Tris chelating phosphate complexes of bis(thio)urea ligands

Article abstract of DOI:10.1021/ic3028012

Two bisurea (L¹, L²) and one bisthiourea (L ³) ligands were synthesized and their anion coordination behavior was studied. These ligands can readily form the tris chelates [PO ₄(L)₃]^3- (1,

Full text of DOI:10.1021/ic3028012

Article
pubs.acs.org/IC
Tris Chelating Phosphate Complexes of Bis(thio)urea Ligands
Rui Li,†,§ Yanxia Zhao,†,§ Shaoguang Li,† Peiju Yang,† Xiaojuan Huang,† Xiao-Juan Yang,†,‡
and Biao Wu*,‡
†State Key Laboratory for Oxo Synthesis & Selective Oxidation, Lanzhou Institute of Chemical Physics, CAS, Lanzhou 730000, China
‡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
§Graduate University of Chinese Academy of Sciences, Beijing 100049, China
S
* Supporting Information
ABSTRACT: Two bisurea (L1, L2) and one bisthiourea (L3)
ligands were synthesized and their anion coordination behavior
was studied. These ligands can readily form the tris chelates
[PO4(L)3]3− (1, 5, and 6) with phosphate ion (PO43−) in the
solid state, in which the anion is coordinated by six urea groups
1
through 12 hydrogen bonds. Solution binding studies by H
NMR and UV−vis spectroscopy revealed different binding
properties of the ligands toward phosphate ion. While the
bis(p-nitrophenyl)-substituted bisurea L1 retains the 3:1 (host
to guest) binding ratio in solution, the diethyl derivative L2
only forms 1:1 complex with phosphate ion. The more acidic
thiourea L3 undergoes deprotonation/decomposition in the
presence of phosphate ion. Moreover, the sulfate complex (2) of L1 and bicarbonate (3) and carbonate (4) complexes of L2 have
also been obtained, which show lower coordination numbers both in the solid state and in solution.
investigated in helical assembly,5 chiral molecular recognition,6
INTRODUCTION
■
luminescent devices,7 and applications in photonics and
The supramolecular chemistry of anions is an important area
optoelectronics8 and electrochemistry.9
because of the crucial relevance of anions in a range of
biological, chemical, medical, and environmental processes.1 In
Recently our research has focused on anion coordination
chemistry of urea-based ligands.10 A series of ortho-phenylene
1967, Park and Simmons reported the encapsulation of chloride
bridged oligoureas, which display excellent coordination
abilities to the tetrahedral sulfate and phosphate anions, have
been designed by mimicking the well-known oligopyridine
ligands. The tris(urea) ligands10c are highly complementary for
ion inside the cavity of bicyclic diammonium receptors, which
were essentially the first anion complexes.1 On the basis of the
research of cyclic ammonium hosts with halide anions, Lehn
first proposed the concept of anion coordination in 1978.2 This
field has attracted much attention in recent years, and it has
been found that anion complexes also exhibit “double valence”
as transition metal complexes: anions act as the “primary
valence” while hydrogen bonds between the receptor and anion
provide a “coordination number”, acting as the “secondary
valence”.3 Subsequently, anions also require coordination
saturation and geometrical preference, although such features
are not as well-defined as in transition metal coordination.
These similarities not only open a new window to the
theoretical development of anion coordination chemistry, but
also shed light on the design of anion ligands.
PO4 ion in the complexes [(PO4)L2]3− (Scheme 2a, right),
3−
which closely resemble the metal-terpyridine complexes
Scheme 1. Structures of the Ligands L1, L2, and L3
In transition-metal coordination chemistry, bidentate chelat-
ing ligands (e.g., 2,2′-bipyridine, bpy) are widely used in the
construction of coordination and supramolecular compounds.4
For octahedral metal ions, an interesting class of molecules (the
tris chelates) which have a metal ion coordinated by three
bidentate ligands can readily form. In particular, the tris
chelating bpy complexes [M(bpy)3]n+ display remarkable
chemical and physical properties and have thus been extensively
Received: December 20, 2012
© XXXX American Chemical Society
A
dx.doi.org/10.1021/ic3028012 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Interestingly, an unexpected 1:1 bicarbonate complex, [K([18]-
crown-6)]·[(HCO3)(L2)] (3), was isolated from L2, [18]-
crown-6, and K3PO4. However, when L2 was treated with
(TEA)HCO3 (TEA = tetraethylammonium), a complex with
the deprotonated carbonate ion, (TEA)2[(CO3)(L2)2] (4), was
obtained.
Scheme 2. Design of the Trisurea and Bisurea Ligands by
Mimicking the Terpyridine (tpy) and Bipyridine (bpy)
Moieties (a) [M(tpy)2]n+ and [A(trisurea)2]3−;10c and (b)
[M(bpy)3]n+ and [A(bisurea)3]3− (A = PO4
)
3−
Crystal Structures. Ligand L1 and Its Complexs. First, the
symmetric bisurea ligand L1 with two p-nitrophenyl groups as
pendants was employed, whose electron withdrawing property
makes the urea groups more acidic and thus can ensure
effective coordination with anions. Single crystals of the free
ligand L1 were obtained through evaporation of a solution in
acetone−DMSO (v/v 20:1) at room temperature. In the crystal
structure, one of the p-nitrophenyl-urea arms is roughly
coplanar with the o-phenylene bridge (dihedral angle 12°),
while the other arylurea plane is nearly perpendicular to the o-
phenylene ring (dihedral angle 77°). The urea group on the
perpendicular arm uses the carbonyl oxygen to form the typical
six-membered hydrogen bonds (N2···O4, 2.900 Å; N3···O4,
3.062 Å; Figure S1, Supporting Information) with the NH
groups of the other urea arm in an adjacent ligand and binds
with a DMSO molecule via two hydrogen bonds (N4···O7,
2.916 Å; N5···O7, 2.877 Å; Figure S1), leading to an infinite 1D
tape.
[M(tpy)2]n+ (Scheme 2a, left). Moreover, a bis-bisurea
ligand10g assembles with phosphate to form the first triple-
stranded anion helicate, exactly as in the case of bis-bidentate
ligands and metal ions. In these anion complexes, the
phosphate ion (PO43−) displays a strong tendency for
coordination saturation (12 hydrogen bonds or six urea
groups). Therefore, we turned to the bisurea ligands which
should form the [AL3]-type (A = anion) complexes with
phosphate ion like the famous metal-bpy counterpart [M-
(bpy)3]n+. Indeed, some ortho-phenylene bridged bisurea
receptors (and related NH-based receptors)11 have been
synthesized, and their binding properties toward various anions,
Phosphate Complex [K([18]crown-6)]2(TBP)[PO4(L1)3] (1).
The coordination of phosphate ion with ligand L1 was studied
by using different phosphate salts. Note that attempts to grow
crystals of the phosphate complex with various countercations,
such as TBA+ (TBA+ = tetrabutylammonium), TBP+ (TBP+ =
tetrabutylphosphonium), [K([18]crown-6)]+, K+, and Na+,
were unsuccessful. Interestingly, when two mixed counter-
cations ([K([18]crown-6)]+ and TBP+) were present, yellow
block single crystals of the tris-chelating complex 1 were
obtained with the composition [K([18]crown-6)]2(TBP)-
[PO4(L1)3].
The crystal structure clearly shows that a phosphate ion is
coordinated by three ligands via 12 hydrogen bonds from six
urea groups. Notably, the three receptors around the phosphate
ion are not C3-symmetric, displaying two different coordination
manners. Four urea groups from two ligands (green and blue,
Figure 1a) bind four edges of the tetrahedral anion (through
eight-membered H-bonded rings), while the two urea groups
−
−
such as F−, Cl−, H2PO4 , SO42−, CN−, NO3 , RCOO−, have
been examined. However, studies on the binding of the fully
deprotonated PO43− anion are very rare. Very recently, Gale et
al.12 reported a phosphate (PO43−) complex with three 1,3-
diindolylurea ligands. In this present work, we synthesized three
bis(thio)urea ligands (L1−L3; Scheme 1), which can readily
3−
coordinate with PO4 ion to form the desired “trischelate”
[(PO4)L3]3− complexes (1, 5, 6). In addition, a sulfate complex
(2) with L1, bicarbonate complex (3) and carbonate complex
(4) with L2 were also obtained in the solid state. Herein, we
describe the synthesis and structures of these anion complexes,
as well as the coordination behavior of L1, L2, and L3 with a
variety of oxo anions in solution.
