3D coordination polymer of copper (II)-potassium (I): Crystal structure and thermal decomposition kinetics

Article abstract of DOI:10.1016/j.ica.2005.10.009

A new heterometallacrown coordination polymer [K₂Cu(NPA) ₂(H₂O)₄]_n (where H₂NPA = 3-nitro-phthalic acid) has been synthesized and it's crystal structure has been elucidated. In the complex, the o-phthalate group coordinates to metal atoms behaving as both tetradentate and heptadentate coordination, the modes of which have been found for the first time. The thermal behaviors of this complex and the thermal decomposition kinetics have been studied. Kinetic analysis shows that the decomposition of title complex in the main range acts as two separate transitions with the first one being a double-step following reaction, A→F1B→FnC, and the second being a three-step following reaction of t:f,f, A→F2B→F2C→R2D. The kinetic parameters of these processes were also obtained.

Full text of DOI:10.1016/j.ica.2005.10.009

Inorganica Chimica Acta 359 (2006) 642–648
www.elsevier.com/locate/ica
3D coordination polymer of copper (II)–potassium (I):
Crystal structure and thermal decomposition kinetics
b
b
b,
b
Xiao-Qing Shen a,b,c, Hai-Bin Qiao , Zhong-Jun Li , Hong-Yun Zhang *, Hong-Lei Liu ,
b
b
b
Rui Yang , Pei-Kun Chen , Hong-Wei Hou
a
College of Material Engineering, Zhengzhou University, Zhengzhou 450052, China
b
Department of Chemistry, Zhengzhou University, Zhengzhou, 450052, China
College of Chemistry, Northeast Normal University, Changchun 130024, China
c
Received 10 July 2005; received in revised form 11 October 2005; accepted 11 October 2005
Available online 28 November 2005
Abstract
A new heterometallacrown coordination polymer [K2Cu(NPA)2(H2O)4]n (where H2NPA = 3-nitro-phthalic acid) has been synthe-
sized and itÕs crystal structure has been elucidated. In the complex, the o-phthalate group coordinates to metal atoms behaving as both
tetradentate and heptadentate coordination, the modes of which have been found for the first time. The thermal behaviors of this
complex and the thermal decomposition kinetics have been studied. Kinetic analysis shows that the decomposition of title complex in
F1
Fn
the main range acts as two separate transitions with the first one being a double-step following reaction, A ! B ! C, and the second
F2
F2
R2
being a three-step following reaction of t:f,f, A ! B ! C ! D. The kinetic parameters of these processes were also obtained.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Copper complexes; Crystal structure; Thermal behaviors; Kinetics
1. Introduction
In constructing coordination polymers, aromatic dicar-
boxylic acids such as p-phthalic, m-phthalic and o-phthalic
acids are extensively used [8–11]. Among these isomeric
forms the o-phthalate ligand, with two carboxylic groups
in ortho-position, can bind metal ions in the most diverse
bonding modes [7] leading to the formation of polynuclear
complexes ranging from discrete entities to multi-dimen-
sional systems. So far many metal coordination polymers
with o-phthalic acid, including copper (II) [6,7,12], cobalt
(II) [6,7,13], and zinc (II) [2,7,14], have been studied. These
compounds revealed the monodentate as well as chelating
and bridging bonding modes of o-phthalate coordination.
Recently in an effort to explore the copper (II) mixed-
ligand complex with o-phthalate and malonate, we
obtained a novel copper (II)–sodium (I) heterometalla-
crown compound [Na2Cu(PA)2(H2O)2] (H2PA = o-phtha-
lic acid) [15], in which all the four oxygen atoms in one
o-phthalate participate in coordination, with two oxygen
atoms bridging one sodium and one copper atoms, another
Metal coordination polymers containing carboxylate
ions as the organic spacer have received considerable atten-
tion in the past few years due to their fascinating architec-
tures and their advantageous properties such as bulk
magnetic behavior, high dimensionality and optical activity
and thermal stability [1].
Study on the synthetic methods, structures and proper-
ties of metal coordination polymers consolidated by
dicarboxylate groups is particularly of interest [2–7],
because ‘‘dicarboxylic acids have additional coordination
abilities for the formation of new types of polymers and
oligomers, which can considerably influence the magnetic,
optical or catalytic properties of the ultimate products’’ [2].
