Influence Of Guest Molecules Research Articles

Structural and mechanical stability of clathrate hydrates encapsulating monoatomic guest species

Clathrate hydrate (CH) structures find diversely promising applications such as gas and energy storage and transport, carbon capture and storage, gas separation, water desalination, and food and pharmaceutical engineering. However, the influence of guest molecules on their properties remains largely uncharacterized. Here, the critical roles of monoatomic guest size and interaction strength with water molecule in the structural and mechanical stability of clathrate hydrates are explicitly examined by classical molecular dynamics simulations. With increasing guest size or its interaction strength, the lattice constant and mechanical properties such as Young’s modulus, tensile strength, Poisson’s ratio of CHs vary nonlinearly. Based on the characteristics of the contour map of lattice constant, four regions of lattice constant of CHs can be divided. Interestingly, there are crossovers in the iso-lattice constant lines and tensile strength. Upon uniaxial tension, CH destabilizes via brittle or ductile failure, relying on the size and interaction strength of monoatomic guest. The guest size and interaction strength dependent properties can be critically understood by radial distribution function, cage volume and distribution of guest@cages.

Disappeared supramolecular isomer reappears with perylene guest.

Among different types of polymorphism, disappearing polymorphism deals with the metastable kinetic form which can not be reproduced after its first isolation. In the world of coordination polymers (CPs) and metal-organic frameworks (MOFs), despite the fact that many types of supramolecular isomerism exist, we are unaware of disappearing supramolecular isomerism akin to disappearing polymorphism. This work reports a MOF with dia topology that could not be reproduced, but subsequent synthesis yielded another supramolecular isomer, a double-pillared-layer MOF. When perylene was added in the same reaction, the disappeared dia MOF reappeared with perylene as a guest in the channels. Interestingly, the photoluminescence of the dia MOF with a perylene guest is dominated by the emission of the guest molecule. The influence of guest molecules on the stabilization of the supramolecular isomers of a MOF opens up a strategy to access MOFs with different structures.

Theoretical modeling of the thermodynamic properties and the phase diagram of binary gas hydrates of argon and hydrogen

Theoretical calculation of the thermodynamic properties and determining of equilibrium hydrate composition of binary argon + hydrogen hydrates has been performed with taking into account the concurrent cage occupation by different guest types. For this purpose the original previously developed approach has been used that allows to take into account multiple cage occupancy and the possibility of mixed clusters inside the cages as well as the influence of guest molecules on the host lattice. Separately, argon and hydrogen form cubic structure II (sII) hydrates. Therefore, in this work we considered only sII gas hydrates formation. It is shown that thermodynamic stability of binary argon + hydrogen hydrates strongly depends on the presence of argon in the gas phase as the heavier component. Thus, with increasing argon content in the system the hydrate stability field extends to low pressures with increase of argon fraction in the small cavities.

ChemInform Abstract: Influence of Guest Molecules on the Crystal Lattice Structure and Porous Structure Characteristics of Coordination Polymers

AbstractReview: 30 refs.

Temperature dependence of the partially localized state in a 2D molecular nanoporous network

Two-dimensional organic and metal-organic nanoporous networks can scatter surface electrons, leading to their partial localization. Such quantum states are related to intrinsic surface states of the substrate material. We further corroborate this relation by studying the thermally induced energy shifts of the electronic band stemming from coupled quantum states hosted in a metal-organic array formed by a perylene derivative on Cu(111). We observe by angle-resolved photoemission spectroscopy (ARPES), that both, the Shockley and the partially localized states, shift by the same amount to higher binding energies upon decreasing the sample temperature, providing evidence of their common origin. Our experimental approach and results further support the use of surface states for modelling these systems, which are expected to provide new insight into the physics concerning partially confined electronic states: scattering processes, potential barrier strengths, excited state lifetimes or the influence of guest molecules.

Special Features of the Template Effect in the Formation of Porous Coordination Polymers

It was shown that the influence of guest molecules on the structure of porous coordination polymers (PCP) can be considered as the manifestation of a template effect. The presence of such molecules and their nature affect the composition of the PCP and the topology of the polymer framework and can also determine the chirality of the crystal lattice. The criteria that can be used to reach conclusions about the special features of the template effect during the formation of PCPs are analyzed.

