Syntheses, crystal structures and properties of two novel lanthanide-carboxylate polymeric complexes

Article abstract of DOI:10.1039/b109985j

Two novel lanthanide-carboxylate polymeric complexes containing nine-coordinate lanthanide metal centers, [Nd(H₂btec)_1/2(btec)_1/2(H₂O)] _n (1), [Gd(Hbtec)]_n (2), have been prepared by hydrothermal reaction of NdCl₃·6H₂O or Gd(NO₃)₃·6H₂O with 1,2,4,5-benzenetetracarboxylic dianhydride. Complex 1 crystallizes in triclinic space group P1, with a = 6.3822(5), b = 9.3323(7), c = 9.5201(7) A, a = 88.422(2), β = 74.446(2), γ = 76.647(10)°, V = 531.13(7) A³ and Ζ = 2. Complex 2 crystallizes in triclinic space group P1, with a = 7.2325(7), b = 7.9946(8), c = 8.7833(9) A, a = 65.4120(10), β = 86.272(2), γ = 84.377(2)°; V = 459.42(8) A³ and Ζ = 2. The two complexes have high thermal stability and are stable up to 400°C. Magnetic susceptibility measurements for 1 and 2 are consistent with the occurrence of antiferromagnetic interactions through carboxylate bridges.

Full text of DOI:10.1039/b109985j

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Syntheses, crystal structures and properties of two novel
lanthanide-carboxylate polymeric complexes
Daofeng Sun, Rong Cao,* Yucang Liang, Qian Shi and Maochun Hong*
State Key Laboratory of Structural Chemistry,
Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fujian,
Fuzhou, 350002, China
Received 1st November 2001, Accepted 4th February 2002
First published as an Advance Article on the web 19th March 2002
Two novel lanthanide–carboxylate polymeric complexes containing nine-coordinate lanthanide metal centers,
[Nd(H2btec)1/2(btec)1/2(H2O)]n (1), [Gd(Hbtec)]n (2), have been prepared by hydrothermal reaction of NdCl3ؒ6H2O
or Gd(NO3)3ؒ6H2O with 1,2,4,5-benzenetetracarboxylic dianhydride. Complex 1 crystallizes in triclinic space group
3
¯
P1, with a = 6.3822(5), b = 9.3323(7), c = 9.5201(7) Å, α = 88.422(2), β = 74.446(2), γ = 76.647(10)Њ, V = 531.13(7) Å
¯
and Z = 2. Complex 2 crystallizes in triclinic space group P1, with a = 7.2325(7), b = 7.9946(8), c = 8.7833(9) Å,
α = 65.4120(10), β = 86.272(2), γ = 84.377(2)Њ; V = 459.42(8) Å3 and Z = 2. The two complexes have high thermal
stability and are stable up to 400 ЊC. Magnetic susceptibility measurements for 1 and 2 are consistent with the
occurrence of antiferromagnetic interactions through carboxylate bridges.
gray block-like crystals of 1 were obtained in 52% yield. Anal.
Introduction
Calc. for C10H5NdO9: C, 27.90; H, 1.21%; found: C, 27.87; H,
1.26%. IR (KBr, cmϪ1): 3491(s), 2804(m), 2644(m), 1668(vs),
1556(vs), 1394(vs), 1296(s), 1124(s), 879(s), 845(s), 791(s),
588(m).
The solid state assembly of metal–organic polymers has
attracted increasing attention due to the potential applications
in non-linear optics, magnetism and molecular recognition.1
With the aim of investigating the nature of the magnetic
exchange interactions between 3d and 4f metal ions in magnetic
materials, many polymeric complexes comprising of lanthanide
and transition metal ions have been studied in the past two
decades.2–4 Recently, polymeric complexes only constructed by
lanthanide centers have been reported in multicarboxylates5–8
or hybrid nitrogen–oxygen ligand systems,9–11 however, most of
such work focused on studying the framework structures of the
complexes rather than on magnetic properties.12 As known,
benzoic multicarboxylate ligands are versatile building blocks
for the architectures of polymeric structures due to their variety
of bridging abilities,13–15 and a series of interesting lanthanide
polymers have been obtained by employing benzoic multicarb-
oxylate ligands.5 Our previous work has proved that 1,2,4,5-
benzenetetracarboxylic acid (H4btec) is a good building block
for the construction of lanthanide polymers through full
or partial deprotonation of its carboxylic groups. Through
hydrothermal reactions of 1,2,4,5-benzenetetracarboxylic dian-
hydride with Ln(), we have obtained several open framework
structures containing channels with guest water molecules.16
The successful isolation of these complexes prompted us to
assembly lanthanide complexes containing magnetic centers
using H4btec. We selected Nd() and Gd() as the lanthanide
ions and hoped to obtain novel polymers with interesting
structures and magnetic properties. This paper reports the
synthesis and characterization of two magnetic complexes,
[Nd(H2btec)1/2(btec)1/2(H2O)]n (1) and [Gd(Hbtec)]n (2).
