Polyoxotitanate Molecular Cage Featuring Four Types of Ethylenediamines: Formation Mechanism Insight from Host-Guest Interaction and Crystallographic Study

Article abstract of DOI:10.1021/acs.inorgchem.1c01189

Titanium-oxide or polyoxotitanate clusters are a new type of inorganic host materials that can encapsulate inorganic molecules or ions. We report herein a (NH4)4(enH2)[Ti18O27(PhCOO)24(en)9] molecular cage (Ti18) that encapsulates an entire organic ethylenediamine (en) ion. A thorough investigation has revealed the extraordinary versatility of en. Besides being a guest cation, it also functions as chelating and bridging ligand. It balances the charge of the negative Ti18 cage and facilitates the deprotonation of benzoic acid at the early stage of the reaction as well. DFT calculation and a derivative of Ti18 with open sites at its equatorial position shed further light on the formation mechanism. Ti18 strongly absorbs visible light as a result of en coordination, and it exhibits superior photocatalytic activity compared to anatase TiO2.

Full text of DOI:10.1021/acs.inorgchem.1c01189

pubs.acs.org/IC
Article
Polyoxotitanate Molecular Cage Featuring Four Types of
Ethylenediamines: Formation Mechanism Insight from Host−Guest
Interaction and Crystallographic Study
Xiaoqin Cui,§ Fu-Qiang Zhang,§ Xin Li,§ Juan-Juan Hou, Huan Li,* and Xian-Ming Zhang*
Cite This: Inorg. Chem. 2021, 60, 9174−9180
Read Online
sı
*
Metrics & More
Article Recommendations
Supporting Information
ACCESS
ABSTRACT: Titanium-oxide or polyoxotitanate clusters are a
new type of inorganic host materials that can encapsulate inorganic
molecules or ions. We report herein a (NH4)4(enH2)[Ti18O27-
(PhCOO)24(en)9] molecular cage (Ti18) that encapsulates an
entire organic ethylenediamine (en) ion. A thorough investigation
has revealed the extraordinary versatility of en. Besides being a
guest cation, it also functions as chelating and bridging ligand. It
balances the charge of the negative Ti18 cage and facilitates the
deprotonation of benzoic acid at the early stage of the reaction as
well. DFT calculation and a derivative of Ti18 with open sites at its
equatorial position shed further light on the formation mechanism.
Ti18 strongly absorbs visible light as a result of en coordination,
and it exhibits superior photocatalytic activity compared to anatase TiO2.
Inorganic ions or molecules (such as I−,31,32 K+,33 Cs+,34
Br−,35 and H2O36) were found to be accommodated by POTs.
Nevertheless, the door to a variety of fascinating small organic
molecules that could potentially be imprisoned in the POT
cage has yet to be opened. Amine, for example, has been
thoroughly investigated with respect to the host−guest
interaction with crown ether and other hosts for its excellent
ability to form a hydrogen bond as a donor.37−40 Applications
like molecular recognition and chiral resolution, etc., have also
been demonstrated. Unfortunately, whether amine can be
enclosed by a POT cage is still elusive, not to mention figuring
out whether it can direct the formation pathway of a POT
cage.
Herein, we would like to present two carcerand-like POT
molecular containers (NH4)4(enH2)[Ti18O27(PhCOO)24-
(en)9] and (NH4)2(enH2)[Ti18O27(PhCOO)24(en)7(enH)2].
They both enclose an entire ethylenediamine dication
([H3NCH2CH2NH3]2+, enH2) through hydrogen bonds (H-
bonds), which represents the first example of total molecular
encapsulation of an organic guest by a rigid POT host. In
particular, the crystallographic and theoretical studies have
shown that ethylenediamine (en) is much more than just a
INTRODUCTION
■
The host−guest interaction wherein a compound spatially
accommodates a guest molecule through a noncovalent bond
is a core concept of supramolecular chemistry. A profound
comprehension of the host−guest chemistry has become a
stepping stone for understanding many emerging phenomena
in branches of chemistry, such as molecular recognition,1,2 self-
assembly,3−6 gas absorption,7,8 sensing,9,10 and even cataly-
sis.11,12 To these ends, a variety of organic models have been
discovered, such as crown ethers, cryptand, calixarenes, etc.
The molecular cage which encapsulates the entire guest
molecule has drawn special attention. This is not only because
of its aesthetically appealing structure. The underlying
chemistry that guides the guest to be imprisoned also deeply
fascinates the community. In the field, a myriad of inspiring
studies have been reported for the organic and metallo-
supramolecular cages.13−16 Other host materials like full-
erene,17,18 zeolites,19,20 and metal−organic frameworks
(MOFs),21−24 etc., have also shown unique features as
molecular cages.
