19 research outputs found
Synthesis of Triptycene-Based Organosoluble, Thermally Stable, and Fluorescent Polymers: Efficient Host–Guest Complexation with Fullerene
We
report a facile synthesis of 2,6-diethynyltriptycene (DET) in
high yield. Application of DET as monomer in polymer chemistry has
been shown (for the first time) in syntheses of two novel polymers
via Sonogashira cross-coupling reaction in high yield. The newly synthesized
polymers were characterized by FT-IR, UV–vis absorption, and
NMR spectroscopic techniques. The polymers prepared using DET have
interesting properties such as high solubility in common organic solvents,
high thermal stability [decomposition temperatures (<i>T</i><sub>d</sub>) > 495 °C], and high char yield (greater than
81%
at 900 °C). Additionally, polymers are fluorescent. Host–guest
interaction between triptycene-based polymers and fullerene (C<sub>60</sub>) has been studied for the first time. Fluorescence quenching
of our polymers by C<sub>60</sub> has been used to study the extent
of (polymer·C<sub>60</sub>) host–guest complex formation.
Fluorescence quenching studies indicate binding constant for polymer·C<sub>60</sub> complexation on the order of 10<sup>5</sup> M<sup>–1</sup>
Synthesis of Triptycene-Based Organosoluble, Thermally Stable, and Fluorescent Polymers: Efficient Host–Guest Complexation with Fullerene
We
report a facile synthesis of 2,6-diethynyltriptycene (DET) in
high yield. Application of DET as monomer in polymer chemistry has
been shown (for the first time) in syntheses of two novel polymers
via Sonogashira cross-coupling reaction in high yield. The newly synthesized
polymers were characterized by FT-IR, UV–vis absorption, and
NMR spectroscopic techniques. The polymers prepared using DET have
interesting properties such as high solubility in common organic solvents,
high thermal stability [decomposition temperatures (<i>T</i><sub>d</sub>) > 495 °C], and high char yield (greater than
81%
at 900 °C). Additionally, polymers are fluorescent. Host–guest
interaction between triptycene-based polymers and fullerene (C<sub>60</sub>) has been studied for the first time. Fluorescence quenching
of our polymers by C<sub>60</sub> has been used to study the extent
of (polymer·C<sub>60</sub>) host–guest complex formation.
Fluorescence quenching studies indicate binding constant for polymer·C<sub>60</sub> complexation on the order of 10<sup>5</sup> M<sup>–1</sup>
Cooperativity in a New Role: Stabilization of the Ammonium Salts in the Solid State over Their H‑Bonded Complexes in the Gas Phase
Crystal structure of ammonium halides,
carbonates, and sulfates
like NH<sub>4</sub>X (X = F<sup>–</sup>, Cl<sup>–</sup>, Br<sup>–</sup>, NO<sub>3</sub><sup>–</sup>) and (NH<sub>4</sub>)<sub>2</sub>X (X = CO<sub>3</sub><sup>2–</sup> and
SO<sub>4</sub><sup>2–</sup>) exhibit a mode of aggregation
in which the cation (NH<sub>4</sub><sup>+</sup>) and counterion are
well separated, typical of ionic salts. However, in the stoichiometric
limit of the gas phase, they exist only as H-bonded molecular complexes
of the type, H<sub>3</sub>N···HX. Following a bottom
up approach, calculations were performed on these molecular complexes
by increasing the number of molecules to investigate the limit in
which these molecular complexes transformed to their respective salts.
Molecular complex → salt transition is shown to occur for the
2:2 complexes in NH<sub>4</sub>Cl, NH<sub>4</sub>Br, NH<sub>4</sub>HCO<sub>3</sub>, and NH<sub>4</sub>NO<sub>3</sub>, 3:3 complexes
for NH<sub>4</sub>F, and 4:2 complex for (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>. The relative stability of the salt form in comparison
to the H-bonded molecular complex is shown to exhibit interesting
cooperative enhancement as the number of molecules increases. Dispersion
corrected solid state density functional theory calculations for the
crystalline salts reveal that the structures of the higher order aggregates
of these complexes resemble the bulk salt-like structures. The computed
terahertz (THz) spectra for both the H-bonded complexes and the solid
state ionic structures are well resolved to distinguish between the
two forms. Calculations for three solid phases of NH<sub>4</sub>Cl
are in agreement with experimental temperature-dependent relative
order of their stability, and the low frequency THz spectra decipher
the orientational disorder of the phases due to tumbling/rotational
motion of the NH<sub>4</sub><sup>+</sup> ion within the crystals
Synthesis of a Preorganized Hybrid Macrobicycle with Distinct Amide and Amine Clefts: Tetrahedral versus Spherical Anions Binding Studies
A new <i>C</i><sub>3<i>v</i></sub> symmetric amido-amine hybrid
macrobicycle, <b>L</b> is synthesized toward anion recognition
in its protonated states. <b>L</b> contains tri-amide and tetra-amine
clefts separated by <i>p</i>-phenylene spacers. The solid-state
structure of methanol-encapsulated <b>L</b> exhibits an overall
cavity length of ∼12.0 Å where the amide and amine -NH
protons are converged toward the center of the respective cavities.
