Guest Desorption Research Articles

Anisotropic Guest Diffusion in the δ Crystalline Host Phase of Syndiotactic Polystyrene: Transport Kinetics in Films with Three Different Uniplanar Orientations of the Host Phase

The sorption and desorption of a guest (1,2-dichloroethane) in syndiotactic polystyrene (s-PS) films, presenting three different kinds of uniplanar orientation ((010), (2̄10), or (002)) of the nanoporous host δ phase, have been investigated, mainly by Fourier transform infrared measurements. For guest uptake from dilute aqueous solutions (e.g., 50 ppm), the sorption in the amorphous phase is negligible with respect to sorption in the nanoporous crystalline phase. Correspondingly the guest sorption and desorption kinetics are influenced by the orientation of the anisotropic host crystalline phase. In particular, as for the guest diffusivity (D) measured by both sorption and desorption experiments, D(010) ≤ D(002) < D(unoriented) < D(2̄10). These results can be rationalized on the basis of previous molecular dynamics simulations, predicting an anisotropic guest diffusion in the δ crystalline phase.

Simple and Quantitative Mechanochemical Preparation of a Porous Crystalline Material Based on a 1D Coordination Network for Uptake of Small Molecules

Kneading them in: A versatile porous material based on the 1D coordination network [CuCl2(dace)]∞ (dace=trans-1,4-diaminocyclohexane) can be inexpensively prepared by a mechanochemical reaction followed by mild thermal treatment. The system is able to reversibly absorb molecules from solution or by simple kneading, while guest desorption from the product invariably leads back to the unsolvated form.

In Situ Single-Crystal X-ray Diffraction Studies of Desorption and Sorption in a Flexible Nanoporous Molecular Framework Material

The subtle flexibility of the framework material Co(bpy)1.5(NO3)2.(guest) (bpy = 4,4'-bipyridine) (1.(guest)) is demonstrated quantitatively through in situ single-crystal X-ray diffraction measurements of guest desorption and sorption processes. Variable temperature unit cell determinations were employed to monitor the uptake and release of guest species, and full structural determinations have been carried out for the as-grown ethanol-loaded framework (1.(EtOH)), for the empty host framework, and for each of the five introduced guests (methanol: 1.(MeOH), acetone: 1.(ACN), acetonitrile: 1.(MeCN), tetrahydrofuran:1.(THF), dichloromethane: 1.(DCM)). The framework consists of interdigitated two-dimensional bilayers of cobalt(II) centers bridged by bpy ligands, with one-dimensional pores that account for approximately 20% of the total volume. The sorption of guest species of varying size and shape has revealed the framework's ability to adapt to different guests through a range of different framework flexibilities.

Organic Intercalation Material: Reversible Change in Interlayer Distances by Guest Release and Insertion in Sandwich‐Type Inclusion Crystals of Cholic Acid

Cholic acid (CA) forms inclusion crystals that have a sandwich-type lamellar structure constructed by the alternative stacking of host bilayers and guest layers. Five disubstituted benzenes, o-toluidine, m-fluoroaniline, o-chlorotoluene, o-bromotoluene, and indene, are accommodated in the two-dimensional void space between the host bilayers at 1:2 host-guest stoichiometries. Thermal gravimetric analysis of the inclusion crystals revealed that all the guest molecules, except o-toluidine, are released in two separate steps, indicating the formation of intermediate crystals after the first guest release. Adequate heat treatment of the four inclusion crystals induces release of half or three quarters of the guest molecules. X-ray diffraction patterns of the intermediate crystals revealed that the crystals have a bilayer structure the same as those of the common CA inclusion crystals. They have one-dimensional cavities, in which the guest molecules are included at a 1:1 or 2:1 host-guest stoichiometry. These facts indicate that the host bilayers move 1.6-4.5 A perpendicular to the layer direction by desorption of the guest molecules. Furthermore, a reverse structural change is also achieved by absorption of the guest molecules to regenerate the starting sandwich-type inclusion crystals. This reversible change in the host bilayer by the guest sorption and desorption is a novel example of organic intercalation materials.

Guest exchange process in syndiotactic polystyrene thin films measured by ATR-FTIR spectroscopy

Guest exchange and desorption processes in syndiotactic polystyrene(sPS)-solvent complex systems (δ form) were studied by means of ATR-FTIR spectroscopy. The intensities of the bands sensitive to the amount of guest molecules and the conformational order of sPS were followed to clarify the mechanism on the guest exchange. Rapid exchange of the guest molecules was observed on the exposure of the δ form sample to toluene and chloroform vapors. The desorption of guest molecules occurs in two stages, which correspond to the rapid desorption mainly from the amorphous region and the slow desorption mainly from the crystalline region, respectively. The diffusion coefficients of the desorbate molecules were evaluated. The time dependence of the intensities of the sPS bands showed that the conformational regularity of sPS changed during the guest exchange process, and the behavior depended on the combination of sorbate and desorbate.

