Thermoresponsive Organic Inclusion Compounds: Modification of Thermal Expansion Behavior by Simple Guest Replacement

It is demonstrated that guest replacement in a series of isoskeletal organic inclusion compounds can produce drastic changes in thermal expansion behavior. The compounds <b>1</b>, <b>2</b>, and <b>3</b> have 18-crown-6 as host molecule and nitromethane, acetonitrile, and iodomethane, respectively, as guests. Along the principal axis X1 the linear component of thermal expansion is negative for <b>1</b> and <b>2</b> but positive for <b>3</b>. All three compounds have varying degrees of large volumetric thermal expansion, with coefficients of 378(22), 226(3), and 256(8) × 10^–6 K^–1 for <b>1</b>, <b>2</b>, and <b>3</b>, respectively. Crystal structure analysis and computational methods were used to elucidate general features of the underlying mechanism of thermal expansion for the series. The contributions of several factors are described, including host–guest compatibility, electrostatic effects, and steric effects. A tilting mechanism gives rise to the negative components of thermal expansion in <b>1</b> and <b>2</b> but is inhibited by the large molecular volume of the guest in <b>3</b>. In addition, the thermosalient effect was observed for <b>2</b>. To our knowledge this is the first example of thermosalience reported for an inclusion compound

Thermoresponsive Organic Inclusion Compounds: Modification of Thermal Expansion Behavior by Simple Guest Replacement

It is demonstrated that guest replacement in a series of isoskeletal organic inclusion compounds can produce drastic changes in thermal expansion behavior. The compounds <b>1</b>, <b>2</b>, and <b>3</b> have 18-crown-6 as host molecule and nitromethane, acetonitrile, and iodomethane, respectively, as guests. Along the principal axis X1 the linear component of thermal expansion is negative for <b>1</b> and <b>2</b> but positive for <b>3</b>. All three compounds have varying degrees of large volumetric thermal expansion, with coefficients of 378(22), 226(3), and 256(8) × 10^–6 K^–1 for <b>1</b>, <b>2</b>, and <b>3</b>, respectively. Crystal structure analysis and computational methods were used to elucidate general features of the underlying mechanism of thermal expansion for the series. The contributions of several factors are described, including host–guest compatibility, electrostatic effects, and steric effects. A tilting mechanism gives rise to the negative components of thermal expansion in <b>1</b> and <b>2</b> but is inhibited by the large molecular volume of the guest in <b>3</b>. In addition, the thermosalient effect was observed for <b>2</b>. To our knowledge this is the first example of thermosalience reported for an inclusion compound

Reactivity of Bis(pyridyl)‑<i>N</i>‑alkylaminato Methylpalladium Complexes toward Ethylene: Insights from Experiment and Theory

A series of novel neutral and cationic methylpalladium complexes bearing <i>N</i>-alkyl-2,2′-dipyridylaldiminato ligands were prepared and characterized. In the presence of ethylene, the cationic complexes were active as dimerization catalysts, producing a mixture of 1- and 2-butenes. A Pd–ethyl π-ethylene species was identified as the catalyst resting state by low-temperature spectroscopic and DFT studies, which provided insights into the effect of both steric and electronic factors on the observed reactivity

Thermoresponsive Organic Inclusion Compounds: Modification of Thermal Expansion Behavior by Simple Guest Replacement

It is demonstrated that guest replacement in a series of isoskeletal organic inclusion compounds can produce drastic changes in thermal expansion behavior. The compounds <b>1</b>, <b>2</b>, and <b>3</b> have 18-crown-6 as host molecule and nitromethane, acetonitrile, and iodomethane, respectively, as guests. Along the principal axis X1 the linear component of thermal expansion is negative for <b>1</b> and <b>2</b> but positive for <b>3</b>. All three compounds have varying degrees of large volumetric thermal expansion, with coefficients of 378(22), 226(3), and 256(8) × 10^–6 K^–1 for <b>1</b>, <b>2</b>, and <b>3</b>, respectively. Crystal structure analysis and computational methods were used to elucidate general features of the underlying mechanism of thermal expansion for the series. The contributions of several factors are described, including host–guest compatibility, electrostatic effects, and steric effects. A tilting mechanism gives rise to the negative components of thermal expansion in <b>1</b> and <b>2</b> but is inhibited by the large molecular volume of the guest in <b>3</b>. In addition, the thermosalient effect was observed for <b>2</b>. To our knowledge this is the first example of thermosalience reported for an inclusion compound