[Gd(Hbtec)]n (2). A mixture of Gd(NO3)3ؒ6H2O (0.11 g,
0.25 mmol), 1,2,4,5-benzenetetracarboxylic dianhydride (0.1 g,
0.5 mmol) and H2O (16 ml) in a mole ratio of ca. 1 : 2 : 3560 was
sealed in a 25 ml stainless-steel reactor with Teflon liner and
directly heated to 170 ЊC and kept at 170 ЊC for 3 days, then
cooled to room temperature during 5 hours. Colorless prism-
like crystals of 2 were obtained in 35% yield. Anal. Calc. for
C10H3GdO8: C, 29.39; H, 0.73%; found: C, 29.34; H, 0.81%.
IR (KBr, cmϪ1): 2783(s), 2505(s), 1811(w), 1676(vs), 1575(vs),
1493(vs), 1392(vs), 1342(vs), 1255(vs), 1184(s), 1005(m),
879(m), 854(s), 806(s), 548(s).
Crystallography
The intensity data of 1 and 2 were collected on a SIEMENTS
SMART CCD diffractometer with graphite-monochromated
MoKα (λ = 0.71073 Å) radiation at room temperature. All
absorption corrections were performed using the SADABS
program.17 The structures were solved by direct methods18 and
refined on F 2 by full-matrix least squares using the SHELXTL-
97 program package19 on a legend 586 computer. All non-
hydrogen atoms were refined anisotropically. The organic
hydrogen atoms were generated geometrically (C–H 0.96 Å).
The crystallographic data of complexes 1 and 2 are listed in
Table 1 with selected bond lengths and angles in Tables 2 and 3.
CCDC reference numbers 173159 for 1 and 173158 for 2.
See http://www.rsc.org/suppdata/dt/b1/b109985j/ for crystal-
lographic data in CIF or other electronic format.
Experimental
Preparation of complexes
Physical measurements
[Nd(H2btec)1/2(btec)1/2(H2O)]n (1). A mixture of NdCl3ؒ6H2O
(0.09 g, 0.25 mmol), 1,2,4,5-benzenetetracarboxylic dian-
hydride (0.1 g, 0.5 mmol) and H2O (16.0 ml) in a mol ratio of
ca. 1 : 2 : 3560 was sealed in a 25 ml stainless-steel reactor with
Teflon liner and directly heated to 170 ЊC and kept at 170 ЊC for
3 days, then cooled to room temperature during 5 hours. Light
The elementary analyses were performed in this institute.
Thermal gravimetric analysis was performed on a Delta Series
TGA7 instrument. Variable-temperature magnetic susceptibil-
ity data for polycrystalline samples of complexes 1 and 2 were
obtained in an external field of 10.0 kG on a Quantum Design
PPMS Model 6000 magnetometer from 300 to 4 K.
