The effect of the spacer of bis(biurea) ligands on the structure of A2L3-type (A=anion) phosphate complexes

Article abstract of DOI:10.1002/chem.201405235

By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A₂L₃ complexes (A represents anion, here orthophosphate PO₄^3-), namely helicate, mesocate, and mono-bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordinationbased structures as in transition-metal complexes.

Full text of DOI:10.1002/chem.201405235

DOI: 10.1002/chem.201405235
Full Paper
&
Anion Coordination
The Effect of the Spacer of Bis(biurea) Ligands on the Structure of
A2L3-type (A=anion) Phosphate Complexes
Biao Wu,*[a] Shaoguang Li,[b] Yibo Lei,[a] Huaiming Hu,[a] Nader de Sousa Amadeu,[c]
Christoph Janiak,[c] Jennifer S. Mathieson,[d] De-Liang Long,[d] Leroy Cronin,[d] and Xiao-
Juan Yang*[a]
Abstract: By tuning the length and rigidity of the spacer of
bis(biurea) ligands L, three structural motifs of the A2L3 com-
plexes (A represents anion, here orthophosphate PO43À),
namely helicate, mesocate, and mono-bridged motif, have
been assembled by coordination of the ligand to phosphate
anion. Crystal structure analysis indicated that in the three
complexes, each of the phosphate ions is coordinated by
twelve hydrogen bonds from six surrounding urea groups.
The anion coordination properties in solution have also
been studied. The results further demonstrate the coordina-
tion behavior of phosphate ion, which shows strong tenden-
cy for coordination saturation and geometrical preference,
thus allowing for the assembly of novel anion coordination-
based structures as in transition-metal complexes.
Introduction
Control of supramolecular self-assembly to yield desired struc-
tures and functions is a fundamental goal for chemists, where-
in rational design of the ligands (or hosts) and careful choice
of the coordination centers (guests) are key factors. Among
various metal coordination-based supramolecular systems, heli-
cal complexes (helicates) are a very important class of struc-
tures because of their significant aesthetic and biomimetic at-
tractions.[1–5] For the M2L3 complexes with two octahedral
metal ions and three bis(bidentate) ligands, two possible triply
bridged structures are normally encountered: the homochiral
helicates where the two metal centers display identical abso-
lute configurations (DD or LL) and the achiral meso-helicates
(also called mesocates) in which the metal ions possess oppo-
site configurations (DL) (Scheme 1).[6] Although far less
common, there is also a mono-bridged motif for the M2L3-type
[a] Prof. B. Wu, Prof. Y. Lei, Prof. H. Hu, Prof. X.-J. Yang
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 (P. R. China)
E-mail: wubiao@nwu.edu.cn
Scheme 1. Various structural motifs (helicate, mono-bridged, and mesocate)
of the [A2L3] anion complexes with bis(biurea) ligands bearing different
spacers (L1–L4).
yangxiaojuan@nwu.edu.cn
[b] Dr. S. Li
complexes in which only one bis(bidentate) ligand functions as
a bridge between the two metal ions while each of the other
two ligands chelates a metal ion in the terminal tetradentate
fashion (Scheme 1). To control the formation of these struc-
tures, thorough investigations have been carried out on the
self-assembly processes, in particular the influences of li-
gands.[7] On the basis of studies on a series of dicatechol li-
gands with an alkyl spacer, Albrecht[8] suggested the empirical
odd–even rule that demonstrates the effect of the alkyl spacer
on the structure of M2L3 complexes. With an even number of
carbon atoms (methylene groups) of the alkyl linker, the ligand
State Key Laboratory for Oxo Synthesis & Selective Oxidation
Lanzhou Institute of Chemical Physics, CAS
Lanzhou 730000 (P. R. China)
[c] Dr. N. de Sousa Amadeu, Prof. Dr. C. Janiak
Institut fꢀr Anorganische Chemie und Strukturchemie
Universitꢁt Dꢀsseldorf
Universitꢁtsstrasse 1, 40225, Dꢀsseldorf (Germany)
[d] Dr. J. S. Mathieson, Dr. D.-L. Long, Prof. L. Cronin
WestCHEM, School of Chemistry, University of Glasgow
University Avenue, Glasgow G12 8QQ, Scotland (UK)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201405234.
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tends to adopt the S conformation and a helicate is preferred.