Conformational analysis of <b>L</b> in solution is established
by NOESY NMR. Anion binding of [H<sub>3</sub><b>L</b>]<sup>3+</sup> with spherical (Cl<sup>–</sup>, Br<sup>–</sup>, I<sup>–</sup>) and tetrahedral (ClO<sub>4</sub><sup>–</sup>, SO<sub>4</sub><sup>2–</sup>) anions are carried out by isothermal
titration calorimeter in dimethylsulfoxide. The association of halides
with [H<sub>3</sub><b>L</b>]<sup>3+</sup> is endothermic and
entropy driven. However, association of tetrahedral anions is exothermic
in nature and both entropy- and enthalpy-driven. The overall association
constants show the following order: HSO<sub>4</sub><sup>–</sup> > Br<sup>–</sup>> Cl<sup>–</sup> ≈ ClO<sub>4</sub><sup>–</sup>. Single crystal X-ray structures of ClO<sub>4</sub><sup>–</sup> and Br<sup>–</sup> complexes of
protonated <b>L</b> show encapsulation of ClO<sub>4</sub><sup>–</sup> in the amide cleft of [H<sub>2</sub><b>L</b>]<sup>2+</sup> (complex <b>1</b>) and encapsulation of Br<sup>–</sup> in the ammonium cleft of [H<sub>3</sub><b>L</b>]<sup>3+</sup> (complex <b>2</b>). Further, preorganization
of <b>L</b> toward encapsulation of spherical and tetrahedral
anions is established by comparing its amide, amine, and overall cavity
dimensions with <b>1</b> and <b>2</b>
Anion-Assisted Formation of Discrete Homodimeric and Heterotetrameric Assemblies by Benzene Based Protonated Heteroaryl Receptors
Anion-assisted formation of discrete homodimeric and
heterotetrameric
assemblies by benzene based protonated heteroaryl receptors <b>L</b><sup><b>1</b></sup>–<b>L</b><sup><b>6</b></sup> have been studied thoroughly by single crystal X-ray
diffraction studies. Crystallographic results elucidate the fact that
protonated tripodal receptor <b>L</b><sup><b>1</b></sup> formed staggered homodimeric capsular assemblies <b>2</b> and <b>3</b> with CF<sub>3</sub>COO<sup>–</sup> and ClO<sub>4</sub><sup>–</sup> ions, respectively. Protonation of <b>L</b><sup><b>3</b></sup> with trimesic acid also showed the formation
homodimeric assembly, <b>6</b>. In all these cases the anions
are hydrogen bonded to the receptor molecules and show remarkable
influence on the outcome of the self-assembly process to form discrete
capsules. The necessity of the alkyl substitution on the benzene platform
has been established from complexes <b>8</b>, <b>9</b>, and <b>10</b>, which were obtained upon protonation of <b>L</b><sup><b>6</b></sup> with HNO<sub>3</sub>, HI, and HClO<sub>4</sub>, respectively. Interestingly, when a 1:1 mixture of <b>L</b><sup><b>1</b></sup> (tripodal) and <b>L</b><sup><b>5</b></sup> (dipodal) were treated with HClO<sub>4</sub> and HBF<sub>4</sub>, discrete heterotetrameric assemblies have been
isolated as complexes <b>11</b> and <b>12</b>. The detailed
solid state structural analysis of these complexes revealed the formation
of heterotetrameric assemblies assisted by anion–water clusters.
Correlation of these solid state structural assemblies with our previously
reported complexes <b>1</b>, <b>4</b>, <b>5</b>,
and <b>7</b> has also been described. The role of anionic templates
in assisting the formation of discrete capsular assemblies from receptors
possessing heteroaryl units and 1,3,5-methyl substituted benzene platform
has been established
Pyrazine Motif Containing Hexagonal Macrocycles: Synthesis, Characterization, and Host–Guest Chemistry with Nitro Aromatics
The synthesis and characterization
of cationic two-dimensional
metallamacrocycles having a hexagonal shape and cavity are described.
