Syntheses and characterizations of nine coordination polymers of transition metals with carboxylate anions and bis(imidazole) ligands

Article abstract of DOI:10.1016/j.poly.2008.07.026

Nine new compounds, namely [CuL1(biim-6)] · H₂O (1), [ZnL1(biim-6)] · H₂O (2), [MnL1(biim-6)] · H₂O (3), [MnL1(biim-4)] (4), [Co₂(L2)₂(biim-5)₃ · 6H₂O] · 8H₂O (5), [ZnL3(biim-6)] (6), [ZnL3(biim-5)] (7), [CdL3(biim-5) · 1.5H₂O] · 0.5H₂O (8) and [CdL4(biim-6) · 2H₂O] (9) [where L1 = oxalate anion, L2 = fumarate anion, L3 = phthalate anion, L4 = p-phthalate anion, biim-4 = 1,1′-(1,4-butanediyl)bis(imidazole), biim-5 = 1,1′-(1,5-pentanedidyl)bis(imidazole) and biim-6 = 1,1′-(1,6-hexanedidyl)bis(imidazole)] were successfully synthesized. Compounds 1-3 are isostructural, and display 2D polymeric structures. Compound 4 shows a threefold interpenetrating diamondoid framework. In compound 5, the anions act as counterions, and the metal cations are bridged by bis(imidazole) ligands to form 1D polymeric chains. Compounds 6-9 show 2D polymeric structures. The magnetic properties for 1, 3 and 4 and luminescent properties for 2 and 6-9 are discussed. Thermogravimetric analyses (TGA) for these compounds are also discussed.

Full text of DOI:10.1016/j.poly.2008.07.026

Polyhedron 27 (2008) 3351–3358
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Syntheses and characterizations of nine coordination polymers of transition
metals with carboxylate anions and bis(imidazole) ligands
*
Wen-Li Zhang, Ying-Ying Liu, Jian-Fang Ma , Hui Jiang, Jin Yang
Key Laboratory of Polyoxometalate Science, Department of Chemistry, Northeast Normal University, Changchun 130024, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
Nine new compounds, namely [CuL1(biim-6)] ꢀ H2O (1), [ZnL1(biim-6)] ꢀ H2O (2), [MnL1(biim-6)] ꢀ H2O
(3), [MnL1(biim-4)] (4), [Co2(L2)2(biim-5)3 ꢀ 6H2O] ꢀ 8H2O (5), [ZnL3(biim-6)] (6), [ZnL3(biim-5)] (7),
[CdL3(biim-5) ꢀ 1.5H2O] ꢀ 0.5H2O (8) and [CdL4(biim-6) ꢀ 2H2O] (9) [where L1 = oxalate anion, L2 = fuma-
rate anion, L3 = phthalate anion, L4 = p-phthalate anion, biim-4 = 1,10-(1,4-butanediyl)bis(imidazole),
biim-5 = 1,10-(1,5-pentanedidyl)bis(imidazole) and biim-6 = 1,10-(1,6-hexanedidyl)bis(imidazole)] were
successfully synthesized. Compounds 1–3 are isostructural, and display 2D polymeric structures. Com-
pound 4 shows a threefold interpenetrating diamondoid framework. In compound 5, the anions act as
counterions, and the metal cations are bridged by bis(imidazole) ligands to form 1D polymeric chains.
Compounds 6–9 show 2D polymeric structures. The magnetic properties for 1, 3 and 4 and luminescent
properties for 2 and 6–9 are discussed. Thermogravimetric analyses (TGA) for these compounds are also
discussed.
Received 24 May 2008
Accepted 28 July 2008
Available online 25 August 2008
Keywords:
Coordination polymers
Bisimidazole
Carboxylate
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
[CuL1(biim-6)] ꢀ H2O (1), [ZnL1(biim-6)] ꢀ H2O (2), [MnL1(biim-
6)] ꢀ H2O (3), [MnL1(biim-4)] (4), [Co2(L2)2(biim-5)3 ꢀ 6H2O] ꢀ 8H2O
The design and synthesis of coordination polymers with unu-
sual structures and properties are attracting increasing attention,
not only for their intriguing molecular topologies, but also for their
potential applications as functional materials [1–3]. The construc-
tion of molecular architecture depends on the combination of sev-
eral factors, like the coordination geometry of metal salt and ligand
[4–7]. Thus, understanding how these considerations affect metal
coordination and influence crystal packing is at the forefront of
controlling coordination supramolecular arrays. Poly-carboxylates
are widely used in the assembly of supramolecular architectures
because of their diverse coordination modes and bridging abilities
[8–12]. Bis(imidazole) ligands bearing alkyl spacers are a good
choice of N-donor ligand, and the flexible nature of spacers allows
the ligands to bend and rotate when coordinating to metal centers
so as to conform to the coordination geometries of metal ions [13–
18]. The previous studies show that these ligands exhibit special
abilities to formulate the compounds, and the results also indicate
that different organic anions play important roles in directing the
final structures and topologies [19–22]. In this work, several ter-
nary systems containing transition metals, bis(imidazole) ligands
and carboxylate anions are selected to survey the influence factors.
