Solid-state examination of conformationally diverse sulfonamide receptors based on Bis(2-anilinoethynyl)pyridine, -bipyridine, and -thiophene

Article abstract of DOI:10.1021/cg5018856

Utilizing an induced-fit model and taking advantage of rotatable acetylenic C(sp)-C(sp²) bonds, we disclose the synthesis and solid-state structures of a series of conformationally diverse bis-sulfonamide arylethynyl receptors using either pyri

Full text of DOI:10.1021/cg5018856

Article
pubs.acs.org/crystal
Solid-State Examination of Conformationally Diverse Sulfonamide
Receptors Based on Bis(2-anilinoethynyl)pyridine, -Bipyridine, and
-Thiophene
Orion B. Berryman,†,§ Charles A. Johnson, II,† Chris L. Vonnegut,† Kevin A. Fajardo,† Lev N. Zakharov,‡
Darren W. Johnson,*,† and Michael M. Haley*,†
†Department of Chemistry & Biochemistry and the Materials Science Institute, University of Oregon, Eugene, Oregon 97403-1253,
United States
‡CAMCOR, University of Oregon, 1443 East 13th Avenue, Eugene, Oregon 97403, United States
S
* Supporting Information
ABSTRACT: Utilizing an induced-fit model and taking
advantage of rotatable acetylenic C(sp)−C(sp2) bonds, we
disclose the synthesis and solid-state structures of a series of
conformationally diverse bis-sulfonamide arylethynyl receptors
using either pyridine, 2,2′-bipyridine, or thiophene as the core
aryl group. Whereas the bipyridine and thiophene structures
do not appear to bind guests in the solid state, the pyridine
receptors form 2 + 2 dimers with water molecules, two halides,
or one of each, depending on the protonation state of the
pyridine nitrogen atom. Isolation of a related bis-sulfonimide derivative demonstrates the importance of the sulfonamide N−H
−
hydrogen bonds in dimer formation. The pyridine receptors form monomeric structures with larger guests such as BF4 or
−
HSO4 , where the sulfonamide arms rotate to the side opposite the pyridine N atom.
the rigidity, and hence preorganization, they lend to the
structure is particularly important. Furthermore, in the case of
acyclic receptors, the axial rotation around the linear substituted
alkynyl bonds provides receptors that are also conformationally
flexible. Although a wide array of guests have been targeted by
arylethynyl-based hosts, until our entry into this field, receptors
of this type targeting anions were lacking. Given the elegant
metal cation sensors that have been developed using cores such
as this,24−26 our modular receptor class featuring fluorescent
cores has opened up a new area of anion sensing and molecular
probe development and shown that these receptors exhibit a
variety of binding conformations depending on the identity of
the guests. Herein, we describe a complete series of
bis(sulfonamide) receptors built off of a variety of arylethynyl
cores. Each receptor shows a propensity to form strong
hydrogen bonds with various small molecule and ion guests,
and the axial flexibility imparted by the alkynes provides a rich
diversity in host−guest geometries.
INTRODUCTION
■
Induced-fit guest recognition agents and conformationally
flexible hosts provide a complement to traditional lock-and-
key approaches to molecule and ion recognition.1−3 In
traditional lock-and-key approaches, a molecule or ion binding
site on a host molecule is exquisitely tailored to be selective for
the size, shape, charge, polarity, binding preferences, etc. of the
target guest.4−8 Conformationally flexible and adaptable hosts,
on the other hand, allow a guest substrate to induce a specific
organization of the host to create a recognition site,9−12 a motif
frequently encountered in biological molecular recognition.13
In essence, the guest is able to choose the ideal binding site in
these flexible hosts either by altering the host’s conformation or
even reorganizing a dynamic host into a new structure.
The adaptation of arylethynyl scaffolds to supramolecular
chemistry has yielded a surprising array of host−guest and
coordination complexes.14−17 This rigid and linear motif
provides suitable geometric dimensions for both macrocyclic
and acyclic receptors. Furthermore, alteration of the aryl moiety
(e.g., inclusion of N-based heterocycles such as pyridine) has
enabled applications in coordination chemistry, such as
selective transition metal and small molecule complexation as
well as fluorescence sensing.18−21 Addition of simple synthetic
handles to the arenes in these systems has allowed for
substitution of chiral functional groups, yielding macrocycles
capable of saccharide complexation as well as asymmetric
catalysis and chiral recognition.22,23 Of all of the benefits of
using an arylethynyl foundation on which to build a receptor,
In our initial report, we disclosed that sulfonamides 1 and 2
(Figure 1) exhibit an unusual 2 + 2 dimeric self-assembly motif
consisting of two receptors stitched together by either two
water molecules, two halides, or one of each, depending on the
protonation state of the pyridine nitrogen in the receptor.27
The isostructural 2 + 2 dimers exist not only in the crystalline
Received: December 29, 2014
Revised: January 20, 2015
© XXXX American Chemical Society
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Figure 1. Previously reported bis(2-anilinoethynyl)pyridine sulfonamides/ureas 1−8 and related new structures 9−12.
state but also in solution (vide infra), thus complicating
accurate determination of anion binding. We switched to urea
derivatives such as 3−5, as these molecules exhibited simpler
1:1 speciation with anions in solution because of the four
hydrogen bonds that the two urea binding groups afford.28−32
The crystal structure of 3·HCl corroborates 1:1 complex
formation as well in the solid state.28 Interestingly, the urea
derivatives display switchable fluorescent and colorimetric
responses upon protonation: 4 showed an on−off fluorescence
behavior in the presence of chloride in organic solvents,
whereas 5 displayed the reverse off−on fluorescence behavior.29
The magnitude of the fluorescence response was dictated by
the anion, resulting in a rare, fully organic turn-on fluorescent
sensor for chloride, which typically quenches fluorescence.
Sulfonamides 2 and 6 also exhibit an analogous, if slightly
muted, switching response.29 Subsequent studies of a small
library of urea derivatives showed that a similar turn-on
behavior is observable even in relatively polar solvents such as
MeCN.31
Through these studies, it became apparent that the bis(2-
anilinoethynyl)pyridine ureas possess a rich and varied array of
receptor conformations with and without guests. Three
different conformations are observed about the cores of 3−5,
7, and 8: S, U, and W, depending upon the guests or solvents of
crystallization.28,30 The receptors each have rotatable C(sp)−
C(sp2) bond(s) that can potentially adopt a variety of
topological structures, and the interaction of the urea groups
with themselves and with potential guests dictate the
conformations that are observed in the crystal structures. In
fact, some ligands exhibit all three conformations (S, U, and
W), depending on the choice of single, binary, or ternary
solvent systems for crystallization.30,33−37
Because of this rich conformational diversity, we decided to
revisit the sulfonamide class of receptors and thus re-evaluate
their potential use as hosts for neutral molecules and anions.
Herein, we report the synthesis and crystal structures of
pyridine-based sulfonamide 9 and sulfonimide 10. We highlight
the modularity of this ligand class by replacing the pyridine
moiety with other heteroaromatic rings to tailor the size of the
binding cavity, generating expanded core structures based on
either thiophene (11) or 2,2-bipyridine (12). Finally, we
examine the solid-state structures of the sulfonamides with
neutral and anionic guests.
RESULTS AND DISCUSSION
■
Receptor Synthesis. Treatment of previously utilized bis-
aniline 1327−33 in pyridine with an excess of 4-bromophe-
nylsulfonyl chloride gave receptor 9 in excellent yield (Scheme
1). The syntheses of bis-sulfonamides 1,27 2,27 and 629
(performed analogously) have been described previously. As
Scheme 1. Synthesis of Sulfonamide Receptor 9 and
Unanticipated Sulfonimide 10
B
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Scheme 2. Synthesis of Alternative Core Bis-Sulfonamide Analogues 11 and 12
a whole, this afforded a series of molecules where the electronic
nature of the terminal phenyl rings could be tuned from
donating (6, R = OMe) to withdrawing (4, R = NO2).
We next considered a 3,5-bis(trifluoromethyl)-
phenylsulfonamide receptor to examine solid-state and solution
effects of a different substitution pattern and increased electron
deficiency of the peripheral phenyl rings. Surprisingly, product
isolation afforded tetra-substituted bis-sulfonimide 10 (Scheme
1) along with a small amount (<10%) of a trisubstituted mixed
sulfonamide/-imide (not shown), the result of enhanced
reactivity of the electron-deficient bis(trifluoromethyl)-
phenylsulfonyl unit. Subsequent efforts to control substitution
via stoichiometric treatment with the sulfonyl chloride afforded
only a mixture of mono-, di-, and trisubstituted adducts, out of
which the desired product was impossible to separate from
monosubstituted byproduct.
We also sought to examine the effect of changing the size and
shape of the receptor cleft by replacing the central pyridine unit
with other heteroarenes. Simple modeling of both pyrrole and
bipyridine cores indicated the potential to target larger guest
molecules, a direct result of the change in the bite angle of the
functionalized phenylacetylene arms. Dihalo analogues of both
heterocycles are known; however, 2,5-dibromopyrrole has been
reported to decompose rapidly upon concentration.38 Because
of the well-established chemistry of 2,5-difunctionalized
thiophenes,39 a thiophene moiety was utilized as a simple
substitute to model the pyrrole core and determine if further
examination of pyrrole analogues was warranted, specifically via
examination of the solid-state structure.
residual water signal in CDCl3. Normally this resonance
appears as a sharp singlet at ca. 1.55 ppm; however, the peak
broadened significantly and would appear as far downfield as ca.
4 ppm, depending on concentration. This observation strongly
implicated the hydrogen-bonding capacity of the pyridine-
sulfonamide receptors in solution, a result that was also
corroborated in their solid-state structures. Fortunately, the
sulfonamide class of receptors crystallized easily, and we were
able to obtain eight new structures for this study; all of the key
crystal details and structure parameters are compiled in Table 1.
Interestingly, the neutral pyridine-core sulfonamides all
exhibit the same propensity to crystallize as hydrogen-bonded
2 + 2 dimers with water in the solid state. The structures are
very similar throughout the series of receptors, differing only in
minor adjustments to the hydrogen-bonding and π-stacking
distances regardless of the electronic nature of the para
substituent on the terminal phenyl rings. In fact, the structures
are so alike that unit cell dimensions could not be used to
screen each sample reliably. Figure 2 illustrates the similarity
among receptors 1, 2, 6, and 9 in the solid state, with four
different representations of the single-crystal X-ray structures.
Close-in examination shows how the dimers are held
together (Figure 3); hydrogen-bond lengths and bond angles
for all four structures are compiled in Table 2. The respective
pyridine nitrogen atoms accept hydrogen bonds from different
water molecules (2.789(2)−2.804(2) Å, O−H···N angles
172(3)−175(3)°), with one water−water hydrogen bond
present in the binding pocket of the U conformation
(2.866(4)−3.006(7) Å, O−H···O angles 147(5)−178(6)°).
All of the N-substituted sulfonamides adopt the energetically
most favored staggered conformation.42 Each sulfonamide
proton donates a hydrogen bond from the receptors to a
different water molecule (2.852(3)−2.879(2) Å, 157(2)−
164(3)° and 2.963(3)−3.039(3) Å, 158(2)−164(3)°) such
that the 2 + 2 dimer structure is held together by four
sulfonamide−water hydrogen bonds, two pyridine−water
hydrogen bonds, one water−water hydrogen bond, and two
π-stacking interactions between the receptors ranging from
3.2774(5) to 3.617(2) Å.
Synthesis of thiophene analogue 11 began with desilylation
of 1440,41 followed by 2-fold Sonogashira cross-coupling with
commercially available 2,5-dibromothiophene to furnish bis-
aniline 15 (Scheme 2). Known bis-aniline 16 was similarly
prepared from 6,6′-dibromo-2,2′-bipyridine.34 Independent
treatment of 15 and 16 with p-toluenesulfonyl chloride in
pyridine provided expanded receptors 11 and 12 in moderate
to very good yield.
1
Neutral Pyridine-Core Crystal Structures. While the H
NMR signals of pyridine-based receptors 1, 2, 6, and 9
exhibited considerable concentration dependence in organic
solvents, we were especially intrigued by the behavior of the
In one isolated instance, a polymorph of receptor 2 was
obtained while attempting to generate co-crystals of 2 and
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Table 2. Selected Hydrogen-Bond Distances (Å) and Bond
Angles (deg) within the 2 + 2 Water Dimer Structures of
Sulfonamides 1, 2, 6, and 9
1 (R = Me) 2 (R = NO2) 6 (R = OMe) 9 (R = Br)
O−H···N
O−H···N
O−H···O
O−H···O
N−H···O
N−H···O
N−H···O
N−H···O
2.804(2)
175(3)
2.797(4)
172(4)
2.789(2)
172(3)
2.792(2)
174(3)
2.917(5)
164(4)
3.006(7)
178(6)
2.866(4)
151(5)
2.897(4)
147(5)
2.860(3)
157(2)
2.855(4)
164(3)
2.879(2)
157(2)
2.852(3)
157(3)
3.039(3)
158(2)
3.028(4)
164(3)
2.963(3)
161(3)
3.036(3)
158(3)
Figure 2. Four different representations of the 2 + 2 water dimer
formed when sulfonamides 1, 2, 6, and 9 are crystallized in their
neutral form.
Figure 4. Polymorph of 2 dimer notably lacking assisting water
molecules, with each molecule colored differently. ORTEPs are drawn
at 50% probability, and non hydrogen-bonding hydrogens and CHCl3
solvent molecule are removed for clarity.
nitrogen and sulfonamide hydrogens from the adjacent receptor
(2.902(4)−2.919(4) Å, N−H···N angles 166(4)−167(5)°) as
well as intermolecular π-stacking (3.479(15) Å). The CHCl3
solvent molecule occupies a void between the aromatic rings of
three different molecules of 2 and the sulfonamide functionality
of another molecule of 2. This structure remains the only
example of dimer formation in these receptors without assisting
water molecules. In every other crystal structure studied to date,
the sulfonamide receptors crystallize as 2 + 2 dimers with H2O
in solvents dried over 3 Å molecular sieves and even in the
presence of other potential guest molecules (e.g., MeOH,
EtOH, i-PrOH, MeCN, DMSO, THF, acetone, tetra-n-
butylammonium halides), guests that do co-crystallize with
the corresponding urea class of receptors.28,30
The fortuitous isolation of bis-sulfonimide 10, which does
not contain sulfonamide hydrogens, provides crucial solution
evidence for the importance of water−sulfonamide hydrogen
bonds in the self-assembly of 1, 2, 6, and 9. Whereas the
residual water resonance in the 1H NMR spectra for the
sulfonamide receptors shifts markedly downfield to δ 3−4 ppm
(depending upon receptor concentration), no such shift is
observed in the proton spectrum of sulfonimide 10, as the
residual water resonance in CDCl3 is unchanged (δ 1.55 ppm).
These contrasting results clearly support the presence of a
solution-based hydrogen-bonding phenomena in the corre-
sponding sulfonamides.
Figure 3. Close-up view of hydrogen-bonding interactions within the
sulfonamide−water dimers.
Bu4NI under CHCl3/pentane diffusion conditions. In this
structure, 2 crystallizes in the Pcba space group with eight
molecules per unit cell. The receptor forms a dimer, with each
molecule exhibiting the same helical arrangement. A single
sulfonamide functionality from each receptor is interlocked
with the neighboring molecule (Figure 4), whereas the second
sulfonamide functionality hydrogen bonds to a separate dimeric
pair in the solid state (2.904(4)−2.989(4) Å, N−H···O angles
155(4)−159(5)°). The key driving forces for the solid-state
structure are the hydrogen bonds between the pyridine
The importance of the sulfonamide hydrogen was also
corroborated by the solid-state structure of 10 (Figure 5),
E
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through the crystal structure, forming hydrogen-bonding
sheets.
Single crystals of 12 were grown by slowly diffusing hexane
into EtOAc solutions of receptor. Compound 12 crystallizes in
the P1 space group with one molecule contained in the unit
̅
cell. In the solid state, the bipyridine core of 12 is planar with
anti N atoms, a factor that results in rotation of a single
sulfonamide arm away from the proposed binding cavity
(Figure 7, top).34 Intermolecular π-stacking interactions are
observed between the electron-deficient pyridine ring of one
receptor and the electron-rich p-toluene ring of another
(3.658(5) Å). Like thiophene 11, each sulfonamide function-
ality of 12 hydrogen bonds in a head-to-tail fashion with
different adjacent molecules (2.939(4) Å, N−H···O angle
170(3)°), forming an infinite hydrogen-bonding chain in the
solid state (Figure 7, bottom). Also present are nontraditional
intermolecular C−H hydrogen bonds34,35,50−52 between a p-
toluene ring and an adjacent sulfonamide oxygen (3.187(4) Å,
C−H···O angle 134.35(19)°). This weak hydrogen bond is
likely enforced from the packing arrangement of this molecule.
Protonated Pyridine-Core Crystal Structures. As we
demonstrated in the initial sulfonamide communication27 and
subsequently with amide33 and urea derivatives,28,29,32 proto-
nation of the pyridine nitrogen activates the anion binding
capacity of these receptors. In the specific case of the
sulfonamides, the resultant complexes with anions all resemble
the 2 + 2 water dimer structures. For example, (H2+·Cl−)2
(Figure 8, right) is held together by four sulfonamide hydrogen
bonds (3.156(2)−3.229(2) Å, N−H···Cl angles 151(2)−
171(3)°), two pyridinium N−H hydrogen bonds to the
chlorides (3.022(2) Å, 175(3)°), two Caryl−H···Cl hydrogen
bonds (3.688(3) Å), and two π-stacking interactions between
receptors (3.495(3) Å). The numerous hydrogen bonds and
unique dimerization bring the negatively charged chlorides into
close proximity with halide−halide distance of 3.9204(13) Å.
The surprise isolation of heterodimer (1·H2O)·(H1+·Cl−),
which crystallized in the presence of concentrated aqueous HCl
(Figure 8, center), shows that water and hydrogen chloride are
freely exchangeable in this binding pocket and provide
intermediate structural features to the H2O and hydrogen
Figure 5. ORTEP (30%) representation of bis-sulfonimide 10, which
exhibits no interactions with water molecules in the solid state.
which showed no water in the crystal lattice. Sulfonimide 10
crystallizes in the C2/c space group with 16 molecules per unit
cell. Additionally, with no hydrogen bond donor present, this
molecule does not form strong intermolecular hydrogen bonds
in the solid state. The steric bulk of the two sulfonimide
functionalities enforces a W-shaped conformation in the solid
state, with the pyridine nitrogen directed away from the
sulfonimides. Compound 10 crystallizes in a close pack
conformation that places one fluorine from a −CF3 group
directly above the electron-deficient aromatic ring of another
molecule of 10 (F···centroid 3.079(5) Å). Attractive
interactions between electron-rich species and electron-
deficient aromatic rings are an area of current interest.43−49
Expanded-Core Crystal Structures. Substitution of
thiophene and bipyridine into the ligand backbone clearly
increases the binding cavity size and will allow for exploration
of binding larger polyatomic ions and small molecules
compared to that for the pyridine-based system. Single crystals
of 11 were isolated from evaporation of hexane/EtOAc
mixtures. Receptor 11 crystallizes with two molecules per
unit cell in the P1 space group and exhibits a solid-state W
̅
conformation, with both receptor arms rotated away from the
binding cavity due to their participation in intermolecular
hydrogen bonds (2.962(12) and 2.999(15) Å, N−H···O angles
130.1(6)−133.4(6)°) with the arms of two adjacent receptors
(Figure 6). This zigzag ribbon packing arrangement propagates
Figure 6. ORTEP (50%) representation of the crystal structure of sulfonamide 11 with expanded thiophene core. Three molecules are shown to
highlight the intermolecular hydrogen-bonding in the solid state; non-hydrogen-bonding hydrogens atoms are removed for clarity.
F
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Figure 7. ORTEP (50%) representations of the single-crystal X-ray structure of sulfonamide 12 with expanded bipyridine core (top). The extended
hydrogen-bonding chain is displayed below; some hydrogen atoms have been removed for clarity.
Figure 8. Stick representations of the crystal structures of (1·H2O)2 (left), (1·H2O)·(H1+·Cl−) (middle), and (H2+·Cl−)2 (right), highlighting the
interchangeable role that halides and water play in the dimerization of the sulfonamide class of receptors. Hydrogen bonds are illustrated as dashes.
halide dimers. As before, the heterodimer is stabilized by π-
stacking interactions between the two receptors (3.454(5) Å)
and a series of seven guest-assisted hydrogen bonds. Each guest
molecule, water and chloride, accepts two sulfonamide N−H
hydrogen bonds (3.157(3)−3.181(3) Å, N−H···X angles
158(3)−167(3)°) and additionally forms a hydrogen-bonding
pattern running among the pyridinium, chloride, water, and
pyridine heteroatoms (2.926(3)−3.099(2) Å, 164(3)−
176(4)°). Two Caryl−H···Cl hydrogen bonds (3.935(4) Å)
also stabilize the dimer. This is one of the first examples of both
hydrogen halides and water molecules serving the same
structural hydrogen-bonding roles in a synthetic self-assembled
system. This work also sheds light on the complex self-assembly
capabilities of water molecules and anions acting in tandem, a
synergy only recently appreciated as being an important
structural feature in some proteins.53
While the sulfonamide receptors form 2 + 2 dimers in the
solid state with water, halides, or both water and halides, we
found that use of larger anionic guest molecules generates only
monomeric species in the solid state. For example, single
crystals of H1+·BF4 are isolated by dissolving receptor 1 in
−
EtOAc and then adding aqueous HBF4 with vigorous stirring
followed by layering with hexane. H1+·BF4 crystallizes in the
−
P1 space group with two molecules per unit cell. As shown in
̅
−
Figure 9 (top), the larger size of the BF4 anion forces the
receptor arms to the opposite side of the pyridine N and thus
into a W conformation to maintain a strong pyridinium
−
hydrogen bond with the BF4 anion (2.658(2) Å, N−H···F
angle 167(2)°). This interaction is also complemented by a
weak C−H···F hydrogen bond (3.431(3) Å, C−H···F angle
166.85(12)°) from an adjacent phenyl ring. One receptor
sulfonamide forms a head-to-tail intermolecular hydrogen bond
(2.916(2) Å, N−H···O angle 161.0(19)°) with an adjacent
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Figure 10. ORTEP representation (30%) of a portion of the H1+·
−
−
HSO4 crystal structure highlighting the pyridinium and HSO4
hydrogen bonds present in the solid state.
hydrogen bonds (2.864(5) and 2.945(6) Å, N−H···O angle
−
171(5) and 177(5)°). The HSO4 anion also donates a
hydrogen bond to an adjacent THF molecule (2.568(6) Å, O−
H···O angle 176.3(3)°).
Figure 9. (Top) Molecular structure of H1+·BF4− showing the N−H···
CONCLUSIONS
■
F hydrogen bond; (Bottom) ORTEP representation of the polymeric
In summary, we have presented a series of heteroarylacetylene
ligands designed for small molecule and ion recognition. The
receptors are prepared in a modular fashion capable of simple
exchange of binding substituents and core motifs. The facile
synthesis has produced a series of sulfonamide-bearing
receptors that show a predilection for interacting with small
−
hydrogen-bonding chain present in H1+·BF4 in the solid state.
receptor molecule, whereas the other sulfonamide hydrogen
bonds to the BF4− anion of a second receptor (2.907(2) Å, N−
H···F angle 163(2)°). This sequence of hydrogen bonds forms
a polymeric hydrogen-bonding chain in the solid state (Figure
9, bottom). This structure is somewhat unusual considering
that fluorine is typically a poor hydrogen-bond acceptor and
BF4 is typically used as a noncoordinating anion.54 The short
distances, nearly linear X− H···F angles, and the change in
molecules (H2O) or anions (Cl−, Br−, BF4 , and HSO4 ) in
solution and the solid state. Facile axial rotation about the
acetylene C(sp)−C(sp2) bonds allows these molecules to
function as induced-fit receptors. A variety of conformationally
different binding motifs are observed that depend on the size
and shape of the guest present as well as the heterocyclic core.
Solid-state conformations are largely dominated by hydrogen-
bonding interactions and π-stacking. The 2,6-bis(2-
anilinoethynyl)pyridine sulfonamides form 2 + 2 dimers in
solution and the solid state with H2O, halides, or both H2O and
halides. Sulfonamide receptors based on larger heterocyclic core
molecules exhibit larger cavity sizes in the solid state and show
no propensity to form 2 + 2 dimers. The efficiency of our new
system, directly attributed to a straightforward synthesis and
facile derivatization, bodes well for future receptor development
to target remediation and sensing applications for environ-
mental contaminants and biologically relevant anions.
−
−
−
molecular conformation to accommodate the BF4 anion are
consistent with the weak hydrogen bonds suggested here,55
although the existence and frequency of occurrence of
hydrogen bonds to organic fluorine is not without some
controversy in the literature.56−59
The structure of H1+·HSO4 also deviates from the 2 + 2
−
arrangement observed for smaller guests. Single crystals of H1+·
HSO4− were grown by diffusing pentane into THF solutions of
receptor mixed with H2SO4. The H1+·HSO4− salt crystallizes in
the P1 space group with two receptor molecules and three THF
̅
solvent molecules per unit cell. Similar to the H1+·BF4
−
−
structure, the counteranion HSO4 forms a strong hydrogen
bond with the pyridinium nitrogen (2.668(5) Å, N−H···O
angle 173(6)°), resulting once again in a W conformation that
puts the receptor arms on the opposite side of the molecule
EXPERIMENTAL SECTION
Receptor Synthesis. See Supporting Information.
■
General Crystallographic Data. Diffraction intensities for all
structures were collected at low temperature (153 K for 2 and 173 K
for others) on a Bruker Apex CCD diffractometer using Mo Kα
radiation (λ = 0.71073 Å). Space group was determined based on
systematic absences (2 and 10) and intensity statistics. Absorption
corrections were applied by SADABS.60 Structures were solved by
direct methods and Fourier techniques and refined on F2 using full
matrix least-squares procedures. All non-H atoms were refined with
anisotropic thermal parameters. All H atoms in (6·H2O)2 and (9·
H2O)2 were found from the residual density map and refined with
isotropic thermal parameters. All H atoms in 10 and 11 were refined in
calculated positions in a rigid group model. In structures 2, 12, 1·
HBF4, and 1·H2SO4, H atoms involved in hydrogen bonds were found
on the residual density maps and refined with isotropic thermal
−
(Figure 10). The HSO4 anion is also stabilized by three
additional hydrogen bonds. One hydrogen bond is donated
from the sulfonamide N−H of an adjacent molecule of H1+
(2.981(6) Å, N−H···O angle 162(4)°). A second molecule of
H1+ forms a tight head-to-tail dimer with this same HSO4
−
anion (N−H···O of 2.856(6) Å, angle 168(5)° and O−H···O of
−
2.717(6) Å, angle 178.3(3)°). Additionally, the H1+·HSO4
structure is complicated by additional solvents of crystallization.
The second HSO4 anion is stabilized by four different
−
hydrogen bonds. The strongest interaction is with another
pyridinium N−H (2.637(5) Å, N−H···O angle 170(5)°). Two
adjacent molecules of H1+ also donate sulfonamide N−H
H
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Article
parameters; all other H atoms were refined in calculated positions in a
rigid group model. Highly disordered solvent hexane molecules,
C6H14, in 10 were treated by SQUEEZE.61 The correction of the X-ray
data by SQUEEZE (215 electrons) is close to the required value of
200 electrons for four solvent molecules in a symmetrically
independent part of the unit cell. The main crystallographic data
and details of data collection and refinement are given in Table 1. All
calculations have been performed by the SHELXTL-6.10 package.62
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AUTHOR INFORMATION
Corresponding Authors
*(D.W.J.) E-mail: dwj@uoregon.edu.
*(M.M.H.) E-mail: haley@uoregon.edu.
■
(21) Massena, C. J.; Riel, A. M. S.; Neuhaus, G. F.; Decato, D. A.;
Berryman, O. B. Chem. Commun. 2015, 51, 1417−1420.
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Present Address
(23) Fang, J.; Selvi, S.; Liao, J.; Slanina, Z.; Chen, C.; Chou, P. J. Am.
Chem. Soc. 2004, 126, 3559−3566.
§(O.B.B.) Department of Chemistry & Biochemistry, Uni-
versity of Montana, 32 Campus Drive, Missoula, Montana
59812, United States.
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Notes
The authors declare the following competing financial
interest(s): NIH grant R01-GM087398 funded early stage
intellectual property that was licensed by SupraSensor Enter-
prises, a company co-founded by D.W.J. and M.M.H. O.B.B.
and C.A.J. are also shareholders in this company.
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ACKNOWLEDGMENTS
■
This work was funded initially by the National Science
Foundation (CHE-0718242) and subsequently supported by
the National Institutes of Health (R01-GM087398). This
publication was made possible, in part, by the Mass
Spectrometry Facilities and Services Core of the Environmental
Health Sciences Center, Oregon State University, grant no. P30
ES00210, National Institute of Environmental Health Sciences,
National Institutes of Health.
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