In this respect, however, much less attention has been
devoted to titanium-oxide clusters or polyoxotitanates
(POTs).25−28 POTs are widely identified as the molecular
analogue of TiO2, and the latter is renowned for the light-
harvesting properties and related applications. With the Ti−
O−Ti motif resembling the C−O−C group and the out-
standing structural versatility, POT has been expected to
function similarly as organic hosts like crown ether.29,30 Recent
years have indeed witnessed some significant progresses.
Received: April 18, 2021
Published: June 3, 2021
https://doi.org/10.1021/acs.inorgchem.1c01189
© 2021 American Chemical Society
Inorg. Chem. 2021, 60, 9174−9180
9174

Inorganic Chemistry
pubs.acs.org/IC
Article
guest. Its exceptional versatility that sheds light on the
formation mechanism is our primary focus of this work. To
best characterize the broad light absorption of the cluster, its
photocatalytic activity is also evaluated.
(Figure 2b). The remaining six act as chelating ligands, three
on each side (Figure 2c,d). Although such chelation is
prevalent among Ti complexes, integrating both bridging and
chelating modes into one cluster is uncommon. The remaing
three Ti atoms of the top or bottom layer are not chelated by
en but are coordinated with only oxygen. Intriguingly, for each
of them there is one monodentate BA ligand, leaving three
dangling O sites pointing inward. Such an exquisite design is
RESULTS AND DISCUSSION
■
The yellow block-shaped single crystal of (NH4)4(enH2)-
[Ti18O27(PhCOO)24(en)9] (Ti18) was obtained from a one-
pot solvothermal reaction of titanium(IV) isopropoxide, i.e.,
Ti(OiPr)4, benzoic acid (BA), en, and ammonium hydroxide in
acetonitrile at 100 °C for 24 h (Supporting Information, Figure
S1). Crystallographic analysis reveals that Ti18 nanoclusters are
+
perfect for hosting a NH4 ion through three trigonally
distributed H-bonds (Figure 2d). Two such ammonium ions
on each side seal off the cage to keep enH2 from escaping. It is
also worth mentioning that there is one monodentate BA for
each of the six Ti atoms in the middle layer (Figure 1). In all,
12 out of 24 BA are of such a type resulting from the
competitive coordination of en. Also, despite the difference in
coordination number with N (0, 1, or 2), all Ti atoms are hexa-
coordinated in an octahedral geometry (Figure 2c).
Upon protonation, en loses its ability to coordinate with Ti
but becomes a better H-bond donor. This is the case for the
guest ion, enH2. It forms four H-bonds with the interior of the
cage through N−H···O H-bonds (Figure 2a). The average
bond length is 2.147 Å, which is within a reasonable range.41,42
It is clear from the top view that enH2 is sitting on a C3 axis,
indicating there are three possible orientations of enH2. The
conformational flexibility of en in Ti18 is reflected in an analysis
by Newman projection (Figure 2e). The dihedral angle as
calculated is 170° for the bridging en. The angle is 69.9° for
the guest enH2 and even smaller for the chelating en (32.1°).
The value close to 60° indicates the guest enH2 is with a
gauche conformation, a more thermodynamically stable form
of en in the gas phase.43,44
̅
closely packed in a trigonal R3 space group (Figure S2). From
a charge balance point of view, each Ti18 is composed of a
[Ti18O27(PhCOO)24(en)9]6− anion and two kinds of counter-
2+
+
ions: an enH2 dication and four NH4 . Structurally, Ti18 can
be viewed as a BA and en co-protected, bifrustum-shaped cage.
Inside the cage, an enH2 guest ion is encapsulated by the POT
skeleton (Figure 1).
To gain an insight into why the enclosed enH2 also
maintains such a conformation, a comparative study by density
function calculation is performed to analyze two cages
encapsulating two conformational isomers of enH2, respec-
tively.45 One is a gauche conformation as crystallographically
determined. The other is a trans conformer where two amino
groups oriented oppositely (Figure S3). The result has shown
that the one with the gauche enH2 is only ∼0.22 eV
energetically more favored than the trans one (−3522.66 vs
−3522.44 eV). This subtle difference indicates that the
conformation of enH2 is not a significant factor. On the
other hand, however, the energy decomposition analysis of the
host−guest interaction reaches as high as ∼20 eV (Table 1).
More importantly, it mainly comes from electrostatic
Figure 1. A side view of the overall structure of a (NH4)4(enH2)-
[Ti18O27(PhCOO)24(en)9] (Ti18) molecular cage. The guest, ethyl-
enediamine dication (enH2), is drawn in sphere-packing style.