We describe the successful syntheses of nine novel compounds:
(5), [ZnL3(biim-6)] (6), [ZnL3(biim-5)] (7), [CdL3(biim-
5) ꢀ 1.5H2O] ꢀ 0.5H2O (8) and [CdL4(biim-6) ꢀ 2H2O] (9). The crystal
structures of these compounds, along with the systematic investi-
gation of the effect of the anions and the neutral ligands on the
ultimate framework, will be represented and discussed (Schemes
1 and 2).
2. Experimental
All reagents and solvents for syntheses were purchased from
commercial sources and used as received. Biim-4 [23], biim-5
[24] and biim-6 [23] were synthesized in accordance with the pro-
cedure reported. The C, H, and N elemental analysis was conducted
on a Perkin–Elmer 240C elemental analyzer. The FT-IR spectra
were recorded from KBr pellets in the range 4000–400 cm–1 on a
Mattson Alpha-Centauri spectrometer. The excitation and emission
spectra were measured on a Perkin–Elmer LS55 spectrometer. For
the detail syntheses of compounds 1–9, please see Scheme S1 in
the Supplementary data.
2.1. Syntheses of the metal complexes
2.1.1. Synthesis of [CuL1(biim-6)] ꢀ H2O (1)
Oxalic acid dihydrate (0.126 g, 1 mmol) was added to the
Cu(OH)2 (0.098 g, 1 mmol) suspension in water (10 mL) with stir-
* Corresponding author. Tel./fax: +86 431 85098620.
E-mail address: jianfangma@yahoo.com.cn (J.-F. Ma).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.07.026

3352
W.-L. Zhang et al. / Polyhedron 27 (2008) 3351–3358
2.1.4. Synthesis of [MnL1(biim-4)] (4)
A mixture of MnCO3 (0.115 g, 1 mmol), oxalic acid dihydrate
(0.126 g, 1 mmol) in water (8 mL), and biim-4 (0.380 g, 1 mmol)
in ethanol (1 mL) was sealed in a Teflon-lined stainless steel auto-
clave and heated at 140 °C for 4 days prior to being cool to room
temperature at 10 °C hꢁ1. Colorless crystals were obtained in a
69% yield based on MnCO3. Elemental Anal. Calc. for
C12H14MnN4O4: C, 43.26; H, 4.24; N, 16.81. Found: C, 43.14; H,
4.27; N, 16.75%. IR (KBr, cmꢁ1): 3742 (s), 3116 (w), 2928 (w),
1679 (vs), 1652 (vs), 1618 (m), 1515 (vs), 1389 (m), 1229 (w),
1111 (w), 789 (w), 667 (s), 475 (m).
2.1.5. Synthesis of [Co2(L2)2(biim-5)3 ꢀ 6H2O] ꢀ 8H2O (5)
Scheme 1. Structures of bis(imidazole) ligands in this work.
A mixture of CoCO3 (0.119 g, 1 mmol), fumaric acid (0.116 g,
1 mmol) in water was stirring for 10 min at room temperature.
Then biim-5 (0.408 g, 2 mmol) was added to the mixture with stir-
ring for 1 h and pink solution was obtained. Pink crystals were ob-
tained from the filtrate after standing at room temperature for
several days in a 75% yield based on CoCO3. Elemental Anal. Calc.
for C41H80Co2N12O22: C, 40.66; H, 6.66; N, 13.88. Found: C, 40.74;
H, 6.70; N, 13.95%. IR (KBr, cmꢁ1): 3670 (w), 3136 (m), 2945 (w),
2858 (w), 1568 (vs), 1455 (m), 1240 (vs), 1108 (vs), 991 (m), 843
(s), 763 (s), 663 (vs).
2.1.6. Synthesis of [ZnL3(biim-6)] (6)
A mixture of ZnCO3 (0.125 g, 1 mmol), phthalic anhydride
(0.148 g, 1 mmol) in water (8 mL), and biim-6 (0.437 g, 2 mmol)
in ethanol (1 mL) was sealed in a Teflon-lined stainless steel auto-
clave and heated at 180 °C for 4 days, and then it was cooled to
room temperature at 10 °C hꢁ1. Colorless crystals were obtained
Scheme 2. Structures of the carboxylate anions in this work.
in
a 60% yield based on ZnCO3. Elemental Anal. Calc. for
ring. After biim-6 (0.436 g, 2 mmol) in 1 mL ethanol was added, a
blue precipitate was obtained. A minimum amount of ammonia
(14 M) was added to give a blue solution. Suitable crystals were ob-
tained after standing at room temperature for several days. The
crystals were collected in a 75% yield based on Cu2+. Elemental
Anal. Calc. for C14H20CuN4O5: C, 43.35; H, 5.20; N, 14.44. Found:
C, 43.42; H, 5.27; N, 14.57%. IR (KBr, cmꢁ1): 3741 (w), 3110 (s),
2858 (w), 1613 (s), 1560 (vs), 1516 (vs), 1358 (m), 1229 (m),
1109 (s), 829 (w), 784 (m), 663 (s), 659 (s), 487 (w).
