Conformational isomerism of 1,2-bis(imidazol-1′-yl)ethane in five-coordination polymers: Influence of metal ions and m-isophthalate ligands bearing different substituents

Article abstract of DOI:10.1016/j.poly.2007.04.043

Four novel coordination polymers, {[Zn(gauche-bime)(bdc)] · 0.5H₂O}_n (1), {[Zn(anti-bime)(HO-bdc)] · 2.5H₂O}_n (2), [Cu(gauche-bime)_0.5(anti-bime)_0.5(O₂N-bdc)]_n (4) and [Ni₂(gauche-bime)(anti-bime)(O₂N-bdc)₂(H₂O)₂]_n (5) were successfully prepared by the solvothermal reactions of 1,2-bis(imidazol-1′-yl)ethane (bime), m-isophthalic acid (H₂bdc) or its two derivatives (HO-H₂bdc = 5-hydroxyisophthalic acid, O₂N-H₂bdc = 5-nitroisophthalic acid) with different metal ions. Interestingly, bime in the four complexes exhibit different conformations owing to the synergetic influence of coexistent neutral (-H), electron-donating (-OH) or electron-withdrawing (-NO₂) groups of the dicarboxylate ligands and different metal ions. In 1 and 2, only one conformation of bime (gauche in 1 and anti in 2) is displayed, while the mixed conformations of bime (gauche:anti = 1:1) are observed in 4 and 5. At the same time, one previously reported compound {[Zn(anti-bime)(O₂N-bdc)] · H₂O}_n (3) as a comparable substance in the research system was also mentioned, in which the anti-conformation of bime was observed.

Full text of DOI:10.1016/j.poly.2007.04.043

Polyhedron 26 (2007) 3911–3919
www.elsevier.com/locate/poly
Conformational isomerism of 1,2-bis(imidazol-10-yl)ethane
in five-coordination polymers: Influence of metal ions and
m-isophthalate ligands bearing different substituents
a,
a,b
Xiao-Ju Li a,b, Rong Cao *, Zhen-Gang Guo a,b, Ya-Feng Li a,b, Xian-Dong Zhu
a
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences,
Fujian, Fuzhou 350002, PR China
b
Graduate School of the Chinese Academy of Sciences, Beijing 100049, PR China
Received 21 January 2007; accepted 17 April 2007
Available online 16 May 2007
Abstract
Four novel coordination polymers, {[Zn(gauche-bime)(bdc)] Æ 0.5H2O}n (1), {[Zn(anti-bime)(HO-bdc)] Æ 2.5H2O}n (2), [Cu(gauche-
bime)0.5(anti-bime)0.5(O2N-bdc)]n (4) and [Ni2(gauche-bime)(anti-bime)(O2N-bdc)2(H2O)2]n (5) were successfully prepared by the
solvothermal reactions of 1,2-bis(imidazol-10-yl)ethane (bime), m-isophthalic acid (H2bdc) or its two derivatives (HO-H2bdc = 5-hydrox-
yisophthalic acid, O2N-H2bdc = 5-nitroisophthalic acid) with different metal ions. Interestingly, bime in the four complexes exhibit dif-
ferent conformations owing to the synergetic influence of coexistent neutral (–H), electron-donating (–OH) or electron-withdrawing
(–NO2) groups of the dicarboxylate ligands and different metal ions. In 1 and 2, only one conformation of bime (gauche in 1 and anti
in 2) is displayed, while the mixed conformations of bime (gauche:anti = 1:1) are observed in 4 and 5. At the same time, one previously
reported compound {[Zn(anti-bime)(O2N-bdc)] Æ H2O}n (3) as a comparable substance in the research system was also mentioned, in
which the anti-conformation of bime was observed.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Keywords: Conformational isomerisms; Coordination polymers; Solvothermal reaction; X-ray diffraction
1. Introduction
conditions [3]. As to organic ligands, in contrast to the
well-predicted results from rigid ligands [4–6], the prede-
fined information of the products can be greatly reduced
when incorporating a certain degree of flexibility into
the ligands. However, the possibility of generating supra-
molecular isomers and unique frameworks with useful
properties can be increased because of the flexibility and
conformational freedom of these ligands. As a result,
many extended architectures have been prepared from
flexible multidentate N-, O- and S-donor ligands [7–11].
In this context, 1,2-bis(4-pyridyl)ethane, as a well-known
flexible dipyridyl linker, is an excellent candidate for the
preparation of coordination polymers and supramolecular
isomers because of its simple coordinating mode and dif-
ferent conformational performance [12,13], three isomeric
The design and preparation of inorganic–organic
hybrid materials is a rapidly developing area in supramo-
lecular chemistry and crystal engineering. The interest in
this area not only stems from their fascinating structural
motifs and functional properties, but also from under-
standing of the mechanism in their assembly process
[1,2]. Usually, the generation of products from self-assem-
bly reaction heavily depends on the combination of sev-
eral factors, such as structure-directing ligands,
coordination geometries of metal ions and the reaction
*
Corresponding author. Tel.: +86 591 83796710; fax: +86 591
forms of [Co(NO3)2(1,2-bis(4-pyridyl)ethane)1.5 n
]
have
83714946.
been generated under different solvent environments, in
E-mail address: rcao@ms.fjirsm.ac.cn (R. Cao).
