Synthesis, crystal structure and thermal decomposition of a novel praseodymium supermolecular complex

Article abstract of DOI:10.1007/s10973-005-7490-1

A novel complex, [Pr(5-nip)(phen)(NO3)(DMF)] (5-nip: 5-nitroisophthalic acid; phen: 1,10-phenanthroline, DMF: N,N-dimethylformamide), was prepared and characterized by single crystal X-ray diffraction, elemental analysis, IR spectrum and DTG-DSC techniques. The results show that the crystal is monoclinic, space group P2(1)/n with a=11.0876(6) A, b=12.8739(7) A, c=16.9994(8) A; β=91.193(4)°, Z=4, D _c=1.822 Mg m^-3, F(000)=1320. Each Pr(III) ion is nine-coordinated by one chelating bidentate and two monodentate bridging carboxylate groups, one chelating bidentate nitryl group, one DMF molecule and one 1,10-phenanthroline molecule. The complex is constructed with one-dimensional ribbons featuring dinuclear units and the one-dimensional ribbons are further assembled into two-dimensional networks by strong π-π stacking interactions. The complex has high stability up to 500°C. The enthalpy change of formation of the compound in DMF was measured using an RD496-III type microcalorimeter with the value of -9.214±0.173 kJ mol^-1.

Full text of DOI:10.1007/s10973-005-7490-1

Journal of Thermal Analysis and Calorimetry, Vol. 85 (2006) 3, 801–805
SYNTHESIS, CRYSTAL STRUCTURE AND THERMAL DECOMPOSITION
OF A NOVEL PRASEODYMIUM SUPERMOLECULAR COMPLEX
S.-P. Chen1, Y.-X. Ren1,2 and S.-G. Gao1*
1Department of Chemistry, Shaanxi Key Laboratory of Physico-Inorganic Chemistry, Northwest University, Xi’an 710069, P.R. China
2College of Chemistry and Chemical Engineering, Yanan University, Yanan 716000, P.R. China
A
novel complex, [Pr(5-nip)(phen)(NO3)(DMF)] (5-nip: 5-nitroisophthalic acid; phen: 1,10-phenanthroline, DMF:
N,N-dimethylformamide), was prepared and characterized by single crystal X-ray diffraction, elemental analysis, IR spectrum and
DTG-DSC techniques. The results show that the crystal is monoclinic, space group P2(1)/n with a=11.0876(6) , b=12.8739(7) ,
c=16.9994(8) ; b=91.193(4)°, Z=4, Dc=1.822 Mg m–3, F(000)=1320. Each Pr(III) ion is nine-coordinated by one chelating
bidentate and two monodentate bridging carboxylate groups, one chelating bidentate nitryl group, one DMF molecule and
one 1,10-phenanthroline molecule. The complex is constructed with one-dimensional ribbons featuring dinuclear units and the
one-dimensional ribbons are further assembled into two-dimensional networks by strong p–p stacking interactions. The complex
has high stability up to 500°C. The enthalpy change of formation of the compound in DMF was measured using an RD496-III type
microcalorimeter with the value of –9.214±0.173 kJ mol–1.
Keywords: crystal structure, enthalpy change of formation of the compound in DMF, 5-nitroisophthalic acid,
praseodymium complex, thermal analysis
Introduction
Experimental
Supermolecular construction from small molecular
carboxylic acids ligands and metal ions has been de-
veloped remarkably as one of hotspots in coordination
chemistry, supermolecular chemistry and material sci-
ence fields. The p-stacking interaction is a significant
intermolecular interaction in constructing super-
molecular architectures [1–3]. Small molecular aro-
matic carboxylic acids 1,2,4,5-benzenetetracarboxylic
acid [4], 1,3,5-benzenetricarboxylic acid [5], and 1,4-
benzenedicarboxylic acid [6] are used extensively in
the synthesis of coordination polymers for their versa-
tile coordination modes. And the 2,2’-bipylike ligands
involving 2,2’-bipyridine, 1,10-phenanthroline are in-
clined to form p-stacking interaction to enhance the
stability of the supermolecular polymers [7, 8]. A great
deal of lanthanide coordination polymers with aro-
matic polycarboxylic acid are reported in hydrothermal
synthesis for their high coordination numbers and large
ion radii differing from the transition metals com-
plexes [9, 10]. In this paper, we prepared a new coordi-
nation polymer of holmium and 5-nitroisophthalic acid
with 1,10-phenanthroline in DMF, and studied the
crystal structural, thermal stability and measured the
enthalpy change of formation of the compound in
DMF using an RD496-type microcalorimeter.