RESULTS AND DISCUSSION
■
Synthesis. The nitrophenyl-decorated bisurea ligand L1 was
prepared according to the literature procedures.13 The ethyl-
substituted ligand L2 and the thiourea L3 were synthesized by
the reaction of o-phenylenediamine with ethyl isocyanate or p-
nitrophenylisothiocyanate, respectively, as white and yellow
powders. The anion complexes 1−6 were synthesized by
reaction of the ligands with different salts of the anions.
Treatment of L1, L2, or L3 with phosphate salts afforded the
[(PO4)L3]3−complexes 1, 5, and 6, which consist of three
ligands and one PO43− coordinated by 12 hydrogen bonds. The
sulfate complex [K([18]crown-6)]2[SO4(L1)2]·C3H6O (2),
which contains two ligand molecules coordinating to a sulfate
ion, was obtained from L1, K2SO4, and [18]crown-6.
Figure 1. Crystal structure of the phosphate complex [PO4(L1)3]3−
(1). (a) Side view, (b) top view, (c) space-filling representation.
Nonacidic hydrogen atoms and countercations were omitted for
clarity.
B
dx.doi.org/10.1021/ic3028012 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
from the third ligand (orange, Figure 1a) chelate two vertices of
the phosphate ion (six-membered H-bonded rings).14 Thus, the
O19 and O20 atoms of phosphate form three hydrogen bonds
each, but the O21 atom receives four and O22 only two
hydrogen bonds. This is different from the complex [(PO4)-
(tris-urea)2]3−, in which all of the six urea groups chelate an
edge of the tetrahedral anion and each oxygen atom forms
three hydrogen bonds.10c The hydrogen bonds in complex 1
(N···O, 2.935−2.724 Å, 2.809 Å on average; N−H···O, 147−
177°, 162° on average; Table 1) are slightly stronger than those
Sulfate Complex [K([18]crown-6)]2[SO4(L1)2] (2). The
coordination of ligand L1 with sulfate ion was also examined.
Slow diffusion of diethyl ether into an acetone solution
containing L1, [18]crown-6, and K2SO4 afforded yellow crystals
of the sulfate complex [K([18]crown-6)]2[SO4(L1)2]·C3H6O
(2). Unlike the phosphate analogue 1, the sulfate ion is
coordinated by two bisurea molecules through eight N−H···O
hydrogen bonds (N···O distances range from 2.809 to 2.972 Å,
2.890 Å on average; N−H···O angles from 153° to 170°, 161°
on average; Figure 2 and Table S1, Supporting Information),
which are slightly longer than those in complex 1. The
coordination sphere of the sulfate ion is further completed by
one [K([18]crown-6)]+ countercation, which offers two K−O
bonds to two oxygen atoms of sulfate with bond lengths of
Table 1. Hydrogen Bond Parameters (Å, deg) around the
PO4 Ion in [PO4(L1)3]3− (1)
3−
N−H···O
N−H
H···O
N···O
∠NHO
1
2.826 and 2.966 Å (Figure 2a). Interestingly, UV−vis and H
N2−H2···O22
N3−H3···O19
N4−H4···O19
N5−H5···O20
N8−H8···O21
N9−H9···O21
N10−H10···O20
N11−H11···O20
N14−H14···O19
N15−H15···O21
N16−H16···O21
N17−H17···O22
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
2.02
1.87
1.94
1.88
2.09
2.02
2.14
1.88
1.90
1.89
1.92
2.03
2.881(5)
2.744(5)
2.801(6)
2.763(6)
2.910(5)
2.834(5)
2.935(5)
2.724(5)
2.759(5)
2.762(5)
2.791(5)
2.804(6)
164
169
165
177
155
153
151
159
166
170
170
147
NMR titrations revealed that the 1:1 rather than 2:1 (host−
guest) binding mode was formed in solution (vide infra).
Indeed, both the theoretical calculations17 and X-ray
crystallography10e,18 confirmed that sulfate ion can achieve
saturated coordination (12 hydrogen bonds) by six urea groups
chelating the six edges of the tetrahedral anion. However,
sulfate complexes with the coordination number of 6−11 have
also been proven to exist in solid state and in solution.10a,f,h,19
In some cases, the main coordination motif was supplemented
by ion-pair interactions.20a−c Ghosh20b reported a tripodal urea
receptor that encapsulates sulfate ion with the help of two
TBA+ countercations forming five strong C−H···O contacts.
We have also obtained sulfate complexes of bis-bisurea ligands
having nine N−H···O hydrogen bonds from urea groups and
additional C−H···O interactions from TBA+.20c In the present
complex 2, one of the [K([18]crown-6)]+ countercations
participates in ion-pair interaction by direct K−O bonds rather
than hydrogen bonding (such as in the case of TBA+). The
different coordination modes between the phosphate complex
1 and sulfate complex 2 might be attributed to the weaker
basicity and smaller charge of sulfate than phosphate ion.
Complexes of Ligand L2. Bicarbonate Complex [K([18]-
crown-6)]·[(HCO3)(L2)] (3). The bisurea ligand (L2) with the
less electron-withdrawing ethyl groups was synthesized in order
to evaluate the effect of electronic properties of the bisurea
ligands on their anion coordination behavior. When L2 was
mixed with [18]crown-6 and K3PO4 in acetone−water (v/v
40:1), block colorless crystals were obtained upon slow vapor
diffusion of diethyl ether. Unexpectedly, X-ray crystallography
revealed that it is not the phosphate complex but a bicarbonate
in the trisurea complex (av N···O distance 2.829 Å and av N−
H···O angle 164°).10c The expanded structure of complex 1
shows strong interactions between [K([18]crown-6)]+ counter-
cations and p-nitrophenyl groups, which may provide additional
stability for complex 1 despite the sterical repulsion of the p-
nitrophenyl groups.
In the literature, the binding of some anions by bisurea or
analogous ligands has been described. For example, Gale et al.15
reported a series of o-phenylenediamine-based bisureas which
display good selectivity for carboxylate anions. Fabbrizzi et al.16
synthesized a pair of chiral bisurea receptors and studied their
affinity with dihydrogen phosphate and D-2,3-diphosphogly-
cerate anions. A phosphate (PO43−) complex with three 1,3-
diindolylureas was crystallized in the presence of excess
tetrabutylammonium dihydrogen phosphate.12 Complex 1
represents another example of tris-chelating phosphate complex
which is similar to the diindolylurea complex.
Figure 2. Crystal structure of the sulfate complex [SO4(L1)2]2− (2). (a) The coordination sphere of sulfate ion with two L1 ligands and one
[K([18]crown-6)]+ cation. (b) Space-filling representation. Nonacidic hydrogen atoms and noninteracting countercations were omitted for clarity.
C
dx.doi.org/10.1021/ic3028012 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
complex [K([18]crown-6)]·[(HCO3)(L2)] (3), which may
result from the fixation of atmospheric CO2 in basic solution.
oxygen atoms of carbonate are distributed to four positions
with 0.75 occupancy rate each, forming a rhombus (Figure 4a).
2−
−
There are some examples of CO3 or HCO3 binding
originating from CO2. Pfeffer et al.20e demonstrated that a
naphthalimide-based thiourea can form bicarbonate adduct in
the presence of tetrabutylammonium fluoride (TBAF) in
DMSO. Gale et al.20d also showed evidence of carbonate
binding with an amidourea macrocycle under similar
−
conditions. In both cases, the source of the CO32−/HCO3
was the dissolved CO2 that was converted to carbonates. More
recently, Ghosh et al.20f reported a neutral receptor which
displayed efficient fixation of atmospheric CO2 to carbonate
ion.
In complex 3, a bisurea molecule binds one HCO3− ion in its
cleft through three strong hydrogen bonds (N···O, 2.813−
2.979 Å; ∠N−H···O, 144−172°) and a much weaker one
(N4···O7, 3.236 Å; ∠N−H···O, 143°; Figure 3a and Table S2,
Figure 4. Crystal structure of the carbonate complex [(CO3)(L2)2]2−
(4): (a) top view; (b) side view. (Note: the three oxygen atoms of
carbonate anion are distributed to four positions.) Symmetry code: (i)
1 − x, −y, 1 − z.