C20H22ZnN4O4: C, 53.65; H, 4.95; N, 12.51. Found: C, 53.77; H,
4.97; N, 12.65%. IR (KBr, cmꢁ1): 3123 (w), 3090 (w), 2865 (w),
1619 (vs), 1560 (vs), 1524 (s), 1475 (m), 1377 (vs), 1249 (m),
1144 (m), 950 (m), 768 (s), 655 (vs), 454 (w).
2.1.7. Synthesis of [ZnL3(biim-5)] (7)
A mixture of ZnCO3 (0.125 g, 1 mmol), phthalic anhydride
(0.148 g, 1 mmol) in water (8 mL), and biim-5 (0.408 g, 2 mmol)
in ethanol (1 mL) was sealed in a Teflon-lined stainless steel auto-
clave and heated at 170 °C for 4 days, and then it was cooled to
room temperature at 10 °C hꢁ1. Colorless crystals were obtained
2.1.2. Synthesis of [ZnL1(biim-6)] ꢀ H2O (2)
After a mixture of ZnCO3 (0.125 g, 1 mmol), oxalic acid dihy-
drate (0.126 g, 1 mmol) in water was stirring for 10 min at room
temperature, biim-6 (0.436 g, 2 mmol) in 1 mL ethanol was added
to the solution with stirring and still precipitate was obtained. A
minimum amount of ammonia (14 M) was added to give a color-
less solution. Suitable colorless crystals were obtained from the fil-
trate after standing at room temperature in a 45% yield based on
ZnCO3. Elemental Anal. Calc. for C14H20ZnN4O5: C, 43.15; H, 5.26;
N, 14.37. Found: C, 43.27; H, 5.31; N, 14.48%. IR (KBr, cmꢁ1):
3741 (s), 3108 (w), 2933 (w), 1652 (vs), 1611 (s), 1454 (s), 1364
(m), 1313 (m), 1229 (w), 828 (s), 790 (s), 492 (m).
in a 66% yield based on ZnCO3. Elemental Anal. Calc. for
C19H20ZnN4O4: C, 52.61; H, 4.65; N, 12.92. Found: C, 52.77; H,
4.61; N, 12.81%. IR (KBr, cmꢁ1): 3421 (m), 3111 (m), 2938 (w),
1617 (vs), 1565 (vs), 1516 (s), 1457 (s), 1365 (vs), 1246 (m),
1147 (m), 953 (m), 833 (m), 756 (m), 659 (m), 478 (w).
2.1.8. Synthesis of [CdL3(biim-5) ꢀ 1.5H2O] ꢀ 0.5H2O (8)
A mixture of Cd(OH)2 (0.146 g, 1 mmol), phthalic anhydride
(0.148 g, 1 mmol) in water (8 mL), and biim-5 (0.408 g, 2 mmol)
in ethanol (1 mL) was sealed in a Teflon-lined stainless steel auto-
clave and heated at 170 °C for 4 days, and then it was cooled to
room temperature at 10 °C hꢁ1. Colorless crystals were obtained
in a 56% yield based on Cd(OH)2. Elemental Anal. Calc. for
C19H24CdN4O6: C, 44.16; H, 4.68; N, 10.84. Found: C, 44.27; H,
4.60; N, 10.95%. IR (KBr, cmꢁ1): 3742 (w), 3118 (w), 2933 (w),
2862 (w), 1646 (m), 1560 (vs), 1516 (s), 1481 (m), 1397 (vs),
1235 (m), 1112 (m), 937 (m), 841 (m), 751 (s), 652 (vs), 438 (s).
2.1.3. Synthesis of [MnL1(biim-6)] ꢀ H2O (3)
A mixture of MnCO3 (0.115 g, 1 mmol), oxalic acid dihydrate
(0.126 g, 1 mmol) in water (8 mL), and biim-6 (0.436 g, 2 mmol)
in ethanol (1 mL) was sealed in a Teflon-lined stainless steel auto-
clave and heated at 140 °C for 4 days, and then it was cooled to
room temperature at 10 °C hꢁ1. Colorless crystals were obtained
in
a
56% yield based on MnCO3. Elemental Anal. Calc. for
2.1.9. Synthesis of [CdL4(biim-6) ꢀ 2H2O] (9)
C14H20MnN4O5: C, 44.33; H, 5.32; N, 14.77. Found: C, 44.44; H,
5.39; N, 14.70%. IR (KBr, cmꢁ1): 3550 (w), 3413 (m), 3112 (m),
2932 (w), 2858 (w), 1668 (vs), 1615 (vs), 1516 (vs), 1362 (s),
1230 (m), 1227 (m), 1110 (s), 827 (m), 734 (w), 662 (s), 627 (m),
489 (m).
