Syntheses, structures, and luminescence of three metal carboxylate polymers of 2,5-dibenzoylterephthalic acid and N-donor auxiliary ligands

Article abstract of DOI:10.1080/00958972.2012.752466

Three coordination polymers, [CdL(2,2'-bpy)] (1), [ZnL(phen)₂] (2), and [ZnL(2,2'-bpy)] (3) (H2L= 2,5-dibenzoylterephthalic acid, 2,2'-bpy = 2,2'-bipyridine, and phen = 1,10-phenanthroline), were synthesized and crystallographically characterized. The compounds were further characterized by elemental analyses, FTIR, thermogravimetric analyses, and powder X-ray diffraction. Complex 1 exhibits a 2D sheet structure with (4,4) grid units, while 2 and 3 present infinite 1D zig-zag chain structures. The complexes are all extended into high-dimensional supramolecular networks through intermolecular hydrogen bonds and φ-φ stacking interactions. A structural comparison of 1-3 demonstrates that the characteristics of subsidiary ligands and slight difference in coordination models of L play a very important role in construction of the complexes. Additionally, luminescence of the complexes is also investigated at room temperature.

Full text of DOI:10.1080/00958972.2012.752466

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Syntheses, structures, and
luminescence of three metal
carboxylate polymers of 2,5-
dibenzoylterephthalic acid and N-donor
auxiliary ligands
Fengxia Yue a , Bo Li b , Xiaofei Zhu c , Yuhui Luo a , Jukun Hu a ,
Xiaofang Wang a & Hong Zhang a
a Key Laboratory of Polyoxometalate Science of Ministry of
Education, Department of Chemistry , Northeast Normal
University , Changchun , China
b Institute: Hebei Provincial Key Laboratory of Inorganic
Nonmetallic Materials, College of Materials Science and
Engineering , Hebei United University , Tangshan , China
c School of Chemistry and Life Science , Changchun University of
Technology , Changchun , China
Accepted author version posted online: 22 Nov 2012.Published
online: 14 Jan 2013.
To cite this article: Fengxia Yue , Bo Li , Xiaofei Zhu , Yuhui Luo , Jukun Hu , Xiaofang Wang &
Hong Zhang (2013) Syntheses, structures, and luminescence of three metal carboxylate polymers
of 2,5-dibenzoylterephthalic acid and N-donor auxiliary ligands, Journal of Coordination Chemistry,
66:2, 243-253, DOI: 10.1080/00958972.2012.752466
To link to this article: http://dx.doi.org/10.1080/00958972.2012.752466
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Journal of Coordination Chemistry
Vol. 66, No. 2, 20 January 2013, 243–253
Syntheses, structures, and luminescence of three metal
carboxylate polymers of 2,5-dibenzoylterephthalic acid and
N-donor auxiliary ligands
FENGXIA YUEy, BO LIz, XIAOFEI ZHUx, YUHUI LUOy, JUKUN HUy, XIAOFANG
WANGy and HONG ZHANGy*
yKey Laboratory of Polyoxometalate Science of Ministry of Education, Department of
Chemistry, Northeast Normal University, Changchun, China; zInstitute: Hebei Provincial
Key Laboratory of Inorganic Nonmetallic Materials, College of Materials Science and
Engineering, Hebei United University, Tangshan, China; xSchool of Chemistry and Life
Science, Changchun University of Technology, Changchun, China
(Received 18 May 2012; in final form 7 September 2012)
Three coordination polymers, [CdL(2,2′-bpy)] (1), [ZnL(phen)2] (2), and [ZnL(2,2′-bpy)] (3)
(H2L= 2,5-dibenzoylterephthalic acid, 2,2′-bpy = 2,2′-bipyridine, and phen = 1,10-phenanthroline),
were synthesized and crystallographically characterized. The compounds were further characterized
by elemental analyses, FTIR, thermogravimetric analyses, and powder X-ray diffraction. Complex
1 exhibits a 2D sheet structure with (4,4) grid units, while 2 and 3 present infinite 1D zig–zag
chain structures. The complexes are all extended into high-dimensional supramolecular networks
through intermolecular hydrogen bonds and π–π stacking interactions. A structural comparison of
1–3 demonstrates that the characteristics of subsidiary ligands and slight difference in coordination
models of L play a very important role in construction of the complexes. Additionally, lumines-
cence of the complexes is also investigated at room temperature.
Keywords: Coordination polymer; 2,5-Dibenzoylterephthalic acid; 2,2′-bpy; Phen; Luminescence
1. Introduction
Coordination polymers have interesting structures and potentially useful properties (e.g.
luminescence, catalysis, and magnetism) [1]. Noncovalent interactions, like H-bonds, C–
Hꢀ ꢀ ꢀπ, and πꢀ ꢀ ꢀπ interactions, are steering forces of molecular self-assembly [2]. Multi-
carboxylic ligands are widely used in development of networks organized through coordi-
nation bonds, hydrogen bonds, and πꢀ ꢀ ꢀπ stacking interactions [3]. Many investigations
have paid attention to coordination polymers containing asymmetric rigid benzene poly-
carboxylates such as 1,2,3-benzenetricarboxylic acid (1,2,3-H3btc) [4], 1,4-benzenedicarb-
oxylic acid [5], 1,3,5-benzenetricarboxylic acid (1,3,5-H3btc) [6], and 1,2,4,5-
benzenetetracarboxylic acid (1,2,4,5-H4btc) [7]. Compared with those rigid multicarboxy-
lates 2,5-dibenzoylterephthalic acid, grafting benzoyl on terephthalic exhibits more steric
*Corresponding author. Email: zhangh@nenu.edu.cn
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online Ó 2013 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2012.752466

