Cobalt(II) coordination polymers built on isomeric dipyridyl triazole ligands with pyromellitic acid: Synthesis, characterization and their effects on the thermal decomposition of ammonium perchlorate

Article abstract of DOI:10.1007/s11426-012-4527-8

Three new cobalt(II) coordination compounds, [Co(3,3′-Hbpt) ₂(H₂pm)(H₂O)₂]·2H ₂O (1), [Co(4,4′-Hbpt)(pm)_0.5(H₂O)] ·3H₂O (2) and [Co(3,4′-Hbpt)(pm)_0.5(H ₂O)₃]·2H₂O (3) (3,3′-Hbpt = 3,5-bis(3-pyridyl)-1H-1,2,4-triazole; 4,4′-bpt = 3,5-bis(4-pyridyl)-1H-1, 2,4-triazole, 3,4′-Hbpt = 3-(3-pyridyl)-5-(4′-pyridyl)-1H-1,2,4- triazole and H₄pm = pyromellitic acid) have been synthesized by hydrothermal reactions. Single-crystal X-ray diffraction reveals that compound 1 has a one-dimensional (1D) chain network, 2 exhibits a four-connected three-dimensional (3D) structure with 1D open channels encapsulated by water molecules, while 3 displays a regular two-dimensional (2D) architecture connected through 1D metal helical chains. In addition, the efficacy of compounds 1-3 as additives to promote the thermal decomposition of ammonium perchlorate (AP) is explored by differential scanning calorimetry (DSC).

Full text of DOI:10.1007/s11426-012-4527-8

SCIENCE CHINA
Chemistry
March 2012 Vol.55 No.3: 443–450
doi: 10.1007/s11426-012-4527-8
• ARTICLES •
Cobalt(II) coordination polymers built on isomeric dipyridyl
triazole ligands with pyromellitic acid: Synthesis, characterization
and their effects on the thermal decomposition of ammonium
perchlorate
XIE Gang1, LI Bing1,2, CHEN SanPing1*, YANG Qi1, WEI Wei1 & GAO ShengLi1*
1Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education; College of Chemistry and Materials
Science, Northwest University, Xi’an 710069, China
2School of Chemistry & Chemical Engineering, Ningxia University, Yinchuan 750021, China
Received December 5, 2011; accepted December 28, 2011
Three new cobalt(II) coordination compounds, [Co(3,3′-Hbpt)2(H2pm)(H2O)2]·2H2O (1), [Co(4,4′-Hbpt)(pm)0.5(H2O)]·3H2O
(2) and [Co(3,4′-Hbpt)(pm)0.5(H2O)3]·2H2O (3) (3,3′-Hbpt = 3,5-bis(3-pyridyl)-1H-1,2,4-triazole; 4,4′-bpt = 3,5-bis(4-pyridyl)-
1H-1,2,4-triazole, 3,4′-Hbpt = 3-(3-pyridyl)-5-(4′-pyridyl)-1H-1,2,4-triazole and H4pm = pyromellitic acid) have been synthe-
sized by hydrothermal reactions. Single-crystal X-ray diffraction reveals that compound 1 has a one-dimensional (1D) chain
network, 2 exhibits a four-connected three-dimensional (3D) structure with 1D open channels encapsulated by water molecules,
while 3 displays a regular two-dimensional (2D) architecture connected through 1D metal helical chains. In addition, the effi-
cacy of compounds 1–3 as additives to promote the thermal decomposition of ammonium perchlorate (AP) is explored by dif-
ferential scanning calorimetry (DSC).
cobalt(II) coordination compound, 3,5-bis-pyridyl-1H-1,2,4-triazole, combustion catalysis, ammonium perchlorate
of the molecules, making the ligand more flexible [13, 14].
1 Introduction
In addition, the different possible positions of the pyridyl
nitrogen atoms endow the ligands (Scheme 1) with versatile
coordination modes, facilitating the formation of different
topological structures [15].
