Guest Mixtures Research Articles

Exploring the host compound dynamics of 1,4-phenylene-bis(di-p-fluorophenylmethanol) in mixed pyridines

AbstractIn this investigation, the wheel-and-axle host compound, 1,4-phenylene-bis(di-p-fluorophenylmethanol) (H), was demonstrated to have inclusion ability for each of PYR, 2MP, 3MP and 4MP (1:1, 1:2, 1:2 and 1:2 were the H: G ratios). In the equimolar guest competition experiments, H was observed to have an overwhelming affinity for PYR and 4MP relative to 2MP and 3MP. In fact, selectivity coefficients calculated from the non-equimolar binary guest competition experiments suggested that this host compound would be an efficient candidate for the separation of all PYR/2MP mixtures and a 40:60 4MP/3MP solution through host-guest chemistry strategies. SCXRD analyses established the preferred guests (PYR and 4MP) to be involved in significantly shorter stabilizing classical hydrogen bonding interactions with H, explaining the selectivity behaviour of this host compound in the guest mixtures. Additionally, Hirshfeld surface considerations also explained this behaviour, but only for PYR. Furthermore, thermal analyses were used to ascertain the relative thermal stabilities of the four complexes and, satisfyingly, the PYR- and 4MP-containing complexes possessed the greater thermal stabilities compared with H·2(2MP) and H·2(3MP), as was demonstrated by a comparison of their guest release onset temperatures.

Crystallization experiments of the wheel-and-axle host compound, 1,4-phenylene-bis(di-p-tolylmethanol), from pyridine and methylpyridine mixtures

1,4-Phenylene-bis(di-p-tolylmethanol) (H), a host compound with the wheel-and-axle design, formed complexes with organic guest solvents pyridine (PYR) and 2-, 3- and 4-methylpyridine (2MP, 3MP and 4MP). The host: guest (H: G) ratios were 1:3, 1:2, 1:2 and 1:1, respectively. Host crystallization experiments from mixed guests demonstrated H to prefer both PYR and 4MP; however, it was established that these difficult-to-separate (by fractional distillations) guest mixtures cannot be purified/separated by means of H through supramolecular chemistry strategies owing to these selectivities for PYR and 4MP being less than optimal. Single crystal X-ray diffraction experiments showed that each guest compound was held in its complex by means of a classical hydrogen bond with H, and that one of the preferred guests, PYR, experienced a significantly shorter contact of this type than the other guests. Hirshfeld surface analyses demonstrated that PYR was also involved in a greater percentage of (guest)N···H(host) interactions compared with the other guest molecules. Thermal analyses, on the other hand, revealed that 4MP (also a favoured guest species) formed the most stable complex of the four in this investigation. These results with H were compared to those obtained when employing a closely related host compound from a previous report, 1,4-bis(diphenylhydroxymethyl)benzene: while both host species preferred the same guests (PYR and 4MP), the extent of the selectivity of that host compound compared with H in the present work was significantly more enhanced. Thus, minor modifications may deleteriously affect the selectivity behaviour of closely related host compounds.

Trans-α,α,α′,α′-Tetraphenyl-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol and its tetra(p-chlorophenyl) derivative: roof-shaped host compounds for the purification of aromatic C8H10 isomeric guest mixtures

trans-α,α,α′,α′-Tetraphenyl-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol and its tetra(p-chlorophenyl) derivative: roof-shaped host compounds for the purification of aromatic C8H10 isomeric guest mixtures

Composition-Driven Structural Modulation and Guest-Induced Nanotemplate Effects of the Host–Guest Complexes Made by a Unimolecular Q-Clip

