Single-crystal to single-crystal guest exchange and phase transformations in a porous metallocycle

Single crystals of a previously reported porous metallocycle [Ag 2L2](BF4)2·2CH3CN (1), where L is the ligand 1,4-bis(2-methylimidazol-1-ylmethyl)benzene, were grown from acetonitrile and immersed in different organic solvents. The crystals thus treated were subjected to single-crystal X-ray diffraction analysis, which revealed that the acetonitrile guest molecules had been replaced by the solvent that the compound was exposed to, yielding five different solvates: [Ag 2L2](BF4)2·2(CH 3)2CO (2), [Ag2L2](BF 4)2·2CHCl3 (3), [Ag2L 2](BF4)2·C6H6 (4), [Ag2L2](BF4)2·C 6H4F2 (5), [Ag2L2] (BF4)2·C7H8 (6). Thermogravimetric analysis supports these findings. This journal is © the Partner Organisations 2014.</p

A combined stretching-tilting mechanism produces negative, zero and positive linear thermal expansion in a semi-flexible Cd(II)-MOF

A novel semi-flexible Cd(II)-MOF has been synthesized and characterized by variable temperature powder and single-crystal X-ray diffraction. The material displays an unusual combination of thermal expansion (TE) i.e. negative, zero and positive, which is an extremely rare finding, especially for metal-organic frameworks as a result of a combined stretching-tilting mechanism. © The Partner Organisations 2014.</p

Hand-twistable plastically deformable crystals of a rigid small organic molecule

4-Bromobenzonitrile was crystallised by sublimation under vacuum. The crystals show highly flexible plastic bending along two perpendicular faces when a mechanical force is applied. The rare occurrence of bending along two perpendicular faces results in twisting or helix formation. © 2018 The Royal Society of Chemistry.</p

Solvent- and Pressure-Induced Phase Changes in Two 3D Copper Glutarate-Based Metal-Organic Frameworks via Glutarate (+gauche ⇄ -gauche) 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 gauche-gauche enantiomeric interconversion of the glutarate moieties. © 2017 American Chemical Society.</p

Large volumetric thermal expansion of a novel organic cocrystal over a wide temperature range

An organic cocrystal consisting of 4-aminobenzonitrile and 4-(dimethylamino) benzonitrile (ABN·2DMABN) undergoes positive linear thermal expansion along its three principal axes over the temperature range 100-300 K. The associated volumetric thermal expansion coefficient is the largest reported to date for a cocrystal in the wide temperature range investigated. © 2018 The Royal Society of Chemistry.</p

Uniaxial negative thermal expansion facilitated by weak host-guest interactions

A nitromethane solvate of 18-crown-6 was investigated by means of variable-temperature single-crystal X-ray diffraction in response to a report of abnormal unit cell contraction. Exceptionally large positive thermal expansion in two axial directions and negative thermal expansion along the third was confirmed. The underlying mechanism relies exclusively on weak electrostatic interactions to yield a linear thermal expansion coefficient of -129 × 10-6 K-1, the largest negative value yet observed for an organic inclusion compound. © 2014 The Partner Organisations.</p

High Pressure In Situ Single-Crystal X-Ray Diffraction Reveals Turnstile Linker Rotation Upon Room-Temperature Stepped Uptake of Alkanes

The rare availability of suitable single-crystal X-ray diffraction (SCXRD) structural data allows for the direct interpretation of the response of a framework to gas sorption and may lead to the development of improved functional porous materials. We report an in situ SCXRD structural investigation of a flexible MOF subjected to methane, ethane, propane, and butane gas pressures. Supporting theoretical investigations indicate weak host–guest interactions for the crystallographically modelled gaseous guests and, in addition, reveal that a turnstile mechanism facilitates the transport of alkanes through the seemingly nonporous system. Inflections present in the adsorption isotherms are furthermore rationalized as due to gate-opening, but without the expected creation of new accessible space. © 2021 Wiley-VCH GmbH</p

Erratum: A combined stretching-tilting mechanism produces negative, zero and positive linear thermal expansion in a semi-flexible Cd(ii)-MOF (Chemical Communications (2014) (50) (6464-6467) DOI: 10.1039/C4CC02634A)

Correction for 'A combined stretching-tilting mechanism produces negative, zero and positive linear thermal expansion in a semi-flexible Cd(ii)-MOF' by Prem Lama et al., Chem. Commun., 2014, 50, 6464-6467. The authors regret that incorrect values were given in Table 2 of the original article. The correct version of Table 2 is given below. (Table Presented). © 2018 The Royal Society of Chemistry.</p

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 1, 2, and 3 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 1 and 2 but positive for 3. 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 1, 2, and 3, 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 1 and 2 but is inhibited by the large molecular volume of the guest in 3. In addition, the thermosalient effect was observed for 2. To our knowledge this is the first example of thermosalience reported for an inclusion compound. © 2016 American Chemical Society.</p

Carbon dioxide entrapment in an organic molecular host

4-Phenoxyphenol crystallises to yield discrete 60 Å3 cavities that are capable of enclathrating small solvent molecules; the cavities are capped by constricted 6-membered hydrogen-bonded rings and these potential apertures do not appear to facilitate gated porosity when the material is subjected to static CO2 pressure. © 2013 The Royal Society of Chemistry.</p