Ammonium perchlorate (AP) is the most common oxi-
dizer in composite solid propellants and the thermal de-
composition characteristics of AP directly influence the
combustion behavior of such solid propellants [16, 17]. The
reaction rate and pyrolysis temperature of the thermal de-
composition of AP are closely related to the combustion
rate of the solid propellants, with lower pyrolysis tempera-
tures resulting in faster combustion rates.
The design and assembly of metal–organic frameworks
(MOFs) based on triazole and its derivatives are of great
interest in materials science by virtue of their intriguing
architectures and potential applications in luminescence,
nonlinear optics, adsorption and magnetism [1–8]. Due to
their high nitrogen content, triazole and its derivatives are
also widely used as energetic materials [9–12]. As one of
the derivatives of triazole, 3,5-bis-pyridyl-1-H-1,2,4-triazole
serves as an N,N′-donor ligand and acts as a bridging ligand,
thus mediating exchange coupling. Furthermore, the proto-
tropy and conjugation between the 1H-1,2,4-triazole and
pyridyl groups alter the electron density in different sections
In order to study the effects of compounds containing
Hbpt on the thermal decomposition of AP, we chose co-
balt(II) ions as the coordination center and pyromellitic acid
*Corresponding author (email: sanpingchen@126.com; gaoshli@nwu.edu.cn)
© Science China Press and Springer-Verlag Berlin Heidelberg 2012
chem.scichina.com www.springerlink.com

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Xie G, et al. Sci China Chem March (2012) Vol.55 No.3
Scheme 1 The positionally isomeric bridging ligands.
(H4pm) as an auxiliary ligand on the basis of the following
considerations: (1) the cobalt(II) ion shows good catalytic
performance for the decomposition of propellants [18]; (2)
H4pm can improve the oxygen balance of propellant com-
ponents [19–21]. Moreover, H4pm is a good candidate for
the construction of MOFs through full or partial deprotona-
tion [22–24]. In this paper, we report the syntheses and
structures of three cobalt(II) coordination compounds with
Hbpt isomers in the presence of the H4pm ligand, namely,
[Co(3,3′-Hbpt)2(H2pm)(H2O)2]·2H2O (1), [Co(4,4′-Hbpt)
(pm)0.5(H2O)]·3H2O (2) and [Co(3,4′-Hbpt)(pm)0.5(H2O)3]·
2H2O (3). Furthermore, the catalytic performances of 1–3 in
the thermal decomposition of AP were explored.
Hbpt) (260 mg, 25.0% based on 3-cyanopyridine). Anal.
calcd for C12H9N5: C, 64.56; H, 4.06; N, 31.37. Found: C,
64.96; H, 4.40; N, 32.45%. Mp: 232–233 °C; IR (cm–1,
KBr): 3327(s), 3156(s), 3048(m), 2843(m), 1620(s), 1594(s),
1482(w), 1406(s), 1308(s), 1196(w), 1051(m), 821(m),
1
709(m), 625(w); H NMR (400 MHz, DMSO-d6, δ ppm):
7.534–7.552 (2H, m, J = 7.2 Hz), 8.408–8.427 (2H, d, J =
7.6 Hz), 8.723–8.743 (2H, dd, J = 8.0 Hz), 9.272(2H, s),
14.926 (1H, s, triazole-H).
The same procedure as that for the 3,3′-Hbpt ligand was
used for the synthesis of 4,4'-Hbpt except that 3-cyano-
pyridine was replaced by 4-cyanopyridine. (Yield: 420 mg,
40.3% based on 4-cyanopyridine). Mp: 296–297 °C; Anal.
calcd for C12H9N5: C, 64.56; H, 4.06; N, 31.37. Found: C,
64.85; H,4.09; N, 33.04%. IR (cm–1, KBr): 3408(w),
3088(m), 2623(m),1606(s), 1580(s), 1447(m), 1423(m),
1378(m), 1362(m), 1152(s), 1015(m), 987(m), 832(s),
2 Experimental
2.1 Materials
1
720(m), 709(m), 528(s); H NMR (400 MHz, DMSO-d6,
δppm): 8.010–8.025 (4H, d, J = 6.0 Hz), 8.768–8.779 (4H, d,
J = 4.4 Hz), 15.232 (1H, s, triazole-H).
