S Coetzee PhD Abstract

An experimental and computational investigation of the magnetic properties of organic-inorganic hybrids

Magnetochemistry is a multidisciplinary research field that is at the frontier of the development of Quantum Age materials. The purposeful design of materials originates from a fundamental understanding of the factors that affect the desired properties. To this end, magnetochemists have meticulously mapped thousands of compounds with the aim of understanding the factors which affect the magnetic behaviour of a wide variety of materials.

When Cu(II) ions are coordinated to organic ligands and are bridged by halide ligands, the resulting halide-bridged polymers typically exhibit a wide variety of interesting magnetic properties. Here we show that the organic ligands in organic-inorganic hybrids both directly and indirectly affect the magnetic exchange of low-dimensional magnetic materials. This was done by taking two model systems, namely, 1D trans-edge-shared polymers, which are simple structures and 1D magnets, and 1D stacked-dimers, which are significantly more complex (structurally and magnetically) 1D halide-bridged polymers. For each system, the organic ligands were varied, which produced two families of structures. By doing this, an extensive comparison of these structures was performed from both an experimental and theoretical perspective. The 1D trans-edge-shared polymers were used to develop the methodology and validate computational results which were then applied to the more complex stacked-dimer halide-bridged polymers.

It is also demonstrated that the magnetic exchange between Cu(II) ions in halide-bridged polymers is directly affected by peripheral/terminal organic ligands. Previously it was thought that the inorganic ligands in molecular-based magnets determine the type and strength of exchange between the paramagnetic metals with only colloquial evidence available that organic peripheral/terminal organic ligands affect magnetic exchange. Only recent evidence,^[i] similar to what will be presented in this thesis, demonstrated that organic ligands contribute to the magnetic exchange in dimeric Cu(II) acetate adducts.

By the use of First-Principles computational methods in this thesis, it is demonstrated that the organic ligands directly affect the magnetic exchange in halide-bridged polymers which was linked to the π-donor/acceptor ability and the orientation of the organic ligand in addition to the colloquially known effect of the σ-donation/accepting ability of terminal ligands on the overall magnetic exchange between Cu(II) ions in halide-bridged polymers. Peripheral organic ligands, such as O-coordinating amides, that have significant π-donation, are shown in this thesis to increase the magnetic exchange between halide bridged Cu(II) ions, compared to N- donor ligands. The organic ligand identity, as well as it’s orientation, is shown to affect the type and strength of exchange in halide-bridged polymers. Therefore, organic peripheral ligands are highlighted here as excellent choices in creating magnetic materials that may have potential application in molecular spintronics.

^[i] E. М. Zueva, М. М. Petrova, A. V. Shamsieva, K. R. Trigulova, E. I. Musina, R. R. Fayzullin, A. S. Bogomyakov, V. I. Ovcharenko, A. A. Karasik, Int. J. Quantum Chem. 2020, 120, e26145.