Synthesis, crystal structure, and physical properties of a barium(II) p-(Carboxyl-methyloxy)-benzenecarboxylic acid complex

Article abstract of DOI:10.1002/zaac.201000314

A coordination polymer [Ba(pcmb)(H₂O)_2.5] (1) was obtained by self-assembly of the corresponding metal carbonate with a flexible ligand, p-(carboxyl-methyloxy)-benzenecarboxylic acid (H₂pcmb), and its structure was determined by single-crystal X-ray diffraction studies. The result revealed that complex 1 has a three-dimensional structure, in which the barium(II) atom takes a distorted eight-coordinate bicapped anti-prism arrangement. The pcmb^2- anion acts as a μ₄-bridge ligand, in which carboxylate groups adopt monodentate and μ₃- ν²:ν¹-bridging two different coordination models to generate a three-dimensional network structure. The luminescence property and thermal stability of 1 were investigated. Copyright

Full text of DOI:10.1002/zaac.201000314

ARTICLE
DOI: 10.1002/zaac.201000314
Synthesis, Crystal Structure, and Physical Properties of a Barium(II) p-
(Carboxyl-methyloxy)-benzenecarboxylic Acid Complex
[a]
[b]
[b]
[b]
Xiao-Feng Wang, Li Yu, Hao Wei, and Gang Wu*
Keywords: Barium; Crystal structure; Luminescence; Thermal stability; Benzene carboxylic acid
Abstract. A coordination polymer [Ba(pcmb)(H
tained by self-assembly of the corresponding metal carbonate with a acts as a μ
flexible ligand, p-(carboxyl-methyloxy)-benzenecarboxylic acid entate and μ
pcmb), and its structure was determined by single-crystal X-ray erate a three-dimensional network structure. The luminescence prop-
2
O)2.5] (1) was ob- eight-coordinate bicapped anti-prism arrangement. The pcmb2– anion
-bridge ligand, in which carboxylate groups adopt monod-
4
2
1
3
-η :η -bridging two different coordination models to gen-
(H
2
diffraction studies. The result revealed that complex 1 has a three- erty and thermal stability of 1 were investigated.
dimensional structure, in which the barium(II) atom takes a distorted
Introduction
tion compounds have received considerable interest recently
because of their ability to form bonds with oxygen donors,
large radius, various coordination modes, and potential appli-
cations of complexes in several possible applications in lumi-
Metal-organic coordination polymers with specific properties
have attracted enormous interest because of their intriguing
structural motifs and potential applications as functional
[19]
nescent and electronic devices.
material,[
1–5]
such as catalysts,
[3]
optical,
[6]
and magnetic
Herein, we report the synthesis and structural characteriza-
components.[ The final structures and properties of resultant
products are frequently influenced by many factors, such as
coordination preferences of the metal cations, nature of the
ligands, counterions in the system, reaction temperature, sol-
vents, etc,[ but they are mainly affected by the strong coordi-
native bonds between the metal ions and ligands. So the correct
choice of metal atoms and the design of the ligands play deci-
sive roles.
7]
tion of a three-dimensional (3D) coordination polymer,
2–
[
Ba(pcmb)(H O) ] (1), where pcmb is a flexible ligand [p-
2
2.5
(
carboxyl-methyloxy)-benzenecarboxylate] (see Scheme 1)
and luminescent property and thermal stability of complex 1
8]
were investigated.
In the latest decade years, a large number of complexes
synthesized through metal ions and rigid aromatic carboxylate
ligands have[ been reported, such as 1,3,5-benzene-
9–11]
tricarboxylate,
4,4',4''-benzene-1,3,5-triyl-tribenzoic acid
[
12]
[13–15]
(
H btb), 1,4-benzenedicarboxylic acid (p-H bdc),
1,3-
3
2
[16]
2
Scheme 1. Synthesis of ligand H pcmb.
benzenedicarboxylic acid (m-H bdc),
and 1,2,4,5-benzene-
However, coordination poly-
2
[
17]
tetracarboxylic acid (H btec).
4
mers assembled by metal salts with flexible carboxylate-con-
taining ligands are not well done to now, possibly due to the
difficulties in predicting the resulted framework structures.
On the other hand, alkaline-earth-metal-containing coordina-
[18]
Experimental Section
Materials and General Methods
All reagents commercially available were of reagent grade and used
without further purification. Solvents were purified according to the
standard methods. C, H elemental analyses were carried out with a
Perkin–Elmer 240C elemental analyzer. Infrared spectra were recorded
with a Vector22 FT-IR spectrophotometer by using KBr pellet in the
range 4000–400 cm . The fluorescence spectra were recorded with a
Cary Eclipse 300 spectrofluorimeter at room temperature with a xenon
arc lamp as the light source in DMF (N,N-dimethylformamide). In the
measurements of the emission and excitation spectra, the pass width
is 5.0 nm. Thermogravimetric analyses (TGA) were carried out with a
SDT Q600 instrument under 100.0 mL·min–1 flowing nitrogen, and
*
Dr. G. Wu
Fax: +86-0550-3511055
E-Mail: wugangczu@163.com
[
a] Biochemistry & Environment Engineering College
Xiao Zhuang University
Nan Jing 211171, P. R. China
–1
[
b] Department of Chemistry and Life Science
Chu Zhou University
An Hui Province
Chu Zhou 239012, P. R. China
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201000314 or from the
author.
Z. Anorg. Allg. Chem. 2011, 637, 289–292
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
289