Pore Wall-Functionalized Luminescent Cd(II) Framework for Selective CO₂ Adsorption, Highly Specific 2,4,6-Trinitrophenol Detection, and Colorimetric Sensing of Cu²⁺ Ions

Astute combination of basic functionality and luminescence property can pursue multifunctional metal–organic frameworks (MOFs) with assorted applications such as selective CO₂ adsorption, specific detection of explosive nitro compounds, and toxic metal ion sensing. The bifunctional ligand 4-(4-carboxyphenyl)-1,2,4-triazole (H<b>L</b>) is used to build the framework [Cd­(<b><i>L</i></b>)₂]·(DMF)_0.92 (<b>1</b>) (<b><i>L</i></b> = <b>L</b>^<b>–1</b>, DMF = <i>N</i>,<i>N</i>′-dimethylformamide), having a free N atom decorated porous channel. The solvothermal synthesis is extended to produce three isoskeletal frameworks in diverse solvents, where pore size maximizes in <b>2</b> by employing <i>N</i>,<i>N</i>′-diethylformamide solvent. The activated framework [Cd­(<b><i>L</i></b>)₂] exhibits strong CO₂ affinity with good CO₂/N₂ selectivity, and shows minimum CO₂ loss during five adsorption–desorption cycles. Sensing studies for nitro-aromatic compounds in DMF reveal highly specific detection of 2,4,6-trinitophenol (TNP) with remarkable quenching (<i>K</i>_SV = 9.3 × 10⁴ M^–1) and low limit of detection (LOD: 0.3 ppm). The quenching mechanism is ascribed to the combined existence of static and dynamic quenching plus resonance energy transfer. The activated framework further shows highly selective luminescent detection of Cu²⁺ ions with a quenching constant of 4.4 × 10³ M^–1 and very low LOD of 3.9 ppm. The detection of Cu²⁺ ions accompanies a visible color change in solution and solid phase, which validates the present system as a potential colorimetric Cu²⁺ sensor. Of note is that bifunctional sensor shows excellent reusability toward TNP and Cu²⁺ detection. Overall, selective and multicycle CO₂ adsorption, together with efficient sensing of both TNP and Cu²⁺ ion, manifest this pore-functionalized MOF as a versatile material for sustainability

Tunable Anisotropic Thermal Expansion of a Porous Zinc(II) Metal–Organic Framework

A novel three-dimensional metal–organic framework (MOF) that displays anisotropic thermal expansion has been prepared and characterized by single-crystal X-ray diffraction (SCD) and thermal analysis. The as-prepared MOF has one-dimensional channels containing guest molecules that can be removed and/or exchanged for other guest molecules in a single-crystal to single-crystal fashion. When the original guest molecules are replaced there is a noticeable effect on the host mechanics, altering the thermal expansion properties of the material. This study of the thermal expansion coefficients of different inclusion complexes of the host MOF involved systematic alteration of guest size, i.e., methanol, ethanol, <i>n</i>-propanol, and isopropanol, showing that fine control over the thermal expansion coefficients can be achieved and that the coefficients can be correlated with the size of the guest. As a proof of concept, this study demonstrates the realizable principle that a single-crystal material with an exchangeable guest component (as opposed to a composite) may be used to achieve a tunable thermal expansion coefficient. In addition, this study demonstrates that greater variance in the absolute dimensions of a crystal can be achieved when one has two variables that affect it, i.e., the host–guest interactions and temperature

Tunable Anisotropic Thermal Expansion of a Porous Zinc(II) Metal–Organic Framework