*
Corresponding author. Tel.: +86 37167763675; fax: +86 37167761744.
E-mail address: wzhy917@zzu.edu.cn (H.-Y. Zhang).
0020-1693/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.10.009

X.-Q. Shen et al. / Inorganica Chimica Acta 359 (2006) 642–648
643
Table 1
one bridging two sodium atoms and the fourth coordinating
one sodium atom. In an extension of the study in this paper
we report on the synthesis and single crystal structure of a
new copper (II)–potassium (I) heterometallacrown complex
[K2Cu(NPA)2(H2O)4]n, where H2NPA = 3-nitro-phthalic
acid. Thermogravimetry (TG) and differential scanning cal-
orimetry (DSC) have been used to characterize the complex
and to study the thermal behaviors during heat-treatment.
Based on the results of TG and DSC, the kinetic parame-
ters of thermal decomposition have been calculated by
employing Ozawa–Flynn–Wall equation and the reaction
models have been derived by means of non-linear regres-
sion method. The results and information obtained from
thermal analysis can help us understand the structure and
properties of [K2Cu(NPA)2-(H2O)4]n, and also provide
basic data for further application research of this coordina-
tion polymer.
Crystal data and structure refinement parameters for [K2Cu(NPA)2-
(H2O)4]n
Empirical formula
Formula weight
C16H14CuK2N2O16
632.03
ꢀ
Crystal system, space group
triclinic, P1
˚
a (A)
7.4264(15)
10.434(2)
14.864(3)
104.58(3)
92.95(3)
90.27(3)
1113.0(4)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Dc (g cmꢀ3
)
1.886
1.443
l (mmꢀ1
)
Crystal size (mm)
h Range (ꢁ)
Reflections collected/unique
Final R indices [I > 2r(I)]
R indices (all data)
0.2 · 0.18 · 0.18
1.42–24.99
3399/3399 [R(int) = 0.0000]
R1 = 0.0406, wR2 = 0.0879
R1 = 0.0589, wR2 = 0.0967
2. Experimental
I > 2r(I). Details of crystal structure determination are
summarized in Table 1. Full atomic data are available as
a file in CIF format.
2.1. Materials
All chemicals, purchased from Zhengzhou Chemical
Reagent Company, were of analytic reagent grade and used
without further purification.
Thermal decomposition experiments were carried out
using NETZSCH TG 209 and DSC 204 instruments in
N2 atmosphere. The heating rate for thermal decomposi-
tion employed was 10 ꢁC minꢀ1, and the rates for kinetic
analysis were 5, 10, 20 and 30 ꢁC minꢀ1, respectively. The
IR spectra were recorded on a Nicolet IR-470 spectrometer
2.2. Synthesis of complex [K2Cu(NPA)2(H2O)4]n
An aqueous solution of CuCl2 (2 ml, 0.5 mol Lꢀ1) was
added with continuous stirring to 60 ml of water contain-
ing 0.334 g (2.0 mmol) of 3-nitro-phthalic anhydride.
0.5 mol Lꢀ1 KOH solution were added into above-men-
tioned solution to keep pH = 7. The resulting solution
was heated under stirring to reflux for 4 h and then cooled
to room temperature. After two months, 0.258 g (Yield
40.8%) bright blue crystals of title complex suitable for
X-ray diffraction were obtained by being filtrated, washed
with cooled water and dried under vacuum. IR (KBr pellet,
cmꢀ1): 3374s, 3088w, 1616vs, 1539s, 1462m, 1383s, 1349s,
1300w, 925m, 717m. Anal. Calc. for C16H14N2O16CuK2:
C, 30.38; H, 2.42; N, 4.63. Found: C, 30.44; H, 2.48; N,
4.66%.
using KBr pellets in the range of 4000–400 cmꢀ1
.
3. Results and discussion
3.1. Description of crystal structure of
[K2Cu(NPA)2(H2O)4]n
Selected bond distances and angles are listed in Table 2,
the structure unit is depicted in Fig. 1a, the structural core
in Fig. 1b and the packing diagram of the complex in
Fig. 1c, respectively.
