Synthesis and characterization of new polynuclear lanthanide coordination polymers with 4,4′-oxybis(benzoic acid)

Article abstract of DOI:10.1016/j.poly.2005.02.022

Three new polynuclear lanthanide coordination polymers [Ln ₅(μ₃-OH)(oba)₇(H₂O) ₂]_n ? 0.5nH₂O (Ln = Eu (1), Ho (2)) and [Yb₆(oba)₉(H₂O)]_n (3) (H ₂oba = 4,4′-oxybis(benzoic acid)), were prepared by hydrothermal reactions. 1 and 2 are isomorphous and exhibit complicated three-dimensional structures based on [Ln₅(μ ₃-OH)(oba)₇(H₂O)₂] building blocks. In the asymmetric unit, there are five different coordination environments of Ln(III) ions, including a trinuclear hydroxo core. Complex 3 is a three-dimensional coordination polymer built up from a hexanuclear building block. In 3, Yb(III) ions have six different chemical environments and are in a regular arrangement, resulting in pseudohexagonal prisms along the a-axis. The luminescent property of 1 and magnetic behaviors of 2 and 3 have also been studied.

Full text of DOI:10.1016/j.poly.2005.02.022

Polyhedron 24 (2005) 823–830
www.elsevier.com/locate/poly
Synthesis and characterization of new polynuclear
0
lanthanide coordination polymers with 4,4 -oxybis(benzoic acid)
a
Yi-Bo Wang , Chang-Yan Sun , Xiang-Jun Zheng , Song Gao ,
a
a
b
c
Shao-Zhe Lu , Lin-Pei Jin
a,
*
a
Department of Chemistry, Beijing Normal University, Xinjiekou Road, Beijing 100875, PR China
State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and molecular Engineering,
Peking University, Beijing, 100871, PR China
b
c
Laboratory of Excited States Processes, Chinese Academy of Sciences; Changchun Institute of Optics, Fine Mechanics and Physics,
Chinese Academy of Sciences, Changchun 130021, PR China
Received 8 December 2004; accepted 22 February 2005
Available online 14 April 2005
Abstract
Three new polynuclear lanthanide coordination polymers [Ln
0
5
(l
3
-OH)(oba)
7
(H
2
O)
2 n 2
] Æ 0.5nH O (Ln = Eu (1), Ho (2)) and
[
and exhibit complicated three-dimensional structures based on [Ln
Yb (oba) (H O)] (3) (H oba = 4,4 -oxybis(benzoic acid)), were prepared by hydrothermal reactions. 1 and 2 are isomorphous
] building blocks. In the asymmetric unit,
6
9
2
n
2
5
(l
3
-OH)(oba)
7
(H
2
O)
2
there are five different coordination environments of Ln(III) ions, including a trinuclear hydroxo core. Complex 3 is a three-dimen-
sional coordination polymer built up from a hexanuclear building block. In 3, Yb(III) ions have six different chemical environments
and are in a regular arrangement, resulting in pseudohexagonal prisms along the a-axis. The luminescent property of 1 and magnetic
behaviors of 2 and 3 have also been studied.
Ó 2005 Elsevier Ltd. All rights reserved.
Keywords: Polynuclear; Coordination polymer; Lanthanide; Magnetic susceptibility; Photophysical property
1
. Introduction
environments of the lanthanides. However, the intro-
duction of polynuclear lanthanide species into the skel-
eton may create unusual architectures, and polynuclear
lanthanide complexes may also exhibit promising mag-
netic and luminescence properties as a consequence of
the unique spectroscopic and electronic characteristics
Coordination polymers have been extensively studied
recently due to their interesting structures coupled with
their promising applications in ion and solvent molecule
exchanges [1–5], gas sorption [6–10], luminescence
n
[
1
11,12], magnetism [13,14] and catalytic behavior [15–
7]. While much current research has focused on transi-
associated with their 4f electronic configuration. Only
a few examples of polynuclear lanthanide coordination
polymers have been prepared by lanthanide hydrolysis
controlled by different supporting ligands [28–31]. The
tion metal coordination polymers [18–27], lanthanide
coordination polymers, particularly polynuclear sys-
tems, have received less attention owing to the high
coordination number and the variable coordination
8
+
cubane-like tetranuclear [Ln (l -OH) ] unit is a com-
4
3
4
mon structural motif in these complexes [29–31]. Here,
we report pentanuclear lanthanide coordination poly-
mers [Ln (l -OH)(oba) (H O) ] Æ 0.5nH O (Ln = Eu
*
5
3
7
2
2 n
2
Corresponding author. Tel.: +01058805522/861062205522; fax:
8601058802075/861062202075.
