Transformation of a luminescent benzimidazole-based Yb3 cluster into a one-dimensional coordination polymer

Article abstract of DOI:10.1021/cg901283k

Reaction of the benzimidazole-based ligand 2-(1H-benzoimidazol-2-yl)-4- bromo-6-methoxy-phenol (HL) with LnCl₃ · 6H₂O in a 4:3 mol ratio in refluxing EtOH gave the trinuclear complexes [Ln ₃L₄Cl₄(H

Full text of DOI:10.1021/cg901283k

DOI: 10.1021/cg901283k
Transformation of a Luminescent Benzimidazole-Based Yb3 Cluster into a
One-Dimensional Coordination Polymer
2010, Vol. 10
970–976
Xiaoping Yang,† Richard A Jones,*,† Michael J. Wiester,† Michael M. Oye,† and
Wai-Kwok Wong*,‡
†Department of Chemistry and Biochemistry, The University of Texas at Austin, 1 University Station
A5300, Austin, Texas 78712-0165 and ‡Department of Chemistry, Hong Kong Baptist University,
Kowloon Tong, Hong Kong, P. R. China
Received October 15, 2009; Revised Manuscript Received November 18, 2009
ABSTRACT: Reaction of the benzimidazole-based ligand 2-(1H-benzoimidazol-2-yl)-4-bromo-6-methoxy-phenol (HL) with
LnCl3 6H2O in a 4:3 mol ratio in refluxing EtOH gave the trinuclear complexes [Ln3L4Cl4(H2O)2] Cl H2O EtOH (1) (Ln = Tb
3
3
3
3
(a), Er (b), Yb (c)) in 40-59% yields. Under similar conditions, but with the subsequent addition of Zn(OAc)2 2H2O to the
3
reaction mixture, complex {[Yb3L4(OAc)4] Cl EtOH}n (2) can be isolated in 48% yield. 2 has a one-dimensional coordination
structure in the solid state. All complexes display intramolecular π-π stacking and hydrogen bonded interactions in the solid
state as well as lanthanide ion based luminescence in both solution and the solid.
3
3
Introduction
Scheme 1. The Structure of Benzimidazole Ligand H2L0
There is currently considerable interest in metal-organic
coordination polymers or framework materials (MOF) from
both a structural standpoint and for potential application in,
for example, catalysis, molecular recognition, and storage
devices.1 The “node and spacer” methodology has proven to
be a very successful strategy for the design of many metal-
organic architectures including chain, ladder, grid, brick wall,
honeycomb, diamondoid, rutile, and R-polonium structures.2
Most of this work has been focused on coordination polymers
of d-block transition metals. Coordination polymers based on
lanthanides would be of interest for the potential to develop
new optical, electrical, and magnetic materials.3 However,
lanthanide ions generally display high and variable coordina-
tion numbers and their use as nodes for the construction of
coordination polymers is currently of interest.
As part of a general program aimed at the synthesis of
multinuclear lanthanide complexes, we recently reported the
use ofanunusual benzimidazoleligand (H2L0) whichwas used
to stabilize a range of Ln-Cu heterobimetallic complexes
(Scheme 1).4a We have also recently reported the construction
of several different polynuclear lanthanide framework mate-
rials based on 1,4-benzenedicarboxylate and 4-hydroxyben-
zene sulfonate linker units.4b-4e We were therefore interested
in the possibility of constructing a coordination polymer from
benzimidazole-based lanthanide units and carboxylate
linkers. Lanthanide complexes with benzimidazole-based
ligands are of interest since they have the potential to exhibit
ligand-to-metal energy transfer (LMCT) processes as well as
supramolecular architectures based on π-π stacking and
hydrogen bonded interactions.5 In this paper, we describe
the synthesis, structures, and photophysical properties of Ln3
clusters stabilized with the simplified benzimidazole ligand
HL (Scheme 2). In the case of the Yb3 complex 1c we were able
to replace the H2O and Cl- ions with acetate (OAc-) by
treatment of the reaction mixture with Zn(OAc)2 2H2O. The
3
resulting compound has an unusual one-dimensional (1-D)
coordination polymeric structure in the solid state in which
Yb3L4 clusters are linked by double OAc- bridges. We chose
Zn(OAc)2 2H2O for this conversion on the basis that it was
3
reasonably soluble in EtOH. At present we do not know if the
reaction is dependent on Zn2þ, although it seems reasonable
to assume that other metal acetates would be capable of
producing the same result.
