Titanium-oxo-clusters with dicarboxylates: Single-crystal structure and photochromic effect

Article abstract of DOI:10.1021/ic301092b

Two titanium-oxo-clusters Ti₆O₄(o-BDC) ₂(o-BDCⁱPr)₂(OⁱPr)₁₀ (1) and Ti₆O₃(o-BDC)₂(OⁱPr)₁₄ (2) (BDC = benzene dicarboxylate) were prepared by one-step in situ solvothermal synthesis. The compounds are the rare examples of the dicarboxylate-substituted titanium-oxo-clusters. Their crystal structures are successfully measured by single-crystal X-ray analysis. The Ti₆ oxo-clusters of 1 and 2 are constructed by two dual corner-missing cube subunit, Ti₃O₃. The two subunits are linked by double μ₃-O bridges for 1 and single μ₂-O bridge for 2, respectively, and the latter is a new type of carboxylate substituted titanium-oxo-cluster. A photochromic effect was observed upon irradiation of the crystals in the presence of alcohol. The light irradiation changed the color of the crystals from transparent to purple-gray. The Ti(III) signal was detected after the irradiation, and when the sample was exposured in air, superoxide diatomic O₂^·- radical was found. Photodegradation of the methyl orange in aqueous dispersions of microcrystals of the cluster 2 was carried out under UV cut white light with the assistance of H ₂O₂.

Full text of DOI:10.1021/ic301092b

Article
pubs.acs.org/IC
Titanium−oxo−Clusters with Dicarboxylates: Single-Crystal Structure
and Photochromic Effect
Yin-Yin Wu,† Wen Luo,† Yu-Hong Wang,† Ya-Yang Pu,† Xiang Zhang,† Li-Sheng You,† Qin-Yu Zhu,*,†,‡
and Jie Dai*,†,‡
†Department of Chemistry & Key Laboratory of Organic Synthesis of Jiangsu Province, Soochow University, Suzhou 215123,
People’s Republic of China
‡State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, People’s Republic of China
S
* Supporting Information
ABSTRACT: Two titanium-oxo-clusters Ti6O4(o-BDC)2(o-
BDCiPr)2(OiPr)10 (1) and Ti6O3(o-BDC)2(OiPr)14 (2) (BDC = benzene
dicarboxylate) were prepared by one-step in situ solvothermal synthesis.
The compounds are the rare examples of the dicarboxylate-substituted
titanium-oxo-clusters. Their crystal structures are successfully measured
by single-crystal X-ray analysis. The Ti6 oxo-clusters of 1 and 2 are
constructed by two dual corner-missing cube subunit, Ti3O3. The two
subunits are linked by double μ3−O bridges for 1 and single μ2−O bridge
for 2, respectively, and the latter is a new type of carboxylate substituted
titanium-oxo-cluster. A photochromic effect was observed upon
irradiation of the crystals in the presence of alcohol. The light irradiation changed the color of the crystals from transparent
to purple-gray. The Ti(III) signal was detected after the irradiation, and when the sample was exposured in air, superoxide
diatomic O2• − radical was found. Photodegradation of the methyl orange in aqueous dispersions of microcrystals of the cluster 2
was carried out under UV cut white light with the assistance of H2O2.
the sample using powder X-ray diffraction (XRD) data by a
direct method.
