Distinctive Three-Step Hysteretic Sorption of Ethane with In Situ Crystallographic Visualization of the Pore Forms in a Soft Porous Crystal

A soft porous Zn­(II)–MOF (<b>1</b>) displays distinctive three-step hysteretic breathing behavior under ethane gas pressure at ambient temperatures. In situ single-crystal X-ray diffraction analysis was carried out at 298 K using an environmental gas cell in order to elucidate the different porous forms of the breathing framework under ethane gas. The three different phases were further characterized by pressure-gradient differential scanning calorimetry and variable pressure powder X-ray diffraction analysis

Anomalous Anisotropic Thermal Expansion in a One-Dimensional Coordination Polymer Driven by Conformational Flexibility

A one-dimensional lithium­(I) coordination polymer has been characterized by variable-temperature single-crystal X-ray diffraction and differential scanning calorimetry. This compound possesses an anisotropic packing arrangement that, along with a scissor-like or hingelike movement of the pyridyl ligand side arms, results in an extremely rare combination of positive, negative, and zero thermal expansion. Designing such types of materials and understanding the mechanistic details can facilitate the design of new thermoresponsive materials

An unexpected relationship between solvent inclusion and gas sorption properties of chiral calixsalen solids^*

<p>Experimental evidence is provided that tentatively shows a relationship between inclusion and sorption properties within a series of halogenated homochiral calixsalens. Calixsalens with Cl and Br substituents at the C5 position on the aromatic rings display remarkable sorption properties for all of the investigated gases, as well as the ability to form inclusion compounds with chemically different solvents, while unsubstituted (H-) and F-substituted calixsalens do not show any of these properties.</p> <p>There is a tentative relationship between solvent inclusion and gas sorption properties within a series of halogenated homochiral calixsalens. Calixsalens with Cl and Br substituents at the C5 position on the aromatic rings display remarkable sorption properties for a selection of gases, as well as the ability to form inclusion compounds with chemically different solvents, while unsubstituted (H-) and F-substituted calixsalens do not show any of these properties.</p

Anomalous Anisotropic Thermal Expansion in a One-Dimensional Coordination Polymer Driven by Conformational Flexibility

A one-dimensional lithium­(I) coordination polymer has been characterized by variable-temperature single-crystal X-ray diffraction and differential scanning calorimetry. This compound possesses an anisotropic packing arrangement that, along with a scissor-like or hingelike movement of the pyridyl ligand side arms, results in an extremely rare combination of positive, negative, and zero thermal expansion. Designing such types of materials and understanding the mechanistic details can facilitate the design of new thermoresponsive materials

Solvent- and Pressure-Induced Phase Changes in Two 3D Copper Glutarate-Based Metal–Organic Frameworks via Glutarate (+<i>gauche</i> ⇄ −<i>gauche</i>) Conformational Isomerism

Two isoreticular three-dimensional copper­(II) glutarate-based pillared-layered metal–organic frameworks (MOFs) with flexible pillars, [Cu₂(glu)₂(bpa)] and [Cu₂(glu)₂(bpp)] (bpa = 1,2-bis­(4-pyridyl)­ethane; bpp = 1,3-bis­(4-pyridyl)­propane), undergo spontaneous phase changes upon solvent loss at room temperature. Using single-crystal X-ray diffraction analysis (SCXRD), we show that the phase changes result in new narrow-channel forms that experience a large reduction in solvent-accessible volume. Moreover, the [Cu₂(glu)₂(bpa)] MOF displays a stepped sorption isotherm for the uptake of CO₂ at room temperature. This is indicative of reversion of the framework to the wide-channel form under CO₂ pressure. Supercritical CO₂ was used to isolate the gas-included structures, and by means of SCXRD we were able to determine the positions of the CO₂ molecules in the channels of the frameworks. Finally, we report the use of molecular modeling simulations to elucidate the phase-change mechanism, including the energetic changes involved. Structural limitations in both MOFs allow for only direct <i>gauche</i>–<i>gauche</i> enantiomeric interconversion of the glutarate moieties

Direct Evidence for Single-Crystal to Single-Crystal Switching of Degree of Interpenetration in a Metal–Organic Framework

A known doubly interpenetrated metal–organic framework with the formula [Zn₂(ndc)₂(bpy)] possesses minimal porosity when activated. We show not only that the material converts to its triply interpenetrated analogue upon desolvation, but also that the transformation occurs in a single-crystal to single-crystal manner under ambient conditions. The mechanism proposed for the conversion is supported by computational methods and by analogy with the solid-state behavior of an analogous system

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

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

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