0277-5387/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.04.043

3912
X.-J. Li et al. / Polyhedron 26 (2007) 3911–3919
2.2. Synthesis of {[Zn(gauche-bime)(bdc)] Æ 0.5H2O}n (1)
N
N
N
N
A mixture of Zn(NO3)2 Æ 6H2O (0.074 g, 0.25 mmol),
1,2-bis(imidazol-10-yl)ethane (0.040 g, 0.25 mmol), H2bdc
(0.042 g, 0.25 mmol) and KOH (0.028 g, 0.50 mmol) was
dissolved in CH3OH (8 mL) and H2O (10 mL). The mix-
ture was transferred to a 25 mL stainless-steel reactor with
Teflon liner and heated to 160 ꢁC automatically. The tem-
perature was kept at 160 ꢁC for 4 days and cooled to
room temperature during 24 h. Colorless block crystals
of 1 were obtained (yield: 0.042 g, 42%, based on Zn).
Elemental Anal. Calc. for C16H15ZnN4O4.5 (400.69): C,
47.96; H, 3.77; N, 13.98. Found: C, 47.91; H, 3.65; N,
14.02%. IR (KBr, cmꢀ1): 3427 (bs), 1622 (vs), 1347 (vs),
1236 (m), 1104 (m), 1227 (w), 835 (m), 746 (s), 652 (m),
567 (w).
N
N
N
N
gauche
anti
Scheme 1. Two different conformations of 1,2-bis(imidazol-10-yl)ethane.
which two different conformations (gauche and anti) were
included [14]. However, the control of different conforma-
tion of flexible ligands in the synthetic reactions is still a
tremendous challenge to chemists owing to the influence
of many subtle factors, such as solvent, pH value, metal
ions and additional ligands.
1,2-Bis(imidazol-10-yl)ethane (bime), an analogue to
well-investigated 1,2-bis(4-pyridyl)ethane, also possesses
gauche and anti conformations (Scheme 1) as a conse-
quence of the free rotation of the ethyl group. However,
the effect of its isomerism and manifestation on struc-
tures and properties remains to be less explored. To
our knowledge, only one copper–bime complex was pre-
pared, in which both of its isomers (gauche:anti = 1:1.5)
were observed [15]. As a part of our ongoing research
about the effect of neutral, electron-donating and elec-
tron-withdrawing groups in dicarboxylate ligands on
structures and properties of metal–organic compounds
[16], herein, we wish to report the syntheses, crystal
structures and characterizations of four-coordination
polymers {[Zn(gauche-bime)(bdc)] Æ 0.5H2O}n (1), {[Zn-
2.3. Synthesis of {[Zn(anti-bime)(HO-bdc)] Æ 2.5H2O}n
(2)
The process was similar to the synthesis of 1 except that
H2bdc was replaced by HO-H2bdc (0.045 g, 0.25 mmol).
Colorless block crystals of 2 were obtained (yield:
0.041 mg, 36% based on Zn). Elemental Anal. Calc. for
C16H19ZnN4O7.5 (452.72): C, 42.45; H, 4.23; N, 12.38.
Found: C, 42.39; H, 4.17; N, 12.42%. IR (KBr, cmꢀ1):
3462 (bs), 1622 (vs), 1349 (vs), 1244 (m), 1100 (m), 956
(w), 777 (s), 726 (s), 652 (m), 629 (w).
2.4. Synthesis of [Cu(gauche-bime)0.5(anti-bime)0.5
(O2N-bdc)]n (4)
-
(anti-bime)(HO-bdc)] Æ 2.5H2O}n (2), [Cu(gauche-bime)0.5
-
(anti-bime)0.5(O2N-bdc)]n (4) and [Ni2(gauche-bime)(anti-
bime) (O2N-bdc)2(H2O)2]n (5) (H2bdc = m-isophthalic
acid, HO-H2bdc = 5-hydroxyisophthalic acid, O2N-H2bdc =
5-nitroisophthalic acid), in which the conformational
isomerisms of bime are heavily influenced by the coexistent
groups of dicarboxylate ligands and used metal ions. At the
same time, previously reported {[Zn(anti-bime)(O2N-bdc)]
Æ H2O}n (3) [17] as a comparable substance in the research
system was also mentioned.
The process was similar to the synthesis of 1 except
that H2bdc and Zn(NO3)2 Æ 6H2O were replaced by
O2N-H2bdc (0.053 g, 0.25 mmol) and Cu(NO3)2 Æ 3H2O
(0.060 g, 0.25 mmol), respectively. Blue prism crystals of
4 were obtained (yield: 0.031 g, 29% based on Cu). Ele-
mental Anal. Calc. for C16H13CuN5O6 (434.85): C,
44.19; H, 3.01; N, 16.10. Found: C, 44.21; H, 3.05; N,
16.08%. IR (KBr, cmꢀ1): 1614 (vs), 1594 (s), 1344 (vs),
1276 (m), 1100 (m), 843 (w), 726 (s), 703 (s), 653 (m),
551 (w).
2. Experimental
2.5. Synthesis of [Ni2(gauche-bime)(anti-bime)-
(O2N-bdc)2(H2O)2]n (5)
2.1. Materials and general methods
All the reagents were commercially available and used as
purchased except that 1,2-bis(imidazol-10-yl)ethane was
synthesized by the literature method [15]. Thermogravimet-
ric experiments were performed using a TGA/SDTA851
instrument (heating rate of 10 ꢁC/min, air stream). IR spec-
tra as KBr pellets were recorded on a Magna 750 FT-IR
spectrophotometer. Elemental analyses of C, H, and N
were determined using a Perkin–Elmer 240C elemental
analyzer. X-ray powder diffraction measurements were
recorded on RIGAKU DMAX2500PC diffractometer
using Cu Ka radiation.
The process was similar to the synthesis of 1 except that
H2bdc and Zn(NO3)2 Æ 6H2O were replaced by O2N-H2bdc
(0.053 g, 0.25 mmol) and Ni(NO3)2 Æ 6H2O (0.075 g,
0.25 mmol), respectively. Green prism crystals of 5 were
obtained (yield: 0.037 g, 33% based on Ni). Elemental Anal.