Hydrogen bonds between cage and guest are indicated by dotted
yellow lines. Color legend: Ti, orange; O, red; N, blue; C, gray; H,
green. H atoms of benzene rings are omitted for clarity.
2+
interaction between the positive dication enH2 and the
negative shell, which is in sharp contrast with 2.4−3.2 eV of
those coordinated neutral en. As a result, it is reasonable to
propose that the strong electrostatic interaction between the
dication and the cage is the key for directing the formation of
the molecular cage.46,47
En as the structural component of Ti18, either as ligand or
guest ion, is indispensable for shaping the cage. Further
investigation has revealed that en also plays a key role in
directing the formation pathway. First, our multiple attempts
to synthesize Ti18 at lower temperatures (from 50 to 90 °C)
failed to give Ti18. Rather, it constantly produced a crystalline
compound of en and BA in high yield (Figure S4). As a Lewis
base, en can deprotonate benzoic acid to form PhCOO−enH2
ion pairs linked by multiple H-bonds (Figures 3c and S5).48
Considering CH3CN is an aprotic solvent, it is most likely that
such a proton transfer process gave birth to the guest ion,
enH2. Accordingly, the deprotonated BA (benzoate) became a
A view of only the cage skeleton and guest provides a better
illustration of their positioning and bonding. As shown in
Figure 2a, both the congruent top and bottom layers of the
cage are composed of six Ti and equal μ2-O atoms. The middle
layer can be viewed as that three of the bridging O atoms are
replaced by en. The latter is more flexible and has a longer
distance between two binding sites (N atom). This is especially
true when two amino groups are in opposite position (anti
conformation). By doing so, the middle layer is maximally
expanded. A top view image provides a clearer illustration
(Figure 2b). The calculated accessible pore size of the top layer
is 3.1 Å (distance between two μ2-O subtracts twice the radius
of O2−), whereas it is close to 9 Å for the middle layer, which
makes the cage suitable for hosting enH2 (molecular length 4.6
Å).
Nine en’s function as the ligands of Ti18. Three of them are
linking the six Ti atoms of the middle layer, as mentioned
9175
https://doi.org/10.1021/acs.inorgchem.1c01189
Inorg. Chem. 2021, 60, 9174−9180

Inorganic Chemistry
pubs.acs.org/IC
Article
Figure 2. A side view (a) and top view (b) of the bifrustum cage containing enH2. (c) Three coordination modes of Ti. All Ti atoms are hexa-
coordinated with both N and O (blue octahedrons) or with only O (yellow). (d) Two NH4+ locate above the top layer of the cage via H-bonding
with three monodentate BA. (e) Newman projections of different en’s. The dihedral angles are labeled below the diagrams. Color legend: Ti,
orange; O, red; N, blue; C, gray; H, green.
The discovery of another Ti18, (NH4)2(enH2)[Ti18O27(Ph-
COO)24(en)7(enH)2], may shed further light on the formation
mechanism. It appears as a minor product in the synthesis of
Ti18 and has a similar overall structure (Figures 4 and S9). The
difference is that this cluster has two open sites at its equatorial
position (donated as Ti18-OS). At each such site, en has its one
end bonding to Ti and the other being protonated, which
breaks up the Ti−N bond at this end (Figure 4c).
Contrastingly, the third en still functions as a bridging ligand,
as that in Ti18. The emergence of such open sites apparently
results from that Ti−N bonds fail to form. One scenario is that
the as-formed Ti18 gets protonated to give Ti18-OS. We
consider it much less likely, because it would require all the
Ti18 clusters to get protonated at precisely the two positions.
The more reasonable explanation is that the open sites formed
during the building-up process of the cage. This is because
either en gets protonated before it can bond to the second Ti
atom or this Ti atom is pre-occupied by the bidentate BA,
leaving no room for en to bind (Figure 4c). Thus, considering
other parts of Ti18-OS are all in position, we speculate that it is
at such an open site that the cage is eventually closed. Ti18-OS
has other interesting features. First, two en’s at the open sites
also function as a monocation (i.e., enH+). As a result, there
are only two ammonium ions as counterions in one Ti18-OS
cluster, in comparison with four in Ti18 (Figures 4d and S10).
Second, Ti18-OS has lost its C3 symmetry, as shown in the top-
view image (Figures 4b and S11). Consequently, unlike enH2
in Ti18 which has three possible orientations, the conformation
of enH2 in Ti18-OS is unique.