−
2−
In contrast to the 1:1 binding of HCO3 , the CO3 anion is
encapsulated by two L2 ligands in a nearly planar structure
(Figure 4b). Each urea group chelates two partially occupied
oxygen atoms of the anion, forming a total of eight hydrogen
bonds (N···O, 2.728−2.901 Å; N−H···O, 144−167°). The
existence of the CO32− was also confirmed by the IR spectrum
which shows distinct peaks at 1692 and 1372 cm−1 (Figure
S3).21
Figure 3. Crystal structure of the bicarbonate complex [(HCO3)L2]−
(3). (a) The coordination sphere of the [(HCO3)2]2− dimer.
Symmetry codes: (i) 1 + x, y, z; (ii) 1 − x, −y, 1 − z; (iii) 2 − x,
−y, 1 − z. (b) part of the infinite double chain structure.
Phosphate Complex (TMA)3[PO4(L2)3]·4H2O (5). Fortu-
nately, treatment of L2 with (TMA)3PO4 (generated from
(TMA)OH and H3PO4, TMA = tetramethylammonium) in
acetonitrile and diethyl ether afforded rodlike colorless crystals
o f c o m p l e x 5 , w h i c h h a s t h e c o m p o s i t i o n
(TMA)3[PO4(L2)3]·4H2O as confirmed by X-ray crystallo-
graphic and elemental analysis. Utilization of other counter-
cations, such as TBA+, TBP+, K+, and Na+, failed to generate
single crystals. In the structure of 5, three L2 ligands coordinate
to one phosphate ion through six urea groups, each of which
chelates an edge of the anion tetrahedron (Figure 5a). The
N···O distances (2.700−2.943 Å, 2.820 Å on average; Table 2)
are slightly longer than those of complex 1 but are similar to the
complex of tris(urea) ligands.10c Notably, the two ethyl groups
within each ligand adopt the syn-conformation relative to the o-
Supporting Information). Each urea group chelates an edge of
the triangular anion. Notably, two HCO3− anions are associated
to each other through a pair of O−H···O hydrogen bonds
(O7−H7···O5: 2.643 Å, 172°) to form a [(HCO3)2]2− dimer
(Figure 3a). In addition, the [K([18]crown-6)]+ countercation
acts as a bridge between two [(HCO3)(L2)] units, coordinating
−
to two oxygen atoms from a urea carbonyl and a HCO3 ion,
respectively, on its axial positions (K−O bond lengths: 2.811
and 2.744 Å). As a result, a one-dimensional “double chain” is
formed with alternate [K([18]crown-6)]+ ions and
[(HCO3)2(L2)2] moieties (Figure 3b). The presence of
−
HCO3 in complex 3 was proven by the IR spectrum, which
shows new peaks at 1698, 1352, 1215, 961, and 839 cm−1 due
to the stretching and bending of HCO3 ion (Figure S2).21
−
Moreover, ESI-MS studies also confirmed the existence of
−
HCO3 ion in complex 3 by a peak at m/z = 311.1455
corresponding to [(HCO3)L2]− (calculated m/z = 311.1355).
Carbonate Complex (TEA)2[(CO3)(L2)2] (4). Since the
bicarbonate complex 3 was obtained by capturing the
atmospheric CO2, we attempted to repeat the synthesis by
using (TEA)HCO3 directly. However, in this case the complex
(4) of the deprotonated anion (CO32−) was obtained. Similar
phenomena were also observed in the crystallization of
(TEA)HCO3 with a diindolylurea12 or m-nitrophenyl-sub-
stituted bisurea,15a both of which resulted in the binding of the
2−
anion in the form of CO3 and can be attributed to proton
transfer between the bound and free anions. It should be noted
that, due to the crystal-imposed inversion symmetry, the three
Figure 5. Crystal structure of [PO4(L2)3]3− (5): (a) Side view; (b) top
view; (c) space-filling representation.
D
dx.doi.org/10.1021/ic3028012 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
with the thiocarbonyl S (S1) atom from another ligand (N−
H···S: 2.66 Å, 134°; Figure S4).
Table 2. Hydrogen Bond Parameters (Å, deg) around the
PO4 Ion in [PO4(L2)3]3− (5)
3−
Notably, the ligand conformation in L3·2DMSO is
significantly different from L3·DMSO. The ligand molecule is
more flat than the former one, showing approximately a V-
shape. However, the three aryl groups are not coplanar (Figure
6c,d), although the central o-phenylene ring does not bend up
as in the case of L3·DMSO. The two thiourea groups assume
the normal chelating fashion, and each binds a DMSO molecule
above and below the central o-phenylene ring, respectively
(Figure 6d and Figure S5, Supporting Information). Moreover,
both structures are different from the phenyl-substituted
analogue reported by Gale et al.,13 in which one phenyl
group is coplanar with the o-phenylenediamine spacer but the
other phenyl is perpendicular to this plane.
N−H···O
N−H
H···O
N···O
∠NHO
N1−H1···O9
N2−H2···O8
N3−H3···O8
N4−H4···O7
N5−H5···O9
N6−H6···O7
N7−H7···O7
N8−H8···O10
N9−H9···O9
N10−H10···O10
N11−H11···O10
N12−H12···O8
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
2.13
1.82
1.99
1.97
2.11
1.83
2.04
1.94
2.04
1.85
1.95
2.01
2.943(7)
2.700(6)
2.844(6)
2.836(7)
2.942(6)
2.708(5)
2.836(6)
2.820(6)
2.861(7)
2.723(6)
2.812(6)
2.813(6)
153
175
164
168
157
173
150
176
155
173
167
150
Phosphate Complex (TBA)3[PO4(L3)3] (6). When L3 was
treated with TBA3PO4 (TBA = tetrabutylammonium) in
CH2Cl2, golden yellow crystals of the phosphate complex 6
were obtained upon slow vapor diffusion of diethyl ether. Like
the analogous urea complex 1, the structure clearly shows that
three ligands coordinate a phosphate ion using all of the six
thiourea groups with N···O distances ranging from 3.012 to
2.631 Å (average: 2.806 Å) (Table 3), which are comparable to
phenylene ring, but the total six ethyl groups point to different
directions (Figure 5b), possibly due to the small size and
flexibility of the alkyl chain. Such arrangements lower the
symmetry of complex 5 to C1.
Thiourea Ligand L3 and Its Phosphate Complex. The
thiourea group has a strong hydrogen-bond donor capability
and can form two directional hydrogen bonds with the Y-
shaped oxoanions (e.g., carboxylates and phosphates)22 or
chelate spherical anions (e.g., halides22) similar to the urea
group. However, due to the higher acidity of thiourea than urea
(pKA = 21.1 and 26.9, respectively in DMSO),23 it is expected
that thiourea-containing receptors may establish stronger H-
bond interactions and form more stable complexes with anions
than their urea counterparts.24 Thus, we synthesized a
bis(thiourea) ligand L3, which bears two p-nitrophenyl terminal
substituents (Scheme 1) as in the analogous bisurea ligand L1.
The free ligand L3 crystallizes in two distinct structures:
L3·DMSO and L3·2DMSO. In L3·DMSO, the ligand molecule
assumes a largely bent conformation between the o-phenylene
spacer and the thiourea groups, which is different from the urea
analogue L1. The two p-nitrophenyl groups are almost coplanar
(dihedral angle: 6.5°) and are perpendicular to the o-phenylene
spacer (dihedral angle: 89.3° on average). Notably, each
thiourea group adopts an “anti” arrangement; i.e., the two NH
groups within one thiourea unit are located in opposite
directions (Figure 6a,b). As a result, one of the NH donors of
each thiourea (N2, N5) points to the inside of the bent ligand
molecule and binds the DMSO, while the other two NH
donors turn to the “outside” and one of them (N4) contacts
Table 3. Hydrogen Bond Parameters (Å, deg) around the
3−
PO4 Ion in [PO4(L3)3]3− (6)
N−H···O
N−H
H···O
N···O
∠NHO
N2−H2···O15
N3−H3···O16
N4−H4···O16
N5−H5···O13
N8−H8···O16
N9−H9···O16
N10−H10···O14
N11−H11···O14
N14−H14···O14
N15−H15···O15
N16−H16···O13
N17−H17···O13
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
1.79
1.94
2.03
1.79
2.19
2.03
2.09
1.90
2.11
1.76
2.21
1.87
2.645(5)
2.814(5)
2.876(5)
2.653(5)
2.958(5)
2.827(5)
2.912(5)
2.761(5)
2.856(5)
2.631(5)
3.012(5)
2.731(5)
163
170
162
166
145
150
155
167
142
173
151
166
complex 1 (N···O: 2.935−2.724 Å, 2.809 Å on average). This
complex also crystallizes in the space group P1, and there are
̅
two coordination manners for the bis-thiourea ligands, which
are also not arranged in the C3 symmetry. The difference from
complex 1 is that three of the thiourea groups chelate the edges
and the other three bind the vertices of phosphate ion. The
hydrogen bond number on each oxygen atom is also
nonequivalent as in 1. Two oxygen atoms (O13 and O14)
accept three hydrogen bonds each, while one oxygen atom
(O16) forms four hydrogen bonds and the last one (O15) only
two hydrogen bonds (Figure 7a).