244
F. Yue et al.
hindrance than 1,4-benzenedicarboxylic and the aromatic substituent may rotate around the
central phenyl ring. The resulting steric hindrance can play important roles in directing the
extended structures of coordination polymers. Structural sophistication can be further
enhanced through ancillary co-ligands. The multicarboxylate 2,5-dibenzoylterephthalic acid
(Scheme 1) is relatively rare [8]. A series of Sn complexes based on such ligands show
discrete mononuclear molecular structures by virtue of terminal ligands that hinder the
extension of higher dimensional structures.
To seek possible structural variations and property changes of substituents on mono-aro-
matic polycarboxylates [9], we introduced 2,2′-bpy and phen (2,2′-bpy=2,2′-bipyridine and
phen=1,10-phenanthroline) as auxiliary ligands to adjust the network structure. As a result,
[CdL(2,2′-bpy)] (1), [ZnL(phen)2] (2), and [ZnL(2,2′-bpy)] (3) (H2L=2,5-dibenzoyltereph-
thalic acid) with high-dimensional supramolecular networks were obtained via hydrother-
mal reaction of Cd2+ (or Zn2+) salts with 2,2′-bpy and phen. The luminescence of the
three compounds is also studied.
2. Experimental
2.1. Materials and instrumentation
Reagents were purchased commercially and used without purification. The FTIR spectra
were recorded from KBr pellets (4000–400 cm–1) on a Mattson Alpha-Centauri spectrome-
ter. Elemental analyses for C, H, and N were performed on a Perkin-Elmer 2400 Elemental
Analyzer. Thermogravimetric analyses (TGA) were investigated on a Netzsch Sta449C
thermoanalyzer under N2 with a ramp rate of 5 °C minꢁ1. The fluorescence spectra were
obtained using a Cary Eclipse luminescence spectrophotometer (VARIAN, USA). Diamag-
netic corrections were estimated from Pascal’s constants for all constituent atoms.
2.2. Syntheses
2.2.1. Synthesis of [CdL(2,2′-bpy)] (1). A mixture of Cd(NO3)2∙4H2O (30.8 mg,
0.1 mmol), L (37.4 mg, 0.1 mmol), 2,2′–bpy (15.8 mg, 0.1 mmol), and H2O (15 mL) was
stirred for 30 min at room temperature and the pH of the solution was adjusted to 4.5 with
0.1 M NaOH. The mixture was kept stirring for another 30 min, sealed in a 25 mL Teflon-
lined stainless steel vessel, heated at 160 °C for 72 h, and then cooled to 40 °C at a rate of
4 °C hꢁ1. Colorless block crystals were obtained after washing with deionized water and
drying in air, in ꢂ61% yield based on cadmium. Elemental analysis (%) calcd for
C32H20CdN2O6 (640.91): C, 59.97; H, 3.15; N, 4.37. Found (%): C, 60.04; H, 3.13; N,
Scheme 1. The structure of 2,5-dibenzoylterephthalic acid.

