Syntheses, characterization and the liquid-phase formation enthalpy changes of two new one-dimensional ribbon-like lanthanide supermolecular polymers

Article abstract of DOI:10.1016/j.inoche.2006.03.021

Two novel one-dimensional ribbon-like mixed-ligand supermolecular polymers, [Ln(5-nip)(phen)(NO₃) (DMF)]_n (Ln = Pr (1) and Ho (2)), assembled into two-dimensional networks by strong π-π stacking interactions, have been synthesized by

Full text of DOI:10.1016/j.inoche.2006.03.021

Inorganic Chemistry Communications 9 (2006) 649–653
www.elsevier.com/locate/inoche
Syntheses, characterization and the liquid-phase formation
enthalpy changes of two new one-dimensional ribbon-like lanthanide
supermolecular polymers
a
a,
a
Yixia Ren a,b, Sanping Chen , Shengli Gao *, Qizhen Shi
a
Department of Chemistry, Shaanxi Key Laboratory of Physico-Inorganic Chemistry, Northwest University, Shaanxi 710069, PR China
b
Department of Chemistry, Yanan University, Yanan 716000, PR China
Received 15 January 2006; accepted 14 March 2006
Available online 30 March 2006
Abstract
Two novel one-dimensional ribbon-like mixed-ligand supermolecular polymers, [Ln(5-nip)(phen)(NO3) (DMF)]n (Ln = Pr (1) and Ho
(2)), assembled into two-dimensional networks by strong p–p stacking interactions, have been synthesized by reactions of lanthanide (III)
salts with 5-nitroisophatha acid (5-H2nip) and 1,10-phenanthroline (phen) in DMF solvent. They possessed high thermal stabilities and
their liquid-phase formation enthalpy changes were determined in DMF solvent at 25.15 °C using an RD496-III type microcalorimeter,
which were DrHh ð1Þ ¼ ꢀ9:21 kJ molꢀ1, and DrHh ð2Þ ¼ ꢀ11:02 kJ molꢀ1, respectively.
m
m
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Praseodymium; Holmium; 5-Nitroisophatha acid; 1,10-Phenanthroline; Supermolecular polymers
Many interactions including coordination bonding,
hydrogen bonding, aromatic p–p stacking interaction and
van der Waals force construct a great deal of different coor-
dination molecular architectures with different interesting
structural features. Aromatic p–p stacking interaction plays
a significant role in assembly of high-dimensional networks
as a intermolecular force, as hydrogen bonding does [1]. It
was reported that these interplanar distances were aboꢀu1t
their high coordination number [5]. However, owing to large
radii, high and variable coordination numbers, lanthanide
coordination polymers have attracted considerable interest.
In order to decrease the dimension of lanthanide coordina-
tion polymers, 5-nitroisophathaic acid is selected as a rigid
ligand with two kinds of function groups. In the self-assem-
ble process, the carboxyl can provide the probability of the
diversified coordinated modes, and the phenyl rigid skeleton
can be a brace for the framework. Although several transi-
tional metals compounds with 5-nitroisophthalic acid have
been reported [6], its lanthanide compounds are rarely stud-
ied. Additionally, 1,10-phenanthroline as a heteroatoms
cycle ligand is apt to form low-dimension coordination poly-
mers, while the potential p-stacking interaction can enhance
the stability of the polymers. Here we prepared two new
mixed-ligand lanthanide coordination polymers from 5-
nitroisophathalic acid and 1,10-phenanthroline in DMF sol-
vent. As we have predicted, they are one-dimension ribbons
structures and further build two-dimension wavelike layers
via strong offset face-to-face p–p stacking interactions.
˚
3.3–3.8 A [2] with a calculated energy of about 2 kJ mol
[3] for a typical aromatic–aromatic p-stacking interaction.