Calc. for C32H30Ni2N10O14 (896.08): C, 42.89; H, 3.37; N,
15.63. Found: C, 42.92; H, 3.25; N, 15.66%. IR (KBr,
cmꢀ1): 3412 (bs), 1614 (vs), 1528 (vs), 1376 (vs), 1341
(vs), 1287 (w), 1084 (m), 995 (w), 777 (s), 723 (s), 653
(m), 524 (w).

X.-J. Li et al. / Polyhedron 26 (2007) 3911–3919
3913
2.6. Crystal structure determinations
tural frameworks owing to its simple bridging mode and
strong coordination ability to transition metal ions. Usu-
ally, assembly of this ligand with metal ions requires the
presence of counterions to balance the charge [22]. Depro-
tonated di- or polycarboxylate ligands are another excel-
lent candidates for the preparation of coordination
networks owing to the rich coordination modes of carbox-
ylate groups [23], they can serve as anions and balance
charge by themselves. The combination of the foregoing
two types of ligands not only can simplify the effect of
counterions on the final products, but also can produce
compounds with intriguing structures and useful
properties.
Our research aims at synthesizing desired coordination
polymers via combining bime, isophthalic acid or its
derivatives (Scheme 2) and metal ions, and at further
studying the influence of coexistent groups of carboxylate
group and different metal ions on the isomerisms of bime.
The presence of the electron-donating (–OH, –Me) and
electron-withdrawing (–NO2) uncoordination groups in
dicarboxylate ligands changes their electronic property
and steric hindrance, which can generate complexes differ-
ent from those from the common dicarboxylate ligands
[24]. The solvothermal reaction of bime and H2bdc with
Zn(NO3)2 Æ 6H2O gave rise to 1, in which only gauche-
bime was observed. While H2bdc replaced by HO-H2bdc
bearing electron-donating group and O2N-H2bdc bearing
Measurements of 1, 4 and 5 were conducted on a Rigaku
Mercury CCD diffractometer with graphite-monochro-
mated Mo Ka radiation (k = 0.71073 A) at low tempera-
˚
ture (ꢀ100 ꢁC) [18]. Intensity data for 2 were measured
on a Siemens Smart CCD diffractometer with graphite-
˚
monochromated Mo Ka radiation (k = 0.71073 A) at
room temperature, the empirical absorption corrections
were applied by using the SADABS program [19]. All of the
four structures were solved by direct methods with the
SHELX-97 programs [20] and refined on F2 by full-matrix
least-squares using the SHELXL-97 program package [21].
The positions of H atoms were generated geometrically
˚
(C–H bond fixed at 0.96 A), assigned isotropic thermal
parameters, and allowed to ride on their parent carbon
atoms before the final cycle of refinement. Crystal data
and structure determination summaries for 1, 2, 4 and 5
are listed in Table 1. The selected bond lengths and angles
for the four complexes are listed in Table 2.
3. Results and discussion
3.1. Syntheses
Similar to neutral N-donor dipyridyl ligands, bime is a
promising ligand towards the syntheses of extended struc-
Table 1
Crystal data and structure determination summaries for 1, 2, 4 and 5
Compound
1
2
4
5
Formula
C
400.69
0.38 · 0.35 · 0.30
monoclinic
P21/c
16H15ZnN4O4.5
C16H19ZnN4O7.5
452.72
0.42 · 0.22 · 0.20
monoclinic
P21/c
C16H13CuN5O6
434.85
0.20 · 0.15 · 0.03
orthorhombic
Pnna
C32H30Ni2N10O14
896.08
0.25 · 0.20 · 0.15
orthorhombic
Pna21
Formula weight
Crystal size (mm)
Crystal system
Space group
˚
a (A)
9.6110(7)
17.5803(14)
10.2386(8)
90
99.192(3)
90
1707.7(2)
4
1.558
1.470
820
173(2)
0.71073
12994
10.2458(3)
21.9840(3)
9.0406(2)
90
103.010(1)
90
1984.07(8)
4
1.516
1.286
932
293(2)
0.71073
6330
16.4217(17)
19.8241(15)
10.233
90
90
90
3331.3(4)
8
1.734
1.360
1768
293(2)
0.71073
25949
4137
16.4362(9)
10.1770(6)
22.0839(14)
90
90
90
3694.0(4)
4
1.611
1.102
1840
173(2)
0.71073
27412
7135
0.0431
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Dcalc (g cmꢀ3
)
l (mmꢀ1
F(000)
T (K)
)
˚
k(Mo Ka) (A)
Reflections collected
Unique reflections
Rint
3924
0.0262
3467
0.0296
0.0399
Parameters
227
262
253
531
Goodness-of-fit (S) on F2
R1 [I > 2r(I)]a
wR2 [I > 2r(I)]b
R1 (all data)
1.089
0.0434
0.1366
0.0508
0.1446
0.781 and ꢀ0.465
1.686
0.0756
0.2122
0.0945
0.2277
1.665 and ꢀ1.036
1.097
0.0411
0.1367
0.0466
0.1409
0.473 and ꢀ0.417
0.929
0.0431
0.1235
0.0492
0.1290
0.466 and ꢀ0.337
wR2 (all data)b
3
˚
Dqmax and Dqmin (e/A )
P
P
a
R = iFoj ꢀ jFci/ jFoj.
P
P
b
2
wR2 = [ w(Fo ꢀ Fc2)2/ w(Fo2)2]1/2
.