The composition of a self-assembly system has long been an essential factor that governs the resulting supramolecular structures. Nevertheless, due to the rigorous demands of structural compatibility in host–guest chemistry, the molar ratio of host–guest mixtures has not been applied as a significant factor in modulating the supramolecular structures of host–guest complexes. In this study, via using a novel unimolecular quaternary clip (Q-clip) as the host molecule and pyrene as the guest molecule and a nanotemplating reagent, we discovered that the changes in the molar ratios of the Q-clip:pyrene mixtures resulted in the structural modulation of the host–guest complexes. Supramolecular lamellae made by the 1:4 Q-clip:pyrene mixture and a hexagonal columnar phase (Colh) made by the 1:8 Q-clip:pyrene mixture were identified by the 1D powder and 2D fiber WAXS characterizations. Time-resolved synchrotron X-ray characterization and thermal analysis further showed that removing the easily sublimed guest molecules (pyrene) via thermal annealing simply hollowed out the supramolecular structures without damaging the supramolecular scaffolds made by the Q-clips. Pyrene is thus a nanotemplating reagent that can be used to create the hollowed-out 2D lamellar and 1D cylindrical scaffolds of Q-clips. The study thus gave a novel example of a host–guest mixture that is able to carry out composition-driven structural modulation and guest-induced nanotemplates. The finding broadens the horizon of host–guest chemistry and may inspire more nanoinnovation.

Host selectivity behaviour of trans-N,N′-bis(9-phenyl-9-xanthenyl)cyclohexane-1,2-diamine and trans-N,N′-bis(9-phenyl-9-thioxanthenyl)cyclohexane-1,2-diamine when presented with six-membered heterocyclic guest mixtures

Two compounds, trans-N,N′-bis(9-phenyl-9-xanthenyl)cyclohexane-1,2-diamine (1,2-DAX) and trans-N,N′-bis(9-phenyl-9-thioxanthenyl)cyclohexane-1,2-diamine (1,2-DAT), were assessed for their host ability in the presence of four heterocyclic guest species, namely pyridine (PYR), piperidine (PIP), morpholine (MOR) and dioxane (DIO). Each of these guests formed single solvent complexes with both host compounds. When 1,2-DAX and 1,2-DAT were recrystallized from various guest mixtures, it was shown that their selectivity orders were identical, DIO (46.6%) > MOR (23.0%) > PYR (18.9%) > PIP (11.5%) and DIO (85.9%) > MOR (23.7%) > PYR (8.9%) > PIP (8.5%), respectively, but that the thio host derivative possessed a significantly enhanced preference for DIO compared with its oxygen analogue. Additional experiments in order to investigate the various parameters at play in these complexation experiments involved single crystal diffraction experiments and thermal analyses.

Comparing the host behaviour of roof-shaped compounds trans-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid and its dimethyl ester in the presence of mixtures of xylene and ethylbenzene guests

Each p-Xy guest molecule is surrounded by six dicarboxylic acid host molecules, forming a continuous intermolecular hydrogen-bonded motif through their carboxylic acid functionalities to form a cage-like structure in which the guests are trapped.

Selectivity behaviour of two roof-shaped host compounds in the presence of xylene and ethylbenzene guest mixtures

α,α-Diphenyl-9,10-dihydro-9,10-ethanoanthracene-11-methanol possessed an enhanced selectivity for o-Xy when recrystallized from various xylene and EB mixed solvents (84.5–93.7%).

Solid-State NMR Spectroscopy Study of Molecular Dynamics of Pyridine 1-Oxide Encapsulated in p-tert-Butylcalix[4]arene.

The mixture of guests 25% pyridine 1-oxide (PNO) and 75% nitrobenzene (NB) encapsulated in a host cavity of p-tert-butylcalix[4]arene (p-tBC) is a suitable system for the study of intermolecular weak interactions, and the preferred orientation of the guest molecules within the host was derived. Variable temperature deuterium nuclear magnetic resonance line shape and spin-lattice relaxation studies were performed on three samples of 25% PNO as a guest (selectively and entirely deuterated) with 75% NB encapsulated in p-tBC as a host system. It is found that the PNO molecular motion supports the two-site jump model and is highly mobile throughout the temperature range from -130 to 20 °C. PNO reorients about its C2 molecular symmetry axis followed by reorientation around the compound's C4 axis of symmetry of a host. Calculation showed that besides precise molecular jumping, the guest also experiences the vibrational motion with a variation angle dispute about 15°. The correlation times for the molecular guest motion and two-dimensional exchange spectroscopy confirmed a fast exchange limit inside the cavity. These molecular dynamics follow an Arrhenius behavior motion from which the small activation energy is delivered that strongly suggests a relatively weak intermolecular interaction between the host and guest species. PNO has definite dipole orientational motion in the cavity where its aromatic covalent bond structure minimizes contact with the host p-tert-butyl groups. Experimentally found, PNO-d5 deuterons in the single crystal collapse at 55 and 125° at ambient temperature. The first splitting of 124 kHz belongs to D3(D5), the second splitting of 100 kHz belongs to D2(D6), and the last splitting of 52 kHz belongs to D4 of the ring of PNO inside the p-tBC.