Metal polymers of 2,5-dibenzoylterephthalic acid
245
4.36; IR (KBr pellet, cmꢁ1): 1679 (m), 1665 (s), 1574 (w), 1491 (w), 1478 (s), 1342 (s),
1014 (m), 948 (s), 916 (s), 890 (m), 681 (m), 621 (w).
2.2.2. Synthesis of [ZnL(phen)2] (2).
A mixture of Zn(NO3)2∙4H2O (29.7 mg,
0.1 mmol), L (37.4 mg, 0.1 mmol), 1,10′–phen (39.64 mg, 0.2 mmol), and H2O (15 mL)
was stirred for 30 min at room temperature and the pH of the solution was adjusted to 4.0
with 0.1 M NaOH. The mixture was kept stirring for another 30 min, sealed in a 25 mL
Teflon-lined stainless steel vessel, heated at 160 °C for 72 h, and then cooled to 40 °C at a
rate of 4 °C hꢁ1. Colorless block crystals were obtained after washing with deionized water
and drying in air, in ꢂ56% yield based on zinc. Elemental analysis (%) calcd for
C46H28ZnN4O6 (798.11): C, 69.23; H, 3.54; N, 7.02. Found (%): C, 68.97; H, 3.68; N,
7.04; IR (KBr pellet, cmꢁ1): 1672 (s), 1604 (w), 1550 (m), 1418 (s), 1388 (w), 1255 (m),
1069 (s), 1017 (w), 937 (m), 853 (s), 698 (m).
2.2.3. Synthesis of [ZnL(2,2′-bpy)] (3). The procedure is similar to the synthesis of 2
except that 2,2′-bpy (15.8 mg, 0.1 mmol) was used instead of 1,10′-phen. Colorless block
crystals were obtained in ꢂ58% yield based on zinc. Elemental analysis (%) calcd for
C32H20ZnN2O6 (593.89): C, 64.72; H, 3.40; N, 4.72. Found (%): C, 64.46; H, 3.32; N,
4.97; IR (KBr pellet, cmꢁ1): 1670 (m), 1627 (s), 1546 (w), 1449 (s), 1312 (w), 1245 (m),
1175 (w), 1020 (m), 919 (m), 796 (s), 692 (s), 511 (w).
2.3. X-ray crystallography
Appropriate colorless block crystals of 1, 2, and
3
with dimensions of
0.20 mm ꢃ 0.05 mm ꢃ 0.05 mm, 0.16 mm ꢃ 0.13 mm ꢃ 0.10 mm, and 0.16 mm ꢃ 0.14 mm
ꢃ 0.10 mm were attached to a glass fiber for data collections on a SMART (Bruker, 2002)
diffractometer equipped with MoKα radiation (λ1 = 0.71073 Å, λ2 = 0.71073 Å,
λ3 = 0.71073 Å) at 293(2) K from 1.72° < h1 < 25.00°, 1.95° < h2 < 25.02°, and 1.82°
< h3 < 25.02°. Empirical absorption corrections were applied to the data using ABSCOR
[12]. The structure was solved by direct methods followed by difference Fourier method
and refined by full-matrix least-squares on F2 using the SHElXTL-97 package [13]. All
nonhydrogen atoms were refined anisotropically. The polymer 1 gave R = 0.0459 and
2
2
wR = 0.1163 (w = 1/[σ2(F0 )
+
(0.0918P)2 + 0.0000P], where P= (F02 + 2Fc )/3).
GOF = 1.041, (Δρ)max = 0.769, (Δρ)min = –0.789e/Å3 and (Δ/σ)max = 0.191.
2
gave
R = 0.0317 and wR = 0.0867 (w = 1/[σ2(F0 )
+
(0.0505P)2 + 0.7251P], where P=
2
(F02 + 2Fc )/3). GOF = 1.061, (Δρ)max = 0.673, (Δρ)min = –0.373e/Å3 and (Δ/σ)max = 0.047. 3
2
gave R = 0.0599 and wR = 0.1621 (w = 1/[σ2(F0 ) + (0.1245P)2 + 0.0000P], where P=
2
(F02 + 2Fc )/3). GOF = 1.003, (Δρ)max = 0.483, (Δρ)min = –0.420e/Å3 and (Δ/σ)max = 0.093.
2
Details of crystal data collection and structure refinements for 1–3 are listed in table 1 and
selected bond parameters are listed in table 2. In addition, tables 3 and 4 show πꢀ ꢀ ꢀπ inter-
actions in 1 and 2 and hydrogen-bonding geometry parameters for 3, respectively. The
CCDC reference numbers for 1–3 are 843,558, 843,560, and 726,169, respectively. Copy
of the data can be obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [Fax:+44(1223)336–033; E-mail: deposit@ccdc.cam.ac.uk].