3914
X.-J. Li et al. / Polyhedron 26 (2007) 3911–3919
Table 2
R
˚
Selected bond lengths (A) and angles (ꢁ) for 1, 2, 4, and 5
Compound 1
Zn–O4A
Zn–O2
1.9431(18)
1.9766(19)
Zn–N4B
Zn–N1
1.998(2)
2.008(2)
O4A–Zn–O2
O4A–Zn–N4B
O2–Zn–N4B
118.26(8)
107.64(9)
101.78(9)
O4A–Zn–N(1)
O2–Zn–N1
N4B–Zn–N1
115.01(9)
98.41(9)
115.15(9)
HOOC
COOH
Compound 2
Zn–O(1)
Zn–N4B
R = H, m-isophthalic acid
1.987(4)
1.992(4)
Zn–N(1)
Zn–O4A
1.993(5)
2.007(4)
R = -OH, 5-hydroxylisophthalic acid
R = -NO2, 5-nitroisophthalic acid
Scheme 2.
O1–Zn–N4B
O1–Zn–N1
N4B–Zn–N1
102.96(18)
105.51(19)
124.3(2)
O1–Zn–O4A
N4B–Zn–O4A
N1–Zn–O4A
101.85(16)
110.66(17)
108.9(2)
Compound 4
Cu–O4B
Cu–N3
1.9651(17)
1.976(2)
Cu–O2
Cu–O3A
2.029(2)
2.3317(19)
3.2. Description of crystal structures
Cu–N1
1.9880(19)
3.2.1. {[Zn(gauche-bime)(bdc)] Æ 0.5H2O}n (1)
O4B–Cu–N3
O4B–Cu–N1
N3–Cu–N1
O4B–Cu–O2
N3–Cu–O2
89.25(8)
88.87(8)
173.26(9)
161.06(7)
91.04(7)
N1–Cu–O2
88.65(7)
106.29(7)
93.48(7)
93.26(7)
92.59(6)
Single-crystal X-ray diffraction analysis reveals that 1 is
a 1D linear coordination polymer containing only gauche
isomer of bime. As shown in Fig. 1, each ZnII center is
coordinated by two oxygen atoms and two nitrogen atoms
from different bdc and bime ligands, respectively, in a dis-
torted tetrahedral geometry. The bond angles range from
98.41(9)ꢁ to 118.26(8)ꢁ, and the average bond lengths of
O4B–Cu–O3A
N3–Cu–O3A
N1–Cu–O3A
O2–Cu–O3A
Compound 5
Ni1–N1
Ni1–O1
Ni1–N5
Ni2–N8
2.053(4)
2.064(3)
2.071(4)
2.050(4)
2.051(3)
2.070(4)
Ni1–OW1
Ni1–O4A
Ni1–O3A
Ni2–OW2
Ni2–O10A
Ni2–O9A
2.106(3)
2.145(3)
2.175(3)
2.077(3)
2.119(3)
2.195(3)
˚
Zn–O and Zn–N are 1.9596(19) and 2.003(2) A, respec-
tively. The deprotonated bdc serves as [a] bridge through
its bis-monodentate carboxylate groups. The bime ligand
adopts gauche-conformation to connect two zinc(II) cen-
ters, and the dihedral angle between two imidazolyl rings
is 50.5ꢁ. Therefore, two bime link two zinc(II) centers to
generate a –Zn–bime–Zn–bime– closed circuit, and the
bis-monodentate bdc further extend the closed circuits into
a 1D bamboo-like chain, in which the distances of adjoin-
ing zinc(II) centers separated by bime and bdc are 6.244
Ni2–O7
Ni2–N4B
N1–Ni1–O1
N1–Ni1–N5
O1–Ni1–N5
90.75(13)
176.66(16)
88.38(13)
90.17(15)
98.33(12)
86.76(15)
92.64(14)
97.00(12)
92.29(14)
172.40(16)
94.65(14)
85.71(15)
95.70(13)
90.49(16)
89.09(14)
97.32(12)
N5–Ni1–O4A
OW1–Ni1–O4A
N1–Ni1–O3A
O1–Ni1–O3A
N5–Ni1–O3A
OW1–Ni1–O3A
O4A–Ni1–O3A
90.68(14)
164.38(12)
88.74(12)
158.17(12)
93.27(12)
103.49(12)
61.24(11)
N1–Ni1–OW1
O1–Ni1–OW1
N5–Ni1–OW1
N1–Ni1–O4A
O1–Ni1–O4A
N8–Ni2–O7
N8–Ni2–N4B
O7–Ni2–N4B
N8–Ni2–OW2
O7–Ni2–OW2
N4B–Ni2–OW2
N8–Ni2–O10A
O7–Ni2–O10A
˚
and 9.611 A, respectively (Fig. 2). The crystal packing
N4B–Ni2–O10A
OW2–Ni2–O10A
N8–Ni2–O9A
93.11(14)
166.16(12)
86.26(13)
158.37(13)
88.43(13)
105.69(13)
61.10(11)
O7–Ni2–O9A
N4B–Ni2–O9A
OW2–Ni2–O9A
O10A–Ni2–O9A
Symmetry codes for 1: A x ꢀ 1, y, z; B ꢀx + 2, ꢀy, ꢀz + 1. For 2:
A x ꢀ 1, y, z; B ꢀx, y ꢀ 1/2, ꢀz + 1/2. For 4: A x, ꢀy + 1/2, ꢀz ꢀ 1/2, B
x, y, z + 1; 5 A x, y + 1, z, B ꢀx ꢀ 1/2, y + 1/2, z ꢀ 1/2.
electron-withdrawing group, respectively, 2 and 3 were
generated, in which only anti-bime were exhibited. As
compared with 3, when using Cu(NO3)2 Æ 3H2O and
Ni(NO3)2 Æ 6H2O instead of Zn(NO3)2 Æ 6H2O, 4 and 5
were generated, respectively, where both gauche- and
anti-conformations (1:1) of bime were displayed. This
may indicate that the coordination geometries of different
metal ions are also critical factors in the control of differ-
ent conformation of bime ligand.