Guest exchange process in syndiotactic polystyrene thin films measured by ATR-FTIR spectroscopy

Guest exchange and desorption processes in syndiotactic polystyrene(sPS)-solvent complex systems (δ form) were studied by means of ATR-FTIR spectroscopy. The intensities of the bands sensitive to the amount of guest molecules and the conformational order of sPS were followed to clarify the mechanism on the guest exchange. Rapid exchange of the guest molecules was observed on the exposure of the δ form sample to toluene and chloroform vapors. The desorption of guest molecules occurs in two stages, which correspond to the rapid desorption mainly from the amorphous region and the slow desorption mainly from the crystalline region, respectively. The diffusion coefficients of the desorbate molecules were evaluated. The time dependence of the intensities of the sPS bands showed that the conformational regularity of sPS changed during the guest exchange process, and the behavior depended on the combination of sorbate and desorbate.

Guest sorption and desorption in the metal-organic framework [Co(INA)(2)] (INA=isonicotinate)--evidence of intermediate phases during desorption.

The metal-organic framework [Co(INA)(2)]x0.5EtOH (INA = isonicotinate, NC(5)H(4)-4-CO(2)(-)), was synthesised under solvothermal conditions. Its X-ray crystal structure shows channels containing ethanol guests which are hydrogen-bonded to carboxylate oxygens of the framework. The pyridyl rings of the framework alternate between 'open' and 'closed' positions along the channels resulting in large variation in the channel cross-sectional area from ca. 1.4 by 2.3 A at the narrowest point to 4.9 by 5.3 A at the widest. Despite the very small windows, the ethanol guests (of van der Waals diameter ca. 4.2-6.1 A) may be reversibly desorbed and sorbed into the structure quantitatively, as shown by in situ variable-temperture IR spectroscopy and XRPD. The single-crystal structure of the desolvated form [Co(INA)(2)] shows that there is no change in the overall connectivity on desolvation, but the rotational positions of the pyridine rings are altered. This suggests that pyridyl rotation may occur to allow guests to pass in and out. When the synthesis was conducted in 1-propanol solvent [Co(INA)(2)]x0.5Pr(n)OHxH(2)O, was obtained, and a single-crystal X-ray structure revealed the same overall connectivity as in but with pyridine rings disordered over closed and open positions. There was no evidence of included guests from X-ray crystallography, suggesting that they are also highly disordered. Variable-temperature XRPD performed on bulk samples showed peaks which were unsymmetrical and exhibited shoulders, suggesting that for each pattern obtained the material actually consisted of several closely-related phases. The movements of the peaks during desolvation showed the presence of intermediate phases before the final desolvated product was formed. The peak positions of the intermediate phases matched more closely with the calculated pattern for than with or, suggesting that they may have disordered structures similar to. The results also suggest that the intermediate phase represents an initial increase in volume before a larger decrease in volume occurs to give the final desolvated material.

Porous silver(I) organometallic coordination polymer of triptycene, and the guest desorption and absorption

On the basis study of porous silver(I) complex of triptycene (tpty), [Ag 3(tpty) 3(ClO4) 3](toluene) 2 ( 1), its toluene desorbed complex ( 2) and absorbed complex ( 3) have been synthesized and confirmed by 1H NMR spectra and X-ray powder diffraction. In complex 1, a 3D architecture with triptycene exhibits an unprecedented μ–η 2–η 2 or μ–η 2–η 2–η 1 coordination mode depending on the steric requirements of the network. The desorption and absorption of guest molecules occur in this complex accompanying the structure change. The potential study of these complexes for the rational control and synthesis of porous organometallic coordination network is discussed.

A Robust Two-Dimensional Hydrogen-Bonded Network. Reversible Guest Adsorption/Desorption without a Phase Change

Abstract 9-(3,5-Dihydroxyphenyl)acridine (3) forms a 1:1 benzene adduct 3·(benzene) having a novel O–H···O–H···N hydrogen-bonded 2D network. Partial (50%) guest desorption occurs in a reversible manner without undergoing a phase change.