Transformation Network Culminating in a Heteroleptic Cd6L6L'2 Twisted Trigonal Prism.

Transformations between three-dimensional metallosupramolecular assemblies can enable switching between the different functions of these structures. Here we report a network of such transformations, based upon a subcomponent displacement strategy. The flow through this network is directed by the relative reactivities of different amines, aldehydes, and di(2-pyridyl)ketone. The network provides access to an unprecedented heteroleptic Cd6L6L′2 twisted trigonal prism. The principles underpinning this network thus allow for the design of diverse structural transformations, converting one helicate into another, a helicate into a tetrahedron, a tetrahedron into a different tetrahedron, and a tetrahedron into the new trigonal prismatic structure type. The selective conversion from one host to another also enabled the uptake of a desired guest from a mixture of guests.

Four xanthenyl-derived compounds: a comparative investigation of their host behaviour in the presence potential saturated and unsaturated heterocyclic six-membered ring guest solvents

Four xanthenyl-derived host compounds, namely trans-N,N′-bis(9-phenyl-9-xanthenyl)cyclohexane-1,4-diamine (1,4-DAX), trans-N,N′-bis(9-phenyl-9-thioxanthenyl)cyclohexane-1,4-diamine (1,4-DAT), N,N′-bis(9-cyclohexyl-9-xanthenyl)ethylenediamine (OED) and N,N′-bis(9-cyclohexyl-9-thioxanthenyl)ethylenediamine (SED) were assessed for their selectivity behaviour in the presence of both the saturated and unsaturated heterocyclic six-membered ring guest solvents morpholine (MOR), piperidine (PIP), dioxane (DIO) and pyridine (PYR). Related compounds OED and SED behaved similarly when each was recrystallized from mixtures of these guests, both selecting for MOR and discriminating against PYR, while, surprisingly, the performance of structurally-similar 1,4-DAX and 1,4-DAT in equivalent conditions, on the other hand, was entirely contrasting: only 1,4-DAX formed complexes from such guest mixtures and 1,4-DAT failed to do so in each instance. Furthermore, 1,4-DAX preferred PYR, an observation distinct from that of OED and SED. Single crystal diffraction (SCXRD) experiments were carried out on suitable crystals formed by 1,4-DAX with these guests, and it was revealed that the preference for PYR may be attributed to both host–guest π–π interactions and a shorter H-bond between molecules of the host and PYR compared with other complexes. SCXRD experiments were not possible for OED, SED and 1,4-DAT owing to either the inability of the host compound to complex with these guests or poor crystal quality of the resultant complexes.

Hydrates of Binary Guest Mixtures: Fugacity Model Development and Experimental Validation

