Porous barium-organic frameworks with highly efficient catalytic capacity and fluorescence sensing ability

Article abstract of DOI:10.1039/c5ta03680a

The current study describes the first barium-organic framework with permanent porosity, efficient catalytic capacity, and highly selective luminescence sensing of DMSO molecules and metal ions. Single-crystal-to-single-crystal transformations (from comple

Full text of DOI:10.1039/c5ta03680a

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Journal of Materials Chemistry A
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DOI: 10.1039/C5TA03680A
Journal Name
RSCPublishing
ARTICLE
Porous Barium-Organic Frameworks with Highly
Efficient Catalytic Capacity and Fluorescent Sensing
Ability†
Cite this: DOI: 10.1039/x0xx00000x
Fuling Liu,b Yuwen Xu,a Lianming Zhao,a Liangliang Zhang,a Wenyue Guo,a*
Rongming Wang,a and Daofeng Sun*a
Received 00th January 2015,
Accepted 00th January 2015
DOI: 10.1039/x0xx00000x
The current study describes the first bariumꢀorganic framework with permanent porosity,
efficiently catalytic capacity, and highly selective luminescent sensing of DMSO molecule and
www.rsc.org/
metal ions. The singleꢀcrystalꢀtoꢀsingleꢀcrystal transformations (from complex
and ) were used to thermally generate coordinatively unsaturated metal sites (CUSs) as
catalytically active sites (CASs). Complex exhibits efficiently catalytic capacity for the
cyanosilylation of aldehydes and ketones, and the cycloaddition of CO2 and epoxides. To the
best of our knowledge, complex keeps a record among the MOFꢀbased catalysts for the
cyanosilylation of aldehydes and ketones. The generation of Ba2+ CUSs with highly catalytic
activity through SCSC fashion is responsible for the excellent property of , which is further
can highly sense DMSO molecule
1 to complexes
2
3
3
3
3
confirmed by the theoretical calculation. Besides, complex
through fluorescence enhancement.
2
with exposed Mn2+ coordination sites as CASs can efficiently
catalyze the cyanosilyations of benzaldehyde and 1ꢀnaphthaldehyde
to give 98 and 90% yields, respectively. In contrast, for the
cyanosilyations of acetophenone and 1ꢀ(naphthalenꢀ1ꢀyl)ethanone,
the yields are only 28 and 1%, respectively, although the reaction
time extends to 24 hours from 9 hours.11 Besides the effect of steric
hindrance, the reason may derive from the low activity or stability
of the CUSs. Hence, high activity and stability of CUSs are needed
for construction of functional MOFs with highly efficient catalytic
capacity.
Recently, many porous MOFs with catalytic ability by use of
CUSs as catalytically active sites were documented. Most of the
CUSs in the porous MOFs were limited to the first row transition
metals such as Cu2+, Mn2+, Fe3+, Co2+, Ni2+, Cr3+ etc.12,13
Surprisingly, porous materials based on sꢀblock metals (alkali
metals and alkaline earth metals) are relatively less explored14,
which may be due to the lack of predictive coordination behavior
of sꢀblock metal centers.15 Furthermore, it is normally difficult to
form stable or fixed SBUs when sꢀblock metal ions coordinate to
carboxylate ligands. However, these porous MOFs based on sꢀ
block metal ions with CUSs may generate functional materials with
highly efficient catalytic capacity.
Introduction
Porous MOFs with highly thermal stability possess potential
applications in molecular separation, gas storage, catalysis and
sensor devices.1,2 In the past two decades, many porous MOFs with
high surface area were designed and synthesized, and their
application in gas storage/separation was widely and deeply
studied.3,4 The next challenges are to construct porous MOFs with
capacities for heterogeneous catalysis and fluorescence sensor .5,6
As is known, MOFs possess tunable channels/pores and can be
readily introduced specific functional groups acting as catalytically
active sites (CASs).7 For example, though introducing chiral small
molecules as cooperative organocatalytic active sites into a Zn
MOF, Duan et al. developed a new type of catalyst that can prompt
the asymmetric α–alkylation of aliphatic aldehydes in
a
heterogeneous manner.8 Another strategy on generating CASs in an
MOF is to thermally release coordinated solvates on the metal
center to generate coordinatively unsaturated metal sites (CUSs). In
general, the CUSs in an MOF can act as Lewis acid catalyst to
catalyze cyanosilylation of aldehydes and ketones, and some other
organic reactions such as the cycloaddition of CO2 and epoxides.
