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COMMUNICATION
Cite this: Dalton Trans., 2013, 42, 13335
Received 31st May 2013,
Accepted 19th July 2013
DOI: 10.1039/c3dt51414e
www.rsc.org/dalton
A luminescent metal–organic framework for sensing
methanol in ethanol solution†
Zhao Jin,
a
Hongming He,
a
Huanyu Zhao,
b
Tsolmon Borjigin,
a
Fuxing Sun,
a
Daming Zhang
c
and Guangshan Zhu*
a,b
A new luminescent Zn-MOF has been synthesized under hydro-
thermal condition using a semi-rigid ligand H
3
pcoip (4-(2-
carboxyphenoxy)isophthalic acid) is reported. The luminescence
properties of 1 in methanol, ethanol, and water have been investi-
gated. Interestingly, compound 1 has a unique response to metha-
nol compared to ethanol and water. Moreover, 1 displays a turn-
on switching property triggered by methanol solvent molecules
and a high sensitivity towards methanol concentration as low as
2×10
−7
(V
MeOH
/V
total
) in ethanol solution. The results indicate
that the Zn-MOF has potential application as a sensor for detect-
ing methanol in ethanol solution with excellent selectivity and
high sensitivity.
In the last two decades, porous metal–organic framework
(MOF) materials, which are constructed from metal ions/metal
clusters as nodes and multitopic organic ligands as linkers,
have drawn widespread attention not only because of their
intriguing varieties of architectures and topologies
1–6
but also
owing to their wide range of potential applications in selective
adsorption/separation,
7–9
heterogeneous catalysis,
10–13
light-
emission diodes (LED)
14–17
etc. Among a plethora of porous
frameworks investigated, a large number of luminescent MOFs
have been reported in the literature. However, only a few of
them, which have a specific and detectible change in lumine-
scence when in contact with an analyte, have potential appli-
cation as chemical sensors.
Generally, luminescent MOFs are classified as transition-
metal MOFs and lanthanide-MOFs (Ln-MOFs) according to the
type of metal used. In Ln-MOF systems, an intensity change in
the lanthanide luminescence signal caused by analyte–metal
or analyte–ligand interaction occurs.
18–20
By contrast, many
luminescent transition-metal MOFs exhibit a turn-on switch-
ing property triggered by the analyte.
21–26
Position of their
responsive emission usually changes upon those interactions.
Compared to common luminescence-enhancing/quenching
methods, detection occurring relative to a dark background is
intrinsically more sensitive.
As a very important raw material, ethanol is widely used in
many fields, such as the chemical industry, food industry etc.
Methanol, a cheaper and more easily accessible analogue of
ethanol, sometimes is mixed into ethanol to reduce the cost of
ethanol production, and sometimes it is even used in produ-
cing imitation spirits and wine. But, methanol is an alcohol
toxic to mammals, consumption of the compound will cause
headaches, vomiting, blindness or even worse, which leads to
one of the highest risks to food safety worldwide. Therefore
detection of methanol in ethanol and alcoholic beverages is of
great significance and necessity. Actually, it is hard to differen-
tiate methanol and ethanol because of their similar chemical
and physical properties. Generally, high performance liquid
chromatography,
27
gas chromatography,
28
Raman spectro-
scopy
29
etc. are usually used for detecting methanol. But their
high cost, inconvenience and inefficiency impede their wide
application in daily life. Herein, we report a novel luminescent
transition-metal MOF exhibiting efficient turn-on switching
property triggered by solvent molecules, with fast response,
excellent selectivity and high sensitivity for methanol mole-
cules. To the best of our knowledge, this is the first report of a
luminescent-MOF based sensor displaying such capability.
Colorless crystals of [Zn
3
(cpoip)
2
(4,4′-bpy)
2
·H
2
O] (1)‡ (4,4′-
bpy = 4,4′-bipyridine) have been synthesized by heating a solu-
tion of Zn(NO
3
)
2
·6H
2
O (0.03 g), 4,4′-bpy (0.016 g), H
3
cpoip
(0.03 g), NaOH (0.01 g) and H
2
O (7 mL) at 130 °C. The crystal
structure of 1 is shown in Fig. 1 and S2.† Two adjacent Zn1
atoms linked by four carboxylate groups from four ligands give
a binuclear paddle-wheel unit (Fig. S2a†). The modes of
metal–ligand connectivity at Zn2 and Zn3 are quite similar
and both of them contain tetrahedral Zn centers of which the
† Electronic supplementary information (ESI) available: Details of experimental
results, ORTEP drawing, TGA-DSC, PXRD patterns, luminescence spectrum.
CCDC 891964. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c3dt51414e
a
State Key Laboratory of Inorganic Synthesis & Preparative Chemistry,
Jilin University, Changchun 130012, China. Fax: +86 431-8516-8331
b
Queensland Micro- and Nanotechnology Centre, Griffith University, Nathan,
QLD 4111, Australia. E-mail: g.zhu@griffith.edu.au
c
College of Electronic Science & Engineering, Jilin University, Changchun 130012,
China. Tel: +86 0431-85168097(0)
This journal is © The Royal Society of Chemistry 2013 Dalton Trans., 2013, 42, 13335–13338 | 13335
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