Table 1. Energy Decomposition Analysis of Ti18 Cages
Encapsulating enH2
a
OI
PR
3.14
EI
OOI
−6.44
gauche-guest
−20.84
−17.55
gauche-chelating −3.14/−
5.55/5.56 −5.55/5.48
−3.14/3.00
2.93
gauche-bridging
trans-guest
−2.42
−20.51
6.95
3.59
−6.20
−17.63
−3.16
−6.47
trans-chelating
−3.20/−
5.60/5.79 −5.60/−5.71 −3.00/−3.13
3.20
trans-bridging
−2.35
6.55 −5.90 −3.00
a
Energies (eV) of orbital interaction (OI), Pauli repulsion (PR),
electrostatic interaction (EI), and overall orbital interactions (OOI).
more efficient nucleophile for the Ti4+ ion. In this sense, en
and BA cooperatively functioned at the early stage of the
reaction. When the synthesis was performed in the absence of
en, a Ti6 cluster ([Ti6(μ3-O)2(μ2-O)4(PhCOO)10(OiPr)2·
2BA]) (denoted as Ti6) was collected (Figures 3a and S6).
All BA ligands adopted a common μ2 bridging mode, and every
Ti atom is hexa-coordinated with O atoms. On the other side,
the synthesis using en but not BA afforded an infinite one-
dimensional Ti complex (Figures 3b and S7). It can be viewed
as every two Ti2(OiPr)8 units being connected by one en
through coordinate bonds.49 Interestingly, its bonding mode
also resembles that of Ti18’s middle layer, where two amine
groups are at opposite positions (Figure S8).
These crystallographic results suggest that, without either en
or BA, the products are relatively simple. Both ligands tend to
adopt their most predictable coordination modes with Ti. If
BA and en are introduced simultaneously, they would
competitively bond to Ti. The fact that 12 out of 24 BA
ligands of Ti18 are monodentate is a vivid illustration of such a
mechanism (Figure 1). We believe it is the multiplicity of
bonding modes of BA and en that makes the emergence of
such a complex structure as Ti18 possible.
On the basis of the results above, it seems appropriate to
propose a plausible formation pathway of the Ti18 molecular
cage. First, BA protonates en in acetonitrile to give birth to the
dication enH22+. The latter as a highly efficient hydrogen bond
donor acts as a template, around which a negatively charged
cage is gradually built up based on its strong electrostatic
interaction. During the process, en and BA competitively
coordinated with Ti atoms and this finally gives Ti18. Also, the
9176
https://doi.org/10.1021/acs.inorgchem.1c01189
Inorg. Chem. 2021, 60, 9174−9180

Inorganic Chemistry
pubs.acs.org/IC
Article
Figure 3. Control experiments. (a) Ti(OiPr)4 reacting with BA at the given conditions yields [Ti6(μ3-O)2(μ2-O)4(PhCOO)10(OiPr)2·2BA] (Ti6).
(b) Reacting Ti(OiPr)4 and en gives a linear complex {[Ti2(OiPr)8(en)]∞}. (c) A proton transfer from BA to en at milder condition gives rise to
the compound, PhCOO−enH2. (d) The synthesis of Ti18 by reacting Ti(OiPr)4 with BA and en. The solvent for all the above reactions is
acetonitrile. Color legend: Ti, orange; O, red; N, blue; C, gray; H, green.
cage might be closed by the coordination of bridging en with a
Ti atom at the equatorial position. If this step fails, Ti18-OS
would be produced instead.
The amine ligand also exerted a direct influence on the
optical properties of Ti18. A light absorption ranging from 300
to 700 nm was recorded for Ti18, contrasting sharply with
anatase (Figure 5a). In fact, such a wide-range absorption
feature is rare for POTs without a chromophore.50 For bulk or
nanoscale TiO2, doping it with N species is a practical
approach to acquire a wider absorption range. We thus
envision Ti18 as a molecular analogue of N-doped TiO2. The
band gap of Ti18 is calculated to be 2.4 eV (Figure S12). The
electron binding energy is 458.44 eV for Ti 2p3/2, which is
typical for Ti4+ (Figures 5b and S13). The N 1s core level
shows a major peak at 399.6 eV and a shoulder at 401.22 eV.
+
The former is assigned to Ti−N, while the latter is for NH4
(Figure 5c).51 The C 1s peak can be properly fitted into three
components, which correspond to carboxyl (C−O), amine
(C−N), and benzene ring (C−C), respectively (Figure S13).52
Figure 4. Comparison of the top view of the middle layers of Ti18 (a)
and Ti18-OS (b). The local coordination pattern of Ti18-OS at the
These results are in good agreement with the structural
+
open site (c). One NH4 bonding with three BA through H-bonds
observation.