In the context of the metal compounds of mixed 2,20-bipyr-
idyl-like and carboxylate ligands, 2,20-bipyridyl-like ligands
such as bpy, phen, are able to engender the p–p stacking
interactions which enhances the stability of the compounds
both in solution and solid states [4]. In contrast to transition-
metal compounds, most of the lanthanide coordination
polymers are reported with high-dimension structures for
*
Corresponding author. Tel.: +86 29 88302604; fax: +86 29 88303798.
E-mail address: gaoshli@nwu.edu.cn (S. Gao).
1387-7003/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2006.03.021

650
Y. Ren et al. / Inorganic Chemistry Communications 9 (2006) 649–653
Fig. 1. The Pr(III) coordination environments in compound 1(a) and the infinite chain in 1 made up of binuclear Pr(III) SBUs (b). The hydrogen atoms are
˚
omitted for clarity. Selected bond lengths (A): Pr(1)–O(2) #1 2.392 (4), Pr(1)–O(1) 2.404 (3), Pr(1)–O(7) 2.469 (4), Pr(1)–O(4) #2 2.522 (4), Pr(1)–O(8) 2.570
(4), Pr(1)–O(3) #2 2.591 (3), Pr(1)–O(9) 2.628 (4), Pr(1)–N(1) 2.629 (4), Pr(1)–N(2) 2.679 (4). Symmetry code : #1 ꢀx + 1,ꢀy + 1,ꢀz + 2, #2 x+1, y, z.
Table 1
NO2
Crystal data and structure refinement for compound 1 and compound 2
M
1
2
O
O
O
O
Empirical formula
Formula weight
Crystal system
Space group
C
665.33
23H18N5O10Pr
C23H18N5O10Ho
689.35
Monoclinic
P2(1)/n
10.906 (3)
12.804 (3)
16.987 (4)
91.400 (5)
2371.4 (10)
4
M
C
C
Monoclinic
P2(1)/n
11.0876 (6)
12.8739 (7)
16.9994 (8)
91.193 (4)
2426.0 (2)
4
1320
1.822
2.077
14735
M
˚
a (A)
˚
Scheme 1. 5-nip2ꢀ coordination mode in compounds.
b (A)
˚
c (A)
b (°)
Reaction of the ligands 5-H2nip and phen with
Pr(NO3)3 Æ 6 H2O gave the one-dimensional ribbon-like
coordination polymer 1, [Pr(5-nip)(phen)(NO3)(DMF)]n
[7,8], (82% yield based on praseodymium). X-ray single-
crystal diffraction of 1 reveals that the Pr(III) ion is located
at the center of a distinctly distorted three-capped triangu-
3
˚
V (A )
Z
F(000)
1352
1.931
3.407
14808
Dcalc (Mg/m3)
l (mmꢀ1
)
Reflections collected
Independent reflections
Data/restraints/parameters 4322/0/354
Final R indices [I > 2r(I)]
˚
4322 [Rint = 0.0806] 5772 [Rint = 0.0982]
lar prism (Pr–O 2.391(4)–2.625 (4) A; Pr–N 2.627 (5)–2.681
(4) A), being coordinated by two oxygen atoms from two
5772/0/354
˚
R1 = 0.0382,
wR2 = 0.0740
R1 = 0.0739,
wR2 = 0.0810
R1 = 0.0616,
wR2 = 0.1318
R1 = 0.1282,
wR2 = 0.1574
1,3-bridged carboxyl groups of 5-nip ligands, two oxygen
atoms from one chelating carboxyl groups of 5-nip ligand,
two nitrogen atoms from a chelating phen molecule, two
oxygen ones from one nitrate group and one oxygen atom
from one DMF molecule (Fig. 1(a)). Herein, 5-nip ligand
acts in only a chelate-bidentate coordination mode
(Scheme 1). Each pair of Pr(III) ions is bridged by a pair
R indices (all data)
of syn–syn 5-nip carboxylate groups into a dimeric subunit
˚
with an intradimer Pr ꢁ ꢁ ꢁ Pr distance of 5.669 (1) A. The
different adjacent dimmers are doubly interlinked by the
Fig. 2. Perspective views of (a) the two-dimensional networks parallel to the ab plane and (b) the three-dimensional ꢁ ꢁ ꢁ ABAB ꢁ ꢁ ꢁ stacking fashion in
compound 1. The NOꢀ3 and hydrogen atoms are omitted for clarity.