All the reagents used were Analar grade and used
without further purification.
Pr(NO3)3·6H2O (0.4352 g), 5-H2nip (0.2113 g)
and 1,10-phen (0.1980 g) were dissolved in 5 mL
DMF, respectively, and the DMF solution of
Pr(NO3)3 was added dropwise to the mixture DMF so-
lution of the two ligands. Then a pellucid green solu-
tion was obtained. After 6 months placed in air, some
green block crystals were recovered in the DMF solu-
tion and the structure of the suitable crystal for mea-
surement was established by X-ray crystallography.
These crystals were washed with anhydrous alcohol
for 3 times and dried at room temperature (82% yield
based on praseodymium).
Elemental analyses (C, H, N) were performed on
an Elemental Vario EL III CHNOS analyzer. The con-
tent of praseodymium was checked using EDTA titra-
tion method. The IR spectra were recorded with a
BEQ VZNDX-550 FTIR spectrometer using the KBr
pellets technique over the range 4000–400 cm–1. X-ray
diffraction data collection was performed on an Apple
Smart-CCD diffractometer with graphite-mono-
chromated MoKa (l=0.71073 ) radiation in the phi
and omega scanning mode at 273 K. 4322 Unique data
(Rint=0.0806) were used to solve the structure by direct
methods and refined on F2 by the full-matrix least-
squares methods using the SHELXL-97 (Sheldrick,
*
Author for correspondence: gaoshli@nwu.edu.cn
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2006 Akadémiai Kiadó, Budapest

CHEN et al.
ment with the value of 17.241±0.018 kJ mol–1
from [13]. The accuracy was 0.02% and the precision
was 0.3%, which indicates that the calorimetric system
was accurate and reliable.
Table 1 Crystallographic data and structure refinement for
[Pr(5-nip)(phen)(NO3)(DMF)]n
Empirical formula
C23H18N5O10Pr
Formula mass
Temperature/K
Crystal system
Space group
a/
665.33
273(2)
monoclinic
P2(1)/n
Results and discussion
The analysis data of the element content are shown in
Table 2. From these values, we can find that the ex-
perimental data are consistent with the calculated
values.
11.0876(6)
12.8739(7)
16.9994(8)
91.193(4)
2426.0(2)
4
b/
c/
b/°
The band of the COOH group for 5-nitroiso-
phthalic acid ligand at 1709 cm–1, completely vanishes
in the spectrum of the complex. 1627 and 1465 cm–1
are assigned to asymmetric and symmetric vibrations
of the COO– group, indicating that the carboxyl group
is coordinated to Pr(III) ion in two coordination
modes [14], which is confirmed by X-ray diffraction
analysis. The bands of the nitro group for the ligand
at 1556 and 1349 cm–1 do not moved and suggested the
group is not involved in coordinated. The bands
at 1299, 1036, 794 and 733 cm–1 emerge, which could
be considered as the coordinated group with C2v sym-
metry [15]. A strong band appears at 1653 cm–1, which
could be attributed to the carboxyl group of the DMF
molecule and a lower moving proves the coordination
of the group to holmium ion [16]. IR spectrum of the
complex is consistent with the structure analysis from
the X-ray diffraction.
3
V/
Z
F(000)
1320
D
calc/Mg m–3
1.822
Absorption coefficient/mm–1
2.077
Crystal size/mm
0.310×0.129×0.092
–13£h£11
–15£k£13
–20£l£19
Range h k l collected
Reflections collected
14735
Independent reflections
Completeness to q (=26.00°)
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I>2s(I)]
R indices (all data)
4322 [Rint=0.0806]
99.9%
4322/0/354
0.868
R1=0.0382, wR2=0.0740
R1=0.0739, wR2=0.0810
In Table 3 the final atomic coordinates and
thermal parameters for the title complex are showed.
Selected bond lengths and angles are listed in Table 4.
In the asymmetric unit, there are a 5-nitroisophthalic
acid ligand, a phen ligand, a NO–3 ion and a DMF
molecule as showed in Fig. 1. The nine-coordinated
praseodymium ion lies in a distorted tricapped
triangular prism environment (Fig. 2), in which the
two faces comes from N(1), O(1), O(9) and O(2),
O(3), O(7) as the sections, and O(4), O(8) and N(2) as
the three capstones. The average Pr–O distance
is 2.510  and the mean bond length of Pr–N
is 2.655 . In the complex, 5-nip ligand acts in only a
chelate-bidentate coordination mode.