The crystal structure of [K2Cu(NPA)2(H2O)4]n consists
of a centrosymmetric polynuclear [K4Cu2(NPA)4(H2O)8]
structural unit (Fig. 1a). Each Cu(II) atom in the unit
has a approximately square pyramidal (CuO5) coordina-
tion environment. For Cu1 the basal plane of the square
pyramid is defined by three carboxylate-oxygen atoms
(O8, O2 and O10A) belonging to three different NPA
groups and one oxygen atom (O13) from a H2O molecule.
The fifth axial coordination site is occupied by one oxygen
atom (O14) of bridging water ligand. The distance of Cu1
2.3. Experimental equipment and conditions
The single crystal structure was measured on a Rigaku-
Raxis-VI X-ray diffractometer using graphite-monochro-
mated Mo Ka radiation (k = 0.71073 A) at 293(2) K,
˚
3399 reflections were measured over the ranges
1.42 6 h 6 24.99, ꢀ8 6 h 6 8, 0 6 k 6 12, ꢀ17 6 l 6 17,
yielding 3399 unique reflections. Raw data were corrected
and the structure was solved using the SHELX-97 program.
Non-hydrogen atoms were located by direct phase determi-
nation and subjected to anisotropic refinement [16]. The
full-matrix least-squares calculations on F2 were applied
on the final refinement. The refinement converged at
R1 = 0.0406 and wR2 = 0.0879 values for reflections with
˚
and the plane center is 0.145 A and four in-plane atoms,
O(2), O(8), O(10A) and O(13) are almost coplanar with
˚
mean deviation from plane of 0.0144 A.
There are two kinds of coordination environment for
potassium atoms. The K1 atom is 9-coordinated by three
H2O molecules (O15, O16, O14) and three carboxylate-
oxygen atoms (O2, O3, O7) from two NPA groups in the

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X.-Q. Shen et al. / Inorganica Chimica Acta 359 (2006) 642–648
Table 2
˚
Selected bond distances (A) and angles (ꢁ) for complex [K2Cu(NPA)2-
(H2O)4]n
Bond distance
Cu(1)–O(10)#1
Cu(1)–O(2)
Cu(1)–O(13)
Cu(1)–O(8)
Cu(1)–O(14)
K(1)–O(7)
1.966(3) K(1)–O(9)#4
1.971(3) K(1)–O(6)#3
1.997(4) K(2)–O(8)
2.020(3) K(2)–O(8)#1
2.310(4) K(2)–O(7)#4
2.773(3) K(2)–O(12)#5
3.142(4) C(11)–N(2)
2.812(3) O(11)–N(2)
3.171(3)
2.830 (4)
2.854(3)
2.841(3)
2.671(3)
2.823(4)
1.469(5)
1.214(5)
K(1)–O(14)
K(1)–O(1)#2
Bond angles
O(10)#1–Cu(1)–O(14)
O(10)#1–Cu(1)–O(8)
O(10)#1–Cu(1)–O(2)
O(3)–K(1)–O(1)#2
92.50(14) O(16)–K(1)–O(7)
90.08(12) O(12)#5–K(2)–O(9)
170.74(11) O(10)#1–K(2)–O(8)#1
129.26(10) K(2)#1–O(1)–K(1)#6
146.62(13)
154.38(10)
72.05(9)
87.82(9)
O(7)#4–K(2)–O(8)#1 147.28(9)
O(7)#4–K(2)–O(8)
Cu(1)#1–O(10)–K(2)#1 102.41(12)
95.80(10) Cu(1)–O(14)–K(1)
89.41(12)
Fig. 1c. The packing of [K2Cu(NPA)2(H2O)4]n.
Symmetry transformations used to generate equivalent atoms: #1 ꢀx,ꢀy
+ 1,ꢀz #2 x + 1,y,z #3 ꢀx + 1,ꢀy + 2,ꢀz + 1 #4 ꢀx + 1,ꢀy + 1,ꢀz #5
x,y ꢀ 1,z #6 x ꢀ 1,y,z.