Influence of Guest Molecules on the Crystal Lattice Structure and Porous Structure Characteristics of Coordination Polymers

The influence of guest molecules, including the solvent, on the structure of porous coordination polymers (PCP) and, as a consequence, their adsorption properties is analyzed. It was suggested that the nature of the solvent can predetermine the selectivity of PCP adsorption only when the solvent acts as a template in the formation of such a polymer. In contrast to PCP with rigid crystal lattices, the characteristics of PCP with labile lattices and their adsorption properties depend significantly on the nature of guest molecules.

In-situ analysis of gas-loaded porous materials

In order to understand gas sorption processes at the molecular level it is important to correlate physico-chemical data (e.g. sorption isotherms and calorimetric analysis) with structural data. It is therefore desirable to carry out structural elucidation and calorimetric analysis under conditions that closely mimic those of the sorption/desorption experiments. However, the crystallographic analysis of samples under controlled gas environments poses significant technical challenges, particularly given the limited space associated with the sample compartment of standard commercial diffractometer. In this regard, an environmental gas cell has been developed in parallel with a pressure-programmed differential scanning calorimeter. Use of these complementary techniques has provided new insight into features such as pressure-induced phase transformations that give rise to inflections and hysteresis in sorption isotherms. The influence of guest molecules on aspects such as structural flexibility, linear thermal expansion and changes in network interpenetration will be discussed.

Thermodynamic stability of C3H8 hydrate of cubic structure IV using lattice dynamics

The thermodynamic properties of propane clathrate hydrate with cubic structure IV were studied using a method based on the solid solution theory of van der Waals and Platteeuw but allows one to take into account the influence of guest molecules on the host lattice and guest-guest interactions. The free energies, equations of state, and chemical potentials of this hydrate were estimated using this approach. The proposed theory was used for construction of “guest gas–hydrate–ice I h ” equilibrium curves of propane hydrates. It was found that the water framework of structure IV was dynamically stable and that the fully C3H8 filled structure was thermodynamically stable in the region of pressure from 43 to 50 MPa as compared with the hexagonal ice. The formation pressure of propane hydrate with structure IV is higher than that of propane hydrate with cubic structure II. However, a structural transformation from structure II to IV of propane hydrate was estimated under a pressure of 78 MPa at 290 K.

Porous 2D coordination polymeric formate built up by Mn(ii) linking of Fe3O units: influence of guest molecules on magnetic properties

A first representative of coordination polymers, built from polynuclear carboxylate bridged by mononuclear carboxylate, has been synthesised and structurally characterized. The compound [{Fe(3)O(HCOO)(6)}{Mn(HCOO)(3)(H(2)O)(3)}].3.5HCOOH crystallised in the hexagonal system (space group P6(3)), a = b = 12.369(5) A, c = 12.992(5) A, alpha = beta = 90 degrees , gamma = 120 degrees , V = 1721.4(12) A(3). The crystal structure is built from 2D layers, which are formed by the linking of trinuclear {Fe(3)O(HCOO)(6)}(+) units by mononuclear {Mn(HCOO)(3)(H(2)O)(3)}(-) bridges. These 2D honeycomb layers are connected by molecules of formic acid through a hydrogen bond network. The compound has the voids at the centre of the hexagons. These voids are filled by captured solvent molecules. Solvate molecules are also located between the 2D layers, linking them through a system of H-bonds. All these solvates can be easily removed and/or exchanged, which results in the formation of [{Fe(3)O(HCOO)(6)}{Mn(HCOO)(3)(H(2)O)(3)}].0.5HCOOH.H(2)O and [{Fe(3)O(HCOO)(6)}{Mn(HCOO)(3)(H(2)O)(3)}]. Magnetic properties of the compounds can be considered as the superposition of magnetism of Fe(3)O trinuclear units, for which magnetism is governed by the superexchange interaction between Fe(3+) spins (with one Fe-Fe superexchange parameter J) and the magnetism of spins of Mn(2+) ions, the interactions between these units can be taken into account by molecular field, zJ'. The destruction of the hydrogen bond network caused by evacuation of solvent molecules significantly modifies the overall magnetism. It was found that zJ' depends on the presence of solvent molecules in the structure.

Influence of the guest molecule on the rotational potential for NH 3 groups in Hofmann clathrates

Inelastic neutron scattering has been used to investigate the influence of different guest molecules, G, on the rotational hindering potential for NH 3 in Hofmann clathrates Ni(NH 3) 2Ni(CN) 4 · mG. Non-polar guests (benzene and biphenyl) lead to quasi-free rotor environments. For polar guests (water, aniline, phenol, dioxane), dipolar interactions give rise to an increase of the rotational barrier; most often, complex spectra result from statistical orientational disorder of the guest molecules.