Synthesis and characterization of four coordination polymers constructed with d10 metals and mixed flexible ligands under solvothermal conditions

Article abstract of DOI:10.1016/j.ica.2012.04.044

Solvothermal reactions of flexible 1,2-phenylenedioxydiacetic acid (H ₂PDA) or hydroquinone-O,O′-diacetic acid (H₂QDA) with zinc nitrate or cadmium nitrate in the presence of auxiliary 1,1′-(1,4-butanediyl)bis(imidazole) (BBI) ligand gave rise to four coordination polymers, namely, {[Zn(PDA)(BBI)]·3H₂O} _n (1), {[Zn(PDA)(BBI)]·DMF}_n (2), {[Cd ₂(QDA)(BBI)]·4H₂O}_n (3), [Cd(QDA)(BBI)]_n (4). All the compounds were characterized by elemental analysis, IR and single-crystal X-ray diffraction methods. Compound 1 exhibits a puckered (2D) (4, 4) grid net with a Schlafli symbol of 4⁴ 6². Compound 2 has the dinuclear Zn₂(PDA)₂ loops which are further connected by BBI ligands into 2D sheet along (0 1 -1) plane with a Schlafli symbol of 2.6⁵. Interestingly, the Zn₂(PDA)₂ loops are penetrated by BBI ligands of the other equivalent net. Thus an unusual 2D polyrotaxane-like structure is formed containing rotaxane-like motifs. Compound 3 possesses a three-dimensional (3D) diamond-type network with a Schlafli symbol of 6⁶. Compound 4 has the dinuclear cadmium core as the node and shows a 3D threefold interpenetrating 8-connected uninodal network with a Schlafli symbol of 3 ⁶4¹⁸5³6. The structural differences of these complexes give some insights into the effect of solvent on the construction of coordination polymers with the same components under solvothermal conditions. In addition, the fluorescent properties of 1-4 were also investigated.

Full text of DOI:10.1016/j.ica.2012.04.044

Inorganica Chimica Acta 391 (2012) 58–65
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis and characterization of four coordination polymers constructed
with d10 metals and mixed flexible ligands under solvothermal conditions
⇑
Bao-Yong Zhu , Xiu-Ling Zhang, Feng Guo, Xin-Hua Liu
Department of Chemistry, Dezhou University, Dezhou 253023, PR China
a r t i c l e i n f o
a b s t r a c t
Solvothermal reactions of flexible 1,2-phenylenedioxydiacetic acid (H2PDA) or hydroquinone-O,O0-diacetic
acid (H2QDA) with zinc nitrate or cadmium nitrate in the presence of auxiliary 1,10-(1,4-but-
anediyl)bis(imidazole) (BBI) ligand gave rise to four coordination polymers, namely, {[Zn(PDA)(B-
BI)]ꢀ3H2O}n (1), {[Zn(PDA)(BBI)]ꢀDMF}n (2), {[Cd2(QDA)(BBI)]ꢀ4H2O}n (3), [Cd(QDA)(BBI)]n (4). All the
compounds were characterized by elemental analysis, IR and single-crystal X-ray diffraction methods.
Compound 1 exhibits a puckered (2D) (4, 4) grid net with a Schlafli symbol of 44 62. Compound 2 has the
dinuclear Zn2(PDA)2 ‘‘loops’’ which are further connected by BBI ligands into 2D sheet along (01ꢁ1) plane
with a Schlafli symbol of 2.65. Interestingly, the Zn2(PDA)2 ‘‘loops’’ are penetrated by BBI ligands of the other
equivalent net. Thus an unusual 2D polyrotaxane-like structure is formed containing rotaxane-like motifs.
Compound 3 possesses a three-dimensional (3D) diamond-type network with a Schlafli symbol of 66. Com-
pound 4 has the dinuclear cadmium core as the node and shows a 3D threefold interpenetrating 8-con-
nected uninodal network with a Schlafli symbol of 36418536. The structural differences of these
complexes give some insights into the effect of solvent on the construction of coordination polymers with
the same components under solvothermal conditions. In addition, the fluorescent properties of 1–4 were
also investigated.
Article history:
Received 25 January 2011
Received in revised form 20 April 2012
Accepted 24 April 2012
Available online 4 May 2012
Keywords:
Metal organic coordination polymers
Topology
Fluorescent property
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
ible ligands in the hope of getting novel metal–organic coordination
polymers.
