A two-dimensional Cd(II) coordination polymer: [Cd(1,4-BDOA)(1,10-phen)] ·H2O with strong blue fluorescent emission constructed by benzene-1,4-dioxydiacetate ligand

Article abstract of DOI:10.1016/j.inoche.2005.01.020

Hydrothermal reaction of Cd(NO₃)₂·4H ₂O with 1,10-phen and 1,4-BDOAH₂ yields a two-dimensional cadmium(II) coordination polymer, [Cd(1,4-BDOA)(1,10-phen)]·H ₂O, in which CdN₂O₅ pentagonal bipyramids are linked together to construct a lamellar structure. It exhibits strong blue fluorescent upon photoexcitation.

Full text of DOI:10.1016/j.inoche.2005.01.020

Inorganic Chemistry Communications 8 (2005) 361–364
www.elsevier.com/locate/inoche
A two-dimensional Cd(II) coordination polymer:
[Cd(1,4-BDOA)(1,10-phen)] Æ H2O with strong blue
fluorescent emission constructed by
benzene-1,4-dioxydiacetate ligand
a,
a
a
a
Shan Gao *, Ji-Wei Liu a,b, Li-Hua Huo , Ying-Ming Xu , Hui Zhao
a
School of Chemistry and Materials Science, Heilongjiang University, Harbin 150080, China
b
College of Chemistry and Chemical Technology, Da Qing Petroleum Institute, Da Qing 163318, China
Received 10 January 2005; accepted 27 January 2005
Abstract
Hydrothermal reaction of Cd(NO3)2 Æ 4H2O with 1,10-phen and 1,4-BDOAH2 yields a two-dimensional cadmium(II) coordina-
tion polymer, [Cd(1,4-BDOA)(1,10-phen)] Æ H2O, in which CdN2O5 pentagonal bipyramids are linked together to construct a lamel-
lar structure. It exhibits strong blue fluorescent upon photoexcitation.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Cd(II) Carboxylate coordination polymer; Benzene-1,4-dioxyacetic acid; Hydrothermal synthesis; Fluorescent property
In recent years, extensively attention has been fo-
cused on the design and synthesis of cadmium(II) car-
boxylate coordination polymers for their intriguing
structural motifs, photoluminescent properties and
other potential applications in molecular-based materi-
als [1–4]. Some rigid aromatic carboxylic acids such as
isophthalic acid or the related species are often chosen
to fabricate these supramolecular architectures [5,6].
The flexible benzene-1,4-dioxydiacetic acid (1,4-
BDOAH2), analogue to phthalic acids, possesses the
versatile binding fashions and the capability of forming
coordination architectures of diverse sizes and shapes,
etc., and hence it is an attractively choice for the con-
struction of coordination polymers [7,8]. However, the
coordination chemistry and structural properties of cad-
mium(II) polymers based on 1,4-BDOAH2 ligand have
been documented very little to date. Recently, we have re-
ported the structure of one 1D polymer, [Cd(1,4-
BDOA)(imidazole)3]n, (I), in which the Cd(II) atom exists
in a distorted octahedral coordination sphere and this li-
gand acts in a g1:g1:g1:l2 bridging mode [9] (Scheme 1).
Herein is described the synthesis, structure, thermal and
luminescent properties of a novel two-dimensional (2D)
cadmium(II) polymer, [Cd(1,4-BDOA)(1,10-phen)] Æ
H2O (II), with the 1,4-bdoa2À ligand showing the unprec-
edented g1:g1:g1:g1:l2 and g1:g2:g1:g2:l4 modes. More-
over, it also exhibits a strong blue fluorescent emission in
the solid state.
Hydrothermal reaction of Cd(NO3)2 Æ 4H2O with
1,10-phen, 1,4-BDOAH2 and NaOH in the molar ratio
of 1:1:1:2 at 433 K (five days) leads to the formation
of colorless prismatic crystals of II in 67% yield based
on cadmium. Anal. Calc. for C22H18N2O7Cd: C, 49.41;
H, 3.39; N, 5.24. Found: C, 49.68; H, 3.49; N, 5.09%.
*
Corresponding author. Tel.: +86 0451 88543639; fax: +86 0451
86608040.
E-mail address: shangao67@yahoo.com (S. Gao).
1387-7003/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2005.01.020

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S. Gao et al. / Inorganic Chemistry Communications 8 (2005) 361–364
one bidentate chelating 1,10-phen ligand. It is noted that
the C1–C2–O3–C3 and C6–C7–O6–C8 torsion angles
are À73.7(3)° and 69.4(3)°, respectively. Whereas in
the reported I, the oxyacetate groups and benzene ring
are almost coplanar, with the torsion angles being
À174.2(3)° and 178.7(2)°, respectively. This demon-
strates that the 1,4-BDOA2À ligand has remarkable flex-
ibility corresponding to the rigid aromatic carboxylic
acid ligand such as terephthalate. It is obviously ob-
served from the reported complex, [Cd(bipy)(terephthal-
ate)(H2O)]n, (III), in which the dihedral angles of the
two carboxyl groups and the phenyl are 5.63° and
12.58°, respectively [13].
In 2D coordination polymer, there are two coordina-
tion types of 1,4-BDOA2À ligands that are distinguished
by their direction bridging Cd atoms (Fig. 2). In the for-
mer case, two CdN2O5 pentagonal bipyramids are com-
bined by the carboxyl O2 and O2i atoms to form a
binuclear unit. There is a crystallographic inversion cen-
ter between the two Cd atoms whose separation is
˚
3.84 A. All the binuclear units are joined by the carbox-
ylate groups in a g1:g2:g1:g2:l4 mode to produce a 1D
chain, with the CdÁ Á ÁCd distances of 11.91 and
Scheme 1. The coordination modes of 1,4-BDOA2À group in the Cd
complexes (I) and (II): (I) g1:g1:g1:l2; (II) g1:g1:g1:g1:l2; (III)
g1:g2:g1:g2:l4.
˚
14.22 A, respectively. In the latter case, infinite chains
are further connected together by another carboxylate
groups in a g1:g1:g1:g1:l2 mode, generating a 2D porous
architecture parallel to (110). Adjacent CdÁ Á ÁCd dis-
IR (KBr, cmÀ1): 3438w [m(O–H)]; 1606m [masym(OCOÀ)];
1417s, 1332s [msym(OCOÀ)]; 1217s, 1067s [masym(COC),
˚
tance is 11.80 A, which is significantly shorter than the
˚
m
sym(COC)]; 856m, 727s [d(C–H)].
The molecular structure of II is shown in Fig. 1, and
corresponding CdÁ Á ÁCd distance of 15.01 A in I, but
˚
somewhat longer than that in III (11.30 A). Moreover,
it is established by single crystal X-ray diffraction anal-
ysis [10–12]. Two crystallographically independent
‘‘half’’ 1,4-bdoa2À ligands occupy different inversions
in the middle of the benzene rings, respectively. Each
Cd atom displays a distorted pentagonal bipyramidal
geometry, with five carboxylate oxygen donors from
three 1,4-bdoa2À ligands, two nitrogen donors from
there exist p–p stacking interactions between the adja-
cent 1,10-phen rings [centroid–centroid distance =
˚
3.68(2) A] and intramolecular hydrogen bonds, which
are formed between the free water molecules and car-
boxylate oxygen atoms [OÁ Á ÁO distances, 2.951(6) and
˚
3.082(6) A], resulting in a three-dimensional (3D) supra-
molecular network.
i
Fig. 1. The coordination environments of the CdII atom in II (at 30% probability level). Selected bond distances (A) and angles (°): Cd(1)–O(2)
2.3365(19); Cd(1)–N(1) 2.347(2); Cd(1)–O(1) 2.581(2); Cd(1)–N(2) 2.339(2); Cd(1)–O(2) 2.343(2); Cd(1)–O(4) 2.451(2); Cd(1)–O(5) 2.341(2) and
O(2)i–Cd(1)–O(5) 103.86(8); O(2)i–Cd(1)–O(2) 69.93(8); O(2)–Cd(1)–O(1) 52.12(6); N(1)–Cd(1)–O(1) 89.31(8); N(2)–Cd(1)–N(1) 71.45(8); N(2)–
Cd(1)–O(4) 86.97(7). Symmetry codes: (i) Àx + 1, Ày + 1, Àz + 1; (ii) Àx + 1, Ày + 1, Àz + 2; (iii) Àx + 2, Ày, Àz + 1.
˚