AbstractA fugacity-based thermodynamic model for hydrate has been used to determine the equilibrium pressures of hydrate formation. This fugacity-based model uses the PRSV equation of state, which is used to represent the gas phases in the hydrate. The parameters of the model are fitted to the experimental data of binary guest hydrates. The present study is aimed at investigating binary mixtures of {\text{CH}_{4}}–{\text{H}_{2}}S, {\text{C}_{3}}{\text{H}_{8}}–{\text{N}_{2}}, {\text{N}_{2}}–{\text{CO}_{2}}, {\text{CH}_{4}}–i-butane, {\text{C}_{3}}{\text{H}_{8}}–i-butane, {\text{CH}_{4}}–n-butane, {\text{C}_{3}}{\text{H}_{8}}–n-butane, i-butane–{\text{CO}_{2}}, and n-butane–{\text{CO}_{2}} hydrates, which have not been modeled before. Unlike previous studies, the Kihara potential parameters were obtained using the second virial coefficient correlation and the data of viscosity for gases. The fugacity-based model provides reasonably good predictions for most of the binary guest hydrates ({\text{CH}_{4}}–{\text{C}_{3}}{\text{H}_{8}}). However it does not yield good prediction for hydrates of ({\text{CO}_{2}}–{\text{C}_{3}}{\text{H}_{8}}). The transitions of hydrate structure from sI to sII and from sII to sI have been also predicted by this model for binary guest hydrates. The AAD % calculated using the experimental data of natural gas hydrates is only 10 %, which is much lower than the AAD % calculated for the equilibrium data predicted by the VdP-w model.

Inclusion ability and selectivity of ethylenediamine derivatives for pyridine in the presence of methylpyridine isomers

The inclusion behaviour of compounds N,N′-bis(9-cyclohexyl-9-xanthenyl)ethylenediamine (OED) and N,N′-bis(9-cyclohexyl-9-thioxanthenyl)ethylenediamine (SED) was assessed in the presence of pyridine (PYR) and its three methylpyridine isomers (2MP, 3MP and 4MP). PYR, 3MP and 4MP were each enclathrated by OED when it was recrystallized independently from each guest solvent, but failed to include 2MP. The thio host derivative, SED, was less efficient, forming a complex only with PYR. When these guests were mixed in equimolar amounts and each host recrystallized from the mixture, OED constantly displayed a significantly enhanced preference for 4MP (near-complete in many instances), while complexation failed under these circumstances for SED, even when PYR was present in the guest mixture (despite PYR having been included in the single solvent experiment). A selectivity order of 4MP (92.8%) ≫ PYR (6.0%) > 3MP (0.9%) > 2MP (0.3%) was noted for OED when it was recrystallized from the equimolar quaternary mixed solvent system. The selectivity of OED towards 4MP was investigated using single crystal diffraction (SCXRD) and thermal (TA) analyses: interestingly, only 4MP experienced a strong classical hydrogen bond with OED, in direct relation to the enhanced selectivity of OED for 4MP while, additionally, this complex displayed an increased thermal stability relative to the other two complexes with OED.

Inclusion ability of host TETROL [(+)-(2R,3R)-1,1-4,4-tetraphenylbutane-1,2,3,4-tetraol] for selected saturated cyclic and aromatic alcohol, ketone and amine guest compounds

In this work, we investigated the host ability of TETROL [(+)-(2R,3R)-1,1-4,4-tetraphenylbutane-1,2,3,4-tetraol] in the presence of two guest series, namely saturated cyclohexanone, cyclohexanol and cyclohexylamine on the one hand, and aromatic/saturated combinations of aniline, cyclohexylamine, phenol and cyclohexanol on the other. TETROL formed complexes with all of these guests in single solvent experiments, while mixed complexes were obtained when the host was recrystallized from guest mixtures. However, most notably, TETROL showed enhanced selectivities for the amino-containing cyclic organic compounds compared with the ketone and alcohol, results of which allude to the potential of purifying various combinations of such compounds through host‒guest chemistry. We conducted single crystal X-ray diffraction experiments in order to reveal the underlying reasons for the selectivity displayed by TETROL for these amines.