A Molecular Dynamics Study of the Structure and Evolution of the 4,4′-Bis(diphenylhydroxymethyl)biphenyl/Acetone Host-Guest System

The 4,4′-bis(diphenylhydroxymethyl)biphenyl/acetone (DHMB-Ac) system was studied by NPT molecular dynamics (MD) calculations; the study was prompted by the availability of X-ray single-crystal diffraction and calorimetric data (L. Johnson, L. Nassimbeni, E. Weber and K. Skobridis, J. Chem. Soc. Perkin Trans. 2, 1992, 2131). Potential energies were calculated by using the UNI-FF or the OPLS all-atom force fields. The kinetics of formation of hydrogen-bonded aggregates between the DHMB molecule and acetone was sampled, and the persistence and fluxionality of the O−H·;OC hydrogen bond are clearly revealed. Extensive MD runs at variable temperature on the inclusion compound in its crystalline state allow a description of the thermal motion and eventual reorientation within its cavity of the acetone molecule; the host crystalline matrix does not survive when guests are removed. The dynamic evolution of a slab of 60 DHMB and 120 acetone molecules, which has the experimental crystal structure, was also simulated at the temperature experimentally observed for guest desorption, and the loss of solvent molecules was monitored. Crystalline order is very quickly lost; then, guest molecules can easily diffuse away from the surface without a noticeable swelling of the material. The molecular reorganization of the remaining host liquid back to the crystal structure of one of the two polymorphs of pure DHMB could not be observed, owing to the short simulation times and to the smallness of the computational sample.

A molecular dynamics study of the structure and evolution of the 4,4'-bis(diphenylhydroxymethyl)biphenyl/acetone host-guest system

The 4,4'-bis(diphenylhydroxymethyl)biphenyl/acetone (DHMB-Ac) system was studied by NPT molecular dynamics (MD) calculations; the study was prompted by the availability of X-ray single-crystal diffraction and calorimetric data (L. Johnson, L. Nassimbeni, E. Weber and K. Skobridis, J. Chem. Soc. Perkin Trans. 2, 1992, 2131). Potential energies were calculated by using the UNI-FF or the OPLS all-atom force fields. The kinetics of formation of hydrogen-bonded aggregates between the DHMB molecule and acetone was sampled, and the persistence and fluxionality of the O-H...O=C hydrogen bond are clearly revealed. Extensive MD runs at variable temperature on the inclusion compound in its crystalline state allow a description of the thermal motion and eventual reorientation within its cavity of the acetone molecule; the host crystalline matrix does not survive when guests are removed. The dynamic evolution of a slab of 60 DHMB and 120 acetone molecules. which has the experimental crystal structure, was also simulated at the temperature experimentally observed for guest desorption, and the loss of solvent molecules was monitored. Crystalline order is very quickly lost; then, guest molecules can easily diffuse away from the surface without a noticeable swelling of the material. The molecular reorganization of the remaining host liquid back to the crystal structure of one of the two polymorphs of pure DHMB could not be observed, owing to the short simulation times and to the smallness of the computational sample.

Regeneration of nanoporous crystalline syndiotactic polystyrene by supercritical CO2

Guest desorption procedures for s-PS clathrate samples, leading to formation and regeneration of the nanoporous δ phase, are compared. An extraction procedure, based on supercritical carbon dioxide, allows an easy and fast recovery of the guest molecules operating under relatively mild conditions (90–200 bar, 40°C) and generates a completely empty δ form, also starting from the most stable s-PS clathrate forms. In agreement with a previously proposed crystal structure of the nanoporous δ form, X-ray diffraction patterns of δ form powders obtained by this procedure do not show the peak, which is reduced but still apparent in samples extracted with previous procedures based on boiling solvents. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2077–2082, 1999

Isothermal Guest Desorption from Crystalline and Amorphous Phases of Syndiotactic Polystyrene

Isothermal desorption kinetics at different temperatures of 1,2-dichloroethane (DCE) from syndiotactic polystyrene films have been studied by Fourier transform infrared spectroscopy. For β-form films, where DCE is present only into the amorphous phase, nearly equal populations of trans and gauche conformers, during the whole desorption processes, are observed. On the other hand, for clathrate films, where DCE is present in both amorphous and crystalline phases, its trans conformer becomes largely predominant, as the desorption processes proceed. In agreement with previous FTIR and X-ray diffraction studies, these results can be rationalized by assuming that essentially only the DCE trans conformer is present in the clathrate phase. In this assumption, experimental desorption kinetics from clathrate samples can be separated into faster processes from the amorphous phase and slower processes from the crystalline phase. The validity of this separation procedure is confirmed by the close similarity between th...

