Anion-coordination-induced turn-on fluorescence of an oligourea- functionalized tetraphenylethene in a wide concentration range

Article abstract of DOI:10.1002/anie.201402169

A tetrakis(bisurea)-decorated tetraphenylethene (TPE) ligand (L ²) was designed, which, upon coordination with phosphate ions, displays fluorescence "turn-on" over a wide concentration range, from dilute to concentrated solutions and to the sol

Full text of DOI:10.1002/anie.201402169

.
Angewandte
Communications
DOI: 10.1002/anie.201402169
Anion Coordination
Anion-Coordination-Induced Turn-On Fluorescence of an Oligourea-
Functionalized Tetraphenylethene in a Wide Concentration Range**
Jie Zhao, Dong Yang, Yanxia Zhao, Xiao-Juan Yang, Yao-Yu Wang, and Biao Wu*
Abstract:
A
tetrakis(bisurea)-decorated tetraphenylethene
membrane integrity, bone mineralization, cellular signaling,
muscle function, and other vital biological processes.[7]
Inorganic phosphates (Pi) are crucial for the maintenance of
phosphate balance and homeostasis of the body and are
involved in most metabolic processes and enzymatic reac-
tions.[8] Therefore, the study of phosphate-ion coordination is
very important for understanding cellular activities.
We have recently reported a class of ortho-phenylene-
bridged[9] oligourea ligands, which display excellent coordi-
nation properties with phosphate in terms of coordination
geometry and coordination number.[10] The similarities to
transition-metal coordination[6b] suggest that anion complexes
might also find applications in various fields. To explore the
potential of these oligourea ligands in fluorescent materials
and biosensors (e.g. for the detection of phosphate), we
designed tetrakis(bisurea) derivatives L1 and L2, in which four
bisurea moieties are attached to a tetraphenylethene (TPE)
core (Scheme 1). It is expected that the rotation of the phenyl
rings of TPE about the ethene core would be restricted by
(TPE) ligand (L2) was designed, which, upon coordination
with phosphate ions, displays fluorescence “turn-on” over
a wide concentration range, from dilute to concentrated
solutions and to the solid state. The fluorescence enhancement
can be attributed to the restriction of the intramolecular
rotation of TPE by anion coordination. The crystal structure of
the A4L2 (A = anion) complex of L2 with monohydrogen
phosphate provides direct evidence for the coordination mode
of the anion. This “anion-coordination-induced emission”
(ACIE) is another approach for fluorescence turn-on in
addition to aggregation-induced emission (AIE).
T
he search for efficient luminescent materials continues to
be a topic of great interest.[1] Many fluorescent chromophores
show strong emission in dilute solutions but are only weakly
or non-emissive in concentrated solutions or the solid state
owing to aggregation-caused quenching (ACQ).[2] In 2001,
Tang and co-workers discovered “aggregation-induced emis-
sion” (AIE) for some compounds which are non-luminescent
in solution but are emissive in the aggregated state.[3] Since
this pioneering work, AIE luminogen molecules have
attracted much attention in fluorescent sensors, biological
probes, and solid-state lighting materials.[4] The AIE phenom-
enon is primarily caused by the restriction of intramolecular
rotation (RIR) which activates the fluorescence. This implies
that the fluorescence might also be switched on by restrictions
other than aggregation, such as the recently reported metal
coordination or metal-anion binding.[5]
Anion coordination chemistry has developed rapidly
because of the relevance of anions in many areas, such as in
biology, medicine, and the environment.[6] Phosphates (lipid
phosphates, inorganic phosphates, and phosphate esters) are
ubiquitous in biological systems and play important roles in
[*] J. Zhao, D. Yang, Dr. Y. Zhao, Prof. X.-J. Yang, Prof. Y.-Y. Wang,
Prof. B. Wu
Key Laboratory of Synthetic and Natural Functional Molecule
Chemistry of the Ministry of Education, College of Chemistry and
Materials Science, Northwest University
Xi’an 710069 (China)
Scheme 1. a) Structural formula of ligands L1 and L2; b) Schematic
illustration of the anion-coordination-induced emission.
E-mail: wubiao@nwu.edu.cn
Prof. B. Wu
anion coordination, thereby turning on the fluorescence. TPE
is a well-studied, iconic AIE chromophore.[11] However, the
deliberate design of fluorescent anion complexes with the
TPE backbone have not yet been reported. Herein, we
present the fluorescence turn-on properties of ligand L2 in
a wide concentration range through coordination to phos-
phate ions, which can be regarded as “anion-coordination-
induced emission” (ACIE).