246
F. Yue et al.
Table 1. Details of crystal data collection and structure refinement for 1–3.
Polymers
1
2
3
Formula
M
C32H20CdN2O6
640.91
C46H28ZnN4O6
798.11
C32H20ZnN2O6
593.89
Color
Temperature/K
Colorless
293(2)
Colorless
293(2)
Colorless
293(2)
Wavelength/Å
Crystal system
Space group
0.71073
Triclinic
P-1
0.71073
Monoclinic
P21/c
0.71073
Triclinic
P-1
a/Å
b/Å
c/Å
α/°
β/°
10.0065(14)
11.5311(16)
12.5543(17)
70.960(2)
82.651(2)
82.555(2)
1352.1(3)
2
9.8650(8)
20.8697(17)
17.5587(14)
90
101.278(1)
90
3545.2(5)
4
1.495
10.3643(18)
11.972(2)
12.052(2)
109.389(2)
94.847(3)
101.401(3)
1364.4(4)
2
γ/°
V/Å3
Z
ρ
calcd/g cmꢁ3
1.574
0.857
1.446
0.949
μ/mmꢁ1
0.754
F(0 0 0)
644.0
1640.0
608.0
Crystal size/mm
h Range/°
0.20 ꢃ 0.05 ꢃ 0.05
1.72–25.00
6878
0.16 ꢃ 0.13 ꢃ 0.10
1.95–25.02
17,631
0.16 ꢃ 0.14 ꢃ 0.10
1.82–25.02
6858
Reflections collected
Independent reflections
Rint
4705
0.0276
1.041
6232
0.0263
1.061
4748
0.0312
1.003
GOF on F2
Final R indices [I > 2σ(I)]
aR1 = 0.0459,
bwR2 = 0.1163
0.0641, 0.1481
R1 = 0.0317,
wR2 = 0.0867
0.0402, 0.0917
R1 = 0.0599,
wR2 = 0.1621
0.0980, 0.2046
Largest diff. peak and hole/
e·Å3
aR1 = ∑||F0| – |Fc||/∑|F0|; bwR2 = ∑[w(F0 – Fc2)2]/∑[w(F02)2]1/2
.
2
3. Results and discussion
3.1. Synthesis and IR spectroscopy
Colorless crystals of 1–3 were hydrothermally synthesized by assembly of metal (cadmium
and zinc) salt with 2,5-dibenzoylterephthalic acid and co-ligands (phen or 2,2′-bpy) in
H2O, and furthermore, structurally determined by single-crystal X-ray diffraction.
The IR spectra of 1–3 exhibit absorptions from 1600–1450 cm–1, ascribed to skeletal
vibrations of the aromatic rings. The νas(COO) and νs(COO) bands at 1665, 1574, 1478,
and 1342 cm–1 for 1 and 1604, 1550, 1418, and 1388 cm–1 for 2, and 1627, 1546, 1449,
and 1312 cm–1 for 3 are from carboxylates. The Δν values [Δν = νas(COO) – νs(COO)]
(187, 232 cm–1 in 1 and 178, 234 cm–1 in 3) indicate two different coordination modes of
carboxylates of O2N-btc3- [10]. Absorptions νas(COO) at 1604 and 1550 cm–1 and νs(COO)
at 1418 and 1388 cm–1 in IR spectra of 2 with Δν values of 186 cm–1 and 162 cm–1 indi-
cate monodentate and chelating coordination of carboxylates in 2.
3.2. Description of the structures
3.2.1. [CdL(2,2′-bpy)] (1). X-ray single-crystal diffraction reveals that 1 contains binu-
clear Cd(II) with nonbonding Cd∙∙∙Cd distances of 3.831(7) Å. As shown in figure 1(a),