Comparing the effect of selected substituent changes on host ability and selectivity in four xanthenyl-type host compounds in the presence of cyclohexanone and methylcyclohexanone isomers

Four related xanthenyl and thioxanthenyl host compounds, N,N′-bis(9-phenyl-9-thioxanthenyl)ethylenediamine (H1), N,N′-bis(9-phenyl-9-xanthenyl)ethylenediamine (H2), N,N′-bis(9-cyclohexyl-9-thioxanthenyl)ethylenediamine (H3) and N,N′-bis(9-cyclohexyl-9-xanthenyl)ethylenediamine (H4) were synthesized and compared for their host ability and selectivity in the presence of cyclohexanone and the methylcyclohexanone isomers. Surprisingly, only H1 was an effective host compound in these conditions, clathrating all four potential guest solvents; H2 failed to crystallize from these compounds, while both H3 and H4 included only cyclohexanone, also failing to crystallize from the methylcyclohexanone isomers. H1 was further assessed for any selectivity when presented with mixtures of these guests, and a host selectivity order of 2MeCy (67.6%) > 3MeCy (23.1%) > 4MeCy (9.3%) was observed, while the addition of cyclohexanone to these experiments resulted in an adaptation of this order [Cy (39.2%) = 2MeCy (41.7%) ≫ 3MeCy (13.5%) > 4MeCy (5.6%)]. SCXRD analysis demonstrated that the host packing in H1·Cy, H1·2MeCy and H1·3MeCy was isostructural (monoclinic, P21/n), while H1·4MeCy crystallized in a different crystal system (triclinic, P − 1). All four guests experienced (host)C–H···O–C(guest) interactions, with Cy, a preferred guest, experiencing the shortest of these (2.40 A, 167°). Thermal analyses showed the preferred guests (cyclohexanone and 2-methylcyclohexanone) to form complexes with enhanced thermal stabilities relative to the other two (3- and 4-methylcyclohexanone) (Tp 129.8 and 99.0 °C vs. 97.9 and 95.3 °C, respectively). This investigation has demonstrated that subtle changes in the structures of these xanthenyl- and thioxanthenyl-type host systems may instigate dramatic host behaviour changes in the presence of these cyclohexanone guest solvents.

Embedding and Positioning of Two FeII4 L4 Cages in Supramolecular Tripeptide Gels for Selective Chemical Segregation.

An unreported d,l‐tripeptide self‐assembled into gels that embedded FeII 4L4 metal–organic cages to form materials that were characterized by TEM, EDX, Raman spectroscopy, rheometry, UV/Vis and NMR spectroscopy, and circular dichroism. The cage type and concentration modulated gel viscoelasticity, and thus the diffusion rate of molecular guests through the nanostructured matrix, as gauged by 19F and 1H NMR spectroscopy. When two different cages were added to spatially separated gel layers, the gel–cage composite material enabled the spatial segregation of a mixture of guests that diffused into the gel. Each cage selectively encapsulated its preferred guest during diffusion. We thus present a new strategy for using nested supramolecular interactions to enable the separation of small molecules.

Embedding and Positioning of Two FeII4L4 Cages in Supramolecular Tripeptide Gels for Selective Chemical Segregation

AbstractAn unreported d,l‐tripeptide self‐assembled into gels that embedded FeII4L4 metal–organic cages to form materials that were characterized by TEM, EDX, Raman spectroscopy, rheometry, UV/Vis and NMR spectroscopy, and circular dichroism. The cage type and concentration modulated gel viscoelasticity, and thus the diffusion rate of molecular guests through the nanostructured matrix, as gauged by 19F and 1H NMR spectroscopy. When two different cages were added to spatially separated gel layers, the gel–cage composite material enabled the spatial segregation of a mixture of guests that diffused into the gel. Each cage selectively encapsulated its preferred guest during diffusion. We thus present a new strategy for using nested supramolecular interactions to enable the separation of small molecules.

Occupancy Dependency of Maxwell-Stefan Diffusivities in Ordered Crystalline Microporous Materials.

