Coordination Frameworks: Host-Guest Chemistry and Structural Dynamics

Abstract

This thesis investigates the host-guest chemistry and structural dynamics in three families of coordination frameworks – Prussian blue analogues (PBAs), zeolitic imidazolate frameworks (ZIFs), and lanthanoid metal-organic frameworks (MOFs). This was primarily achieved using in situ gas-loading neutron powder diffraction (NPD) to examine various guests in the pore space of these materials. Each of these frameworks contain structural motifs that have previously been identified as influential in the uptake of gases. Gas-loaded NPD of the PBA Fe¬3[Co(CN)6]2 revealed two CO2 adsorption sites, both of which interact with the coordinatively-unsaturated Fe(II) sites. A linear relationship was also observed between the material's thermal expansion behaviour when dosed with increasing amounts of CO2, suggesting the potential for controlled thermal expansion properties. NPD analysis of gas-loaded Co(nIm)2-RHO has revealed five adsorption sites each when this material was dosed with CO2 or D2. Host-guest interactions at CO2 and D¬2 adsorption sites are observed to be predominantly driven by electrostatic interactions with the nitro functional group of the 2 nitroimidazolate bridging ligand. Analysis of CO2-loaded NPD data for Co(mIm)2-SOD revealed only a single CO2 adsorption site that accounted for ca. 17% of the total amount of CO2 dosed. This comparison has helped to confirm the necessity of having ligands with strong charge polarisation in order to achieve guest interaction and crystallographic ordering. NPD analysis of gas-loaded Y(btc) has revealed multiple adsorption sites with dosed with CO2, CD4, and O2. These host-guest adsorption sites typically occur between the guest molecule and the carboxylate functional groups of the bridging ligand. Despite the presence of bare metal sites, only the O2 guest is seen to interact weakly. This has been attributed to the contraction in O-Y-O coordination angles upon desolvation of the host material.