Skipper, CVJ; (2013) The Kubas Interaction in Transition Metal Based Hydrogen Storage Materials. Doctoral thesis , UCL (University College London).

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Abstract

This PhD is a computational study of the hydrogen storage materials made by the Antonelli group based in Glamorgan using Density Functional Theory (DFT) and the Quantum Theory of Atoms In Molecules (QTAIM). These materials are either silica based or hydrazine linked with transition metal binding sites to which, it is thought, the hydrogen binds through the Kubas interaction. All of the materials display rising hydrogen binding enthalpies with increasing hydrogen coverage. The first QTAIM study of the Kubas interaction was performed on molecules, to which it is agreed the hydrogen binds through the Kubas interaction, in order to benchmark this technique before applying it to the studied materials. The binding sites were modelled as fragments representing the active sites in the extended structures. Evidence has been found for the hydrogen binding through the Kubas interaction and the results were benchmarked against the available experimental data. The transition metals of the binding sites and their associated ancillary ligands were altered in order to probe the possible effect that this could have on the experimental system. It was found that poor π-acceptor ancillary ligands increase the strength of the interaction between the metal and the hydrogen and that changing the metal from Ti to V to Cr to Mn reduces the number of the H2 molecules that can be bound. Cr and Mn are considered to be poor choices for incorporation as binding sites in hydrogen storage materials. Explanations for the rising hydrogen binding enthalpies with increasing hydrogen coverage have been presented for the silica based and hydrazine linked materials based on local perturbation of the molecular orbitals and metal to metal cooperativity respectively. The study was extended further to include hydrazine linked materials based on Ni(II), Cu(I) and Cu(II) metal centres to probe their potential as hydrogen storage materials.

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