Commercially available reagents were used as received
without further purification. Elemental analyses (C, H and
N) were performed on a Vario EL III analyzer. Infrared
spectra were obtained using KBr pellets on a BEQ VZNDX
3,4′-Hbpt was synthesized according to ref. [25] and
characterized by IR and elemental analysis. Anal. calcd for
C12H9N5: C, 64.56; H, 4.06; N, 31.37. Found: C, 64.88;
1
550 FTIR instrument within the 400–4000 cm–1 region. H
o
H,4.56; N, 32.88%. Mp: 240–241 C; IR (cm–1, KBr):
NMR spectra were recorded on a Varian Inova 400 instru-
ment using tetramethylsilane (TMS) as an internal standard.
Thermal analyses were performed on a NETZSCH STA
449C instrument under an atmosphere of hydrostatic air at a
heating rate of 10 °C min–1. Differential scanning calorime-
try (DSC) experiments were performed on a Perkin-Elmer
Pyris 6 DSC thermal analyzer (calibrated using pure indium
and zinc as standards) from 50 to 500 °C.
3408(w), 3088(m), 2623(m), 1606(s), 1580(s), 1447(m),
1423(m), 1378(m), 1362(m), 1152(s), 1015(m), 987(m),
832(s), 720(m), 709(m), 528(s); 1H NMR (400 MHz,
DMSO-d6, δ ppm): 6.951–6.980 (1H, d, J = 11.6 Hz),
7.508–7.539 (1H, m, J = 12.4 Hz), 7.797–7.810 (2H, d,
J = 5.2 Hz), 8.220–8.240 (1H, d, J = 8.0 Hz), 8.662–
8.674 (2H, d, J = 4.8 Hz), 9.054 (1H, s ); 10.329 (1H, s,
triazole-H).
2.2 Synthesis of Hbpt
2.3 Synthesis of [Co(3,3′-Hbpt)2(H2pm)(H2O)2]∙2H2O
(1)
The 3,3′-Hbpt ligand was synthesized via an in situ met-
al/ligand reaction and demetallation as follows (Scheme 2):
A mixture of 3-cyanopyridine (1.04 g, 10.0 mmol), aqueous
ammonia (1.0 mL), Cu(NO3)2·6H2O (0.296 g, 1.0 mmol)
and water (5 mL) was sealed in a 15 mL Teflon-lined auto-
clave and treated at 140 °C for 60 h. The resulting mixture
was filtered to give crystalline [Cu2(bpt)2] in 40% yield
based on 3-cyanopyridine. The product then underwent a
process of demetallation: The as-synthesized [Cu2(bpt)2]
was placed in a 200 mL flask containing 100 mL of water,
into which 2 mL of ammonium sulfide solution was added
dropwise with stirring. After 0.5 h, the solution was boiled
and filtered to give a colorless solution and then concen-
trated to afford 3,5-bis(3-pyridyl)-1H-1,2,4-triazole (3,3′-
A mixture containing cobalt(II) acetate (Co(OAc) 2·4H2O)
(12.4 mg, 0.05 mmol), 3,3′-Hbpt (11.2 mg, 0.05 mmol),
H4pm (12.7 mg, 0.05 mmol) and water (6 mL) was sealed in
a 15 mL Teflon-lined stainless steel vessel and heated at
140 °C for 3 days and then cooled to room temperature at a
rate of 5 °C/h. Red prismatic crystals of 1 were collected in
a yield of 50% (based on Co). Anal. calcd for 1
(C34H30CoN10O12) (%): C, 49.23; H, 3.64; N, 16.88. Found:
C, 49.56; H, 3.95; N, 16.33%. IR (cm–1, KBr): 3332(s),
3168(s), 3051(m), 1695(s), 1615(s), 1591(m), 1571(s),
1436(s), 1399(s), 1221(m), 1036(w), 917(w), 823(s), 720(s),
625(m).