Metal polymers of 2,5-dibenzoylterephthalic acid
Table 2. Selected bond lengths /Å and angles /° for 1–3.
247
1
Cd(1)–O(4)
Cd(1)–N(1)
Cd(1)–O(2)
Cd(1)–N(2)
Cd(1)–O(5)#1
Cd(1)–O(1)
Cd(1)–O(4)#1
O(4)–Cd(1)–N(1)
O(4)–Cd(1)–O(2)
N(1)–Cd(1)–O(2)
O(4)–Cd(1)–N(2)
N(1)–Cd(1)–N(2)
O(2)–Cd(1)–N(2)
O(4)–Cd(1)–O(5)#1
2
2.324(4)
2.337(5)
2.347(4)
2.371(5)
2.385(4)
N(1)–Cd(1)–O(5)#1
O(2)–Cd(1)–O(5)#1
N(2)–Cd(1)–O(5)#1
O(4)–Cd(1)–O(1)
N(1)–Cd(1)–O(1)
O(2)–Cd(1)–O(1)
83.02(16)
86.11(15)
120.34(16)
83.86(14)
147.97(18)
54.87(15)
91.74(19)
128.97(15)
75.30(14)
112.46(16)
88.10(15)
172.19(14)
53.28(13)
90.24(15)
2.433(4)
2.512(4)
N(2)–Cd(1)–O(1)
80.71(16)
135.63(15)
143.05(18)
112.43(16)
68.9(2)
O(5)#1–Cd(1)–O(1)
O(4)–Cd(1)–O(4)#1
N(1)–Cd(1)–O(4)#1
O(2)–Cd(1)–O(4)#1
N(2)–Cd(1)–O(4)#1
O(5)#1–Cd(1)–O(4)#1
O(1)–Cd(1)–O(4)#1
86.87(18)
113.36(14)
Zn(1)–O(3)
Zn(1)–O(1)
Zn(1)–N(1)
Zn(1)–N(4)
Zn(1)–N(2)
Zn(1)–N(3)
O(3)–Zn(1)–O(1)
O(3)–Zn(1)–N(1)
O(1)–Zn(1)–N(1)
O(3)–Zn(1)–N(4)
O(1)–Zn(1)–N(4)
3
2.0377(13)
2.0636(13)
2.1711(17)
2.1930(17)
2.2332(17)
2.2939(17)
92.22(6)
99.08(6)
93.92(6)
93.90(6)
101.84(6)
N(1)–Zn(1)–N(4)
O(3)–Zn(1)–N(2)
O(1)–Zn(1)–N(2)
N(1)–Zn(1)–N(2)
N(4)–Zn(1)–N(2)
O(3)–Zn(1)–N(3)
O(1)–Zn(1)–N(3)
N(1)–Zn(1)–N(3)
N(4)–Zn(1)–N(3)
N(2)–Zn(1)–N(3)
159.15(6)
170.97(6)
95.22(6)
75.34(6)
89.58(6)
90.72(6)
175.20(6)
89.36(6)
74.15(6)
82.22(6)
Zn(1)–O(3)
Zn(1)–N(2)
Zn(1)–N(1)
Zn(1)–O(2)
1.914(4)
2.048(5)
2.067(5)
2.114(4)
2.193(4)
123.7(2)
107.49(19)
79.4(2)
O(3)–Zn(1)–O(2)
N(2)–Zn(1)–O(2)
N(1)–Zn(1)–O(2)
O(3)–Zn(1)–O(1)
N(2)–Zn(1)–O(1)
N(1)–Zn(1)–O(1)
O(2)–Zn(1)–O(1)
106.75(17)
129.19(18)
91.90(17)
109.67(18)
93.89(17)
138.99(18)
61.25(15)
Zn(1)–O(1)
O(3)–Zn(1)–N(2)
O(3)–Zn(1)–N(1)
N(2)–Zn(1)–N(1)
Symmetry transformations used to generate equivalent atoms: #1 –x + 1,–y, –z + 1; #2 –x + 1, –y, –z + 2; #3 –x + 2,
–y, –z + 1 for 1.
Table 3. πꢀ ꢀ ꢀπ Interactions in 1 and 2.
Complex
Two rings
Symmetry code
Centroid-to-centroid distance (Å)
1
2
Cg(2) > Cg(2)
Cg(11) > Cg(12)
1 – x, 1 – y, 1 – z
x, 1/2 – y, –1/2 + z
3.5999
3.5722
Complex
Dihedral angle (°)
Perpendicular distance
of Cg(I) on ring J (Å)
3.546
Perpendicular distance
of Cg(J) on ring I (Å)
3.546
1
2
0
2.66
3.361
3.411
Cg(2): N(2) > C(28) > C(29) > C(30) > C(31) > C(32) Cg(11): C(26) > C(27) > C(28) > C(29) > C(30) > C(31) Cg(12):
C(38) > C(39) > C(40) > C(41) > C(42) > C(43).
Cd1 lies at an inversion center in a pentagonal bipyramidal environment, seven-coordinate
by five oxygens from three L1 (Cd–O 2.325(4)–2.511(4) Å) and two nitrogens (Cd–N