X.-F. Wang, L. Yu, H. Wei, G. Wu
ARTICLE
increase the temperature at a rate of 20 °C·min from 30 to 1200 °C. 97.[20, 21] The non-hydrogen atoms were refined anisotropically, and
–1
1
H NMR was carried out with a Bruker Avance 300 spectrometer.
hydrogen atoms isotropically. A summary of the crystallographic data
and structure refinement results for complex 1 are given in Table 1.
Selected bond lengths and angles with their estimated standard devia-
tions are listed in Table 2.
X-ray Crystallography
A suitable single crystal of the as-synthesized compound 1 was care- Crystallographic data for the structure of complex 1 in this paper have
fully selected under an optical microscope and glued to a thin glass been deposited with the Cambridge Crystallographic Data Centre as sup-
fiber with epoxy resin. The data were collected with a Bruker Smart plementary publication no. CCDC-787389. Copies of the data can be ob-
Apex II CCD diffractometer equipped with a graphite monochromatic tained free of charge on application to CCDC, 12 Union Road, Cambridge
Mo-K
α
(λ = 0.71073 Å) radiation for data collection using ω scan CB2 1EZ, UK (Fax: +44-1223-336-033; E-Mail: deposit@ccdc.cam.ac.uk;
mode at 296(2) K. The structure was solved by direct methods and http://www.ccdc.cam.ac.uk/conts/retrieving.html).
2
refined on F by full-matrix least-squares techniques using SHELXTL
Preparation of the Ligand and Complex 1
Table 1. Crystallographic data and refinement results for complex 1.
p-(Carboxyl-methyloxy)benzenecarboxylic Acid (H pcmb): The li-
2
gand H
2
pcmb was prepared by a similar method as reported for the
Formula
9
C H11BaO7.50
[22]
preparation of 1,3,5-tris(carboxymethoxyl)benzene.
chloroacetic acid (12.29 g, 130 mmol) and K CO (9.67 g, 70 mmol)
in DMF (30 mL) was stirred 1 h at room temperature. Afterwards, a
mixture of p-hydroxybenzoic acid (18.0 g, 130 mmol) and K CO
9.67 g, 70 mmol) in DMF (30 mL) (stirred for 1 h) was added. The
A mixture of
Formula weight
376.52
C2/c
2
3
Space group
Crystal system
monoclinic
26.0856(16)
11.9296(7)
7.6285(5)
90.00
2
3
a /Å
b /Å
c /Å
α /°
β /°
γ /°
(
mixture was further stirred for 12 h at 74–78 °C. After evaporation of
DMF under vacuum, the mixture was dissolved in water. Afterwards,
concentrated sulfuric acid was added slowly to the aqueous solution
until pH = 3 under ice bath condition. The product p-(carboxyl-methy-