DOI: 10.1039/b109985j
J. Chem. Soc., Dalton Trans., 2002, 1847–1851
This journal is © The Royal Society of Chemistry 2002
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Table 1 The crystallographic data for complexes 1 and 2
Table 3 Selected bond lengths (Å) and angles (Њ) for 2
1
2
Gd–O(8)#1
Gd–O(1)#2
Gd–O(5)#3
Gd–O(7)#4
Gd–O(4)#5
Gd–O(3)#5
Gd–O(2)
2.363(6)
2.374(6)
2.432(6)
2.445(7)
2.451(7)
2.483(7)
2.485(7)
2.547(6)
2.588(6)
C(1)–O(1)
C(1)–O(2)
C(4)–O(3)
C(4)–O(4)
C(7)–O(5)
C(7)–O(6)
C(9)–O(7)
C(9)–O(8)
1.252(11)
Empirical formula
Mw
Space group
T /ЊC
a/Å
b/Å
c/Å
α/Њ
β/Њ
C10H5O9Nd
413.38
C10H3O8Gd
408.37
1.267(12)
1.278(12)
1.240(11)
1.208(12)
1.283(14)
1.240(12)
1.285(12)
¯
¯
P1
293
P1
293
6.3822(5)
9.3323(7)
9.5201(7)
88.422(2)
74.446(2)
76.647(10)
531.13(7)
2
2.585
0.71073
4.937
0.0281
0.0727
7.2325(7)
7.9946(8)
8.7833(9)
65.4120(10)
86.272(2)
84.377(2)
459.42(8)
2
2.952
0.71073
7.260
0.0432
0.1057
Gd–O(8)#4
Gd–O(1)
γ/Њ
O(8)#1–Gd–O(1)#2
O(8)#1–Gd–O(5)#3
O(1)#2–Gd–O(5)#3
O(8)#1–Gd–O(7)#4
O(1)#2–Gd–O(7)#4
O(5)#3–Gd–O(7)#4
O(8)#1–Gd–O(4)#5
O(1)#2–Gd–O(4)#5
O(5)#3–Gd–O(4)#5
O(7)#4–Gd–O(2)
156.4(2)
84.9(2)
86.3(2)
119.0(2)
78.9(2)
73.2(2)
84.0(2)
83.2(2)
124.9(2)
96.6(2)
74.6(2)
124.7(2)
67.2(3)
130.2(2)
72.9(2)
52.1(2)
145.5(2)
134.3(2)
O(7)#4–Gd–O(4)#5
O(8)#1–Gd–O(3)#5
O(1)#2–Gd–O(3)#5
O(5)#3–Gd–O(3)#5
O(7)#4–Gd–O(3)#5
O(4)#5–Gd–O(3)#5
O(8)#1–Gd–O(2)
O(1)#2–Gd–O(2)
O(5)#3–Gd–O(2)
O(2)–Gd–O(8)#4
O(8)#1–Gd–O(1)
O(1)#2–Gd–O(1)
O(5)#3–Gd–O(1)
O(7)#4–Gd–O(1)
O(4)#5–Gd–O(1)
O(3)#5–Gd–O(1)
O(2)–Gd–O(1)
153.7(3)
81.0(2)
75.5(2)
72.4(2)
138.0(2)
52.6(2)
78.1(2)
117.1(2)
152.8(2)
80.9(2)
127.5(2)
66.6(2)
146.8(2)
82.7(2)
472.5(2)
115.7(2)
50.8(2)
109.7(2)
V/Å3
Z
Dc/g cmϪ3
λ/Å
µ/mmϪ1
R1
wR2
Table 2 Selected bond lengths (Å) and angles (Њ) for 1
O(4)#5–Gd–O(2)
O(3)#5–Gd–O(2)
Nd–O(4)#1
Nd–O(3)#2
Nd–O(9)
2.376(3)
2.430(3)
2.458(4)
2.493(3)
2.505(3)
2.528(3)
2.528(3)
2.558(3)
2.599(3)
C(7)–O(1)
C(7)–O(2)
C(8)–O(3)
C(8)–O(4)
C(9)–O(5)
C(9)–O(6)
C(10)–O(7)
C(10)–O(8)
1.216(6)
1.314(6)
1.267(6)
1.252(6)
1.272(6)
1.257(6)
1.242(6)
1.248(6)
O(8)#1–Gd–O(8)#4
O(1)#2–Gd–O(8)#4
O(5)#3–Gd–O(8)#4
O(7)#4–Gd–O(8)#4
O(4)#5–Gd–O(8)#4
O(3)#5–Gd–O(8)#4
Nd–O(6)
Nd–O(5)#3
Nd–O(8)#4
Nd–O(1)
Nd–O(7)#4
Nd–O(5)
O(8)#4–Gd–O(1)
Symmetry transformations used to generate equivalent atoms: #1 Ϫx,
Ϫy, Ϫz ϩ 2. #2 Ϫx, Ϫy, Ϫz ϩ 1. #3 x ϩ 1, y ϩ 1, z Ϫ 1. #4 x, y ϩ 1,
z Ϫ 1. #5 x ϩ 1, y, z.