Molecular dynamics simulation data for a variety of binary guest mixtures (H2/CO2, Ne/CO2, CH4/CO2, CO2/N2, H2/CH4, H2/Ar, CH4/Ar, Ar/Kr, Ne/Ar, CH4/C2H6, CH4/C3H8, C2H6C3H8, CH4/nC4H10, and CH4/nC5H11) in zeolites (MFI, BEA, ISV, FAU (all-silica), NaY, NaX, LTA, CHA, DDR) and metal–organic frameworks (MOFs) (IRMOF-1, CuBTC, MgMOF-74) show that the Maxwell–Stefan (M–S) diffusivities, Đ1, Đ2, Đ12, are strongly dependent on the molar loadings. The main aim of this article is to develop a fundamental basis for describing the loading dependence of M–S diffusivities. Using the ideal adsorbed solution theory, a thermodynamically rigorous definition of the occupancy, θ, is derived; this serves as a convenient proxy for the spreading pressure, π, and provides the correct metric to describe the loading dependence of diffusivities. Configurational-bias Monte Carlo simulations of the unary adsorption isotherms are used for the calculation of the spreading pressure, π, and occupancy, θ. The M–S diffusivity, Đi, of either constituent in binary mixtures has the same value as that for unary diffusion, provided the comparison is made at the same θ. Furthermore, compared at the same value of θ, the M–S diffusivity Đi of any component in a mixture does not depend on it partner species. The Đi versus θ dependence is amenable to simple interpretation using lattice-models. The degree of correlations, defined by the ratio Đ1/Đ12, that characterizes mixture diffusion shows a linear increase with occupancy θ, implying that correlations become increasingly important as pore saturation conditions are approached.

A comparison of the behaviour of two closely related xanthenyl-derived host compounds in the presence of vaporous dihaloalkanes

The behaviour of two closely related xanthone-derived host compounds, N,N’-bis(9-phenyl-9-xanthenyl)ethylenediamine and N,N′-bis(9-phenyl-9-thioxanthenyl)ethylenediamine, which formed complexes with CH2Cl2, CH2Br2 and CH2I2 after recrystallization from each of these solvents, was compared when subjected to these guest and guest mixtures in the vapour phase. Surprisingly, these hosts displayed entirely different behaviours under these conditions, with only the thioxanthenyl derivative possessing the ability to clathrate these guests (or guest mixtures) from the gas phase; this ability was entirely absent in the xanthenyl host. All novel complexes were subjected to single crystal diffraction analyses in order to investigate the interactions present, as well as thermal and Hirshfeld surface experiments. The host selectivity and host–guest interactions were correlated with the differences observed in the recrystallization and vapour experiments. Furthermore, data obtained for the novel complexes by employing various analytical techniques were related back to the observed selectivity order.

Separation of Trimethoxybenzene Isomers by Bile Acids

Cholic acid (CA) and deoxycholic acid (DCA) have been employed to separate the three isomers of trimethoxybenzene (TMB). The selectivity preference is CA: TMB135 > TMB123 ≈ TMB124, while it is reversed for DCA: TMB123 > TMB124 > TMB135. Some of the crystal structures with CA as host suffered from partial disorder, while the DCA structures were grown from pairs of equimolar guest mixtures, and all contained both guests in different proportions. Packing analysis revealed the importance of layering of the hydrophilic and lipophilic regions of the structures with the TMB guests accommodated in the lipophilic layers.

N,N′-Bis(9-phenyl-9-thioxanthenyl)ethylenediamine: Highly Selective Host Behavior in the Presence of Xylene and Ethylbenzene Guest Mixtures

Host compound N,N′-bis(9-phenyl-9-thioxanthenyl)ethylenediamine formed 1:1 host:guest complexes with o- and p-xylene, and ethylbenzene, when recrystallized from them. The meta-isomer was not included. Competition experiments using equimolar binary and ternary mixtures of the three xylenes demonstrated that this host is markedly selective for p-xylene (≥94% on both a milligram- and gram-scale), while 68% of this guest was extracted from an equimolar quaternary mixture of the three xylenes and ethylbenzene. This selectivity was also evident when guest ratios in binary mixtures containing p-xylene were varied. The observed high affinity for the para-isomer was explained using single crystal X-ray diffraction, Hirshfeld surface analysis and thermoanalytical experiments. Furthermore, the host was subjected to gas phase guests in order to establish whether the ability existed for complexation of these guests from the solid state.