Xie G, et al. Sci China Chem March (2012) Vol.55 No.3
445
Scheme 2 In situ synthesis of Hbpt.
2.4 Synthesis of [Co(4,4′-Hbpt)(pm)0.5(H2O)]∙3H2O (2)
H, 4.05; N, 14.08. Found: C, 41.65; H, 4.18; N, 14.85%. IR
(cm–1, KBr): 3332(s), 1635(s), 1615(s), 1581(m), 1544(s),
1456(s), 1399(s), 1220(m), 1036(w), 917(w), 836(s), 740(s),
720(s), 615(m).
A mixture containing Co(OAc)2·4H2O (24.9 mg, 0.10
mmol), 4,4′-Hbpt (11.2 mg, 0.05 mmol), H4pm (25.4 mg,
0.10 mmol) and water (6 mL) was sealed in a 15 mL Tef-
lon-lined stainless steel vessel and heated at 160 °C for 3
days and then cooled to room temperature at a rate of 5 °C/h.
Red prism crystals of 2 were collected in a yield of 55%
(based on Co). Anal. calcd for 2 (C17H18CoN5O8): C, 42.60;
H, 3.79; N, 14.61. Found: C, 42.91; H, 3.51; N, 15.15%. IR
(cm–1, KBr): 3396(m), 3262(s), 3088(m), 2643(w), 1604(s),
1550(s), 1485(s), 1461(s), 1403(s), 1378(s), 1225(m),
1038(w), 1060(w), 1020(s), 995(m), 952(w), 839(m),
771(m), 721(m), 704(s), 604(s), 508(m).
2.6 Single crystal X-ray crystallography
All diffraction data for compounds 1–3 were collected on a
Bruker SMART APEX II CCD diffractometer with graphite
monochromated Mo Kα radiation (λ = 0.071073 nm) at
293(2) K. Absorption corrections were applied using
SADABS [26]. All structures were solved by direct methods
using SHELXS-97 [27] and refined with full-matrix least-
squares refinements based on F2 using SHELXL-97 [28].
All non-hydrogen atoms were refined anisotropically. Hy-
drogen atoms were placed in geometrically calculated posi-
tions. Crystallographic details for 1–3 are summarized in
Table 1. Selected bond lengths and angles of the compounds
are indicated in Table S1. Possible partial hydrogen bond
geometries of compounds are listed in Table S2.
2.5 Synthesis of [Co(3,4′-Hbpt)(pm)0.5(H2O)3]∙2H2O (3)
The same procedure as that for 2 was used for the synthesis
of 3 except that 4,4′-Hbpt was replaced by 3,4′-Hbpt, and
red prismatic crystals of 3 were collected in a yield of 30%
(based on Co). Anal. calcd for 3 (C17H20CoN5O9): C, 41.06;
Table 1 Crystallographic data and structure refinement details for compounds 1–3
Compound
Empirical formula
Formula weight
Crystal system
Space group
a (nm)
1
C34H30CoN10O12
829.61
2
C17H18CoN5O8
479.29
3
C17H20CoN5O9
497.31
Triclinic
Pī
Triclinic
Pī
monoclinic
P21/n
0.80718(10)
0.99614(12)
1.14448(14)
110.032(2)
90.134(2)
97.081(2)
0.85699(18)
1
0.87880(13)
1.09939(16)
1.10850(17)
76.825(2)
77.100(2)
67.533(2)
0.9525(2)
2
0.73533(5)
1.94938(14)
1.39685(10)
90
b (nm)
c (nm)
α (°)
β (°)
97.5660(10)
90
γ (°)
V (nm3)
1.9849(2)
4
Z
 (mm–1)
Unique reflect
Observed reflect
Rint
0.584
0.960
0.929
3576
3334
3538
4973
4804
9833
0.0196
0.0172
0.0254
Final R indices
[I>2sigma(I)]
R1 = 0.0486,
wR2 = 0.1296
R1 = 0.0383,
wR2 = 0.0957
R1 = 0.0407,
wR2 = 0.1096

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Xie G, et al. Sci China Chem March (2012) Vol.55 No.3
tate carboxylate groups (Co1–O2 0.2069(18) nm) and two
3 Results and discussion
nitrogen atoms of two Hbpt molecules (Co1–N2 0.2186
(27) nm) in the basal plane, in which the cobalt(II) ion and
the basal atoms are absolutely coplanar. Meanwhile, Co2
lies on the symmetry center, and shows an elongated oc-
tahedral coordination environment with axial Co2–N1
bonds of length 0.2163(22) nm to two Hbpt ligands, with