Investigation on novel coordination polymers constructed with
transition metals and organic ligands has attracted much attention
due to their intriguing architectures and potential applications as
functionalmaterials [1–12]. During the past decades, a large number
of coordination polymers have been successively designed and syn-
thesized through rational combination of the organic ligands and
metal ions. In particularly, many researchers paid much attention
on the exploitation of rigid pyridine- or imidazole-based and multi-
carboxylates ligands such as 1,3-benzenedicarboxylate, 1,3,5-ben-
zenetricarboxylate and 4,40-biphenyldicarboxylate [13–17].
Compared with the rigid ligands with single conformation, flexible
ligands may adopt several kinds of conformations when coordinate
to metal ions, which make it more difficult to predict and control the
final coordination networks. So the use of flexible ligands in the for-
mation of coordination polymers may generate novel complexes
with interesting topologies and attractive properties [18–21]. In this
respect, Our research are mainly focused on the exploitation of flex-
In this paper, 1,2-phenylenedioxydiacetic acid (H2PDA), hydro-
quinone-O,O0-diacetic acid (H2QDA) and 1,10-(1,4-butanediyl)
bis(imidazole) (BBI) were selected as the mixed ligands based on
the following considerations: (1) both H2PDA and H2QDA possess
flexibilityowingtothepresenceof–O–CH2–groupbetweenthephe-
nyl ring and carboxyl moiety, the flexible and multifunctional coor-
dination sites provide a high likelihood for generation of structures
with high dimensions; (2) the flexible nature of –CH2– spacers in
BBI ligand allows the ligand to bend and rotate freely when coordi-
nating to metal centers so as to conform to the coordination geome-
tries of metal ions. The solvothermal reactions of these mixed
flexible ligands with d10 metals (Zn and Cd) in different solvents,
such as water or N,N-dimethyl formamide (DMF), gave rise to four
coordination polymers, {[Zn(PDA)(BBI)]ꢀ3H2O}n (1), which forms a
puckered 2D layer, {[Zn(PDA)(BBI)]ꢀDMF}n (2), which forms an
intriguing 2D ? 2D self-catenated net, {[Cd(QDA)(BBI)]ꢀ3H2O}n (3),
which forms an uninterpenetrated diamond-like 3D net,
[Cd(QDA)(BBI)]n (4), which forms a threefold interpenetrated 3D
net. The different outcomescould be definitely ascribed to the differ-
ent solvent system. We herein report on their reactions, crystal
structures and photoluminescent properties.
⇑
Corresponding author. Tel./fax: +86 534 8985835.
E-mail address: zhubaoyong@yahoo.cn (B.-Y. Zhu).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.04.044

B.-Y. Zhu et al. / Inorganica Chimica Acta 391 (2012) 58–65
59
Table 2
2. Experimental
Selected bond lengths (Å) and angles (°) for 1–4.
2.1. Materials and physical measurements
Compound 1
Zn(1)–N(2)
1.994(3)
2.069(3)
2.069(3)
107.11(12)
106.72(12)
130.65(14)
Zn(1)–N(3)
Zn(1)–O(6)
1.999(3)
1.970(2)
Zn(1)–O(1)#1
O(1)–Zn(1)#2
O(6)–Zn(1)–N(2)
N(2)–Zn(1)–N(3)
N(2)–Zn(1)–O(1)#1
The ligand BBI was synthesized as previous literature [22].
Other chemicals and reagents were obtained from commercial
sources and used as received. All Powder X-ray diffraction (PXRD)
analyses were recorded on a Rigaku Dmax2500 diffractometer
O(6)–Zn(1)–N(3)
O(6)–Zn(1)–O(1)#1
N(3)–Zn(1)–O(1)#1
116.49(12)
98.19(12)
98.28(13)
with Cu K
a radiation (k = 1.5406 Å) with a step size of 0.02°. The
Compound 2
Zn(1)–N(2)
Zn(1)–O(2)#3
O(2)–Zn(1)#3
O(5)–Zn(1)–O(2)#3
O(2)#3–Zn(1)–N(3)
O(2)#3–Zn(1)–N(2)
2.009(2)
1.976(2)
1.976(2)
106.56(9)
111.57(10)
108.42(9)
Zn(1)–N(3)
Zn(1)–O(5)
1.994(2)
1.966(2)
experimental PXRD patterns are in good agreement with the corre-
sponding simulated ones (Fig. A.10, Supplementary data). The ele-
mental analyses for C, H and N were performed on an Elementar
Vario Micro Cube analyzer. The IR spectra were recorded on a Ther-
mo Nicolet IR200 FT-IR spectrometer as KBr pellets (4000–
400 cmꢁ1). Thermal analysis was performed with a Shimadzu
DTG-60 thermogravimetric analyzer at a heating rate of 5 °C/min
and a flow rate of 100 cm3/min (N2). The fluorescent spectra were
obtained on a Hitachi F-4600 spectrofluorometer.