Experimental Section
General Methods. All reactions were performed under dry
oxygen-free dinitrogen atmospheres using standard Schlenk
techniques. Solvents and starting materials were purchased from
Aldrich and used without further purification unless noted. 1H
NMR spectra were recorded on a Varian-500 NMR spectrometer
with SiMe4 as an internal standard, infrared spectra from 4000 to
400 cm-1 on a Bruker EQINOX 55 FT-IR, and ESI-MS mass
spectra on a Finnigan MAT TSQ 700. Elemental analyses were
performed by Atlantic Microlab, Norcross, GA. Melting points
were in sealed capillaries under nitrogen and are uncorrected. The
solvents used for the photophysical investigations were dried and
freshly distilled under nitrogen. Absorption spectra were obtained
on a BECKMAN DU 640 spectrophotometer, excitation and
visible emission spectra on a QuantaMaster PTI fluorimeter.
Near-infrared (NIR) emission spectra were measured with a 1-m
SPEX 1704 spectrometer and a liquid-nitrogen cooled Ge detector,
using an argon ion laser as the excitation source.
X-ray Crystallography. Data were collected on a Nonius Kappa
CCD diffractometer with graphite monochromated Mo-KR radia-
tion (λ = 0.71073 A) at 153 K. Absorption corrections were applied
using GAUSSIAN. The structuresweresolvedbydirect methods and
*To whom correspondence should be addressed. (R.A.J.) Tel: (512)471-
1706. E-mail: rajones@mail.utexas.edu; (W.-K.W.) tel: 852-3411-7011.
E-mail: wkwong@hkbu.edu.hk.
˚
r
pubs.acs.org/crystal
Published on Web 12/08/2009
2009 American Chemical Society

Article
Crystal Growth & Design, Vol. 10, No. 2, 2010 971
Scheme 2. Formation of Lanthanide Complexes 1a-c and 2
Table 1. Crystal Data and Structure Refinement for the Free Ligand HL, 1a-c and 2
HL
1a
1b
1c
2
formula
fw
C14H11BrN2O2
319.16
triclinic
P1
7.2664(15)
11.972(2)
14.604(3)
75.96(3)
89.72(4)
86.96(3)
1230.8(4)
4
1.722
153(1)
640
3.338
2.98-25.00
5950
4283
C58H52Br4Cl5N8O12Tb3
2026.68
tetragonal
P4/ncc
25.992(4)
25.992(4)
23.403(5)
90
C58H52Br4Cl5N8O12Er3
2051.70
tetragonal
P4/ncc
25.943(4)
25.943(4)
23.312(5)
90
90
90
15689(4)
8
1.732
153(1)
7800
5.442
3.14-25.00
24665
6907
C58H52Br4Cl5N8O12Yb3
2069.04
tetragonal
P4/ncc
25.902(4)
25.902(4)
23.203(5)
90
90
90
15567(4)
8
1.761
153(1)
7848
5.855
3.17-25.00
24214
6856
C64H52Br4ClN8O16Yb3
2063.35
tetragonal
P4/ncc
25.912(4)
25.912(4)
22.760(5)
90
90
90
15281(4)
8
1.794
153(1)
7896
5.833
2.96-25.00
64718
6653
cryst syst
space group
˚
a, A
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
90
118.08(3)
15810(4)
8
1.698
153(1)
7728
4.900
2.93-25.00
35599
6804
3
˚
V, A
Z
Dcalc, g cm-3
temp, K
F(000)
μ, mm-1
θ range, deg
reflns meas
reflns used
params
343
426
426
426
434
Ra (I > 2σ(I))
R1 = 0.0378
wR2 = 0.0894
R1 = 0.0515
wR2 = 0.0976
1.072
R1 = 0.0962
wR2 = 0.2024
R1 = 0.1879
wR2 = 0.2334
1.026
R1 = 0.0615
wR2 = 0.1563
R1 = 0.1026
wR2 = 0.1864
1.050
R1 = 0.0563
wR2 = 0.1461
R1 = 0.0897
wR2 = 0.1716
1.077
R1 = 0.0958
wR2 = 0.1656
R1 = 0.1578
wR2 = 0.2484
0.989
Ra (all data)
S
a R1 = Σ Fo| - |Fc /Σ|Fo|. wR2 = [Σ[w(Fo2 - Fc2)2]/Σ[w(Fo2)2]]1/2. w = 1/[σ2(Fo2) þ (mP)2 þ nP], where P = (Fo þ 2Fc2)/3.