Largest different peak and
hole/e 
1.078 and –0.860
–3
1997) program package [11]. All non-hydrogen atoms
were refined anisotropically and all the H atoms at-
tached to the carbon were placed geometrically. The
crystal data and refinement details of the complex are
summarized in Table 1.
The TG-DSC curves were obtained with a Perkin
Elmer thermogravimetric analyzer in air atmosphere
with a heating rate of 10°C min–1. The calorimetric ex-
periments were performed with an RD496-III type
microcalorimeter [12]. The calorimetric constants
at 25.15°C was determined by the Joule effect before
experiment, which is 63.901±0.030 mV mW–1. The
enthalpy of dissolution of KCl (spectral purity) in
Each pair of holmium ions is bridged by a pair of
syn–syn 5-nip carboxylate groups into a dimeric sub-
unit with an intradimer Pr×××Pr distance of 5.669(1) .
The different adjacent dimmers are doubly interlinked
by the 5-nip ligands to form an infinite ribbon. The
deionized
water
was
measured
to
be 17.238±0.048 kJ mol–1, which was in good agree-
Table 2 The analysis data of the element content for [Pr(5-nip)(phen)(NO3)(DMF)]n (%)
Mass fraction/%
Complex [Pr(5-nip)(phen)(NO3)(DMF)]n
C
H
N
Pr
Experimental data
Calculated values
42.05
41.52
2.56
2.73
10.33
10.53
20.95
21.18
802
J. Therm. Anal. Cal., 85, 2006

NOVEL PRASEODYMIUM SUPERMOLECULAR COMPLEX
Table 3 Atomic coordinates (×104) and equivalent isotropic
displacement parameters (2×103) for the title complex
x
y
z
U(eq)
Pr(1)
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
O(7)
O(8)
O(9)
O(10)
N(1)
N(2)
N(3)
N(4)
N(5)
C(1)
C(1)
C(1)
C(1)
C(1)
C(1)
C(1)
C(1)
C(1)
C(1)
C(1)
C(1)
C(1)
C(1)
C(1)
C(1)
C(1)
C(1)
C(1)
C(1)
C(1)
C(1)
C(1)
6584(1)
4572(3)
3178(3)
–1199(3)
–1644(3)
1595(5)
3343(4)
7723(4)
6705(4)
6029(4)
6137(5)
5791(4)
5040(4)
2329(5)
9642(5)
6277(5)
6192(5)
5706(6)
4779(6)
4348(5)
3413(6)
3083(6)
3600(5)
3319(6)
3869(5)
4709(5)
4510(5)
4889(5)
2531(5)
2859(5)
1953(5)
771(5)
3647(1)
4323(3)
5169(3)
4286(3)
2943(3)
954(5)
9207(1)
9051(2)
9716(2)
9226(2)
8469(2)
7275(3)
7213(3)
10153(2)
8197(3)
7697(2)
6966(3)
8763(3)
10136(3)
7453(3)
10610(3)
7600(4)
8119(3)
7805(4)
8172(4)
8869(4)
9324(4)
10012(4)
10308(3)
11053(4)
11307(4)
10828(3)
9875(3)
9155(3)
8845(3)
8318(3)
8003(3)
8161(3)
8656(3)
9004(3)
9228(3)
8795(3)
11012(4)
10306(5)
10501(3)
33(1)
39(1)
48(1)
42(1)
51(1)
104(2)
76(2)
56(1)
51(1)
53(1)
82(2)
37(1)
37(1)
55(2)
54(1)
53(1)
47(2)
53(2)
55(2)
43(2)
60(2)
59(2)
44(2)
53(2)
50(2)
48(2)
37(1)
35(1)
33(1)
36(1)
37(1)
37(1)
31(1)
33(1)
32(1)
36(1)
72(2)
87(2)
48(2)
1613(4)
2549(3)
5127(3)
3692(4)
5074(4)
1809(3)
2653(3)
1613(4)
2469(4)
4632(5)
1360(5)
442(5)
Fig. 1 The asymmetry unit of the complex. H atoms are omit-
ted for clarity
–16(5)
409(5)
–83(5)
322(5)
1265(5)
1678(5)
2566(5)
3036(5)
1773(4)
1327(4)
3849(4)
3074(4)
2451(4)
2565(4)
3369(4)
3977(4)
4494(4)
3547(5)
2984(6)
1436(6)
2915(5)
Fig. 2 The tricap-triangular prism environment of praseodym-
ium ion
face-to-face distance of ca. 3.31  in offset fashion
into 2D wavelike layers. The 2D layers are arranged in
an ···ABAB··· fashion along c axis into 3D framework.