1
Solution Binding Behavior. H NMR Studies. Compared
1
to the free ligand L1, the H NMR spectrum of the phosphate
complex 1 showed large downfield shifts (Δδ 2.97−3.24 ppm)
of the two NH groups in DMSO-d6 (Figure 8a). The upfield
shifts of H1 and H2 on the terminal aromatic ring (see Scheme
1 for the numbering of protons) induced by the shielding effect
provide another evidence for the anion coordination in
solution. During the titration of phosphate ions to the ligand
in DMSO-d6−5% H2O, a new set of signals corresponding to
complex 1 appeared when 0.05 equiv of phosphate ions were
added. With the addition of more phosphate ions, the peaks of
Figure 6. Crystal structures of L3·DMSO (a, b) and L3·2DMSO (c, d).
E
dx.doi.org/10.1021/ic3028012 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 9. (a) 1H NMR spectra of L1 and complex 2 in DMSO-d6. (b)
1H NMR titration of L1 (5.0 × 10−3 M) with TBA2SO4 in DMSO-d6.
Figure 7. Crystal structure of the phosphate complex [PO4(L3)3]3−
(6): (a) side view, (b) top view, (c) space-filling representation.
interactions with sulfate. It is noticeable that sulfate ion was
bound by less ligands (1:1) in solution than in the solid state
(2:1 host to guest), and in both cases the binding stoichiometry
is smaller than the phosphate ion (3:1 binding mode both in
the solid state and in solution). As mentioned above, this may
be attributed to the higher negative charge density and stronger
basicity of phosphate ion, and a similar phenomenon has also
been observed in our previous work.10g The association
2−
constant was estimated to be larger than 104 M−1 for SO4
ion by using EQNMR (Table 4, Figure S11).
Table 4. Association Constants (K, M−1) of Ligands L1 and
a
1
L2 with Different Anions from H NMR Titrations in
DMSO-d6 at 298 K
AcO−
3−
2−
−
anion
PO4
SO4
H2PO4
L1
L2
b
>104
>104
3090
2884
>104
>104
1950
a
−
−
Figure 8. (a) 1H NMR spectra of L1 and complex 1 in DMSO-d6. (b)
1H NMR titration of L1 (5.0 × 10−3 M) with K3PO4 in DMSO-d6−5%
H2O (v/v).
Very weak binding for NO3 and ClO4 . log K could not be
b
determined. Errors <15%. Association constant could not be
calculated due to broadening of NMR signals.
ligand L1 gradually diminished while the new signals of complex
1 increased. Finally, after addition of ca. 0.35 equiv of
phosphate ions, the signals of free L1 disappeared completely
and the new peaks reached saturation, indicating the formation
of the 3:1 complex in solution (Figure 8b). However, when
more than 1.0 equiv of phosphate anions were added, the NH
peaks of complex 1 were broadened again and disappeared
gradually with accompanying changes in the aromatic region,
which were caused by the through-bond and through-space
effects during the deprotonation of ligand L1 and decom-
position of complex 1 (Figure S6).25 This is consistent with the
UV−vis titration results (vide infra). Due to the severe
broadening and even disappearance of NH signals during the
titration process, the association constant for phosphate could
not be determined.
Since phosphate and sulfate display different binding modes,
competitive experiments between the two anions were carried
out both in solution and solid conditions to investigate the
selectivity of them. In the NMR studies, when 1.0 equiv of
PO4 and 1.0 equiv of SO4 ions were mixed with L1 in
DMSO-d6, the spectrum showed mainly the signals of the
phosphate complex 1 with only minor amount of the sulfate
complex 2 (less than 10%; Figure S7). Moreover, IR spectra
and powder X-ray diffraction (PXRD) patterns of the crystals
grown from the mixture of L1, [K([18]crown-6)]3PO4,
TBP3PO4, and [K([18]crown-6)]2SO4 are also close to
complex 1, indicating the preference of L1 for the phosphate
ion (Figures S8, S9). In addition, we have studied the solution
3−
2−
−
binding properties of L1 with other oxoanions, such as H2PO4 ,
−
−
1
AcO−, NO3 , and ClO4 , by H NMR titrations. The results
demonstrated significant binding affinity of L1 to H2PO4 and
−
In contrast to the slow exchange process observed in the
2−
phosphate binding, when L1 was titrated with SO4 (as TBA+
AcO− ions, with association constants of 3.09 × 103 M−1 and
>104 M−1, respectively, while NO3 and ClO4 showed almost
no binding with L1 (Table 4 and Figures S10−14).
−
−
salt) in DMSO-d6, a fast exchange occurred. Upon addition of
0.5 equiv of sulfate ions, the spectrum is very close to the 2:1
(host to guest) complex 2 (Figure 9a). The spectrum reached
saturation with 1.0 equiv of sulfate ions (Figure 9b), indicating
the formation of the 1:1 complex. The saturated downfield
shifts of the urea NH signals (Δδ 0.84−1.06 ppm) are much
smaller than those for the phosphate ion, implying weaker
In the case of ligand L2, the urea NH protons of its
phosphate complex 5 displayed smaller downfield shifts (Δδ
1
1.26−1.97 ppm; Figure S15a) compared to 1. In the H NMR
titration experiments, on adding 0.1 equiv of phosphate ions to
a solution of L2, the NH groups experienced some downfield
F
dx.doi.org/10.1021/ic3028012 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
3−
shifts. However, when more anions were added, the NH signals
broadened severely and even disappeared (with 0.3 to 0.5 equiv
of PO43−), which sharpened again upon addition of ca. 0.7
equiv of PO43− ions, and no more changes were observed after
addition of 1.0 equiv of anions (Figure S15b). Subsequent Job’s
plot also demonstrated a binding mode of 1:1 (Figure S16). It
can be seen that the diethyl-substituted ligand L2 displays a
much weaker binding affinity than the electron withdrawing
nitrophenyl analogue L1, which is reflected not only by the
smaller downfield shifts of the NH groups on binding the anion
but also by the different binding ratios (1:3 for L1 and 1:1 for
L2).
0.35 equiv. of PO4 ions (Figure S31a). The fitting curve at
360 nm also revealed a 3:1 (H/G) binding mode that is
consistent with the solid-state structure. When sulfate ions were
added to the solution of L1, a red shift of ca. 18 nm was
observed with an isosbestic point at 356 nm. However, the
plateau was reached after the addition of 1.0 equiv of the anion
(Figure S31b), indicating a binding mode of 1:1 in solution,
which is different from the crystal structure (2:1 H/G). For
H2PO4− and AcO− ions, the binding mode obtained from UV−
1
vis (Figure S31c,d) is in good agreement with the H NMR
titration.27 It is worth noting that, when large amounts of
PO43− ions were added to the solution of L1, a new band at ca.
475 nm emerged with accompanying decrease of the
absorbance at 375 nm and appearance of an isosbestic point
at ca. 411 nm, demonstrating the deprotonation of L1 ligand
(Figure S32).11c,25b For the thiourea receptor L3, the titration
profiles either displayed more than one isosbestic points (for
The binding behavior of L2 with HCO3− (as TEA+ salt) and
CO3 (as K+ salt) ions in solution was also studied. H NMR
spectrum of the bicarbonate complex 3 showed some downfield
shifts for NHa and NHb (Δδ 0.53 and 0.76 ppm) relative to
ligand L2 (Figure S17a). In the titration experiments, the
chemical shifts of all of the protons in L2 kept changing until
2.0 equiv of HCO3− ions were added (Figure S17b). The Job’s
plot revealed a binding mode of 1:2 (host to guest) (Figure
S18), with K1 = 2.76 × 102 M−1 and K2 = 5.97 × 102 M−1
(Figure S19).26 For the carbonate complex 4, the downfield
shifts of NHa and NHb (Δδ 1.68 and 2.38 ppm) are much
larger than those of 3, indicating a higher affinity (Figure S20a).