E-mail address: lpjin@bnu.edu.cn (L.-P. Jin).
(1), Ho (2)), in which both hydroxyl and carboxyl
groups link the lanthanide (III) ions into building
+
0
277-5387/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.02.022

824
Y.-B. Wang et al. / Polyhedron 24 (2005) 823–830
blocks, and a hexanuclear ytterbium coordination poly-
mer [Yb (oba) (H O)] (3).
heated at 200 °C for 72 h, then slowly cooled to room
temperature. Colorless crystals of 1 were obtained.
Yield: 0.02 g (38.4%). Anal. Calc. for C H Eu O38.50:
6
9
2
n
9
8
62
5
C, 45.00; H, 2.37; Found: C, 44.89; H, 2.32%. IR
ꢀ
1
(KBr, cm ): 3447m, 1598s, 1524s, 1400s, 1253s,
2
. Experimental
1
233s, 1160s, 1012w, 881m, 784s, 656w.
[Ho (oba) (OH)(H O) ] Æ 0.5nH O (2). Light yel-
2
.1. Chemicals and measurements
5
7
2
2 n
2
low crystals of 2 were prepared in the same manner as
above. Yield: 0.017 (31.9%). Anal. Calc. for
C H Ho O : C, 43.91; H, 2.11; Found: C, 44.05;
EuCl Æ 6H O, HoCl Æ 6H O and YbCl Æ 6H O
g
3
2
3
2
3
2
were prepared by dissolving their oxides in concen-
trated hydrochloric acid, respectively, and the solvents
were evaporated to dryness. The lanthanide and water
contents of the lanthanide chloride hydrates were
determined by EDTA titration. All the other reagents
were commercially available and used without further
purification. Elemental analyses were performed on an
Elementar Vario EL analyzer. The IR spectra were
recorded with a Nicolet Avatar 360 FT-IR spectrom-
eter using the KBr pellet technique. The luminescence
spectra were recorded at 77 K using a YAG:Nd laser
with an excitation wavelength of 355 nm and a SPEX
9
8
62
5
38.50
ꢀ
1
H, 2.30%. IR (KBr, cm ): 3459m, 1599s, 1526s,
1414s, 1254s, 1235s, 1161s, 1012w, 882m, 784s, 658m.
[Yb (oba) (H O)] (3). Colorless crystals of 3 were
6
9
2
n
obtained in the same manner. Yield: 0.048 g (43.5%).
Anal. Calc. for C126H O Yb : C, 45.01; H, 2.16;
74
46
6
ꢀ
1
Found: C, 44.99; H, 2.24%. IR (KBr, cm ): 3439m,
1599s, 1533s, 1417s, 1305m, 1252s, 1161s, 1097m,
1012w, 881m, 783s, 656w.
2.3. X-ray diffraction determination
1
403 double grating monochromator. The tempera-
The X-ray single crystal data collections for com-
plexes 1–3 were performed on a Bruker Smart 1000
CCD diffractometer, using graphite-monochromated
ture dependence of magnetic susceptibility for crystal-
line samples was recorded on an Oxford MagLab
˚
2
2
000 magnetometer in the temperature range of
–300 K.