(Fig. 1b). The K2 atom is 7-coordinated by five carboxyl-
ate-oxygen atoms (O8, O9, O8A, O1A, O10A) from three
NPA groups within the same structural unit (Fig. 1a), as
well as one carboxylate-oxygen atom (O7) and one nitro-
oxygen atom (O12) of two NPA groups belonging to the
other structural unit (Fig. 1b). The difference between
Cu–O bond and K–O bond results from the disparity in
bonding characteristic of copper and potassium atoms.
The copper atom can accept the electron pair from oxygen
atom forming Cu–O coordination bond, while the potas-
sium atom forms the K–O bond through the electrostatic
attraction of K+ for O2ꢀ or polar H2O molecule. As the
electrostatic attraction has no saturation level and direc-
tionality, K+ can interact with the electronegative groups
around it as more as possible and exhibit high coordination
numbers. The K–O bonds formed between the neighboring
structural units play an important role in constructing the
coordination polymer.
Fig. 1a. ORTEP drawing of [K2Cu(NPA)2(H2O)4] unit (with 50%
probability displacement ellipsoids).
NPA adopts two kinds of coordination mode in the
complex, in one of which three of the four carboxylate-oxy-
gen atoms in one NPA group are used to coordinate the
metals acting as a tetradentate ligand apart from the
nitro-oxygen atom which also participates in coordination,
in the other mode all of the four carboxylate-oxygen atoms
take part in coordination acting as a heptadentate ligand.
In the tetradentate form of NPA group (Fig. 1a), one oxy-
gen atom (O1) from one carboxylate group coordinates a
potassium atom (K2A), and another oxygen atom (O2)
from the same carboxylate group bridges a copper atom
(Cu1) and a potassium atom (K1). The coordination of
oxygen atom (O2) to copper atom (Cu1), together with that
of oxygen atom (O1) to potassium atom (K2A), gives rise
to a 1,3-bridging mode. The one oxygen atoms (O3) of
another carboxylate group also coordinates the K1 atom
forming a 1,6-chelating mode together with oxygen atom
(O2). This kind of coordination mode, which can be shown
by structure representation I (Scheme 1), has not been
reported in the literature [7].
Fig. 1b. Core of the complex along a-axis.
same structural unit (Fig. 1a), as well as two carboxylate-
oxygen atoms (O1, O9) and one nitro-oxygen atom (O6)
of two NPA groups belonging to the other structural unit

X.-Q. Shen et al. / Inorganica Chimica Acta 359 (2006) 642–648
645
3.2. Thermal decomposition and non-isothermal kinetics of
[K2Cu(NPA)2(H2O)4]n
K
K
K
Cu
Cu
K
K
Cu
O
O
O
O
O
O
O
O
3.2.1. Thermal decomposition
The typical TG and DSC curves of title complex are
shown in Fig. 2. It can be seen that there are three transi-
tions appeared in the decomposition process. The first tran-
sition, which starts from 85 ꢁC and ends at 175 ꢁC, giving
total DH value of 375.5 J gꢀ1 with two endothermic peaks
at 121.1 and 148.9 ꢁC, is due to the loss of coordinated
H2O from [K2Cu(NPA)2(H2O)4]n. The calculated mass loss
of 11.35% for this thermal event agrees well with that
revealed by the TG curve (11.34%).
The second transition, which ranges from 175 to 335 ꢁC,
is a consecutive complicated process containing three exo-
thermic peaks at 198.1, 215.3 and 276.7 ꢁC. This thermal
event, giving total DH value of ꢀ731.1 J gꢀ1 (DSC curve)
with mass loss of 29.18%, is due to the decomposition of
[K2Cu(NPA)2]n and accompanied by the formation of
CuO [7] and KOCN. The third transition is beyond
335 ꢁC and is related to the gradual elimination of carbon
deposition resulted from [K2Cu(NPA)2]n decomposition in
N2 atmosphere [17]. The total mass loss up to 760 ꢁC is
59.0%, which agrees with the theoretical value (60.4%) cal-
culated by taking KOCN and CuO as the final products.
The characterization frequencies of the IR spectra of
[K2Cu(NPA)2(H2O)4]n and the decomposed products at
335 and 760 ꢁC confirmed the deduction above. The peaks
at 1523 and 1500 cmꢀ1 in the IR spectrum of the complex,
which are assigned to the characteristic vibration band of
benzene rings, disappear in the spectrum of the decom-
posed products, and a new characteristic absorption peak
of OCNꢀ appears at 2223 cmꢀ1 in the spectrum of both
the decomposed products.