O(5)–Zn(1)–N(3)
O(5)–Zn(1)–N(2)
N(3)–Zn(1)–N(2)
113.84(10)
104.90(9)
111.16(10)
Compound 3
Cd(1)–N(1)
Cd(1)–O(2)
N(1)–Cd(1)–N(1)#4
N(1)#4–Cd(1)–O(2)
2.195(2)
2.2166(18) Cd(1)–O(2)#4
113.88(11)
105.75(7)
Cd(1)–N(1)#4
2.195(2)
2.2166(18)
121.38(7)
N(1)–Cd(1)–O(2)
N(1)–Cd(1)–O(2)#4 105.75(7)
N(1)#4–Cd(1)–O(2)#4 121.38(7)
O(2)–Cd(1)–O(2)#4
86.90(9)
2.2. Synthesis of complexes
Compound 4
Cd(1)–N(1)
Cd(1)–O(2)
2.364(5)
2.475(3)
Cd(1)–N(3)
Cd(1)–O(3)
2.233(4)
2.331(4)
2.2.1. Synthesis of {[Zn(PDA)(BBI)]ꢀ3H2O}n (1)
Cd(1)–O(5)
2.306(3)
Cd(1)–O(6)
2.622(4)
A mixture of H2PDA (0.023 g, 0.1 mmol), BBI (0.021 g, 0.1 mmol)
and Zn(NO3)2ꢀ6H2O (0.030 g, 0.1 mmol) in H2O (7.0 mL) was placed
in a 16 mL Teflon-lined stainless steel vessel and heated to 160 °C
for 72 h to give rise to colorless block crystals of 1, which were col-
lected by filtration. The colorless crystals obtained were washed
with water and dried in air. Yield: 0.038 g (70% based on Zn). Anal.
Calc. for C20H28N4O9Zn: C, 45.00; H, 5.29; N, 10.50. Found: C, 44.74;
H, 5.02; N, 10.36%. IR (KBr pellet, cmꢁ1): 3426 w, 3138 w, 2902 w,
1662 m, 1605 s, 1585 s, 1509 s, 1426 s, 1341 m, 1320 w, 1231 s,
1112 m, 1070 m, 944 w, 828 m, 807 m, 702 m, 657 w.
Cd(1)–O(5)#5
2.506(3)
O(5)–Cd(1)#5
N(3)–Cd(1)–O(3)
N(3)–Cd(1)–N(1)
O(3)–Cd(1)–N(1)
O(5)–Cd(1)–O(2)
N(1)–Cd(1)–O(2)
O(5)–Cd(1)–O(5)#5
2.506(3)
N(3)–Cd(1)–O(5)
O(5)–Cd(1)–O(3)
O(5)–Cd(1)–N(1)
N(3)–Cd(1)–O(2)
O(3)–Cd(1)–O(2)
N(3)–Cd(1)–O(5)#5
O(3)–Cd(1)–O(5)#5
O(2)–Cd(1)–O(5)#5
O(5)–Cd(1)–O(6)
N(1)–Cd(1)–O(6)
O(5)#5–Cd(1)–O(6)
103.45(14)
96.21(13)
127.27(16)
103.73(13)
54.34(12)
85.75(13)
92.36(13)
84.50(12)
51.73(11)
76.18(16)
119.46(11)
158.04(14)
87.91(16)
87.90(17)
140.07(13)
82.38(17)
68.97(12)
N(1)–Cd(1)–O(5)#5 163.65(16)
N(3)–Cd(1)–O(6)
O(3)–Cd(1)–O(6)
O(2)–Cd(1)–O(6)
95.98(15)
103.92(15)
150.22(14)
Symmetry codes: #1: x + 1, y, z; #2: x ꢁ 1, y, z; #3: ꢁx + 1, ꢁy, ꢁz + 1; #4: ꢁx, y,
ꢁz + 3/2; #5: ꢁx + 1, ꢁy, ꢁz + 1.