In contrast, when the alkyl linker has an odd number of carbon
atoms, the ligand will display the C conformation, and thus
favors a mesocate structure (Scheme 1).
Anion coordination chemistry has been rapidly developed
and applied in anion binding in recent years. It has been
shown that anions also display some stereoelectronic and geo-
metrical preference as the transition-metal ions.[9,10] Therefore,
it should be possible to construct novel anion-based structures
such as cages, knots, and helicates in which the coordination
centers are anions instead of metal ions.[11] Although this area
is still under exploration, it already led to an exciting branch of
coordination chemistry. Inspired by the coordination behavior
of the well-known oligo-pyridine ligands, we have recently de-
signed a class of oligo-urea anion receptors[12] with the ortho-
phenylene bridge[13] between two urea groups, which has
proven to be able to provide complementary anion binding
sites. The results clearly demonstrated the resemblance of
oligo-urea and oligo-pyridine ligands in anion and metal coor-
dination, in which each urea subunit (two NH donors) indeed
serves as a coordination vector towards an anion, like a pyridyl
group towards a metal ion. By using a bis(biurea) ligand with
an ethylene spacer (L1), the first triple-stranded anion helicate,
[(PO4)2(L1)3]6À (1), was successfully obtained upon coordinating
to phosphate ions.[12d]
Figure 1. a) Molecular structure of the mono-bridged [(PO4)2(L2)3]6À (2), and
b) illustration of the different ligand conformations in this meso-structure.
The two PO43À coordination octahedra were generated by connecting the
six coordination vectors (urea groups). Other atoms and groups were omit-
ted for clarity. (A color version of this figure can be found in the Supporting
Information).
structure expected for ligand L2 with an odd spacer (propyl-
ene). Instead, the mono-bridged motif (Figure 1 and Scheme 1)
was formed, which is an unusual alternative of the triple-
stranded architectures. In the [(PO4)2(L2)3]6À complex, only one
of the three ligands acts as a bridge between the two phos-
phate ions, while the other two ligands function in a terminal
“tetradentate” chelating manner to bind the two anions. The
bridging ligand adopts a “C”-shaped (AA-trans) conformation
for the propylene spacer, but its two biurea moieties are ar-
ranged in an anti fashion. The other two ligands adopt such
a conformation that three of the urea groups are roughly co-
planar, occupying three edges of a square, while the fourth
urea arm is almost perpendicular to the plane, resulting in
In the helicate 1, each phosphate center is coordinated by
twelve hydrogen bonds (saturated coordination for tetrahedral
anions)[10c] from six urea groups in an approximately octahedral
coordination geometry (Scheme 1). This coordination satura-
tion and geometrical preference is very similar to transition-
metal ions, which not only endows the anion center chirality,
but also ensures the formation of the desired triple-stranded
structure. Moreover, the formation of 1 follows the odd–even
rule just like the metal helicates with the ethylene spacer.
These facts encouraged us to further explore the assembly of
the A2L3 complexes. It was supposed that the mesocate topol-
ogy for A2L3-type complexes should also be obtained by
tuning the spacer of the bis(biurea) building blocks. To this
end, a series of bis(biurea) ligands (L2–L4) with different spacers
(R group; see Scheme 1) have been synthesized. Herein we
report the self-assembly of dinuclear phosphate complexes
with these bis(biurea) ligands both in the solid state and in so-
lution. It is very interesting that three types of structures, in-
cluding the less common, mono-bridged motif (2), the meso-
cate (3), and the helicate (4), have been obtained from these li-
gands (Scheme 1).
3À
a folded GG-cis conformation. Thus, each PO4 center is ac-
tually coordinated by a whole and a half ligand rather than
three half ligands found in the triple-bridged helicate or meso-
cate structure. This mono-bridged topology has been reported
in M2L3 transition-metal complexes; for example, the iron(III)
and nickel(II) coordination architectures with alcaligin (AG) and
a tetradentate bis(pyrazolyl pyridine) with an o-xylylene space,
respectively.[14] Notably, the two anions within one
[(PO4)2(L2)3]6À unit in complex 2 display opposite absolute con-
figurations (D and L), indicating a meso-structure (space
group P21/c).