Mo Ka radiation (k = 0.71073 A). Semi-empirical
absorption corrections were applied using the SADABS
program. The structures were solved by direct methods
2
and refined by full-matrix least square on F using the
2
.2. Synthesis
SHELXTL-97 program [32]. All non-hydrogen atoms were
refined anisotropically. The hydrogen atoms were gener-
ated geometrically and treated by a mixture of indepen-
dent and constrained refinement. The crystallographic
data for complexes 1–3 are listed in Table 1, and selected
[
Eu (oba) (OH)(H O) ] Æ 0.5n(H O) (1). A mix-
5
7
2
2 n
2
ture of EuCl Æ 6H O (0.037 g, 0.1 mmol), H oba
0.039 g, 0.15 mmol), H O (10 ml) and 0.65 M NaOH
2
3
2
2
(
aqueous solution (0.31 ml, 0.20 mmol) was sealed in a
3-ml stainless-steel reactor with a Teflon liner and
˚
2
bond lengths (A) in Table 2.
Table 1
Crystal data for 1–3
Compound
1
2
3
Empirical formula
Formula weight
Crystal system
Space group
C
2615.28
98
H
62Eu
5
O
38.50
C
2680.13
98
H
62Ho
5
O
38.50
C
3360.08
126 74 6
H O46Yb
monoclinic
P2(1)/c
27.983(7)
20.538(5)
15.833(4)
90
monoclinic
P2(1)/c
27.947(9)
20.367(6)
15.730(5)
90
monoclinic
Pc
˚
a (A)
14.657(4)
23.113(7)
20.187(5)
90
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
Z
90.736(5)
90
90.572(5)
90
115.408(16)
90
4
4
2
˚
V (A )
3
9099(4)
1.909
8953(5)
1.988
6177(3)
1.806
293(2)
ꢀ
3
q
Temperature (K)
calcd (g cm
)
293(2)
3.491
293(2)
4.464
ꢀ1
l (mm
Reflections collected
)
4.584
31616, 19620
0.0536
26254, 12718
0.1724
0.71073
48535, 18197
0.0651
0.71073
Total, independent, Rint
˚
k (Mo Ka), (A)
0.71073
0.0611, 0.1343
R
1
, wR
2
[I > 2r(I)]
0.0560, 0.0742
0.0504, 0.1105

Y.-B. Wang et al. / Polyhedron 24 (2005) 823–830
825
Table 2
Selected bond lengths (A) for 1–3
˚
1
Eu(1)–O(1)
Eu(1)–O(2)
2.68(1)
Eu(2)–O(35)#1
Eu(2)–O(37)
Eu(2)–O(38)
Eu(3)–O(7)
2.28(2)
2.43(1)
2.48(1)
2.53(1)
2.33(2)
2.29(1)
2.26(1)
2.33(1)
2.42(1)
2.36(1)
2.30(1)
2.37(1)
2.43(1)
Eu(4)–O(20)
Eu(4)–O(24)
Eu(4)–O(26)#7
Eu(4)–O(29)#3
Eu(4)–O(31)#3
Eu(5)–O(5)
2.71(1)
2.33(1)
2.41(1)
2.49(1)
2.42(1)
2.39(1)
2.27(1)
2.36(1)
2.32(1)
2.53(1)
2.44(1)
2.61(1)
2.43(1)
2.42(1)
2.45(1)
2.48(2)
2.43(1)
2.36(2)
2.47(2)
2.36(1)
2.39(1)
2.58(1)
2.49(1)
2.40(1)
2.35(1)
Eu(1)–O(6)#3
Eu(1)–O(11)
Eu(1)–O(15)#2
Eu(1)–O(17)#1
Eu(1)–O(34)#1
Eu(1)–O(38)
Eu(2)–O(1)
Eu(3)–O(12)
Eu(3)–O(14)#2
Eu(3)–O(21)#4
Eu(3)–O(27)#6
Eu(3)–O(36)
Eu(3)–O(38)
Eu(4)–O(4)
Eu(5)–O(9)
Eu(5)–O(20)
Eu(5)–O(25)
Eu(5)–O(29)
Eu(5)–O(30)
Eu(5)–O(31)
Eu(5)–O(32)
Eu(2)–O(6)
Eu(2)–O(7)
Eu(2)–O(16)#4
Eu(2)–O(22)#4
Eu(4)–O(10)#3
Eu(4)–O(19)
Symmetry operation: #1 x + 1, ꢀy + 1/2, z ꢀ 1/2; #2 ꢀx, ꢀy + 1, ꢀz ꢀ 1; #3 x, ꢀy + 1/2, z ꢀ 1/2; #4 x + 1, y, z; #5 x, ꢀy + 1/2, z + 1/2; #6 ꢀx,
y + 1/2, ꢀz + 1/2; #7 x, y, z ꢀ 1.