the basal four oxygen atoms coming from two pairs of
neighboring carboxylic groups (Co2–O1 0.2104(25),
Co2–O4 0.2089(21) nm). In 2, H4pm is completely depro-
tonated and exhibits monodentate and bis(monodentate)
coordination modes. The pm4– moieties connect the Co(II)
ions giving a two-dimensional (2D) layer pattern with (4,4)
network topology, in which the grid size is 0.989 nm × 1.06
nm (Figure 2(b)).These sheets are further linked by Hbpt
ligands along the c axis to form a pillared-grid three-
dimensional (3D) open framework with 1D open channels.
From a topological point of view, 2 can be described as a
3D NbO network with (64.82) topology.
Surprisingly, there are three uncoordinated water mole-
cules in every primary channel unit (Figure 2(c)). A calcu-
lation using PLATON [35] leads to a potential solvent area
of 0.1686 nm3 per unit cell volume of 0.9525 nm3, namely
17.7% of the total crystal volume. In view of such a low
cavity ratio, the channel is filled by free water molecules,
which can be attributed to larger space occupation and the
longer distance of the bi-pillar shutters [36].
3 is a 2D coordination polymer. The Co(II) ion is six-
coordinated in a distorted octahedral coordination geometry
by one oxygen atom from pm4, two pyridyl nitrogen atoms,
and three water oxygen atoms (Figure 3(a)). The Co–O
bond distances range from 0.2064(2) to 0.2135(2) nm, while
the Co–N bond lengths are slightly longer, ranging from
0.2140(4) to 0.2143(2) nm. The adjacent Co(II) ions are
linked together by N atoms from 3,4′-Hbpt to form a metal
helical chain. Interestingly, such chains crystallize in both
right- and left-handed fashions. The pm4– acts as a bridge in
a bis(monodentate) binding mode linking adjacent helical
chains through its para-positioned carboxylic groups, re-
sulting in a regular 2D architecture (Figure 3(b)).
3.1 Synthesis
1,2,4-triazoles and their derivatives are generally prepared
by multi-step procedures, which usually involve hydrazine
derivatives as starting agents [29–31]. Since in situ met-
al/ligand reactions show great merits in both coordination
chemistry and organic synthesis [32–34], herein, 3,5-
bispyridyl-1H-1,2,4-triazole has been synthesized via an in
situ metal/ligand reaction, using a coordination compound
as an intermediate. Such an approach not only represents a
widely applicable nonhydrazine-based synthetic route for
triazolates but also simplifies the synthesis and purification
processes.
3.2 Structural analysis
Single crystal X-ray analysis shows that 1 has a one-
dimensional (1D) array structure. The asymmetric unit of 1
has one crystallographically independent Co(II) center, dis-
playing a slightly distorted octahedral geometry involving
coordination to two O atoms from H2pm2, two coordinated
water molecules in the equatorial plane and two N atoms
from two 3,3′-Hbpt ligands in the axial position (Figure
1(a)). The H2pm2– ligand acts as a bis(monodentate) mode
to link the adjacent metal ions through its deprotonated
carboxylic groups. It is worth noting that the 3,3′-Hbpt is
not deprotonated, and a (4,4) topological layer is formed by
the parallel 1D neighboring chains using O–H∙∙∙∙hydrogen
bonding interactions between carboxylic groups and nitro-
gen atoms of the 3,3′-Hbpt (Figure 1(b)).