2.2.2. Synthesis of {[Zn(PDA)(BBI)]ꢀDMF}n (2)
Compound 2 was prepared in a manner similar to that de-
scribed for 1, using the same components in the same molar ratio
except that DMF was used as solvent instead of H2O. Colorless
Table 1
Summary of crystallographic data for 1–4.
Compounds
1
2
3
4
Chemical formula
Formula Mass
Crystal system
Space group
a (Å)
C
20H28N4O9Zn
C23H28N5O7Zn
551.87
C20H28N4O9Cd
580.86
monoclinic
C2/c
10.296(1)
15.522(1)
15.603(1)
90
96.021(1)
90
2479.8(3)
296(2)
4
C20H22N4O6Cd
526.82
533.83
monoclinic
P21/n
11.037(1)
16.559(1)
13.018(1)
90
95.524(5)
90
2368.1(3)
296(2)
4
triclinic
triclinic
ꢀ
ꢀ
P1
P1
9.367(1)
10.250(1)
13.849(2)
78.883(1)
86.361(2)
80.004(2)
1284.3(1)
296(2)
2
9.663(1)
9.762(1)
12.051(1)
100.725(1)
94.975(1)
106.713(1)
1057.8(2)
296(2)
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
T (K)
Z
2
Dcalc (g cmꢁ3
1.497
1.094
1.427
1.007
1.556
0.935
1.654
1.077
l
(mmꢁ1
)
F(000)
1112
574
1184
532
No. of reflections measured
No. of independent reflections
No. of parameters
11954
4167
307
7994
5671
325
6254
2179
155
5499
3692
280
Rint
0.0214
0.0431
0.0999
0.0539
0.1044
1.057
0.0137
0.0427
0.1273
0.0499
0.1331
1.077
0.0157
0.0233
0.0659
0.0240
0.0664
1.063
0.0133
0.0373
0.1064
0.0396
0.1080
1.009
a
Final R1 values (I > 2
r
(I))
(I))
Final R1 values (all data)
b
Final wR2 values (I > 2
r
Final wR2 values (all data)
Goodness of fit (GOF) on F2
Largest difference in peak and hole (e Åꢁ3
)
1.068 and ꢁ0.709
0.993 and ꢁ0.626
0.899 and ꢁ0.282
0.982 and ꢁ1.103
P
P
a
R ¼ ðjjF0j ꢁ FcjjÞ= jF0j.
P
P
2
2
2
2
1=2
b
wR2 ¼ ½ wðjF0j ꢁ jFcj Þ = wðjF0j Þꢂ
.

60
B.-Y. Zhu et al. / Inorganica Chimica Acta 391 (2012) 58–65
Fig. 1. (a) View of the coordination environment of Zn1 in 1. The solvent water molecules and hydrogen atoms are omitted for clarity. Symmetry codes: (A) 1 + x, y, z; (B)
2 ꢁ x, 1 ꢁ y, 2 ꢁ z; (C) 1 ꢁ x, 1 ꢁ y, 1 ꢁ z. (b) View of a section of the 1D chain extending along the a axis. (c) View of the 2D layer of 1 extending along the (010) plane. (d)
Schematic representation the (4, 4) net of 1.
Scheme 1. Coordination modes of PDA2ꢁ and QDA2ꢁ ligands in complexes 1–4.
block crystals of 2 were collected by filtration, washed with water
and dried in air. Yield: 0.036 g (66% based on Zn). Anal. Calc. for
and heated to 160 °C for 72 h to give rise to colorless block crystals
of 3, which were collected by filtration. The colorless crystals ob-
tained were washed with water and dried in air. Yield: 0.037 g
(63% based on Cd). Anal. Calc. for C20H28N4O9Cd: C, 41.36; H,
4.86; N, 9.65. Found: C, 41.17; H, 4.62; N, 9.36%. IR (KBr pellet,
cmꢁ1): 3431 w, 3121 w, 2936 w, 1605 s, 1506 s, 1416 s, 1329 w,
1293 w, 1237 m, 1202 s, 1093 m, 948 w, 829 m, 723 m, 658 m.