Both macrocycles utilize a pyrazine motif containing an organometallic
acceptor tecton with platinumÂ(II) centers along with different donor
ligands. While one macrocycle is a relatively larger [6 + 6], the
other is a relatively smaller [2 + 2] polygon. A unique feature of
the smaller ensemble is that it is an irregular polygon in which all
six edges are not of equal length. Molecular modeling of these macrocycles
confirmed the presence of hexagonal cavities. The ability of these
Ï€-electron rich macrocycles to act as potential hosts for relatively
electron deficient nitroaromatics (DNT = 2,4-dinitrotoluene and PA
= picric acid) has been studied using isothermal titration calorimetry
(ITC) as a tool. Molecular dynamics simulation studies were subsequently
performed to gain critical insight into the binding interactions between
the nitroaromatic guest molecules (PA/DNT) and the ionic macrocycles
reported herein
Synthesis of a Preorganized Hybrid Macrobicycle with Distinct Amide and Amine Clefts: Tetrahedral versus Spherical Anions Binding Studies
A new <i>C</i><sub>3<i>v</i></sub> symmetric amido-amine hybrid
macrobicycle, <b>L</b> is synthesized toward anion recognition
in its protonated states. <b>L</b> contains tri-amide and tetra-amine
clefts separated by <i>p</i>-phenylene spacers. The solid-state
structure of methanol-encapsulated <b>L</b> exhibits an overall
cavity length of ∼12.0 Å where the amide and amine -NH
protons are converged toward the center of the respective cavities.
Conformational analysis of <b>L</b> in solution is established
by NOESY NMR. Anion binding of [H<sub>3</sub><b>L</b>]<sup>3+</sup> with spherical (Cl<sup>–</sup>, Br<sup>–</sup>, I<sup>–</sup>) and tetrahedral (ClO<sub>4</sub><sup>–</sup>, SO<sub>4</sub><sup>2–</sup>) anions are carried out by isothermal
titration calorimeter in dimethylsulfoxide. The association of halides
with [H<sub>3</sub><b>L</b>]<sup>3+</sup> is endothermic and
entropy driven. However, association of tetrahedral anions is exothermic
in nature and both entropy- and enthalpy-driven. The overall association
constants show the following order: HSO<sub>4</sub><sup>–</sup> > Br<sup>–</sup>> Cl<sup>–</sup> ≈ ClO<sub>4</sub><sup>–</sup>. Single crystal X-ray structures of ClO<sub>4</sub><sup>–</sup> and Br<sup>–</sup> complexes of
protonated <b>L</b> show encapsulation of ClO<sub>4</sub><sup>–</sup> in the amide cleft of [H<sub>2</sub><b>L</b>]<sup>2+</sup> (complex <b>1</b>) and encapsulation of Br<sup>–</sup> in the ammonium cleft of [H<sub>3</sub><b>L</b>]<sup>3+</sup> (complex <b>2</b>). Further, preorganization
of <b>L</b> toward encapsulation of spherical and tetrahedral
anions is established by comparing its amide, amine, and overall cavity
dimensions with <b>1</b> and <b>2</b>
Anion-Assisted Formation of Discrete Homodimeric and Heterotetrameric Assemblies by Benzene Based Protonated Heteroaryl Receptors
Anion-assisted formation of discrete homodimeric and
heterotetrameric
assemblies by benzene based protonated heteroaryl receptors <b>L</b><sup><b>1</b></sup>–<b>L</b><sup><b>6</b></sup> have been studied thoroughly by single crystal X-ray
diffraction studies. Crystallographic results elucidate the fact that
protonated tripodal receptor <b>L</b><sup><b>1</b></sup> formed staggered homodimeric capsular assemblies <b>2</b> and <b>3</b> with CF<sub>3</sub>COO<sup>–</sup> and ClO<sub>4</sub><sup>–</sup> ions, respectively. Protonation of <b>L</b><sup><b>3</b></sup> with trimesic acid also showed the formation
homodimeric assembly, <b>6</b>. In all these cases the anions
are hydrogen bonded to the receptor molecules and show remarkable
influence on the outcome of the self-assembly process to form discrete
capsules. The necessity of the alkyl substitution on the benzene platform
has been established from complexes <b>8</b>, <b>9</b>, and <b>10</b>, which were obtained upon protonation of <b>L</b><sup><b>6</b></sup> with HNO<sub>3</sub>, HI, and HClO<sub>4</sub>, respectively. Interestingly, when a 1:1 mixture of <b>L</b><sup><b>1</b></sup> (tripodal) and <b>L</b><sup><b>5</b></sup> (dipodal) were treated with HClO<sub>4</sub> and HBF<sub>4</sub>, discrete heterotetrameric assemblies have been
isolated as complexes <b>11</b> and <b>12</b>. The detailed
solid state structural analysis of these complexes revealed the formation
of heterotetrameric assemblies assisted by anion–water clusters.
