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>_d) > 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 (C₆₀) has been studied for the first time. Fluorescence quenching of our polymers by C₆₀ has been used to study the extent of (polymer·C₆₀) host–guest complex formation. Fluorescence quenching studies indicate binding constant for polymer·C₆₀ complexation on the order of 10⁵ M^–1

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>_d) > 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 (C₆₀) has been studied for the first time. Fluorescence quenching of our polymers by C₆₀ has been used to study the extent of (polymer·C₆₀) host–guest complex formation. Fluorescence quenching studies indicate binding constant for polymer·C₆₀ complexation on the order of 10⁵ M^–1

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 NH₄X (X = F^–, Cl^–, Br^–, NO₃^–) and (NH₄)₂X (X = CO₃^2– and SO₄^2–) exhibit a mode of aggregation in which the cation (NH₄⁺) 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, H₃N···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 NH₄Cl, NH₄Br, NH₄HCO₃, and NH₄NO₃, 3:3 complexes for NH₄F, and 4:2 complex for (NH₄)₂SO₄. 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 NH₄Cl 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 NH₄⁺ 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>_3<i>v</i> 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 [H₃<b>L</b>]³⁺ with spherical (Cl^–, Br^–, I^–) and tetrahedral (ClO₄^–, SO₄^2–) anions are carried out by isothermal titration calorimeter in dimethylsulfoxide. The association of halides with [H₃<b>L</b>]³⁺ 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: HSO₄^– > Br^–> Cl^– ≈ ClO₄^–. Single crystal X-ray structures of ClO₄^– and Br^– complexes of protonated <b>L</b> show encapsulation of ClO₄^– in the amide cleft of [H₂<b>L</b>]²⁺ (complex <b>1</b>) and encapsulation of Br^– in the ammonium cleft of [H₃<b>L</b>]³⁺ (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>^<b>1</b>–<b>L</b>^<b>6</b> have been studied thoroughly by single crystal X-ray diffraction studies. Crystallographic results elucidate the fact that protonated tripodal receptor <b>L</b>^<b>1</b> formed staggered homodimeric capsular assemblies <b>2</b> and <b>3</b> with CF₃COO^– and ClO₄^– ions, respectively. Protonation of <b>L</b>^<b>3</b> 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>^<b>6</b> with HNO₃, HI, and HClO₄, respectively. Interestingly, when a 1:1 mixture of <b>L</b>^<b>1</b> (tripodal) and <b>L</b>^<b>5</b> (dipodal) were treated with HClO₄ and HBF₄, 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 platinum­(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 π-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>_3<i>v</i> 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 [H₃<b>L</b>]³⁺ with spherical (Cl^–, Br^–, I^–) and tetrahedral (ClO₄^–, SO₄^2–) anions are carried out by isothermal titration calorimeter in dimethylsulfoxide. The association of halides with [H₃<b>L</b>]³⁺ 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: HSO₄^– > Br^–> Cl^– ≈ ClO₄^–. Single crystal X-ray structures of ClO₄^– and Br^– complexes of protonated <b>L</b> show encapsulation of ClO₄^– in the amide cleft of [H₂<b>L</b>]²⁺ (complex <b>1</b>) and encapsulation of Br^– in the ammonium cleft of [H₃<b>L</b>]³⁺ (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>^<b>1</b>–<b>L</b>^<b>6</b> have been studied thoroughly by single crystal X-ray diffraction studies. Crystallographic results elucidate the fact that protonated tripodal receptor <b>L</b>^<b>1</b> formed staggered homodimeric capsular assemblies <b>2</b> and <b>3</b> with CF₃COO^– and ClO₄^– ions, respectively. Protonation of <b>L</b>^<b>3</b> 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>^<b>6</b> with HNO₃, HI, and HClO₄, respectively. Interestingly, when a 1:1 mixture of <b>L</b>^<b>1</b> (tripodal) and <b>L</b>^<b>5</b> (dipodal) were treated with HClO₄ and HBF₄, 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 platinum­(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 ¹H 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 π-rich neutral guests with <b>L</b> and anions with [H₆<b>L</b>]⁶⁺ are examined thoroughly. <b>L</b> forms inclusion complexes with π-rich solvents, 2DMSO⊂<b>L</b> (<b>1</b>), 3DMF⊂<b>L</b>₂ (<b>2</b>), (DMF·benzene·DMF)⊂<b>L</b>₂ (<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, CHCl₃, and CH₂Cl₂ are unsuccessful. Single crystal X-ray diffraction study has also shown the encapsulation of nitrate in the cleft of [H₆<b>L</b>]⁶⁺ via N–H···O hydrogen bonding interactions in [H₆<b>L</b>]­[NO₃]₆·HNO₃·6H₂O (<b>6</b>), whereas in [H₆<b>L</b>]₂[ClO₄]₁₂·CH₃OH·17H₂O (<b>7</b>) perchlorates are recognized in the cavity and side pockets of [H₆<b>L</b>]⁶⁺. This receptor has previously shown encapsulation of iodide (<b>8</b>), and Cl^–···H₂O (<b>9</b>). A potentiometric study of <b>L</b> exhibits the maximum concentration of [H₆<b>L</b>]⁶⁺ species at pH 2–3 in MeOH/H₂O 1:1 (v/v) binary solvent. Anion binding studies with <b>L</b> at pH 2.0 in MeOH/H₂O 1:1 (v/v) solvent system are examined by isothermal titration calorimetric (ITC) experiments