2
Ho(1)–O(1)
Ho(1)–O(2)
2.76(1)
2.35(1)
2.40(1)
2.40(1)
2.33(1)
2.31(1)
2.37(1)
2.33(1)
2.32(1)
2.54(1)
2.43(1)
2.32(1)
2.31(1)
Ho(2)–O(35)#1
Ho(2)–O(37)
Ho(2)–O(38)
Ho(3)–O(7)
2.20(1)
2.39(1)
2.42(1)
2.55(1)
2.28(1)
2.26(1)
2.24(1)
2.27(1)
2.35(1)
2.32(1)
2.25(1)
2.30(1)
2.37(1)
Ho(4)–O(20)
Ho(4)–O(24)
Ho(4)–O(26)#6
Ho(4)–O(29)#3
Ho(4)–O(31)#3
Ho(5)–O(5)
2.71(1)
2.28(1)
2.36(1)
2.46(1)
2.36(1)
2.33(1)
2.26(1)
2.32(1)
2.25(1)
2.48(1)
2.37(1)
2.62(1)
2.37(1)
Ho(1)–O(6)#3
Ho(1)–O(11)
Ho(1)–O(15)#2
Ho(1)–O(17)#1
Ho(1)–O(34)#1
Ho(1)–O(38)
Ho(2)–O(1)
Ho(3)–O(12)
Ho(3)–O(14)#2
Ho(3)–O(21)#4
Ho(3)–O(27)#5
Ho(3)–O(36)
Ho(3)–O(38)
Ho(4)–O(4)
Ho(5)–O(9)
Ho(5)–O(20)
Ho(5)–O(25)
Ho(5)–O(29)
Ho(5)–O(30)
Ho(5)–O(31)
Ho(5)–O(32)
Ho(2)–O(6)
Ho(2)–O(7)
Ho(2)–O(16)#4
Ho(2)–O(22)#4
Ho(4)–O(10)#3
Ho(4)–O(19)
Symmetry operation: #1 x + 1, ꢀy + 1/2, z ꢀ 1/2; #2 ꢀx + 2, ꢀy + 1, ꢀz + 1; #3 x, ꢀy + 1/2, z ꢀ 1/2; #4 x + 1, y, z; #5 ꢀx + 2, y + 1/2, ꢀz + 5/2; #6
x, y, z ꢀ 1.
3
Yb(1)–O(2)
Yb(1)–O(7)
2.23(3)
2.24(2)
2.25(2)
2.22(2)
2.26(2)
2.30(4)
2.59(2)
2.33(2)
2.30(2)
2.58(2)
2.25(2)
2.20(2)
2.32(2)
2.29(2)
Yb(3)–O(15)
Yb(3)–O(21)
Yb(3)–O(22)
Yb(3)–O(25)#2
Yb(3)–O(26)
Yb(3)–O(30)#4
Yb(3)–O(31)
Yb(4)–O(1)#6
Yb(4)–O(6)#6
Yb(4)–O(7)#6
Yb(4)–O(9)#5
Yb(4)–O(27)
Yb(4)–O(29)#4
Yb(4)–O(32)
2.31(2)
2.47(2)
2.34(2)
2.15(2)
2.23(2)
2.25(2)
2.20(2)
2.29(4)
2.25(2)
2.60(2)
2.20(1)
2.26(2)
2.15(2)
2.28(2)
Yb(5)–O(12)
2.23(2)
2.23(2)
2.20(2)
2.51(4)
2.27(3)
2.33(2)
2.60(2)
2.26(4)
2.31(2)
2.22(2)
2.22(2)
2.21(2)
2.20(2)
2.22(2)
Yb(5)–O(35)#4
Yb(5)–O(37)#5
Yb(5)–O(39)
Yb(1)–O(10)#1
Yb(1)–O(11)
Yb(1)–O(42)#1
Yb(1)–O(45)
Yb(2)–O(4)#3
Yb(2)–O(5)#3
Yb(2)–O(14)
Yb(2)–O(15)
Yb(2)–O(16)
Yb(2)–O(20)#2
Yb(2)–O(21)
Yb(2)–O(24)#2
Yb(5)–O(40)
Yb(5)–O(41)#1
Yb(5)–O(42)#1
Yb(5)–O(44)
Yb(6)–O(4)#6
Yb(6)–O(17)#7
Yb(6)–O(19)#8
Yb(6)–O(34)#4
Yb(6)–O(36)#5
Yb(6)–O(47)
Symmetry operation: #1 x ꢀ 1, ꢀy + 1, z ꢀ 1/2; #2 x ꢀ 1, ꢀy, z ꢀ 1/2; #3 x, y ꢀ 1, z + 1; #4 x + 1, y, z; #5 x ꢀ 1, y, z; #6 x, ꢀy + 1, z + 1/2; #7 x,
y, z ꢀ 1/2; #8 x ꢀ 1, y, z ꢀ 1.