Scheme 1.
In the heptadentate form of NPA group (Fig. 1a), one
oxygen atom (O7) from one carboxylate group coordinates
K1 atom, and another oxygen atom (O8) from the same
carboxylate group bridges Cu1, K2 and K2A atoms. The
one oxygen atom (O9) of another carboxylate group also
coordinates the K2 atom forming a 1,6-chelating mode
together with oxygen atom (O8), and the remaining oxygen
atom (O10) bridges Cu1A and K2A atoms. The coordina-
tion of oxygen atom (O10) to copper atom (Cu1A),
together with that of oxygen atom (O9) to potassium atom
(K2), leads to a 1,3-bridging mode, and the coordination of
O10 and O8 atoms to K2A atom at the same time forms a
1,6-chelating mode. The o-phthalate group acts as heptad-
entate coordination to metal centers forming two seven-
membered cycles using 1,6-chelating mode. This kind of
coordination mode, which can be shown by structure rep-
resentation II (Scheme 1), has also not been reported in
the literature [7].
Water coordinates to metal ions in two fashions, in one
of which water (O14) is linked to two metal atoms (Cu1
and K1) behaving as a bridging ligand, in another one each
water (O13, O15, O16) coordinates one metal atom (Cu1 or
K1). There are two kinds of hydrogen bond formed
between and within the structural units, one of which is
formed between H2O molecules, and another one between
carboxylate-oxygen atoms and H2O molecules. The hydro-
gen bonds formed between the structural units provide
extra stability to the coordination polymer structure.
A special characteristic of this crystal structure is that
four potassium atoms (K1C, K2AE, K1AE and K2C)
and two copper atoms (Cu1E and Cu1J) from adjacent
structural units build a 6-center metallocycle through
bridging carboxylate-oxygen atoms, in which K2AE,
Cu1J, K2C and Cu1E atoms are in the same plane, while
K1C and K1AE atoms are slightly out of it with mean
It is of interest to further investigate the enthalpy
changes of this complex in first transition. Two overlapped
endothermic peaks appeared in DSC curve (see Fig. 2) with
the peak temperatures at 121.1 and 148.9 ꢁC, giving total
DH value of 375.5 J gꢀ1, correspond to the removal of
˚
deviation from the main plane both of 0.2109 A. The
metallocycle extends to form a metal framework along
a-axis direction (Fig. 1b). This structure is analogous to
the previously reported copper (II) complex [15], but in this
complex each K atoms can also link nitro-oxygen atoms of
˚
neighboring units at K(2)–O(12)#5 distance of 2.823(4) A
˚
and K(1)–O(6)#3 distance of 2.830(4) A to form a grid
structure extending along benzene ring plane. This arrange-
ment leads to form tunnel cavities with the biggest hole
˚
diameter of 19.065 A in the assembled 3D polymer crystal
(Fig. 1c).
Fig. 2. TG and DSC curves of [K2Cu(NPA)2(H2O)4]n.

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X.-Q. Shen et al. / Inorganica Chimica Acta 359 (2006) 642–648
Fig. 4. TG curves with different heating rates. Heating rates listed are
setting values.
Fig. 3. Peak-separation of first transition of DSC curve.
Table 3
where b is the heating rate, a the degree of conversion, g(a)
the mechanism function, E the activation energy, A the pre-
exponential factor and R the gas constant.
Peak-separation result for the first transition of decomposition
Shape
Position (ꢁC)
Onset (ꢁC)
Endset (ꢁC)
Area (J molꢀ1
)
From Eq. (1) it can be seen that the graphs ln b versus
1/T show straight lines with slopes m = ꢀ1.052E/R. The
slopes of these straight lines are directly proportional to
the reaction activation energy (E). The calculated results
of the first and the second transition by using Eq. (1) are
listed in Table 4.
1
2
118.9945
148.9254
84.137
126.779
134.999
164.158
277.5173
98.6287
mono-coordinated water and bridging water, respectively.