Nevertheless, within each half of the mono-bridged com-
3À
plex, the PO4 ion is coordinated by six urea groups from
Results and Discussion
three biurea domains through twelve hydrogen bonds (N···O
distances range from 2.746 (5) to 2.928(5) ꢁ, and NÀH···O
angles from 149 to 1778; Figure 1, Supporting Information,
Table S2). This is similar to the helicate 1 and further reveals
the strong binding ability of phosphate ion and its require-
ment for saturated coordination. The average N···O distance in
Synthesis and crystal structures of the phosphate complexes
2–4
From a mixture of L2, K3PO4, and 18-crown-6, crystals of com-
plex
2
with the composition [K(18-crown-6)]6[(PO4)2(L2)3]·
3Et2O·2Me2CO·H2O were isolated in high yield (>85%). Sur-
prisingly, although the complex has the anion-to-ligand ratio
of 2:3 (A2L3), it does not display the triple-stranded mesocate
2 (2.800 ꢁ) is almost identical to that in the helicate
1 (2.802 ꢁ). Furthermore, as in the helicate structure 1, T-
shaped CÀH···p interactions (about 3.6 ꢁ) are also observed in
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the meso complex 2 between the terminal aromatic rings and
o-phenylene planes.[15]
In complex 2, it appears that the propylene spacer has con-
siderable flexibility and can assume both the “C”-shaped bis(bi-
dentate) conformation and the folded tetradentate motif. To
evaluate the energy preference of the different conformations,
DFT calculations were carried out on the A2L3 phosphate com-
plexes of L2 at the B3LYP/6-31G level. All of the three struc-
tures (helicate a, mesocate b, and mono-bridged motif c; Sup-
porting Information, Figure S1) have been built and opti-
mized.[16] The total energies revealed that the mono-bridged
species c (complex 2) is indeed the most stable structure,
whose energy is 59.5 and 95.9 kJmolÀ1 lower than the meso-
cate (b) and helicate (a), respectively. This is in good agree-
ment with the experimental formation of complex 2. Overall
the homochiral helicate (a) has the highest energy, which is
consistent with the odd–even rule that an odd spacer prefers
the meso structure rather than the helicate. However, even the
lower-energy mesocate b was not favored in this case and the
structure c (complex 2) was chosen as the optimal mode. The
reason why the structure c but not b was formed might be at-
tributed to the repulsive forces of the three intertwined alkyl
groups in model (b) as well as ligand strains caused by coordi-
Figure 2. Molecular structure of the mesocate [(PO4)2(L3)3]6À (3). a) Side view,
b) top view, and c) space-filling representation. There is a mirror plane (s)
across the m-xylylene groups. The counter-cations, non-acidic hydrogen
atoms, and nitro groups are omitted for clarity. (A color version of this figure
can be found in the Supporting Information).
even number of carbon atoms, gave the expected helicate
[K(18-crown-6)]6[(PO4)2(L4)3] (4) following the odd–even rule
(Scheme 1). In the triple-stranded anion complex [(PO4)2(L4)3]6À
,
the two phosphate centers assume the same configuration
(DD or LL), each of which is coordinated by six urea groups
through twelve hydrogen bonds. Unfortunately, we have only
obtained the preliminary crystal structure for this complex,
which showed the backbone of the helicate but did not allow
further refinement of the structure.
3À
nation with the PO4 ions.
It should be noted that although most M2L3 systems follow
the odd–even rule, there are also considerable exceptions in
the literature. For instance, Dolphin et al. reported the observa-
tion of both helicate and mesocate structures formed by the
same bis(dipyrromethene) ligand and studied the isomeriza-
tion of the two conformers.[17] In some other cases, the triple-
stranded helicate is in competition with more complicated
structures (for example, tetrahedral cage).[14] Thus, other factors
(such as the coordination center, solvent, counterions, and
templates) should also be considered when applying this em-
pirical rule.