(d). There are two such ions in each Ti18-OS, in comparison with four
Given the optical feature and its small size, Ti18 is expected
for Ti18. Color legend: Ti, orange; O, red; N, blue; C, gray; H, green.
to be effective for photocatalysis under visible light. Indeed, in
the model reaction of methyl orange (MO) degradation, Ti18
9177
https://doi.org/10.1021/acs.inorgchem.1c01189
Inorg. Chem. 2021, 60, 9174−9180

Inorganic Chemistry
pubs.acs.org/IC
Article
Figure 5. (a) The solid-state UV−vis absorption spectra of Ti18 and anatase TiO2. Ti 2p (b) and N 1s (c) XPS spectra of Ti18. Photodegradation of
MO catalyzed by Ti18 and anatase under a Xe lamp (d) and that with a 420 nm cut filter (e). (f) The recyclability test of Ti18. Reaction conditions:
24 mg of catalyst, 30 mL of aqueous solution of MO (20 mg/L), a catalytic amount of H2O2 (30%, 80 μL).
consumed more than 95% of MO in 50 min. For the same
Details of the syntheses, characterization, supporting
reaction by nanoscale anatase, the conversion was 37% (Figure
5d). The difference became sharper when the reaction was
irradiated by visible light (>420 nm). Anatase hardly degraded
MO. Ti18 still afforded a conversion of 95% in about 90 min,
due to its wide absorption range (Figure 5e). Ti18 can be
reused for another four times, and no significant loss of activity
was observed (Figure 5f). Furthermore, the XRD of the used
catalyst showed poor crystallinity but maintained its spectro-
scopic feature in the visible range (Figure S14).
figures, crystallographic data, and supporting references
(PDF)
Accession Codes
CCDC 1981480, 2056740−2056742, and 2080587 contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge via www.ccdc.cam.ac.uk/
data_request/cif, or by emailing data_request@ccdc.cam.ac.
uk, or by contacting The Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44
1223 336033.
CONCLUSION
■
We report a host−guest interaction of an ethylenediamine
dication inside a Ti18 polyoxotitanate molecular cage. It
represents the first crystallographic example of an entire
organic molecule encapsulation by a polyoxotitanate. The
extraordinary versatility of ethylenediamine is revealed in
detail. It is the guest ion, peripheral ligand, and counterion. It
also plays a critical role in directing the formation of Ti18. With
the unique absorption feature, the title cluster has also proved
to be an efficient photocatalyst under visible light. Given the
vast number of amines and the fact that the host−guest
research about polyoxotitanate nanoclusters is at its infant
stage, it is optimistic that more such molecular cages will
emerge in the future.
AUTHOR INFORMATION
■
Corresponding Authors
Huan Li − Institute of Crystalline Materials, Shanxi
University, Taiyuan 030006, Shanxi, China; orcid.org/
0000-0003-4229-2796; Email: 59584340@sxu.edu.cn
Xian-Ming Zhang − Institute of Crystalline Materials, Shanxi
University, Taiyuan 030006, Shanxi, China; School of
Chemistry and Material Science, Shanxi Normal University,
Linfen 041004, Shanxi, China; Email: xmzhang@
sxu.edu.cn
Authors
Xiaoqin Cui − Institute of Crystalline Materials, Shanxi
University, Taiyuan 030006, Shanxi, China
Fu-Qiang Zhang − School of Chemistry and Material Science,
Shanxi Normal University, Linfen 041004, Shanxi, China
Xin Li − Institute of Crystalline Materials, Shanxi University,
Taiyuan 030006, Shanxi, China
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.1c01189.
9178
https://doi.org/10.1021/acs.inorgchem.1c01189
Inorg. Chem. 2021, 60, 9174−9180

Inorganic Chemistry
pubs.acs.org/IC
Article
(16) Brown, C. J.; Toste, F. D.; Bergman, R. G.; Raymond, K. N.
Supramolecular Catalysis in Metal−Ligand Cluster Hosts. Chem. Rev.
2015, 115, 3012−3035.
(17) Yang, S.; Wei, T.; Jin, F. When Metal Clusters Meet Carbon
Cages: Endohedral Clusterfullerenes. Chem. Soc. Rev. 2017, 46, 5005−
5058.
Juan-Juan Hou − School of Chemistry and Material Science,
Shanxi Normal University, Linfen 041004, Shanxi, China;
orcid.org/0000-0002-9258-1476
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.1c01189
(18) Zhang, J.; Stevenson, S.; Dorn, H. C. Trimetallic Nitride
Template Endohedral Metallofullerenes: Discovery, Structural Char-
acterization, Reactivity, and Applications. Acc. Chem. Res. 2013, 46,
1548−1557.
Author Contributions
§X.C., F.-Q.Z., and X.L. contributed equally to this work.