ꢀ
3
. Results and discussion
phous and thus only the structures of 1 and 3 will be dis-
cussed here.
3
.1. Description of the structures
[Eu (oba) (OH)(H O) ] Æ 0.5nH O (1). Complex 1
5
7
2
2 n
2
is a three-dimensional polymer containing rugby-like
2
ꢀ
In complexes 1–3, the carboxyl groups of the H oba
2
channels. Three types of coordination modes of oba
ligands are present in the structure: (a) one carboxylate
ligands are all deprotonated and adopt four kinds of
coordination modes (see Scheme 1). 1 and 2 are isomor-
2
group of the oba ligand adopts a bridging bidentate
ꢀ

826
Y.-B. Wang et al. / Polyhedron 24 (2005) 823–830
Ln
O
Ln
Ln
Ln
O
O
Ln
Ln
O
O
O
O
Ln
Ln
C
C
O
C
C
C
O
C
O
Ln
(
a)
(b)
Ln
Ln
O
O
O
O
Ln
Ln
Ln
Ln
O
O
O
C
O
C
O
Ln
O
(
c)
(d)
2
Scheme 1. The coordination modes of oba ligands in 1–3.
ꢀ
mode, while the other adopts a chelating-bridging tri-
2ꢀ
two coordinated water molecules and half a lattice water
molecule. The coordination environments of five Eu(III)
ions are shown in Fig. 1(a) and the details are listed in
Table 3. For clarity, we may divide the coordination
environments into two parts (Fig. 1(b) and (c)), which
a
dentate mode, connecting four Eu(III) ions ( oba
,
2
ꢀ
Scheme 1(a)); (b) one carboxylate group of the oba li-
gand adopts a bridging bidentate mode, while the other
adopts a chelating-bridging tetradentate mode, connect-
b
2ꢀ
a
2ꢀ
b
2ꢀ
ing five Eu(III) ions ( oba , Scheme 1(b)); (c) each car-
are connected by one oba and two oba ligands.
In Fig. 1(b), Eu1, Eu2 and Eu3 are linked together by
2
boxylate group of the oba ligand adopts a bridging
ꢀ
c
2ꢀ
bidentate mode, connecting four Eu(III) ions ( oba
Scheme 1(c)). The asymmetric unit of 1 consists of five
2
Eu(III) ions, seven oba ligands, one hydroxyl group,
,
one l -OH, and therefore a distorted tetrahedron is
3
3
+
formed by three Eu
ions and one oxygen atom
ꢀ
of l -OH, where the distance of the oxygen atom of
3
(
a)
(
b)
(c)
3+
3+
Fig. 1. (a) The coordination environment of Eu ions in 1; (b) The coordination environment of Eu ions of the trinuclear core; (c) The
3+
coordination environment of the other two Eu ions in 1 with thermal ellipsoids at 20% probability. All hydrogen atoms and partial carbon atoms
are omitted for clarity.