Correlation of these solid state structural assemblies with our previously
reported complexes <b>1</b>, <b>4</b>, <b>5</b>,
and <b>7</b> has also been described. The role of anionic templates
in assisting the formation of discrete capsular assemblies from receptors
possessing heteroaryl units and 1,3,5-methyl substituted benzene platform
has been established
Pyrazine-Based Organometallic Complex: Synthesis, Characterization, and Supramolecular Chemistry
The
design, synthesis, and characterization of a new pyrazine-based ditopic
platinumÂ(II) organometallic complex are reported. The molecular structure
of the organoplatinum pyrazine dipod was determined by single-crystal
X-ray crystallography. The potential utility of this organometallic
ditopic acceptor as a building block in the construction of neutral
metallasupramolecular macrocycles containing the pyrazine motif was
explored. Pyrazine motifs containing supramolecules were characterized
by multinuclear NMR (including <sup>1</sup>H DOSY), mass spectrometry,
and elemental analysis. The geometry of each supramolecular framework
was optimized by employing the PM6 semiempirical molecular orbital
method to predict its shape and size. The ability of the pyrazine-based
organoplatinum complex to act as a host for nitroaromatic guest (2,4-dinitrotoluene
and PA) molecules was explored by isothermal titration calorimetry
(ITC). The binding stoichiometry and thermodynamic parameters of these
host–guest complexation reactions were evaluated using ITC.
Theoretical calculations were performed to obtain insight into the
binding pattern between the organometallic host and nitroaromatic
guests. The preferable binding propensity of the binding sites of
complex <b>1</b> for both nitroaromatics (PA and 2,4-dinitrotoluene)
determined by molecular simulation studies corroborates well with
the experimental results as obtained by ITC experiments
Binding Studies on an Arene-Capped Bicyclic Cyclophane with π‑Rich Neutral Guests and Anions
Structural aspects of binding of
Ï€-rich neutral guests with <b>L</b> and anions with [H<sub>6</sub><b>L</b>]<sup>6+</sup> are examined thoroughly. <b>L</b> forms inclusion complexes
with π-rich solvents, 2DMSO⊂<b>L</b> (<b>1</b>), 3DMF⊂<b>L</b><sub>2</sub> (<b>2</b>), (DMF·benzene·DMF)⊂<b>L</b><sub>2</sub> (<b>3</b>), MeCN⊂<b>L</b> (<b>4</b>), and MeCOMe⊂<b>L</b> (<b>5</b>) in dimethylsulfoxide (DMSO), dimethyl formamide (DMF), benzene/DMF,
acetonitrile (MeCN), and acetone (MeCOMe) respectively. The single
crystal X-ray structural analysis of complexes illustrates cavity
and cleft binding of these guests via N–H···O
interactions in <b>1</b>, <b>2</b>, <b>3</b>, <b>5</b> and N–H···N interactions in <b>4</b> with the secondary nitrogen center of <b>L</b> and
the hydrogen bonding acceptor atoms of the solvent guests. Inclusion
of benzene in the side pocket is also observed in <b>3</b>.
Our efforts to isolate single crystals with solvents such as MeOH,
EtOH, CHCl<sub>3</sub>, and CH<sub>2</sub>Cl<sub>2</sub> are unsuccessful.
Single crystal X-ray diffraction study has also shown the encapsulation
of nitrate in the cleft of [H<sub>6</sub><b>L</b>]<sup>6+</sup> via N–H···O hydrogen bonding interactions
in [H<sub>6</sub><b>L</b>]Â[NO<sub>3</sub>]<sub>6</sub>·HNO<sub>3</sub>·6H<sub>2</sub>O (<b>6</b>), whereas in [H<sub>6</sub><b>L</b>]<sub>2</sub>[ClO<sub>4</sub>]<sub>12</sub>·CH<sub>3</sub>OH·17H<sub>2</sub>O (<b>7</b>) perchlorates are
recognized in the cavity and side pockets of [H<sub>6</sub><b>L</b>]<sup>6+</sup>. This receptor has previously shown encapsulation
of iodide (<b>8</b>), and Cl<sup>–</sup>···H<sub>2</sub>O (<b>9</b>). A potentiometric study of <b>L</b> exhibits the maximum concentration of [H<sub>6</sub><b>L</b>]<sup>6+</sup> species at pH 2–3 in MeOH/H<sub>2</sub>O 1:1
(v/v) binary solvent. Anion binding studies with <b>L</b> at
pH 2.0 in MeOH/H<sub>2</sub>O 1:1 (v/v) solvent system are examined
by isothermal titration calorimetric (ITC) experiments