State Key Laboratory of Applied Organic Chemistry, College of
Chemistry and Chemical Engineering, Lanzhou University
Lanzhou 730000 (China)
[**] This work was supported by the National Natural Science
Foundation of China (21271149 and 21325102). We thank the
referees for their helpful comments.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201402169.
6632
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 6632 –6636

Angewandte
Chemie
Initially, the nitrophenyl-substituted ligand L1 (Scheme 1)
was chosen as this substituent can enhance the anion binding
ability of the urea groups.[10] However, L1 showed very weak
emission even at high concentrations (Figure S20 in the
Supporting Information), possibly owing to the electron-
withdrawing effect of the nitro group. Therefore, the nitro
groups were replaced by methyl and L2 was synthesized
(Scheme 1; see Supporting Information for synthetic details).
Ligand L2 displayed almost no emission in dilute solution, but
the intensity of fluorescence at l = 500 nm (lex = 429 nm) was
significantly enhanced by increasing the concentration or
adding a poor solvent (Figure S20, S21), which is typical of
AIE activity.
Interestingly, ligand L2, non-emissive in the absence of
anions in dilute solution (1 ꢀ 10À5 m, DMSO), started to
exhibit fluorescent emission upon gradual addition of phos-
phate ions. When 10 equivalents of PO43À or 16 equivalents of
2À
HPO4
ions (generated in situ from (TBA)OH and
(TBA)H2PO4, TBA = tetrabutylammonium) were added,
the fluorescence intensity showed maximum enhancement,
by approximately 27- and 20-fold, respectively (Figure 1). The
Figure 2. a) Fluorescence emission spectra (lex =429 nm) of L2 (10 mm
in DMSO) upon addition of various anions (10 equiv); b) Variation of
fluorescence intensity at l=494 nm.
3À
ions (PO4 or HPO42À) by adding 100 equivalents of other
anions. The emission intensity was not affected by a 10-fold
excess of NO3À, BrÀ, ClÀ, ClO4À, and IÀ but was partially
quenched by HSO4À, CO32À, AcOÀ, HCO3À, and FÀ. How-
ever, the fluorescence was almost turned off when 100 equiv-
alents of SO42À ions were present (Figure S22).
1
In addition, H NMR spectroscopic studies were carried
out to study the interactions of these anions with L2. Addition
of SO4 and CO3 ions (10 equiv) to L2 caused large
downfield shifts of the resonance signals arising from the
urea NH protons, comparable to the shifts induced by
2À
2À
HPO42À, while AcOÀ, HCO3À, or H2PO4 ions resulted in
À
moderate downfield shifts. The 1H NMR spectrum of L2
showed no change or slight changes in the presence of
10 equivalents of NO3À, BrÀ, ClO4À, IÀ, HSO4À, ClÀ, or
À
HCO3 ions, implying very weak binding. Deprotonation of
the urea NH groups was observed upon addition of 10 equiv-
Figure 1. Fluorescence emission spectra (lex =429 nm) of L2 (10 mm in
DMSO) upon addition of a) 0–10 equiv of PO43À; and b) 0–16 equiv of
HPO42À. Insets: The increase of fluorescence intensity at l=494 nm.
alents of FÀ ions to L2 (Figure S15, S16).
The results of both NMR and fluorescence studies
indicate that the presence of other anions has different
influences on the fluorescence of the L2–phosphate system.
À
binding of L2 with various other anions was also examined.
The ClÀ, BrÀ, IÀ, NO3À, and ClO4 ions exhibited weak
2À
The addition of 10 equivalents of SO4 ions resulted in an
binding by L2 and thus did not affect the fluorescence. The
2À
2À
approximately 50% enhancement of the fluorescence inten-
sity (by 13-fold), while other anions induced either no obvious
SO4 and CO3 ions alone showed rather strong binding to
L2 but less fluorescence enhancement, suggesting that the
coordination mode may be different from (less restricting
than) that of the phosphate ion in solution. Nonetheless, these
anions can affect the fluorescence of the phosphate system
through competitive binding to the ligand. The situation for
the other anions, such as HSO4À, FÀ and HCO3À, may be more
complicated because of the possibility of multiple protona-
change (NO3À, BrÀ, ClÀ, ClO4À, IÀ, and HSO4 ) or only slight
À
enhancement (CO32À, as [K([18]crown-6)]+ salt; HCO3À, as
[Na([15]crown-5)]+ salt; H2PO4À, AcOÀ, and FÀ, as TBA+
salts; 10 equiv; Figure 2).