Y.-B. Wang et al. / Polyhedron 24 (2005) 823–830
827
Table 3
The coordination environment of Eu in 1
3+
Metal atom
CN
No. of Coordinated l
3
-OH
No. of coordinated carboxyl oxygen atoms
2
No. of coordinated H O
a
2ꢀ
b 2ꢀ
oba
c
2ꢀ
oba
oba
Eu1
Eu2
Eu3
Eu4
Eu5
8
8
7
8
8
1
1
1
4
3
1
6
6
1
2
1
1
1
2
1
3
1
1
1
1
CN, coordination number; No, number.
˚
l -OH to the triangular metal face is 0.639A. In the
3
europium hydroxo core, the separations of Eu1ꢁ ꢁ ꢁEu2,
Eu2ꢁ ꢁ ꢁEu3 and Eu1ꢁ ꢁ ꢁEu3 are 3.898, 3.977 and 4.119
3
A, respectively, and a pair of adjacent Eu ions are
+
˚
2
ꢀ
bridged by two carboxylate groups of two oba ligands
through bridging bidentate and chelating-bridging tri-
dentate fashion. Thus the europium hydroxo core is sur-
rounded by the six carboxyl groups and a cage-like
structure is produced. In the trinuclear core, the average
ꢀ
ꢀ
distances of Eu1–O(COO ), Eu2–O(COO ), Eu3–
ꢀ
ꢀ
O(COO ) and Eu–O(OH ) are 2.470, 2.416, 2.347 and
2
˚
.400 A, respectively, which are in accord with the val-
2
4+
ues in [Eu (l -OH) (l -X)]
[33]. The other two
Eu ions (Fig. 1(c)), Eu4 and Eu5, are bridged by three
1
5
3
20
5
3
+
2
ꢀ
carboxyl groups of three oba ligands through bridging
bidentate and chelating-bridging tridentate coordination
ꢀ
modes. The average distances of Eu4–O(COO ) and
ꢀ
˚
Eu5–O(COO ) are 2.430 and 2.418 A, which are in
ꢀ
agreement with the common distances of Eu–O(COO ),
˚
and the distance of Eu4ꢁ ꢁ ꢁEu5 is 4.281 A. The Eu(III)
a
ions along the a-axis are bridged by oba and oba
2ꢀ
b
2ꢀ
ligands into one-dimensional double-chains with rugby-
like micropores. These chains are further cross-linked by
2
ꢀ
oba ligands, resulting in the formation of a three-
dimensional network, as shown in Fig. 2. There are
small rugby-like channels along the c-axis.
[Yb (oba) (H O)] (3). Complex 3 is a three-
6 9 2 n
dimensional polymer. The hexanuclear species [Yb6-
Fig. 2. The three-dimensional network of 1 viewed along the c-axis.
(
There are three types of coordination modes of oba
ligands in 3: (a) one carboxylate group of the oba
oba) (H O)] may be viewed as the building block.
9
2
2
ꢀ
ꢀ
in Table 4. For clarity we can also divide the Yb(III)
ions into two parts: part 1 consists of Yb1, Yb5 and
Yb6; while part 2 consists of Yb2, Yb3 and Yb4. The
2
ligand adopts a bridging bidentate mode, while the other
adopts a chelating-bridging tridentate mode, connecting
a
2ꢀ
two parts are linked by two oba ligands. In part 1,
Yb5 and Yb6 are connected by two bridging bidentate
a
four Yb(III) ions ( oba , Scheme 1(a)); (b) each car-
2ꢀ
2
boxylate group of the oba ligand adopts a bridging
ꢀ
2ꢀ
carboxyl groups of two oba ligands; while Yb5 and
Yb1 are connected by two bridging bidentate carboxyl-
ate groups and one chelating-bridging tridentate car-
c
bidentate mode, connecting four Yb(III) ions ( oba
2ꢀ
ꢀ
,
2
Scheme 1(c)); (c) one carboxylate group of the oba li-
gand adopts a bridging bidentate mode, while the other
adopts a chelating bidentate mode, connecting three
2
ꢀ
boxyl group of three oba ligands. In part 2, Yb3 is
connected to Yb4 by three bridging bidentate carboxyl
d
2ꢀ
2ꢀ
Yb(III) ions ( oba , Scheme 1(d)). In the asymmetrical
groups of three oba ligands, and connected to Yb2
by two chelating-bridging tridentate carboxyl groups
and one bridging bidentate carboxylate group of three
2
ꢀ
unit of 3, there are six Yb(III) ions, nine oba ligands
and one aqua ligand. The coordination environment of
Yb(III) ions is shown in Fig. 3 and the details are listed
2
oba ligands. The average distances of Yb–O(COO )
ꢀ
ꢀ

828
Y.-B. Wang et al. / Polyhedron 24 (2005) 823–830
2
ꢀ
coordination modes of oba ligands lead to the differ-
ent structures.