To examine the effect of positional isomerism on the
structure, 2 was synthesized in the presence of 4,4′-Hbpt.
The asymmetric unit of 2 consists of a pair of Co(II) ions,
one Hbpt, one coordinated water molecule, half a pyro-
mellitate ligand, and three free water molecules (Figure
2(a)). Co1 adopts a distorted octahedral geometry with two
water molecules in trans apical position (Co1–O5 0.2105
(25) nm), two oxygen atoms from two different monoden-
Figure 1 (a) Coordination environment of Co2+ in 1 (lattice water and H atoms are omitted for clarity); (b) (4,4) topological layer formed by the 1D parallel
neighbor chains by using O–H∙∙∙∙N hydrogen bonding interactions.

Xie G, et al. Sci China Chem March (2012) Vol.55 No.3
447
Figure 2 (a) Coordination environment of Co2+ in 2 (lattice water and H atoms are omitted for clarity); (b) the 2D layer extended in the ab plane based on
pm and Co ions; (c) free water molecules encapsulated in a 1D channel along the a axis.
Figure 3 (a) Coordination environment of Co2+ in 3 (lattice water and H atoms are omitted for clarity); (b) 2D architecture assembled by both right- and
left-handed helical chains.
3.3 Coordination modes for the positionally isomeric
ligands
from 50 to 800 °C (see Figures S1–S3 for TGA curves). 1
loses lattice water at about 60 °C with a weight loss of
4.47% (calc. 4.34%), and then remains stable up to 360 °C
before undergoing successive weight losses. 2 experiences
consecutive weight loss steps, which do not end until
800 °C. 3 is stable up to 100 °C and then undergoes a two
step weight loss of 10.2% from 100 to 360 °C, corre-
sponding to the release of the lattice water molecules (calc.
10.8%).
It is noteworthy that the positionally isomeric ligands in
MOFs 1–3 are all neutral but still exhibit a variety of coor-
dination modes, as illustrated in Scheme 3. Hbpt acts as
monodentate and bis (monodentate) connectors. Further-
more, the triazole moiety in Hbpt is involved in strong hy-
drogen bonds, which contributes to the supramolecular
network. It is obvious that the introduction of the auxiliary
H4pm greatly influences the final structures. The carboxylic
groups adopt monodentate, chelating and bridging modes,
which is mostly responsible for the structural diversity.
With the variation in coordination patterns of Hbpt and
H4pm, the network arrays show 1D chains, a 2D network
and a 3D framework in 1–3 respectively.
3.4 Thermal gravimetric analysis
Thermal gravimetric analyses (TGA) were carried out
Scheme 3 Coordination modes of Hbpt.

448
Xie G, et al. Sci China Chem March (2012) Vol.55 No.3
3.5 Effects on the thermal decomposition of ammoni-
um perchlorate
to the heating rate (as shown in the Supporting Information).
The relationship between decomposition temperature and
heating rate can be described by the Kissinger correlation,
as shown in eq. (1).
Compounds 1–3 and AP were mixed in a mass ratio of 1:3
to prepare samples for thermal decomposition analyses. The
total sample mass used was less than 1.0 mg for all runs.
From Figure 4, the endothermic peak at 245 °C for pure AP
is due to a crystallographic transition of AP from the ortho-
rhombic to the cubic phase. The second and third peaks for
pure AP are exothermic, and correspond to the low-
temperature decomposition (LTD) process and the high-
temperature decomposition (HTD) process [37, 38]. The
exothermic peak of the LTD process occurs at about 290 °C
at a heating rate of 10 °C min–1, corresponding to the de-
composition of AP with a heat of 0.735 kJ g–1. The exo-
thermic peak for the HTD process is at 442 °C with a heat
of 0.787 kJ g–1.