Upon titration of the anion, NH protons disappeared before
the spectrum reached saturation at 1.0 equiv of carbonate ions
(Figure S20b), which is consistent with the result of Job’s plot
(Figure S21), and fitting the titration curve to a 1:1 binding
ratio gave an association constant of 1.88 × 103 M−1 (Figure
S22).
2−
1
PO4 and SO42−) or kept changing (for H2PO4 and AcO−)
with the addition of anions, which provide another evidence for
the decomposition of L3 in the presence of anions (Figure
S33).
3−
−
CONCLUSION
■
The coordination behavior of bisurea (L1 and L2) and
bisthiourea (L3) ligands with the phosphate anion was studied
both in the solid state and in solution. The three ligands can
readily form the tris-chelate complexes [(PO4)L3]3− (1, 5, 6)
with orthophosphate ion in the solid state, in which the anion is
coordinated by six urea groups through 12 hydrogen bonds
(the saturated coordination of tetrahedral anion). The structure
of these complexes can be viewed as the counterpart of the
well-known [M(bpy)3]n+ complexes, thus providing further
evidence for the resemblance between anion coordination and
transition-metal coordination. However, the coordination
number in solution is different from the solid state. Although
ligand L1 shows the 3:1 binding ratio with phosphate ion in
solution, the diethyl-substituted analogue L2 forms only the 1:1
complex, which can be attributed to the weaker hydrogen
bonding affinity of L2 due to the lack of electron-withdrawing
substituents. The thiourea ligand L3, on the other hand, exhibits
the typical deprotonation with basic anions. The results once
again demonstrated the strong tendency of phosphate ion to
form 12 hydrogen bonds in the solid state, which makes a
promising coordination center to oligoureas.
−
−
Some other oxoanions (SO42−, H2PO4 , AcO−, NO3 , and
−
ClO4 ) were tested in the binding with L2 by 1H NMR
titrations. Job’s plots revealed 1:1 stoichiometry for the first
−
−
three anions (Figure S10), while NO3 and ClO4 ions were
not bound as in the case of L1 (Figure S14). The association
constants were calculated by EQNMR program, which indicate
3−
2−
that L2 binds PO4 and SO4 (K > 104 M−1) more strongly
than H2PO4 (2.89 × 103 M−1) and AcO− (1.95 × 103 M−1)
−
and shows relatively low affinity compared to L1 (Table 4;
Figures S23−26).
Moreover, 1H NMR titration was also carried out for the bis-
thiourea ligand L3. When 0.1 equiv of PO4 ions (as
3−
[K[18]crown-6)]+ salt) were titrated to a solution of L3 in
DMSO-d6, the NH protons shifted downfield. However, with
the increase of phosphate ions (0.2 equiv and more), the NH
signals disappeared, and the aromatic region showed gradual
appearance of new peaks (Figure S27). Similar phenomena
EXPERIMENTAL SECTION
■
were also observed with other anions (SO42−, H2PO4 , and
−
General. 1,2-Phenylenediamine, p-nitrophenyl isocyanate, and
ethyl isocyanate were purchased from Alfa Aesar and used as received.
All solvents and other reagents were of reagent grade quality. Ligand
L1 was synthesized following the literature procedures.13 1H and 13C
NMR spectra were recorded on a Mercury plus-400 spectrometer at
400 and 100 MHz, respectively, using TMS as an internal standard.
UV−vis spectra were performed on an HP8453 spectrophotometer (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 were carried out using a Waters
ZQ4000 spectrometer. Melting points were detected on an X-4 Digital
Vision MP Instrument.
AcO−; Figures S28−30), which may be attributed to the partial
deprotonation/decomposition of the bisthiourea in the binding
of anions. Thus, the association constants cannot be calculated.
The multicomponent equilibria were also proven by the UV−
vis titration (vide infra).
UV−Vis Titrations. The anion coordination behavior of L1
and L3, which bear the nitrophenyl chromophores, with PO4
,
3−
SO42−, H2PO4 , AcO−, NO3 , and ClO4 (PO4 as [K([18]-
crown-6)]+ salt and others as TBA+ salt) was also investigated
by UV−vis spectroscopy. Upon titration of these anions, the
absorption spectrum of L1 exhibited bathochromic shifts except
−
−
−
3−
Synthesis of Ligands L2, L3 and the Anion Complexes 1−6.
For L2, a solution of 1,2-phenylenediamine (0.324 g, 3 mmol) in 120
mL of THF was added dropwise to a solution of ethyl isocyanate (665
μL, 8.4 mmol) in CH2Cl2 (100 mL). After refluxing under stirring for
24 h, the precipitate was filtered off and washed several times with
THF and diethyl ether and then recrystallized from CH2Cl2/DMSO
−
−
for NO3 and ClO4 which showed almost no change (Figure
3−
S31). With the addition of PO4 ions, the absorption band at
352 nm shifted to ca. 363 nm with the appearance of a distinct
isosbestic point and slowly reached a plateau on addition of ca.
G
dx.doi.org/10.1021/ic3028012 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(v/v 40:1) by diffusion of hexane to yield L2 as a white solid (0.644 g,
70%). Mp: 189 °C. H NMR (400 MHz, DMSO-d6, ppm): 7.75 (s,
X-ray Crystallography. Diffraction data were collected on a
Bruker SMART APEX II diffractometer at 150 K with graphite-
monochromated Mo Kα radiation (λ = 0.710 73 Å). 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 parameters equivalent to 1.2 times
those of the atom to which they were attached. Some residual peaks
around [K([18]crown-6)]+ and TBP+ in complex 1 were squeezed due
to severe thermal vibration, and the disordered solvents were also
squeezed.
1
2H, Ha), 7.45 (m, 2H, H3), 6.95 (m, 2H, H4), 6.48 (t, J = 5.6 Hz, 2H,
Hb), 3.10 (m, 4H, H2), 1.05 (t, J = 5.2 Hz, 6H, H1). 13C NMR (100
MHz, DMSO-d6): 155.7 (C), 131.5 (C), 123.4 (CH), 123.1 (CH),
34.1 (CH2), 15.4 (CH3). IR (KBr, ν/cm−1): 3319, 2974, 2930, 1636,
1551, 1567, 1481, 1454, 757. Anal. Calcd for C12H18N4O2: C, 57.58;
H, 7.25; N, 22.38%. Calcd for C12H18N4O2·0.2C4H8O: C, 58.08; H,
7.46; N, 21.16%. Found: C, 57.65; H, 7.00; N, 21.37%. ESI-MS: m/z
249.14 [M−H]−; 285.14 [M + Cl]−.
For L3, A solution of 1,2-phenylenediamine (0.114 g, 1.06 mmol) in
20 mL of THF was added dropwise to a solution of p-
nitrophenylisothiocyanate (0.576 g, 3.20 mmol) in THF (20 mL).
After refluxing under stirring for 36 h, the precipitate was filtered off
and washed several times with THF and diethyl ether and then dried
in vacuum to yield L3 as a yellow solid (248 mg, 50%). Mp: 176 °C.
1H NMR (400 MHz, DMSO-d6, ppm): 10.61 (s, 2H, Ha), 9.65 (s, 2H,
Hb), 8.18 (d, J = 9.2 Hz, 4H, H4), 7.88 (d, J = 9.2 Hz, 4H, H3), 7.53
(m, 2H, H2), 7.32 (m, 2H, H1). 13C NMR (100 MHz, DMSO-d6):
179.9 (C), 145.9 (C), 142.4 (C), 134.0 (C), 128.1 (CH), 126.7 (CH),
124.3 (CH), 121.5 (CH). IR (KBr, ν/cm−1): 3221, 3104, 2963, 1528,
1510, 1298, 1178, 1110, 854. Anal. Calcd for C20H16N6O4S2·2DMSO:
C, 46.14; H, 4.52; N, 13.45%. Found: C, 46.47; H, 4.15; N, 12.86%.
ESI-MS: m/z 467.03 [M−H]−, 504.01 [M + Cl]−.
Crystal Data for L1. C23H19N6O8S (539.50), yellow block,
orthorhombic, space group P212121, a = 4.433(2) Å, b = 20.900(11)
Å, c = 30.555(16) Å, V = 2831(3) Å3, T = 153(2) K, Z = 4, Dcalcd
=
1.266 g cm−3, F000 = 1116, μ = 0.168 mm−1, 18 803 reflections
collected, 4996 unique (Rint = 0.0494), no. of observed reflections
3447 [I > 2σ(I)]; R1 = 0.0699, wR2 = 0.2065 [I > 2σ(I)].