Fig. 1. The coordination geometry of ZnII in 1 with the thermal ellipsoids
at 30% probability level, free water molecule and hydrogen atoms were
omitted for clarity.

X.-J. Li et al. / Polyhedron 26 (2007) 3911–3919
3915
Fig. 2. View of the 1D bamboo-like chain, in which the –Zn–bime–Zn–bime– closed circuits are exhibited.
diagram for 1 is shown in Fig. 3, which reveals that there
are free water molecules situated in the crystal lattice.
ABAB mode, and the abundant hydrogen bonding interac-
tions between free water molecules and carboxylate groups,
free water molecules and free water molecules as well as the
above-mentioned the hydroxyl groups and the hydroxyl
groups, connect the 2D layer into a 3D supramolecular
3.2.2. {[Zn(anti-bime)(HO-bdc)] Æ 2.5H2O}n (2)
When HO-H2bdc replaced H2bdc under the same condi-
tion, 2 was successfully isolated. Different from the 1D lin-
ear structure of 1, 2 is a 3D supramolecular architecture in
which only anti isomer of bime is included. The asymmetric
unit consists of one ZnII, one HO-bdc, one bime and two
and half free water molecules (Fig. 4). Similar to that in
1, each ZnII center is in a distorted tetrahedral geometry,
determined by two oxygen atoms and two nitrogen atoms
from the carboxylate groups of different HO-bdc and bime
ligands with the average bond lengths of Zn–O and Zn–N
architecture [OW1–Hꢁ ꢁ ꢁO2ii 2.798 A; OW2–Hꢁ ꢁ ꢁO3iii
˚
˚
˚
2.790 A; OW1–Hꢁ ꢁ ꢁOW3 2.699 A; OW2–Hꢁ ꢁ ꢁOW3
˚
being 1.997(4) and 1.992(5) A, respectively. Each HO-bdc
ligand bridges two ZnII centers through its bis-monoden-
tate carboxylate groups, the hydroxyl group (–OH) is
involved in hydrogen bonding interactions with another
adjacent hydroxyl group [O5–Hꢁ ꢁ ꢁO5Ai 2.840 A, (i)
˚
ꢀx + 1, ꢀy, ꢀz + 2], although it does not take part in
coordination. Different from that found in 1, bime adopts
only anti-conformation to coordinate to two zinc centers.
The two imidazolyl rings are almost coplanar with the
dihedral angle between them being 163.0ꢁ. Thereby, the
bis-monodentated HO-bdc and the anti-conformational
bime connect ZnII centers into a 2D (4,4) network with cav-
2
˚
ities of 10.246 · 11.358 A determined by adjoining
Znꢁ ꢁ ꢁZn distances separated by HO-bdc and bime, respec-
tively (Fig. 5). In order to minimize the void cavities and
stabilize the whole framework, the crystal packing adopts
Fig. 4. The coordination geometry of ZnII in 2 with the thermal ellipsoids
at 30% probability level, free water molecules and hydrogen atoms were
omitted for clarity.
Fig. 3. View of the packing diagram of 1 along c-axis.

3916
X.-J. Li et al. / Polyhedron 26 (2007) 3911–3919
3.2.4. [Cu(gauche-bime)0.5(anti-bime)0.5(O2N-bdc)]n (4)
Compound 4 is a 2D wave-like layer consisting of dinu-
clear units, in which both gauche- and anti-conformations
of bime are observed. There is only one unique CuII center
in 4, its coordination environment is shown in Fig. 7. CuII
is surrounded by five atoms in a distorted trigonal bipyra-
midal coordination geometry. The equatorial plane is
determined by three carboxylate oxygen atoms from differ-
ent O2N-bdc with the bond angles ranging from 92.59(6)ꢁ
to 161.06(7)ꢁ, while the axial positions are occupied by
two nitrogen atoms from different bime with the N1–Cu–
N3 bond angle and the average Cu–N bond length being
˚
173.26(9)ꢁ and 1.982 (2) A, respectively. Each O2N-bdc
Fig. 5. View of the 2D (4,4) network.
˚
2.690 A; symmetry codes: (ii) x, ꢀy + 1/2, ꢀz + 1; (iii) x, y,
z + 1] (Fig. 6). Compared to 1, it is notable that the elec-
tron-donating hydroxyl group in the dicardoxylate ligand
plays an important role in the change of the conforma-
tional isomerism of bime in 2.
3.2.3. {[Zn(bime)(O2N-bdc)] Æ H2O}n (3)
When selected bime, O2N-H2bdc and Zn(NO3)2 Æ 6H2O
as starting materials, 3 was generated. As previously
reported, 3 is a tetrahedrally four-connected 6.6.6.6.62.83
topological network. Similar to that in 2, the ZnII center
is in a distorted tetrahedral geometry and the bime ligand
also behaves in anti-conformation to link zincII centers
(see Fig. S1). The Znꢁ ꢁ ꢁZn distance across bime is
˚
11.762 A, slightly longer than that in 2. Based on 3, differ-
ent metal ions possessing different coordination geometries
were induced into the reaction system in order to further
study the conformation preference of bime. Therefore,
the following 4 and 5 were generated from the solvothermal
reactions of bime and O2N-H2bdc with Cu(NO3)2 Æ 3H2O
and Ni(NO3)2 Æ 6H2O, respectively, in which both gauche-
and anti-conformations (1:1) of bime were exhibited.