Thermal gravimetric analysis (DTG-DSC) for
the crystal sample was performed from 30 to 1000°C
at a heating rate of 10°C min–1 under a static air
atmosphere (Fig. 3) and the thermal decomposed
procedure are deduced as Scheme 1.
For the title complex, the thermal decomposition
procedure is divided into three stages. At the first
stage, the mass loss of 11.18% corresponds to the loss
of the DMF molecule (ca. 11.13% for one DMF),
which is consistent with the absence of the ex-
pected 1652 cm–1 for the carbonyl of DMF molecule in
IR spectrum of the middle product 1 at 320°C (Fig. 4).
The DMF molecule leaving process is an endothermal
one with the value of 66 J g–1 from the DSC curve in
Fig. 3. The further mass decrease from 320 to 418°C
425(4)
1314(4)
3506(5)
–887(5)
10642(6)
9852(7)
8608(6)
phen ligands are extended in a parallel fashion on both
sides of the 1D ribbon at a face to face distance
of 7.504  to give a spatial arrangement that is suitable
for aromatic intercalation. So the adjacent ribbons in-
teract strongly through p–p stacking interaction be-
tween the lateral slanted phen ligands at an offset
J. Therm. Anal. Cal., 85, 2006
803

CHEN et al.
30~164~345°C, 83.83% (84.18%)
[Pr(NO2 - bdc)(phen)(NO3 )(DMF)]¾¾¾¾¾¾¾¾¾® [Pr(NO2 - bdc)(phen)(NO3 )]
320~380.1~418°C, 70.06% (69.60%)
¾¾¾¾¾¾¾¾¾¾® [Pr(NO2 - bdc)(phen)(NO3 )]× Pr2O3
418~483.7~514°C, 24.83% (25.16%)
¾¾¾¾¾¾¾¾¾¾® 1/ 2Pr2O3
Scheme 1 Thermal decomposed procedure for the title complex
Fig. 4 The IR spectra for the a – title complex, b – middle
product 1 and c – middle product 2
Fig. 3 Thermal gravimetric curves for the title complex
is completely converted to Pr2O3 of 24.83%
(ca. 25.16%) at 514°C, and the metal content is ana-
suggests the stepwise decomposition of the compound
lyzed using the EDTA titration with 84.96%
and partly decomposition to Pr2O3, which could be
(ca. 85.45%). The heat sent out in the second stage is
proved by the IR spectrum of the middle product 2 for
measured as the value of 3465 J g–1 from DSC experi-
all the other characterized bands existed, expect for
ment. These results show the complex has high stabil-
the 1652 cm–1 for DMF molecule disappeared (Fig. 4).
ity partly due to strong supramolecular interactions.