The DSC curves of AP in the presence of compounds
1–3 are also shown in Figure 4. In each case, there is no
effect on the crystallographic transition temperature of APP.
In the presence of compound 1, the exothermic peak oc-
curred at 318 °C, indicating that AP is completely decom-
posed at a lower temperature than for pure AP. Similarly, in
the presence of 2, a sharp decomposition peak was observed
at 300 °C, showing that AP is decomposed in a much short-
er time than for pure AP. In the presence of compound 3,
the LTD and HTD peaks converged to 338 and 457 °C. The
onsets of thermal decomposition of the pure AP and AP in
the presence of compounds 1–3 were all at about 300 °C,
while the end temperatures were about 490, 343, 335 and
476 °C, respectively. The thermal decomposition rate of AP
in presence of compounds 1 and 2 occurs more rapidly than
pure AP, while addition of compound 3 to AP reduces the
rate of decomposition. Moreover, in the presence of com-
pounds 1, 2 and 3, the decomposition heats are 2.58, 2.00,
and 0.82 kJ g–1, respectively, significantly higher than the
corresponding heat value for neat AP.
Ea

Tp2
AR
ln
 ln

(1)
Ea RTp
where Ea is the apparent activation energy, β is the heating
rate, R is the gas constant, Tp is the peak temperature, and A
is the pre-exponential factor. According to this equation, the
values of the activation energy Ea were obtained by Kissin-
ger’s method at four different heating rates (see Figures
S4–S6 for DSC curves). For pure AP, the calculated activa-
tion energy is 74.65 kJ mol–1. As shown in Table 2, in
presence of 1, 2 and 3, the activation energies increased to
170.03, 249.47 and 124.31 kJ mol–1, respectively. The in-
crease in activation energy and the corresponding increase
in the A value can be attributed to the kinetic compensation
effect as reported previously [39]. The ratio of Ea/ln(A) can
be used to describe the reactivity [40]. Usually, a larger ra-
tio means a much greater stability of the reactant. The ratios
of Ea/ln(A) are 14.1, 13.06 ,12.13 and 14.81 for pure AP, AP
with 1, AP with 2 and AP with 3, respectively. Obviously, 1
and 2 show a better catalytic activity toward AP decomposi-
tion than 3, which is consistent with the single exothermic
peak in the corresponding DSC curves,.
4 Conclusion
We have demonstrated here three new Co(II) MOFs gener-
ated from mixed-ligand systems containing three position-
ally isomeric ligands (3,3′-Hbpt, 4,4′-Hbpt and 3,4′-Hbpt)
and H4pm under coordination-driven assembly. The intro-
duction of H4pm greatly influences the coordination modes
of Hbpt as well as the final supramolecular structures.
Moreover, the effects of the three compounds on the ther-
mal decomposition of AP have also been studied. Com-
pounds 1 and 2 show good catalytic performance in AP de-
composition, which could make them promising energetic
additives for AP-based propellants.
It is known that the decomposition temperature is related
Table 2 Kinetic parameters of the thermal decomposition of pure AP
and AP with additives (Tp and ∆H were measured at the heating rate of
10 °C min–1)
Tp (°C)
290
Ea (kJ mol–1)
74.65
ln[A/s]
5.71
r
H (kJ g–1)
0.735
AP
0.9830
0.9785
0.9784
0.9911
1 +AP
2 +AP
3+AP
318
2.582
170.03
13.01
20.56
8.391
310
2.008
249.47
338
0.816
124.31
Figure 4 DSC curves for AP, 1 + AP, 2 + AP and 3+AP.

Xie G, et al. Sci China Chem March (2012) Vol.55 No.3
449
This work was supported by the National Natural Science Foundation of
China (21073142, 21173168 and 21127004), the Natural Science Founda-
tion of Shaanxi Province (SJ08B09) and the Natural Science Foundation of
the Department of Education of Shaanxi Province (2010JK882,
2010JQ2007 and 11JS110).
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