248
F. Yue et al.
Table 4. Hydrogen-bonding parameters (Å, °) for 3.
DꢁH···A
C(14)ꢁH(14)···O(5)
d(DꢁH)
0.93
d(H···A)
2.39
d(D···A)
3.1811
\ (DHA)
143.57
2.337(5)–2.371(5) Å) from two 2,2′-bpy ligands. In 1, two Cd1 ions are linked by a
μ2:η1:η2-L, resulting in a binuclear [Cd2(COO)2] building unit; binuclear units are further
connected by four L1 to construct a 2D layer [figure 1(b)] with 36-membered macrocyclic
rings. The 2D layer shows large rhombic (4,4) grids with approximate size of
15.617 ꢃ 14.460 Å2. Consequently, a 3D supramolecular framework is formed in 1 through
πꢀ ꢀ ꢀπ interactions between two benzene rings of 2,2′-bpy. The centroid to centroid dis-
tances between the benzene rings are 3.599 Å (table 3).
3.2.2. [ZnL(phen)2] (2). Compound 2 crystallizes in monoclinic space group P2(1)/c
with a zinc ion, a L, and two phen in the asymmetric unit. Zn1 displays octahedral geome-
try surrounded by two oxygens (Zn–O 2.0636(13)–2.0377(13) Å) from two bridging L
and four chelating nitrogens (Zn–N 2.1710(18)–2.2938(17) Å) from different phen ligands.
Each Zn(II) is further connected via L to generate a 1D zig–zag chain structure [figure 2
(b)] and also, show π–π interactions between arene cores of adjacent phen from a neigh-
boring chain (3.572(2) Å) [figure 2(c)] (table 3).
3.2.3. [ZnL(2,2′-bpy)] (3). When phen was replaced by 2,2′-bpy, a different 2D net was
formed in 3. The structure of 3 is a 1D zig–zag chain and crystallizes in the triclinic space
group P-1. The asymmetric unit of 3 is composed of one Zn(II), one 2,2′-bpy, and one L.
Each Zn(II) is five-coordinate by three oxygens (Zn–O 1.914(4)–2.193(4) Å) from one
chelating and one bridging L and two nitrogens (Zn–N 2.067(5)–2.048(5) Å) from a che-
lating 2,2′-bpy. Each Zn(II) is linked to adjacent Zn(II) through bridging L which adopts a
chelating and bridging coordination mode alternately forming a unique 1D zig–zag chain
structure [figure 3(b)], and the 1D zig–zag chains are extended into a 2D structure via
hydrogen bonds (C(14)ꢁH(14)∙∙∙O(5) 2.390 Å, C(14)ꢁH(14)∙∙∙O(5) 143.57°) [figure 3(c)]
(table 4).
3.3. Thermal stability
TGA measurements are performed for crystalline samples of 1–3 from 25–900 °C in N2 at
a heating rate of 5 °C minꢁ1. A weight loss at 280–420 °C corresponds to release of the
organic groups and the remaining product is CdO (obsd. 21.90%, Calcd 20.00%) for 1.
Complex 2 begins to decompose at 300 °C and ends above 490 °C, attributed to loss of
organic ligands. The remaining weight (Obsd. 11.15%) indicates that the final product is
ZnO (Calcd 10.20%). Complex 3 is stable to 320 °C and then, the organic groups decom-
pose gradually from 320 to 540 °C, with the remaining product ZnO (Obsd. 14.10%, Calcd
13.70%) (Supplementary material).

Metal polymers of 2,5-dibenzoylterephthalic acid
249
Figure 1. (a) Coordination environments of cadmium(II) centers in 1. Hydrogens are omitted for clarity.
Symmetry codes: i = –x + 1, –y, –z + 1. (b) Views showing the (4,4) networks formed by connecting the clusters
with L linkers. (c) The Cd∙∙∙Cd distances in the 36-membered macrocyclic ring. (d) Perspective view of abutting
layers. Hydrogen bonds are indicated by dotted lines.
3.4. The powder X-ray diffraction analysis (PXRD)
In order to check phase purity of the complexes, powder X-ray diffraction (PXRD) pat-
terns of 1–3 were determined at room temperature. The peak positions of the measured
PXRD patterns are in agreement with patterns simulated from single-crystal data for
the three compounds, confirming the good phase purity of the samples (Supplementary
material).
3.5. Luminescent property
The solid-state photoluminescence spectra of 1–3 and L were measured at room
temperature as depicted in figure 4. All of the measurements were performed at excitation
wavelength 380 nm. L displays a strong emission peak at 472 nm, while 1–3 exhibit
intense emission at 425 nm, 420 nm, and 457 nm, respectively [11]. These emissions are
neither metal-to-ligand charge transfer (MLCT) nor ligand-to-metal transfer (LMCT), since
it is difficult to oxidize or reduce Zn(II) and Cd(II). Compared with L, the significantly
shifted emissions for 1–3 may be attributed to deprotonation of the ligand and the coordi-
nation interaction between L and the metal cations (ZnII/CdII) [11].

250
F. Yue et al.
Figure 2. (a) Coordination environments of zinc(II) centers in 2. Hydrogens are omitted for clarity. Symmetry
codes: i = –x + 1, –y + 1, –z + 2; ii = –x, –y + 1, –z + 1. (b) The 1D polymeric structure of 2. (c) Perspective view of
abutting chains; hydrogen bonds are indicated by dotted lines.

Metal polymers of 2,5-dibenzoylterephthalic acid
251
Figure 3. (a) Coordination environments of Zn(II) in 3. Hydrogens are omitted for clarity. Symmetry codes: i = –
x + 2, ꢁy, –z; ii = –x + 1, –y + 1, –z + 1. (b) The 1D polymeric structure of 2. (c) Perspective view of abutting
chains. Hydrogen bonds are indicated by dotted lines.

252
F. Yue et al.
Figure 4. The emission spectra of 1–3 and L at room temperature.
4. Conclusion
Three new coordination polymers containing 2,5-dibenzoylterephthalic acid and 2,2′-bpy
or phen with ZnII and CdII have been hydrothermally prepared and isolated. Comparing
the three ZnII and CdII complexes with previously reported similar ones containing ZnII
and CdII metals [14] indicates that p-benzenedicarboxylates, rather than o- and m-ones,
have the innate ability to provide a 3D structure with or without auxiliary ligands. Thus,
terminal ligands phen and 2,2′-bipy are utilized to tailor the preferential 3D structures to
generate low-dimensional structures and one 2D and two zig–zag ones as expected. The
compounds display different photoluminescent properties influenced by structures and
bridging modes. Comparison of the crystal structures of 1–3 demonstrates that both the
multicarboxylate and the chelate ligands are efficient for construction of high-dimensional
supramolecular structures based on noncovalent interactions (π–π and C–Hꢀ ꢀ ꢀπ). It is chal-
lenging to further research 2,5-dibenzoylterephthalic acid or more auxiliary ligands which
may result in high-dimensional frameworks.
Acknowledgments
We gratefully acknowledge financial support by the NSF of China (21071027, 20771023),
the China High-Tech Development 863 Program (2007AA03Z218) and analysis & testing
foundation of Northeast Normal University, and Research Fund for the Doctoral Program
of Hebei United University (2012).
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