C
23H28N5O7Zn: C, 50.02; H, 5.11; N, 12.69. Found: C, 49.54; H,
5.06; N, 12.51%. IR (KBr pellet, cmꢁ1): 3422 w, 3123 w, 2936 w,
1637 s, 1524 w, 1504 s, 1409 s, 1310 w, 1290 w, 1252 s, 1207 m,
1129 s, 1106 m, 1046 m, 954 w, 839 w, 755 m, 656 m.
2.2.3. Synthesis of {[Cd2(QDA)(BBI)]ꢀ4H2O}n (3)
A
mixture of H2QDA (0.023 g, 0.1 mmol), BBI (0.021 g,
2.2.4. Synthesis of [Cd(QDA)(BBI)]n (4)
0.1 mmol) and Cd(NO3)2ꢀ4H2O (0.038 g, 0.1 mmol) in H2O
Compound 4 was prepared in a manner similar to that de-
scribed for 3, using the same components in the same molar ratio
(7.0 mL) was placed in a 16 mL Teflon-lined stainless steel vessel

B.-Y. Zhu et al. / Inorganica Chimica Acta 391 (2012) 58–65
61
Fig. 2. (a) View of the coordination environment of Zn1 in 2. The solvent DMF molecules and hydrogen atoms are omitted for clarity. Symmetry codes: (A) ꢁ1 ꢁ x, ꢁy, 1 ꢁ z;
(B) ꢁx, 1 ꢁ y, 2 ꢁ z; (C) 1 ꢁ x, ꢁy, 1 ꢁ z. (b) View of a dinuclear [Zn2(PDA)2] unit in 2. (c) View of one 2D layer extending along (01ꢁ1) plane. (d) The 4-connected (2.65)
topology of 2. (e) The two fold interpenetrating layer of 2. (f) The 3D packing of 2 viewed along the approximate a axis.
except that DMF was used as solvent instead of H2O. Colorless
block crystals of 4 were collected by filtration, washed with water
and dried in air. Yield: 0.048 g (75% based on Cd). Anal. Calc. for
intensity corrections for the Lorentz and Polarization effects. Semi-
empirical absorption correction was applied using the SADABS pro-
gram [24]. The crystal structures of 1–4 were solved by direct
method using SIR97 program [25] and refined anisotropically for
all non-hydrogen atoms by full-matrix least squares on all F2 data
using SHELXL97 [26], The single suite WINGX was used as an integrated
system for all the crystallographic programs [27]. The hydrogen
atoms of the water solvent molecules in 1 and 3 were located from
the Fourier map with the O–H distances being fixed at 0.85 Å and al-
lowed to ride on their parent oxygen atoms before the final cycle
refinement, the Uiso(H) = 1.2 Ueq(O). All other hydrogen atoms were
added according to theoretical models, assigned isotropic displace-
ment parameters and allowed to ride on their respective parent
atoms, the Uiso(H) = 1.2 Ueq(C) or 1.5Ueq(C). Crystal data and a struc-
ture determination summary for 1–4 are listed in Table 1. The se-
lected bond lengths and angles for 1–4 are listed in Table 2. The
hydrogen bonds are listed in Table A1 (Supplementary data).
C
20H22N4O6Cd: C, 45.60; H, 4.21; N, 10.64. Found: C, 45.23; H,
4.16; N, 10.28%. IR (KBr pellet, cmꢁ1): 3426 w, 3138 w, 2902 w,
1662 s, 1585 s, 1509 s, 1426 s, 1341 m, 1283 w, 1112 m, 1070 s,
944 m, 828 m, 807 m, 767 w, 702 m, 657 m.
2.3. Crystal structure determination
Single crystals of 1–4 suitable for X-ray analysis were selected di-
rectly from the above preparations. These crystals were mounted on
glass fibers and then the crystallographic data collections were car-
ried out on a Bruker Smart ApexII CCD area-detector diffractometer
with graphite-monochromated Mo K
23 °C using - and -scan technique. The diffraction data was inte-
grated by using the SAINT program [23], which was also used for the
a radiation (k = 0.71073 Å) at
x
u

62
B.-Y. Zhu et al. / Inorganica Chimica Acta 391 (2012) 58–65
Fig. 3. (a) View of the coordination environment of Cd1 in 3. The solvent water molecules and hydrogen atoms are omitted for clarity. Symmetry codes: (A) 1 ꢁ x, 2 ꢁ y, 2 ꢁ z;
(B) ꢁ0.5 ꢁ x, 1.5 ꢁ y, 1 ꢁ z; (C) ꢁx, y, 1.5 ꢁ z. (b) A diamond-type network in 3. (c) View of the double left- and right-handed helical chain. (d) 3D net work of 3 constructed by
the double helical chains and QDA anions.