Y. Ren et al. / Inorganic Chemistry Communications 9 (2006) 649–653
651
Table 2
˚
Selected bond lengths (A) and angle (°) for compounds
1
2
Pr(1)–O(2) #1
Pr(1)–O(1)
Pr(1)–O(7)
Pr(1)–O(4) #2
Pr(1)–O(8)
Pr(1)–O(3) #2
Pr(1)–O(9)
Pr(1)–N(1)
2.392 (4)
2.404 (3)
2.469 (4)
2.522 (4)
2.570 (4)
2.591 (3)
2.628 (4)
2.629 (4)
2.679 (4)
Ho(1)–O(5)
Ho(1)–O(4) #1
Ho(1)–O(10)
Ho(1)–O(7) #2
Ho(1)–O(1)
Ho(1)–N(2)
Ho(1)–O(6) #2
Ho(1)–O(2)
2.283 (6)
2.312 (5)
2.357 (6)
2.417 (6)
2.445 (7)
2.521 (8)
2.531(5)
2.533 (7)
2.559 (7)
84.9 (2)
Pr(1)–N(2)
Ho(1)–N(1)
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)
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)
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)
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)
O(5)–Ho(1)–O(4) #1
O(5)–Ho(1)–O(10)
O(4) #1–Ho(1)–O(10)
O(5)–Ho(1)–O(7) #2
O(4) #1–Ho(1)–O(7) #2
O(10)–Ho(1)–O(7) #2
O(5)–Ho(1)–O(1)
O(4) #1–Ho(1)–O(1)
O(10)–Ho(1)–O(1)
O(7) #2–Ho(1)–O(1)
O(5)–Ho(1)–N(2)
O(4) #1–Ho(1)–N(2)
O(10)–Ho(1)–N(2)
O(7) #2–Ho(1)–N(2)
O(1)–Ho(1)–N(2)
O(5)–Ho(1)–O(6) #2
O(4) #1–Ho(1)–O(6) #2
O(10)–Ho(1)–O(6) #2
O(7) #2–Ho(1)–O(6) #2
O(1)–Ho(1)–O(6) #2
N(2)–Ho(1)–O(6) #2
O(5)–Ho(1)–O(2)
O(4) #1–Ho(1)–O(2)
O(10)–Ho(1)–O(2)
O(7) #2–Ho(1)–O(2)
O(1)–Ho(1)–O(2)
N(2)–Ho(1)–O(2)
O(6) #2–Ho(1)–O(2)
O(5)–Ho(1)–N(1)
O(4) #1–Ho(1)–N(1)
O(10)–Ho(1)–N(1)
O(7) #2–Ho(1)–N(1)
O(1)–Ho(1)–N(1)
N(2)–Ho(1)–N(1)
O(6) #2–Ho(1)–N(1)
O(2)–Ho(1)–N(1)
81.1 (2)
138.5 (2)
123.34 (19)
142.7 (2)
75.0 (2)
90.2 (2)
74.0 (2)
144.3 (2)
81.4 (2)
146.4 (2)
91.0 (2)
80.2 (2)
77.8 (2)
120.7 (2)
71.87 (19)
137.7 (2)
73.0 (2)
52.26 (19)
71.4 (2)
127.5 (2)
138.1 (2)
71.1 (2)
138.9 (2)
71.6 (2)
50.8 (2)
69.9 (2)
103.5 (2)
83.5 (2)
69.3 (2)
70.4 (2)
131.7 (2)
143.2 (2)
64.0 (2)
138.4 (2)
117.0 (2)
Symmetry transformations used to generate equivalent atoms for compound 1: #1 ꢀx + 1,ꢀy + 1,ꢀz + 2, #2 x + 1, y, z; for compound 2 : #1
ꢀx + 2,ꢀy + 1,ꢀz + 1; #2 ꢀx + 1, ꢀy + 1, ꢀz + 1.
