Topological insulators are a novel class of quantum materials wherein the bulk of the material is an insulator, while the surface or edge states are quantum mechanically protected and conducting. This class of materials offers a lot of promise in the fields of quantum computing and spintronics due to their inherent ability to conduct electrons without the loss of any energy over longer distances, thereby theoretically being able to solve the problems of heat accumulation and leaking of electrons due to tunnelling in current devices. To this end, this work focussed on three main objectives: (a) investigate known bismuth structures as hosts for topological and quantum effects, in particular as potential topological insulators; (b) exploring the possibilities of magnetic substitutions in both known weak 3D topological insulators and further bismuth subhalide structures; and (c) gaining an understanding of the formation processes of the aforementioned substitutions into the bismuth subhalide compounds through extensive thermal analyses. This was realised by investigating Bi2[PtBi6I12]3 and Bi14Rh3I9 as host structures, with the former being a topologically trivial compound and the latter a weak 3D topological insulator. Due to previous difficulties in substituting magnetic cations into Bi14Rh3I9, the initial focus of this work lay in substituting magnetic cations into Bi2[PtBi6I12]3. This work then showed that not only could infinite cluster strands containing the [PtBi6I12]2- clusters be formed with Pb, Sn and Sb in the counter-cation site between them, but that magnetic cations such as Mn, Fe and Co could also be substituted into bismuth subhalide structures. The latter in particular gave rise to novel physical properties in this class of compounds and illuminated and helped explain the previous challenges in substituting magnetic cations into the bismuth subhalides.