Moreover, competition experiments were conducted for
the system composed of L2 and 10 equivalents of phosphate
Angew. Chem. Int. Ed. 2014, 53, 6632 –6636
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
6633

.
Angewandte
Communications
2À
tion/deprotonation processes, which also interfere with the
phosphate coordination and the fluorescence properties.
To further understand the coordination mode of L2 with
phosphate and how it restricts the intramolecular rotation,
single crystals were grown of the monohydrogen phosphate
complex [K([18]crown-6)]8[(HPO4)4(L2)2] (1) from L2, K3PO4,
and [18]crown-6.[12] The existence of phosphate in its mono-
protonated form is confirmed by the eight [K([18]crown-6)]+
countercations and by the hydrogen-bond-donor character of
one of the oxygen atoms (see below). Efforts to crystallize the
orthophosphate complex have so far been unsuccessful even
under more basic conditions.
Notably, the HPO4 ions are not only hydrogen-bond
À
acceptors but also hydrogen-bond donors, forming a P
OH···O bond with one crown ether oxygen atom (O···O bond
length 2.885(9) and 2.771(7) ꢁ, O H···O angle 101.38 and
166.88; Figure 3c,d). This binding mode is quite similar to the
À
phosphate-binding protein (PBP), which forms twelve hydro-
2À
gen bonds with a HPO4 ion including one from the OH of
the anion.[13] Moreover, two CH···p interactions are formed
between the terminal p-tolyl rings and the bridging o-
phenylene planes within the A4L2 unit, with CH···plane
distances of 3.84–3.98 ꢁ (Figure S9), in a similar range to
those observed in our previous work.[10]
Complex 1 shows a 4:2 anion-to-ligand ratio, in which the
four HPO4 ions are sandwiched by two ligand molecules
The crystal structure clearly shows that the TPE chromo-
phore is “fixed” by the HPO4 coordination to the bisurea
2À
2À
stacking in a face-to-face fashion (Figure 3a,b). In the C2-
symmetric complex (space group C2221), the four terminal
bisurea arms of each ligand point to the same side of the
rectangular TPE moiety, entangling with the bisurea groups
arms, while the fluorescence of complex 1 increased greatly
compared to ligand L2 (Figure 4). However, for an unambig-
uous assignment of whether the fluorescence turn-on is
caused by anion coordination or by aggregation, more
evidence is necessary. An inspection of
the solid-state packing structure of com-
plex
1
indicates that the shortest
phenyl···phenyl separation between the
two TPE cores within one A4L2 complex
is 3.778 ꢁ (C17···C64; Figure S11). This
“intramolecular” (from the viewpoint of
the anion complex 1) contact may be
a result of the anion coordination that
brings the two ligands together. The dis-
tance is slightly longer than the closest
phenyl···phenyl contact (3.4 ꢁ) observed
for TPE derivatives, while larger separa-
tions (4.7 ꢁ) were reported for MOFs
(metal–organic frameworks) with TPE
cores, in which the fluorescence enhance-
ment is attributed to metal coordina-
tion.[5a] However, the shortest contact
between the phenyl rings of TPE in two
adjacent A4L2 moieties is much longer, at
9.89 ꢁ (Figure S10), suggesting that there
is essentially no further “intermolecular”
contact of the TPE chromophores even in
the solid-state structure. Therefore, the
fluorescence can be attributed to the
restriction effect of the sandwiched anion
Figure 3. Crystal structure of [(HPO4)4(L2)2]8À (1). a) The coordination of four HPO42À ions by
two ligands; b) Side view of the space-filling representation; c,d) Hydrogen bonds (broken
2À
lines) around the HPO4 ions.
of the other ligand to coordinate the anions. The P···P
separations between phosphate groups are 8.18 and 14.00 ꢁ,
and the distance between the central vinyl groups of the two
ligands is 5.78 ꢁ. The TPE cores of the two ligands are in
a slightly staggered conformation, with a torsion angle of 18.08
2À
=
between the two C C bonds. The four HPO4 ions display
two different coordination environments. Two (C2-related)
2À
HPO4 ions (P2 and P2B) are each coordinated by two
À
bisurea moieties through a total of twelve N H···O hydrogen
bonds, seven of which have N···O distances less than 3.2 ꢁ and
the other five in the range 3.2–3.5 ꢁ. The other type of
HPO42À (P1 and P1A) is also coordinated by four urea groups
À
Figure 4. Fluorescence emission spectra of L2 (10 mm and 1 mm in
DMSO) and complex 1 (1 mm in DMSO). Inset: magnified curves
(fluorescence intensity=0–160).
(through eight N H···O hydrogen bonds with N···O distances
in the range 2.7–3.2 ꢁ). There is an additional contact from
one O atom of the anion to a K+ countercation.
6634 www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 6632 –6636

Angewandte
Chemie
coordination. In other words, the solid-state anion complex 1,
the dimer, can be viewed as the smallest aggregate of TPE,
and gives rise to strong emission, fivefold higher than that of
L2 (Figure S23).
cations. Two C2-related CO32À anions are each coordinated by
À
four urea groups through nine N H···O hydrogen bonds, as
À
well as by an O H···O bond (O···O distance 2.744(7) ꢁ) to
a water molecule that is coordinated to a K+ countercation.
The other two CO3 anions are each coordinated by four
2À
In addition, dynamic light scattering (DLS) measure-
ments revealed no significant change in the light-scattering
À
urea groups through ten N H···O hydrogen bonds. Solution
binding studies demonstrated that ten equivalents of CO3
3À
2À
2À
intensity when 10 equivalents of PO4 or HPO4 ions were
added to L2, despite the obvious enhancement of the
fluorescence (Figure S24). On the other hand, when water
(a poor solvent for L2) was introduced to the solution of L2,
the fluorescence intensity (in DMSO-90% H2O) increased by
only a factor of five compared to that in DMSO (1 ꢀ 10À5 m;
Figure S21). However, the DLS intensity displayed a large
ions induced only a slight fluorescence enhancement and the
maximum intensity was observed with 120 equivalents of
2À
CO3 ions (11-fold increase; Figure S26), possibly owing to
a different binding mode in solution.
In conclusion, we have designed a tetrakis(bisurea) ligand
(L2) that incorporates the tetraphenylethene (TPE) chromo-
phore. The non-emissive ligand L2 displays a large fluores-
cence enhancement in the presence of phosphate ions in
a wide range of concentrations (dilute and concentrated
solutions, and solid state), which is attributable to the
restriction of the intramolecular rotation of TPE by anion
coordination. This unique “anion-coordination-induced emis-
sion” (ACIE) may find application in various areas such as
fluorescent sensors. Investigations on other ACIE systems
and their applications are currently underway.
3À
2À
increase (about 14 times that caused by PO4 or HPO4
ions), implying that the aggregation of L2 itself in the free
ligand has little contribution to the fluorescence. These results
further confirm that the large fluorescence enhancement is
predominantly induced by anion coordination rather than the
aggregation of L2.[5b]
The 1H NMR spectrum of complex 1 in [D6]DMSO
displays large downfield shifts (Dd = 1.88–2.80 ppm; Fig-
ure S13) for all of the resonance signals arising from urea
1
NH protons compared to the free ligand L2. The H NMR
Received: February 6, 2014
Published online: May 18, 2014
titration experiment (Figure S14) showed a slow exchange
process with broadened NH signals for the formed anion
complex. The signals became well-resolved when 2.0 equiv-
alents of HPO42À ions were added, and no further change was
observed with more HPO42À. The spectrum is very similar to
that of complex 1, indicating the formation of the 1:2 (host/
guest) species. Moreover, the NOESY spectrum of complex
1 (Figure S17, S18) reveals cross-peaks between H6-H7/H8,
H4/H5–H7, and H4/H5–H8 (see Scheme 1 for the proton
numbering) on the terminal p-tolyl and bridging o-phenylene
rings, respectively, because of through-space coupling inter-
actions. These interactions suggest that the A4L2 complex may
be persistent in solution. This is further supported by the Jobꢂs
plot of the fluorescence spectra at l = 505 nm, which gives
a 1:2 (2:4) stoichiometry (Figure S25), consistent with com-
plex 1.
Keywords: anion coordination · fluorescence turn-on ·
.
oligourea · phosphate · tetraphenylethene
[1] a) S. W. Thomas III, G. D. Joly, T. M. Swager, Chem. Rev. 2007,
107, 1339 – 1386; b) Y. Hong, J. W. Y. Lam, B. Z. Tang, Chem.
Commun. 2009, 4332 – 4353.
[2] J. B. Birks, Photophysics of Aromatic Molecules, Wiley, London,
1970.
[3] a) J. Luo, Z. Xie, J. W. Y. Lam, L. Cheng, H. Chen, C. Qiu, H. S.
Kwok, X. Zhan, Y. Liu, D. Zhu, B. Z. Tang, Chem. Commun.
2001, 1740 – 1741; b) B. Z. Tang, X. Zhan, G. Yu, P. P. S. Lee, Y.
Liu, D. Zhu, J. Mater. Chem. 2001, 11, 2974 – 2978.
[4] a) Aggregation-Induced Emission: Applications (Eds.: B. Z.
Tang, A. Qin), Wiley, Hoboken, 2013; b) Y. Hong, J. W. Y.
Lam, B. Z. Tang, Chem. Soc. Rev. 2011, 40, 5361 – 5388; c) J.
Huang, N. Sun, J. Yang, R. Tang, Q. Li, D. Ma, J. Qin, Z. Li, J.
Mater. Chem. 2012, 22, 12001 – 12007; d) C. W. T. Leung, Y.
Hong, S. Chen, E. Zhao, J. W. Y. Lam, B. Z. Tang, J. Am. Chem.
Soc. 2013, 135, 62 – 65; e) E. Quartapelle Procopio, M. Mauro,
M. Panigati, D. Donghi, P. Mercandelli, A. Sironi, G. DꢂAlfonso,
L. De Cola, J. Am. Chem. Soc. 2010, 132, 14397 – 14399; f) W. Z.
Yuan, P. Lu, S. Chen, J. W. Y. Lam, Z. Wang, Y. Liu, H. S. Kwok,
Y. Ma, B. Z. Tang, Adv. Mater. 2010, 22, 2159 – 2163; g) H. Shi, J.
Liu, J. Geng, B. Z. Tang, B. Liu, J. Am. Chem. Soc. 2012, 134,
9569 – 9572.
The change in the emission intensity of complex 1 with
varying concentration (from 10 mm to 1 mm in DMSO)
displays very interesting features. In dilute solutions (10 mm
to 0.1 mm), the fluorescence intensity showed a nearly linear
increase. After 0.25 mm, the fluorescence increased slightly
and reached a plateau at about 1 mm (Figure S27). Therefore,
the fluorescence of ligand L2 can be “turned on” by phosphate
in a rather wide concentration range, from dilute to concen-
trated solutions as well as in the solid state, which is
significantly different from both the ACQ and AIE chromo-
phores. The quantum yields (F) of L2 and complex 1 in
solution (1 ꢀ 10À4 m, DMSO) are 9.1% and 41.3%, respec-
tively, as measured using an integrating sphere (Table S4).
Efforts have also been made to synthesize complexes of
other anions, and a similar A4L2 (A = anion) complex of
carbonate, [K([18]crown-6)]8[(CO3)4(L2)2] (2), has been iso-
lated. Complex 2 (space group C2/c) is essentially isostruc-
˘
[5] a) N. B. Shustova, B. D. McCarthy, M. Dinca, J. Am. Chem. Soc.
2011, 133, 20126 – 20129; b) T. Noguchi, B. Roy, D. Yoshihara, Y.
Tsuchiya, T. Yamamoto, S. Shinkai, Chem. Eur. J. 2014, 20, 381 –
384.
[6] a) J. M. Lehn, Acc. Chem. Res. 1978, 11, 49 – 57; b) Anion
Coordination Chemistry, (Eds.: K. Bowman-James, A. Bianchi,
E. Garcꢃa-EspaÇa), Wiley-VCH, Weinheim, 2011; c) P. D. Beer,
P. A. Gale, Angew. Chem. 2001, 113, 502 – 532; Angew. Chem.
Int. Ed. 2001, 40, 486 – 516; d) E. A. Katayev, Y. A. Ustynyuk,
J. L. Sessler, Coord. Chem. Rev. 2006, 250, 3004 – 3037; e) J. W.
2À
tural to the HPO4 analogue 1 (Figure S12). There are also
two types of coordination mode for the four CO32À ions: with
or without the anion–K coordination to the [K([18]crown-6)]+
Angew. Chem. Int. Ed. 2014, 53, 6632 –6636
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
6635

.
Angewandte
Communications
Steed, Chem. Soc. Rev. 2009, 38, 506 – 519; f) C. Caltagirone,
P. A. Gale, Chem. Soc. Rev. 2009, 38, 520 – 563.
[7] a) F. H. Westheimer, Science 1987, 235, 1173 – 1178; b) T.
Berndt, R. Kumar, Physiology 2009, 24, 17 – 25.
[8] a) A. I. Jonckheere, J. A. M. Smeitink, R. J. T. Rodenburg, J.
Inherited Metab. Dis. 2012, 35, 211 – 225; b) A. Munshi, R.
Ramesh, Genes Cancer 2013, 4, 401 – 408; c) D. Fisher, L.
Krasinska, D. Coudreuse, B. Novꢄk, J. Cell Sci. 2012, 125, 4703 –
4711.
[9] a) S. J. Brooks, P. A. Gale, M. E. Light, CrystEngComm 2005, 7,
586 – 591; b) S. J. Brooks, P. A. Gale, M. E. Light, Chem.
Commun. 2005, 4696 – 4698.
[11] a) W. Qin, D. Ding, J. Liu, W. Z. Yuan, Y. Hu, B. Liu, B. Z. Tang,
Adv. Funct. Mater. 2012, 22, 771 – 779; b) L. Liu, G. Zhang, J.
Xiang, D. Zhang, D. Zhu, Org. Lett. 2008, 10, 4581 – 4584; c) T.
Noguchi, T. Shiraki, A. Dawn, Y. Tsuchiya, L. T. N. Lien, T.
Yamamoto, S. Shinkai, Chem. Commun. 2012, 48, 8090 – 8092.
[12] Crystal
data
for
complex
1:
red-brown
block,
C280H388K8N32O88P4, M = 6046.90, orthorhombic, space group
C222(1), a = 29.419(6), b = 44.908(9), c = 28.031(5) ꢁ, V=
37033(12) ꢁ3, T= 150 K, Z = 4, 114503 refl. collected, 31522
unique (Rint = 0.0799), R1 = 0.1172 (I > 2s(I)), wR2 = 0.3215 (all
data). Crystal data for complex 2: yellowish-brown block,
C138H177K4N17O39, M = 2854.37, monoclinic, space group C2/c,
[10] a) C. Jia, B. Wu, S. Li, Z. Yang, Q. Zhao, J. Liang, Q.-S. Li, X.-J.
Yang, Chem. Commun. 2010, 46, 5376 – 5378; b) C. Jia, B. Wu, S.
Li, X. Huang, X.-J. Yang, Org. Lett. 2010, 12, 5612 – 5615; c) C.
Jia, B. Wu, S. Li, X. Huang, Q. Zhao, Q.-S. Li, X.-J. Yang, Angew.
Chem. 2011, 123, 506 – 510; Angew. Chem. Int. Ed. 2011, 50, 486 –
490; d) S. Li, C. Jia, B. Wu, Q. Luo, X. Huang, Z. Yang, Q.-S. Li,
X.-J. Yang, Angew. Chem. 2011, 123, 5839 – 5842; Angew. Chem.
Int. Ed. 2011, 50, 5721 – 5724; e) B. Wu, F. Cui, Y. Lei, S. Li,
N. D. S. Amadeu, C. Janiak, Y.-J. Lin, L.-H. Weng, Y.-Y. Wang,
X.-J. Yang, Angew. Chem. 2013, 125, 5200 – 5204; Angew. Chem.
Int. Ed. 2013, 52, 5096 – 5100.
a = 44.964(12), b = 27.634(7), c = 27.188(7) ꢁ, b = 91.159(8)8,
V= 33776(15) ꢁ3, T= 150 K, Z = 8, 135746 refl. collected,
28561 unique (Rint = 0.0948), R1 = 0.1249 (I > 2s(I)), wR2 =
0.2987 (all data). CCDC 985431 (1) and 985432 (2) contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[13] P. S. Ledvina, N. H. Yao, A. Choudhary, F. A. Quiocho, Proc.
Natl. Acad. Sci. USA 1996, 93, 6786 – 6791.
6636 www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 6632 –6636