Solution coordination studies of the ligands with phosphate
anion
3À
The assembly of the ligands and PO4 ions in solution was in-
vestigated by UV/Vis, NMR, and ESI-MS techniques. In the case
of L2 (complex 2), Job’s plot of UV/Vis titrations revealed that
3À
As the propylene-linked ligand L2 did not form the triple-
bridged anion mesocate, which is partially due to its flexibility,
we replaced the propylene spacer with m-xylylene, which is
semi-rigid and also has an odd number of carbon atoms, and
synthesized the bis(biurea) ligand L3 (Scheme 1). Promisingly,
the ligand and PO4 anion form the 3:2 binding mode in
DMSO/5% H2O (Supporting Information, Figure S2). The
1H NMR, 2D-TOCSY, 2D-NOE, and 2D-DOSY studies were carried
out by using the isolated complex 2 dissolved in [D6]DMSO. In
1
the H NMR spectrum of 2, all of the urea NH groups showed
3À
in this case the assembly of ligand L3 and PO4 anion afforded
very large downfield shifts compared with the free ligand
(Dd=3.01–4.41 ppm; Figure 3a). These values are even larger
than those (Dd=2.86–3.90 ppm) in the helicate 1, suggesting
stronger hydrogen bonding in 2 as also proved by the hydro-
gen bonding parameters in the crystal structure. An obvious
upfield shift (Dd=À0.6 ppm) of the H8 proton on the terminal
nitrophenyl rings (see Scheme 1 for the numbering of the pro-
tons) was observed that is due to the shielding effects caused
by the formation of the anion complex. The most interesting
feature of the NMR spectrum, however, is the slow equilibrium
of the complex with other components on the NMR timescale
(because of the strong interactions between L2 ligands and
the desired triple-bridged mesocate complex 3 with the com-
position [K(18-crown-6)]6[(PO4)2(L3)3]·3H2O. In the [(PO4)2(L3)3]6À
3À
unit three C-shaped ligands coordinate with two PO4 anions
to form the dinuclear triple-stranded complex. The two phos-
phate anion centers, which reside in pseudo-octahedral coordi-
nation geometries, assume opposite configurations (D/L) on
the two sides of a mirror plane (Figure 2a). As in the analogous
helicate 1, each phosphate ion is also bound by six urea
groups from three different bis(biurea) ligands through twelve
hydrogen bonds (N···O distances range from 2.606(3) to
2.994(2) ꢁ, and NÀH···O angles from 145 to 1688; Figure 2, Sup-
porting Information, Table S3). The average N···O distance
(2.819 ꢁ) in the mesocate 3 is slightly longer than that in 2
and the helicate 1.
3À
PO4 ions). This character leads to well-resolved NMR signals
and allows for clear elucidation of the structure in solution.
Although the UV/Vis results point to the formation of an
[A2 L3] complex, they are not sufficient for the discrimination
among the helicate, mesocate, and mono-bridged motif. To
The p-xylylene-spaced bis(biurea) ligand L4, which has
a spacer that is one carbon longer than L3 and thus has an
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well-resolved spectrum of structure 2 (seven) but is more than
three (for helicate) and four (for mesocate), indicating the pres-
ence of structure 2. When the sample was heated, the signals
of Ha and Hb protons broadened gradually and showed an ob-
vious coalescence at 309 K, indicating the inversion of the con-
figurations at the two coordination centers (D1L2 to L1D2) on
the NMR timescale. This temperature is just slightly higher
than room temperature, and the free-energy barrier of the dy-
namic process was calculated to be 24.1 kJmolÀ1 (from the
Eyring equation).
In the 2D-TOCSY (total correlation spectroscopy) spectrum
of complex 2 (Supporting Information, Figures S5, S6), NHa1
and NHb1, NHa2 and NHb2, NHc1 and NHd, and NHc2 and NHd
are correlative, which means that they belong to their respec-
tive spin systems and further confirms their 1H NMR assign-
ments in Figure 3. The H7 and H8 signals at around 7.6 ppm
(7.4–7.7 ppm) can be assigned as a same spin system, and the
2D-NOE spectrum of 2 (Supporting Information, Figure S7) re-
vealed their spatial proximity with the bridging phenylene pro-
tons (H3 to H6). The 2D diffusion ordered spectroscopy (2D-
DOSY) in [D6]DMSO at 300 K was also performed (Supporting
Information, Figure S8). For L2, the measured diffusion coeffi-
cient (D=1.44ꢂ10À10 m2 sÀ1) corresponds to a hydrodynamic
radius (rs, calculated from the Stokes–Einstein equation) of
7.7 ꢁ. For complex 2, all the peaks correlating to L2 are in a hor-
izontal line with a D value of 8.09ꢂ10À11 m2 sÀ1, corresponding
to an rs value of 13.1 ꢁ that is much larger than the single
ligand. This radius and the calculated hydrodynamic volume
(9412 ꢁ3) are very close to the estimated rotary radius and
volume (13.4 ꢁ, 10051 ꢁ3) for [(PO4)2(L2)3]6À in the crystal struc-
ture of 2 (Supporting Information, Figure S9), which confirmed
the persistence of the complex in solution.