On the basis of the analysis of the reported results, the “naked”
metal sites in an MOF can efficiently catalyze cyanosilylation of
aldehydes and normally give moderate or high yield.9 However,
low yields are observed for some cyanosilyations of aldehydes with
substituent groups on the central benzene ring. Furthermore, the
yields are much lower for the cyanosilyations of ketones.10 For
instance, a porous MOF based on 1,3,5ꢀbenzenetristetrazolꢀ5ꢀyl
Another potential application of CUSs in porous MOFs is the
fluorescent sensing of small molecules. Recently, much effort has
been made to rational design and synthesis of porous MOFs for
sensing ions and organic molecules. Several recent reviews have
highlighted the exciting and compelling developments in porous
MOFꢀbased chemical sensors.16 In particular, sensing metal ions or
This journal is © The Royal Society of Chemistry 2013
J. Name., 2013, 00, 1-3 | 1

Journal of Materials Chemistry A
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DOI: 10.1039/C5TA03680A
Synthesis of MOFs.
Synthesis of 1: A mixture of Ba(NO3)2 (20 mg, 0.07mmol)
and
4LOMe (3 mg, 0.005mmol) was dissolved in
NMP/DMA/H2O mixed solvents (1 mL, v/v/v 1/1/1). Then,
the solution was sealed in a pressureꢀresistant glass tube,
slowly heated to 130 °C from room temperature in 8 hours,
kept at 130 °C for 50 hours, and then slowly cooled to 30 °C
in 13 hours. The dark red crystals that formed were collected
and dried in the air. (Yield: 57%, based on barium.). Its purity
was confirmed by Xꢀray power diffraction (XRD). Elemental
organic small molecules by porous MOFs with open metal sites or
Lewis basic sites have been documented by Chen, Li and other
groups.17 However, highly selective luminescent sensing of organic
molecules or metal ions by porous MOF based on sꢀblock metals
has been seldom reported so far. In this paper, we describe, for the
first time, the synthesis and singleꢀcrystalꢀtoꢀsingleꢀcrystal
transformation of bariumꢀorganic frameworks with permanent
porosity, efficiently catalytic capacities, and highly selective
sensing of organic molecules and metal ions.
H
Solvothermal reaction of 5,5'ꢀ(2,3,6,7ꢀtetramethoxyꢀanthraceneꢀ
9,10ꢀdiyl) diisophthalic acid (H4LOMe) and Ba(NO3)2 salt resulted
in the formation of a microporous bariumꢀorganic framework,
Ba2(H2LOMe)2(NMP)·NMP (1) with highly thermal stability. When
analysis (%) for 1: Calcd: C 54.40, H 3.86, N 1.63; Found: C
52.62, H 3.85, N 1.50.
heated
[Ba(H2LOMe
crystal transformation. It is interesting to find that the porous
material of can highly sense DMSO molecule through
at
325
oC,
1
can
transform
to
2,
Synthesis of 2: The asꢀsynthesized crystals of
1 were
heated at 325 oC for 20 minutes in the air, then cooled to room
)
0.5(H2O)·4H2O]n, through a singleꢀcrystalꢀtoꢀsingleꢀ
temperature to generate
2. Elemental analysis (%) for 2:
Calcd: C 47.93, H 4.02; Found: C 46.77, H 3.51.