A novel three-dimensional metal–organic framework (MOF) that displays anisotropic thermal expansion has been prepared and characterized by single-crystal X-ray diffraction (SCD) and thermal analysis. The as-prepared MOF has one-dimensional channels containing guest molecules that can be removed and/or exchanged for other guest molecules in a single-crystal to single-crystal fashion. When the original guest molecules are replaced there is a noticeable effect on the host mechanics, altering the thermal expansion properties of the material. This study of the thermal expansion coefficients of different inclusion complexes of the host MOF involved systematic alteration of guest size, i.e., methanol, ethanol, <i>n</i>-propanol, and isopropanol, showing that fine control over the thermal expansion coefficients can be achieved and that the coefficients can be correlated with the size of the guest. As a proof of concept, this study demonstrates the realizable principle that a single-crystal material with an exchangeable guest component (as opposed to a composite) may be used to achieve a tunable thermal expansion coefficient. In addition, this study demonstrates that greater variance in the absolute dimensions of a crystal can be achieved when one has two variables that affect it, i.e., the host–guest interactions and temperature

Pore Wall-Functionalized Luminescent Cd(II) Framework for Selective CO₂ Adsorption, Highly Specific 2,4,6-Trinitrophenol Detection, and Colorimetric Sensing of Cu²⁺ Ions

Astute combination of basic functionality and luminescence property can pursue multifunctional metal–organic frameworks (MOFs) with assorted applications such as selective CO₂ adsorption, specific detection of explosive nitro compounds, and toxic metal ion sensing. The bifunctional ligand 4-(4-carboxyphenyl)-1,2,4-triazole (H<b>L</b>) is used to build the framework [Cd­(<b><i>L</i></b>)₂]·(DMF)_0.92 (<b>1</b>) (<b><i>L</i></b> = <b>L</b>^<b>–1</b>, DMF = <i>N</i>,<i>N</i>′-dimethylformamide), having a free N atom decorated porous channel. The solvothermal synthesis is extended to produce three isoskeletal frameworks in diverse solvents, where pore size maximizes in <b>2</b> by employing <i>N</i>,<i>N</i>′-diethylformamide solvent. The activated framework [Cd­(<b><i>L</i></b>)₂] exhibits strong CO₂ affinity with good CO₂/N₂ selectivity, and shows minimum CO₂ loss during five adsorption–desorption cycles. Sensing studies for nitro-aromatic compounds in DMF reveal highly specific detection of 2,4,6-trinitophenol (TNP) with remarkable quenching (<i>K</i>_SV = 9.3 × 10⁴ M^–1) and low limit of detection (LOD: 0.3 ppm). The quenching mechanism is ascribed to the combined existence of static and dynamic quenching plus resonance energy transfer. The activated framework further shows highly selective luminescent detection of Cu²⁺ ions with a quenching constant of 4.4 × 10³ M^–1 and very low LOD of 3.9 ppm. The detection of Cu²⁺ ions accompanies a visible color change in solution and solid phase, which validates the present system as a potential colorimetric Cu²⁺ sensor. Of note is that bifunctional sensor shows excellent reusability toward TNP and Cu²⁺ detection. Overall, selective and multicycle CO₂ adsorption, together with efficient sensing of both TNP and Cu²⁺ ion, manifest this pore-functionalized MOF as a versatile material for sustainability

Giant Negative Area Compressibility Tunable in a Soft Porous Framework Material

A soft porous material [Zn­(L)₂(OH)₂]_<i>n</i>·Guest (where L is 4-(1<i>H</i>-naphtho­[2,3-<i>d</i>]­imidazol-1-yl)­benzoate, and Guest is water or methanol) exhibits the strongest ever observed negative area compressibility (NAC), an extremely rare property, as at hydrostatic pressure most materials shrink in all directions and few expand in one direction. This is the first NAC reported in metal–organic frameworks (MOFs), and its magnitude, clearly visible and by far the highest of all known materials, can be reversibly tuned by exchanging guests adsorbed from hydrostatic fluids. This counterintuitive strong NAC of [Zn­(L)₂(OH)₂]_<i>n</i>·Guest arises from the interplay of flexible [−Zn–O­(H)−]<i>_n</i> helices with layers of [−Zn–L−]₄ quadrangular puckered rings comprising large channel voids. The compression of helices and flattening of puckered rings combine to give a giant piezo-mechanical response, applicable in ultrasensitive sensors and actuators. The extrinsic NAC response to different hydrostatic fluids is due to varied host–guest interactions affecting the mechanical strain within the range permitted by exceptionally high flexibility of the framework