Sorption and Desorption of Inclusion Compound Guests Different Types of Inclusion Compounds

The guests present in inclusion compounds participate in bonding with the hosts. The conditions for the sorption and desorption of the guests are decisive for the properties of the inclusion compounds. They are surveyed for many types of inclusion compounds.

Crystal Structures and Thermal Analysis of Hexakis(3-hydroxy-3,3-diphenyl-2-propynyl)benzene with 1,4-dioxane, and 1,3-dioxolan-2-one

Structures of the inclusion compounds of hexakis(3-hydroxy-3,3-diphenyl-2-propynyl)benzene with 1,4-dioxane (1) and 1,3-dioxolan-2-one (2) have been determined. 2 illustrates the selectivity of the host for carbonyl compounds as it was grown from a solution of 1,3-dioxolane with 1,3-dioxolan-2-one as a minor impurity. The thermal analysis (TG and DSC) of both compounds was carried out. Guest desorption from 1 was found to follow the F1 mechanism with an activation energy of 148(2) kJmol−1.

Isothermal decomposition kinetics of Werner-type β-[Ni(NCS) 2(4-MePy) 4] clathrates with aromatic guests

Guest desorption from clathrates formed by β-[Ni(NCS) 2(4-methylpyridine) 4] host with benzene, toluene and p-xylene was studied under isothermal conditions within the temperature range from 6 to 30°C. Possible mechanisms of decomposition of these clathrates are discussed. In the decomposition of β-[Ni(NCS) 2(4-methylpyridine) 4]·C 6H 6 clathrate, guest diffusion in the solid is the rate-determining step. The activation energy of this process was found to be 38.5 ± 2.5 kJ mol −1.

About the inclusion of an insecticide in zeolitic materials

The commercial product Supercypermetrin (3-phenoxy-α-cyanobenzyl-3-(2,2-dichlorovinyl)-2-(2,2-dimetyl)-cyclopropanecarboxylate) [SCM] in the liquid form was included in the zeolitic host. A natural zeolitic material of clinoptilolite type [CT] from a Slovakian deposit was used. The chemical control of the guest desorption was used for checking the existence of a new inclusion compound. The desorption of the insecticide under relatively drastic conditions (12 g of product in 200 ml H2O) showed a hindered and regulated release of the insecticide. Thermal curves obtained by means of a derivatograph and IR spectra were used for the study of the insecticide [SCM] enclosed (10%) in the zeolitic host and its desorption.

Inclusion of organic vapours by crystalline hosts. Chemical-sensitive coatings for sensor applications

Solid inclusion hosts, such as derivatives of bis-fluorenyl ( 1, 2) and maleic acid ( 3), can include organic solvent vapour molecules such as acetone, cyclohexanone, methanol, ethanol, 1-butanol and dioxane to form stoichiometric inclusion complexes. Due to their ability to be used as gas-sensing layers, the absorption and desorption of acetone by crystalline host 1 is on-line monitored by a recording balance. For sensitivity improvement hosts 1 and 3 are coated onto the surface of a quartz crystal, the indicating device of the quartz microbalance. In the presence of various saturated vapour atmospheres we obtained reversible and reproducible signals within a short response time. Stoichiometrics of sorptive clathrate formations with 1– 3 are determined by weighing. By differential scanning calorimetry (DSC) temperature dependence and enthalpies of guest desorption from host 1 can be determined, thus indicating weak host-guest interactions.

Crystal structure of the clathrate compound [dibromotetra(pyridine)copper(II)]�pyridine. Characterization by EXAFS of the pyridine desorption product

Powder samples of the new compound [Cu(C5H5N)4·Br2](C5H5N) and of its desorption product have been studied by EXAFS. The crystal structure of [Cu(C5H5N)4Br2]·(C5H5N) has been determined from three-dimensional X-ray diffraction data and refined to theR value 0.038 for 379 observed reflections. (orthorhombic,Ccca,a=12.033(8),b=14.764(3),c=16.768 A,V=1897(3) A3,Z=4). The copper atom lies on a 222 symmetry site and is hexacoordinated with four nitrogen and two bromine atoms, forming an elongated octahedron with the bromine atoms in apical positions (Cu−Br distance: 3.201(2) A, Cu−N1/N2 distances: 2.02(1)/2,07(1) A). The host molecules (Cu(C5H5N)4Br2) form layers parallel to the (001) plane. Cavities in the space between these layers, bound by pyridine ligands protruding into this space, are occupied by the guest molecules (C5H5N). The guest desorption at room temperature is accompanied by a chemical and structural destruction of the host, leading to the known compound Cu(C5H5N)2Br2.