O(4)#1–Nd–O(3)#2
O(4)#1–Nd–O(9)
O(3)#2–Nd–O(9)
O(4)#1–Nd–O(6)
O(3)#2–Nd–O(6)
O(9)–Nd–O(6)
76.96(12)
139.98(14)
66.75(13)
81.07(12)
72.28(12)
102.48(14)
O(6)–Nd–O(1)
158.54(12)
85.70(12)
70.72(11)
73.40(13)
O(5)#3–Nd–O(1)
O(8)#4–Nd–O(1)
O(4)#1–Nd–O(7)#4
kinds of carboxylate ligands, H2btec2Ϫ and btec4Ϫ, in the struc-
ture. H2btec2Ϫ acts as µ6-bridge to link six neodymium atoms,
in which each protonated carboxylic group coordinates to one
neodymium atom through carbonyl oxygen atoms, while each
deprotonated carboxylic group bridges two neodymium atoms
(Scheme 1(a)); btec4Ϫ also acts as µ6-bridge linking six neo-
dymium atoms, in which two para-carboxylate groups adopt a
bidentate chelating mode coordinating to one neodymium atom
while the other two para-carboxylate groups adopt a bidentate
chelating-bridging mode connecting two neodymium atoms
(Scheme 1(c)). Thus, the neodymium atom is coordinated by
nine oxygen atoms, three from H2btc2Ϫ, five from btec4Ϫ and one
from a coordinated water molecule, the Nd–O distances range
from 2.376(3) to 2.599(3) Å and the nearest Nd ؒ ؒ ؒ Nd distance
is 4.350(3) Å, indicating the absence of a direct metal–metal
interaction. The C–O distances of the deprotonated carboxylic
groups are typical, ranging from 1.242(6) to 1.272(6) Å while a
clear difference of C–O bond distances within the protonated
carboxylic group is observed: C(7)–O(1) (1.216(6) Å) is much
shorter than C(7)–O(2) (1.314(6) Å), in accord with IR data. If
we neglect the bridging functions of the carboxylate groups in
H2btc2Ϫ and btec4Ϫ, each btec4Ϫ ligand links two Nd()-couples
and vice versa to form a one-dimensional chain structure. Every
two adjacent chains is linked by the carbonyl oxygen in H2btc2Ϫ
to generate a two-dimensional layer structure (Fig. 2(a)), and all
ligands in the layer are almost coplanar. The bridging carboxyl-
ate groups in H2btc2Ϫ and btec4Ϫ further connect the layers,
producing the final three-dimensional structure (Fig. 3(a)).
O(3)#2–Nd–O(7)#4 137.29(11)
O(9)–Nd–O(7)#4
O(6)–Nd–O(7)#4
O(5)#3–Nd–O(7)#4
O(8)#4–Nd–O(7)#4
O(1)–Nd–O(7)#4
O(4)#1–Nd–O(5)
O(3)#2–Nd–O(5)
O(9)–Nd–O(5)
146.27(13)
73.32(11)
80.83(11)
50.93(11)
121.59(11)
128.18(12)
101.92(11)
77.29(14)
51.13(10)
63.13(13)
114.19(11)
143.24(12)
74.48(11)
O(4)#1–Nd–O(5)#3 145.42(12)
O(3)#2–Nd–O(5)#3 136.54(11)
O(9)–Nd–O(5)#3
O(6)–Nd–O(5)#3
O(4)#1–Nd–O(8)#4
70.08(13)
113.35(10)
72.42(12)
O(3)#2–Nd–O(8)#4 142.26(12)
O(9)–Nd–O(8)#4
O(6)–Nd–O(8)#4
O(5)#3–Nd–O(8)#4
O(4)#1–Nd–O(1)
O(3)#2–Nd–O(1)
O(9)–Nd–O(1)
130.26(14)
122.73(11)
73.49(12)
88.51(13)
87.16(12)
73.85(14)
O(6)–Nd–O(5)
O(5)#3–Nd–O(5)
O(8)#4–Nd–O(5)
O(1)–Nd–O(5)
O(7)#4–Nd–O(5)
Symmetry transformations used to generate equivalent atoms: #1 Ϫx,
Ϫy ϩ 2, Ϫz. #2 x ϩ 1, y Ϫ 1, z. #3 Ϫx, Ϫy ϩ 1, Ϫz ϩ 1. #4 x, y ϩ 1, z.
Results and discussions
Crystal structures
[Nd(H2btec)1/2(btec)1/2(H2O)]n (1). Single crystal X-ray analy-
sis reveals complex 1 is a three-dimensional framework contain-
ing nine-coordinate neodymium centers; the local environment
around Nd() ion is depicted in Fig. 1(a). The observation of
an absorption peak at 1668 cmϪ1 for –COOH in the IR spec-
trum indicates the presence of protonated carboxylic groups in
the complex, and structural data (see below) show there are two
Scheme 1
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Fig. 2 The 2-D layer structure: (a) for 1, (b) for 2.
connected by bridging carboxylate groups, generating the final
three-dimensional network structure (Fig. 3b).