Crystal Data for L3·DMSO. C22H22N6O5S3 (546.64), yellow block,
monoclinic, space group P21/c, a = 18.144(7) Å, b = 9.602(4) Å, c =
14.162(6) Å, β = 90.816(6)°, V = 2466.9(17) Å3, T = 153(2) K, Z = 4,
Dcalcd = 1.472 g cm−3, F000 = 1136, μ = 0.347 mm−1, 15 544 reflections
collected, 4362 unique (Rint = 0.0686), no. of observed reflections
3120 [I > 2σ(I)]; R1 = 0.0482, wR2 = 0.0924 [I > 2σ(I)].
[K([18]crown-6)]2(TBP)[PO4(L1)3] (1). L1 (19.6 mg, 0.045 mmol),
K3PO4 (3 mg, 0.015 mmol), [18]crown-6 (14 mg, 0.045 mmol), and
tetrabutylphosphonium phosphate (generated from TBPOH and
H3PO4, 0.015 mmol) were suspended in acetone (2 mL). After
stirring for 1 h at room temperature, a clear yellow solution was
obtained. Slow vapor diffusion of diethyl ether into this solution
afforded yellow crystals of complex 1 within 1 day (22 mg, 65%). Mp:
160 °C. Anal. Calcd for C100H132K2N18O34P2: C, 52.90; H, 5.86; N,
11.10%. Found: C, 52.82; H, 5.78; N, 11.08%.
Crystal Data for L3·2DMSO. C24H28N6O6S4 (624.76), yellow
block, monoclinic, space group P21/n, a = 13.657(8) Å, b = 12.406(7)
Å, c = 17.445(10) Å, β = 90.859(8)°, V = 2955(3) Å3, T = 153(2) K, Z
= 4, Dcalcd = 1.404 g cm−3, F000 = 1304, μ = 0.370 mm−1, 19 184
reflections collected, 5122 unique (Rint = 0.0402), no. of observed
reflections 2965 [I > 2σ(I)]; R1 = 0.0936, wR2 = 0.1612 [I > 2σ(I)].
Crystal Data for 1. C100H132K2N18O34P2 (2270.38), yellow block,
triclinic, space group P1, a = 15.349(3) Å, b = 17.380(4) Å, c =
̅
[K([18]crown-6)]2[SO4(L1)2]·C3H6O (2). L1 (19.6 mg, 0.045 mmol),
K2SO4 (3 mg, 0.015 mmol), and [18]crown-6 (14 mg, 0.045 mmol)
were suspended in mixed solvents of acetone (2 mL) and DMSO (200
μL). After stirring for 1 h at room temperature, a clear yellowish
solution was obtained. Slow vapor diffusion of diethyl ether afforded
yellow crystals within 1 day (20 mg, 55%). Mp: 204 °C. Anal. Calcd
for C67H86K2N12O29S: C, 49.26; H, 5.31; N, 10.29%. Found: C, 48.92;
H, 5.04; N, 10.71%.
25.465(5) Å, α = 109.489(2)°, β = 106.656(3)°, γ = 90.163(3)°, V =
6099(2) Å3, T = 153(2) K, Z = 2, Dcalcd = 1.236 g cm−3, F000 = 2396, μ
= 0.184 mm−1, 40 494 reflections collected, 21 027 unique (Rint
=
0.0358), no. of observed reflections 149 21 [I > 2σ(I)]; R1 = 0.1099,
wR2 = 0.2166 [I > 2σ(I)].
Crystal Data for 2. C67H86K2N12O29S (1633.74), yellow block,
triclinic, space group P1, a = 12.0010(9) Å, b = 15.0158(12) Å, c =
̅
22.8150(18) Å, α = 85.9980(10)°, β = 86.3910(10)°, γ =
71.3080(10)°, V = 3881.4(5) Å3, T = 153(2) K, Z = 2, Dcalcd
=
[K([18]crown-6)]·[(HCO3)(L2)] (3). L2 (11.2 mg, 0.045 mmol),
K3PO4 (3 mg, 0.015 mmol), and [18]crown-6 (14 mg, 0.045 mmol)
were suspended in acetone/water (2 mL, 40:1 v/v) and stirred for 1 h
at room temperature to give a clear colorless solution. Slow vapor
diffusion of diethyl ether afforded colorless crystals within 1 day (5.5
mg, 20%). Mp: 133 °C. Anal. Calcd for C25H43KN4O11: C, 48.85; H,
7.05; N, 9.11%. Found: C, 48.94; H, 6.71; N, 8.62%. ESI-MS: m/z
311.14 [M + HCO3]−.
1.398 g cm−3, F000 = 1716, μ = 0.239 mm−1, 25 841 reflections
collected, 13 410 unique (Rint = 0.0226), no. of observed reflections
11 455 [I > 2σ(I)]; R1 = 0.0379, wR2 = 0.0839 [I > 2σ(I)].
Crystal Data for 3. C25H43KN4O11 (614.73), colorless block,
triclinic, space group P1, a = 8.3476(7) Å, b = 11.1908(10) Å, c =
̅
16.6700(15) Å, α = 87.8650(10)°, β = 85.2360(10)°, γ =
77.4120(10)°, V = 1514.3(2) Å3, T = 153(2) K, Z = 2, Dcalcd
=
1.348 g cm−3, F000 = 656, μ = 0.238 mm−1, 10 012 reflections collected,
5205 unique (Rint = 0.0174), no. of observed reflections 4463 [I >
2σ(I)]; R1 = 0.0351, wR2 = 0.0830 [I > 2σ(I)].
(TEA)2[(CO3)(L2)2] (4). L2 (11.2 mg, 0.045 mmol) and TEAHCO3
(11.2 mg, 0.045 mmol) were suspended in acetone and stirred for 10
min at room temperature to give a clear colorless solution. Slow vapor
diffusion of diethyl ether afforded colorless crystals within 1 day (11.1
mg, 60%). Mp: 182 °C. Anal. Calcd for C41H76N10O7: C, 59.97; H,
9.33; N, 17.06%. Found: C, 59.85; H, 9.05; N, 16.82%.
Crystal Data for 4. C41H76N10O7 (821.12), colorless block,
monoclinic, space group P21/n, a = 9.123(2) Å, b = 20.426(5) Å, c =
13.377(4) Å, β = 107.893(3)°, V = 2372.1(11) Å3, T = 153(2) K, Z =
2, Dcalcd = 1.150 g cm−3, F000 = 896, μ = 0.079 mm−1, 15 911
reflections collected, 4277 unique (Rint = 0.0269), no. of observed
reflections 2515 [I > 2σ(I)]; R1 = 0.0924, wR2 = 0.1540 [I > 2σ(I)].
Crystal Data for 5. C48H98N15O14P (1140.38), colorless block,
monoclinic, space group Cc, a = 24.135(6) Å, b = 13.340(3) Å, c =
22.620(9) Å, β = 112.186(3)°, V = 6744(3) Å3, T = 153(2) K, Z = 4,
Dcalcd = 1.123 g cm−3, F000 = 2472, μ = 0.105 mm−1, 21 488 reflections
collected, 11 628 unique (Rint = 0.0418), no. of observed reflections
7482 [I > 2σ(I)]; R1 = 0.0772, wR2 = 0.1669 [I > 2σ(I)].
(TMA)3[PO4(L2)3]·4H2O (5). L2 (11.2 mg, 0.045 mmol) was reacted
with (TMA)3PO4 (generated from (TMA)OH and H3PO4, 0.015
mmol) in acetonitrile (2 mL). A clear colorless solution was obtained
soon. Slow vapor diffusion of diethyl ether afforded colorless crystals
within 1 day (10 mg, 62%). Mp: 173 °C. Anal. Calcd for
(TMA)3[PO4(L2)3]·7H2O (C48H104N15O17P): C, 48.27; H, 8.78; N,
17.59%. Found: C, 48.55; H, 8.36; N, 17.43%.
(TBA)3[PO4(L3)3] (6). L3 (10.5 mg, 0.0225 mmol) was reacted with
(TBA)3PO4 (generated from (TBA)OH and (TBA)H2PO4, 0.0075
mmol) in CH2Cl2 (1 mL). A clear orange solution was obtained soon.