2
refined anisotropically using full-matrix least-squares methods with
the SHELX 97 program package.6 Coordinates of the non-hydrogen
atoms were refined anisotropically, while hydrogen atoms were
included in the calculation isotropically but not refined. Neutral
atom scattering factors were taken from Cromer and Waber.7
Preparation of the Ligand HL. The new benzimidazole ligand
(HL) was synthesized with 5-bromo-2-hydroxy-3-methoxybenzal-
dehyde (2.31 g, 0.01 mol) and o-phenylenediamine (1.08 g, 0.01 mol)
in nitrobenzene (30 mL) according to well-established proce-
dures.8,8b A solution of 5-bromo-2-hydroxy-3-methoxybenzalde-
hyde (2.31 g, 0.01 mol) in nitrobenzene (10 mL) was dropwise added
to a solution of o-phenylenediamine (1.08 g, 0.01 mol) in nitroben-
zene (20 mL) over a period of 30 min. The mixture was heated under
reflux (12 h). During this time, the color changed from yellow to
dark red. The reaction mixture was then allowed to cool to room
temperature and volatile materials were removed under vacuum.
The residue was treated with EtOH (20 mL), and the mixture was
stirred (30 min) and then filtered. The colorless residue (HL) that
remained was washed with ethanol (15 mL).Yield 2.39 g, 75%.
Anal. Found: C, 52.60; H, 3.34; N, 8.84. Calc. for C14H11BrN2O2:
C, 52.69; H, 3.47; N, 8.78. FABMS: m/z 320 ([M þ H]þ). mp 230-1
°C. 1H NMR (400 MHz, CD3CN): δ (ppm) 3.924 (s, 3H), 7.204 (d,
1H), 7.350-7.381 (m, 2H), 7.628-7.657 (m, 2H), 7.647 (d, 1H). IR
(CH3CN, cm-1): 3348 (br), 1621 (m), 1589 (m), 1525 (m), 1490 (m),
1463 (s), 1444 (m), 1398 (m), 1250 (m), 1052 (w) and 745 (m).
Figure 1. Crystal structure and packing of the free ligand HL:
˚
C(4c) C(10a): 3.575 A. C(2c) C(13a): 3.387 A. N(1a) C(4e):
˚
3 3 3
3 3 3
3 3 3
˚
3.355 A. N(2a) C(2e): 3.503 A. H atoms have been omitted for
˚
3 3 3
clarity and thermal ellipsoids are drawn at the 25% probability
level.
Colorless single crystals for X-ray crystallography were obtained
from an EtOH solution in air at room temperature.
Synthesis of [Ln3L4Cl4(H2O)2] Cl H2O EtOH (1) (Ln = Tb (a),
3
3
3
Er (b), Yb (c)). A solution of LnCl3 6H2O (0.03 mmol) in EtOH
3

972 Crystal Growth & Design, Vol. 10, No. 2, 2010
Yang et al.
˚
Table 2. Selected Bond Lengths (A) and Angles (°) for the Free Ligand
HL, 1a-c and 2
Free Ligand HL
Br(1)-C(4)
1.897(4)
1.378(5)
1.376(5)
1.389(5)
1.371(4)
1.426(5)
1.355(4)
107.0(3)
126.5
N(1)-C(8)
1.315(5)
115.3(3)
120.3(3)
117.5(3)
118.0(3)
122.6(3)
112.0(3)
122.5(3)
125.6(3)
130.9(3)
108.6(3)