loxy)benzenecarboxylic acid was obtained by filtration and washed
with water till sulfate anions were removed completely, and dried in
vacuo to give a pale powder in 43 % yield based on p-hydroxybenzoic
acid (10.99 g, 56.04 mmol). IR (KBr): ν˜ = 1735 s, 1618 s, 1583 m,
100.250(3)
90.00
3
V /Å
2336.0(3)
8
Z
T /K
λ /Å
296(2)
0.71073
2.141
–
3
Dc /g·cm
F(000)
–
1
1
1
548 s, 1435 m, 1267 m, 1173 s, 903 w, 813 w cm . H NMR
1448
–
1
(500 MHz, D O): δ = 8.11 (d, 2 H); 6.79 (d, 2 H); 4.56 (s, 2 H). The
2
μ /mm
3.426
melt point of recrystallized ligand is 274.1–274.5 °C.
R
int
0.0233
2688
unique reflns
[
Ba(pcmb)(H
and H pcmb (19.6 mg, 0.1 mmol) was dissolved in H
5:1) (6 mL) at room temperature. The mixture was heated to boil for
0 min, and filtered off. The filtrate was left to stand at ambient tem-
perature for one week. Platelet colorless crystals were obtained (Yield
)2|1/2, where w = 12.9 mg). C
11BaO7.50: calcd.: C 28.71; H 2.94 %; found: C 28.65;
H 3.02 %. IR (KBr): ν˜ = 3369 (bs), 1606 s, 1594 s, 1541s, 1507 m,
2
O)2.5] (1): A mixture of BaCO
3
(19.7 mg, 0.1 mmol)
obsd reflns
2456
parameters
179
2
2
O/DMF (v/v:
a)
R
1
wR
(all data)
0.0193
0.0419
1.054
2
(all data)
1
2
Goodness of fit on F
a) R = Σ||F
o
|–|F
c
||/Σ|F
o
|
;
wR = |Σw(|F
o
)/3.
|2–|F
c
|2)|/Σ|w(F
o
9
H
2
2
2
2
2
1
/[σ (F
o
)+(aP) +bP]. P = (F
o
+2F
c
Table 2. Selected bond lengths /Å and angles /° for complex 1.
Ba1–O(1)
2.7038(17)
2.7144(15)
2.7356(14)
2.9579(14)
90.19(7)
Ba1–O8
2.7119(17)
2.7319(18)
2.7889(9)
3.0075(14)
97.37(5)
94.15(6)
145.00(5)
76.05(5)
114.79(6)
151.25(6)
77.71(6)
147.02(5)
79.45(4)
67.74(5)
86.79(5)
69.17(4)
56.20(4)
121.32(4)
Ba1–O4#1
Ba1–O6
Ba1–O5#2
Ba1–O5#3
Ba1–O7
Ba1–O3#2
O1–Ba1–O8
O8–Ba1–O4#1
O8–Ba1–O6
O1–Ba1–O5#2
O1–Ba1–O4#1
O1–Ba1–O6
136.68(5)
75.92(6)
O6–Ba1–O4#1
O8–Ba1–O5#2
O6–Ba1–O5#2
O8–Ba1–O7
142.96(5)
72.46(4)
#
1O4–Ba1–O5#2
O1–Ba1–O7
80.46(4)
O7–Ba1–O4#1
O7–Ba1–O5#2
O8–Ba1–O5#3
O6–Ba1–O5#3
O7–Ba1–O5#3
O8–Ba1–O3#2
O6–Ba1–O3#2
O7–Ba1–O3#2
71.83(5)
O6–Ba1–O7
126.27(4)
114.78(6)
73.09(5)
O1–Ba1–O5#3
#1O4–Ba1–O5#3
#2O5–Ba1–O5#3
O1–Ba1–O3#2
#1O4–Ba1–O3#2
#2O5–Ba1–O3#2
#3O5–Ba1–O3#2
67.27(3)
68.77(5)
144.68(5)
136.83(5)
Symmetry transformation used to generate equivalent atoms: #1: –x+1/2, y+1/2, –z+3/2; #2: –x+1/2, –y+3/2, –z+2; #3: x–1/2, –y+3/2, z+1/2.
2
90
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© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2011, 289–292