INTRODUCTION
■
Nanostructural titanium dioxide has been widely used as a
photocatalyst for solar energy conversion and environmental
applications, because of its low toxicity, abundance, high
photostability, and high efficiency.1 The titanium oxo-clusters,
as the model of the bulk nanoscale titanium oxides, offer the
opportunity to understand the information of the bulk
nanoscale oxides in terms of both atomic structure and
chemical reactivity.2,3 The titanium-oxo-clusters
[TinOm(OR)x(L)y] exhibit rich variations in structural types
characterized by the different coordination modes of the ligands
(O, OR, and L), in linkages of the coordination polyhedra, in
degrees of condensation O/Ti, and in coordination numbers of
titanium atoms, which have been reviewed recently by Rozes.4
The carboxylate-substituted titanium oxo-clusters constitute
an important subclass of titanium-oxo-clusters whose nuclearity
varies from 2, [Ti2O(OiPr)2-(HOiPr)2(OOCCCl3)4],5 to 28,
[Ti28O40(OtBu)20(OOAc)12].3 The hydrolytic stability of the
carboxylate-coordinated titanium oxo-alkoxy clusters is higher
than that of the pure titanium oxo-alkoxy clusters. About 20
monocarboxylates have been used for the synthesis of the
carboxylate-coordinated titanium−oxo clusters
[TinOm(OR)x(OOCR′)y], but no crystal structure with
dicarboxylate has been reported for such clusters, except
Ti8O8(OH)4(O2C−C6H4−CO2)6, which is a recently reported
titanium−oxo− hydroxy cluster with dicarboxylate linkers.6
However, only microcrystalline sample of the compound was
obtained, and the crystal structure was solved by ab initio on
We successfully introduced phthalic acid (benzene dicarbox-
ylate acid, H2BDC) into titanium−oxo clusters and got two
new compounds, Ti6O4(o-BDC)2(o-BDC-iPr)2(OiPr)10 (1) and
Ti6O3(o-BDC)2(OiPr)14 (2), in large single crystals, by one step
in situ solvothermal synthesis. Crystal structures of such
dicarboxylate clusters are first obtained by single-crystal
analysis. Moreover, the crystals showed a reversible photo-
chromic behavior in the presence of alcohol, and Ti(III) signal
was detected after irradiation. In the presence of oxygen, back-
oxidation of titanium(III) ions into titanium(IV) can be
associated with the reduction of molecular oxygen into
• −
superoxide diatomic O2
radical. Photodegradation of the
Methyl Orange with the assistance of tiny amount of H2O2 in
aqueous dispersions of microcrystals of the cluster 2 is
investigated.
EXPERIMENTAL SECTION
■
General Remarks. All analytically pure reagents are
purchased commercially and used without further purification.
The IR spectra are recorded as KBr pellets on a Nicolet Magna
550 FT-IR spectrometer. Elemental analyses of C and H are
performed using a VARIDEL III elemental analyzer, while the
Ti contents are determined by titration using Al-NH4Fe(SO4)2
Received: May 24, 2012
© XXXX American Chemical Society
A
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method. Solid-state room-temperature optical diffuse reflec-
tance spectra of the microcrystal samples are obtained with a
Shimadzu Model UV-3150 spectrometer. Room-temperature
XRD data are collected on a D/MAX-3C diffractometer using a
Cu tube source (Cu Kα, λ = 1.5406 Å). Solid-state ESR spectra
are recorded by an EMX-10/12 spectrometer at 110 K.
Thermal analysis is conducted on a TGA-DCS 6300 micro-
analyzer. The samples are heated under a nitrogen stream of
100 mL min−1 with a heating rate of 20 °C min−1.
Table 1. Crystal Data and Structural Refinement Parameters
for 1 and 2
1
2
formula
Fw
cryst size (mm3)
cryst syst
space group
a (Å)
C68H100O30Ti6
1684.88
C174H318O75Ti18
4471.91
0.50 × 0.50 × 0.30
monoclinic
P21/n
0.40 × 0.38 × 0.25
triclinic
P1
̅
Synthesis of Ti6O4(o-BDC)2(o-BDC-iPr)2(OiPr)10 (1).
Analytically pure Ti(OiPr)4 (0.1 mL, 0.26 mmol) and phthalic
acid (0.03 g, 0.18 mmol) are mixed in 0.5 mL anhydrous
toluene. The mixture is placed in a thick Pyrex tube (0.7 cm
diameter, 18 cm length) and quickly degassed by argon. The
sealed tube is heated under autogenous pressure at 100 °C for 6
days to yield colorless rhombus crystals (32% yield based on
Ti(OiPr)4). The crystals are rinsed with toluene, and dried. The
compound is preserved under dark and dry environment. Anal.
Calcd for C68H100O30Ti6 (MW 1684.88): C, 48.48; H, 5.98; Ti,
17.05. Found: C, 47.90; H, 5.63; Ti, 17.63. Important IR data
(KBr, cm−1): 2970(s), 2930(m), 1736(s), 1568(s), 1475(s),
1271(m), 1130(vs), 1007(s), 947(w), 854(m), 563(s), 511(m).
Synthesis of Ti6O3(o-BDC)2(OiPr)14 (2). Analytically pure
Ti(OiPr)4 (0.1 mL, 0.26 mmol), and phthalic acid (0.03 g,
0.018 mmol) are mixed in 0.5 mL of anhydrous isopropanol.