132.2(3)
105.9(3)
N(1)-C(9)
O(1)-C(2)-C(7)
C(5)-C(4)-Br(1)
C(3)-C(4)-Br(1)
O(2)-C(7)-C(2)
O(2)-C(7)-C(6)
N(1)-C(8)-N(2)
N(1)-C(8)-C(6)
N(2)-C(8)-C(6)
N(1)-C(9)-C(10)
N(1)-C(9)-C(14)
C(13)-C(14)-N(2)
N(2)-C(14)-C(9)
N(2)-C(8)
N(2)-C(14)
O(1)-C(2)
O(1)-C(1)
O(2)-C(7)
C(8)-N(1)-C(9)
C(8)-N(1)-H(1A)
C(9)-N(1)-H(1A)
C(8)-N(2)-C(14)
C(2)-O(1)-C(1)
O(1)-C(2)-C(3)
126.5
106.4(3)
116.0(3)
124.4(3)
1a
1b
1c
2
Tb(1)-O(20)
Tb(1)-O(1W)
Tb(1)-O(2)
Tb(1)-N(10)
Tb(1)-O(1)
Tb(1)-Cl(1)
Tb(1)-Cl(2)
Tb(2)-O(20)
Tb(2)-O(2)
Tb(2)-N(1)
Tb(2)-O(10)
O(20)-Tb(1)-O(2)
2.260(13)
2.285(17)
2.334(13)
2.449(17)
2.474(15)
2.556(8)
2.554(8)
2.256(12)
2.260(13)
2.369(16)
2.529(13)
68.7(4)
O(20)-Tb(1)-N(10)
O(2)-Tb(1)-N(10)
O(20)-Tb(1)-O(1)
O(2)-Tb(1)-O(1)
N(10)-Tb(1)-O(1)
O(20)-Tb(2)-O(2)
O(20)-Tb(2)-N(1)
O(2)-Tb(2)-N(1)
O(20)-Tb(2)-O(10)
O(2)-Tb(2)-O(10)
N(1)-Tb(2)-O(10)
74.1(5)
134.9(5)
120.3(5)
65.2(5)
159.8(6)
70.0(5)
137.2(5)
75.1(5)
65.9(5)
112.9(5)
154.1(5)
Er(1)-O(20)
2.235(7)
2.255(9)
2.315(7)
2.416(10)
2.247(7)
2.364(9)
2.510(8)
68.5(2)
Er(1)-O(1)
2.455(8)
2.549(4)
2.595(4)
2.242(8)
160.2(3)
69.6(3)
Er(1)-O(1W)
Er(1)-O(2)
Er(1)-Cl(2)
Er(1)-Cl(1)
Er(1)-N(10)
Er(2)-O(2)
Er(2)-O(20)
N(10)-Er(1)-O(1)
O(2)-Er(2)-O(20)
O(2)-Er(2)-N(1)
O(20)-Er(2)-N(1)
O(2)-Er(2)-O(10)
O(20)-Er(2)-O(10)
N(1)-Er(2)-O(10)
Er(2)-N(1)
Er(2)-O(10)
75.7(3)
O(20)-Er(1)-O(2)
O(20)-Er(1)-N(10)
O(2)-Er(1)-N(10)
O(20)-Er(1)-O(1)
O(2)-Er(1)-O(1)
137.7(3)
113.8(3)
66.2(3)
74.5(3)
135.0(3)
119.2(3)
64.7(3)
153.7(3)
Yb(1)-O(20)
Yb(1)-O(1W)
Yb(1)-O(2)
Yb(1)-N(10)
Yb(1)-O(1)
Yb(1)-Cl(2)
Yb(1)-Cl(1)
Yb(2)-O(2)
Yb(2)-O(20)
Yb(2)-N(1)
Yb(2)-O(10)
O(20)-Yb(1)-O(2)
2.234(6)
2.247(7)
2.319(6)
2.397(8)
2.456(7)
2.543(3)
2.587(3)
2.233(6)
2.243(6)
2.354(7)
2.496(7)
68.5(2)
O(20)-Yb(1)-N(10)
O(2)-Yb(1)-N(10)
O(20)-Yb(1)-O(1)
O(2)-Yb(1)-O(1)
N(10)-Yb(1)-O(1)
O(2)-Yb(2)-O(20)
O(2)-Yb(2)-N(1)
O(20)-Yb(2)-N(1)
O(2)-Yb(2)-O(10)
O(20)-Yb(2)-O(10)
N(1)-Yb(2)-O(10)
74.5(3)
135.4(3)
119.8(2)
64.7(2)
159.8(3)
69.9(2)
75.5(2)
137.6(2)
113.4(2)
66.2(2)
153.7(2)
Figure 2. Crystal structure of 1a. H atoms have been omitted for
clarity and thermal ellipsoids are drawn at the 25% probability
level. (a) View showing intramolecular π-π stacking interac-
˚
˚
tions: X1A X1B: 3.958 A, X1C X1D: 3.872 A, X1E X1F:
3 3 3
3 3 3
3 3 3
˚
3.891 A, X1G X1H: 3.891 A. (b) View showing the crossed ligand
˚
3 3 3
configuration.
(5 mL) was added to a solution of HL (0.013 g, 0.04 mmol) in EtOH
(5 mL) and the mixture was stirred and heated under reflux (2 h).