Although the ‘‘O’’ atoms between two benzene rings
2
ꢀ
in each oba ligand do not participate in the coordina-
tion to Ln(III) ions, however, they are important in the
2
ꢀ
structure. With the presence of these ‘‘O’’ atoms, oba
ligands act as V-shaped, not linear ligands. It is the
2
ꢀ
V-shaped configuration of oba ligands, which facili-
tates the benzene rings and carboxylate groups to adjust
their steric configurations more freely and allow the
2ꢀ
oba ligands to display a variety of coordination modes.
3
.2. Photophysical properties of complex 1
The room temperature spectra of powders for 1 are
less developed, we comment about low temperature
spectra only. The high-resolution emission spectrum of
3
+
Fig. 3. The coordination environment of Yb ions in 3 with thermal
ellipsoids at 20% probability. All hydrogen atoms are omitted for
clarity.
5
7
1
cited by 355 nm at 77 K is shown in Fig. 5. The most
corresponding to D ! F (J = 0–4) transitions ex-
0
J
5
7
intensive transition is D ! F , which implies red
0
2
Table 4
The coordination environment of Yb in 3
emission light of 1. The number of components of the
3+
5
7
D ! F transition indicates the presence of more
0
1
CN
No. of carboxyl oxygen atoms
No. of coordinated
H
than one chemically different Eu(III) ions site [34]. The
a
2ꢀ
c
2ꢀ
d
oba
2ꢀ
2
O
5
7
oba
oba
intensity of the D ! F transition is relatively weak
0
0
Yb1
Yb2
Yb3
Yb4
Yb5
Yb6
6
8
7
7
8
6
6
6
4
4
4
1
and the emission band is broad (see the inserted spec-
trum in Fig. 5). The inhomogeneous broadening of the
2
3
3
1
3
5
7
D ! F emission band arises from the site to site
0
0
variation of the local field acting on the ions, and has
consequently been studied by selective excitation
techniques.
3
1
1
CN, coordination number; No, number.
ꢀ
1
Setting the analyzing wavenumber to 16233 cm
and scanning in the range of 578.72–580.4 nm
7
5
(
F ! D ), the excitation spectrum (Fig. 6) was ob-
0
0
tained. There are two obvious groups of peaks located
at about 579.4 and 580.0 nm. The negative charges on
the ligands around Eu1, Eu2, Eu3, Eu4 and Eu5 are
approximately 3.4, 2.5, 2.6, 3.3 and 3.2, respectively.
They can be divided into two groups. One group (3.4,
3.3 and 3.2) contains Eu1, Eu4 and Eu5. The other
group (2.5 and 2.6) contains Eu2 and Eu3. As is known,
(from Yb1 to Yb6) are 2.249, 2.356, 2.280, 2.290, 2.330
˚
and 2.231 A, respectively, and the separations of
Yb1ꢁ ꢁ ꢁYb5, Yb5ꢁ ꢁ ꢁYb6, Yb2ꢁ ꢁ ꢁYb3 and Yb3ꢁ ꢁ ꢁYb4
˚
are 4.002, 4.510, 3.823 and 4.330 A, respectively.
In each asymmetrical unit of 3, six Yb(III) ions are
arranged in the form of a non-planar six-member ring.