2
fluorescence enhancement. Fortunately, the intermediate (3) of the
transformation from 1 to 2 was captured and characterized by
Capture of the intermediate 3: The crystals of
2 were
o
heated at 127 C for 1 hour to generate the intermediate
3
,
singleꢀcrystal Xꢀray diffraction. Complex
3
exhibits highly
o
which crystal data was collected at 127 C.
3
can only exist at
catalytic ability to the cyanosilylation of aldehydes and ketones, as
well as the cycloaddition of CO2 and epoxides. The existence of
highly active Ba2+ open metal sites in the framework is responsible
for the highly efficient catalytic capacities for 3, which is further
confirmed by the theoretical calculation.
high temperature, and can transform to
air when the temperature decrease to room temperature.
3
2 immediately in the
X-ray Structure Determination and Structure Refinement.
Singleꢀcrystal Xꢀray diffraction for 1 and 2 were performed
using a Bruker Apex II CCD diffractometer equipped with a fineꢀ
focus sealedꢀtube Xꢀray source (Mo Kα radiation), and the crystal
data for 3 was collected on an Agilent Xcalibur Eos Gemini
diffractometer with Enhance (Cu) Xꢀray Source (CuꢀKα, λ =
1.54178 Å). Structures were solved by direct methods using
SHELXTL and were refined by fullꢀmatrix leastꢀsquares on F2
using SHELXꢀ97. Contributions to scattering from all solvent
molecules were removed using the SQUEEZE routine of
PLATON; structures were then refined again using the data
generated. Crystal Date for 1: triclinic, Pꢀ1, a = 9.0362(15) Å, b =
17.484(3) Å, c = 24.772(4) Å, α = 69.717(3)°, β = 84.873(3)°, γ =
82.904(3)°, V = 3638.3(10) Å3; Z= 2; calculated cell density, Dc =
1.481 g cmꢀ3; reflections collected/independent: 18155/12676; Rint
= 0.0834; final R1 = 0.1012, wR2 = 0.2099, GOF = 1.051. Crystal
Date for 2: monoclinic, C2/c, a = 32.24(5) Å, b = 12.209(19) Å, c =
8.885(13) Å, β = 97.56(3)°, V = 3467(9) Å3; Z = 4; calculated cell
density, Dc = 1.494 g cmꢀ3; reflections collected/independent:
7731/2978; Rint = 0.0849; final R1 = 0.1383, wR2 = 0.2241, GOF =
1.013. Crystal Date for 3: monoclinic, C2/c, a = 32.2746(7) Å, b =
12.6358(6) Å, c = 8.9507(2) Å, β = 98.533(2)°, V = 3609.8(2) Å3; Z
= 4; calculated cell density, Dc = 1.402 g cmꢀ3; reflections
Scheme 1. The tetracarboxylate ligand in this work.
Experimental
Materials and Methods
All chemicals and solvents used in the syntheses were of
analytical grade and used without further purification. The ligand
H4LOMe was prepared according to SI (supporting information).
Elemental analyses (C, H, N) were obtained on a PerkinElmer 240
elemental analyzer. The thermogravimetric analysis (TGA) for
complexes 1 and 2 were carried out between room temperature and
600 °C in a static N2 with a heating rate of 10°C/min.
Photoluminescence spectra were measured on Fꢀ280 fluorescence
spectrophotometer. Low pressure (< 800 torr) gas (N2, CO2 and
CH4) sorption isotherms were measured using a Micrometrics
ASAP 2020 surface area and pore size analyzer. 1H NMR spectra
were measured on a Bruker AVANCEꢀ300 NMR Spectrometer.
collected/independent: 12228/3429; Rint = 0.0604; final R1
=
0.0718, wR2 = 0.1625, GOF = 1.046. Crystallographic data for the
structures reported in this paper have been deposited in the
Cambridge Crystallographic Data Center with CCDC reference
numbers 981821, 981822, and 981823 for 1, 2, 3, respectively.
Results and Discussion
Single-Crystal-to-Single-Crystal Transformation.
