± 0.08
1.75 ± 0.09
2.95 ± 0.01
3.14 ± 0.004
0.999998
0.997951
0.999998
0.993862
0.996045
0.994710
0.999983
0.999998
1.0236E−3 (n = 2.08)
n = 0.6582
−1.8412 (n = 2.07)
1.00
180.5
1.00
289.4
207.3
247.6
1.09
1.09
1.10
1.09
1.09
1.09
1.09
1.09
8.58
1.18
Fn
n = 2.0883

6
S.K. Padhi / Thermochimica Acta 448 (2006) 1–6
present the solid state kinetics a neat through appropriate itera-
tions.
[6] G.M. Sheldrick, SHELXS-97 and SHELXL-97, University of G o¨ ttingen,
G o¨ ttingen, Germany, 1997.
[7] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordina-
tion Compounds. Part B, 5th ed., Wiley, New York, 1997.
Acknowledgements
[8] C. Kittel, Introduction to Solid State Physics, 7th ed., Wiley, New York,
1996.
I am grateful to Indian Institute of Technology, Guwahati
providing the institute fellowship. Special thanks to Mr. G.
Padmanabhan providing NETZSCH TA4 software for kinetic
analysis.
[9] H.L. Friedman, J. Polym. Lett. 4 (1966) 323–328.
[10] S. Vyazovkin, J. Comput. Chem. 22 (2001) 178–183.
[
[
[
[
[
[
11] S. Vyazovkin, Int. J. Chem. Kinet. 28 (1996) 95–101.
12] S. Vyazovkin, Thermochim. Acta 355 (2000) 155–163.
13] A. Burnham, Thermochim. Acta 355 (2000) 165–170.
14] M. Maciejewski, Thermochim. Acta 355 (2000) 145–154.
15] H.E. Kissinger, J. Res. Nat. Bur. Stds. 57 (1956) 217–221.
16] H.E. Kissinger, Anal. Chem. 29 (1957) 1702–1706.
References
[
[
[
1] S. Tanase, M. Ferbinteanu, M. Andruh, C. Mathoni e` re, I. Strenger, G.
Rombaut, Polyhedron 19 (2000) 1967–1973.
2] C. Paraschiv, M. Andruh, J–P. Sutter, Inorg. Chim. Acta 351 (2003)
[17] S. Vyazovkin, C.A. Wight, Thermochim. Acta 340-341 (1999)
53–68.
[18] S. Vyazovkin, J.S. Clawson, C.A. Wight, Chem. Mater. 13 (2001)
960–966.
[19] M.E. Brown, M. Maciejewski, S. Vyazovkin, R. Nomen, J. Sempere,
A. Burnham, J. Opfermann, R. Strey, H.L. Anderson, A. Kemmler, R.
Keuleers, J. Janssens, H.O. Desseyn, C.-R. Li, T.B. Tang, B. Roduit, J.
Malek, T. Mitsuhashi, Thermochim. Acta 355 (2000) 125–143.
3
85–388.
3] S. Bruda, M.M. Turnbull, C.P. Landee, Q. Xu, Inorg. Chim. Acta 359
2006) 298–308.
(
[
[
4] L. ORTEP III, J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
5] SMART, SAINT, Siemens Analytical X-ray, Instruments Inc., Madison,
WI, 1996.