And along the a-axis, two adjacent six-member rings
are parallel to each other. As shown in Fig. 4, for in-
stance, a six-member ring constructed by Yb2J, Yb3J,
Yb4J, Yb1J, Yb5J and Yb6J is parallel to an adjacent
six-member ring formed by Yb2M, Yb3M, Yb4M,
Yb1M Yb5M and Yb6M. These two rings are pillared
by oba ligands along the a-axis to yield a pseudohex-
agonal prism, which is the first example of such an array
of lanthanide (III) ions. These pseudoprisms are cross-
linked by oba ligands, resulting in the formation of
a three-dimensional network.
Comparing the structures of 1–3, it can be seen that
7
5
the peak position of F
! D
will shift to lower energy
0
0
with increasing negative charge on the ligands [35]. So
the left peak denoted as A in Fig. 6 can be ascribed to
5
the contribution of D
levels of Eu2 and Eu3, and the
right peak denoted as B in Fig. 6 can be ascribed to
0
5
the contribution of D
levels of Eu1, Eu4 and Eu5.
0
2
ꢀ
3.3. Magnetic properties
2
ꢀ
The temperature dependence of the magnetic suscep-
tibility of 2 was measured in the temperature range
2–300 K (Fig. 7). The magnetic susceptibility above 50
K obeys the Curie–Weiss law [v = C/(T ꢀ h)] with
2
ꢀ
oba ligands display different coordination modes. In
2ꢀ
2
and 2, there are three kinds of oba ligands: oba
ꢀ
a
3
ꢀ1
1
b
,
2ꢀ
C = 71.43 cm mol K and h = ꢀ10.79 K. The C value
ꢀ1
3+
2ꢀ
c
oba and oba ; while in 3, the three kinds of oba
2ꢀ
3
is close to the expected value of 70.35 cm mol K for
a
ligands are oba , oba and oba . The different
2ꢀ
c
2ꢀ
d
2ꢀ
five non-interacting Ho free ions. The continuous

Y.-B. Wang et al. / Polyhedron 24 (2005) 823–830
829
Fig. 4. The hexagonal pseudoprism distribution of Yb(III) ions in 3.
6000
5000
4000
3000
2000
1000
5
D0
7
F2
A
5
7
D
F
0
0
B
17150
17200
17250
17300
-1
Wavenumber/cm
5
D0
7
5
7
F1
D0
F4
5
7
F3
D0
5
7
F0
D0
1
4250
15000
15750
16500
17250
5
78.8
579.2
579.6
580.0
580.4
-1
Wavenumber/cm
Wavelength/nm
5
7
Fig. 5. Emission spectrum of 1 corresponding to D
transitions at 77 K, kexc = 355 nm.
0
! F
J
(J = 0–4)
7
F
5
Fig. 6.
7 K, k
0
! D
0
excitatation spectrum of powders for 1 recorded at
7
m
= 616 nm.
decrease in v T upon cooling should be mainly attrib-
M
3
+
uted to the crystal field splitting of a single Ho ion to-
gether with the possible contribution of the weak
interaction through oxygen atoms of hydroxyl and car-
decreases steadily and fast at low temperatures. These
results primarily arise from the splitting of the ligand
field of the Yb(III) ion together with the possible contri-
bution of the weak antiferromagnetic coupling between
Yb(III) ions, considering a possible interaction through
˚
boxylate bridge with 3.910–4.043 A Hoꢁ ꢁ ꢁHo distances.
The variable-temperature magnetic susceptibility of 3
is displayed in Fig. 8, where vM is the corrected molar
magnetic susceptibility per [Yb ] unit. At room temper-
˚
two carboxylate bridges with 3.823–4.510 A Ybꢁ ꢁ ꢁYb
distances. The magnetic susceptibility above 100 K
obeys the Curie–Weiss law with the Weiss constant
h = ꢀ42.61 K and the Curie constant C = 15.43
6
3
ꢀ1
ature, the value of v T is 13.41 cm mol K, which is
M
approximately close to the calculated value for six Yb
3
ꢀ1
3
ꢀ1
free ions (15.42 cm mol K). Upon cooling, v T
M
cm mol K.

830
Y.-B. Wang et al. / Polyhedron 24 (2005) 823–830
5
4
3
2
1
0
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