Slow vapor diffusion of diethyl ether afforded golden yellow crystals
within 1 day (6.7 mg, 40%). Mp: 121 °C. Anal. Calcd for
(TBA)3[PO4(L3)3]·H2O (C108H158N21O17PS6): C, 57.76; H, 7.09; N,
13.10%. Found: C, 58.08; H, 6.82; N, 12.47%.
Crystal Data for 6. C108H156N21O16PS6 (2227.87), yellow block,
triclinic, space group P1, a = 18.1963(16) Å, b = 18.2842(16) Å, c =
̅
22.399(2) Å, α = 77.7590(10)°, β = 72.8240(10)°, γ = 61.7220(10)°,
V = 6247.1(10) Å3, T = 153(2) K, Z = 2, Dcalcd = 1.184 g cm−3, F000
=
2380, μ = 0.188 mm−1, 40 116 reflections collected, 21 028 unique
H
dx.doi.org/10.1021/ic3028012 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(Rint = 0.0352), no. of observed reflections 13 777 [I > 2σ(I)]; R1 =
0.0846, wR2 = 0.1788 [I > 2σ(I)].
Bianchi, A.; García-Espana, E. Anion Coordination Chemistry; Wiley
VCH: Weinheim, 2011.
̃
1H NMR Titration. Stock solutions of L (L = L1, L2, L3) (1.0 ×
10−2 M) in DMSO-d6 (0.5 mL), [K([18]crown-6)]3PO4, and
[K([18]crown-6)]2CO3 in H2O (0.3 mL, 0.25 M) and TBA2SO4,
(4) (a) Juris, A.; Barigelletti, S.; Campagna, S.; Balzani, V.; Belser, P.;
von Zelewsky, A. Coord. Chem. Rev. 1988, 84, 85−277. (b) Reedijk, J.;
Wilkinson, S. G.; Gillard, R. D.; McCleverty, J. A.; Press, P.
Comprehensive Coordination Chemistry; Oxford University Press:
Oxford, U.K., 1987. (c) Constable, E. C.; Steel, P. J. Coord. Chem.
Rev. 1989, 93, 205−223. (d) Kaes, C.; Katz, A.; Hosseini, M. W. Chem.
Rev. 2000, 100, 3553−3590. (e) Constable, E. C. Comprehensive
Supramolecular Chemistry; Pergamon: Oxford, U.K., 1996. (f) Sauvage,
J. P. Transition Metals in Supramolecular Chemistry; Wiley: New York,
1999.
1
TEAHCO3 in DMSO-d6 (0.3 mL, 0.25 M) were prepared for the H
NMR titrations. Small portions (2−10 μL) of the anion solution were
added to the solution of ligand L (DMSO-d6), and the spectrum was
recorded after each addition.
1H NMR Job’s Plot. Stock solutions of host (5.0 mM) and guest
(5.0 mM) in DMSO-d6 (5.0 mL) were prepared in separate volumetric
flasks. The 5 mm-o.d. NMR tubes were separately filled with a total of
500 μL solution of the host and guest in the following ratios (μL,
host/guest) at 297 K: 10:0, 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, 1:9. The
1H NMR spectra were obtained for each tube, and the H3 and H4
signals were used to calculate the complex concentration, [HG] = [H]t
× (δobsd − δfree)/(δcom− δfree), where [H]t is the total concentration of
the host, δobsd is the chemical shift observed on every point, and δfree
and δcom correspond to the chemical shifts of the free ligand and the
complex. This value was plotted against the molar fraction of the host.
The association constants (K’s) were determined by EQNMR.26
UV−Vis Titration. Stock solutions of L (L = L1, L3) (2.0 × 10−2
M) in DMSO (1 mL) and K3PO4 (4 × 10−3 M) in H2O (1 mL) were
prepared for the UV−vis titrations. Small portions (2−4 μL) of the
anion solution were added to the solution of ligand L (2.0 μL in 2.0
mL DMSO−5% H2O), and the spectrum was recorded after each
addition.
(5) Piguet, C.; Bernardinelli, G.; Hopfgartner, G. Chem. Rev. 1997,
97, 2005−2062.
(6) (a) Knof, U.; von Zelewsky, A. Angew. Chem., Int. Ed. 1999, 38,
302−322. (b) Belser, P.; Bernhard, S.; Jandrasics, E.; von Zelewsky, A.;
De Cola, L.; Balzani, V. Coord. Chem. Rev. 1997, 159, 11.
(7) (a) Balzani, V.; Juris, A.; Venturi, M.; Campagna, S.; Serroni, S.
Chem. Rev. 1996, 96, 759−833. (b) Ward, M. D.; White, C. M.;
Barigelletti, F.; Armaroli, N.; Calogero, G.; Flamigni, L. Coord. Chem.
Rev. 1998, 171, 481−488.
(8) (a) Kalyanasundaram, K.; Gratzel, M. Coord. Chem. Rev. 1998,
̈
177, 347−414. (b) Baxter, S. M.; Jones, W. E., Jr.; Danielson, E.; Worl,
L.; Strouse, G.; Younathan, J.; Meyer, T. J. Coord. Chem. Rev. 1991,
111, 47−71.
(9) Venturi, M.; Credi, A.; Balzani, V. Coord. Chem. Rev. 1999, 186,
233−256.
(10) (a) Wu, B.; Liang, J.; Yang, J.; Jia, C.; Yang, X.-J.; Zhang, H.;
Tang, N.; Janiak, C. Chem. Commun. 2008, 1762−1764. (b) Jia, C.;
Wu, B.; Li, S.; Huang, X.; Yang, X.-J. Org. Lett. 2010, 12, 5612−5615.
(c) Jia, C.; Wu, B.; Li, S.; Yang, Z.; Zhao, Q.; Liang, J.; Li, Q.-S.; Yang,
X.-J. Chem. Commun. 2010, 46, 5376−5378. (d) Jia, C.; Wu, B.; Li, S.;
Huang, X.; Zhao, Q.; Li, Q.-S.; Yang, X.-J. Angew. Chem., Int. Ed. 2011,
50, 486−490. (e) Li, S.; Jia, C.; Wu, B.; Luo, Q.; Huang, X.; Yang, Z.;
Li, Q.-S.; Yang, X.-J. Angew. Chem., Int. Ed. 2011, 50, 1−5. (f) Yang, Z.;
Wu, B.; Huang, X.; Liu, Y.; Li, S.; Xia, Y.; Jia, C.; Yang, X.-J. Chem.
Commun. 2011, 47, 2880−2882. (g) Li, S.; Wei, M.; Huang, X.; Yang,
X.-J.; Wu, B. Chem. Commun. 2012, 48, 3097−3099. (h) Wu, B.; Jia,
C.; Wang, X.; Li, S.; Huang, X.; Yang, X.-J. Org. Lett. 2012, 14, 684−
687.
ASSOCIATED CONTENT
■
S
* Supporting Information
Additional crystal structures and hydrogen bonding parameters,
1
IR spectra of the complexes, H NMR and UV−vis titrations,
and detailed information of the X-ray crystal structure analysis
of compounds 1−6 (CIF). This material is available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: wubiao@nwu.edu.cn.
■
(11) (a) Dydio, P.; Zielinski, T.; Jurczak, J. Chem. Commun. 2009,
4560−4562. (b) Kondo, S.-i.; Hiraoka, Y.; Kurumatani, N.; Yano, Y.
Chem. Commun. 2005, 1720−1722. (c) Odago, M. O.; Colabello, D.
M.; Lees, A. J. Tetrahedron 2010, 66, 7465−7471.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(12) Caltagirone, C.; Hiscock, J. R.; Hursthouse, M. B.; Light, M. E.;
Gale, P. A. Chem.Eur. J. 2008, 14, 10236−10243.
This work was supported by the National Natural Science
Foundation of China (Grant 21271149).
(13) Brooks, S. J.; Edwards, P. R.; Gale, P. A.; Light, M. E. New J.
Chem. 2006, 30, 65−70.
(14) Bryantsev, V. S.; Hay, B. P. J. Am. Chem. Soc. 2006, 128, 2035−
2042.
REFERENCES
■
(1) (a) Steed, J. W.; Atwood, J. L. Supramolecular Chemistry. John
Wiley & Sons, Ltd.: New York, 2009. (b) Sessler, J. L.; Gale, P. A.;
Cho, W.-S. Anion Receptor Chemistry; Royal Society of Chemistry:
Cambridge, U.K., 2006. (c) Lehn, J.-M. Supramolecular Chemistry:
Concepts and Perspectives; VCH: Weinheim: 1995. (d) Gale, P. A. Acc.