The reaction mixture was then allowed to cool to room temperature
and filtered. Diethylether was allowed to diffuse slowly into the
filtrate at room temperature and yellow crystalline 1a-c was
obtained
(1 month). The product was isolated by filtration. For 1a, Yield
0.008 g (40%). ESI-MS (CH3CN) m/z: 1906 ([M-Cl-2H2O-
EtOH]þ). IR (CH3CN, cm-1): 3458 (br), 1620 (s), 1609 (s), 1566
(s), 1525 (m), 1462 (m), 1398 (m), 1202 (m), 1050 (w), 956 (m) and
745 (m). For 1b, Yield 0.009 g (45%). ESI-MS (CH3CN) m/z: 1915
([M-Cl-3H2O-EtOH]þ). mp > 245 °C (dec). IR (CH3CN, cm-1):
3500 (br), 1621 (s), 1607 (s), 1567 (m), 1512 (s), 1456 (m), 1410 (m),
1200 (m), 1048 (w), 957 (m) and 742 (m). 1H NMR (500 MHz, CD3-
CN): δ (ppm) -18.953 (3H), -11.520 (1H), -10.687 (2H), -9.907
(1H), 6.692 (2H), 14.402 (2H), 25.387 (2H), 42.151 (3H), 54.313
(1H), 59.711 (1H). For 1c, Yield 0.012 g (59%). ESI-MS (CH3CN)
m/z: 1966 ([M-Cl-H2O-EtOH]þ). IR (CH3CN, cm-1): 3469 (br),
Yb(1)-O(3)
2.207(15)
2.279(14)
2.44(2)
2.444(15)
2.439(18)
2.370(14)
2.40(2)
2.270(14)
161.7(5)
69.8(5)
75.6(5)
137.8(6)
Yb(2)-O(20)
2.288(13)
2.371(18)
2.510(16)
68.2(5)
Yb(1)-O(20)
Yb(2)-N(2)
Yb(1)-N(20)
Yb(2)-O(10)
Yb(1)-O(1)
O(20)-Yb(1)-O(2)
O(20)-Yb(1)-N(20)
O(2)-Yb(1)-N(20)
O(20)-Yb(1)-O(1)
O(2)-Yb(1)-O(1)
O(2)-Yb(2)-O(10)
O(20)-Yb(2)-O(10)
N(2)-Yb(2)-O(10)
Yb(1)-O(5)
72.4(6)
Yb(1)-O(2)
133.3(5)
119.0(5)
64.5(5)
111.4(5)
65.8(6)
152.8(6)
Yb(1)-O(6)
Yb(2)-O(2)
N(20)-Yb(1)-O(1)
O(2)-Yb(2)-O(20)
O(2)-Yb(2)-N(2)
O(20)-Yb(2)-N(2)

Article
Crystal Growth & Design, Vol. 10, No. 2, 2010 973
Figure 3. View of Cl H-O hydrogen bonded interactions between the coordinated Cl- ion and H2O in 1a, which result in a 1-D wave-like
3 3 3
˚
strand: Cl(1) O(1w): 2.839 A.
3 3 3
1620 (s), 1606 (s), 1567 (s), 1515 (s), 1465 (s), 1407 (m), 1201 (m),
1046 (w), 959 (m) and 741 (m).
Synthesis of {[Yb3L4(OAc)4] Cl EtOH}n (2). A solution of
(Scheme 2). Single crystals of these complexes suitable for
X-ray diffraction studies were obtained by allowing Et2O to
diffuse into the reaction mixture at room temperature. The
compounds 1a-c are isomorphous and crystallize in the
tetragonal space group P4/ncc with eight Ln3L4 units per unit
cell. The view of the X-ray structure of the Tb complex 1a is
shown in Figure 2. Crystallographic details are provided in
Table 1, and selected bond lengths and angles are given in
Table 2. The structure of 1a contains of three nonlinear
Tb(III) ions (Tb-Tb-Tb angle 141.15°) bound by four
deprotonated L- ligands. Interestingly, the L- ligands bind
in two distinct ways. Two are arranged so that each pair of
phenolic and methoxy O atoms is bound in a chelating fashion
to the central Tb(2) ion. The imidazole nitrogen atoms from
these groups are then bound to each of the terminal Tb ions.
This pair of ligands is arranged so that the aromatic rings are
roughly parallel with each other. The distances between rings
3
3
YbCl3 6H2O (0.012 g, 0.03 mmol) in EtOH (5 mL) was added to
3
a solution of HL (0.013 g, 0.04 mmol) in EtOH (5 mL) and the
mixture was stirred and heated under reflux (2 h). The mixture was
allowed to cool to room temperature. A solution of Zn(OAc)2
3
2H2O (0.110 g, 0.50 mmol) in EtOH (5 mL) added and the mixture
was heated under reflux (1 h). The mixture was then allowed to cool
to room temperature and filtered. Diethylether was allowed to
diffuse slowly into the filtrate and pale yellow single crystals of 2
were obtained after two weeks. Yield 0.010 g (48%). ESI-MS
(CH3CN) m/z: 636 ([Yb3L4(OAc)2]3þ). mp > 272 °C (dec). IR
(CH3CN, cm-1): 3488 (br), 1626 (s), 1606 (s), 1597 (s), 1560 (s), 1515
(s), 1483 (s), 1465 (s), 1436 (m), 1410 (m), 1202 (m), 1040 (w), 958 (m)
and 740 (m).
Results and Discussion
A view of the molecular structure of the free benzimidazole
ligand HL along with a view of its packing in the solid state is
shown in Figure 1. Details of crystallographic parameters,
data collection, and refinements are listed in Table 1, and
selected bond lengths and angles are given in Table 2. In the
solid state, the molecule packs in an offset head-to-head
fashion with the five-membered ring of the imidazole moiety
stacked closest to the phenylene ring of its nearest neighbor,
resulting in a herringbone effect (Figure 1). As described
below this kind of π-π stacking interaction is also found in
the lanthanide complexes 1a-c and 2.
˚
˚
are 3.958 A (X1A X1B) and 3.872 A (X1C X1D)
3 3 3
3 3 3
(Figure 2a). The other two ligands are coordinated so that
the imidazole nitrogen atoms are bound to the central Tb(2)
with the O2 binding set of each ligand being coordinated to the
two terminal Tb ions. The phenolic oxygen atoms for all four
ligands bind to the central Tb and also bridge the outer Tb
ions. The latter pair of ligands is also roughly parallel to each
˚
other, and the distance between rings is 3.891 A (Figure 2a).
The molecule contains a C2 rotation axis which passes
through Tb(2), and so the two terminal Tb atoms are crystal-
˚
lographically equal. The unique Tb-Tb distance is 3.737 A.
This ligand configuration results in the central Tb ion having a
coordination number of 8. The terminal Tb ions are each
Reactions of the substituted benzimidazole (HL) with
LnCl3 6H2O in a 4:3 molar ratio in refluxing EtOH produce
3
the trinuclearlanthanidecomplexes1a-c in ca. 40-60% yield

974 Crystal Growth & Design, Vol. 10, No. 2, 2010
Yang et al.
Figure 6. Space filling view of 2 along the c-axis showing the 3-D
network.
between the least-squares planes of each being 66.8° and 89.5°
(Figure 2b). The terminally bound Cl- and H2O groups
appear to play a key role in the crystal packing of the Ln3 clus-
ters since there are close Cl H-O interactions which link
3 3 3
˚
adjacent molecules (Cl O 2.839 A, Figure 3) forming 1-D
3 3 3
structures. The structures are further connected by Cl H-N
3 3 3
hydrogen bonding between the uncoordinated Cl- ion and the
˚
˚
N-H group of the L ligand (Cl N 3.178 A and 3.111 A).
3 3 3
This results in a three-dimensional open network which has
extended channels running along the c-axis (Figure 4). These
˚
channels measure approximately 7 ꢀ 7 A and accommodate
guest molecules of H2O and EtOH. Hydrogen bonded inter-
actions are present between the entrapped molecules and the
surrounding supramolecular framework.
Figure 4. View of Cl H-N hydrogen bonded interactions be-
3 3 3
tween uncoordinated Cl- ions and N-H groups of L- ligands in 1a,
The addition of Zn(OAc)2 2H2O to the original reaction
3
which result in a 3-D open network viewed along [110]: Cl(3) N-
0
3 3 3
mixture obtained in the synthesis of 1c produces the acetate
derivative {[Yb3L4(OAc)4] Cl EtOH}n (2). The key differ-
˚
(2): 3.178 A, Cl(3) N(2 ): 3.111 A.
˚
3 3 3
3
3
ence between the structures 1a-c and 2 is that the coordinated
Cl- and H2O units are now replaced with OAc- groups. The
acetates create a zigzag 1-D polymer by forming double
(OAc-) bridges between Yb3L4 units (Figure 5). Interestingly,
2 crystallizes in the same space group as 1a-c (P4/ncc) and the
1-D structure exhibit similar crystal packing behavior in the
solid state. Thus, 2 also has a Cl H-N hydrogen bonding
3 3 3
interaction between uncoordinated Cl- and the N-H group
˚
of the imidazole ligand (Cl N 3.215 and 3.305 A). The
3 3 3
resulting 3-D open network structure has extended channels
running along the c-axis which are again approximately 7 ꢀ 7
˚
A in size and accommodate EtOH molecules (Figure 6). The
overall structure of the Yb3L4 core of 2 is similar to that of
1a-c with the exception that each terminal Yb (III) ion now
bears a chelating OAc- group. This results in the terminal Yb
(III) ions having a coordination number of 8. In previous
studies of heteropolynuclear Zn4Eu2 cage complex, we dis-
covered that aryl-Br units could engage in short intermolecu-
Figure 5. Crystal structure of 1-D coordination polymer 2. H
atoms have been omitted for clarity and thermal ellipsoids drawn
at the 25% probability level.
lar Br
O interactions resulting in interesting 3-D
3 3 3
frameworks.9 However, in the complexes described in this
paper no such interactions were observed.
bound to two Cl- groups and a water molecule in addition to
the L- ligands and are seven-coordinate. The pairs of L-
ligands are aligned in a criss-cross fashion with the angles
The 1H NMR spectrum of 1b supports a structure in
solution which is similar to that found in the solid state. The
1H NMR spectra of the free ligand HL and 1b at 298 K in

Article
Crystal Growth & Design, Vol. 10, No. 2, 2010 975
Figure 7. 1H NMR spectra of the free ligand HL (a) and complex 1b (b) in CD3CN at 298 K. In b, the peaks of solvent, H2O and EtOH,
together with the signal at 6.692 ppm of L-, have been omitted for clarity.