Notes
(19) Wöhrle, D.; Schulz-Ekloff, G. Molecular Sieve Encapsulated
Organic Dyes and Metal Chelates. Adv. Mater. 1994, 6, 875−880.
(20) Davis, M. E. Zeolites and Molecular Sieves: Not Just Ordinary
Catalysts. Ind. Eng. Chem. Res. 1991, 30, 1675−1683.
(21) Douglas, T.; Young, M. Host−Guest Encapsulation of
Materials by Assembled Virus Protein Cages. Nature 1998, 393,
152−155.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We express our gratitude to the National Natural Science
Foundation of China (21972080, 21503123, 91961201,
21871167), Sanjin Scholar, Shanxi “1331 Project” for financial
support.
(22) Muller, A.; Penk, M.; Rohlfing, R.; Krickemeyer, E.; Döring, J.
̈
Topologically Interesting Cages for Negative Ions with Extremely
High “Coordination Number”: An Unusual Property of V−O
Clusters. Angew. Chem., Int. Ed. Engl. 1990, 29, 926−927.
(23) Davis, M. E. Ordered Porous Materials for Emerging
Applications. Nature 2002, 417, 813−821.
REFERENCES
■
(1) Schneider, H.-J.; Yatsimirsky, A. K. Selectivity in Supramolecular
Host−Guest Complexes. Chem. Soc. Rev. 2008, 37, 263−277.
(2) Cram, D. J.; Cram, J. M. Host−Guest Chemistry. Science 1974,
183, 803−809.
(3) Menger, F. M. Supramolecular Chemistry and Self-Assembly.
Proc. Natl. Acad. Sci. U. S. A. 2002, 99, 4818−4822.
(24) Ziv, A.; Grego, A.; Kopilevich, S.; Zeiri, L.; Miro, P.; Bo, C.;
Muller, A.; Weinstock, I. A. Flexible Pores of a Metal Oxide-Based
̈
Capsule Permit Entry of Comparatively Larger Organic Guests. J. Am.
Chem. Soc. 2009, 131, 6380−6382.
(25) Fang, W.-H.; Zhang, L.; Zhang, J. A 3.6 nm Ti52−Oxo
Nanocluster with Precise Atomic Structure. J. Am. Chem. Soc. 2016,
138, 7480−7483.
(4) Baxter, P. N. W.; Lehn, J.-M.; Baum, G.; Fenske, D. The Design
and Generation of Inorganic Cylindrical Cage Architectures by Metal-
Ion-Directed Multicomponent Self-Assembly. Chem. - Eur. J. 1999, 5,
102−112.
(5) Harada, A.; Kobayashi, R.; Takashima, Y.; Hashidzume, A.;
Yamaguchi, H. Macroscopic Self-Assembly through Molecular
Recognition. Nat. Chem. 2011, 3, 34−37.
(6) Lehn, J.-M. Perspectives in Supramolecular ChemistryFrom
Molecular Recognition towards Molecular Information Processing
and Self-Organization. Angew. Chem., Int. Ed. Engl. 1990, 29, 1304−
1319.
(7) Kosaka, W.; Yamagishi, K.; Zhang, J.; Miyasaka, H. Gate-
Opening Gas Adsorption and Host−Guest Interacting Gas Trapping
Behavior of Porous Coordination Polymers under Applied AC
Electric Fields. J. Am. Chem. Soc. 2014, 136, 12304−12313.
(8) Guo, X.; Zhang, P.; Navrotsky, A. The Thermodynamics of Gas
Absorption and Guest-Induced Flexibility in Zeolite Y. Microporous
Mesoporous Mater. 2020, 294, 109893.
(9) Chung, Y. M.; Raman, B.; Kim, D.-S.; Ahn, K. H. Fluorescence
Modulation in Anion Sensing by Introducing Intramolecular H-
Bonding Interactions in Host−Guest Adducts. Chem. Commun. 2006,
186−188.
(10) Lin, R.-B.; Liu, S.-Y.; Ye, J.-W.; Li, X.-Y.; Zhang, J.-P.
Photoluminescent Metal-Organic Frameworks for Gas Sensing. Adv.
Sci. 2016, 3, 1500434.
(11) Zhang, D.; Martinez, A.; Dutasta, J.-P. Emergence of
Hemicryptophanes: From Synthesis to Applications for Recognition,
Molecular Machines, and Supramolecular Catalysis. Chem. Rev. 2017,
117, 4900−4942.
(12) Hong, C. M.; Bergman, R. G.; Raymond, K. N.; Toste, F. D.
Self-Assembled Tetrahedral Hosts as Supramolecular Catalysts. Acc.