Fig. 7. The coordination geometry of CuII in 4 with the thermal ellipsoids
at 30% probability level, hydrogen atoms were omitted for clarity.
Fig. 6. View of the 3D supramolecular architecture of 2 along a-axis.

X.-J. Li et al. / Polyhedron 26 (2007) 3911–3919
3917
behaves as a l3-bridge linking three CuII centers through
one monodentate carboxylate and one l2,g2-carboxylate
groups into a 1D double-chain, in which dinuclear units
are exhibited (Fig. 8), the nitro group (–NO2) neither takes
part in coordination nor involves in hydrogen bonding
interaction. Interestingly, there are two kinds of bime:
one adopts gauche-conformation and acts as a bridge
between two CuII centers in the dinuclear unit; while the
other adopts anti-conformation to extend the 1D double-
chain into a 2D wave-like layer (Fig. 9). The ratio of bime
conformation is 1:1, which is different from that found in
another copper–bime complex [7]. With respect to the
gauche-bime, the dihedral angle between two imidazolyl
rings is 30.9ꢁ, smaller than that in 1, and the Cuꢁ ꢁ ꢁCu dis-
˚
tance across it is 4.445 A. The two imidazolyl rings in anti-
bime are almost coplanar with the dihedral angle between
them being 180.0ꢁ, and the adjoining Cuꢁ ꢁ ꢁCu distance sep-
˚
arated by it is 11.543 A. The packing diagram displays that
no guest molecules and weak interactions are included
between layers, although there are large void spaces in
the wave-like layer (Fig. S2).
Fig. 10. The coordination geometries of NiII ions in 5 with the thermal
ellipsoids at 30% probability level, hydrogen atoms were omitted for
clarity.
3.2.5. [Ni2(gauche-bime)(anti-bime)(O2N-bdc)2(H2O)2]n
(5)
torial plane. Firstly, the O2N-bdc acts as a bridge linking
adjoining NiII centers to give rise to a 1D chain through
its monodentate and chelating carboxylate groups, the
nitro group (–NO2) neither participates in coordination
nor involves in hydrogen bonding interaction (Fig. 11).
Secondly, the 1D chain is extended by two kinds of bridg-
ing bime to generate a 2D wave-like layer, in which the
intramolecular hydrogen bonding interaction between
coordinated water molecule and carboxylate group further
stabilize the framework (Fig. 12 and Fig. S3). Similar to
Compound 5 is also a 2D wave-like layer including both
gauche- and anti-conformations of bime, but the bridging
fashion of O2N-bdc and coordination environments of
metal centers are different from those in 4. The coordina-
tion environments of NiII centers are shown in Fig. 10.
Both NiII ions adopt distorted octahedral coordination
geometries, in which two nitrogen atoms from different
bime stand at the apical positions, and three carboxylate
oxygen atoms and one water molecule consist of the equa-
Fig. 8. View of the 1D double chain along different directions, (a) for a-axis, (b) for c-axis, in which the dinuclear units are exhibited.
Fig. 9. View of the 2D wave-like layer.

3918
X.-J. Li et al. / Polyhedron 26 (2007) 3911–3919
first weight loss of 1.98% from 45 to 130 ꢁC is equivalent to
the loss of half free water molecule [0.5H2O/[Zn(gauche-
bime)(bdc)] Æ 0.5H2O, calculated: 2.25%]. The second weight
loss of 77.18% from 386 to 582 ꢁC, corresponds to the
decomposition of 1. The residual weight of 20.40% is
ascribed to ZnO (ZnO/[Zn(gauche-bime)(bdc)] Æ 0.5(H2O),
calculated 20.31%). Similar to 1, the TGA curve of 2 also
shows two significant weight losses: 9.76% between 49 and
120 ꢁC, and 71.98% between 365 and 552 ꢁC. The former
can be ascribed to the loss of two and half free water mole-
cules (2.5H2O/[Zn(anti-bime)(HO-bdc)] Æ 2.5H2O, calcu-
lated 9.94%), while the latter suggests the chemical
decomposition of 2. The residue composition is attributed
to ZnO (ZnO/[Zn(anti-bime)(HO-bdc)] Æ 2.5H2O, calculated
17.97%, found 18.26%). For 4, the TGA curve exhibits only
one weight loss (80.91% from 281 to 520 ꢁC), which indicates
the decomposition of 4. The residual weight of 19.09% corre-
Fig. 11. View of the 1D chain.
those found in 4, both gauche- and anti-isomers of bime are
observed in 5, and the ratio of the different conformations
is also 1:1. The dihedral angle between two imidazolyl rings
in gauche-bime is 50.6ꢁ, almost equivalent to that in 1 but
larger than that in 4, while the two imidazolyl rings in anti-
bime is approximately coplanar with the dihedral angle
being 166.3ꢁ. The neighboring Niꢁ ꢁ ꢁNi distances separated
˚
by gauche- and anti-bime are 5.873 and 11.715 A,
respectively.
sponds to CuO (CuO/Cu(gauche-bime)0.5(anti-bime)0.5
-
3.3. Infrared spectroscopy
(O2N-bdc), calculated 18.29%). For 5, the TGA curve
displays two weight losses: one (3.96% from 124 to 162 ꢁC)
corresponds to the loss of coordinated water molecule
(2H2O/Ni2(gauche-bime)(anti-bime)(O2N-bdc)2(H2O)2, cal-
culated 4.02%); the other (78.96% from 396 to 538 ꢁC)
indicates the decomposition of 5. The residue is attributed
to NiO (2NiO/Ni2(gauche-bime)(anti-bime)(O2N-bdc)2-
(H2O)2, calculated 16.67%, found 17.08%).
