Computational studies Of manganese-ligand clusters in the gas-phase and manganese atoms in graphene and metal-organic frameworks

The work in this thesis deals with computational studies of manganese ions and atoms in the gas-phase and in the solid phase. The results are divided into three chapters, and the theory and methods used are explained and discussed in a separate theory chapter. The first results on manganese and its coordination to water and methanol molecules in the gas-phase are discussed in the light of physical properties for different ligands including water and methanol. Preferred coordination of a specific ligand type, preferred complex or cluster size as well as coordination modes are thoroughly investigated. Also discussed is stability against proton-transfer reactions for a few manganese-water and manganese-methanol clusters. The work is carried out at the HF/6- 31G(d), MP2/6-311G(d,p) and B3LYP/6-311(3df,3pd)-level of theory using the computer code Gaussian. The results presented here are in good agreement with experimental results and findings. It is concluded that mixing between 4s and 3d orbitals on the manganese atom is responsible for preference for a specific cluster size and that occupation of anti-bonding orbitals destabilizes the cluster, for a specific coordination mode. The next results are for manganese atoms in a double layer of graphite, using the computer code Aimpro. Different coordination modes are investigated as are magnetic properties upon adsorption and modification of the band structure compared to a pristine double layer of graphene. Only one case of a significantly high spin polarization is encountered, and the spin polarization on the manganese atom and the surrounding carbon atoms is investigated with Mulliken analysis. This study is in agreement with previous work in the same field, but provides a more realistic picture since a larger system is considered here. The final chapter deals with manganese atoms in metal-organic frameworks, MOFs, using the Aimpro code. Magnetic properties and binding energies for adsorption of selected molecules are discussed in this chapter. Magnetic properties are discussed using Mulliken analysis. Modification of the band structure upon coordination of these gas molecules is shown and investigated. Very few experimental results exist in this field for this structure, but its role as a potential candidate for hydrogen storage will specifically be discussed.