Guest Molecules In Crystals Research Articles

Encapsulating Organic Crystals (EnOCs)

Achieving efficient capture, storage and release of small molecules is a challenge. Most materials that can harbor small molecules have been studied in the context of gas storage or separation. Formulations for hazardous reagents have only recently attracted attention, when organic compounds were discovered that encapsulate a broad range of guest molecules in crystals. Such encapsulating organic crystals (EnOCs) can suppress problematic properties of reagents and allow for controlled release in reaction mixtures. Unlike materials used for gas storage, which possess permanent porosity, their cavities are not held together by covalent or strong noncovalent interactions. Instead, EnOCs crystallize with the help of weaker packing forces. Substituted tetraaryladamantane octaethers can form high-loading inclusion compounds with reagents as guests, but they can also transition into tightly packed, solvate-free forms. Here we highlight the differences between EnOCs and known porous materials and discuss the potential of EnOCs as formulations in organic synthesis.

Origin and structure of polar domains in doped molecular crystals.

Doping is a primary tool for the modification of the properties of materials. Occlusion of guest molecules in crystals generally reduces their symmetry by the creation of polar domains, which engender polarization and pyroelectricity in the doped crystals. Here we describe a molecular-level determination of the structure of such polar domains, as created by low dopant concentrations (<0.5%). The approach comprises crystal engineering and pyroelectric measurements, together with dispersion-corrected density functional theory and classical molecular dynamics calculations of the doped crystals, using neutron diffraction data of the host at different temperatures. This approach is illustrated using centrosymmetric α-glycine crystals doped with minute amounts of different L-amino acids. The experimentally determined pyroelectric coefficients are explained by the structure and polarization calculations, thus providing strong support for the local and global understanding of how different dopants influence the properties of molecular crystals.

Assessing Surface Permeabilities from Transient Guest Profiles in Nanoporous Host Materials

Easy come, easy go? Transport resistances on particle surfaces are important for mass transfer in nanoporous materials and bulk diffusion in crystals. Interference microscopy and IR micro-imaging are shown to be excellent tools for determining such transport resistances. By studying short-chain-length alkane guest molecules in crystals of the metal-organic framework compound Zn(tbip) a data collection of surface permeabilities is established.

Incorporation mechanism of guest molecules in crystals: solid solution or inclusion?

Guest molecules (impurities or additives), together with some crystallization solvent, are often incorporated into the host crystals during crystallization from solution. The guest molecules may be incorporated either in solid solution or in liquid inclusions, or by both mechanisms. The mechanism of guest incorporation has been examined by a simple calculation method which is based on the equality of the guest/solvent mole ratio in the initial crystallization medium and in the putative inclusions. Application of this calculation method to eight guest+host systems described in the literature has shown that a negligible amount (at most 0.2%) of the guest molecules is incorporated into the crystal lattice in liquid inclusions. Therefore, it is concluded that the vast majority of the guest molecules are incorporated into the crystals in solid solution, as previously suggested, but hitherto unproven, for these guest–host systems.

Designing multi-dimensional host structures of cyanometallate systems; static and dynamic behaviour of guest molecules in crystal

Designing multi-dimensional host structures of cyanometallate systems; static and dynamic behaviour of guest molecules in crystal