A mixture of Cd(OH)2 (0.146 g, 1 mmol), p-phthalic acid
(0.166 g, 1 mmol) in water (8 mL), and biim-6 (0.436 g, 2 mmol)
in ethanol (1 mL) was sealed in a Teflon-lined stainless steel auto-
clave and heated at 180 °C for 4 days, and then it was cooled to
room temperature at 10 °C hꢁ1. Colorless crystals were obtained

W.-L. Zhang et al. / Polyhedron 27 (2008) 3351–3358
3353
in a 67% yield based on Cd(OH)2. Elemental Anal. Calc. for
C20H26CdN4O6: C, 45.25; H, 4.94; N, 10.55. Found: C, 45.17; H,
4.86; N, 10.42%. IR (KBr, cmꢁ1): 3743 (w), 3414 (vs), 2935 (w),
2862 (w), 1643 (s), 1616 (s), 1560 (vs), 1515 (s), 1465 (s), 1383
(vs), 1235 (w), 1116 (m), 745 (m), 651 (m), 452 (m).
2.2. X-ray crystallography
Single-crystal X-ray diffraction data for compounds 1, 2 and 4
were recorded on a Bruker Apex CCD diffractometer with graph-
ite-monochromated Mo Ka radiation (k = 0.71073 Å) at 293 K.
Crystallographic data for compounds 3 and 5–9 were collected
on a Rigaku RAXIS-RAPID single-crystal diffractometer with Mo
Ka radiation (k = 0.71073 Å) at 293 K. Absorption corrections were
applied using multi-scan technique. All the structures were solved
by Direct Method of SHELXS-97 [25] and refined by full-matrix least-
squares techniques using the SHELXL-97 program [26] within WINGX
[27]. Non-hydrogen atoms were refined with anisotropic tempera-
ture parameters. The hydrogen atoms attached to carbons were
generated geometrically; the aqua hydrogen atoms were located
from difference Fourier maps and refined with isotropic displace-
ment parameters. Analytical expressions of neutral-atom scatter-
ing factors were employed, and anomalous dispersion corrections
were incorporated [28]. The disordered C atoms in compounds 4
and 5 and disordered O atoms in compound 8 were refined using
C or O atoms split over two sites, with a total occupancy of 1.
The water H atoms in compounds 1–3 and 8 could not be posi-
tioned reliably and were omitted from the final model. The bond
distance restraints were used in the refinement for the water mol-
ecules in compound 5.
Detailed crystallographic data and structure refinement param-
eters for 1–9 are summarized in Table 1. Selected bond distances
and angles for compounds 1–9 are listed in Table S1 (see the
Supplementary data).
Fig. 1. (a) Coordination environment of the copper cation in 1. (b) View of a single
layer of 1.
O 2.006(1)–2.321(1) Å) and two N atoms from biim-6 ligands (Cu–
N 2.011(2) Å). Due to the Jahn–Teller effect, the Cu–O distance of
axial site is much longer than those in the equatorial plane. Each
oxalate anion coordinates to two Cu atoms to form a 1D chain with
a CuꢀꢀꢀCu distance of 5.58 Å. The neutral ligand biim-6 connects
two Cu atoms and a 2D network is obtained (Fig. 1b).
3. Results and discussion
3.1. Descriptions of crystal structures
3.1.1. Structure of [CuL1(biim-6)] ꢀ H2O (1)
Compounds 1–3 are isostructural and crystallize in the mono-
clinic C2/c space groups; therefore the structure descriptions of
compounds 2 and 3 will be neglected.
3.1.2. Structure of [MnL1(biim-4)] (4)
As illustrated in Fig. 2a, each central Mn(II) atom in 4 is coordi-
nated by four O atoms (Mn–O 2.199(3)–2.211(3) Å) of two oxalate
anions and two N atoms (Mn–N 2.198(4)–2.231(4) Å) from biim-4
As shown in Fig. 1a, each Cu(II) atom lies on an inversion center
and six-coordinated by four O atoms from two oxalate anions (Cu–
Table 1
Crystal data and structure refinements for compounds 1–9
1
2
3
4
5
6
7
8
9
Formula
Molecular
weight
C14H20CuN4O5 C14H20N4O5Zn C14H20MnN4O5 C12H14MnN4O4 C41H80Co2N12O22 C20H22ZnN4O4 C19H20ZnN4O4 C19H24CdN4O6 C20H26CdN4O6
387.88
389.71
379.28
333.21
1211.03
447.79
433.76
516.82
530.85
Crystal system monoclinic
monoclinic
C2/c
12.758(7)
13.876(8)
9.437(7)
90.