Chem. Res. 2006, 39, 465−475. (e) Katayev, E. A.; Ustynyuk, Y. A.;
Sessler, J. L. Coord. Chem. Rev. 2006, 250, 3004−3037. (f) Gale, P. A.;
García-Garrido, S. E.; Garric, J. Chem. Soc. Rev. 2008, 37, 151−190.
(g) Gale, P. A.; García-Garrido, S. E.; Garric, J. Chem. Soc. Rev. 2008,
37, 151−190. (h) Caltagirone, C.; Gale, P. A. Chem. Soc. Rev. 2009, 38,
520−563. (i) Steed, J. W. Chem. Soc. Rev. 2009, 38, 506−519. (j) Gale,
P. A. Chem. Soc. Rev. 2010, 39, 3746−3771. (k) Wenzel, M.; Hiscock,
J. R.; Gale, P. A. Chem. Soc. Rev. 2012, 41, 480−520.
(15) (a) Moore, S. J.; Haynes, C. J. E.; Gonzal
Brooks, S. J.; Light, M. E.; Herniman, J.; Langley, G. J.; Soto-Cerrato,
V.; Perez-Tomas, R.; Marque, I.; Costa, P. J.; Felix, V.; Gale, P. A.
́
ez, J.; Sutton, J. L.;
́
́
́
Chem. Sci. 2013, 4, 103−117. (b) Brooks, S. J.; Gale, P. A.; Light, M. E.
CrystEngComm 2005, 7, 586−591. (c) Brooks, S. J.; Gale, P. A.; Light,
M. E. Chem. Commun. 2005, 4696−4698.
́
(16) Amendola, V.; Boiocchi, M.; Esteban-Gomez, D.; Fabbrizzi, L.;
Monzani, E. Org. Biomol. Chem. 2005, 3, 2632−2639.
(17) Hay, B. P.; Firman, T. K.; Moyer, B. A. J. Am. Chem. Soc. 2005,
127, 1810−1819.
(18) (a) Custelcean, R.; Moyer, B. A.; Hay, B. P. Chem. Commun.
2005, 5971−5973. (b) Custelcean, R.; Remy, P.; Bonnesen, P. V.;
Jiang, D.-e.; Moyer, B. A. Angew. Chem., Int. Ed. 2008, 47, 1866−1870.
(c) Custelcean, R.; Bosano, J.; Bonnesen, P. V.; Kertesz, V.; Hay, B. P.
Angew. Chem., Int. Ed. 2009, 48, 4025−4029. (d) Ravikumar, I.;
Lakshminarayanan, P. S.; Arunachalam, M.; Suresh, E.; Ghosh, P.
Dalton Trans. 2009, 4160−4168. (e) Yi, S.; Brega, V.; Captaina, B.;
Kaifer, A. E. Chem. Commun. 2012, 48, 10295−10297.
(2) (a) Lehn, J.-M. Acc. Chem. Res. 1978, 11, 49−57. (b) Lehn, J. M.
Pure Appl. Chem. 1978, 50, 871−892.
(3) (a) Atwood, J. L.; Steed, J. W. Supramolecular Chemistry of Anions;
VCH: Weinheim, 1997. (b) Bowman-James, K. Acc. Chem. Res. 2005,
38, 671−678. (c) Kang, S. O.; Begum, R. A.; Bowman-James, K.
Angew. Chem., Int. Ed. 2006, 45, 7882−7894. (d) Bowman-James, K.;
I
dx.doi.org/10.1021/ic3028012 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(19) (a) Zhuge, F.; Wu, B.; Liang, J.; Yang, J.; Liu, Y.; Jia, C.; Janiak,
C.; Tang, N.; Yang, X.-J. Inorg. Chem. 2009, 48, 10249−10256.
(b) Jose, D. A.; Kumar, D. K.; Ganguly, B.; Das, A. Inorg. Chem. 2007,
46, 5817−5819. (c) Pflugrath, J. W.; Quiocho, F. A. Nature 1985, 314,
257−260. (d) Custelcean, R.; Sellin, V.; Moyer, B. A. Chem. Commun.
2007, 1541−1543. (e) Gale, P. A.; Hiscock, J. R.; Jie, C. Z.;
Hursthouse, M. B.; Light, M. E. Chem. Sci. 2010, 1, 215−220. (f) Kim,
J.-i.; Juwarker, H.; Liu, X.; Lah, M. S.; Jeong, K.-S. Chem. Commun.
2010, 46, 764−766. (g) Mendy, J. S.; Pilate, M. L.; Horne, T.; Day, V.
W.; Hossain, M. A. Chem. Commun. 2010, 46, 6084−6086.
(20) (a) Busschaert, N.; Wenzel, M.; Light, M. E.; Iglesias-
Hernandez, P.; Perez-Tomas, R.; Gale, P. A. J. Am. Chem. Soc. 2011,
́ ́ ́
133, 14136−14148. (b) Ravikumar, I.; Ghosh, P. Chem. Commun.
2010, 46, 6741−6743. (c) Wei, M.; Wu, B.; Zhao, L.; Zhang, H.; Li, S.;
Zhao, Y.; Yang, X.-J. Org. Biomol. Chem. 2012, 10, 8758−8761.
(d) Brooks, S. J.; Gale, P. A.; Light, M. E. Chem. Commun. 2006,
4344−4346. (e) Gunnlaugsson, T.; Kruger, P. E.; Jensen, P.; Pfeffer, F.
M.; Hussey, G. M. Tetrahedron Lett. 2003, 44, 8909−8913.
(f) Ravikumar, I.; Ghosh, P. Chem. Commun. 2010, 46, 1082−1084.
(21) Quinn, R.; Appleby, J. B.; Pez, G. P. J. Am. Chem. Soc. 1995, 117,
329−335.
(22) (a) Costero, A. M.; Gavina, P.; Rodríguez-Muniz, G. M.; Gil, S.
̃
̃
Tetrahedron 2007, 63, 7899−7905. (b) Al-Sayaha, M. H.; Branda, N.
R. Thermochim. Acta 2010, 503−504, 28−32. (c) Pfeffer, F. M.;
Kruger, P. E.; Gunnlaugsson, T. Org. Biomol. Chem. 2007, 5, 1894−
1902. (d) Pfeffer, F. M.; Gunnlaugsson, T.; Jensen, P.; Kruger, P. E.
Org. Lett. 2005, 7, 5357−5360. (e) Duke, R. M.; Gunnlaugsson, T.
Tetrahedron Lett. 2007, 48, 8043−8047. (f) Liu, S. Y.; Law, K. Y.; He,
Y. B.; Chan, W. H. Tetrahedron Lett. 2006, 47, 7857−7860.
(23) Bordwell, F. G.; Algrim, D.; Harrelson, J. A., Jr. J. Am. Chem. Soc.
1988, 110, 5904−5906.
(24) (a) Nishizawa, S.; Buhlmann, P.; lwao, M.; Umezawa, Y.
̈
Tetrahedron Lett. 1995, 36, 6483−6486. (b) Fan, E.; Arman, S. A. V.;
Kincaid, S.; Hamilton, A. D. J. Am. Chem. Soc. 1993, 11, 369−370.
́
(25) (a) Gomez, D. E.; Fabbrizzi, L.; Licchelli, M.; Monzani, E. Org.
Biomol. Chem. 2005, 3, 1495−1500. (b) Boiocchi, M.; Boca, L. D.;
Gomez, D. E.; Fabbrizzi, L.; Licchelli, M.; Monzani, E. J. Am. Chem.
́
Soc. 2004, 126, 16507−16514. (c) Jia, C.; Wu, B.; Liang, J.; Huang, X.;
Yang, X.-J. J. Fluor. 2010, 20, 291−297. (d) Duke, R. M.; O’Brien, J. E.;
McCabe, T.; Gunnlaugsson, T. Org. Biomol. Chem. 2008, 6, 4089−
4092.
(26) Hynes, M. J. J. Chem. Soc., Dalton Trans. 1993, 311−312.
(27) Boyle, E. M.; McCabe, T.; Gunnlaugsson, T. Supramol. Chem.
2010, 22, 586−597.
J
dx.doi.org/10.1021/ic3028012 | Inorg. Chem. XXXX, XXX, XXX−XXX