The mixture is placed in a thick Pyrex tube (0.7 cm diameter,
18 cm length) and quickly degassed by argon. The sealed tube
is heated under autogenous pressure at ∼100 °C for 6 days to
yield colorless hexagonal prism crystals (40% yield based on
Ti(OiPr)4). The crystals are rinsed with isopropanol, and dried.
The compound is stable and preserved under dark and dry
environment. Anal. Calcd for C58H106O25Ti6 (MW 1490.74):
C, 46.73; H, 7.17; Ti, 19.27. Found: C, 46.48; H, 7.36; Ti,
20.01. Important IR data (KBr, cm−1): 2970(m), 2930(w),
2862(w), 1525(m), 1489(w), 1413(vs), 1121(m), 1012(s),
952(m), 855(w), 593(m), 486(w).
X-ray Crystallographic Study. The measurement is
carried out on a Rigaku Mercury CCD diffractometer at low
temperature with graphite-monochromated Mo Kα (λ =
0.71075 Å) radiation at 223 and 192 K. X-ray crystallographic
data for all the compounds are collected and processed using
CrystalClear (Rigaku).7 The structures are solved by direct
methods using SHELXS-97 and the SHELXS-97 program, and
the refinement is performed against F2 using SHELXL-97.8 All
the non-hydrogen atoms are refined anisotropically. The
hydrogen atoms are positioned with idealized geometry and
refined with fixed isotropic displacement parameters. Relevant
crystal data, collection parameters, and refinement results can
be found in Table 1.
10.9658(12)
13.3174(14)
15.1216(15)
95.939(2)
102.390(2)
107.205(2)
2027.1(4)
1
171044(10)
39.111(2)
34.202(2)
90.00
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
90.244(2)
90.00
22880(2)
4
ρcalcd (g cm−3
)
1.380
1.298
F(000)
880
9432
μ (mm−1
T (K)
Rint
)
0.640
0.666
223(2)
193(2)
0.0335
0.0735
reflns collected
unique reflns
observed reflns
no. params
19526
106645
9131
40004
7303
28578
482
2486
restraints
30
10
GOF on F2
1.010
1.123
a
R1[I > 2σ(I)]/R1
0.0603/0.0792
0.1581/0.1743
0.0892/0.1272
b
wR2[I > 2σ(I)]/wR2
0.1329/0.1503
a
b
2
2
2
1/2
2
2
R1 = ||Fo| − |Fc||/∑|Fo|. wR2 = {[w(Fo − Fc ) ]/w(Fo ) ]}
.
RESULTS AND DISCUSSION
Synthesis. Compounds 1 and 2 are obtained as colorless
■
crystals by a similar solvothermal technique. The experimental
conditions are optimized in order to obtain single crystals with
high quality. By carefully selecting the mole ratio and the
volume of the solvents, bulky crystals of the clusters crystallize
directly from the reaction mixtures after a few days. Most
carboxylate-substituted titanium(IV)-oxo- clusters were ob-
tained by mixing Ti(OR)4 and the corresponding acid, and the
solutions were refluxed or solvothermal treated, but usually the
excessive solvent must be removed slowly under inert
atmosphere for the crystallization. Only a few examples were
reported that the single crystals could be obtained directly from
the solvothermal systems: [Ti4O(OEt)15(ZnCl)] (from ref 9)
and [Ti28O40(OtBu)20(OAc)12] (from ref 3). The in situ crystal
growth using titanium(IV) isopropoxide, [Ti(OiPr)4], is better
than that using titanium(IV) n-butyloxide, [Ti(OnBu)4], in this
case, due to the high hydrolysis tendency of [Ti(OiPr)4]. The
production of water allows a controllable growth of carboxylate-
substituted oxo clusters by hydrolysis of OR groups. Temper-
ature has an important role in the preparation of the
compounds and should not be too high. No crystalsonly
clear liquidare obtained when the temperature is higher than
100 °C or the reaction time is prolonged.
Photochemical Degradation of Dye. A 70-W halogen
lamp, positioned 15 cm over the surface of the reaction
solution, is employed as light source. A UV cutoff filter
(Kenko) is used to eliminate radiation at wavelengths below
420 nm and to ensure illumination by visible light only. The
aqueous dispersions of catalysts are prepared by addition of 22
mg 2 to 30 mL aqueous solutions containing the dye of Methyl
Orange (MO). Prior to irradiation, the suspensions are
magnetically stirred in the dark for ca. 1.0 h to ensure the
establishment of adsorption/desorption equilibrium of dye on
the surface of the microcrystals. The dispersions are added
H2O2 (3%, 150 μL) before irradiation. At given time intervals, 2
mL of aliquots are sampled, centrifuged, and then the supernate
are analyzed by recording variations of the absorption spectra.
In a general way, ester was observed by the reaction of
Ti(OR)4 with more than one molar equivalent of carboxylic
acid.4 For a dicarboxylic acid, using more than half one molar
equivalent of the acid in the reaction results in the formation of
carboxylate ester, a product of competing reactions. The
fundamental reactions of Ti(OR)4 with Ph(COOH)2 (BCD)
can be found in the Supporting Information. Compound 1 is a
B
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good example of reaction system, in which carboxylate ester is
characterized crystallographically (see the structural section).
To further characterize the bulk samples of 1 and 2, IR, XRD,
TGA, and optical diffuse-reflection spectrum are carried out.
The XRD patterns of the powder microcrystals are in
agreement with that simulated from the data of single-crystal
analysis (see Figure S1 in the Supporting Information). For
each compound, the FTIR stretches of the BDC acid (1568 and
1432 cm−1 for 1, and 1556 and 1413 cm−1 for 2) indicate the
chelating coordination of the carboxyl group. Isopropoxy
groups are detected by the νC−H (between 2970 cm−1 and
2850 cm−1) and νTi−O−C (1013 cm−1 and 1007 cm−1)
vibrations. The bands below 720 cm−1 are attributed to the
Ti−O vibrations (see Figure S2 in the Supporting Informa-
tion). The bands at 1735 and 1271 cm−1 for 1 are assigned to
the CO and C−O−C characteristic bands of the ester group
of o-BDC-iPr that is absent in the spectrum of 2. The TGA
results are also given in the Supporting Information (Figure
S3).
1.847(3) Å, shorter than the former. The Ti−O distances of the
μ3−O bridges at the Ti3O3 clusters in 1 and 2 are comparable
to each other. The remainder sites of the structures are
compensated by OiPr and carboxylate groups. Important Ti−O
bond lengths and angles are listed in Tables S1 and S2 in the
Supporting Information). Besides the difference in central μ−O
bridges, the coordination number of the titanium(IV) in
compound 1 is also different from that in 2. Figure 2 illustrates
Structures of Compounds 1 and 2. The ball−stick plots
of the cores of 1 and 2 are shown in Figure 1 (the isopropane
Figure 2. Clusters of (a) 1 and (b) 2, illustrating the coordination
polyhedra of each Ti and the coordination of BDC.
the coordination polyhedra of each Ti in 1 and 2 and the
coordination of BDC. The coordination spheres of six Ti are all
octahedral in 1, but four octahedral and two bipyramidal in 2.
All the o-BDC are in bridging modes that two of the
carboxylate groups coordinate to different Ti3 subunits, while
two mono-esterified o-BDC in 1 only act as monocarboxylate
coordinating at two sides of the Ti6 cluster. All the bridging
modes of the o-BDC in 1 and 2 are asymmetrical. As an
example, in compound 1, one carboxylate group bridges Ti1
and Ti3, and the other bridges Ti1 and Ti2 of the Ti3O3
subcluster (Figure 3).
The skeletal arrangements of known Ti6 carboxylate
substituted oxo-clusters are shown in Figures 4a−c, except
the hexaprism of [Ti6O6(OR)6(OOCR′)6].5,10 The basic
structural arrangements of this family of compounds are best
described as two trinuclear oxo-centered units, [TiO]4 cubes
with one or two corners removed, linked by oxo-bridge with a
Figure 1. The core structures of compounds (a) 1 and (b) 2 with 50%
thermal ellipsoid; the isopropane and benzene groups are omitted for
the sake of clarity.
and benzene groups are omitted for clarity). The structures of
this family of compounds are best described as two trinuclear
oxo-Ti3 subunits linked by μ3−O or μ2−O bridges. The two
Ti3O3 clusters are linked by two μ3−O bridges in 1 and by one
μ2−O bridge in 2, forming Ti6 clusters. The O6−Ti2, O6−Ti3,
and O6−Ti2# (#: 1 − x, −y, 1 − z) distances of μ3−O bridges
in 1 are 2.080(2), 1.872(2), and 1.958(2) Å, and the O11−Ti2
and O11−Ti4 distances of μ2−O bridges in 2 are 1.784(3) and
C
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Figure 3. Asymmetric bridging mode of o-BDC in 1 and 2.
center of symmetry.4,11 The skeletal arrangements of the two
new Ti6 carboxylate substituted oxo-clusters are shown in
Figures 4d and 4e. Similar to the type (c) compound (Figure
4c), there are two dual corner-missing cube subunits Ti3O3
bridged by two μ3-O in compound 1 (Figure 4d), but with
different arrangement. The skeletal arrangement of 2 is a new
type of Ti6 carboxylate substituted oxo-clusters that has only a
mono μ2−O bridge in cluster center (Figure 4e).
Figure 5. Light irradiation changes the color of the crystals of 1 from
(a) transparent to (b) purple-gray.
Studies of the Photochromic Effect. A photochromic
effect is observed on both 1 and 2 upon UV−vis excitation by a
halogen lamp or sunlight in the presence of alcohol. The light
irradiation changes the color of the crystals from transparent to
purple-gray (see Figure 5 and Figure S4 in the Supporting
Information). Optical diffuse reflectance spectra of the micro
crystal samples of 2 before and after irradiation are measured
and the absorption data in the visible-near-IR range are
calculated from the reflectance using the Kubelka−Munk
function, α/S = (1 − R)2/(2R) (from ref 12; see Figure 6).
The colored photochromic sample exhibits a new broad band
with a maximum located at 2.46 eV (504 nm), and it can be
assigned to the overlapped Ti(III) d−d transition and
intervalence transition. The ESR spectra recorded at 110 K
for the samples of 1 and 2 after irradiation are shown in Figure
7. The irradiated samples exhibit characterized signals of
paramagnetic Ti(III) centers in a distorted rhombic ligand field
with parameters 1.968 (g1), 1.943 (g2), 1.923 (g3), and 1.970
(g1), 1.944 (g2), 1.926 (g3), respectively.6 To ensure the Ti(III)
ions were not oxidized in the sample preparation, the crystal
samples for ESR measurement were not powdered. For this
reason, the signals show some noise. Moreover, when the gray
Figure 6. Absorption spectra of compound 2, showing the
characteristic photoinduced change.
samples are ground in air for a short time (several minutes),
• −
super oxide diatomic O2
ion is detected with the
• −
disappearing of Ti(III) signal. The observed O2 resonances
of 1 and 2 are 2.029 (g1), 2.013 (g2), 2.007 (g3), and 2.030 (g1),
2.013 (g2), 2.008 (g3), respectively, which disappear gradually
by laying the gray sample in air and avoid the light irradiation
(see Figure 8 and Figure S5 in the Supporting Information). It
is also demonstrated by the color change from gray to pale
yellow. The ESR result is similar to the characteristic
• −
orthorhombic signals reported for super oxide diatomic O2
ions.13
Figure 4. Skeletal arrangements of the Ti6 carboxylate-substituted oxo clusters: (a−c) reported, (d) 1, and (e) 2.
D
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Figure 7. ESR spectra recorded at 110 K for the gray samples (after irradiation) of (a) 1 and (b) 2.
Figure 8. Detected ESR signal of super oxide diatomic O2• − ion in 1
when the gray sample is exposed in air for a short time (minutes) and
long time (1 day).
The experiments reveal that the cluster structures play an
important role in the photochromic effect, because no such
phenomenon happens if Ti(OiPr)4 is used under the same
condition. The density of states (DOS) of the simplified
models of Ti(OH)4 and trinuclear Ti3O(OH)7 are calculated
by Material Studio program (Release 4.0; Accelrys Software,
Inc., San Diego, 2006). The result is shown in Figure 9. It is
seen clearly from the DOS plots that the energy of unoccupied
Ti 3d orbit (green) of the Ti(OH)4 is ∼2.5−5.0 eV, while that
of the Ti3O(OH)7 is approximately −1.0−3.0 eV. The dropped
band energy considerably stabilized the Ti(III) species and the
broadened band structure (trinuclear) is in favor of electron
conjugation.
Single-crystal structure analysis of the irradiated gray crystal
Figure 9. Density of states (DOS) plots of the simplified models of (a)
Ti(OH)4 and (b) Ti3O(OH)7; the red, blue, green, and red contour
lines are the s, p, d, and total DOS plots, respectively.
of 1 is performed to know if the crystal parameters, such as
bond distances and angles, are changed due to the reduction of
Ti(IV) to Ti(III). The result is negative that no obvious
changes are detected, which indicate that the photochemical
reaction only occurs on the surface of the crystals. Therefore, it
further demonstrates that alcohol as a reduction reagent is
necessary in the photoassisted reduction of Ti(IV) into Ti(III).