(010) plane (Fig. 1c). From the topological point of view, the 2D
plane of 1 can be reduced to a (4, 4) grid net with a Schlafli symbol
of 44 62 (Fig. 1d). There are two kinds of the smallest four-mem-
bered circuits in the network (Fig. A.2, Supplementary data). Each
circuit consists of four Zn(II) cations at the corners connected by
two BBI molecules and two PDA anions, which make up four edges.
In both of the two circuits, the Zn(II) ions are bridged by BBI and
PDA alternatively. In circuits I and II, the length of PDA edge is
11.037(5) Å, while the length of the BBI edge is different, in I the
length of the BBI edge is 14.473(3) Å, and in II the length of the
BBI edge is 12.007(3) Å. The adjacent 2D layers are further con-
nected via hydrogen bonds between PDA and solvent water mole-
cules to form the resultant supramolecular architectures (Fig. A.3,
Table A1, Supplementary data).
3. Results and discussions
3.1. Crystal structures of complexes 1–4
3.1.1. {[Zn(PDA)(BBI)]ꢀ3H2O}n (1)
Compound 1 crystallizes in the monoclinic space group P2(1)/n,
and the asymmetric unit contains one PDA anion, one BBI mole-
cule, one Zn cation and three water solvent molecules. In the crys-
tal structure, there is only one crystallographically unique Zn(II)
atom. Each Zn(II) center is tetrahedrally coordinated by two N
atoms from two BBI ligands(Zn1–N2 = 1.994(3) Å, Zn1–N3 =
1.999(3) Å), two
O atoms from two PDA ligands(Zn1–O6 =
1.970(2) Å, Zn1–O1A = 2.069(3) Å) (Fig. 1a). Each PDA anion
bridges two Zn(II) cations to yield a wave like chain through bis-
monodentate coordination mode (Scheme 1a) along
a axis
(Fig. 1b). The two kinds of BBI ligands (Fig. A.1, Supplementary
data), exhibiting trans-conformation, act as bidentate bridging li-
gands. All the two kinds of BBI ligands have a dihedral angle of
0° between two imidazole rings, which indicate that the two imid-
azole rings are absolutely parallel. The Zn–PDA chain and its sym-
metry-related ones are connected by the two kinds of BBI ligands
alternatively to form puckered 2D sheet extending along the
3.1.2. {[Zn(PDA)(BBI)]ꢀDMF}n (2)
ꢀ
Compound 2 crystallizes in triclinic space group P1 and the
asymmetric unit contains one PDA anion, one BBI ligand, one Zn(II)
cation and one DMF solvent molecule. As shown in Fig. 2a, the
crystallographically unique Zn(II) is four-coordinated by two oxy-
gen atoms from two PDA anions (Zn1–O5 = 1.966(2) Å, Zn1–
O2C = 1.976(2) Å) and two nitrogen atoms from two BBI ligands

B.-Y. Zhu et al. / Inorganica Chimica Acta 391 (2012) 58–65
63
Fig. 4. (a) View of the coordination environment of Cd1 in 4. The hydrogen atoms are omitted for clarity. Symmetry codes: (A) 1 ꢁ x, 1 ꢁ y, ꢁz; (B) 2 ꢁ x, 1 ꢁ y, 2 ꢁ z; (C) 1 ꢁ x,
ꢁy, 1 ꢁ z; (D) 2 ꢁ x, ꢁy, ꢁz; (E) 2 ꢁ x, ꢁ1 ꢁ y, 1 ꢁ z. (b) View of a dinuclear [Cd2(QDA)4(BBI)4] unit in 4. (c) View of the 2D (4, 4) layer extending along (2ꢁ1ꢁ1) plane. (d) 3D
net work of 4 constructed by the double helical chains and 2D step-shaped layers. (e) Schematic representation of a 36418536 topological net of 4, the ball represents the
dinuclear Cd(II) unit.