Figure 8. Excitation and emission spectra of 1a in CH3CN (5 ꢀ
Figure 9. NIR emission spectra of 1b (5 ꢀ 10-6 M) and 2 (2 ꢀ 10-6
10-6 M) at 298 K.
M) in CH3CN at 298 K.
CD3CN are shown in Figure 7. The free ligand shows the
presence of five peaks corresponding to nine C-H protons. In
the H NMR spectrum of 1b, there are 10 reasonably sharp
luminescence of the Er3þ ion assigned to the I13/2 f I15/2
transition at 1510 nm, and complexes 1c and 2 show that of the
Yb3þ ion assigned to the 2F5/2 f 2F7/2 transition at about 978
nm (Figure 9). A similar luminescence is observed for each
lanthanide complex in the solid state. The fluorescence quan-
tum yield (Φem) of Tb3þ complex 1a in CH3CN is 0.218,10
while the NIR luminescence quantum yields of 1b-c and 2
could not be measured due to instrumental limitations. The
relative emission intensities of 1c and 2 were determined under
the same experimental conditions. With the same absorbance
value at 275 nm, the relative emission intensity at 978 nm was
estimated to be 3.6 for 2:1c in CH3CN, indicating that 2 has
superior luminescence properties compared to 1c. The differ-
ence in luminescence properties may be because there are no
coordinated H2O molecules in 2 which can efficiently quench
lanthanide luminescence.11
4
4
1
peaks which are assigned to the ligands bound in two different
ways as described above. The spectra are unchanged after one
month at room temperature indicating that 1b is thermally
stable in solution under these conditions. A detailed analysis of
the NMR data (2D-COSY) allows the assignment of these
signals. Each L- displays one signal for the three methoxy
protons, two signals for the two benzyl protons, and two
signals for the four benzimidazole protons. Mass spectro-
scopic studies (ESI-MS) for 1a-c support the presence of
the Ln3L4 unitsinsolution(experimental). For2, ESI-MS data
indicate that the 1-D polymeric structure in the solid state does
not persist in solution (m/z = 636, [Yb3L4(OAc)2]3þ). The
photophysical properties of complexes 1a-c and 2 have been
studied at 298 K both in the solid state and in solution. Upon
excitation of the ligand-centered absorption band, all com-
plexes show typical emission spectra of the Ln(III) ions. Com-
plex 1a shows visible emission bands of Tb3þ ion ((5D0 f 7Fj
transitions, j=1, 2, 3, and 4, Figure 8), while 1b shows the NIR
Conclusions
A series of luminescent Ln3 clusters of formula [Ln3L4Cl4-
(H2O)2] Cl H2O EtOH (1) (Ln = Tb (a), Er (b), Yb (c))
3
3
3

976 Crystal Growth & Design, Vol. 10, No. 2, 2010
Yang et al.
[Ln3L4Cl4(H2O)2] Cl H2O EtOH (1) (Ln=Tb (a), Er (b),
W. L.; Spek, A. L.; Reedjik, J. Chem. Commun. 2002, 1488. (d) Blake,
A. J.; Champness, N. R.; Hubberstey, P.; Li, W.-S.; Withersby, M. A.;
Schroder, M. Coord. Chem. Rev. 1999, 183, 117.
3
3
3
Yb (c)) have been synthesized and characterized (HL=2-(1H-
benzoimidazol-2-yl)-4-bromo-6-methoxy-phenol). The Yb3
cluster 1c may be converted into a 1-D coordination polymer
(3) (a) Lehn, J. M. Supramolecular Chemistry: Concepts and Perspec-
tives; VCH: Weinheim, 1995; (b) Piguet, C.; B€unzli, J.-C. G. Chem.
Soc. Rev. 1999, 28, 347. (c) Piguet, C. Chimia 1996, 50, 144. (d)
Guerriero, P.; Tamburini, S.; Vigato, P. A. Coord. Chem. Rev. 1995,
139, 17.