99.557(2)
90
1648(2)
4
monoclinic
C2/c
12.640(3)
14.330(3)
9.680(2)
90
98.400(9)
90
1734.5(7)
4
triclinic
P1
triclinic
P1
triclinic
P1
orthorhombic monoclinic
triclinic
P1
ꢀ
ꢀ
ꢀ
ꢀ
Space group
a (Å)
b (Å)
C2/c
Pbca
C2/c
12.721(9)
13.578(8)
9.624(9)
90
8.056(2)
9.889(3)
9.989(2)
103.585(4)
97.253(6)
107.040(4)
723.1(3)
2
9.021(3)
13.004(5)
25.752(7)
82.51(1)
86.76(1)
71.12(1)
2834(2)
2
9.677(4)
9.968(5)
11.716(6)
78.69(2)
74.02(3)
68.61(4)
1005.8(9)
2
10.340(2)
13.539(3)
27.813(7)
90
16.591(7)
16.472(4)
14.641(6)
90
5.669(2)
8.868(6)
10.497(8)
76.781(3)
86.480(4)
84.391(3)
510.9(6)
1
c (Å)
a
(°)
b (°)
99.761(1)
90
1638(2)
4
90
90
92.564(2)
90
c
(°)
V (Å3)
3894(1)
8
3997(3)
8
Z
Goodness-of-
fit
1.127
1.036
1.176
1.031
1.061
1.050
1.046
1.006
1.085
R1[I > 2
wR2 [all data]
r
(I)]
0.0309
0.0895
0.0450
0.1323
0.1016
0.1994
0.0630
0.1709
0.0461
0.1276
0.0330
0.0764
0.0345
0.0811
0.0568
0.1291
0.0399
0.0780
P
P
P
P
R1
=
||Fo| ꢁ |Fc||/ |Fo|, wR2 = | w(|Fo|2 ꢁ |Fc|2)|/ |w(Fo2)2|1/2
.

3354
W.-L. Zhang et al. / Polyhedron 27 (2008) 3351–3358
Fig. 2. (a) Coordination environment of the manganese cation in 4. (b) Single
adamantanoid cage. (c) Three interpenetrating diamondoid cages.
ligands to furnish a disordered octahedron geometry. Two crystal-
lographically biim-4 ligands adopt ‘‘S” shaped and ‘‘zigzag” shaped
conformations, respectively. The topology of the whole structure
can be described as a typically diamondoid framework (Fig. 2b).
As can be seen, the diamondoid cage are elongated significantly
in one direction, and exhibit maximum dimensions (corresponding
to the longest intracage MnꢀꢀꢀMn distances) of 21.37 Å ꢂ
20.18 Å ꢂ 18.90 Å. Because of the spacious nature of the single
network, it allows two identical diamondoid networks to interpen-
etrate it in a normal mode giving rise to a threefold interpenetrat-
ing structure (Fig. 2c). According to topology classification,
compound 4 belongs to Class Ia (all the independent nets are re-
lated by a single vector and the whole interpenetrating arrays
are generated by translating a single net 2 times) [29], with the
translating vector of [100] (8.06 Å).
Fig. 3. (a) Coordination environment of the cobalt cations in 5. (b) View of single
chain composed of Co1 and biim-5 ligands. (c) View of double-stranded chain
composed of Co2, Co3 and biim-5 ligands. (d) The hydrogen-bonded layer of L2 and
water molecules.
chain (Fig. 3c). These two kinds of chains are connected by hydro-
gen bonds to construct a 3D supramolecular structure (Fig. S1a). As
shown in Fig. 3d, the hydrogen bonds lead the water molecules and
L2 anions to a 2D supramolecular network. In addition, a notable
feature of 6 is the presence of two types of water clusters, namely
(H2O)12 and (H2O)8. Within the (H2O)12 cluster, four water mole-
cules (O8W, O8W#13, O13W#5 and O13W#12, symmetry code:
#5
ꢁx + 1, ꢁy + 1, ꢁz; #121 + x, y, z; #132 ꢁ x, 1 ꢁ y, ꢁz) act as hydro-
gen bonds donors and others act as both donors and acceptors (Fig.