We use the peak-separation technology to calculate the
DH value of each peak. The calculated curves are presented
in Fig. 3 and the calculated results shown in Table 3. The
DH values given for these two endothermic areas are
277.5 and 98.6 J gꢀ1, respectively. DH1/DH2 ꢁ 3:1 agrees
with the ratio of the number of mono-coordinated water
and bridging water. That is to say, two types of coordinat-
ing mode result in these water being lost at different tem-
peratures and the heat absorbed is proportional to the
number of water molecules eliminated. On the other hand
this conclusion also indicates that DSC measurement can
provide a valuable way to infer unknown coordination
modes of water.
From the thermal analysis above it can be seen that
the main process of the decomposition of [K2Cu(NPA)2-
(H2O)4]n occurs within the temperature range of
85–335 ꢁC. In order to simplify the problem only this
temperature range would be taken into consideration in
the following kinetic analysis.
The dependence of E on a given in Table 4 shows that the
activation energy is not a constant and two maximums
appear at a = 0.05 and 0.9 for first transition and three max-
imums at a = 0.3, 0.6 and 0.9 for the second, which indicates
that the thermal decomposition of [K2Cu(NPA)2(H2O)4]n
can be separated into a double-step and a three-step reaction,
respectively [19]. According to OFW method, the activation
energies and pre-exponential factors of thermal decomposi-
tion for the first transition are, E1 = 71.4 kJ molꢀ1
E2 = 97.8 kJ molꢀ1, respectively; for second transition, the
values of these parameters are E1 = 154.8 kJ molꢀ1
E2 = 173.1 kJ molꢀ1 E3 = 216.2 kJ molꢀ1
respectively.
,
,
,
,
These values would offer initial values for getting reaction
Table 4
Parameters E (kJ molꢀ1) and lg(A/sꢀ1) for main thermal decomposition of
[K2Cu(NPA)2(H2O)4]n
Partial mass
loss (a)
First transition
E (kJ molꢀ1
Second transition
E (kJ molꢀ1
)
lg(A/sꢀ1
)
)
lg(A/sꢀ1
)
3.2.2. Non-isothermal kinetics of [K2Cu(NPA)2(H2O)4]n
A series of dynamic scans with different heating rates
results in a set of data, which exhibits the same degree of
conversion (a) at different temperatures. Fig. 4 shows the
thermal decomposition curves of title complex at heating
rates of 5, 10, 20 and 30 ꢁC minꢀ1 in N2 atmosphere. The
basic data (b,a,T) taken from the TG curves are used in
the equations below:
0.02
0.05
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
0.95
0.98
71.43 9.43
66.54 5.61
54.47 3.57
44.70 2.43
41.04 2.14
40.15 2.15
40.91 2.34
42.69 2.74
45.14 3.45
50.06 4.87
71.36 10.89
97.77 19.56
88.36 16.09
7.89
6.65
4.89
3.50
3.01
2.91
3.04
3.32
3.70
4.41
7.16
10.65
9.33
139.76 11.38
135.46 7.20
135.57 4.35
154.84 5.79
158.48 5.88
158.08 7.15
173.07 14.34
160.62 12.15
163.69 11.63
170.56 12.70
198.47 24.25
216.17 37.34
214.67 43.92
12.21
11.93
12.04
14.20
14.55
14.39
15.53
13.77
13.78
14.20
16.49
17.84
17.51
Ozawa–Flynn–Wall equation [18],
ꢀ
ꢁ
AE
R
E
RT
ln b ¼ ln
ꢀ ln gðaÞ ꢀ 5:3305 ꢀ 1:052 ꢂ
;
ð1Þ

X.-Q. Shen et al. / Inorganica Chimica Acta 359 (2006) 642–648
647
Table 5
Kinetic parameters and fitting quality after NLR method
Transition
1st
Corr. coeff.
0.999836
Reg. par.
0.00100
Step
E (kJ molꢀ1
)
lg(A/sꢀ1
)
Order
0.74
I F1
II Fn
78.67363
102.90499
8.22818
11.93783
2nd
0.999817
0.00100
I F2
II F2
III R2
157.21424
184.2119
215.7978
16.85279
15.2992
17.8387
model by means of non-linear regression (NLR) and would
be optimized finally.
the first transition assigned to water loss is a double-step
following reaction: an 1st-order reaction (F1) is followed
by an nth reaction (Fn) with n = 0.74; The second transi-
tion responsible for main decomposition of [K2Cu(NPA)2]n
preferably performs as a three-step following reaction: two
following 2nd-order reactions (F2) are followed by a 2-
dimensional phase boundary reaction (R2).