The IR spectrum of 1 shows a strong and broad peak at
3427 cmꢀ1, which indicates the presence of water mole-
cules. The strong peaks at 1622 cmꢀ1 and 1347 cmꢀ1 are
attributed to the asymmetric and symmetric vibrations of
carboxylate groups, respectively. For 2, similar to that in
1, the strong and broad peak at 3462 cmꢀ1 suggests the
existence of water molecules, the characteristic bands of
carboxylate groups are shown at 1622 cmꢀ1 for asymmetric
stretching vibration and 1349 cmꢀ1 for symmetric stretch-
ing vibration. The similar splitting of 1 and 2 reveals the
similar bis-monodentate coordination fashion of dicarb-
oxylate ligands. For 4, the characteristic bands of asym-
metric and symmetric stretching vibrations of carboxylate
3.5. X-ray powder diffraction
The original samples of the four complexes were also
characterized by X-ray powder diffraction (XRPD) at
room temperature (Figs. S8–S11). The experimental pat-
terns are in good agreement with the theoretical ones gen-
erated from the single-crystal X-ray data of the complexes,
which clearly indicate the good purity of the four
complexes.
groups are shown at 1614 cmꢀ1
,
1594 cmꢀ1 and
1344 cmꢀ1, respectively. For 5, the strong and broad peak
at 3412 cmꢀ1 suggests the presence of hydrogen bonding
interactions. The strong peaks at 1614 cmꢀ1, 1528 cmꢀ1
and 1376 cmꢀ1, 1341 cmꢀ1 are attributed to the asymmetric
and symmetric stretching vibrations of carboxylate groups,
respectively.
4. Conclusions
The solvothermal reactions of m-isophthalic acid or its
derivatives bearing electron-donating and electron-with-
drawing coexistent groups, bime and different metal ions
generated five novel coordination polymers, in which bime
adopt gauche (1), anti (2 and 3) and mixed conformations
of gauche and anti (1:1) (4 and 5), respectively. This
3.4. Thermogravimetric analyses
The thermal stability of the four complexes was deter-
mined by thermogravimetric analysis (TGA) on polycrystal-
line samples in an air atmosphere (Figs. S4–S7). For 1, the
Fig. 12. View of the 2D wave-like layer.

X.-J. Li et al. / Polyhedron 26 (2007) 3911–3919
3919
´
´
(b) N. Fatin-Rouge, E. Toth, D. Perret, R.H. Backer, A.E. Merbach,
research reveals that (i) the electron-donating and electron-
withdrawing coexistent groups in dicarboxylate ligands are
not involved in coordination, but they have important
effect on the conformational preference of bime; (ii) the
coordination geometries of different metal ions also play
critical roles on the conformational preference of bime;
and (iii) the conformational isomerisms of bime make it a
good candidate to the construction of supramolecular
networks.
J.G. Bunzli, J. Am. Chem. Soc. 122 (2000) 10810;
¨
(c) Y. Kim, D.Y. Jung, Inorg. Chem. 39 (2000) 1470.
[8] (a) F.M. Tabellion, S. Russell Seidal, A.M. Arif, P.J. Stang, Angew.
Chem., Int. Ed. 40 (2001) 1529;
(b) K.I. Na¨ttinen, K. Rissanen, Inorg. Chem. 42 (2003) 5126;
(c) L. Carlucci, G. Ciani, D.M. Proserpio, Chem. Commun. (2004)
380.
[9] (a) X.H. Bu, W. Chen, S.L. Lu, R.H. Zhang, D.Z. Liao, W.M. Bu, M.
Shionova, F. Brisse, J. Ribas, Angew. Chem., Int. Ed. 40 (2001) 3201;
(b) K. Kasai, M. Aoyagi, M. Fujita, J. Am. Chem. Soc. 122 (2000)
2140;
(c) R.H. Wang, M.C. Hong, J.H. Luo, R. Cao, J.B. Weng, Chem.
Commun. (2003) 1018.
Acknowledgments
[10] (a) L. Pan, K.M. Adams, H.E. Hernandez, X. Wang, C. Zheng, Y.
Hattori, K. Kaneko, J. Am. Chem. Soc. 125 (2003) 3062;
(b) Y. Qi, Y. Wang, C. Hu, M. Cao, L. Mao, E. Wang, Inorg. Chem.
42 (2003) 8519.
[11] (a) L. Carlucci, G. Ciani, M. Moret, D.M. Proserpio, S. Rizzato,
Angew. Chem., Int. Ed. 39 (2000) 1506;
This work was supported by the National Natural Sci-
ence Foundation of China (Nos. 90206040, 20325106,
and 20333070), Natural Science Foundation of Fujian
Province and ‘‘One Hundred Talent Project’’ from CAS.
(b) H.F. Zhu, L. Li, T. Okamura, W. Zhao, W.Y. Sun, N. Ueyama,
Bull. Chem. Soc. Jpn. 76 (2003) 761.
Appendix A. Supplementary material
´
[12] (a) M.L. Hernandez, M. Karmele Urtiaga, M. Gotzone Barandika,
CCDC 615191, 615192, 615193 and 615194 contain the
supplementary crystallographic data for 1, 2, 4 and 5.
These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-
mail: deposit@ccdc.cam.ac.uk. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.poly.2007.04.043.
´
R. Cortes, L. Lezama, N. de la Pinta, M. Isabel Arriortua, T. Rojo, J.
Chem. Soc., Dalton Trans. (2001) 3010;
(b) L. Carlucci, G. Ciani, D.M. Proserpio, S. Rizzato, Chem.