(Zn1–N2 = 2.009(2)Å, Zn1–N3 = 1.994(2)Å), showing a tetrahedral
coordination geometry (ZnO2N2). Two PDA anions act as bis-mono-
dentate coordination mode (Scheme 1a) to link adjacent Zn(II)
atoms to yield Zn2(PDA)2 ‘‘loops’’ (Fig. 2b). The BBI ligands with
the same conformation as in 1 then further connect the ‘‘loops’’
into 2D sheet along (01ꢁ1) plane (Fig. 2c). Two identical 2D single
nets are interpenetrated with each other and form an interesting
twofold parallel interpenetrated 2D ? 2D architecture (Fig. A.4,
Supplementary data). The Zn2(PDA)2 ‘‘loops’’ are penetrated by
BBI ligands of the other net and if the loops are considered as single
links, the whole structure of 2 can be described as a (6, 3) networks
which can not properly describe the topology of interpenetration
as it would require the links to pass through the middle of other
links. The PDA anions of the Zn2(PDA)2 ‘‘loops’’ must be viewed
as 2-connected nodes instead of single links, which results in a
4-connected (2.65) topology (Fig. 2d) [28]. Thus an unusual 2D
polyrotaxane-like structure is formed containing rotaxane-like
motifs. Although the single net of 2 has large channels, they are
mainly filled by the other equivalent net, leaving only small voids
to host the guest DMF molecules (Fig. 2e). The interpenetrated 2D
sheets are further connected with their symmetry-related ones via
weak interlayer C–Hꢀ ꢀ ꢀO hydrogen bonds forming the resultant 3D
supramolecular architecture (Fig. 2f and Table A1, Supplementary
data).
3.1.3. {[Cd2(QDA)(BBI)]ꢀ4H2O}n (3)
Single crystal X-ray diffraction reveals that compound 3 crystal-
lizes in monoclinic space group C2/c and has a 3D porous architec-
ture based on 1D Cd–BBI chains. The asymmetric unit of 3 consists
of half of the QDA anion, half of the BBI ligand, one Cd(II) cation and

64
B.-Y. Zhu et al. / Inorganica Chimica Acta 391 (2012) 58–65
two solvent water molecules. Fig. 3a shows the coordination envi-
ronment of the Cd(II) cation in 3. Each Cd(II) adopts a tetrahedral
geometry and is coordinated by two O atoms each from two differ-
ent QDA anions (Cd1–O2 = 2.217(2) Å, Cd1–O2C = 2.217(2) Å) two
dinuclear unit interconnects its equivalent ones via QDA bridges
to form a step-shaped 2D (4, 4) layer (Fig. A.7a, Supplementary
data) with parallelogram grids (14.685 ꢃ 16.861 Å2) extending
along the (2ꢁ1ꢁ1) plane (Fig. 4c). As in compound 3, the BBI li-
gands in 4 bridge the Cd(II) ions to form alternate left- and right-
N
atoms each from two different BBI ligands(Cd1–N1 =
2.195(2) Å, Cd1–N1C = 2.195 Å).
handed helical double chains with a pitch of 16.861(5) Å
From the topological point of view, each Cd(II) ion can be con-
sidered as a single node and the QDA anions and the BBI ligands
as linear bridging linkers, and then the structure possesses a dia-
mond-type network with a Schlafli symbol of 66, as shown in
Fig. 3b.
(Fig. A.7b, Supplementary data), but it is different that BBI ligands
display only one conformation in 3 while two different conforma-
tions in 4. The aforementioned 2D layer is connected to its neigh-
boring ones by such helical chains to form a 3D net (Fig. 4d). If the
dinuclear Cd(II) unit is considered as 8-connecting nodes, the QDA
anion and BBI ligand as connector, the whole structure of 4 can be
described as a 8-connected uninodal net with a Schlafli symbol of
36418536 (Fig. 4e). Although the single net of 4 has large channels,
they are mainly penetrated by the other two equivalent nets, leav-
ing only 19 Å3 cavities per unit cell (1.8% of the total cell volume
calculated by the PLATON program) (Fig. A.7c, Supplementary data).
The cavities are too small to host the solvent DMF molecules.
Unlike that found in compounds 1 and 2 in which the BBI ligand
adopts two different trans-conformation, the BBI ligand in 3 adopts
only one trans-conformation (Fig. A.3, Supplementary data). The
Cd(II) ions are connected by BBI ligands to form the alternate left-
and right-handed helical chains along [101] direction with the
pitches of 17.769(4) Å(Fig. 3c), these double chains are further
interlinked by QDA anions through monodentate carboxylate
groups with a trans-conformation (Scheme 1b) to form 3D network
(Fig. 3d). It is worth noting that there are alternate left- and right-
handed helices in the double chains, so the whole framework does
not show chirality. To the best our knowledge, the connection of
metal ions by a bridging BBI ligand in the S-shaped conformation
normally generates one single left- or right-handed helices
[29,30]. The 1D alternate left- and right-handed helices chains as
found in 3 are heretofore unreported in the study of BBI ligand
and its derivatives.