Non-linear regression [20] allows a direct fit of the model
to the experimental data without a transformation and
there are no limitations with respect to the complexity of
the model. For this reason, NLR method can be employed
for estimating the decomposition model of [K2Cu(NPA)2-
(H2O)4]n. Selecting mechanism function f(a) of different
singular reaction types [21]; testing all double-step and
three-step reaction types to which individual steps are
linked for the first and second transition, respectively
[21]. Setting the initial values of the parameters of E and
lgA according to OFW method, the calculated curves were
obtained by means of NLR. These curves were fitted to the
experimental ones and corrected with LSQ. During this
procedure in order to get high fitting quality kinetic param-
eters of initial values are optimized. Considering fitting
quality (characterized by correlation coefficient), the mech-
4. Conclusions
1. Complex [K2Cu(NPA)2(H2O)4]n shows triclinic struc-
ꢀ
ture with space group P1. The crystal structure consists
of a centrosymmetric polynuclear structural unit. Cu(II)
atom has a approximately square pyramidal (CuO5)
coordination environment and four potassium atoms
together with two copper atoms build a 6-center metal-
locycle through bridging carboxylate-oxygen atoms
along a-axis. In this complex, the o-phthalate group
coordinates to metal atoms behaving as tetradentate
and heptadentate coordination, the modes of which
have not been reported in the literature.
F1
Fn
anism of d:f, A ! B ! C, is the most suitable for water loss
F2
F2
R2
reaction. And the mechanism of t:f,f, A ! B ! C ! D, for
the decomposition of [K2Cu(NPA)2]n. The kinetic parame-
ters and statistical characterization after the NLR are listed
in Table 5, graphic presentation of the curve fitting for the
second transition are presented in Fig. 5, which shows that
the experimental data and the non-linear regression curves
fit very well.
2. Thermal analysis indicates that the process of [K2Cu(N-
PA)2(H2O)4]n decomposition includes two transitions.
First transition is assigned to the loss of coordinated
water, the second corresponds to the decomposition of
[K2Cu(NPA)2]n. Two types of coordinating mode result
in the coordinated H2O being lost at different tempera-
tures and the heat quantity absorbed is proportional
to the number of water molecules eliminated.
In short, the result of the kinetic analysis above shows
the mechanism of [K2Cu(NPA)2(H2O)4]n decomposition:
3. Kinetic analysis shows the mechanism of [K2Cu(NPA)2-
(H2O)4]n decomposition: the first transition is a double-
F1
Fn
step following reaction, A ! B ! C, with E1 = 78.7
kJ molꢀ1, lg(A1/sꢀ1) = 8.2; E2 = 102.9 kJ molꢀ1, lg-
(A2/sꢀ1) = 11.9, n = 0.74; The second transition is a
F2
F2
R2
three-step following reaction, A ! B ! C ! D, with
E1 = 157.2 kJ molꢀ1, lg(A1/sꢀ1) = 16.9; E2 = 184.2
kJ molꢀ1, lg(A2/sꢀ1) = 15.3; E3 = 215.8 kJ molꢀ1, lg-
(A3/sꢀ1) = 17.8.
5. Supplementary material
Supplementary crystallographic data have been depos-
ited with the Cambridge Crystallographic Data Center,
CCDC No. 228386. Copies of this information may be
obtained free of charge on application to The Director,
12 Union Road, Cambridge CB2 2EZ, UK (fax: +44
Fig. 5. Curve fitting of second transition, simulated with reaction types
F2, F2 and R2. $, e, D, h experimental plots, – integral plots. Heating
rates listed are measured values.

648
X.-Q. Shen et al. / Inorganica Chimica Acta 359 (2006) 642–648
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Acknowledgements
We thank the Natural Science Foundation of China
(20271046), the Natural Science Foundation of Henan
Province (0211020300) and the Natural Science Founda-
tion of Henan Education Department (2004150004) to pro-
vide financial support.
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