Commun. (2000) 1319;
(c) M. Du, C.P. Li, X.J. Zhao, CrystEngComm 8 (2006) 552.
´
[13] (a) M.L. Hernandez, M. Gotzone Barandika, M. Karmele Urtiaga,
´
R. Cortes, L. Lezama, M. Isabel Arriortua, T. Rojo, J. Chem. Soc.,
Dalton Trans. (1999) 1401;
(b) Q.M. Wang, G.C. Guo, T.C.W. Mak, Chem. Commun. (1999)
1849;
(c) F.A. Almeida, J. Klinowski, Inorg. Chem. 43 (2004) 3948.
[14] T.L. Hennigar, D.C. MacQuarrie, P. Losier, R.D. Rogers, M.J.
Zaworotko, Angew. Chem., Int. Ed. Engl. 36 (1997) 972.
[15] L.P. Wu, Y. Yamagiwa, T. Kuroda-Sowa, T. Kamikawa, M.
Munakata, Inorg. Chim. Acta 256 (1997) 155.
[16] (a) X.J. Li, R. Cao, W.H. Bi, Y.Q. Wang, Y.L. Wang, X. Li, Z.G.
Guo, Cryst. Growth Des. 5 (2005) 1651;
(b) X.J. Li, R. Cao, D.F. Sun, W.H. Bi, Y.Q. Wang, X. Li, M.C.
Hong, Cryst. Growth Des. 4 (2004) 775.
[17] X.J. Li, R. Cao, Z.G. Guo, W.H. Bi, D.Q. Yuan, Inorg. Chem.
Commun. 9 (2006) 551.
[18] CRYSTALCLEAR, Version 1.36, Molecular Structure Corporation Rig-
aku, MSC/SSI, 491, South Orem Boulevard, Orem, UT 84058, 2001.
[19] G.M. Sheldrick, SADABS: Program for Empirical Absorption Correc-
tion of Area Detector Data, University of Go¨ttingen, Go¨ttingen,
Germany, 1996.
[20] G.M. Sheldrick, SHELXS-97: Program for Crystal Structure Solution,
University of Go¨ttingen, Go¨ttingen, Germany, 1997.
[21] G.M. Sheldrick, SHELXS-97: Program for Crystal Structure Refine-
ment, University of Go¨ttingen, Go¨ttingen, Germany, 1997.
[22] J.F. Ma, J.F. Liu, Y. Xing, H.Q. Jia, Y. H Lin, J. Chem. Soc., Dalton
Trans. (2000) 2403.
[23] (a) Y. Liu, V.C. Kravtsov, D.A. Beauchamp, J.F. Eubank, M.
Eddaoudi, J. Am. Chem. Soc. 127 (2005) 7266;
(b) Z. Ni, A. Yassar, T. Antoun, O.M. Yaghi, J. Am. Chem. Soc. 127
(2005) 12752.
[24] (a) H. Abourahma, B. Moulton, V. Kravtsov, M.J. Zaworotko, J.
Am. Chem. Soc. 124 (2002) 9990;
References
[1] (a) H.J. Choi, T.S. Lee, M.P. Suh, Angew. Chem., Int. Ed. 38 (1999)
1405;
(b) P.J. Hagrman, D. Hagrman, J. Zubieta, Angew. Chem., Int. Ed.
38 (1999) 2638.
[2] (a) O.R. Evans, W. Lin, Acc. Chem. Res. 35 (2002) 511;
(b) S. Horike, R. Matsuda, D. Tanaka, M. Mizuno, K. Endo, S.
Kitagawa, J. Am. Chem. Soc. 128 (2006) 4222;
(c) J.L.C. Rowsell, O.M. Yaghi, Microporous Mesoporous Mater. 73
(2004) 3.
[3] (a) K.A. Hirsch, S.R. Wilson, J.S. Moore, Chem. Commun. (1998)
13;
(b) D.M. Shin, I.S. Lee, Y.K. Chung, M.S. Lah, Inorg. Chem. 42
(2003) 5459;
(c) L. Carlucci, G. Ciani, D.M. Proserpio, F. Porta, CrystEngComm
7 (2005) 78.
[4] (a) S.L. Zheng, M.L. Tong, H.L. Zhu, Y. Fang, X.M. Chen, J. Chem.
Soc., Dalton Trans. (2001) 2049;
(b) A.J. Blake, N.R. Champness, A.N. Khlobystov, S. Parsons, M.
Schro¨der, Angew. Chem., Int. Ed. 39 (2000) 2317.
[5] (a) D.A. Beauchamp, S.J. Loeb, Chem. Commun. (2002) 2484;
(b) M. Du, S.T. Chen, X.H. Bu, Cryst. Growth Des. 2 (2002) 625.
[6] (a) M. Fujita, K. Umemoto, M. Yoshizawa, N. Fujita, T. Kusukawa,
K. Biradha, Chem. Commun. (2001) 509;
(b) H.K. Fun, S. Shanmuga Sundara Raj, R.G. Xiong, J.L. Zuo, Z.
Yu, X.L. Zhu, X.Z. You, J. Chem. Soc., Dalton Trans. (1999) 1711.
[7] (a) S.Y. Yu, Z.X. Zhang, E.C.C. Cheng, Y.Z. Li, V.W.W. Yam, H.P.
Huang, R. Zhang, J. Am. Chem. Soc. 127 (2005) 17994;
(b) M. John Plater, M.R.S.J. Foreman, R. Alan Howie, J.M.S.
Skakle, S.A. McWilliam, E. Coronado, C.J. Gomez-Garca¨a, Polyhe-
dron 20 (2001) 2293.
´