3.1.3. Structure of [Co2(L2)2(biim-5)3 ꢀ 6H2O] ꢀ 8H2O (5)
S1b). In this water cluster, O1W#2, O2W, O6W#5, O13W#5 and
#2
As shown in Fig. 3a, there are three kinds of crystallographically
unique Co centers in the structure of 5. Co1 is coordinated by two N
atoms (Co–N 2.111(2)–2.112(2) Å) from two neutral ligands and
four water molecules (Co–O 2.095(2)–2.153(2) Å), showing a
slightly disordered octahedral geometry. Co2 lies at an inversion
center and is six-coordinated by four N atoms (Co–N 2.128(2)–
2.137(2) Å) from biim-5 ligands and two water molecules (Co–O
2.154(2) Å). Co3 has the same coordination environment to that
of Co2. The fumariate anions act as counterions. There exist two
kinds of chains. For Co1, each biim-5 ligand connects two Co1
atoms to a 1D polymeric chain (Fig. 3b). For Co2 and Co3, the Co(II)
atoms are joined by biim-5 ligands to form a double-stranded
O1W#3
,
O2W#13
,
O6W#12
,
O13W#12 (symmetry code:
ꢁx,
ꢁy + 2, ꢁz; #31 + x, ꢁ1 + y, z) form two types 4-membered (H2O)4
rings, respectively and these rings are connected by O7W#2 and
O7W#3 to form a much lager (H2O)10 ring. The (H2O)10 ring are
joined by O8W and O8W#13 to form a (H2O)12 cluster. Moreover,
the oxygen atoms O2, O3, O19 and O9 from L2 anions are involved
in hydrogen bonds with water molecules, which helped to stabilize
the (H2O)12 cluster. In (H2O)12 cluster, the average hydrogen bond
is 2.78 Å, while these distances in regular ice, liquid water, and
water vapor are 2.74, 2.85, and 2.98 Å, respectively [30]. In
(H2O)8 cluster, four crystallographically unique lattice water mole-
cules (O3W#8, O4W and O5W#9 act as both hydrogen-bond donors

W.-L. Zhang et al. / Polyhedron 27 (2008) 3351–3358
3355
Fig. 4. (a) Coordination environment of the zinc cation in 6. (b) View of a single
layer.
and acceptors, while O14W#4 only acts as a hydrogen-bond donor)
and their symmetry-related molecules link to each other to form a
(H2O)8 cluster through hydrogen bonds (Fig. S1c). Furthermore, the
oxygen atoms O1, O6#14, O21 and O22#8 from L2 anions (symmetry
code: #142 ꢁ x, 1 ꢁ y, 1 ꢁ z) are involved in hydrogen bonds with
water molecules to stabilize the (H2O)8 cluster.
3.1.4. Structure of [ZnL3(biim-6)] (6)
In compound 6, L3 was introduced to replace L1 ligand of com-
pound 2. As illustrated in Fig. 4a, each Zn(II) atom is four-coordi-
nated by two O atoms (Zn–O 1.951(2)–1.957(2) Å) from two L3
anions and two N atoms (Zn–N 2.003(2)–2.035(2) Å) from biim-6
ligands to furnish a distorted tetrahedron geometry. The phthalate
anions adopt bis(monodentate) coordination mode to connect two
central Zn(II) atoms. Every two L3 anions coordinate with the same
two Zn(II) atoms and form a dimer. Biim-6 ligands display two
kinds of conformations, which link the dimers to a 2D layer net-
work (Fig. 4b).
3.1.5. Structure of [ZnL3(biim-5)] (7)
As shown in Fig. 5a, every Zn(II) atom in 7 is four-coordinated
by two O atoms from two L3 anions and two N atoms from two
biim-5 ligands. The L3 anion adopts bis(monodentate) coordina-
tion mode and connects two Zn(II) atoms. As bridged ligand, each
biim-5 connects two Zn(II) atoms to form a dimer (Fig. 5b). These
dimers are connected by L3 anions to a 2D network with (6,3)
topology (Fig. 5c).
Fig. 5. (a) Coordination environment of the zinc cation in 7. (b) View of the large
ring of (6, 3) network. (c) View of a layer of (6, 3) topology.
ions, two N atoms from two biim-6 ligands and two water
molecules. Each L4 adopts bis(monodentate) coordination mode
and connects with two Cd(II) atoms to a 1D chain. These chains
are joined by biim-6 ligands to propagate a 2D layer network
(Fig. 7b). In addition, hydrogen bonds between L4 and water mol-
ecules exist in 9. These hydrogen bonds link L4 anions and water
molecules resulting a 1D infinite chain. These chains stabilize the
structure and connect the adjacent layers to form a 3D supramo-
lecular structure (Fig. 7c).
3.1.6. Structure of [CdL3(biim-5) ꢀ 1.5H2O] ꢀ 0.5H2O (8)
In compound 8, cadmium ion was introduced to replace zinc ion
in compound 7. As illustrated in Fig. 6a, each Cd(II) atom is eight-
coordinated by four O atoms (Cd–O 2.359(5)–2.626(7) Å) [31,32]
from two L3 anions, two N atoms (Cd–N 2.264(5)–2.278(5) Å) from
two biim-5 ligands and two water molecules (Cd–O 2.487(6)–
2.56(2) Å). Two L3 anions connect to the same two Cd(II) atoms
in the chelating modes to form a dimer (Fig. 6b). These dimers
are joined by biim-5 ligands to a 2D layer network (Fig. 6b).