Similarly, the heat of this process could be estimated
The enthalpy change of formation of the title
by DSC experiment as 59 J g–1. Finally, the compound
complex in DMF can be represented as:
Table 4 Selected bond lengths () and angle (°) for the complex
Pr(1)–O(2) #1
2.392(4)
2.404(3)
Pr(1)–O(3) #2
Pr(1)–O(9)
Pr(1)–N(1)
Pr(1)–N(2)
2.591(3)
2.628(4)
2.629(4)
2.679(4)
Pr(1)–O(1)
Pr(1)–O(7)
2.469(4)
Pr(1)–O(4) #2
2.522(4)
Pr(1)–O(8)
2.570(4)
O(2) #1–Pr(1)–O(1)
O(2) #1–Pr(1)–O(7)
O(1)–Pr(1)–O(7)
O(2) #1–Pr(1)–O(4) #2
O(1)–Pr(1)–O(4) #2
O(7)–Pr(1)–O(4) #2
O(2) #1–Pr(1)–O(8)
O(1)–Pr(1)–O(8)
O(7)–Pr(1)–O(8)
O(4) #2–Pr(1)–O(8)
O(2) #1–Pr(1)–O(3) #2
O(1)–Pr(1)–O(3) #2
O(7)–Pr(1)–O(3) #2
O(4)–Pr(1)–O(3) #2
O(8)–Pr(1)–O(3) #2
O(2) #1–Pr(1)–O(9)
O(1)–Pr(1)–O(9)
O(7)–Pr(1)–O(9)
86.62(12)
79.62(15)
137.72(13)
122.36(12)
143.73(12)
74.02(14)
91.88(14)
73.71(12)
145.76(14)
83.24(13)
72.47(12)
139.86(12)
72.62(13)
51.09(12)
73.19(13)
138.88(14)
71.71(12)
139.03(14)
O(4) #2–Pr(1)–O(9)
O(8)–Pr(1)–O(9)
O(3) #2–Pr(1)–O(9)
O(2) #1–Pr(1)–N(1)
O(1)–Pr(1)–N(1)
O(7)–Pr(1)–N(1)
O(4) #2–Pr(1)–N(1)
O(8)–Pr(1)–N(1)
O(3) #2–Pr(1)–N(1)
O(7)–Pr(1)–N(2)
O(2) #1–Pr(1)–N(2)
O(1)–Pr(1)–N(2)
O(7)–Pr(1)–N(2)
O(4) #2–Pr(1)–N(2)
O(8)–Pr(1)–N(2)
O(3) #2–Pr(1)–N(2)
O(9)–Pr(1)–N(2)
N(1)–Pr(1)–N(2)
72.02(13)
49.11(14)
102.04(13)
145.43(14)
89.41(13)
80.49(14)
78.06(13)
119.81(14)
126.93(13)
70.70(13)
85.12(13)
68.57(13)
70.55(13)
129.45(14)
142.27(13)
139.63(13)
116.51(14)
61.61(14)
*Symmetry transformations used to generate equivalent atoms for compound: #1 – –x+1, –y+1, –z+2, #2 – x+1, y, z
804
J. Therm. Anal. Cal., 85, 2006

NOVEL PRASEODYMIUM SUPERMOLECULAR COMPLEX
Table 5 Experimental data of the liquid phase formation
Acknowledgements
reaction for the title complex
Q1/mJ
Q2/mJ
We gratefully acknowledge the financial support from the Na-
tional Natural Science Foundation of China (Grant
No. 20471047), Education Committee Foundation of Shaanxi
Province (Grant No. 05JK291), the Nature Science Foundation
of Shaanxi Province (Grant No. FF05201 and FF05203).
–428.352
–428.732
32.603
32.542
–427.963
32.018
–428.015
32.332
–428.629
32.722
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–427.981
32.397
–428.279±0.140
32.436±0.101
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In the table, Q1 is the heat of formation reaction of the
complex in 0.5 mL DMF including 0.1 mol L–1 Pr(NO3)3
and 1.0 mL mixed DMF solution of 0.1 mol L–1 H2nip and
0.1 mol L–1 phen; Q2 is the diluted heat of 0.5 mL DMF
added into 1.0 mL mixed DMF solution of 0.1 mol L–1
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Pr(NO3 )3 + H2nip + phen + DMF ¾¾¾®
(1)
Pr(nip)(phen)(NO3 )(DMF) + 2HNO3
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according to [17–19]. The heat of formation reaction
Q1 and the solvent diluted heat Q2 were measured for
six times in DMF at 25.15°C (Table 5). The first
process is an exothermic one, while the second
process is an endothermic one at 25.15°C. Thus, the
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(2)
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molar number of praseodymium ion in the reaction).
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Conclusions
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We have prepared successfully the title complex
[Pr(5-nip)(phen)(NO3)(DMF)]. The crystal structure of
the complex was determined by single crystal X-ray
diffraction. In the complex each praseodymium(III)
ion is nine-coordinated. There exists strong p–p stack-
ing supramolecular interactions between two adjacent
ribbons, resulting in the high stability of the title com-
plex. The thermal decomposition procedure of the title
complex could be expressed by the scheme shown in
Scheme 1 and witnessed by IR spectra of the middle
produces. The enthalpy change of formation of the title
complex in DMF was obtained with the value of
–9.214±0.173 kJ mol–1.
19 S. Gao, S. Chen, G. Xie, G. Fan and Q. Shi,
J. Therm. Anal. Cal., 81 (2005) 387.
Received: December 25, 2005
Accepted: March 10, 2006
OnlineFirst: May 29, 2006
DOI: 10.1007/s10973-005-7490-1
J. Therm. Anal. Cal., 85, 2006
805