5-nip ligands to form an infinite ribbon (Fig. 1(b)). The
phen ligands are extended in a parallel fashion on both
sides of the 1D ribbon at a face to face distance of
arranged in an ꢁ ꢁ ꢁABABꢁ ꢁ ꢁ fashion along c axis into 3D
framework (Fig. 2(a) and (b)) (see Tables 1 and 2).
Reaction of the ligands 5-H2nip and phen with Ho-
(NO3)3 Æ 6H2O gave compound 2, [Ho(5-nip)(phen)(NO3)-
(DMF)]n [7,8], (78% yield based on holmium), which is
isomorphic as compound 1. The Ho ion is also in a nine-
˚
7.504 A to give a spatial arrangement that is suitable for
aromatic intercalation. The nitrate radicals and DMF mol-
ecules are decorated between the gaps of phen ligands to
occupy two coordinated sites of each Pr(III) ion and pre-
vent a 2D network from forming via coordinated bonds.
So the adjacent ribbons interact strongly through p–p
stacking interaction between the lateral slanted phen
˚
coordinated environment (Ho–O 2.283 (6)–2.533 (7) A;
˚
Ho–N 2.521 (8)–2.559 (7) A) (the Ho(III) ion coordination
environment figure is omitted.) and in the ribbon the intra-
˚
dimer metals distance is 5.572 (1) A . More interestingly, in
˚
ligands at a offset face-to-face distance of ca. 3.31 A in off-
the compound 2, the centroid-plane distance of the packed
phen ligands forming offset p–p stacking interaction is
set fashion into 2D wavelike layers. The 2D layers are

652
Y. Ren et al. / Inorganic Chemistry Communications 9 (2006) 649–653
the final produce was identified by the EDTA titration with
87.06% (ca. 87.30%).
In order to further study the thermal stabilities of the
two Lanthanide coordination polymers, we have measured
their enthalpy changes of liquid-phase formation reaction
in DMF solvent at 25.15 °C using an RD496-III type
microcalorimeter [10]. The reaction equation for com-
pounds is showed as:
LnðNO3Þ3 þ 5 ꢀH2nip þ phen þ DMF
DMF
! Lnð5 ꢀnipÞðphenÞðNO3ÞðDMFÞ þ 2HNO3
ð1Þ
ðLn¼Pr;HoÞ
The experiments were performed for the two com-
pounds according to ref [11]. UV spectrum of the final reac-
tion solutions is identical with that of solution of single
crystal sample in DMF. The enthalpy changes of liquid-
phase formation reaction for compound 1 is DrHhmð1Þ ¼
Fig. 3. The strong offset p–p stacking interaction with distance of ca.
3.27 A existing in Complex 2. The hydrogen atoms are omitted for clarity.
˚
ꢀ9:21 kJmolꢀ1, and DrHh ð2Þ ¼ ꢀ11:02 kJmolꢀ1 for com-
m
pound 2.
˚
ca.3.27 A (Fig. 3). The p–p stacking interaction is stronger
than that of 1 and embodied in the following thermal sta-
bilities of the two coordination polymers. The existences of
strong p–p stacking interaction between adjacent ribbons
by the phen rings in these compounds are alike as that of
some transitional metals compounds[9], such as a shorter
distance of p–p stacking in [Cd(mpa)(phen)]n (the distance
Acknowledgements
We gratefully acknowledge the financial support from
the National Natural Science Foundation of China (Grant
No. 20471047), Education committee Foundation of Sha-
anxi Province (Grant No. 05JK291), the Nature Science
Foundation of Shaanxi Province (Grant Nos. FF05201
and FF05203).