3.2. Discussion
3.2.1. Effect of carboxylate anions
3.1.7. Structure of [CdL4(biim-6) ꢀ 2H2O] (9)
As expected, carboxylate anion plays an important role in deter-
mining the final structures. All of the L1 anions in 1-4 adopt
bis(chelating) coordination modes, and M(II) centers are bridged
As illustrated in Fig. 7a, each Cd(II) atom in 9 lies on an inver-
sion center and is six-coordinated by two O atoms from two L4 an-

3356
W.-L. Zhang et al. / Polyhedron 27 (2008) 3351–3358
bis(monodentate) coordination modes; and L3 anion in 8 adopts
bis(chelating) coordination mode. The M(II) centers in 6 and 8
are linked by L3 anions to dimers, respectively, and the M(II) cen-
ters in 7 are linked by L3 anions to a chain. L4 anion in 9 adopts
bis(monodentate) mode, and the L4 anions link M(II) center to
form a chain.
3.2.2. Effect of bis(imidazole) ligands
In the structures of biim-6, biim-5 and biim-4, the imidazole
groups are bridged by different spacers: 1,6-hexyl, 1,5-pentyl and
1,4-butyl. By comparing of the structures of compounds 1–9, it
was found that the flexibilities of the bis(imidazole) methylene
groups have a great influence to the frameworks, because adjust-
ments in the framework occur to accommodate the bend of the
molecules. In compounds 1–3, 6 and 9, the neutral ligands are
biim-6. The methylene groups of 1–3 display ‘‘S” conformations,
with the distance between neighboring M(II) centers linked by
biim-6 ligands being 11.77–12.34 Å. The methylene groups of 6
and 9 display zigzag conformations, with the distance between
neighboring M(II) centers linked by biim-6 ligands being 14.19–
16.49 Å. In compounds 5, 7 and 8, the neutral ligands are biim-5,
and the methylene groups display ‘‘S” and ‘‘3” formed conforma-
tions, the distance between neighboring M(II) centers linked by
biim-5 ligands are 8.39–15.12 Å. In compounds 4, the neutral li-
gand is biim-4, and the methylene groups display ‘‘S” and zigzag
conformations, with the distance between neighboring Mn(II) cen-
ters linked by the biim-4 ligands being 13.74 and 14.06 Å.
Comparing compounds 6 with 7, it can be seen that the neutral
ligands biim-6 of 6 display two kinds of conformations. The
[Zn(L3)2Zn] dimers are linked by biim-6 to a 2D network (Fig.
4b). In 7, biim-5 adopt only one kind of conformation to connect
the central Zn(II) atoms to [Zn(biim-5)2Zn] dimers (Fig. 5b). By
comparing 3 with 4, the changes are more noticeable. Compound
3 has a 2D layer network, while compound 4 displays a 3D network
with diamondoid topology.
Fig. 6. (a) Coordination environment of the cadmium cation in 8. (b) View of a
single layer of compound 8.
3.3. Thermal analysis
In order to characterize the compounds more fully in terms of
thermal stability, some of their thermal behaviors were studied
by TGA (Fig. S2). The experiments were performed on samples con-
sisting of numerous single crystals of 3, 5 and 8–9 under N2 atmo-
sphere with a heating rate of 10 °C/min.
For compound 3, the weight loss corresponding to the release of
water molecules are observed from room temperature to 135 °C
(obsd 3.9%, calcd 4.75%). The anhydrous compound begins to
decompose at 253 °C. For compound 5, the weight loss correspond-
ing to the release of water molecules are observed from room tem-
perature to 105 °C (obsd 19.1%, calcd 20.83%). The anhydrous
compound begins to decompose at 253 °C. For compound 8, the
weight loss corresponding to the release of water molecules are
observed from room temperature to 175 °C (obsd 4.7%, calcd
3.57%). The anhydrous compound begins to decompose at 240 °C.
For compound 9, the weight loss corresponding to the release of
water molecules are observed from 120 to 236 °C (a weight loss
of 5.1% is smaller than the calculated value 6.78% probably result-
ing from a slow losing of the guest molecules in the air at room
temperature). The anhydrous compound begins to decompose at
305 °C.
Fig. 7. (a) Coordination environment of the cadmium cation in 9. (b) View of a
single layer. (c) View of the 3D supramolecular structure formed by hydrogen
bonds.
3.4. Luminescent properties
by L1 anions to form 1D chain skeletons. L2 anions in 5 act as coun-
terions. Although the L2 anions in 5 are not coordinated with Co(II)
ions, they joined by hydrogen bonds with water molecules, which
also modulate the whole structure of 5. L3 anions in 6 and 7 adopt
The luminescence spectra of neutral ligands biim-5 and biim-6
were examined in an ethanol solution, because the solid samples
cannot be isolated at room temperature (Table 2, Fig. S3). The solid
state luminescence spectra of free carboxylate ligands, compounds

W.-L. Zhang et al. / Polyhedron 27 (2008) 3351–3358
3357
Table 2
The wavelengths of the emission maximums and excitation (nm)
a
700
600
500
400
300
200
100
0
0.60
0.56
0.52
0.48
0.44
(1)
Compound
2
6
7
8
9
kem
kex
403
348
427
315
406
346
441
366
429
352
Ligand
Biim-5
Biim-6
Phthalic anhydride
H2L4
kem
kex
400
342
363, 379
343
389
352
390
347
χ
χ
2 and 6–9 were examined at room temperature (Table 2, Figs. S4
and S5).
