Computational investigations into the structure and reactivity of small transition metal clusters.

Abstract

This thesis presents a number of largely independent forays into developing an understanding of the unique chemistry of transition metal clusters. The first chapter of this thesis represents an initial foray into mapping the chemical reactivity of transition metal clusters - a monumental task that will doubtless continue for some time. The small slice undertaken in this work investigates the reactivity with CO of a series of the smallest possible metal clusters; 4d (Nb - Ag) homonuclear metal trimers. In Chapter 2, two known transition metal clusters were studied using CASSCF (MCSCF) and MRCI methods, only to find that DFT methods provided more accurate Ionisation Potentials (IPs). Thus Chapter 3 was devoted to optimising a density functional to predict IPs. As clusters get larger, the number of possible structures grows rapidly too large for human intuition to handle, thus Chapter 4 is devoted to the use of an automated stochastic algorithm, “Kick”, for structure elucidation. Chapter 5 improves on this algorithm, by permitting chemically sensible molecular fragments to be defined and used. Chapter 6 then comes full circle and uses the new Kick algorithm to investigate the reaction of CO with a series of mono-substituted niobium tetramers (i.e. Nb₃X).