Chem. Res. 2018, 51, 2447−2455.
(26) Wu, Y.-Y.; Wang, P.; Wang, Y.-H.; Jiang, J.-B.; Bian, G.-Q.; Zhu,
Q.-Y.; Dai, J. Metal−Phenanthroline Fused Ti17 Clusters, a Single
Molecular Source for Sensitized Photoconductive Films. J. Mater.
Chem. A 2013, 1, 9862−9868.
(27) He, Y.-P.; Chen, G.-H.; Li, D.-J.; Li, Q.-H.; Zhang, L.; Zhang, J.
Combining a Titanium−Organic Cage and a Hydrogen-Bonded
Organic Cage for Highly Effective Third-Order Nonlinear Optics.
Angew. Chem., Int. Ed. 2021, 60, 2920−2923.
(28) Albrecht, M.; Janser, I.; Fröhlich, R. Catechol Imine Ligands:
from Helicates to Supramolecular Tetrahedra. Chem. Commun. 2005,
157−165.
(29) Timco, G. A.; Fernandez, A.; Kostopoulos, A. K.; Charlton, J.
F.; Lockyer, S. J.; Hailes, T. R.; Adams, R. W.; McInnes, E. J. L.; Tuna,
F.; Vitorica-Yrezabal, I. J.; Whitehead, G. F. S.; Winpenny, R. E. P.
Hybrid Organic−Inorganic Rotaxanes, Including a Hetero-Hybrid
[3]Rotaxane Featuring Two Distinct Heterometallic Rings and a
Molecular Shuttle. Angew. Chem., Int. Ed. 2018, 57, 10919−10922.
(30) Liu, C.; Wang, Y. Supramolecular Chemistry of Titanium-oxide
Clusters. Chem. - Eur. J. 2021, 27, 4270−4282.
(31) Hou, J.; Hu, J.; Sun, Q.; Zhang, G.; Tung, C.-H.; Wang, Y. A
Post-Functionalizable Iso-Polyoxotitanate Cage Cluster. Inorg. Chem.
2016, 55, 7075−7078.
(32) Coppens, P.; Chen, Y.; Trzop, E. b. Crystallography and
Properties of Polyoxotitanate Nanoclusters. Chem. Rev. 2014, 114,
9645−9661.
(33) Albrecht, M.; Janser, I.; Runsink, J.; Raabe, G.; Weis, P.;
Fröhlich, R. Selecting Different Complexes from a Dynamic
Combinatorial Library of Coordination Compounds. Angew. Chem.,
Int. Ed. 2004, 43, 6662−6666.
(34) Zhang, G.; Li, W.; Liu, C.; Jia, J.; Tung, C.-H.; Wang, Y.
Titanium-Oxide Host Clusters with Exchangeable Guests. J. Am.
Chem. Soc. 2018, 140, 66−69.
(35) Lv, Y.; Willkomm, J.; Steiner, A.; Gan, L.; Reisner, E.; Wright,
D. S. Encapsulation of a ‘Naked’ Br− Anion in a Polyoxotitanate Host.
Chem. Sci. 2012, 3, 2470−2473.
(36) Zhu, B. C.; Fang, W. H.; Wang, J.; Du, Y.; Zhou, T.; Wu, K.;
Zhang, L.; Zhang, J. Host−Guest and Photophysical Behavior of
Ti8L12 Cube with Encapsulated [Ti(H2O)6] Species. Chem. - Eur. J.
2018, 24, 14358−14362.
(13) Amouri, H.; Desmarets, C.; Moussa, J. Confined Nanospaces in
Metallocages: Guest Molecules, Weakly Encapsulated Anions, and
Catalyst Sequestration. Chem. Rev. 2012, 112, 2015−2041.
(14) Wang, L.-J.; Li, X.; Bai, S.; Wang, Y.; Han, Y.-F. Self-Assembly,
Structural Transformation, and Guest-Binding Properties of Supra-
molecular Assemblies with Triangular Metal-Metal Bonded Units. J.
Am. Chem. Soc. 2020, 142, 2524−2531.
(15) Cook, T. R.; Stang, P. J. Recent Developments in the
Preparation and Chemistry of Metallacycles and Metallacages via
Coordination. Chem. Rev. 2015, 115, 7001−7045.
9179
https://doi.org/10.1021/acs.inorgchem.1c01189
Inorg. Chem. 2021, 60, 9174−9180

Inorganic Chemistry
pubs.acs.org/IC
Article
(37) Zhang, X. X.; Bradshaw, J. S.; Izatt, R. M. Enantiomeric
Recognition of Amine Compounds by Chiral Macrocyclic Receptors.
