Exploring The Structure of Polar Lanthanide-based MOFs

The incorporation of organic linkers and a lanthanide metal centre into metal- organic frameworks (MOFs) is a topic that is relatively less explored than their transition metal analogues. So far, these materials have been mainly discussed in terms of their luminescence, which leads them onto being used in sensors, optical devices and for biological markers/sensors but in this thesis we will highlight the potential to realise polar MOFs. The first chapter of this thesis will introduce the MOFs alongside the dielectric properties that provide the impetus for searching for polar phases within them and then introducing some known lanthanide MOFs that inspired this work. Following a discussion of the key experimental methods for this work, the third chapter thesis will focus on the new series of materials synthesised, the Ln(HCO2)3(CO(NH2)2)2 (where Ln= Tb, Dy, Ho, Er, Tm, Yb, and, Lu) frameworks. Structural characterisation of these materials show they adopt either P43 tetragonal or Aea2 orthorhombic symmetry, with the former in which the formate links the lanthanide into a 3D coordination framework being more commonly observed. Secondary harmonic generation measurements of the tetragonal Tb and Er phases, performed by collaborators, confirmed that they are non-centrosymmetric at ambient temperature. The Er phase also showed some indication of a dielectric transition, with some associated relaxation, but the lack of a phase transition in both heat capacity and X-ray crystallography suggests this is an extrinsic feature. The fourth chapter of this thesis reports a short investigation into the attempted synthesis of hybrid perovskites with a Bi3+ centre, specifically for its lone pair which can enhance piezoelectric properties within the material. These were, unfortunately unsuccessful, primarily yielding a known bismuth oxalate hydroxide.