PAGE 2

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Journal of Materials Chemistry A
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DOI: 10.1039/C5TA03680A
Singleꢀcrystal Xꢀray diffraction study reveals that 1 is a threeꢀ
dimensional porous framework based on a 1D barium rodꢀshaped
SBU. The organic ligand of H4LOMe was partly deprotonated during
the solvothermal reaction. There are two types of barium ions with
different coordination environments: Ba1 is coordinated by eight
oxygen atoms from H4LOMe ligands and one NMP molecule, and
Ba2 is coordinated by eight oxygen atoms from H4LOMe ligands.
Thus, the barium ions are connected by carboxylate groups
generating infinite BaꢀOꢀC rods along [1 0 0] direction with the
nearest BaꢀBa distance of 4.937 Ǻ. In the rodꢀshaped SBU, the
protonated carboxylate groups formed strong hydrogen bonds with
the adjacent deprotonated carboxylate groups to further stabilize
the SBU (Figure 1). The BaꢀOꢀC rods are stacked in parallel and
linked by the backbone of H4LOMe forming two kinds of 1D
channels along a axis with the dimensions of 8.5 × 9.0 Ǻ for
channel A, in which uncoordinated solvates reside, and 8.0 × 11.5
Ǻ for channel B, in which coordinated NMP molecules reside
(Figure 1). The solventꢀaccessible volume of 1 is 21.5 % calculated
with PLATON after the removal of the coordinated NMP
molecules.18 To check the permanent porosity of 1, the freshly
prepared samples were soaked in methanol to exchange the less
volatile solvent, followed by evacuation under a dynamic vacuum
at 90 oC overnight. Desolvated 1 displays typical TypeꢀI adsorption
isotherm with a BrunauerꢀEmmettꢀTeller (BET) surface area of
310.6 m2 gꢀ1, suggesting the retention of the microporous structure
after the removal of solvents from the crystalline samples (Figure
S7ꢀ9). Actually, the crystal structure of the desolvated 1 was also
determined through singleꢀcrystal Xꢀray diffraction (see below).
one aqua ligand, suggesting the coordinated NMP molecule on the
barium in 1 was replaced by water molecule. Furthermore, the
eightꢀcoordinated barium ion in 1 changed to nineꢀcoordination in
2. Thus, the 3D porous framework of complex 2 possesses only one
kind of channel, in which coordinated water molecules reside
(Figure 1d). The solventꢀaccessible volume of 2 is 18.3 %
calculated with PLATON after the removal of the coordinated
water molecules.
Figure 2. The SCSC transformations among 1, 2 and 3. Method 1: crystals
of 1 were immersed into methanol for 2 days, then heated at 360 K and
cooled to R.T. Method 2: crystals of 1 were heated directly to 598 K for 20
minutes, then cooled to R.T.; SCSC represents singꢀcrystalꢀtoꢀsingleꢀcrystal
transformation.
Fortunately, the intermediate of the transformation from 1 to 2
was captured. The coordinated water molecules on the barium ion
in 2 can be removed to generate the intermediate 3 when heated at
400 K. The crystal data for 3 was collected at 400 K and the careful
refinement of the crystal data can give good crystallographic
parameters including R value. Complex 3 possesses the similar
structure with 2, except that the central barium ions in 3 are eightꢀ
coordinated. The solventꢀaccessible volume of 3 is 19.1 %
Figure 1. (a) the coordination mode of the ligand in 1. (b) the 1D rodꢀ
shaped SBU in 1. (c) the 3D open framework of 1 with the coordinated
NMP in a spaceꢀfilling mode. (d) the 3D porous framework of 2 showing
coordinated water molecules in the channels.
calculated with PLATON. Complex
3 only exists at high
temperature. When cooled to room temperature, 3 can transform to
2 again. Thus, complex 3 should be the intermediate between 1 and
2. More interestingly, the coordinated water molecules can lead to
the color change significantly. As shown in Figure 2, the crystal
color of 2 is deep brown, however, after the removal of the
coordinated water molecules to generate 3, the color changed to
yellow (Figure 2), and the transformation is reversible. In the past
Thermogravimetric analysis indicates that the coordinated NMP
o
molecules are completely released before 325 C and 1 can be
o
o
stable up to 400 C. When heated at 325 C for 20 minutes then
cooled to room temperature, 1 can transform to 2 through singleꢀ
crystalꢀtoꢀsingleꢀcrystal transformation. Normally, porous MOFs
possess less thermal stability and when heated at high temperature,
most of them will lose crystalline. The SCSC transformation at
high temperature like complex 1 is quite rare. The crystal system
changes from triclinic for 1 to monoclinic for 2, indicating the
symmetry increases. The central barium ion in 2 is nineꢀ
coordinated by eight oxygen atoms from five H4LOMe ligands and
decades,
although
many
singleꢀcrystalꢀtoꢀsingleꢀcrystal
transformations based on MOFs were reported, the SCSC
transformation including a color change induced by the change in
the metal coordination geometry is still rare.19
Catalytic Property.

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Considering the highly thermal stability and the existence of
Enetry Aldehyde/Ketone Product
1a
Time(h) Yield (%)c
CUSs in 3, the Lewis acidꢀcatalyzed reactions of carbonyl
compounds with cyanide, and the cycloaddition of CO2 and
epoxides were carried out. The freshly prepared sample of 3 was
used for the catalytic test.
2
2
100
100
Cyanosilylation of aldehydes and ketones. Cyanohydrins,
which can be synthesized by cyanosilylation of aldehydes and
ketones, are a class of important organic intermediates for both
biological processes and synthetic chemistry.20 On the basis of
current research, most of porous MOFs with open metal sites can
catalyze the cyanosilylation of benzaldehyde and give high yield,
but for the benzaldehyde with substituent group, low yield can
normally be observed. However, in this work, compound 3 displays
high activity not only in benzaldehyde but also in the derivative of
benzaldehyde. As shown in Table 1, complex 3 shows high activity
in the cyanosilylation of benzaldehyde, and the conversion can
reach completion within 2 h. For some aldehydes with electronꢀ
donating or electronꢀwithdrawing groups (Table 1, entry 2ꢀ7),
almost 100% yields were also reached after 2 h at room
temperature, which outperform some MOF catalysts. For example,
Nd(btc)ꢀMOFs afforded 88% conversion of benzaldehye but only
18% of αꢀnaphthaldehyde.21a As is wellꢀknown, for the
cyanosilylation of ketones,21 the yields were normally lower than
the cyanosilylation of aldehydes due to the steric hindrance and the
lower activity of ketone. For instance, ScꢀMOF, CuꢀDDQ and
CPOꢀ27ꢀMn catalyzed benzaldehyde with high conversions of 90%,
95% and 100%, respectively, however, the conversions of
acetophenone are 55%, 7% and 17%, respectively.21bꢀd Unlike them,
complex 3 also performs excellent activity in the cyanosilylation of
ketones. The yields of some ketones such as acetophenone, pꢀ
2a
3a
2
100
4a
5a
6a
7a
2
2
2
2
100
100
100
100
8b
2
100
9b
2
2
2
100
100
100
10b
11b
methylacetophenone,
parachloroacetophenone,
pꢀ
nitroacetophenone, 4ꢀphenylbutꢀ3ꢀenꢀ2ꢀone, can be obtained almost
100% within 2 h at room temperature (Table 1, entry 8ꢀ12). For
propiophenone and a larger 1ꢀ(naphthalenꢀ1ꢀyl)ethanone, the yields
can still be reached ~100% in 2 h, further indicating the highly
catalytic activity of 3. Moreover, the turnover number (TON) and
the turnover frequency (TOF) for the cyanosilylation of
benzaldehyde can reach 192 and 384 hꢀ1, respectively, which are
much higher than other reported results (Table S3).21 These
excellently catalytic results make complex 3 a record in the
cyanosilylation of aldehydes and ketones among reported MOFꢀ
based catalysts. The catalytic capacity of 3 is even much higher
than polymerꢀsupported metal complexes and SbCl3ꢀbased
catalysts.22 Besides, to demonstrate its recyclability, successive
reactions in 3 were carried out for the cyanosilylation of
benzaldehyde, showing that the yield of benzaldehyde remains at
~100 % without any loss of catalytic activity for three cycles at
least (Figure S10).
12b
2
100
13b
14b
2
2
100
100
[a] Reaction conditions: TMSCN (4 mmol), aldehyde (2 mmol), 3 (7.8 mg,
0.01 mmol), room temperature, under N2. [b] Reaction conditions: TMSCN
(2 mmol), ketone (0.5 mmol), 3 (7.8 mg, 0.01 mmol), room temperature,
under N2. [c] Determined by 1H NMR based on the carbonyl substrate.
Cycloaddition of CO2 and Epoxides. To further explore the
catalytic performances of 3 as Lewis acid, we decided to use the
reaction of the cycloaddition of CO2 and epoxides to form cyclic
carbonates, since CO2 is considered as a cheap Cꢀ1 source for the
preparation of various chemicals and cyclic organic carbonates.23
Recently, porous MOF materials with open metal sites have proved
to be efficiently heterogeneous catalysts for the cycloaddition of
Table 1. Cyanosilylation of a variety of aldehydes and ketones
catalyzed by 3.
PAGE 2

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DOI: 10.1039/C5TA03680A
CO2 and epoxides because these materials can catalyze the
cycloaddition under relative mild condition.24 For instance, MILꢀ68
(In) and MILꢀ68(In)ꢀNH2 demonstrates catalytic activity for
cycloaddition of 2ꢀphenyloxirane with CO2 at 150 °C under 0.8
MPa CO2 pressure within 8 h with yields of 36% and 48%,
adsorption on Baꢀ3, it is found that there is 0.08 |e| transferred from
the adsorbed benzaldehyde molecule to the Baꢀ3 cluster, while the
natural bond orbital (NBO) charge on Ba changes from 1.36 to 1.28
|e| with the formation of the C6H5CHOꢀBaꢀ3 complex. All these
results suggest that the Ba atom in Baꢀ3 serves as a strong Lewis
acid site. Furthermore, due to a positive charge distribution on Ba
atom (1.36 |e|), the adsorption of benzaldehyde on it via the O end
could strengthen the polarization of the aldehyde CꢀO localized
molecular orbitals, and thus lead to a weaker CꢀO covalent bonding
in C6H5CHOꢀBaꢀ3, which is confirmed by the elongation of
aldehyde CꢀO bond from 1.222 Å in free benzaldehyde to 1.230 Å
in C6H5CHOꢀBaꢀ3. Further NBO analysis shows that when
benzaldehyde is adsorbed on the Baꢀ3, the charges on aldehyde O
and C increase to ꢀ0.56 and 0.43 |e| from ꢀ0.53 and 0.39 |e| in free
benzaldehyde, respectively. The apparent increase of positive
respectively.24a
Ni(salphen)ꢀMOF
catalyzed
2ꢀ
(phenoxymethyl)oxirane with CO2 at 80 °C under 2 MPa CO2
pressure over 8 h with yield of 55%.24b However, complex 3
demonstrates highly efficient catalytic activity for reaction of CO2
and epoxides such as 2ꢀphenyloxirane, 2ꢀ(phenoxymethyl)oxirane,
and 2ꢀdecyloxirane and the yields for each reaction are above 80%
over 4 hours at 80 oC under 0.6 MPa CO2 pressure, which are much
higher than the results mentioned above.24 Although several MOFꢀ
based catalysts exhibiting higher yields than that of 3 were
reported,25 these catalytic experiments were run under the
conditions with much higher CO2 pressure and temperature.
Considering the high yields of cycloaddition of CO2 and epoxides
charge on aldehyde
benzaldehyde.
C
favors further cyanosilylation of
under low temperature and pressure, complex
significant advantages on chemical fixation of CO2 and preparation
of cyclic organic carbonates.
3 possesses
Scheme 2. The possible mechanism for the cyanosilylation of
aldehydes and ketones in the case of 3.
Table 2. Yields for 3-catalyzed cycloaddition of CO2 and
epoxides.[a]
Enetry Epoxides
1
Product
Time(h) Yield (%)b
4
80
2
3
4
4
98
89
Table 3. Calculated NBO charges on different atom of
C6H5CHO, Ba-3, and C6H5CHO-Ba-3 (unit of |e|).
Species
C6H5CHO
C1
C6H5CHO
0
Ba-3
C6H5CHO-Ba-3
0.08
0.43
-0.56
1.28
[a] Reaction conditions: substrate (15mmol), TBAB (1 mmol), 3 (15 mg,
0.02 mmol), 80 oC under 0.6 MPa CO2 pressure. [b] Calculated by GC.
0.39
Theoretical Calculation. It is well known that cyanosilylation
of aldehydes and ketones is a class of organic reaction catalyzed by
Lewis acid. In the case of 3, the possible mechanism for the
cyanosilylation reaction is shown in Scheme 2. Considering the
highly efficient catalytic capacity of 3 in the cyanosilylation of
aldehydes and ketones, density functional theoretical (DFT)
calculations were performed based on a cluster model (Baꢀ3) via
the adsorption of benzaldehyde (Figures S11 and Tables S6) to
evaluate the Lewis acid sites in 3. When the benzaldehyde
molecule is adsorbed through the O end, it is located at the Ba top
site with the BaꢀO distance of 2.910 Å. The corresponding
adsorption energy is calculated to be 18.8 kcal/mol, and thus
indicates a strong bonding between benzaldehyde and Baꢀ3. Upon
O1
-0.53
Ba1
1.36
Fluorescencent
Sensing
Properties.
The solidꢀstate
luminescent emission spectra of 1, 2 and H4LOMe were studied at
room temperature (Figure S5, S6). H4LOMe and 1 have slightly
different emissions at 467 and 506 nm upon 270 and 360 nm
excitations, respectively, which can be ascribed to the π*→n or
π*→π electronic transitions. However, the emission spectra of 2 is
at 345 nm upon 230 nm excitation, 122 and 161 nm blue shift
compared to H4LOMe and 1, respectively. In this case, the emission

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of 2 can probably be assigned to metalꢀtoꢀligand charge transfer
(MLCT) or ligandꢀtoꢀmetal charge transfer (LMCT).26
enhancement. In contrast, addition of DMSO molecule to the
toluene emulsion of 1 led to a slight increase of its luminescence
intensity, indicating there is no selectivity to DMSO molecule for 1.
Although detailed study for the mechanism is still needed, the
gradual replacement of coordinated water molecules on the barium
sites by DMSO molecules is crucial to the fluorescence
enhancement.17a
Due to the existence of dimethoxy groups that point toward the
channels and can chelate metal ions,27 the sensing of metal ions by
2 emulsion was also carried out. The freshly prepared sample of 2
was ground and dispersed in DMF solvent to generate 2ꢀDMF
emulsion, into which different metal ions were added. For the
addition of Mg2+, Ca2+, K+ cations, the luminescence intensities
increased slightly, and the opposite results were observed for the
addition of Cd2+, Mn2+, Zn2+ cations. However, the luminescence
intensities decreased significantly upon the addition of Co2+, Pb2+,
Cu2+, and Ni2+ cations, suggesting the selective sensing of these
metal ions through fluorescence quenching (Figure S34,35).
More interestingly, 1 and 2 show different responses to small
organic molecules. Complex 2 can selectively sense DMSO
molecule through fluorescence enhancement, whereas 1 can not. To
examine the potential of 2 for the sensing of small molecules, we
select toluene as the standard emulsion. The asꢀsynthesized sample
of 2 was ground and suspended in toluene solution, and different
organic molecules (DMSO, DMF, methanol, ethanol, 1ꢀpropanol,
2ꢀpropanol, hexane, acetone, dichloromethane, THF, acetonitrile)
were dropwise added. The luminescent properties are recorded and
listed in Figure 3. Interestingly, most of organic molecules have
slight effects on the luminescence intensity, except for DMSO. For
example, with the dropwise addition of methanol,
Conclusions
In conclusion, a microporous bariumꢀorganic framework (1)
based on a new anthraceneꢀfunctionality tetracarboxylic acid was
synthesized and characterized. When heated at 598 K to thermally
release coordinated NMP molecules and cooled to room
temperature, 1 can transform to 2 through a singleꢀcrystalꢀtoꢀ
singleꢀcrystal (SCSC) transformation involving the change of the
coordination number of the central metal ion. Fortunately, the
intermediate (3) of this SCSC transformation was also obtained
when 2 was heated to 400 K. Although complexes 1 and 2 possess
similar structures, they exhibit different luminescent response to
DMSO molecule: 2 can highly sense DMSO molecule through
fluorescence enhancement, whereas 1 cannot. More interestingly,
Complex 3 possesses highly efficient catalytic capacities in the
cyanosilylation of aldehydes and ketones, and the cycloaddition of
CO2 and epoxides due to the existence of Ba2+ CUSs with high
activity, which was confirmed by theoretical simulation. To the
best of our knowledge, there is no report on porous Ba MOFs with
high thermal stability, SCSC transformation, and exhibiting highly
catalytic activity. These results presented here indicate that Ba2+
CUSs may possess high activity to some organic reactions, which
provide a new strategy on design and synthesis of porous materials
with highly efficient catalytic capacity.
Figure 3. (a) Photoluminescence intensities of 2 introduced into various
organic solvents (excited at 380 nm), showing high selectivity to DMSO
molecule. (b) Comparison of the selectivities to DMSO molecule for 1 and
2.
Acknowledgements
This work was supported by the NSFC (Grant Nos. 21001115,
21271117), NCETꢀ11ꢀ0309, the Shandong Natural Science Fund
for Distinguished Young Scholars (JQ201003), and the
Fundamental Research Funds for the Central Universities
(13CX05010A).
ethanol, 2ꢀpropanol, hexane, acetone, dichloromethane, THF,
acetonitrile, the luminescence intensities increase slightly. With the
addition of DMF and 1ꢀpropanol, the luminescence intensities
increase 6 and 4 times, respectively, compared to the original one.
However, addition of DMSO molecule to the toluene emulsion of 2
led to a significant increase of its luminescence intensity, and the
enhancement attained saturation when about 0.7 mL DMSO was
added. The maximum of the luminescence intensity is about 41
times greater than the original one, indicating that 2 exhibits high
selectivity to sensing of DMSO molecule through fluorescence
Notes and References
a
State Key Laboratory of Heavy Oil Processing, China University of
Petroleum (East China), College of Science, China University of
PAGE 2

Page 7 of 8
Journal Name
Journal of Materials Chemistry A
View ArticAle ROnTliInCeLE
DOI: 10.1039/C5TA03680A
Galli, H. J. Choi, G. D. Han, A. Maspero, G. Palmisano, N.
Masciocchi, J. R. Long, Chem. Sci., 2011, , 1311ꢀ1319.
Petroleum (East China), Qingdao, Shandong, 266580, People’s
2
Republic of China. Email: dfsun@upc.edu.cn
;
wyguo@upc.edu.cn
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Journal of Materials Chemistry A
Page 8 of 8
VJieowuArrtnicalelONnlainme e
ARTICLE
DOI: 10.1039/C5TA03680A
Graphical Abstract
Through singleꢀcrystalꢀtoꢀsingleꢀcrystal transformation, highly active Ba2+ open metal sites are achieved in a porous metalꢀorganic
framework, which exhibits efficiently catalytic capacity to the cyanosilylation of aldehydes and ketones and shows excellent fluorescent
sensing of DMSO molecule and metal ions.
PAGE 2