Novel flexible MOFs, their application and in situ scXRD studies of gas loaded MOFs

Abstract

Metal-organic frameworks (MOFs) are an exciting class of porous materials with a large variety of potential applications. Finding and analysing new MOF systems is important for the development of new technologies, including in medicine and pollution capture. Furthermore, using high quality in situ single crystal X-ray diffraction (scXRD) is necessary to understand how MOFs capture, store and release gas molecules.

Presented here are novel frameworks based on 2,3-dihydroxyterephthalic acid and the M(II) metal ions Mg, Ni, Co, Ca and Cu. So far nine different phases have been solved structurally with six new to this body of work. SIMOF-3 (St Andrews Isoreticular MOF) can be formed from Mg, Ni and Co. It contains a disordered pillar linker that may be flexible. The Ca phase SIMOF-4 is denser with a phase change to an even denser phase on solvent removal. However, this material did show utility as an anode in a sodium battery. Cu produced two distinct phases both showing breathing behaviour. The more stable phase has shown excellent capacity for the storage and release of the drug molecules Ibuprofen, Flutamide and caffeine as well as the adsorbtion of the medicinal gas nitric oxide (NO).

In addition, in situ scXRD studies have been performed on Ni-CPO-27 and Co-4,6-dhip to investigate the binding of the polar gases NO, CO and SO₂. This has uncovered the relative binding strengths of these gases, their competitive interactions with water and the presence of physisorbed binding sites.

Finally, a series of mixed metal Ni/Cu CPO-27 analogues were synthesised that could release preadsorbed NO on addition of moisture as well as catalytically generate NO from S-nitrosoglutathione. The framework and its stability in biological media were investigated with Ni₀.₁Cu₀.₉-CPO-27 showing excellent all round properties suitable for inclusion into future medical devices.