Figure 3. 1H NMR spectra of L2 and complex 2 in [D6]DMSO. a) The low- and
b) high-field regions (see Scheme 1 for the numbering of the protons).
confirm that the “folded” structure of 2 is preferred in solution,
other evidence is necessary. One of the most important fea-
tures of complex 2 is that the three ligands adopt two confor-
mations, while they are identical in both the C3-symmetric heli-
cate and mesocate. This difference should be reflected in the
NH protons and the CH2CH2CH2 spacer. Notably, the urea NH
signals of complex 2 split into two sets with a 2:1 integral
ratio, which perfectly demonstrates the presence of two differ-
ent conformers of the ligands (the tetradentate form and bis-
(bidentate) form). Moreover, this splitting decreases when the
chemical environment of the NH protons becomes closer, from
152.1 and 176.0 Hz for the “inner” NHa and NHb to complete
overlapping (0 Hz) for the far end NHd protons (Figure 3a).
The CH2CH2CH2 spacer is also a good stereochemical probe
for determining the topology of the M2L3 complexes.[8a] In the
helicate and mesocate, the Hb protons (Figure 3b) are diaste-
ESI-MS studies were carried out for the complexes. In the
mono-bridged structure 2, the A2L3 anion complex [(PO4)2(L2)3]
was detected at m/z 1140.8 for [(PO4)2(L2)3H2K2]2À (calcd.
1140.76), 1272.9 for [(PO4)2(L2)3H2K2(18-crown-6)]2À (calcd.
1272.84), and 1405.0 for [(PO4)2(L2)3K2H2(18-crown-6)2]2À (calcd.
1404.92), respectively (Supporting Information, Figure S10 and
Table S4). Furthermore, in our previous experiment for the heli-
cate [(PO4)2(L1)3]6À (1), the 2:3 species could not be observed.
However, by increasing the concentration of the sample,
1
reotopic, which could result in two multiplets in the H NMR
spectrum. Moreover, in the helicate, the central Ha protons are
enantiotopic, leading to one signal in solution. In contrast, the
Ha protons present diastereotopic behavior (two multiplets) in
the mesocate. Thus, the propylene protons should show three
multiplets in the helicate, but they could exhibit four signals in
the mesocate. The situation is even more complicated for the
mono-bridged complex 2. Considering the two different con-
formations of the three ligands, the Ha protons of the
the
A2 L3
species
[(PO4)2(L1)3H2K2(18-crown-6)]2À
and
[(PO4)2(L1)3H2K2(18-crown-6)]2]2À at m/z 1251.9 and 1383.9
(calcd. 1251.81 and 1383.90), respectively, were observed in
CH2Cl2 (Supporting Information, Figure S11 and Table S5). In
these MS spectra, however, other fragments, including the de-
protonated ligand, and the 1:1, 1:2 and 1:3 (guest to host)
anion coordination species, are also present, indicating that
the anion complexes are labile during the ionization processes.
CH2CHa CH2 spacer could cause up to three signals (the chemi-
2
cal environments of the two Ha protons in the bridging ligand
are very close, but they are different for the terminal ligands)
and the Hb protons could induce up to four peaks. Therefore,
the propylene spacer of 2 might show seven signals (or less if
overlap occurs).