A Barium(II) p-(Carboxyl-methyloxy)-benzenecarboxylic Acid Complex
1
1
7
440 m, 1424 s, 1382 s, 1342 m, 1228 m, 1172 m, 1139 w, 1063 m, C4, C5, C6, C7, and O3 and C7, O1, and O2 amounts 11.6°,
–1 1
017 w, 856 m, 786 m, 672 m cm . H NMR (500 MHz, D
2
O): δ =
and between planes C7, O1, and O2 and O3, O4, O5, C8, and
C9 it amounts 10.4°, which means that the carboxymethyl and
carboxyethyl groups are not co-planar.
.8 (d, 2 H); 7.0 (d, 2 H); 4.56 (s, 2 H). The complex is decomposed
at 447 °C.
Complex 1 is a 3D coordination polymer, in which pcmb2–
acts as μ -bridge ligand coordinating barium(II) ions, in which
Supporting Information (see footnote on the first page of this article):
TGA curve of the ligand H
4
1
pcmb, H NMR spectrum of complex 1.
the carboxymethyl group adopts a monodentate mode coordi-
nating to one barium atom, while the oxy-carboxyethyl group
2
2
1
adopts a μ -η :η -bridging (namely one oxygen atom of the
3
Results and Discussion
carboxylate connects two metal ions, the other one connects
one metal ion, and the carboxylate group coordinates to three
metal ions) coordination model connecting three barium(II) at-
oms. The oxygen atoms of ether, oxy-carboxyethyl group, and
μ2-water molecule (O7) coordinate to four different barium(II)
atoms form a one-dimensional chain with channel. Further, the
pcmb2– anions connect these one-dimensional chains to give
rise to three-dimensional coordination polymer (Figure 2).
Compound 1 is stable in air. It is moderately soluble in water
and DMF but almost insoluble in common organic solvents. In
this complex, structure analyses shows that all carboxyl groups
of 4-carboxymethoxy-benzoic acids are deprotonated, which is
in good agreement with the IR spectroscopic data since no
strong bands around 1700 cm–1 for –COOH were observed.
A summary of crystal data, intensity measurements, structure
solution, and refinement is collected in Table 1.
As shown in Figure 1, the asymmetric unit consists of one
crystallographically independent barium(II) ion, one pcmb2–
anion and 2.5 coordinated H O molecules. The barium(II)
2
atom is octacoordinated by eight oxygen atoms. Among them,
2–
five oxygen atoms are from four different pcmb ligands, the
others are from three water molecules. It is expected that the
oxygen atom (O3) of the ether bond participates in the coordi-
2
+
nation with Ba with a distance of 3.0075(14) Å, which is the
longest among of eight Ba–O distances. The O–Ba–O coordi-
nation angles vary from 56.20(4)° to 151.25(6)° (see Table 2).
One of three water molecules (O7) acts as a μ -didenate ligand,
2
which coordinates with two different barium(II) atoms The co-
ordination arrangement around the barium(II) atom is a dis-
torted bicapped anti-prism (Figure 1). Two groups of Ba–O
distances can be observed: 270–279 pm and 296–301 pm, sim-
ilar to other related Ba–O distances. The longer distance of
the last group is perhaps owing to steric restrictions and miss-
ing electrostatic attractions for the ether unit.
Figure 2. Crystal packing diagram for 1.
[23]
Luminescence of Complex 1
The luminescence of complex 1 was investigated at room
temperature in DMF (N,N-dimethylformamide). The emission
Figure 1. . The ORTEP view of coordination environment of the ba-
rium(II) atom in 1 with 50 % probability displacement, the hydrogen
atoms omitted for clarity (Ba1A: x+1/2, –y+3/2, z–1/2; Ba1B: –x+1/2,
y+3/2, –z+5/2; O3A: –x+1/2, y+3/2, –z+5/2; O4A: x, –y, z+1/2; O5A: –
x+1/2, y+3/2, –z+5/2; O5B: x–1/2, –y+3/2, z+1/2).
The atoms C1, C2, C3, C4, C5, C6, C7, and O3 lie in a plane
with a mean deviation of 0.0025 Å. The atoms O3, O4, O5,
C8, and C9 are located in another plane with a deviation of
Figure 3. Emission and excitation spectra of complex 1 in DMF at
0.0006 Å. The dihedral angle between the planes C1, C2, C3, room temperature.
Z. Anorg. Allg. Chem. 2011, 289–292
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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291

X.-F. Wang, L. Yu, H. Wei, G. Wu
ARTICLE
spectrum is shown in Figure 3. It is obvious that complex 1 Acknowledgement
exhibits narrow radiation emission maxima at 528 nm upon
photo excitation at 210 nm. To ascertain the adscription of The authors are grateful to the University Science Foundation of An
Hui Provience (Grant No. KJ2009B104) and The Applied Chemistry
emission spectra, the photoluminescence of pure H pcmb and
2
Key Constructing Subject of Anhui Province (No. 200802187C) for
solvent DMF were measured under the same conditions. How-
financial support of this work.
ever, the free H pcmb ligand displays weak emission maxima
2
at 528 nm, DMF exhibits an emission peak at 406 nm. Such
fluorescence behavior suggests that the emission of complex 1
is mainly attributed to π–π* or n–n* intraligand fluorescence.
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The complex 1 could be a good photoactive material because
of its colorlessness.
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Received: August 11, 2010
Published Online: October 21, 2010
Figure 4. TG / DTA curve of 1.
2
92
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© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2011, 289–292