S. Gao et al. / Inorganic Chemistry Communications 8 (2005) 361–364
363
Fig. 2. Two-dimensional network structure of II with phen and water molecules omitted for clarity.
In the IR spectra of II, the observation of a strong
and broad m(OH) absorption around 3438 cmÀ1 is
coherent with the presence of hydrogen bonds or water
molecules. The masym(OCOÀ) and msym(OCOÀ) absorp-
tions appear in 1606, 1427 and 1332 cmÀ1, respectively,
and the values of D(OCOÀ) suggest there are different
coordinated modes of the carboxylate groups [14].
TG results show that the first weight loss of 3.67%
from 317 to 594 K corresponds to the loss of the lattice
water molecule (Calc. 3.36%), and then the loss steps are
observed continuously with the burning 1,4-BDOA2À
group and 1,10-phen ligand in the range of 594–822 K.
The final residual weight is 23.77% (Calc. 24.01%) corre-
sponding to CdO. This suggests that its skeleton pos-
sesses higher thermal stability.
Fig. 3. The emission spectrum of II measured in solid state at room
temperature.
The fluorescent emission spectrum of II was mea-
sured in solid state at room temperature (as shown in
Fig. 3). Upon photoexcitation at 258 nm, it exhibits
two intense fluorescent emission bands at 483, 419 nm
and one weak fluorescent emission band at 320 nm.
Since free 1,4-BDOAH2 ligand is observed the similar
photoemissions at 316 and 416 nm at the same photoex-
citation condition, the emission bands at 320 and
419 nm come from the intraligand fluorescent emissions
in II. Whereas the strong blue emission, kmax = 483 nm,
may be assigned to the ligand-to-metal-charge-transfer
(LMCT) [15,16]. The II may be a candidate for light
emitting device for its high thermal stability and the
insolubility in many common solvents.
mids are joined by 1,4-BDOA2À ligands with the
unprecedented g1:g1:g1:g1:l2 and g1:g2:g1:g2:l4 modes
to form a lamellar structure. Its skeleton is thermally
stable up to 594 K, and its strong blue fluorescent emis-
sion of kmax = 483 nm shows that it may be promising as
optoelectronic devices. Further study about this subject
is underway and will be reported in a full paper.
Acknowledgements
The authors acknowledge the National Natural Sci-
ence Foundation (No. 20101003), the Scientific Fund
of Remarkable Teachers of Heilongjiang Province
(No. 1054G036) and Heilongjiang University for sup-
porting this work.
In conclusion, a novel cadmium polymer based on
1,4-bdoa2À ligand has been synthesized by the hydro-
thermal reaction, in which CdN2O5 pentagonal bipyra-

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S. Gao et al. / Inorganic Chemistry Communications 8 (2005) 361–364
[8] S. Gao, J.W. Liu, L.H. Huo, H. Zhao, J.G. Zhao, Acta Cryst. C
61 (2004) 25.
Appendix A. Supplementary data
[9] S. Gao, J.W. Liu, L.H. Huo, H. Zhao, J.G. Zhao, Acta Cryst. E
60 (2004) 1308.
Crystal data and structure refinement, atomic coordi-
nates, bond lengths and angles, IR, PL and TG results of
the complex were available from the authors on request.
CCDC Reference No. 220444.
Supplementary data associated with this article can
be found, in the online version at doi:10.1016/
j.inoche.2005.01.020.
ꢀ
[10] Crystal data for C22H18N2O7Cd: triclinic, P1, unit cell para.
˚
˚
˚
a = 9.1880(18) A, b = 10.925(2) A, c = 11.907(2) A, a = 65.23(3)°,
3
˚
b = 75.63(3)°,
c = 89.58(3)°.
V = 1044.9(5) A ,
Z = 2,
Dc = 1.700 g/m3, l = 1.093 mmÀ1, F(000) = 536. Data collections
(3.26 6 h 6 27.30°) were performed at 293 K on RIGAKU
RAXIS–RAPID single X-ray diffractometer (Mo Ka,
˚
k = 0.71073 A) for 1. The structures were solved with direct
methods (SHELXS-97) [11] and refined by full-matrix least
squares (SHELXL-97) [12]. Unique reflections were obtained
from a total of 4619 measured reflections (Rint = 0.0165). Struc-
ture solution and refinement based on 4116 independent reflec-
tions with I > 2r(I ) and 295 parameters gave the final R = 0.0290,
wR = 0.0669 and S = 1.068.
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