Conclusion
Variable-temperature 1H NMR experiments in [D6]DMSO/
CDCl3 have been conducted (Supporting Information, Fig-
ure S4). At room temperature, two multiplets of the Ha protons
and three signals of the Hb protons were observed. The total
number of visible peaks (five) is less than expected for the
A series of new bis(biurea) ligands (with the flexible propylene
and semi-rigid m-xylylene and p-xylylene spacer, respectively)
coordinate with phosphate ions to generate the A2L3-type
anion complexes. The biurea coordination domains exhibited
3À
excellent complementarity to the PO4 ions. Because of the
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1
L4: Light yellow solid. M.p.: >3008C. H NMR (400 MHz, [D6]DMSO,
ppm): d 9.87 (s, 2H, Hd), 8.25 (s, 2H, Hc), 8.18 (d, J=8.0 Hz, 4H,
H6), 7.99 (s, 2H, Hb), 7.70 (d, J=8.0 Hz, 4H, H5), 7.59 (d, J=8.0 Hz,
2H, H4), 7.51 (d, J=8.0 Hz, 2H, H1), 7.27 (s, 4H, Ha), 7.06 (m, 6H,
Ha, H2, H3), 4.28 (d, J=8.0 Hz, 4H, Hb). 13C NMR (100 MHz,
[D6]DMSO), 155.7 (CO), 152.6 (CO), 146.6 (C), 140.8 (C), 138.6 (C),
132.7 (C), 129.6 (C), 127.2 (CH), 125.1 (CH), 124.9 (CH), 124.7 (CH),
123.2 (CH, CH), 122.9(CH), 117.2 (CH), 42.7 (CH2). IR (KBr): n˜ =3354,
coordination saturation requirement of the phosphate ion (12
hydrogen bonds) and its octahedral coordination geometry, as
well as the intrinsic stereochemical preference of the spacer in
the bis(biurea) ligands, these species make ideal building
blocks for the construction of novel anion-based architectures
similar to those of the metal ion-based systems. By altering the
rigidity and conformation of the spacer of bis(biurea) recep-
tors, the three topologies of the A2L3 complexes (helicate, mes-
ocate, and mono-bridged structure) can be successfully assem-
bled. The present work provides a helpful approach to the
control of the configuration in the self-assembly of helical
structures. Furthermore, these results may help the design of
new anion ligands and construction of anion-coordination ar-
chitectures. Assembly of other novel anion coordination-based
topologies is currently underway in our laboratory.
3294, 3076, 1655, 1597, 1579, 1502, 1321, 1200 cmÀ1
. Anal.
calcd (%) for C36H32N10O8: C 59.01, H 4.40, N 19.12; found: C 58.73,
H 4.45, N 18.82. ESI-MS: m/z 100%, 733.2 [M+H]+; 70%, 755.2
[M+Na]+.
[K(18-crown-6)]6[(PO4)2(L2)3]·3Et2O·2Me2CO·H2O (2): Ligand L2
(33.5 mg, 0.5 mmol), K3PO4·10H2O (18.5 mg, 0.5 mmol), and 18-
crown-6 (39.6 mg, 1.5 mmol) were suspended in acetone (5 mL).
After stirring for 2 h at room temperature, a clear reddish-orange
solution was obtained. Slow vapor diffusion of diethyl ether into
this solution provided yellow crystals of complex 2 within 3 days
(67 mg, 85%). M.p. 1588C. Anal. calcd (%) for C165H236K6N30O69P2:
C 49.05, H 5.89, N 10.40; found: C 48.82, H 5.73, N 9.98.
[K(18-crown-6)]6[(PO4)2(L3)3]·3H2O (3): A mixture of L3 (36.6 mg,
0.5 mmol), K3PO4·10H2O (18.5 mg, 0.5 mmol), and 18-crown-6
(39.6 mg, 1.5 mmol) in acetone (5 mL) was stirred for 5 h at room
temperature to give an orange solution. Slow vapor diffusion of di-
ethyl ether yielded yellow crystals of complex 3 (crystal yield:
46 mg, 60%). M.p. 1708C. Anal. calcd (%) for C180H246K6N30O71P2:
C 50.72, H 5.82, N 9.86; found: C 50.51, H 5.90, N 9.63.
[K(18-crown-6)]6[(PO4)2(L4)3] (4): Complex 4 was synthesized by
a similar method to that used for 3, from L4 (36.6 mg, 0.5 mmol),
K3PO4·10H2O (18.5 mg, 0.5 mmol), and 18-crown-6 (39.6 mg,
1.5 mmol), as yellow crystals (50 mg, 70%). M.p. 1928C. Anal.
calcd (%) for C180H240K6N30O68P2: C 51.37, H 5.75, N 9.98; found:
C 51.03, H 5.87, N 9.66.
Experimental Section
General considerations
o-Nitrophenylisocyanate and p-nitrophenylisocyanate were pur-
chased from Alfa Aesar and used as received. All solvents and
other reagents were of reagent-grade quality. 1H and 13C NMR
spectra were recorded on a Mercury plus-400 spectrometer at
400 MHz and 100 MHz, respectively, using TMS as an internal stan-
dard. UV/Vis spectra were performed on an HP8453 spectropho-
tometer (1 cm quartz cell). Elemental analyses were performed on
an Elementar VarioEL instrument. IR spectra were recorded on
a Bruker IFS 120HR spectrometer. ESI-MS measurements of the li-
gands and anion complexes were carried out using a Waters
ZQ4000 spectrometer and a Bruker MicrOTOF-Q spectrometer, re-
spectively. Melting points were detected on an X-4 Digital Vision
MP Instrument.