3.2. Effect of solvents on the structures of 1–4
It is well known that the solvent can have a significant structure
directing effect on the formation of the final structures [31]. The
same reaction in different solvents may result in different struc-
tural topologies [32–34]. The ratio of reagents, the reaction tem-
perature and time are the same for the syntheses of complexes 1
and 2, as well as 3 and 4, only differing in solvents used. But the
resultant structures are quite different for 1 and 2, as well as 3
and 4: complex 1 is a 2D wave like uninterpenetrating layer, while
complex 2 is a 2D ? 2D interpenetrating layer; complex 3 is an
uninterpenetrating diamond like 3D framework, while complex 4
is a threefold interpenetrating 3D framework. The structural differ-
ences between them results from the different solvents used in the
synthesis. 1 and 3 were synthesized using H2O as solvent, while 2
and 4 were obtained using DMF as solvent. Because the polarity of
H2O is bigger than that of DMF, the conformation of the flexible li-
gands BBI, PDA2ꢁ and QDA2ꢁ are induced differently by solvents,
which resulted in the different adaptive packing patterns.
3.1.4. [Cd(QDA)(BBI)]n (4)
Single crystal X-ray diffraction reveals that Compound 4 crys-
ꢀ
tallizes in triclinic space group P1 and the asymmetric unit con-
tains one QDA anion, one BBI ligand and one Cd(II) cation. The
coordination environment around the Cd(II) can be described as
a distorted pentagonal bipyramid (Fig. 4a). Cd(II) ion is seven-coor-
dinated by four carboxylic oxygen atoms (O2, O5, O5C, O6) and one
nitrogen atom (N1) from BBI ligand at the equatorial plane, and
one other carboxylic oxygen atom (O3) and one other nitrogen
atom (N3) at the axial positions. The Cd–O (carboxylate) bond
lengths are in the range of 2.306(3)–2.622(4) Å and Cd–N (BBI)-
bond lengths are 2.233(4), 2.364(5) Å, respectively.
3.3. Thermal stability
The QDA ligands display two coordination modes (Scheme 1c
and d) and the BBI ligands show two different conformation modes
(Fig. A.6, Supplementary data). Cd1 and its symmetry-related Cd1A
Thermogravimetric analysis (TGA) experiments were conducted
to determine the thermal stability of 1–4. The experiments were
performed on samples consisting of numerous single crystals un-
der N2 atmosphere with a heating rate of 5 °C minꢁ1, as shown in
Fig. A.8 in Supplementary data. For compound 1, the weight losses
of guest water molecules were observed in the temperature ranges
of 37–75 °C, and then until 270 °C large amounts of weight losses
were observed. For 2, the TGA curve showed the weight losses of
DMF molecules occurred in the temperature ranges of 25–80 °C,
and then until 270 °C large amounts of weight losses were ob-
served. In the case of 3, the consecutive weight loss of the guest
water molecules occurred during 25–280 °C, and then large
amounts of weight losses were observed. For 4, there was no
weight loss until 220 °C at which point large amounts of weight
losses occurred because it did not include solvent molecules. The
weight loss of 4 corresponded well to the expected from composi-
tional formula, however, due to the volatility of the guest mole-
cules included in 1–3, the experimental weight losses for solvent
molecules from TGA measurements did not coincide with the cal-
culated from the formula.
are bridged by two QDA ligands to generate
a dinuclear
[Cd2(QDA)4(BBI)4] unit (Fig. 4b). Each pair of Cd(II) atoms in this
3.4. Fluorescent properties
Coordination polymers constructed with d10 metal centers and
conjugated organic ligands have been investigated for fluorescence
Fig. 5. The fluorescent emission spectra of 1–4 in solid state at room temperature.

B.-Y. Zhu et al. / Inorganica Chimica Acta 391 (2012) 58–65
65
properties because of their various applications in chemical sen-
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Appendix A. Supplementary material
CCDC 800454, 800455, 800456 and 800457 contain the supple-
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tary data associated with this article can be found, in the online
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