Synthetic, spectroscopic and structural studies of chalcogen peri-substituted heterocycles : a solid-state NMR perspective

Abstract

Chalcogen-containing materials are an area of increasing interest for spintronic applications. The synthesis, structures and reactivity of these novel compounds are normally studied by solution-state nuclear magnetic resonance (NMR) spectroscopy, density functional theory (DFT) calculations and single-crystal X-ray diffraction. In this thesis, a range of chalcogen-containing heterocycles has been explored, focussing on the solid-state nature and exploring the bulk samples. Therefore, all materials were studied by powder X-ray diffraction and solid-state NMR, in addition to conventional solution-state NMR and single-crystal X-ray diffraction. DFT calculations were also used to interpret the solid-state NMR spectra and to gain insight into the NMR parameters. In the first chapter of results, a series of mixed Te, Se acenaphthenes is investigated. ⁷⁷Se and ¹²⁵Te NMR parameters are explored to determine whether changes in the Te aryl-group have an impact on the local environments of both nuclei. Dynamics and the requirement to consider relativistic effects for calculations of NMR parameters of heavy atoms is discussed. In the second results chapter, a series of novel P-S and P-Se six-membered heterocycles are described in terms of their synthesis, reactivity, and ³¹P and ⁷⁷Se local environments. We observed and measured some unusual “through-space” couplings that occur between molecules and which mechanism and pathways are supported by DFT calculations. In the third results chapter, these heterocycles are oxidised with O, S and Se and the NMR parameters are discussed in terms of the structure. Polymorphism, phase transitions and weak interactions are some of the phenomena present in these novel compounds. This thesis demonstrated that solid-state NMR is a very good probe to study Se- and Te-containing materials.