X-ray crystallography
Diffraction data were collected on a Bruker SMART APEX II diffrac-
tometer at 173 K with graphite-monochromated Mo-Ka radiation
(l=0.71073 ꢁ) for complex 2 or Cu-K radiation (l=1.54178 ꢁ) for
complex 3. An empirical absorption correction using SADABS was
applied for all data. The structures were solved by direct methods
using the SHELXS program. All non-hydrogen atoms were refined
anisotropically by full-matrix least-squares on F2 by the use of the
SHELXL program. Hydrogen atoms bonded to carbon and nitrogen
were included in idealized geometric positions with thermal pa-
rameters equivalent to 1.2 times those of the atom to which they
were attached. Hydrogen atoms on the water oxygen atoms for
complex 3 were located from the difference Fourier map and then
refined considering their chemical environments with restraints
(OÀH 0.85(2) ꢁ), with U(H) fixed at 0.08 ꢁ2. Crystal data and refine-
ment details of complexes 2 and 3 are given in the Supporting In-
formation, Table S1. CCDC 902016 (2) and CCDC 902017 (3) 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.
Synthesis
Detailed synthetic processes for ligands L2–L4 are given in the Sup-
porting Information.
L2: Light yellow solid. M.p.: 2158C. 1H NMR (400 MHz, [D6]DMSO,
ppm): d 9.83 (s, 2H, Hd), 8.22 (s, 2H, Hc), 8.17 (d, J=9.2 Hz, 4H,
H8), 8.00 (s, 2H, Hb), 7.63 (m, 4H, H7), 7.48 (m, 2H, H3), 7.46 (d, J=
8.0 Hz, 2H, H6), 7.03 (m, 4H, H4+H5), 6.61 (s, 2H, Ha), 3.23 (m, 4H,
b-CH2), 1.64 (m, 4H, a-CH2). 13C NMR (100 MHz, [D6]DMSO), 156.6
(CO), 152.4 (CO), 146.6 (C), 140.8 (C), 131.6 (C), 125.0 (CH), 124.3
(CH), 123.9 (CH), 106.7 (CH), 36.4 (a-CH2), 30.1 (b-CH2). IR (KBr): n˜ =
3357, 3299, 3081, 1664, 1593, 1571, 1500, 1329, 1299 cmÀ1. Anal.
calcd (%) for C31H30N10O8: C 55.52, H 4.51, N 20.89; found: C 55.84,
H 4.43, N 20.75. ESI-MS: m/z 100%, 671.2 [M+H]+; 40%, 693.2
[M+Na]+.
L3: Light yellow solid. M.p.: 2748C. 1H NMR (400 MHz, [D6]DMSO,
ppm): d 9.86 (s, 2H, Hd), 8.25 (s, 2H, Hc), 8.18 (m, 4H, H8), 8.00 (s,
2H, Hb), 7.70 (m, 4H, H7), 7.60 (m, 2H, H3), 7.51 (m, 2H, H6), 7.26
(m, 2H, Hg), 7.20 (m, 2H, Ha), 7.06 (m, 4H, Hb), 7.04 (s, 2H, Ha),
4.30 (m, 4H, CH2). 13C NMR (100 MHz, [D6]DMSO), 155.9 (CO), 152.7
(CO), 146.7 (C), 140.8 (C), 140.2 (C), 132.8 (C), 129.7 (C), 128.3 (CH),
126.3 (CH), 125.7 (CH), 125.1 (CH), 124.9 (CH, CH), 123.1 (CH), 117.3
(CH), 43.0 (CH2). IR (KBr): n˜ =3352, 3299, 3078, 1659, 1593, 1575,
1500, 1327, 1205 cmÀ1. Anal. calcd (%) for C36H32N10O8: C 59.01,
H 4.40, N 19.12; found: C 58.86, H 4.37, N 18.89. ESI-MS: m/z 100%,
733.2 [M+H]+; 60%, 755.2 [M+Na]+.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (21271149 and 21325102).
Chem. Eur. J. 2015, 21, 2588 – 2593
www.chemeurj.org
2592
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
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Keywords: anion coordination
oligourea · phosphates
· helicates · mesocates ·
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Received: September 11, 2014
Published online on December 11, 2014
Chem. Eur. J. 2015, 21, 2588 – 2593
www.chemeurj.org
2593
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim