Binding of HgCl2 by a nitro functionalized tripodal receptor and its decomplexation controlled by anion complexation

Article abstract of DOI:10.1002/ejic.201000825

The presence of a nitro functionality on N-bridged tripodal receptors has an effect on its binding ability towards HgCl₂ by coordination through one of the nitro oxygen atoms, ethereal oxygen and the bridgehead nitrogen atom. Decomplexation of HgCl₂ and recovery of the receptor L can be accomplished by the formation of anion complexes with [L·HgCl₂]. The complexation of different anions with multiple protonated receptor units is attributable to intramolecular (N-H) ⁺·A·A·on interactions, at the same time the presence of multiple C- HA·A·A·anion and interligand C-H·A·A·O_nitro hydrogen bonds provide added stabilization. Protonation at the bridgehead nitrogen atom and the presence of the nitro functionality render the aliphatic and aryl protons sufficiently acidic for their active participation in moderate to weak C-H·A·A·anion and C- H·A·A·O_nitro interactions. Spectroscopic studies provide evidence for the formation of anion complexes from [LA·HgCl₂] by extrusion of HgCl_2. The strategic use of anion binding as a driving force for the templated assembly of the tripodal ligand L has been accomplished by the reversible complexationand decomplexation of [LA·HgCl₂] extruding HgCl₂ by employing mildly acidic ammonium salts. Copyright

Full text of DOI:10.1002/ejic.201000825

FULL PAPER
DOI: 10.1002/ejic.201000825
Binding of HgCl2 by a Nitro Functionalized Tripodal Receptor and Its
Decomplexation Controlled by Anion Complexation
Sandeep Kumar Dey[a] and Gopal Das*[a]
Keywords: Mercury / Hydrogen bonds / Anions / Anionic templates / Tripodal receptor / Molecular transformation
The presence of a nitro functionality on N-bridged tripodal
receptors has an effect on its binding ability towards HgCl2
by coordination through one of the nitro oxygen atoms, ether-
eal oxygen and the bridgehead nitrogen atom. Decomplex-
of multiple C–H···anion and interligand C–H···Onitro hydro-
gen bonds provide added stabilization. Protonation at the
bridgehead nitrogen atom and the presence of the nitro func-
tionality render the aliphatic and aryl protons sufficiently
ation of HgCl2 and recovery of the receptor L can be ac- acidic for their active participation in moderate to weak C–
complished by the formation of anion complexes with
[L·HgCl2]. The complexation of different anions with mul-
tiple protonated receptor units is attributable to intramolecu-
lar (N–H)+···anion interactions, at the same time the presence
H···anion and C–H···Onitro interactions. Spectroscopic studies
provide evidence for the formation of anion complexes from
[L·HgCl2] by extrusion of HgCl2.
is bound to HgCl2 through the bridgehead N and one or
two ethereal O atoms from the flexible side arms, depending
upon the position (ortho, meta or para) of the substituents
in the terminal phenyl ring.[4] However, we report here the
unusual participation of a nitro oxygen atom from one of
the flexible arms of the podand binding the Hg2+ as well as
the conventional N (apical) and O (ethereal) donor atoms.
The binding ability of Hg2+ towards ethereal oxygen and
nitrogen donors is well known and its structural versatility
Introduction
Podands, cavitands, hemicarcerands and capsules are
interesting members of the receptor family, in which the
confined interior space (or cavity) formed either by self-
assembly of the monomeric unit through noncovalent inter-
actions or by metal–ligand coordination, have been em-
ployed in various applications.[1] The use of anionic tem-
plates for the synthesis of superstructures has become an
attractive strategy in recent years.[2] However, the strategic
use of anion binding as a driving force for templated as-
sembly by decomplexation of metal complexes is rare. Hy-
drogen bonds formed with anions are weaker and more dif-
ficult to control than metal–cation coordination bonds.
Thus, anion template-induced transformation of molecular
species represents a new approach in the control of supra-
molecular assembly formation.[3] Although numerous syn-
thetic molecular transformations have been achieved by the
variation of an integral part of supramolecular aggregates,
it is still a challenge to control the assembly and transfor-
mation processes when a guest acts as a template.
n–
is displayed by HgIIxCly anions.[5] Tripodal ligands are
likely to form complexes that are thermodynamically stable
and kinetically not labile. However, the tertiary nitrogen of
N-bridged tripodal podands is susceptible to protonation
and the hydrogen of the protonated nitrogen atom could
become exo- or endo-orientated with respect to the side
arms depending on the nature of the anion.[6] Thus, the
counter anion(s) could play an important role in assembling
and controlling the structural topologies of the podands in
the solid state.[7] Moreover, by varying the geometry of the
anions involved in the self-assembly of a receptor, it should
be possible to reorient or rupture the self-assembled archi-
tectures based on the number of hydrogen bonding contacts
required by different anions. Recently, we have demon-
strated the aryl azo imidazole-assisted assembly of anion–
water through salt formation in the presence of mildly
acidic ammonium salts and have also explored the charge
assisted complexation of anions of varied dimensionality by
a para-nitro-functionalized tripodal podand.[8] Thus, we
have made an attempt to explore the transformation of a
tripodal metal complex with mercury into supramolecular
complexes with anions by extrusion of HgCl2, employing
mildly acidic ammonium salts as decomplexation agents in
moist MeOH (Scheme 1). Furthermore, the tripodal recep-
In the present study, we report an ortho-nitro function-
alized tripodal receptor possessing O- and N-donors
(Scheme 1) that reversibly bind Hg2+ and form the basis for
anion templated supramolecular self-assembly of a tripodal
ligand by decomplexation of the Hg complex. In all re-
ported HgII complexes of tripodal ether ligands, the ligand
[a] Department of Chemistry, Indian Institute of Technology
Guwahati,
North Guwahati, Assam 781039, India
Fax: +91-361-258-2349
E-mail: gdas@iitg.ernet.in
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000825.
Eur. J. Inorg. Chem. 2011, 429–438
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
429

S. K. Dey, G. Das
FULL PAPER
tor can be recovered in good yield by stirring a methanolic
solution of the anion complex in the presence of excess
Et3N.
Scheme 1. Schematic representation of the reversible binding of
HgCl2 by L controlled by anion complexation.
Results and Discussion
Single-Crystal X-ray Structural Study of [L·HgCl2]
The tripodal ligand L readily reacts with HgCl2 at room
temperature, in MeOH affording a five-coordinate HgII
complex which crystallizes in the monoclinic space group
P21/c with Z = 4. An ORTEP plot of [L·HgCl2] complex is
depicted in part a of Figure 1 with the atom numbering
scheme. The ligand is bound to HgCl2 through the bridge-
head N atom and one of the ethereal oxygen atoms O1 in
the flexible side arm of the podand (N1···Hg1 2.554 Å;
O1···Hg1 3.029 Å). In addition, the nitro oxygen atom O2
from the same arm is coordinated to HgCl2 with a bond
length of 2.728 Å. The unusual coordination mode of the
nitro oxygen atom with HgCl2 is possibly due to the inward
orientation of the coordinating nitro group towards HgCl2
Figure 1. (a) ORTEP plot (50% probability ellipsoids) of
[L·HgCl2]; (b) ball and stick representation of the C–H···Cl hydro-
gen bonded dimeric units with relevant hydrogen bond lengths. Se-
lected bond [Å] and angle (°) parameters for [L·HgCl2]: N1–Hg1
2.554(4), O1–Hg1 3.029, O2–Hg1 2.728, Hg1–Cl1 2.3083(16), Hg1–
Cl2 2.3154(16), Cl1–Hg1–Cl2 162.82(7), Cl1–Hg1–N1 101.94(9),
Cl2–Hg1–N1 94.36(9).
Formation of Anion Complexes by Decomplexation of
HgCl2
When a methanolic solution of the Hg complex is treated
resulting in the formation of a six-membered ring that in- with 1 equiv. an ammonium salt [NH4Cl, NH4Br, NH4NO3,
cludes the coordinated ethereal oxygen O1. One oxygen NH4ClO4 or (NH4)2SiF6] it forms a supramolecular com-
atom from each of the noncoordinating nitro groups O6 plex of the anion by extrusion of Hg2+ from the complex
and O8 is involved in interligand C–H···O interactions with as HgCl2. The ammonium ion is mildly acidic and reacts
the alkyl hydrogen atoms H10B and H5, respectively with Brønsted bases (i.e., the N-bridged podand) to return
(C10···O6 3.336 Å; C5···O8 3.402 Å). The aromatic hydro- to ammonia. After stirring for 4 h with heating, the yellow
gen atom H6 from the coordinating side arm is involved in solution became colourless, was filtered and left undis-
a weak dimeric interaction with the chlorine atom Cl1 of turbed in a beaker to crystallize. Slow evaporation of the
the adjacent [L·HgCl2] unit through C–H···Cl hydrogen solvent at room temperature afforded colourless crystals of
bonds (3.865 Å) and face to face (π···π) interactions be- the anion complexes in greater than 75% yields.
tween the identical phenyl rings (C1g···C1g 4.121 Å).
Structural information obtained from single-crystal X-
Furthermore, each dimeric unit interacts with two other di- ray analysis of the anionic complexes provides an insight
mers through aliphatic C–H···π interactions and π···π stack- into the binding topology of anions with the protonated
ing (Figure 1, b). The aliphatic H2B protons of the coordi- tripodal podand receptor and the nature of the intermo-
nating side arm and H18B from a noncoordinating side lecular hydrogen bond-directed self-assembly of the com-
arm of a dimeric unit interact with the phenyl rings plexes. In the supramolecular complexes, independent of
(through C1g and C2g) of two different units with bond the geometry and charge of the anion, the L:anion stoichi-
distances of 4.041 and 3.708 Å.
ometry is 1:1 except for [HL+]·[0.5SiF6–2] (5), which has a
430
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 429–438

Binding of HgCl2 by a Functionalized Tripodal Receptor
2:1 L:anion ratio. Complexation with different anions by L teractions between the aliphatic hydrogen atom H17B and
is principally governed by two different types of supra- the phenyl ring carbon atoms C19–C24 (C17···C3g 3.970 Å,
molecular interactions. In all complexes, the exo-orientated C17–H17B···C3g 134°).
hydrogen atom of the protonated bridgehead nitrogen atom
of L participate in a comparatively strong intramolecular
(N–H)+···anion bonding as hydrogen-bond donors. In ad-
dition to the (N–H)+···anion interaction, the anions are fur-
ther involved in several C–H···anion interactions with dif-
ferent alkyl and aryl hydrogen atoms from the protonated
podand satisfying the geometrical necessity of the flexible
LH+ units to respond to the demands of anions of different
sizes and geometries. The complexes are further stabilized
by various weak interligand directional hydrogen bonds,
which induce rigidity in the cationic podand formed and
serve as the foundation for the selective crystallization of
desired salts.
Single-Crystal X-ray Structural Studies of Anion
Complexes
The chloride complex [HL+]·[Cl–] (1) crystallizes in the
monoclinic space group P21/c, with Z = 4. The hydrogen
atom of the protonated apical nitrogen is exo-orientated
with respect to the tripodal arms. The torsion angles (τether
Figure 2. (a) Magnified view of the three hydrogen-bonding con-
tacts on the chloride anion (dashed lines) with three LH+ units with
the interligand C–H···π interactions; (b) crystal packing diagram of
1 viewed down the b-axis showing the bilayer assembly formation
of cationic ligand moieties along the c-axis with the chloride anions
situated between the adjacent bilayers.
)
involving N1amino–C–C–Oether are all in the folded confor-
mation for the three tripodal arms (Table S4). A magnified
view of the hydrogen bonding interactions with the chloride
ion together with the relevant edge-to-face interactions,
shown in Figure 2 (a), demonstrates that each chloride
The bromide complex [HL+]·[Br–] (2) crystallizes in the
¯
anion is involved in a three-point attachment provided by lower symmetry triclinic space group P1 with Z = 2. The
three LH+ units with two C–H···Cl– contacts. The exo-ori- torsion τether involving N1amino–C–C–Oether is in the folded
entated proton H1N is involved in an intramolecular (N–H) conformation for two side arms composed of the ethereal
+···Cl– interaction with the anion with a hydrogen bonding oxygen atoms O1 and O4 and is in the extended conforma-
distance of 3.015 Å and a N–H···Cl angle of 165°. The ali- tion for the third arm composed of the ethereal oxygen
phatic hydrogen atom H9A and aryl hydrogen atom H14 atom O7 (Table S4). Similar to 1, the bromide ion is in-
of two different units make weak intermolecular C–H···Cl– volved in a three-point hydrogen bond contact provided by
contacts with hydrogen bonding distances of 3.645 and three encircling cationic tripodal units. In addition to the
3.598 Å, respectively (Table S2). The C–H···Cl angle of 140° electrostatic (N–H)+···Br– interaction (N···Br 3.303 Å, N–
further implies the comparatively weak nature of the C–H H···Br 150°), the aliphatic hydrogen atom H1A and aryl
hydrogen bonds involving hydrogen atoms H9A and H14 hydrogen atom H7 of two different tripodal units are en-
(Table S2). The crystal packing diagram viewed along the gaged in forming weak intermolecular C–H···Br– contacts
b-axis (Figure 2, b) reveals that the receptor molecules pack with hydrogen bonding distances of 3.566 and 3.730 Å,
in a bilayer array forming a hydrophobic chain of ligand respectively. The C–H···Br angles of 129 and 133° suggest
moieties. The chloride ions are trapped between the adja- the feeble nature of the C–H hydrogen bonds (Table S2). A
cent bilayers generating a hydrophilic chain parallel to the magnified view of the bromide binding with relevant con-
c-axis. Intermolecular C–H···Onitro hydrogen bonding be- tact distances is depicted in Figure 3. The unusual three-
tween alkyl hydrogen atom H18B and nitro oxygen atom point contacts in both 1 and 2 suggest that the interactions
O2 (C18···O2 3.630 Å, C18–H18B···O2 163°) bridges the re- with the C–H donors are too weak to impose a definite
ceptor moieties along the c-axis. The adjacent monolayers coordination structure around the halide anions, and in-
of the ligand array are further connected through C– stead the C–H groups on the flexible arms of the receptor
H···Onitro hydrogen bonds involving the aryl hydrogen atom embrace the anion so as to match its size and shape to pro-
H23 with the nitro oxygen atom O6 (C23···O6 3.401 Å, vide a favourable electrostatic environment around it. The
C23–H23···O6 155°) and interligand edge to face (C–H···π) cationic tripodal units are self assembled by four intermo-
interactions between the aliphatic hydrogen atom H1B with lecular C–H···Onitro interactions between different alkyl and
the phenyl ring involving carbon atoms C3–C8 (C1···C1g aryl hydrogen atoms (H2B, H10A, H12 and H21) and one
4.258 Å, C1–H1B···C1g 120°) forming bilayers along c-axis. of the oxygen atoms (O3, O6 and O9) from each nitro
Two such bilayers are themselves interlinked by C–H···π in- group with an average hydrogen bond length of 3.255 Å,
Eur. J. Inorg. Chem. 2011, 429–438
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
431

S. K. Dey, G. Das
FULL PAPER
where O9 acts as a bifurcated hydrogen-bond acceptor with O12 through weak C–H···O hydrogen bonds complet-
(Table S3). In addition, the tripodal cations are cross-linked ing the eight-point contacts that stabilize the nitrate in the
by means of an interligand edge to face interaction between receptor channel (Figure 4, b). The cationic ligand moieties
aryl hydrogen atom H5 and the phenyl ring carbon atoms are self-organized by four interligand C–H···Onitro hydrogen
C18–C24 (C5···C3g 3.886 Å, C5–H5···C3g 130°) and a face bonds between different aliphatic protons (H1B, H9A, H9B
to face interaction between two identical phenyl rings and H10B) and one of the oxygen atoms (O3, O6 or O9)
(C3g···C3g 3.694 Å) of adjacent tripodal cations forming a from each nitro group, where O9 behaves as bifurcated hy-
bilayer assembly of ligand moieties (Supporting Infor- drogen-bond acceptor. Intermolecular C–H···Onitro hydro-
mation).
gen bonding between the alkyl hydrogen H1B and nitro
oxygen O3 (C1···O3 3.224 Å, C1–H1B···O3 125°) bridges
the tripodal molecules in a zigzag fashion forming bilayers
along the a-axis. Adjacent bilayers of the ligand array are
further interconnected through C–H···Onitro hydrogen
bonding interactions involving the aliphatic hydrogen atoms
H9A and H10B with the nitro oxygen atoms O9 and O6
(Supporting Information).
Figure 3. Magnified view of the three hydrogen bonding interac-
tions involving the bromide anion (dashed lines) with three neigh-
bouring LH+ units.
–
The nitrate complex [LH+]·[NO3 ]·0.5H20 (3) crystallizes
in the orthorhombic space group Pbcn with Z = 4. The
structure of the salt comprises a protonated tripodal cation
with NO3– and half a water molecule as solvent of crystalli-
zation. The solid-state structure of 3 shows a bifurcated (N–
H)+···O interaction between the hydrogen atom H1N of the
protonated amine with the nitrate oxygen atoms O10 and
O12 through N···O distances measuring 2.809 and 3.299 Å
and N–H···O angles of 166 and 136°, respectively. In ad-
dition, the nitrate oxygen atoms are C–H hydrogen bonded
to four encircling podand molecules with an average hydro-
gen bonding distance of 3.390 Å (ranging from 3.259 to
3.626 Å) and C–H···O angles between 131 and 175° (Table
S2). The nitrate oxygen atom O10 is involved in a moderate
aliphatic C–H···O interaction with the methylene hydrogen
atom H10A (C10···O10 3.259 Å, C10–H10A···O10 139°) of
the same tripodal unit forming bifurcated (N–H)+···O hy-
drogen bonds. The lattice water molecule (O13w) displays P1 with Z = 2. The tripodal arms are orientated in a similar
bridge hydrogen bonding with the oxygen atom O10 of two fashion to that of 2 with two arms in the folded conforma-
adjacent nitrate anions through hydrogen bonds measuring tion and the third arm orientated in the extended confor-
2.953 Å, forming a nitrate–water–nitrate adduct (Figure 4, mation (Table S4). Similar to 3, there exist bifurcated (N–
a). Two arms of each cationic L unit are projected in one H)+···O interactions but the perchlorate oxygen atoms O11
direction to form a cleft shaped cavity and two such tripo- and O13 involved in the electrostatic hydrogen bond forma-
dal clefts intercalate face to face to encapsulate the water tion come from two different perchlorate anions (N1···O11
bridged nitrate–water–nitrate adduct. The water molecule is 2.860 Å, N1–H···O11 143°; N1···O13 2.990 Å, N1–H···O13
further engaged in bifurcated C–H···O hydrogen bond for- 116°). In addition, there are seven C–H···O hydrogen bond
mation with the aliphatic proton H10A of the individual contacts formed between the perchlorate oxygen atoms and
tripodal cations stabilizing the trapped nitrate and water different alkyl and aryl hydrogen atoms of the four coordi-
molecules within the tripodal cleft. O11 is C–H hydrogen nating tripodal units surrounding the anion with an average
bonded to two aryl protons (H6 and H20), whereas the hydrogen bond length of 3.254 Å and a C–H···O angle
methylene proton H9A and aryl proton H7 make contacts range from 110–141°. An average C–H···O distance of
Figure 4. (a) Crystal structure of 3 depicting the encapsulation of
the nitrate–water–nitrate adduct within the dimeric cleft of the trip-
odal cations along with the relevant hydrogen bond interactions;
(b) magnified view of the seven hydrogen bonding interactions of
the nitrate anion (dashed lines) with four surrounding LH+ units
and the lattice water molecule (O13w).
–
[HL+]·[ClO4 ] (4) crystallizes in the triclinic space group
¯
432
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 429–438

Binding of HgCl2 by a Functionalized Tripodal Receptor
3.254 Å implies a better participation of the C–H donors and F3 behave as trifurcated C–H···F hydrogen-bond ac-
towards perchlorate binding than nitrate. A magnified view ceptors, each interacting with two methylene and one aryl
of the perchlorate binding with the receptor is shown in proton from the surrounding ligand moieties. The aliphatic
Figure 5. The methylene protons H18B and H2B from the protons H9B and H18B of one cation and the aryl hydrogen
same cation interact with perchlorate oxygen atoms O10 atom H24 from an adjacent LH+ unit make contacts with
and O11, respectively, whereas O12 of the perchlorate ion F2. Similarly, F3 is involved in an interaction with the ali-
forms a bifurcated acceptor C–H···O hydrogen bond with phatic protons H1B and H2B and the aryl hydrogen atom
the aliphatic hydrogen atom H17A and the aromatic hydro- H15 of two different tripodal cations. Details of the C–
gen atom H15 of two different receptor units. Finally, O13 H···F interactions are provided in Table S2. The tripodal
is involved in a trifurcated acceptor C–H···O hydrogen bond units in 5 pack into a bilayer structure (Figure 6, b) by ef-
with the aliphatic protons H1B and H17B of the same trip- fective intermolecular C–H···Onitro interactions involving
odal cation and another H1B proton of a neighbouring cat- one or both of the oxygen atoms from each nitro group
ion. Thus, the nine-point attachment through strong (O2, O6, O8 and O9) with the alkyl and aryl hydrogen
(N–H)+···O and weak C–H···O interactions is responsible atoms (H1A, H6, H14 and H21) and π···π interactions be-
for the binding and stabilization of perchlorate with mul- tween the phenyl rings involving carbon atoms C3–C8
tiple protonated LH+ units. The details of the C–H···anion (C1g) and C11–C16 (C2g). In addition, the complex also
interactions are provided in Table S2. As observed in 2, a demonstrates the formation of intermolecular C–H···Oether
bilayer arrangement of the ligand moiety is retained (Fig- hydrogen bonds between the aryl hydrogen atom H8 of one
ure 4, b) by multiple interligand C–H···Onitro interactions, cation with the ethereal oxygen atom O7 of an adjacent
an edge to face interaction (C–H···π) between the aryl hy- tripodal cation. The details of these interactions are pro-
drogen H5 with the phenyl ring involving carbon atoms vided in Table S3.
C18–C24 (C3g) and a face to face interaction (π···π) be-
tween two identical phenyl rings (C3g) of successive tripo-
dal units. Details of these interactions are provided in Table
S3.
Figure 5. Magnified view of the nine hydrogen bond contacts be-
tween the perchlorate anion (dashed lines) and the four encircling
LH+ units.
The silicon hexafluoride salt [HL+]·[0.5SiF6–2] (5) was
obtained by reaction of the tripodal complex [L·HgCl2]
with (NH4)2SiF6. The complex is a 2:1 ionic salt of L and
H2SiF6, and crystallizes in the monoclinic space group
2–
Figure 6. (a) Magnified view of the 24 hydrogen bonding interac-
P21/n with Z = 2. Interactions of the SiF6 anion with the
tions of hexafluorosilicate anion (dashed lines) with six encircling
surrounding LH+ moieties comprise similar bifurcated (N–
LH+ units; (b) crystal packing diagram of 5 viewed down the c-
H)+···O intramolecular hydrogen bonding as observed in 3
axis depicting the bilayer assembly formation of cationic ligand
2–
(N1···F1 2.730 Å, N1–H···F1 152°; N1···F2 2.928 Å, N1– moieties along the a-axis with the SiF6 anions sandwiched be-
H···O13 129°). The fluoride atoms F2 and F3 each make
tween the adjacent bilayers.
three C–H···F hydrogen bond contacts, whereas F1 makes
four contacts with the surrounding receptor moieties re-
2–
sulting in 24 hydrogen bonding contacts on SiF6 together
Rationalization of Structural Features
with four (N–H)+···O hydrogen bond interactions (Fig-
ure 6,a). An average hydrogen bond length of 3.271 Å im-
The hydrogen atom of the protonated bridgehead nitro-
plies the active participation of the alkyl and aryl C–H do- gen in L is exo-orientated in all of the anion complexes
nors towards hexafluorosilicate binding through moderate and is involved in forming intramolecular (N–H)+···anion
C–H···F interactions. F1 is involved in aliphatic C–H···F interactions with anions of different dimensionalities with
interactions with the methylene hydrogen atoms H1B, H2A, hydrogen bond lengths ranging from 2.730 to 3.303 Å. The
H18A and H18B involving two different cations. Both F2 absence of intramolecular noncovalent interactions between
Eur. J. Inorg. Chem. 2011, 429–438
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
433

S. K. Dey, G. Das
FULL PAPER
the receptor arms is likely to be responsible for the flat and feeble nature of the C–H hydrogen bonds is reflected in the
extended orientation of the tripodal arms in the LH+ units marginal upfield chemical shift of C–H proton resonances
1
in the complexes.[9] In all of these supramolecular com- in H NMR spectra and an average aliphatic/aromatic C–
plexes the anions are engaged in multiple weak C–H···O H···anion contact angle of 136°.
hydrogen bonds with methylene and aryl hydrogen atoms
The binding properties of [HL+]·[Ts] with different
presented from the neighbouring tripodal cations. Proton- anions in solution state were further investigated by 1H
ation at the apical nitrogen and the presence of the electron NMR titration experiments in CDCl3 at 298 K in the pres-
–
–
withdrawing nitro functionality in the ortho-position of the ence of nBu4N+X– (X– = Br–, NO3 , ClO4 ). Upon addition
terminal aryl render the methylene and aryl hydrogen atoms of aliquots from a stock solution of nBu4N+X– (15 mm) to
sufficiently acidic for their participation in weak C– the initial solution of [HL+]·[Ts] (5 mm), a gradual upfield
H···anion interactions. Although not typically considered to shift of the CH protons was observed (Supporting Infor-
be significant donors, there is increasing evidence that C– mation). The most substantial changes were observed for
H groups can participate in hydrogen bonding and lead to the aliphatic –CH2 protons (–NCH2 and –OCH2), indicat-
enhanced anion binding affinity.[10] This evidence comes in ing that the aliphatic protons adjacent to the protonated
the form of direct observation of close contacts in crystallo- nitrogen atom provide the maximum interaction between
graphic structures, anion induced chemical shifts of C–H the receptor and anions. The upfield shift of the aliphatic
protons in NMR spectra and theoretical calculations.[11] protons with Δδ –NCH2 ca. 0.052 and –OCH2 ca. 0.056
The binding ability of tripodal receptors for anions varies ppm on addition of nBu4NBr, Δδ –NCH2 ca. 0.044 and
with the functionality of the tripodal unit as functional –OCH2 ca. 0.049 ppm on addition of nBu4NNO3 and Δδ
groups modify the hydrogen bonding capability. A recent –NCH2 ca. 0.049 and –OCH2 ca. 0.047 ppm on addition of
theoretical investigation by Hay et al. showed that the effect nBu4NClO4. The association constants (K) calculated for
of electron withdrawing substituents on the aryl moiety sig- the anions by a nonlinear regression curve[13e] indicate that
nificantly enhances the stability of anion complexes.[12] bromide, nitrate and perchlorate bind only weakly with the
Though charge neutralisation in the crystals and conven- protonated ligand having logK values of 0.245, 0.232 and
tional hydrogen bonds are the main driving forces in the 0.227 m–1, respectively. Titration data gave the best fit for
formation of supramolecular complexes, weak C–H hydro- 1:1 association models of receptor to anion (Figure 7). The
gen bonds provide added stabilization and satisfy the geo- similar logK values suggest that, irrespective of their size
–
metric needs of the LH+ units by providing a favourable and geometry (spherical Br–, planar NO3 and tetrahedral
–
electrostatic environment around the anions. Moreover, in- ClO4 ), the anions interact with the protonated receptor to
terligand C–H···Onitro interactions provide further stabiliza- almost the same extent. This is also evident from the struc-
tion to all anion complexes resulting in the bilayer assembly tural studies of complexes 2, 3 and 4 where the respective
of ligand moieties in the solid state.
anions are involved in electrostatic (N–H)+···anion interac-
tions with the concomitant formation of weak C–H···anion
hydrogen bonds provided by four receptor units in each
case.
Studies on Anion Binding in Solution
To investigate the binding of different anions with the
cationic receptor molecule in solution, we have protonated
L with p-toluenesulfonic acid and monitored its spectral
changes in the presence of various tetrabutylammonium
(TBA) salts.[13] The addition of an equivalent amount of
TBA salts of Br–, NO3– or ClO4– to a solution of [HL+]·[Ts]
in CDCl3 resulted in a notable upfield chemical shift of the
aliphatic CH2 proton resonances (Δδ = 0.048–0.053 ppm),
which indicates participation of the receptor in anion bind-
ing through weak hydrogen bonding interactions involving
C–H protons (Supporting Information). Moreover, spectral
changes were also observed for the aromatic C–H reso-
nances. As most of the aliphatic CH···anion contacts are
formed with the H atoms on carbon atoms adjacent to the
ammonium ion, it can be argued that these H atoms are
simply in the way due to the close approach of anions to
the positively charged N atom and form electrostatic (N–
H)+···anion interactions. The other possibility is that pro-
tonation at the apical nitrogen atoms renders the methylene
CH2 groups sufficiently acidic for their active participation
Figure 7. Plot of change in chemical shift of the aliphatic –NCH2
protons of [HL+]·[Ts] with increasing addition of nBu4N+X– (X– =
–
–
Br–, NO3 , ClO4 ) in CDCl3 at 298 K.
Recovery of Receptor L from Anion Complexes
The receptor L can be recovered from the anion com-
towards anion binding by weak CH···anion interactions plexes in good yield simply by stirring a MeOH solution of
with an average C–H hydrogen bond length of 3.436 Å. The the anion complex in the presence of excess Et3N at room
434
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 429–438

Binding of HgCl2 by a Functionalized Tripodal Receptor
temperature for about an hour. Evaporation of methanol (9:1, v/v) shows a broad intraligand π-π* transition band
under reduced pressure followed by extraction into CHCl3 centred around 326 nm and an intense high energy absorp-
results in a yellow colouration of the organic layer due to tion band centred at 259 nm (Figure 8, a). The absorption
the presence of L. Upon removal of CHCl3, L is obtained spectrum of [L·HgCl2] shows a significant blueshift of 7 nm
as viscous oily liquid in greater than 85% yield. The recep- of the high energy absorption band but the peak position
tor L can be dissolved in methanol and treated with HgCl2 of the lower energy absorption band remains the same. Ad-
to afford the HgII complex again, this cycle is represented dition of NH4Cl to the [L·HgCl2] solution results in a con-
in Scheme 1.
siderable blueshift (ca. 5 nm) of the lower energy band with
an isosbestic point at 321 nm but the peak position of the
high energy band (ca. 252 nm) remains the same with a
gradual increase in its intensity (Figure 8, b). In order to
validate the recovery of L in solution, we have monitored
the absorption spectrum of 1 at a similar concentration.
The peak positions of both absorption bands remain almost
identical to that of the spectrum obtained upon titration of
[L·HgCl2] with NH4Cl. Addition of Et3N to a solution of
1 results in a redshift of 6 nm of the lower energy band with
an isosbestic point at 321 nm as observed in the previous
process, and the peak position of the higher energy band
(ca. 252 nm) remains the same with a gradual decrease in
its intensity (Figure 8, c).
Spectroscopic Evidence for the Formation of Anion
Complexes
The transformation of [L·HgCl2] into anion complexes
followed by recovery of L has also been investigated in solu-
tion using UV/Vis and H NMR spectroscopy. The elec-
1
tronic absorption spectrum of receptor L in methanol/H2O
The excellent solubility of [L·HgCl2] in MeCN allowed
1
us to perform a H NMR experiment in CD3CN. A com-
1
parison of the H NMR spectra of [L·HgCl2] with that of
L shows a downfield shift of the aliphatic CH2 protons (Δδ
= 0.07–0.09 ppm) with marginal changes in the resonances
of aromatic CH protons. The addition of 1 equiv. of NH4Cl
(D2O solution) to the [L·HgCl2] solution in CD3CN results
in a significant downfield shift of the aliphatic CH2 reso-
nances (Δδ = 0.48–0.88 ppm), which indicates the influence
of protonation at the apical nitrogen on the neighbouring
methylene protons by extrusion of HgCl2 (Figure 9). No-
Figure 8. Absorption spectral changes of (a) L (10 μm) upon ad-
dition of HgCl2 solution in MeOH/H2O (9:1, v/v); (b) [L·HgCl2]
(10 μm) upon addition of NH4Cl solution in MeOH/H2O (9:1, v/v)
and (c) 1 (10 μm) upon addition of Et3N solution in MeOH/H2O
(9:1, v/v).
1
Figure 9. Partial H NMR spectra (400 MHz, CD3CN) of L (bot-
tom), [L·HgCl2] (middle) and [L·HgCl2] with 1 equiv. of NH4Cl in
CD3CN/D2O (ca. 9:1) (top).
Eur. J. Inorg. Chem. 2011, 429–438
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
435

S. K. Dey, G. Das
FULL PAPER
CD3CN): δ = 3.10 (t, J = 5.4 Hz, 6 H, NCH2), 4.15 (t, J = 5.4 Hz,
6 H, OCH2), 6.98 (t, J = 7.8 Hz, 3 H, ArH), 7.16 (d, J = 8.8 Hz,
3 H, ArH), 7.50 (t, J = 5.6 Hz, 3 H, ArH), 7.71 (d, J = 8.0 Hz, 3
H, ArH) ppm. 13C NMR (100 MHz, CD3CN): δ = 54.85 (ϫ3 C,
NCH2), 69.94 (ϫ3 C, OCH2), 115.89 (ϫ3 C, ArH), 121.28 (ϫ3 C,
ArH), 126.10 (ϫ3 C, ArH), 135.29 (ϫ3 C, ArH), 140.79 (ϫ3 C,
ArH), 152.91 (ϫ3 C, ArH) ppm.
table downfield chemical shifts have also been observed for
the aromatic CH protons. Thus, solution studies also give
evidence for the formation of anion complexes from
[L·HgCl2] by extrusion of HgCl2 employing ammonium
salts as decomplexation agents.
Synthesis of [L·HgCl2]: The Hg complex was synthesized by adding
a solution of HgCl2 (0.458 g, 1.95 mmol) in methanol (10 mL) to
a well stirred solution of L (1 g, 1.95 mmol) in methanol (20 mL)
at room temperature. The mixture was stirred for 3 h during which
a light yellow precipitate was formed. The volume of the solution
was reduced to ca. 10 mL. The precipitate was collected by fil-
tration under cold conditions and washed with diethyl ether and
dried in a vacuum desiccator. Yield: 72% (1.10 g) based on L. Sin-
gle crystals suitable for X-ray analysis were grown from an acetoni-
trile solution over 1 week. 1H NMR (400 MHz, CD3CN): δ3.19 (t,
J = 4.8 Hz, 6 H, NCH2), 4.22 (t, J = 5.2 Hz, 6 H, OCH2), 7.04 (t,
J = 7.6 Hz, 3 H, ArH), 7.21 (d, J = 8.8 Hz, 3 H, ArH), 7.54 (t, J
= 7.2 Hz, 3 H, ArH), 7.77 (d, J = 8.0 Hz, 3 H, ArH) ppm. 13C
NMR (100 MHz, CD3CN): δ = 55.68 (ϫ3 C, NCH2), 65.62 (ϫ3
C, OCH2), 116.34 (ϫ3 C, ArH), 122.77 (ϫ3 C, ArH), 126.89 (ϫ3
C, ArH), 136.22 (ϫ3 C, ArH), 140.59 (ϫ3 C, ArH), 152.03 (ϫ3 C,
ArH) ppm. C24H24Cl2HgN4O9 (783.96): calcd. C 36.76, H 3.08, N
7.14; found C 35.24, H 2.59, N 7.35.
Conclusions
In conclusion, we have been able to show the reversible
complexation and decomplexation of HgCl2 with a tripodal
podand receptor bearing nitro functionality, employing
readily available ammonium salts as Hg removal reagents.
This study provides a new insight into the transformation of
tripodal complexes of soft metal ions into supramolecular
complexes including anions. We have also revealed solid
state evidence for the active participation of both aliphatic
CH2 and aryl CH groups in the binding of different anions
with L, exhibiting aliphatic C–H···anion hydrogen bond
strengths comparable to those of aryl C–H···anion hydro-
gen bonds. These hydrogen bonds are also actively involved
in providing further stabilization to the complexes by form-
ing directional interligand C–H···Onitro hydrogen bonds
with the oxygen atoms of the nitro groups establishing a
bilayer structure in the solid state. A detailed structural in-
vestigation clearly demonstrates that the self-alignment,
flexibility and orientation of the ligand moiety play a cru-
cial role in making a variety of molecular interactions pos-
sible in the binding of HgCl2 and anions of different dimen-
sionality. Therefore, complexes with L provide excellent ex-
amples of HgII complexation and C–H···anion hydrogen
bonding in anion complexes.
Synthesis Complexes 1–5: Anion complexes 1–5 were synthesized
by reacting [L·HgCl2] with equivalent amounts of NH4Cl, NH4Br,
NH4NO3, NH4ClO4 or (NH4)2SiF6. As (NH4)2SiF6 cannot be ob-
tained commercially, this was prepared by reacting an aqueous
30% ammonia solution with HF in a glass beaker. To form the
complexes, [L·HgCl2] (100 mg) was dissolved in MeOH (20 mL)
and 1 equiv. of the ammonium salt dissolved in minimum volume
of water (ca. 2 mL) was added at once. The solution mixture was
then stirred with gentle heating (ca. 60 °C) for about 4 h, allowed
to cool to room temp. and filtered. Slow evaporation of the filtrate
at room temp. yielded colourless block/rectangular crystals suitable
for X-ray analysis.
Experimental Section
Materials and Methods: All reagents and solvents were obtained
from commercial sources and used as received unless specified.
NMR spectra were recorded with a Varian FT-400 MHz instru-
ment. Chemical shifts were recorded in ppm using tetramethylsil-
ane (TMS) as a reference. IR spectra were recorded with a Perkin–
Elmer-Spectrum One FT-IR spectrometer as KBr disks in the
range 4000–450 cm–1. Absorption spectra were recorded with a Per-
kin–Elmer Lambda-25 UV/Vis spectrometer at 298 K. Elemental
analyses were carried out with a Perkin–Elmer 2400 automatic car-
bon, hydrogen and nitrogen analyzer.
[HL+]·[Cl–] (1): Colourless crystals; yield of crystallization: 82%
(58 mg) based on [L·HgCl2]; mp: 175 °C; 1H NMR (400 MHz,
[D6]DMSO): δ = 3.90 (s, 6 H, NCH2), 4.68 (s, 6 H, OCH2), 7.17
(t, J = 7.2 Hz, 3 H, ArH), 7.39 (d, J = 8.4 Hz, 3 H, ArH), 7.70 (t,
J = 6.8 Hz, 3 H, ArH), 7.92 (d, J = 8.0 Hz, 3 H, ArH) ppm. IR
(KBr disk): ν = 1242, 1519, 1606, 3422 cm–1. C H ClN O
˜
24 25
4
9
(548.93): calcd. C 52.51, H 4.59, N 10.20; found C 52.98, H 4.13,
N 9.56.
[HL+]·[Br–] (2): Colourless crystals; yield of crystallization: 76%
(56 mg) based on [L·HgCl2]; mp: 198 °C; 1H NMR (400 MHz,
[D6]DMSO): δ = 3.54 (s, 6 H, NCH2), 4.65 (s, 6 H, OCH2), 7.15
(t, J = 7.8 Hz, 3 H, ArH), 7.37 (d, J = 8.4 Hz, 3 H, ArH), 7.68 (t,
J = 7.8 Hz, 3 H, ArH), 7.89 (d, J = 8.0 Hz, 3 H, ArH) ppm. IR
Synthesis of Tripodal Receptor L: The receptor L was synthesized
by modification of our recent literature procedure.[14] To a solution
of 2-nitrophenol (5 g, 36 mmol) in dry n-propanol (30 mL) was
added crushed NaOH (1.77 g, 43 mmol), and the solution was
stirred at room temperature for 1 h. To the resulting suspension was
added tris(2-chloroethyl)amine hydrochloride (2.88 g, 12 mmol) at
once, and the mixture was stirred for another 1 h at room tempera-
ture and then heated to reflux for 8 h. The solvents were removed
under reduced pressure and cold water (20 mL) was added. The
product was extracted into CHCl3 (3ϫ20 mL) and the organic
layer was washed with water and dried with anhydrous Na2SO4
before the solvents were removed under reduced pressure. The
crude product was purified by column chromatography with 75%
ethyl acetate (in petroleum ether) as the eluent. The product was a
viscous brown liquid. Yield: 66% (1.40 g). 1H NMR (400 MHz,
(KBr disk): ν = 1272, 1526, 1609, 3444 cm–1. C H BrN O
˜
24 25
4
9
(593.38): calcd. C 48.57, H 4.24, N 9.44; found C 48.49, H 4.58, N
9.25.
–
[HL+]·[NO3 ]·0.5H2O (3): Colourless crystals; yield of crystalli-
1
zation: 80% (115 mg) based on [L·HgCl2]; mp: 192 °C; H NMR
(400 MHz, [D6]DMSO): δ = 3.89 (s, 6 H, NCH2), 4.57 (s, 6 H,
OCH2), 7.15 (t, J = 6.8 Hz, 3 H, ArH), 7.36 (d, J = 8.0 Hz, 3 H,
ArH), 7.68 (t, J = 7.2 Hz, 3 H, ArH), 7.89 (d, J = 7.2 Hz, 3 H,
ArH) ppm. IR (KBr disk): ν = 1278, 1384, 1526, 1607, 3436 cm–1.
˜
C24H26N5O12.5 (583.49): calcd. C 50.00, H 4.55, N 12.15; found C
49.88, H 4.26, N 11.76.
436
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 429–438

Binding of HgCl2 by a Functionalized Tripodal Receptor
[HL+]·[ClO4 ] (4): Colourless crystals; yield of crystallization: 75%
–
Acknowledgments
(58 mg) based on [L·HgCl2]; mp: 181 °C; 1H NMR (400 MHz,
[D6]DMSO): δ = 3.89 (s, 6 H, NCH2), 4.55 (s, 6 H, OCH2), 7.15
(t, J = 7.8 Hz, 3 H, ArH), 7.32 (d, J = 8.4 Hz, 3 H, ArH), 7.66 (t,
J = 7.6 Hz, 3 H, ArH), 7.86 (d, J = 8.0 Hz, 3 H, ArH) ppm. IR
G. D. acknowledges the Department of Science and Technology
(DST), Grant No. SR/S1/IC-01/2008 and the Council of Scientific
and Industrial Research (CSIR), Grant No. 01-2235/08/EMR-II,
New Delhi, India for financial support and DST-FIST for single-
crystal X-ray diffraction measurements. S. K. D. acknowledges IIT
Guwahati, India for a fellowship.
(KBr disk): ν = 1085, 1274, 1526, 1609, 3110 cm–1. C H ClN O
˜
24 25
4
13
(612.93): calcd. C 47.02, H 4.11, N 9.14; found C 46.84, H 4.42, N
9.26.
[HL+]·[0.5SiF6–2] (5): Colourless crystals; yield of crystallization:
76% (110 mg) based on [L·HgCl2]; mp: 207 °C; 1H NMR
(400 MHz, [D6]DMSO): δ = 4.39 (s, 6 H, OCH2), 7.12 (t, J =
7.6 Hz, 3 H, ArH), 7.34 (d, J = 8.4 Hz, 3 H, ArH), 7.65 (t, J =
7.2 Hz, 3 H, ArH), 7.86 (d, J = 8.0 Hz, 3 H, ArH) ppm. IR (KBr
[1] a) D. J. Cram, Science 1983, 219, 1177–1182; b) R. Warmuth,
J. Yoon, Acc. Chem. Res. 2001, 34, 95–105; c) J. Rebek Jr., Acc.
Chem. Res. 1999, 32, 278–286; d) A. Shivanyuk, J. Rebek Jr.,
J. Am. Chem. Soc. 2002, 124, 12074–12075; e) T. Amaya, J.
Rebek Jr., Chem. Commun. 2004, 1802–1803; f) A. S. Singh,
P. K. Bharadwaj, Dalton Trans. 2008, 738–741; g) S. Rieth, Z.
Yan, S. Xia, M. Gardlik, A. Chow, G. Fraenkel, C. M. Hadad,
J. D. Badjic, J. Org. Chem. 2008, 73, 5100–5109; h) A. Kumar,
S.-S. Sun, A. J. Lees, Coord. Chem. Rev. 2008, 252, 922–939.
[2] a) A. Bianchi, K. Bowman-James, E. Garcia-Espana, Supra-
molecular Chemistry of Anions; Wiley-VCH, Weinheim, Ger-
many, 1997; b) S. S. Zhu, H. Staats, K. Brandhorst, J. Grunen-
berg, F. Gruppi, E. Dalcanale, A. Lutzen, K. Rissanen, C. A.
Schalley, Angew. Chem. Int. Ed. 2008, 47, 788–792; c) M. J.
Chmielewski, L. Zhao, A. Brown, D. Curiel, M. R. Sambrook,
A. L. Thompson, S. M. Santos, V. Felix, J. J. Davis, P. D. Beer,
Chem. Commun. 2008, 3154–3156; d) M. D. Lankshear, P. D.
Beer, Acc. Chem. Res. 2007, 40, 657–665; e) N. Gimeno, R.
Vilar, Coord. Chem. Rev. 2006, 250, 3161–3189; f) . S. J. Coles,
J. G. Frey, P. A. Gale, M. B. Hursthouse, M. E. Light, K. Na-
vakhun, G. L. Thomas, Chem. Commun. 2003, 568–569; g) J. L.
Atwood, A. Szumna, Chem. Commun. 2003, 940–941; h) R. L.
Paul, Z. R. Bell, J. C. Jeffery, J. A. McCleverty, M. D. Ward,
Proc. Natl. Acad. Sci. USA 2002, 99, 4883–4888; i) D. Rais, J.
Yau, D. M. P. Mingos, R. Vilar, A. J. P. White, D. J. Williams,
Angew. Chem. Int. Ed. 2001, 40, 3464–3467; j) R. Vilar,
D. M. P. Mingos, A. J. P. White, D. J. Williams, Angew. Chem.
Int. Ed. 1998, 37, 1258–1262.
disk): ν = 1274, 1528, 1607, 3436 cm–1. C H F N O Si
(584.52): calcd. C 50.53, H 4.42, N 9.82; found C 50.84, H 4.22, N
9.48.
˜
24 25
3
4
9
0.5
Single-Crystal X-ray Studies: The crystallographic data and details
of data collection and refinement for [L·HgCl2] and 1–5 are given
in Table S1 in the Supporting Information. In each case, a single
crystal of suitable size was selected from the mother liquor at room
temp. immersed in Paratone oil and then mounted on the tip of a
glass fibre and cemented using epoxy resin. The intensity data were
collected using a Bruker SMART APEX-II CCD diffractometer,
equipped with a fine focus 1.75 kW sealed tube Mo-Kα radiation
(λ = 0.71073 Å) at 298(3) K, with increasing ω (width of 0.3° per
frame) at a scan speed of 6 s/frame. SMART software was used for
data acquisition. Data integration and reduction were undertaken
with SAINT and XPREP[15] software. Multiscan empirical absorp-
tion corrections were applied to the data using the program SAD-
ABS.[16] Structures were solved by direct methods using SHELXS-
97[17] and refined with full-matrix least-squares on F2 using
SHELXL-97.[18] All non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms attached to all carbon atoms were geometri-
cally fixed whereas the hydrogen atoms of the tertiary amino nitro-
gen of the salts were located from the difference Fourier map, and
the positional and temperature factors are refined isotropically.
However, we were unable to locate the hydrogen atoms of the lattice
water molecule in 3 from the difference Fourier map. Structural
illustrations have been generated using ORTEP-3[19] and MER-
CURY 1.3[20] for Windows.
1H NMR Titration Experiments: Binding constants were obtained
by 1H NMR (400 MHz, Bruker) titrations of [HL+]·[Ts] with tetra-
butylammonium salts in CDCl3 at 25 °C. The initial concentration
of receptor was 5 mm. Aliquots of anions were added from a stock
solution 15 mm of anions. TMS in CDCl3 was used as an internal
reference, and each titration was performed by 10 measurements at
room temperature. All the proton signals were referred to TMS.
Association constants were calculated by fitting the change in the
N–CH2 chemical shift with a 1:1 association model with nonlinear
least square analysis. WINEQNMR 2.0 was employed in the calcu-
lation of association constants.[21] The error limit in K was about
10%.
[3] a) D. H. Busch, N. A. Stephenson, Coord. Chem. Rev. 1990,
100, 119–154; b) S. Anderson, H. L. Anderson, J. K. M. San-
ders, Acc. Chem. Res. 1993, 26, 469–475; c) R. Vilar, Angew.
Chem. Int. Ed. 2003, 42, 1460–1477.
[4] a) A. S. Singh, P. K. Bharadwaj, Dalton Trans. 2008, 738–741;
b) A. S. Singh, B. Chen, Y. Wen, C. Tsai, S. Sun, Org. Lett.
2009, 11, 1867–1870.
[5] a) M.-R. Huang, X.-G. Li, Chem. Eur. J. 2007, 13, 6009–6018,
and references cited therein; b) L. Praveen, G. R. Thirumalai,
T. Sreeja, M. L. P. Reddy, R. L. Varma, Inorg. Chem. 2007, 46,
6277–6282; c) G. K. Patra, I. Goldberg, Polyhedron 2002, 21,
2195–2199; d) D. C. Bebout, S. W. Stokes, R. J. Butcher, Inorg.
Chem. 1999, 38, 1126–1133; e) D. A. House, W. T. Robinson,
V. M c Ke e, Coord. Chem. Rev. 1994, 135/136, 533–585; f) G. A.
Bowmaker, B. Assadollahzadeh, A. M. Brodie, E. W. Ain-
scough, G. H. Freeman, G. R. Jameson, Dalton Trans. 2005,
1602–1612; g) D. G. Morris, K. W. Muir, C. O. W. Chii, Polyhe-
dron 2003, 22, 3345–3353.
[6] a) A. Oehmen, R. Viegas, S. Velizarov, M. A. M. Reis, J. G.
Crespo, Desalination 2006, 199, 405; b) A. Kowalski, Metals
Removal to Low Levels Using Precipitants, presented at the
AESF/EPA Conference, Orlando, FL, January 28–30, 2002.
[7] M. Arunachalam, P. Ghosh, Chem. Commun. 2009, 3184–3186.
[8] a) A. Pramanik, S. Majumdar, G. Das, CrystEngComm 2010,
12, 250; b) S. K. Dey, B. Ojha, G. Das, Cryst. Eng. Commun.
2010; DOI: 10.1039/c0ce00316f.
The following equation was used to determine K values, where A
and R are the anion and [HL+]·[Ts], respectively.
Δδ = {([A]0 + [R]0 + 1/K) +/– (([A]0 + [R]0 + 1/R)2 – 4[R]0[A]0)1/2}-
Δδmax/2[R]0
Supporting Information (see also the footnote on the first page of
this article): Further crystallographic details involving tables of the
crystal structure determination, selected hydrogen bond parameters
and selected torsion angles, H NMR spectra and titrations, ther-
mal ellipsoid plots (50% probability model) of complexes 1–5 and
[9] a) P. S. Lakshminarayanan, I. Ravikumar, E. Suresh, P. Ghosh,
Inorg. Chem. 2007, 46, 4769–4771; b) A. Pramanik, M. Bhu-
yan, R. Choudhury, G. Das, J. Mol. Struct. 2008, 879, 88–95;
c) M. A. Hossain, J. A. Liljegren, D. Powell, K. Bowman-
James, Inorg. Chem. 2004, 43, 3751–3755.
1
packing diagrams.
Eur. J. Inorg. Chem. 2011, 429–438
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
437

S. K. Dey, G. Das
FULL PAPER
[10] a) R. K. Castellano, Curr. Org. Chem. 2004, 8, 845–865; b) Z.
Xu, S. K. Kim, J. Yoon, Chem. Soc. Rev. 2010, 39, 1457–1466.
[11] a) K. J. Wallace, W. J. Belcher, D. R. Turner, K. F. Syed, J. W.
Steed, J. Am. Chem. Soc. 2003, 125, 9699–9715; b) C. A. Ili-
oudis, D. A. Tocher, J. W. Steed, J. Am. Chem. Soc. 2004, 126,
12395–12402; c) D. R. Turner, E. C. Spencer, J. A. K. Howard,
D. A. Tocher, J. W. Steed, Chem. Commun. 2004, 1352–1353; d)
M. J. Chmielewski, M. Charon, J. Jurczak, Org. Lett. 2004, 6,
3501–3504; e) S. O. Kang, D. VanderVelde, D. Powell, K. Bow-
man-James, J. Am. Chem. Soc. 2004, 126, 12272–12273; f) J. Y.
Kwon, Y. J. Jang, S. K. Kim, K.-H. Lee, J. S. Kim, J. Yoon, J.
[13] a) M. A. Saeed, J. J. Thompson, F. R. Fronczekb, M. A. Hos-
sain, CrystEngComm 2010, 12, 674–676; b) M. A. Saeed, F. R.
Fronczekb, M. A. Hossain, Chem. Commun. 2009, 6409–6411;
c) M. A. Saeed, F. R. Fronczekb, M. Huang, M. A. Hossain,
Chem. Commun. 2010, 404–406; d) J. S. Mendy, M. L. Pilate,
T. Horne, V. W. Dayb, M. A. Hossain, Chem. Commun. 2010,
6084–6086; e) P. Morehouse, M. A. Hossain, J. M. Llinares, D.
Powell, K. Bowman-James, Inorg. Chem. 2003, 42, 8131–8133.
[14] S. K. Dey, G. Das, Cryst. Growth Des. 2010, 10, 754–760.
[15] SAINT, SMART and XPREP, Siemens Analytical X-ray In-
struments Inc., Madison, Wisconsin, USA, 1995.
Org. Chem. 2004, 69, 5155–5157; g) A. M. Costero, M. J. Ban- [16] G. M. Sheldrick, SADABS: Software for Empirical Absorption
uls, M. J. Aurell, M. D. Ward, S. Argent, Tetrahedron 2004, 60,
9471–9478; h) S. Ghosh, A. R. Choudhury, T. N. G. Row, U.
Maitra, Org. Lett. 2005, 7, 1441–1444; i) K. Hiraoka, S. Mi-
zuse, S. Yamabe, Chem. Phys. Lett. 1988, 147, 174; j) Z. M.
Loh, R. L. Wilson, D. A. Wild, E. J. Bieske, J. Chem. Phys.
2003, 119, 9559–9567; k) F. M. Raymo, M. D. Bartberger,
K. N. Houk, J. F. Stoddart, J. Am. Chem. Soc. 2001, 123, 9264–
9267.
Correction, University of Göttingen, Göttingen, Germany,
1999–2003.
[17] G. M. Sheldrick, SHELXS-97, University of Göttingen, Ger-
many, 1997.
[18] G. M. Sheldrick, SHELXL-97, Program for Crystal Structure
Refinement, University of Göttingen, Germany, 1997.
[19] L. J. Farrugia, J. Appl. Crystallogr. 1997, 30, 565–566.
[20] Mercury 1.3 Supplied with Cambridge Structural Database,
CCDC, Cambridge, U. K., 2003–2004.
[12] a) V. S. Bryantsev, B. P. Hay, Org. Lett. 2005, 7, 5031–5034; b)
O. B. Berryman, V. S. Bryantsev, D. P. Stay, D. W. Johnson,
B. P. Hay, J. Am. Chem. Soc. 2007, 129, 48–58; c) B. P. Hay,
V. S. Bryantsev, Chem. Commun. 2008, 2417–2428.
[21] M. J. Hynes, J. Chem. Soc., Dalton Trans. 1993, 311–312.
Received: July 30, 2010
Published Online: December 10, 2010
438
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 429–438