It has been said that such reaction is of interest because it
underlines a possible photocatalytic activity for titanium-oxo-
clusters.
to be advantageous and useful in the photodegradation of
dyes.14 The photoinduced O2• − ions can be correlated with the
photocatalytic effect. The photodegradation of the Methyl
Orange (MO) in aqueous dispersions of microcrystals of the
cluster 2 are carried out under UV cut white light (>420 nm) in
the presence of a tiny amount of H2O2.15 The degradation of
MO is investigated under various conditions, including the use
of irradiation or in darkness, and with or without H2O2. It is
interesting that a synergistic effect is observed in the system of
Photochemical Degradation of Methyl Orange. During
the past decades, photocatalytic processes involving TiO2
semiconductor particles under illumination have been shown
E
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TiO2/H2O2 for the photodegradation of MO. The reaction is
not obvious if no H2O2 is added. As shown in Figure 10, it is
is a new type of Ti6 carboxylate-substituted oxo clusters that has
only a mono μ2−O center bridge. Moreover, the crystals show a
photochromic behavior in the presence of alcohol, and Ti(III)
signal can be detected after irradiation. In the presence of
oxygen, titanium(III) reduces molecular oxygen to superoxide
• −
diatomic O2 radical. The photodegradation of the Methyl
Orange (MO) in aqueous dispersions of microcrystals of the
clusters was carried out under UV cut white light in the
presence of tiny amount of H2O2. More than 90% decay of MO
was observed over a period of 100 min. These well-
characterized new clusters are the promised compounds in
photocatalysis and solar harvesting.
ASSOCIATED CONTENT
* Supporting Information
■
S
Crystallographic data of 1 and 2 in CIF format have been
deposited with Inorganic Chemistry. These materials, and figures
showing the XRD, IR ESR, and TGA analyses are available free
of charge via the Internet at http://pubs.acs.org.
Figure 10. Photodegradation of MO versus irradiation time: blank
(blue) and illuminated by visible irradiation (red) in a 30-mL aqueous
solution of MO (0.10 mmol/L) with 22 mg of suspended 2 and a
catalytic amount of H2O2 (3%, 150 μL).
AUTHOR INFORMATION
Corresponding Author
*E-mails: zhuqinyu@suda.edu.cn (Q.Y.Z.); daijie@suda.edu.cn
(J.D.).
■
noted that more than 90% decay of MO is observed during 100
min in the system of TiO-cluster/H2O2 under the irradiation of
visible light. However, no obvious decay of MO is observed in
the same system without the irradiation (in darkness). The
concentration of MO (C/C0) decreases exponentially with
irradiation time via a pseudo-first-order process (k = 0.0258(8)
min−1, R = 99.7%; see Figure S6 in the Supporting
Information).
The photodegradation of dyes in aqueous dispersions of
TiO2 have been studied in some detail. The major steps in the
mechanism under visible irradiation have been summarized.15
The synergistic effect of H2O2 may be rationalized by the
following:
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge financial support by the NSF of
China (No. 20971092), the Education Committee of Jiangsu
Province (No. 11KJA150001), the Priority Academic Program
Development of Jiangsu Higher Education Institutions, and the
Program of Innovative Research Team of Soochow University.
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■
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Considering the visible-light-induced and dye-sensitized re-
action, and the evidence of Ti(IV)/Ti(III) transfer and the
detected O2• −, the mechanism of the reaction is suggested as
follows:
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CONCLUSIONS
■
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In summary, two dicarboxylate-substituted titanium-oxo-
clusters, Ti6O4(o-BDC)2(o-BDC-iPr)2(OiPr)10 (1) and
Ti6O3(o-BDC)2(OiPr)14 (2), have been prepared successfully
via a one-step in situ solvothermal synthesis. They are the first
examples of dicarboxylate-substituted oxo-alkoxy titanium
clusters that the structures are measured by single-crystal X-
ray analysis. The two Ti6 clusters of 1 and 2 are constructed by
two dual corner-missing cube subunit, Ti3O3, linked by μ3−O
and μ2−O bridges, respectively. The skeletal arrangement of 2
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̈
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̈
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