(4) (a) Yang, X. P; Jones, R. A.; Lai, R. J.; Waheed, A.; Oye, M. M.;
Holmes, A. L. Polyhedron 2006, 25, 881. (b) Yang, X. P.; Jones, R. A.;
Rivers, J. H.; Lai, R. P.-J. J. Chem. Soc., Dalton Trans. 2007, 3936. (c)
L€u, X.-Q.; Bi, W.-Y.; Chai, W.-L.; Song, J.-R.; Meng, J.-X.; Wong, W.
Y.; Wong, W. K.; Yang, X. P.; Jones, R. A. Polyhedron 2009, 28, 27. (d)
Yang, X. P.; Rivers, J. H.; Wiester, M.; Jones, R. A. New J. Chem. 2008,
32, 790. (e) Yang, X. P.; Hahn, B. P.; Jones, R. A.; Wong, W.-K.;
Stevenson, K. J. Inorg. Chem. 2007, 46, 7050.
by treatment with Zn(OAc)2 2H2O. All complexes display
3
intramolecular π-π stacking and hydrogen bonded interac-
tions in the solid state as well as lanthanide ion based
luminescence in both solution and the solid.
Acknowledgment. We thank Hong Kong Baptist University
(FRG/06-07/II-16), the Hong Kong Research Grants Council
(HKBU 202407), the Robert A. Welch Foundation (Grant
F-816), the Texas Higher Education Coordinating Board
(ARP 003658-0010-2006), and the Petroleum Research Fund,
administered by the American Chemical Society (47014-AC5)
for financial support.
(5) (a) Yang, X. P.; Kang, B. S.; Wong, W.-K.; Su, C. Y.; Liu, H. Q.
Inorg. Chem. 2003, 42, 169. (b) Terazzi, E.; Torelli, S.; Bernardinelli,
ꢀ
G.; Rivera, J.-P.; Benech, J.-M.; Bourgogne, C.; Donnio, B.; Guillon,
D.; Imbert, D.; B€unzli, J.-C. G.; Pinto, A.; Jeannerat, D.; Piguet, C.
J. Am. Chem. Soc. 2005, 127, 888.
(6) Sheldrick, G. M. SHELX 97, A Software Package for the Solution
Supporting Information Available: X-ray crystallographic data
for the free ligand HL and lanthanide complexes 1-4 (CIF). This
material is available free of charge via the Internet at http://pubs.
acs.org.
€
€
and Refinement of X-ray Data; University of Gottingen: Gottingen,
Germany (1997).
(7) Cromer, D. T.; Waber, J. T. International Tables for X-Ray
Crystallography; Kynoch Press: Birmingham, 1974; Vol. 4, Table
2.2A.
References
(8) Kitazume, T.; Ishikawa, N. Bull. Chem. Soc. Jpn. 1974, 47, 785. (b)
Kuznetsov, V. S.; Remizov, A. L. Chem. Heterocycl. Compd. 1972, 8,
1292.
(9) Yang, X.; Hahn, B. P.; Jones, R. A.; Stevenson, K. J.; Swinnea,
J. S.; Wu, Q. Chem. Commun. 2006, 3827–3829.
(10) Fluorescence quantum yields were determined by using quinine
sulfate (Φem = 0.546 in 0.5 M H2SO4) as standard for the Tb3þ
complex: Meech, S. R.; Philips, D. J. J. Photochem. 1983, 23, 193.
(11) Sabbatini, N.; Guardigli, M.; Lehn, J. M. Coord. Chem. Rev. 1993,
123, 201.
(1) (a) Moulton, B.; Zaworotko, M. J. Chem. Rev. 2001, 101, 1629.
(b) Fujita, M.; Kwon, Y. J.; Washizu, S.; Ogura, K. J. Am. Chem. Soc.
1994, 116, 1151. (c) Hoskins, B. F.; Robson, R. J. Am. Chem. Soc.
1990, 112, 1546. (d) Li, H.; Eddaoudi, M.; O0Keeffe, M.; Yaghi, O. M.
Nature 1999, 402, 276. (e) Choi, H. J.; Lee, T. S.; Suh, M. P. Angew.
Chem., Int. Ed. 1999, 38, 1405. (f) Kondo, M.; Yoshitomi, T.; Seki, K.;
Matsuzaka, H.; Kitagawa, S. Angew. Chem., Int. Ed. 1997, 36, 1725.
(2) (a) Leininger, S.; Olenyuk, B.; Stang, P. J. Chem. Rev. 2000, 100,
853. (b) Holman, K. T.; Pivovar, A. M.; Ward, M. D. Science 2001, 294,
1907. (c) Gamez, P.; de Hoog, P.; Roubeau, O.; Lutz, M.; Driessen,