Thermal properties
The results of thermalgravimetric analyses (TGA) show that
the two complexes have high thermal stability. For 1, the weight
loss from 264 to 360 ЊC (4.26%) corresponds well to the loss of
the coordination water (calc. 4.35%). The final weight (95.74%)
leaves the framework [Nd(H2btec)1/2(btec)1/2] (calc. 95.64%).
Decomposition of 1 begins at 400 ЊC and is complete at about
480 ЊC. For 2, no weight loss is observed before 410 ЊC,
above which, 2 starts to decompose and the decomposition is
complete above 520 ЊC.
Fig. 1 The local coordination environment of lanthanide ion: (a) for
1, (b) for 2.
[Gd(Hbtec)]n (2). Complex 2 is also a three-dimensional
polymer, Fig. 1(b) shows the local environment around the
Gd() ion. The central gadolinium ion is coordinated by nine
oxygen atoms from six Hbtec3Ϫ ligands with Gd–O distances
ranging from 2.363(6) to 2.588(6) Å with the nearest Gd ؒ ؒ ؒ
Gd distance being 4.150(6) Å. Similarly to 1, a difference of
C–O bond distances is observed in the protonated carboxylic
group: C(7)–O(5) (1.208(12) Å) is shorter than C(7)–O(6)
(1.283(14) Å), in agreement with the presence of the absorption
peak at 1676 cmϪ1 for –COOH in IR spectrum. As depicted in
Scheme 1(b), Hbtec3Ϫ acts as a µ6-bridge linking six Gd atoms;
the protonated carboxylic group coordinates to one Gd atom
via a carbonyl oxygen atom, the carboxylate group at the meta
position of the protonated carboxylic group chelates one Gd
atom, while each of the other two carboxylate groups adopt a
chelating-bridging mode linking two Gd atoms. If the bridging
function of the ligands is neglected each gadolinium atom is
linked by four ligands and vice versa to form a two-dimensional
layer structure (Fig. 2(b)). Every two adjacent layers is further
Magnetic properties
Temperature-dependent magnetic susceptibility measurements
for 1 and 2 were performed for polycrystalline samples from
300 to 4 K on a Quantum Design PPMS Model 6000 magnet-
ometer. For both complexes, as the temperature is lowered, the
χM values increase gradually down to around 25 K, and then
increase dramatically (Fig. 4 and 5). According to the structural
characteristics, complexes 1 and 2 may exhibit Ln()–Ln()
magnetic exchange interactions mediated by carboxylate group
between layers. Scheme 2 shows the possible Ln()–Ln()
magnetic exchange chain.
The magnetic behavior of 1 is well interpreted based on a
modified analytical expression (eqn. (1)),20 which is derived
from Fisher model.
(1)
J. Chem. Soc., Dalton Trans., 2002, 1847–1851
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Fig. 5 Experimental χM and χMT vs. T curves for complex 2.
Where
u = coth(J/kT) Ϫ kT/J. By using least-squares
method, a satisfied fit of the data at 4–300 K was obtained with
the set of parameters of J = Ϫ18.7 K and g = 2. The goodness
of fit R, defined as R = Σ [(χM)obs Ϫ (χM)calc]2/Σ(χM)obs is 5.5 ×
i
i
i
10Ϫ4. The result illustrates the presence of antiferromagnetic
Nd()–Nd() interactions in 1 through bridging carboxylate
groups as shown in Scheme 2. However, the case in 2 is much
more complicated and all our attempts to model the experi-
mental data of 2 were unsuccessful, thus the χM data of 2
were fitted to a modified Curie–Weiss law χ = χ0 ϩ C/(T ϩ θ).
The calculated value of Cm is 7.137 and the Weiss temperature
θ = Ϫ0.834 K. The negative Weiss temperature indicates the
presence of antiferromagnetic Gd()–Gd() though a detailed
elucidation of the magnetic interaction in 2 is still awaited.
Acknowledgements
This work was supported by grants from the NNSF of China,
NSF of Fujian Province and the Key Project from CAS.
Fig. 3 The packing structure: (a) for 1 along the b axis, (b) for 2 along
the a axis.
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Scheme 2 Possible Ln()–Ln() magnetic exchange interactions.
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