Biim-5 shows an emission at 400 nm; and biim-6 shows a max-
imum at 379 nm and a shoulder at 363 nm. The peaks of the li-
0
50
100
150
200
250
300
gands biim-5 and biim-6 are probably due to p*
? p transitions
Temperature (K)
[33].
The emissions of free ligands of phthalic anhydride (389,
kex = 352 nm) and H2L4 (390 nm, kex = 347 nm) [34] can also exhi-
bit fluorescence at room temperature. The emission bands of the
b
6
4
2
60
50
40
30
20
10
(3)
dicarboxylate ligands can be assigned to the
p
* ? n transitions
[35]. The Zn(II) compounds (2, 6 and 7) exhibit emissions at about
403 nm for 2, at 427 nm for 6, and at 406 nm for 7. The emission
peaks for these compounds may be attributed to the ligand-to-me-
tal charge-transfer (LMCT) transitions [36,37]. The luminescent
spectra of Cd(II) compounds 8 (441 nm) and 9 (429 nm) may also
be assigned as LMCT [37].
χ
χ
3.5. Magnetic properties
0
The temperature-dependent magnetic susceptibility data of
compounds 1, 3 and 4 have been measured from polycrystalline
samples at an applied magnetic field of 1000 Oe in the temperature
range of 2–300 K (Fig. 8). Although compounds 1 and 3 are two-
dimensional, and 4 is three-dimensional, from a magnetic point
of view, the systems can be considered as one-dimensional owing
to the long MꢀꢀꢀM distances (11.77 Å for 1, 12.34 Å for 3 and 12.46 Å
for 4) along the bis(imidazole) ligands, for which we can assume a
negligible magnetic exchange through the biim-6 and biim-4 li-
gands [38].
0
50
100
150
200
250
300
Temperature (K)
6
4
2
c
60
50
40
30
20
10
(4)
For 1, the
which is as expected (1.732
netically isolated spin doublet. Upon cooling,
crease, reaching
value of 0.551 cm3 molꢁ1
v
mT value at 300 K is 0.451 cm3 molꢁ1 K (1.900
B, considering g = 2.00) for a mag-
mT gradually in-
at 2 K. This
lB),
l
v
a
K
χ
χ
feature is indicative of the occurrence of an overall weak ferro-
magnetic coupling between the Cu(II) ions [39–43]. The magnetic
susceptibility in the range of 300–100 K obeys the Curie–Weiss
law with the Curie constant, C = 0.451 cm3 molꢁ1 K, and the Weiss
0
0
50
100
150
200
250
300
constant,
For 3, the
which is slightly higher than the spin-only value (5.916
ering g = 2.00) expected for a high-spin d5 Mn(II) ion. Upon cooling,
the values of mT keep smoothly decreasing in 300–34 K range,
H
= 0.329 K.
mT value at 300 K is 5.077 cm3 molꢁ1 K (6.372
B, consid-
Temperature (K)
v
lB),
l
Fig. 8. Plots of the temperature dependence of
compounds 1, 3 and 4.
v
mT (squares) and vꢁm1 (triangles) for
v
and then exhibit a maximum value of 2.899 cm3 molꢁ1 K at 32 K
before goes down quickly to a minimum value of 0.186 cm3 mol
ꢁ1 K at 2 K. This behavior is indicative of antiferromagnetic cou-
pling between the Mn(II) centers through the oxalate-bridging li-
gands. The inflexion at 32 K may be due to a small canting of the
sub-lattice or a small amount of impurity [34]. The magnetic sus-
ceptibility above 34 K can be well fit to Curie–Weiss law with
0.183 cm3 molꢁ1 K at 2 K, indicating an overall antiferromagnetic
coupling in compound 4. There also exists an inflexion at 32 K
[44]. The magnetic susceptibility above 34 K can be well fit to Cur-
ie–Weiss law with C = 5.38 cm3 molꢁ1 K,
H = –35.06 K.
Acknowledgments
C = 5.66 cm3 molꢁ1 K,
H = –35.62 K. The negative H value further
We thank the Program for New Century Excellent Talents in
Chinese University (NCET-05-0320), Program for Changjiang Schol-
ars and Innovative Research Teams in Chinese University and the
Analysis and Testing Foundation of Northeast Normal University
for support.
confirms the presence of antiferromagnetic interaction in 3.
The magnetic behavior of compounds 3 and 4 is quite similar.
For 4, the
cooling, the values of
range, and then go down quickly to
v
mT value at 300 K is 4.841 cm3 molꢁ1 K (6.223
l
B). Upon
mT keep smoothly decreasing in 300–34 K
minimum value of
v
a

3358
W.-L. Zhang et al. / Polyhedron 27 (2008) 3351–3358
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Appendix A. Supplementary data
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graphic data for 1–9. These data can be obtained free of charge
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