˚
is 3.32 A; mpa = m-phthalate) [9a], and in other com-
˚
pounds [Cu(oba)(phen)] (the distance is 3.42 A; H2oba =
4,40-oxybis(benzenecarboxylic acid)) [9b] [Co(oba)(phen)-
˚
(H2O)] (the distance is 3.48 A) [9c]. The interaction in 2 is
Appendix A. Supplementary data
stronger than that in any other coordination polymers
reported. Compared with 1, the mean distances of Ho–O
bonds and Ho–N bonds in 2 are a bit shorter than those
of Pr–O bonds and Pr–N bonds in 1, which could be attrib-
uted to the Lanthanide Contraction effect.
Crystallographic data for 1 and 2 have been deposited at
the Cambridge Crystallographic Data Center as supple-
mentary publications (CCDC: 1, 288565 ; 2, 288566). These
data can be obtained free of charge at http://www.ccdc.
cam.ac.ck/conts/retrieving.html or from the Cambridge
Crystallographic Data Center, 12 union Road, Cambridge
CB2 1EZ, UK (Fax: +44 1223336033; E-mail: deposit@
ccdc.cam.ac.uk).
Thermal gravimetric analyses (TGA) for the two crystal
samples were performed from 30 to 700 °C. For compound
1, the weight loss of 11.18% at the first stage corresponds to
the loss of the DMF molecule from 206 °C (ca. 11.13% for
one DMF), which is consistent with the absence of the
expected 1652 cmꢀ1 for the carbonyl of DMF molecule in
IR spectrum of the middle produce at 320 °C. The further
weight decrease from 320 °C to 418 °C suggests the step-
wise decomposition of the compound and partly decompo-
sition to Pr2O3. Finally, the compound is completely
converted to Pr2O3 of 24.83% (ca. 25.16%) residua rate at
514 °C, and the metal content is analyzed using the EDTA
titration with 84.96% (ca. 85.45%). Although the com-
pound 2 is isomorphic as compound 1, its thermal decom-
position process is only divided into two stages. Its first
stage from 35 °C includes the lost of DMF molecule and
partly decomposition into a middle product, which of the
process at 345 °C could be considered as a mixture. And
it is proved by IR spectrum, in which the 1670 cmꢀ1 for
DMF molecule also disappeared and all the other charac-
terized peaks existed. The mixture is further decomposed
to Ho2O3 up to 601 °C. Similarly, the metal content in
Crystal data and structure refinement, atomic coordi-
nates, bond lengths and angles, the IR spectrum are avail-
able from the authors on request.
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˚
˚
clinic, space group P21/n with a = 11.0876 (6) A, b = 12.8739 (7) A,
3
˚
˚
c = 16.9994 (8) A, b = 91.193(4)°, V = 2426.0 (2) A , Z = 4,
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q
cald = 1.822 Mg mꢀ3, T = 273(2) K, l = 2.077 mmꢀ1. R1 = 0.0382,
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˚
˚
space group P21/n with a = 10.906 (3) A, b = 12.804 (3) A, c = 16.987
3
˚
˚
(4) A, b = 91.400 (5)°, V = 2371.4 (10) A , Z = 4,
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[7] Complex 1: a mixture of Pr(NO3)3 Æ 6H2O (0.4352 g) and 5-H2nip
(0.2113 g) in 10 ml DMF was stirring at room temperature, to
which 5 ml DMF solution of 1,10-phen (0.1980 g) was added, and
a clear green solution was obtained. After 6 months placed in air,
some green block crystals suitable for single crystal X-ray
structural diffraction were recovered in the DMF solution. Anal.
Calcd. For C23H18N5O10Pr: C, 41.52, H, 2.73 and N, 10.53%.
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