Using neutron powder diffraction and first-principles calculations to understand the working mechanisms of porous coordination polymer sorbents

Square Grid Metal-Chloranilate Networks as Robust Host Systems for Guest Sorption

Reaction of the chloranilate dianion with Y(NO₃ )₃ in the presence of Et₄ N⁺ in the appropriate proportions results in the formation of (Et₄ N)[Y(can)₂ ], which consists of anionic square-grid coordination polymer sheets with interleaved layers of counter-cations. These counter-cations, which serve as squat pillars between [Y(can)₂ ] sheets, lead to alignment of the square grid sheets and the subsequent generation of square channels running perpendicular to the sheets. The crystals are found to be porous and retain crystallinity following cycles of adsorption and desorption. This compound exhibits a high affinity for volatile guest molecules, which could be identified within the framework by crystallographic methods. In situ neutron powder diffraction indicates a size-shape complementarity leading to a strong interaction between host and guest for CO₂ and CH₄ . Single-crystal X-ray diffraction experiments indicate significant interactions between the host framework and discrete I₂ or Br₂ molecules. A series of isostructural compounds (cat)[M^III (X-an)₂ ] with M=Sc, Gd, Tb, Dy, Ho, Er, Yb, Lu, Bi or In, cat=Et₄ N, Me₄ N and X-an=chloranilate, bromanilate or cyanochloranilate bridging ligands have been generated. The magnetic properties of representative examples (Et₄ N)[Gd(can)₂ ] and (Et₄ N)[Dy(can)₂ ] are reported with normal DC susceptibility but unusual AC susceptibility data noted for (Et₄ N)[Gd(can)₂ ].

Anisotropic Thermal and Guest-Induced Responses of an Ultramicroporous Framework with Rigid Linkers

The interdependent effects of temperature and guest uptake on the structure of the ultramicroporous metal-organic framework [Cu₃ (cdm)₄ ] (cdm=C(CN)₂ (CONH₂ )^- ) were explored in detail by using in situ neutron scattering and density functional theory calculations. The tetragonal lattice displays an anisotropic thermal response related to a hinged "lattice-fence" mechanism, unusual for this topology, which is facilitated by pivoting of the rigid cdm anion about the Cu nodes. Calculated pore-size metrics clearly illustrate the potential for temperature-mediated adsorption in ultramicroporous frameworks due to thermal fluctuations of the pore diameter near the value of the target guest kinetic diameter, though in [Cu₃ (cdm)₄ ] this is counteracted by a competing contraction of the pore with increasing temperature as a result of the anisotropic lattice response.

Real-time powder diffraction studies of energy materials under non-equilibrium conditions

Energy materials form the central part of energy devices. An essential part of their function is the ability to reversibly host charge or energy carriers, and analysis of their phase composition and structure in real time under non-equilibrium conditions is mandatory for a full understanding of their atomic-scale functional mechanism. Real-time powder diffraction is increasingly being applied for this purpose, forming a critical step in the strategic chemical engineering of materials with improved behaviour. This topical review gives examples of real-time analysis using powder diffraction of rechargeable battery electrodes and porous sorbent materials used for the separation and storage of energy-relevant gases to demonstrate advances in the insights which can be gained into their atomic-scale function.

Powder sample-positioning system for neutron scattering allowing gas delivery in top-loading cryofurnaces

A system for positioning powder samples in top-loading cryofurnaces during neutron scattering experiments, while facilitating the successive delivery of gas doses at set temperatures to the sample, has been designed and tested. The positioning system is compatible with a Hiden Isochema IMI instrument as a gas-dosing platform, enabling gases to be delivered to the sample through a centrally located and thermally stabilized capillary line and valve. The positioning system separates into an upper and a lower section, with the lower section enabling the sample to be isolated and inserted into a glove box. This work describes the system using example neutron powder diffraction results obtained with this system in closed-cycle cryofurnaces.