Chem. Rev. 1997, 97, 3313−3361.
(38) Gokel, G. W.; Leevy, W. M.; Weber, M. E. Crown Ethers:
Sensors for Ions and Molecular Scaffolds for Materials and Biological
Models. Chem. Rev. 2004, 104, 2723−2750.
(39) Xie, J.; Bogliotti, N. Synthesis and Applications of
Carbohydrate-Derived Macrocyclic Compounds. Chem. Rev. 2014,
114, 7678−7739.
(40) Pluth, M. D.; Fiedler, D.; Mugridge, J. S.; Bergman, R. G.;
Raymond, K. N. Encapsulation and Characterization of Proton-Bound
Amine Homodimers in a Water-Soluble, Self-Assembled Supra-
molecular Host. Proc. Natl. Acad. Sci. U. S. A. 2009, 106, 10438−
10443.
(41) Fric, H.; Puchberger, M.; Schubert, U. Two- and Three-
Dimensional Coordination Polymers from the Reaction of Bis- and
Tris(2-aminoethyl)amine with Titanium and Zirconium Alkoxides.
Eur. J. Inorg. Chem. 2007, 2007, 376−383.
(42) Li, M.; Chang, J.; Wang, Z.; Shi, H. (NH3CH2CH2NH3)-
B6O9(OH)2: Synthesis and Crystal Structure of a Novel Layered
Borate Templated by Ethylenediamine. J. Solid State Chem. 2006, 179,
3265−3269.
(43) Xu, M.; Liu, D.; Allen, H. C. Ethylenediamine at Air Liquid and
Air Silica Interfaces Protonation Versus Hydrogen Bonding
Investigated by Sum Frequency Generation Spectroscopy. Environ.
Sci. Technol. 2006, 40, 1566−1572.
(44) Guo, Y.; Shi, Z.; Yu, J.; Wang, J.; Liu, Y.; Bai, N.; Pang, W.
Solvothermal Synthesis and Characterization of a New Titanium
Phosphate with a One-Dimensional Chiral Chain. Chem. Mater. 2001,
13, 203−207.
(45) Kazerouni, M. R.; Hedberg, L.; Hedberg, K. Conformational
Analysis. 16. Ethylenediamine. An Electron-Diffraction and ab Initio
Investigation of the Molecular Structure, Conformational Composi-
tion, Anti-Gauche Energy and Entropy Differences, and Implications
for Internal Hydrogen Bonding. J. Am. Chem. Soc. 1994, 116, 5279−
5284.
(46) Law, T. S. C.; Williams, I. D. Organo-Directed Synthesis of
Manganese Vanadates with Variable Stoichiometry and Dimension-
ality: 1-D [(Hen)2Mn(VO3)4], 2-D [H2en]2[Mn(VO3)6], and 3-D
[H2en][MnF(VO3)3]. Chem. Mater. 2000, 12, 2070−2072.
(47) Bataille, T.; Louër, D. Two New Diamine Templated
Lanthanum Sulfates, La2(H2O)2(C4 H12N2)(SO4 )4 and
La2(H2O)2(C2H10N2)3(SO4)6·4H2O, with 3D and 2D Crystal
Structures. J. Mater. Chem. 2002, 12, 3487−3493.
(48) Wagner, J. P.; McDonald, D. C.; Duncan, M. A. Spectroscopy
of Proton Coordination with Ethylenediamine. J. Phys. Chem. A 2018,
122, 5168−5176.
(49) Fric, H.; Puchberger, M.; Schubert, U. Coordination of Mono-
and Diamines to Titanium and Zirconium Alkoxides. J. Sol-Gel Sci.
Technol. 2006, 40, 155−162.
(50) Narayanam, N.; Fang, W.-H.; Chintakrinda, K.; Zhang, L.;
Zhang, J. Deep Eutectic-Solvothermal Synthesis of Titanium-Oxo
Clusters Protected by π-Conjugated Chromophores. Chem. Commun.
2017, 53, 8078−8080.
(51) Etacheri, V.; Seery, M. K.; Hinder, S. J.; Pillai, S. C. Highly
Visible Light Active TiO2−xNx Heterojunction Photocatalysts. Chem.
Mater. 2010, 22, 3843−3853.
(52) Gerenser, L. J.; Grace, J. M.; Apai, G.; Thompson, P. M. Surface
Chemistry of Nitrogen Plasma-Treated Poly(ethylene-2,6-naphtha-
late): XPS, HREELS and Static SIMS Analysis. Surf. Interface Anal.
2000, 29, 12−22.
9180
https://doi.org/10.1021/acs.inorgchem.1c01189
Inorg. Chem. 2021, 60, 9174−9180